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Shiozaki H, Kuga N, Kayama T, Ikegaya Y, Sasaki T. Selective serotonin reuptake inhibitors suppress sharp wave ripples in the ventral hippocampus. J Pharmacol Sci 2023; 152:136-143. [PMID: 37169478 DOI: 10.1016/j.jphs.2023.04.003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2023] [Revised: 03/23/2023] [Accepted: 04/10/2023] [Indexed: 05/13/2023] Open
Abstract
Biased memory processing contributes to the development and exacerbation of depression, and thus could represent a potential therapeutic target for stress-induced mental disorders. Synchronized spikes in hippocampal neurons, corresponding to sharp wave ripples (SWRs), may play a crucial role in memory reactivation. In this study, we showed that the frequency of SWRs increased in the ventral hippocampus, but not in the dorsal hippocampus, after stress exposure. Administration of the selective serotonin reuptake inhibitors (SSRIs) fluoxetine and fluvoxamine inhibited the generation of ventral hippocampal SWRs and reduced locomotor activity and local field potential power in the gamma bands. These results suggest that the antidepressant effects of SSRIs may be mediated by the suppression of ventral hippocampal SWRs.
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Affiliation(s)
- Hiromi Shiozaki
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan
| | - Nahoko Kuga
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan.
| | - Tasuku Kayama
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan
| | - Yuji Ikegaya
- Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan; Center for Information and Neural Networks, 1-4 Yamadaoka, Suita City, Osaka, 565-0871, Japan; Institute for AI and Beyond, The University of Tokyo, Tokyo 113-0033, Japan
| | - Takuya Sasaki
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3 Aramaki-Aoba, Aoba-Ku, Sendai 980-8578, Japan; Graduate School of Pharmaceutical Sciences, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
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2
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Gioia R, Seri T, Diamanti T, Fimmanò S, Vitale M, Ahlenius H, Kokaia Z, Tirone F, Micheli L, Biagioni S, Lupo G, Rinaldi A, De Jaco A, Cacci E. Adult hippocampal neurogenesis and social behavioural deficits in the R451C Neuroligin3 mouse model of autism are reverted by the antidepressant fluoxetine. J Neurochem 2022; 165:318-333. [PMID: 36583243 DOI: 10.1111/jnc.15753] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 12/07/2022] [Accepted: 12/16/2022] [Indexed: 12/31/2022]
Abstract
Neuron generation persists throughout life in the hippocampus but is altered in animal models of neurological and neuropsychiatric diseases, suggesting that disease-associated decline in cognitive and emotional hippocampal-dependent behaviours might be functionally linked with dysregulation of postnatal neurogenesis. Depletion of the adult neural stem/progenitor cell (NSPCs) pool and neurogenic decline have been recently described in mice expressing synaptic susceptibility genes associated with autism spectrum disorder (ASDs). To gain further insight into mechanisms regulating neurogenesis in mice carrying mutations in synaptic genes related to monogenic ASDs, we used the R451C Neuroligin3 knock-in (Nlgn3 KI) mouse, which is characterized by structural brain abnormalities, deficits in synaptic functions and reduced sociability. We show that the number of adult-born neurons, but not the size of the NSPC pool, was reduced in the ventral dentate gyrus in knock-in mice. Notably, this neurogenic decline was rescued by daily injecting mice with 10 mg/Kg of the antidepressant fluoxetine for 20 consecutive days. Sustained treatment also improved KI mice's sociability and increased the number of c-Fos active adult-born neurons, compared with vehicle-injected KI mice. Our study uncovers neurogenesis-mediated alterations in the brain of R451C KI mouse, showing that the R451C Nlgn3 mutation leads to lasting, albeit pharmacologically reversible, changes in the brain, affecting neuron formation in the adult hippocampus. Our results suggest that fluoxetine can ameliorate social behaviour in KI mice, at least in part, by rescuing adult hippocampal neurogenesis, which may be relevant for the pharmacological treatment of ASDs.
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Affiliation(s)
- Roberta Gioia
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
| | - Tommaso Seri
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
- PhD program in Behavioral Neuroscience, Sapienza University of Rome, Rome, Italy
| | - Tamara Diamanti
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
| | - Stefania Fimmanò
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
| | - Marina Vitale
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
| | - Henrik Ahlenius
- Faculty of Medicine, Department of Clinical Sciences Lund, Neurology, Stem Cells, Aging and Neurodegeneration, Lund University, Lund, Sweden
- Lund Stem Cell Center, Lund, Sweden
| | - Zaal Kokaia
- Lund Stem Cell Center, Department of Clinical Sciences, Lund University Hospital, Lund, Sweden
| | - Felice Tirone
- Institute of Biochemistry and Cell Biology, National Research Council, Rome, Italy
| | - Laura Micheli
- Institute of Biochemistry and Cell Biology, National Research Council, Rome, Italy
| | - Stefano Biagioni
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
| | - Giuseppe Lupo
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
| | - Arianna Rinaldi
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
- Centre for Research in Neurobiology "D. Bovet", Sapienza University of Rome, Rome, Italy
| | - Antonella De Jaco
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
- Centre for Research in Neurobiology "D. Bovet", Sapienza University of Rome, Rome, Italy
| | - Emanuele Cacci
- Department of Biology and Biotechnology "Charles Darwin", Sapienza, University of Rome, Rome, Italy
- Centre for Research in Neurobiology "D. Bovet", Sapienza University of Rome, Rome, Italy
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3
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Moyal R, Turker HB, Luh WM, Swallow KM. Auditory Target Detection Enhances Visual Processing and Hippocampal Functional Connectivity. Front Psychol 2022; 13:891682. [PMID: 35769754 PMCID: PMC9234495 DOI: 10.3389/fpsyg.2022.891682] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Accepted: 05/18/2022] [Indexed: 11/20/2022] Open
Abstract
Though dividing one's attention between two input streams typically impairs performance, detecting a behaviorally relevant stimulus can sometimes enhance the encoding of unrelated information presented at the same time. Previous research has shown that selection of this kind boosts visual cortical activity and memory for concurrent items. An important unanswered question is whether such effects are reflected in processing quality and functional connectivity in visual regions and in the hippocampus. In this fMRI study, participants were asked to memorize a stream of naturalistic images and press a button only when they heard a predefined target tone (400 or 1,200 Hz, counterbalanced). Images could be presented with a target tone, with a distractor tone, or without a tone. Auditory target detection increased activity throughout the ventral visual cortex but lowered it in the hippocampus. Enhancements in functional connectivity between the ventral visual cortex and the hippocampus were also observed following auditory targets. Multi-voxel pattern classification of image category was more accurate on target tone trials than on distractor and no tone trials in the fusiform gyrus and parahippocampal gyrus. This effect was stronger in visual cortical clusters whose activity was more correlated with the hippocampus on target tone than on distractor tone trials. In agreement with accounts suggesting that subcortical noradrenergic influences play a role in the attentional boost effect, auditory target detection also caused an increase in locus coeruleus activity and phasic pupil responses. These findings outline a network of cortical and subcortical regions that are involved in the selection and processing of information presented at behaviorally relevant moments.
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Affiliation(s)
- Roy Moyal
- Cognitive Science Program, Department of Psychology, Cornell University, Ithaca, NY, United States
| | - Hamid B. Turker
- Cognitive Science Program, Department of Psychology, Cornell University, Ithaca, NY, United States
| | - Wen-Ming Luh
- National Institute on Aging, National Institutes of Health, Baltimore, MD, United States
| | - Khena M. Swallow
- Cognitive Science Program, Department of Psychology, Cornell University, Ithaca, NY, United States
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Septotemporal variation in beta-adrenergic modulation of short-term dynamics in the hippocampus. IBRO Neurosci Rep 2021; 11:64-72. [PMID: 34409401 PMCID: PMC8363828 DOI: 10.1016/j.ibneur.2021.07.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2021] [Accepted: 07/31/2021] [Indexed: 12/15/2022] Open
Abstract
Recent evidence shows a greater facilitating effect of beta-adrenergic receptors (β-ARs) on long-term synaptic plasticity in the ventral versus the dorsal hippocampus. Here, using field potentials from the CA1 area and a ten-pulse stimulation train of varying frequency we show that activation of β-ARs by isoproterenol preferentially facilitates the output from the dorsal hippocampus at the frequency range of 3–40 Hz without affecting short-term synaptic plasticity. Furthermore, isoproterenol increases basal synaptic transmission in the dorsal hippocampus only and enhances basal neuronal excitation more in the dorsal than the ventral hippocampus. These results suggest that β-AR-modulation of short-term neuronal dynamics differs along the longitudinal axis of the hippocampus, thereby contributing to functional specialization along the same axis. We studied the effects of isoproterenol (ISO) in dorsal (DH) and ventral (VH) hippocampus. ISO increased synaptic transmission and population spike more in DH than VH. ISO modulated short-term changes of population spike in the dorsal hippocampus only. ISO did not affect short-term changes of synaptic transmission in DH or VH. β adrenergic receptors modulate short-term changes in excitation in DH only.
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Hernandes PM, Batistela MF, Vilela-Costa HH, Sant'Ana AB, Kumpel VD, Tirapelle MC, Bom ADOP, de Andrade TGCS, Zangrossi H. Role of 5-HT 1A receptors in the ventral hippocampus in the regulation of anxiety- and panic-related defensive behaviors in rats. Behav Brain Res 2021; 408:113296. [PMID: 33862061 DOI: 10.1016/j.bbr.2021.113296] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 04/06/2021] [Accepted: 04/11/2021] [Indexed: 01/04/2023]
Abstract
Changes in 5-HT1A receptor (5-HT1AR)-mediated neurotransmission in the hippocampus have been associated with anxiety, depression and in the mode of action of antidepressant drugs. It has been commonly accepted that whereas the dorsal pole of the hippocampus (DH) is involved in cognitive processing, the ventral pole (VH) is associated with emotional regulation. However, to date, only a few studies have directly addressed the role played by VH 5-HT1ARs in anxiety and panic processing, and their results are conflicting. Here we report that intra-VH administration of the 5-HT1A receptor agonist 8-OH-DPAT, the endogenous agonist serotonin (5-HT), or the standard anxiolytic benzodiazepine midazolam impaired the acquisition of inhibitory avoidance in the elevated T-maze (ETM) of male Wistar rats, indicating an anxiolytic effect. Conversely, local injection of the 5-HT1AR antagonist WAY-100635 caused the opposite effect. These results were equally found in the Vogel conflict test. None of these drugs interfered with locomotor activity in the open-field test, nor did they alter the expression of the escape response in the ETM, a defensive behavior associated with panic. Pre-injection of a sub-effective dose of WAY-100635 in the VH blocked the anxiolytic effect of 5-HT or 8-OH-DPAT in the Vogel test, confirming the involvement of 5-HT1AR for this behavioral effect. The effect in this test was anxiety-selective as none of the drugs affected water consumption or nociception. In conclusion, our results suggest that 5-HT1ARs in the VH play a tonic inhibitory role in anxiety processing. These receptors, however, are not involved in the regulation of panic-related escape behavior.
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Affiliation(s)
- Paloma Molina Hernandes
- Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Matheus Fitipaldi Batistela
- Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Heloísa Helena Vilela-Costa
- Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Ana Beatriz Sant'Ana
- Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil
| | - Vinicíus Dias Kumpel
- Department of Biological Science, São Paulo State University (UNESP), Assis, SP, Brazil
| | | | | | | | - Hélio Zangrossi
- Department of Pharmacology, School of Medicine of Ribeirão Preto, University of São Paulo (USP), Ribeirão Preto, SP, Brazil.
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Wang J, John Y, Barbas H. Pathways for Contextual Memory: The Primate Hippocampal Pathway to Anterior Cingulate Cortex. Cereb Cortex 2021; 31:1807-1826. [PMID: 33207365 PMCID: PMC7869091 DOI: 10.1093/cercor/bhaa333] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 10/13/2020] [Accepted: 10/14/2020] [Indexed: 12/27/2022] Open
Abstract
The anterior cingulate cortex (ACC) is one of the few prefrontal areas that receives robust direct hippocampal terminations. This pathway may enable current context and past experience to influence goal-directed actions and emotional regulation by prefrontal cortices. We investigated the still ill-understood organization of the pathway from anterior hippocampus to ACC (A24a, A25, A32) to identify laminar termination patterns and their postsynaptic excitatory and inhibitory targets from system to synapse in rhesus monkeys. The densest hippocampal terminations targeted posterior A25, a region that is involved in affective and autonomic regulation. Hippocampal terminations innervated mostly excitatory neurons (~90%), suggesting strong excitatory effects. Among the smaller fraction of inhibitory targets, hippocampal terminations in A25 preferentially innervated calretinin neurons, a pattern that differs markedly from rodents. Further, hippocampal terminations innervated spines with D1 receptors, particularly in the deep layers of A25, where D1 receptors are enriched in comparison with the upper layers. The proximity of hippocampal terminations to D1 receptors may enable dopamine to enhance information transfer from the hippocampus to A25 and contribute to dopaminergic influence downstream on goal-directed action and emotional control by prefrontal cortices, in processes that may be disrupted by excessive dopamine release during uncontrollable stress.
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Affiliation(s)
- Jingyi Wang
- Department of Health Sciences, Neural Systems Laboratory, Boston University, Boston, MA 02215, USA
| | - Yohan John
- Department of Health Sciences, Neural Systems Laboratory, Boston University, Boston, MA 02215, USA
| | - Helen Barbas
- Department of Health Sciences, Neural Systems Laboratory, Boston University, Boston, MA 02215, USA
- Graduate Program in Neuroscience, Boston University and School of Medicine, Boston, MA 02215, USA
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Lothmann K, Deitersen J, Zilles K, Amunts K, Herold C. New boundaries and dissociation of the mouse hippocampus along the dorsal-ventral axis based on glutamatergic, GABAergic and catecholaminergic receptor densities. Hippocampus 2020; 31:56-78. [PMID: 32986281 DOI: 10.1002/hipo.23262] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 08/31/2020] [Accepted: 09/05/2020] [Indexed: 02/01/2023]
Abstract
In rodents, gene-expression, neuronal tuning, connectivity and neurogenesis studies have postulated that the dorsal, the intermediate and the ventral hippocampal formation (HF) are distinct entities. These findings are underpinned by behavioral studies showing a dissociable role of dorsal and ventral HF in learning, memory, stress and emotional processing. However, up to now, the molecular basis of such differences in relation to discrete boundaries is largely unknown. Therefore, we analyzed binding site densities for glutamatergic AMPA, NMDA, kainate and mGluR2/3 , GABAergic GABAA (including benzodiazepine binding sites), GABAB , dopaminergic D1/5 and noradrenergic α1 and α2 receptors as key modulators for signal transmission in hippocampal functions, using quantitative in vitro receptor autoradiography along the dorsal-ventral axis of the mouse HF. Beside general different receptor profiles of the dentate gyrus (DG) and Cornu Ammonis fields (CA1, CA2, CA3, CA4/hilus), we detected substantial differences between dorsal, intermediate and ventral subdivisions and individual layers for all investigated receptor types, except GABAB . For example, striking higher densities of α2 receptors were detected in the ventral DG, while the dorsal DG possesses higher numbers of kainate, NMDA, GABAA and D1/5 receptors. CA1 dorsal and intermediate subdivisions showed higher AMPA, NMDA, mGluR2/3 , GABAA , D1/5 receptors, while kainate receptors are higher expressed in ventral CA1, and noradrenergic α1 and α2 receptors in the intermediate region of CA1. CA2 dorsal was distinguished by higher kainate, α1 and α2 receptors in the intermediate region, while CA3 showed a more complex dissociation. Our findings resulted not only in a clear segmentation of the mouse hippocampus along the dorsal-ventral axis, but also provides insights into the neurochemical basis and likely associated physiological processes in hippocampal functions. Therein, the presented data has a high impact for future studies modeling and investigating dorsal, intermediate and ventral hippocampal dysfunction in relation to neurodegenerative diseases or psychiatric disorders.
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Affiliation(s)
- Kimberley Lothmann
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany
| | - Jana Deitersen
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany
| | - Karl Zilles
- Institute of Neuroscience and Medicine INM-1, Research Centre Jülich, 52425, Jülich, Germany
| | - Katrin Amunts
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany.,Institute of Neuroscience and Medicine INM-1, Research Centre Jülich, 52425, Jülich, Germany
| | - Christina Herold
- C. & O. Vogt-Institute for Brain Research, Medical Faculty, University Clinic Düsseldof, Heinrich Heine University of Düsseldorf, Düsseldorf, Germany
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Oh SJ, Cheng J, Jang JH, Arace J, Jeong M, Shin CH, Park J, Jin J, Greengard P, Oh YS. Hippocampal mossy cell involvement in behavioral and neurogenic responses to chronic antidepressant treatment. Mol Psychiatry 2020; 25:1215-1228. [PMID: 30837688 DOI: 10.1038/s41380-019-0384-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/05/2018] [Revised: 01/29/2019] [Accepted: 02/14/2019] [Indexed: 12/28/2022]
Abstract
Most antidepressants, including selective serotonin reuptake inhibitors (SSRIs), initiate their drug actions by rapid elevation of serotonin, but they take several weeks to achieve therapeutic onset. This therapeutic delay suggests slow adaptive changes in multiple neuronal subtypes and their neural circuits over prolonged periods of drug treatment. Mossy cells are excitatory neurons in the dentate hilus that regulate dentate gyrus activity and function. Here we show that neuronal activity of hippocampal mossy cells is enhanced by chronic, but not acute, SSRI administration. Behavioral and neurogenic effects of chronic treatment with the SSRI, fluoxetine, are abolished by mossy cell-specific knockout of p11 or Smarca3 or by an inhibition of the p11/AnxA2/SMARCA3 heterohexamer, an SSRI-inducible protein complex. Furthermore, simple chemogenetic activation of mossy cells using Gq-DREADD is sufficient to elevate the proliferation and survival of the neural stem cells. Conversely, acute chemogenetic inhibition of mossy cells using Gi-DREADD impairs behavioral and neurogenic responses to chronic administration of SSRI. The present data establish that mossy cells play a crucial role in mediating the effects of chronic antidepressant medication. Our results indicate that compounds that target mossy cell activity would be attractive candidates for the development of new antidepressant medications.
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Affiliation(s)
- Seo-Jin Oh
- Department of Brain-Cognitive Science, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Hyenpung-myeon, Dalseong-gun, Daegu, Republic of Korea
| | - Jia Cheng
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY, 10065, USA
| | - Jin-Hyeok Jang
- Department of Brain-Cognitive Science, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Hyenpung-myeon, Dalseong-gun, Daegu, Republic of Korea
| | - Jeffrey Arace
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY, 10065, USA
| | - Minseok Jeong
- Department of Brain-Cognitive Science, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Hyenpung-myeon, Dalseong-gun, Daegu, Republic of Korea
| | - Chang-Hoon Shin
- Department of Brain-Cognitive Science, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Hyenpung-myeon, Dalseong-gun, Daegu, Republic of Korea
| | - Jeongrak Park
- Department of Brain-Cognitive Science, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Hyenpung-myeon, Dalseong-gun, Daegu, Republic of Korea
| | - Junghee Jin
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY, 10065, USA
| | - Paul Greengard
- Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY, 10065, USA
| | - Yong-Seok Oh
- Department of Brain-Cognitive Science, Daegu-Gyeongbuk Institute of Science and Technology (DGIST), Hyenpung-myeon, Dalseong-gun, Daegu, Republic of Korea.
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Mlinar B, Corradetti R. Differential modulation of CA1 impulse flow by endogenous serotonin along the hippocampal longitudinal axis. Hippocampus 2018; 28:217-225. [DOI: 10.1002/hipo.22825] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2017] [Revised: 12/11/2017] [Accepted: 12/14/2017] [Indexed: 11/08/2022]
Affiliation(s)
- Boris Mlinar
- Department of Neuroscience, Psychology, Drug Research and Child Health; University of Florence; Florence Italy
| | - Renato Corradetti
- Department of Neuroscience, Psychology, Drug Research and Child Health; University of Florence; Florence Italy
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Lasting Differential Effects on Plasticity Induced by Prenatal Stress in Dorsal and Ventral Hippocampus. Neural Plast 2016; 2016:2540462. [PMID: 26881096 PMCID: PMC4736977 DOI: 10.1155/2016/2540462] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 11/18/2015] [Accepted: 12/20/2015] [Indexed: 12/14/2022] Open
Abstract
Early life adversaries have a profound impact on the developing brain structure and functions that persist long after the original traumatic experience has vanished. One of the extensively studied brain structures in relation to early life stress has been the hippocampus because of its unique association with cognitive processes of the brain. While the entire hippocampus shares the same intrinsic organization, it assumes different functions in its dorsal and ventral sectors (DH and VH, resp.), based on different connectivity with other brain structures. In the present review, we summarize the differences between DH and VH and discuss functional and structural effects of prenatal stress in the two sectors, with the realization that much is yet to be explored in understanding the opposite reactivity of the DH and VH to stressful stimulation.
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12
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Kouvaros S, Papatheodoropoulos C. Major dorsoventral differences in the modulation of the local CA1 hippocampal network by NMDA, mGlu5, adenosine A2A and cannabinoid CB1 receptors. Neuroscience 2016; 317:47-64. [PMID: 26762803 DOI: 10.1016/j.neuroscience.2015.12.059] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Revised: 12/23/2015] [Accepted: 12/30/2015] [Indexed: 11/29/2022]
Abstract
Recent research points to diversification in the local neuronal circuitry between dorsal (DH) and ventral (VH) hippocampus that may be involved in the large-scale functional segregation along the long axis of the hippocampus. Here, using CA1 field recordings from rat hippocampal slices, we show that activation of N-methyl-d-aspartate receptors (NMDARs) reduced excitatory transmission more in VH than in DH, with an adenosine A1 receptor-independent mechanism, and reduced inhibition and enhanced postsynaptic excitability only in DH. Strikingly, co-activation of metabotropic glutamate receptor-5 (mGluR5) with NMDAR, by CHPG and NMDA respectively, strongly potentiated the effects of NMDAR in DH but had not any potentiating effect in VH. Furthermore, the synergistic actions in DH were occluded by blockade of adenosine A2A receptors (A2ARs) by their antagonist ZM 241385 demonstrating a tonic action of these receptors in DH. Exogenous activation of A2ARs by 4-[2-[[6-amino-9-(N-ethyl-β-D-ribofuranuronamidosyl)-9H-purin-2-yl]amino]ethyl]benzenepropanoic acid hydrochloride (CGS 21680) did not change the effects of mGluR5-NMDAR co-activation in either hippocampal pole. Importantly, blockade of cannabinoid CB1 receptors (CB1Rs) by their antagonist 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-4-morpholinyl-1H-pyrazole-3-carboxamide (AM 281) restricted the synergistic actions of mGluR5-NMDARs on excitatory synaptic transmission and postsynaptic excitability and abolished their effect on inhibition. Furthermore, AM 281 increased the excitatory transmission only in DH indicating that CB1Rs were tonically active in DH but not VH. Removing the magnesium ions from the perfusion medium neither stimulated the interaction between mGluR5 and NMDAR in VH nor augmented the synergy of the two receptors in DH. These findings show that the NMDAR-dependent modulation of fundamental parameters of the local neuronal network, by mGluR5, A2AR and CB1R, markedly differs between DH and VH. We propose that the higher modulatory role of A2AR and mGluR5, in combination with the role of CB1Rs, provide DH with higher functional flexibility of its NMDARs, compared with VH.
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Affiliation(s)
- S Kouvaros
- Laboratory of Physiology, Department of Medicine, School of Health Sciences, University of Patras, 26504 Rion, Greece
| | - C Papatheodoropoulos
- Laboratory of Physiology, Department of Medicine, School of Health Sciences, University of Patras, 26504 Rion, Greece.
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Papatheodoropoulos C. Higher intrinsic network excitability in ventral compared with the dorsal hippocampus is controlled less effectively by GABAB receptors. BMC Neurosci 2015; 16:75. [PMID: 26556486 PMCID: PMC4641374 DOI: 10.1186/s12868-015-0213-z] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2015] [Accepted: 11/04/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Elucidating specializations of the intrinsic neuronal network between the dorsal and the ventral hippocampus is a recently emerging area of research that is expected to help us understand the mechanisms underlying large scale functional diversification along the hippocampus. The aim of this study was to characterize spontaneous network activity between the dorsal and the ventral hippocampus induced under conditions of partial or complete blockade of GABAergic inhibition (i.e. disinhibition). RESULTS Using field recordings from the CA3 and CA1 fields of hippocampal slices from adult rats I found that ventral compared with dorsal hippocampus slices displayed higher propensity for and higher frequency of occurrence of spontaneous field potentials (spfps) at every level of disinhibition. Also NMDA receptor-depended spfps (spfps(-nmda)) occurred with higher probability more frequently and were larger in the ventral compared with the dorsal hippocampus. Importantly, blockade of GABA(B) receptors produced a stronger effect in enhancing the probability of generation of spfps and spfps(-nmda) in the dorsal compared with the ventral hippocampal slices and increased spfps(-nmda) only in dorsal slices. CONCLUSION These results demonstrate a higher intrinsic neuronal excitability of the ventral compared with the dorsal local circuitry with the considerable contribution of NMDA receptors. Furthermore, the GABA(B) receptors control the total and the NMDA receptor-dependent excitation much less effectively in the ventral part of the hippocampus. It is proposed that NMDA and GABA(B) receptors significantly contribute to differentiate local network dynamics between the dorsal and the ventral hippocampus with important implications in the information processing performed along the long hippocampal axis.
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Affiliation(s)
- Costas Papatheodoropoulos
- Laboratory of Physiology, Department of Medicine, School of Health Sciences, University of Patras, Rion, 26504, Patras, Greece.
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14
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Kondo M, Nakamura Y, Ishida Y, Shimada S. The 5-HT3 receptor is essential for exercise-induced hippocampal neurogenesis and antidepressant effects. Mol Psychiatry 2015; 20:1428-37. [PMID: 25403840 DOI: 10.1038/mp.2014.153] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 10/03/2014] [Accepted: 10/08/2014] [Indexed: 12/22/2022]
Abstract
Exercise has a variety of beneficial effects on brain structure and function, such as hippocampal neurogenesis, mood and memory. Previous studies have shown that exercise enhances hippocampal neurogenesis, induces antidepressant effects and improves learning behavior. Brain serotonin (5-hydroxytryptamine, 5-HT) levels increase following exercise, and the 5-HT system has been suggested to have an important role in these exercise-induced neuronal effects. However, the precise mechanism remains unclear. In this study, analysis of the 5-HT type 3A receptor subunit-deficient (htr3a(-/-)) mice revealed that lack of the 5-HT type 3 (5-HT3) receptor resulted in loss of exercise-induced hippocampal neurogenesis and antidepressant effects, but not of learning enhancement. Furthermore, stimulation of the 5-HT3 receptor promoted neurogenesis. These findings demonstrate that the 5-HT3 receptor is the critical target of 5-HT action in the brain following exercise, and is indispensable for hippocampal neurogenesis and antidepressant effects induced by exercise. This is the first report of a pivotal 5-HT receptor subtype that has a fundamental role in exercise-induced morphological changes and psychological effects.
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Affiliation(s)
- M Kondo
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Y Nakamura
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - Y Ishida
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, Japan
| | - S Shimada
- Department of Neuroscience and Cell Biology, Graduate School of Medicine, Osaka University, Suita, Japan
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15
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A septo-temporal molecular gradient of sfrp3 in the dentate gyrus differentially regulates quiescent adult hippocampal neural stem cell activation. Mol Brain 2015; 8:52. [PMID: 26337530 PMCID: PMC4559945 DOI: 10.1186/s13041-015-0143-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2015] [Accepted: 08/25/2015] [Indexed: 12/13/2022] Open
Abstract
Background A converging body of evidence indicates that levels of adult hippocampal neurogenesis vary along the septo-temporal axis of the dentate gyrus, but the molecular mechanisms underlying this regional heterogeneity are not known. We previously identified a niche mechanism regulating proliferation and neuronal development in the adult mouse dentate gyrus resulting from the activity-regulated expression of secreted frizzled-related protein 3 (sfrp3) by mature neurons, which suppresses activation of radial glia-like neural stem cells (RGLs) through inhibition of Wingless/INT (WNT) protein signaling. Results Here, we show that activation rates within the quiescent RGL population decrease gradually along the septo-temporal axis in the adult mouse dentate gyrus, as defined by MCM2 expression in RGLs. Using in situ hybridization and quantitative real-time PCR, we identified an inverse septal-to-temporal increase in the expression of sfrp3 that emerges during postnatal development. Elimination of sfrp3 and its molecular gradient leads to increased RGL activation, preferentially in the temporal region of the adult dentate gyrus. Conclusions Our study identifies a niche mechanism that contributes to the graded distribution of neurogenesis in the adult dentate gyrus and has important implications for understanding functional differences associated with adult hippocampal neurogenesis along the septo-temporal axis.
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16
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Wu MV, Sahay A, Duman RS, Hen R. Functional differentiation of adult-born neurons along the septotemporal axis of the dentate gyrus. Cold Spring Harb Perspect Biol 2015; 7:a018978. [PMID: 26238355 DOI: 10.1101/cshperspect.a018978] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Over the past several decades, the proliferation and integration of adult-born neurons into existing hippocampal circuitry has been implicated in a wide range of behaviors, including novelty recognition, pattern separation, spatial learning, anxiety behaviors, and antidepressant response. In this review, we suggest that the diversity in behavioral requirements for new neurons may be partly caused by separate functional roles of individual neurogenic niches. Growing evidence shows that the hippocampal formation can be compartmentalized not only along the classic trisynaptic circuit, but also along a longitudinal septotemporal axis. We suggest that subpopulations of hippocampal adult-born neurons may be specialized for distinct mnemonic- or mood-related behavioral tasks. We will examine the literature supporting a functional and anatomical dissociation of the hippocampus along the longitudinal axis and discuss techniques to functionally dissect the roles of adult-born hippocampal neurons in these distinct subregions.
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Affiliation(s)
- Melody V Wu
- Department of Psychiatry, Columbia University, New York, New York 10027 Division of Integrative Neuroscience, New York State Psychiatric Institute, New York, New York 10032
| | - Amar Sahay
- Center for Regenerative Medicine and Department of Psychiatry, Massachusetts General Hospital, Boston, Massachusetts 02114 Harvard Stem Cell Institute and Harvard Medical School, Boston, Massachusetts 02115
| | - Ronald S Duman
- Department of Psychiatry, Yale University, New Haven, Connecticut 06520 Department of Neurobiology, Yale University, New Haven, Connecticut 06520
| | - René Hen
- Department of Psychiatry, Columbia University, New York, New York 10027 Division of Integrative Neuroscience, New York State Psychiatric Institute, New York, New York 10032 Department of Neuroscience, Columbia University, New York, New York 10027 Department of Pharmacology, Columbia University, New York, New York 10027
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17
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Striking differences in synaptic facilitation along the dorsoventral axis of the hippocampus. Neuroscience 2015; 301:454-70. [DOI: 10.1016/j.neuroscience.2015.06.029] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 05/07/2015] [Accepted: 06/18/2015] [Indexed: 12/23/2022]
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18
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McAvoy K, Russo C, Kim S, Rankin G, Sahay A. Fluoxetine induces input-specific hippocampal dendritic spine remodeling along the septotemporal axis in adulthood and middle age. Hippocampus 2015; 25:1429-46. [PMID: 25850664 DOI: 10.1002/hipo.22464] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/01/2015] [Indexed: 12/15/2022]
Abstract
Fluoxetine, a selective serotonin-reuptake inhibitor (SSRI), is known to induce structural rearrangements and changes in synaptic transmission in hippocampal circuitry. In the adult hippocampus, structural changes include neurogenesis, dendritic, and axonal plasticity of pyramidal and dentate granule neurons, and dedifferentiation of dentate granule neurons. However, much less is known about how chronic fluoxetine affects these processes along the septotemporal axis and during the aging process. Importantly, studies documenting the effects of fluoxetine on density and distribution of spines along different dendritic segments of dentate granule neurons and CA1 pyramidal neurons along the septotemporal axis of hippocampus in adulthood and during aging are conspicuously absent. Here, we use a transgenic mouse line in which mature dentate granule neurons and CA1 pyramidal neurons are genetically labeled with green fluorescent protein (GFP) to investigate the effects of chronic fluoxetine treatment (18 mg/kg/day) on input-specific spine remodeling and mossy fiber structural plasticity in the dorsal and ventral hippocampus in adulthood and middle age. In addition, we examine levels of adult hippocampal neurogenesis, maturation state of dentate granule neurons, neuronal activity, and glutamic acid decarboxylase-67 expression in response to chronic fluoxetine in adulthood and middle age. Our studies reveal that while chronic fluoxetine fails to augment adult hippocampal neurogenesis in middle age, the middle-aged hippocampus retains high sensitivity to changes in the dentate gyrus (DG) such as dematuration, hypoactivation, and increased glutamic acid decarboxylase 67 (GAD67) expression. Interestingly, the middle-aged hippocampus shows greater sensitivity to fluoxetine-induced input-specific synaptic remodeling than the hippocampus in adulthood with the stratum-oriens of CA1 exhibiting heightened structural plasticity. The input-specific changes and circuit-level modifications in middle-age were associated with modest enhancement in contextual fear memory precision, anxiety-like behavior and antidepressant-like behavioral responses.
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Affiliation(s)
- Kathleen McAvoy
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.,Harvard Stem Cell Institute, Harvard University, Boston, Massachusetts.,Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Craig Russo
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.,Harvard Stem Cell Institute, Harvard University, Boston, Massachusetts.,Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Shannen Kim
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.,Harvard Stem Cell Institute, Harvard University, Boston, Massachusetts.,Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Genelle Rankin
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.,Harvard Stem Cell Institute, Harvard University, Boston, Massachusetts.,Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
| | - Amar Sahay
- Center for Regenerative Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts.,Harvard Stem Cell Institute, Harvard University, Boston, Massachusetts.,Department of Psychiatry, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts
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19
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Chronic P7C3 treatment restores hippocampal neurogenesis in the Ts65Dn mouse model of Down Syndrome [Corrected]. Neurosci Lett 2015; 591:86-92. [PMID: 25668489 DOI: 10.1016/j.neulet.2015.02.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2014] [Revised: 01/20/2015] [Accepted: 02/06/2015] [Indexed: 12/11/2022]
Abstract
Down syndrome (DS) is the most common genetic cause of intellectual disability and developmental delay. In addition to cognitive dysfunction, DS patients are marked by diminished neurogenesis, a neuropathological feature also found in the Ts65Dn mouse model of DS. Interestingly, manipulations that enhance neurogenesis - like environmental enrichment or pharmacological agents - improve cognition in Ts65Dn mice. P7C3 is a proneurogenic compound that enhances hippocampal neurogenesis, cell survival, and promotes cognition in aged animals. However, this compound has not been tested in the Ts65Dn mouse model of DS. We hypothesized that P7C3 treatment would reverse or ameliorate the neurogenic deficits in Ts65Dn mice. To test this, adult Ts65Dn and age-matched wild-type (WT) mice were administered vehicle or P7C3 twice daily for 3 months. After 3 months, brains were examined for indices of neurogenesis, including quantification of Ki67, DCX, activated caspase-3 (AC3), and surviving BrdU-immunoreactive(+) cells in the granule cell layer (GCL) of the hippocampal dentate gyrus. P7C3 had no effect on total Ki67+, DCX+, AC3+, or surviving BrdU+ cells in WT mice relative to vehicle. GCL volume was also not changed. In keeping with our hypothesis, however, P7C3-treated Ts65Dn mice had a significant increase in total Ki67+, DCX+, and surviving BrdU+ cells relative to vehicle. P7C3 treatment also decreased AC3+ cell number but had no effect on total GCL volume in Ts65Dn mice. Our findings show 3 months of P7C3 is sufficient to restore the neurogenic deficits observed in the Ts65Dn mouse model of DS.
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20
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O'Leary OF, Cryan JF. A ventral view on antidepressant action: roles for adult hippocampal neurogenesis along the dorsoventral axis. Trends Pharmacol Sci 2014; 35:675-87. [PMID: 25455365 DOI: 10.1016/j.tips.2014.09.011] [Citation(s) in RCA: 138] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2014] [Revised: 09/29/2014] [Accepted: 09/30/2014] [Indexed: 11/26/2022]
Abstract
Adult hippocampal neurogenesis is implicated in antidepressant action, stress responses, and cognitive functioning. The hippocampus is functionally segregated along its longitudinal axis into dorsal (dHi) and ventral (vHi) regions in rodents, and analogous posterior and anterior regions in primates, whereby the vHi preferentially regulates stress and anxiety, while the dHi preferentially regulates spatial learning and memory. Given the role of neurogenesis in functions preferentially regulated by the dHi or vHi, it is plausible that neurogenesis is preferentially regulated in either the dHi or vHi depending upon the stimulus. We appraise here the literature on the effects of stress and antidepressants on neurogenesis along the hippocampal longitudinal axis and explore whether preferential regulation of neurogenesis in the vHi/anterior hippocampus contributes to stress resilience and antidepressant action.
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Affiliation(s)
- Olivia F O'Leary
- Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland; Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland.
| | - John F Cryan
- Department of Anatomy and Neuroscience, University College Cork, Cork, Ireland; Alimentary Pharmabiotic Centre, University College Cork, Cork, Ireland
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21
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Carabelli B, Delattre AM, Pudell C, Mori MA, Suchecki D, Machado RB, Venancio DP, Piazzetta SR, Hammerschmidt I, Zanata SM, Lima MMS, Zanoveli JM, Ferraz AC. The Antidepressant-Like Effect of Fish Oil: Possible Role of Ventral Hippocampal 5-HT1A Post-synaptic Receptor. Mol Neurobiol 2014; 52:206-15. [DOI: 10.1007/s12035-014-8849-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 07/31/2014] [Indexed: 01/05/2023]
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22
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Tannenholz L, Jimenez JC, Kheirbek MA. Local and regional heterogeneity underlying hippocampal modulation of cognition and mood. Front Behav Neurosci 2014; 8:147. [PMID: 24834033 PMCID: PMC4018538 DOI: 10.3389/fnbeh.2014.00147] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 04/11/2014] [Indexed: 11/17/2022] Open
Abstract
While the hippocampus has been classically studied for its role in learning and memory, there is significant support for a role of the HPC in regulating emotional behavior. Emerging research suggests these functions may be segregated along the dorsoventral axis of the HPC. In addition to this regional heterogeneity, within the HPC, the dentate gyrus is one of two areas in the adult brain where stem cells continuously give rise to new neurons. This process can influence and be modulated by the emotional state of the animal, suggesting that adult neurogenesis within the DG may contribute to psychiatric disorders and cognitive abilities. Yet, the exact mechanism by which these newborn neurons influence behavior remains unknown. Here, we will examine the contribution of hippocampal neurogenesis to the output of the HPC, and suggest that the role of neurogenesis may vary along the DV axis. Next, we will review literature indicating that anatomical connectivity varies along the DV axis of the HPC, and that this underlies the functional segregation along this axis. This analysis will allow us to synthesize novel hypotheses for the differential contribution of the HPC to cognition and mood.
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Affiliation(s)
- Lindsay Tannenholz
- Department of Pharmacology, Columbia University New York, NY, USA ; Division of Integrative Neuroscience, New York State Psychiatric Institute New York, NY, USA
| | - Jessica C Jimenez
- Division of Integrative Neuroscience, New York State Psychiatric Institute New York, NY, USA ; Department of Neuroscience, Columbia University New York, NY, USA
| | - Mazen A Kheirbek
- Division of Integrative Neuroscience, New York State Psychiatric Institute New York, NY, USA ; Department of Psychiatry, Columbia University New York, NY, USA
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23
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Latchney SE, Masiulis I, Zaccaria KJ, Lagace DC, Powell CM, McCasland JS, Eisch AJ. Developmental and adult GAP-43 deficiency in mice dynamically alters hippocampal neurogenesis and mossy fiber volume. Dev Neurosci 2014; 36:44-63. [PMID: 24576816 DOI: 10.1159/000357840] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 12/09/2013] [Indexed: 12/29/2022] Open
Abstract
Growth-associated protein-43 (GAP-43) is a presynaptic protein that plays key roles in axonal growth and guidance and in modulating synapse formation. Previous work has demonstrated that mice lacking one allele of this gene (GAP-43+/- mice) exhibit hippocampal structural abnormalities, impaired spatial learning and stress-induced behavioral withdrawal and anxiety, behaviors that are dependent on proper hippocampal circuitry and function. Given the correlation between hippocampal function, synaptic connectivity and neurogenesis, we tested if behaviorally naïve GAP-43+/- mice had alterations in either neurogenesis or synaptic connectivity in the hippocampus during early postnatal development and young adulthood, and following behavior testing in older adults. To test our hypothesis, we examined hippocampal cell proliferation (Ki67), number of immature neuroblasts (doublecortin, DCX) and mossy fiber volume (synaptoporin) in behaviorally naïve postnatal day 9 (P9) and P26, and behaviorally experienced 5- to 7-month-old GAP-43+/- and +/+ littermate mice. P9 GAP-43+/- mice had fewer Ki67+ and DCX+ cells compared to +/+ mice, particularly in the posterior dentate gyrus, and smaller mossy fiber volume in the same region. In young adulthood, however, male GAP-43+/- mice had more Ki67+ and DCX+ cells and greater mossy fiber volume in the posterior dentate gyrus relative to male +/+ mice. These increases were not seen in females. In 5- to 7-month-old GAP-43+/- mice (whose behaviors were the focus of our prior publication), there was no global change in the number of proliferating or immature neurons relative to +/+ mice. However, more detailed analysis revealed fewer proliferative DCX+ cells in the anterior dentate gyrus of male GAP-43+/- mice compared to male +/+ mice. This reduction was not observed in females. These results suggest that young GAP-43+/- mice have decreased hippocampal neurogenesis and synaptic connectivity, but slightly older mice have greater hippocampal neurogenesis and synaptic connectivity. In conjunction with our previous study, these findings suggest that GAP-43 is dynamically involved in early postnatal and adult hippocampal neurogenesis and synaptic connectivity, possibly contributing to the GAP-43+/- behavioral phenotype.
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Affiliation(s)
- Sarah E Latchney
- Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Tex., USA
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24
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Shruster A, Offen D. Targeting neurogenesis ameliorates danger assessment in a mouse model of Alzheimer's disease. Behav Brain Res 2013; 261:193-201. [PMID: 24388979 DOI: 10.1016/j.bbr.2013.12.028] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2013] [Revised: 12/17/2013] [Accepted: 12/21/2013] [Indexed: 01/21/2023]
Abstract
Alzheimer's disease (AD) affects 13% of the population over the age of 65. Behavioral and neuropsychiatric symptoms are frequent and affect 80% of patients. Adult hippocampal neurogenesis, which is impaired in AD, is involved in learning and memory. It remains unclear, however, whether increasing adult neurogenesis improves behavioral symptoms in AD. We report that in the 3xTgAD mouse model of AD, chronic Wnt3a overexpression in the ventral hippocampus dentate gyrus (DG) restored adult neurogenesis to physiological levels. The restoration of adult neurogenesis led to full recovery of danger assessment impairment and the effect was blocked by ablation of neurogenesis with X-irradiation. Finally, using a bed nucleus of stria terminalis (BNST) mRNA expression array, we found that the expression of the 5-HT1A receptor in 3xTgAD mice is selectively decreased and normalized by Wnt3a overexpression in the ventral hippocampus DG, and this normalization is neurogenesis dependent. These findings indicate that reestablishing a functional population of hippocampal newborn neurons in adult AD mice rescues behavioral symptoms, suggesting that adult neurogenesis may be a promising therapeutic target for alleviating behavioral deficits in AD patients.
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Affiliation(s)
- Adi Shruster
- Laboratory of Neuroscience, Felsenstein Medical Research Center, Sackler Faculty of Medicine, Tel-Aviv University, Petah Tikva, Israel.
| | - Daniel Offen
- Laboratory of Neuroscience, Felsenstein Medical Research Center, Sackler Faculty of Medicine, Tel-Aviv University, Petah Tikva, Israel
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25
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Mahar I, Bambico FR, Mechawar N, Nobrega JN. Stress, serotonin, and hippocampal neurogenesis in relation to depression and antidepressant effects. Neurosci Biobehav Rev 2013; 38:173-92. [PMID: 24300695 DOI: 10.1016/j.neubiorev.2013.11.009] [Citation(s) in RCA: 414] [Impact Index Per Article: 37.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Revised: 11/19/2013] [Accepted: 11/25/2013] [Indexed: 01/19/2023]
Abstract
Chronic stressful life events are risk factors for developing major depression, the pathophysiology of which is strongly linked to impairments in serotonin (5-HT) neurotransmission. Exposure to chronic unpredictable stress (CUS) has been found to induce depressive-like behaviours, including passive behavioural coping and anhedonia in animal models, along with many other affective, cognitive, and behavioural symptoms. The heterogeneity of these symptoms represents the plurality of corticolimbic structures involved in mood regulation that are adversely affected in the disorder. Chronic stress has also been shown to negatively regulate adult hippocampal neurogenesis, a phenomenon that is involved in antidepressant effects and regulates subsequent stress responses. Although there exists an enormous body of data on stress-induced alterations of 5-HT activity, there has not been extensive exploration of 5-HT adaptations occurring presynaptically or at the level of the raphe nuclei after exposure to CUS. Similarly, although hippocampal neurogenesis is known to be negatively regulated by stress and positively regulated by antidepressant treatment, the role of neurogenesis in mediating affective behaviour in the context of stress remains an active area of investigation. The goal of this review is to link the serotonergic and neurogenic hypotheses of depression and antidepressant effects in the context of stress. Specifically, chronic stress significantly attenuates 5-HT neurotransmission and 5-HT1A autoreceptor sensitivity, and this effect could represent an endophenotypic hallmark for mood disorders. In addition, by decreasing neurogenesis, CUS decreases hippocampal inhibition of the hypothalamic-pituitary-adrenal (HPA) axis, exacerbating stress axis overactivity. Similarly, we discuss the possibility that adult hippocampal neurogenesis mediates antidepressant effects via the ventral (in rodents; anterior in humans) hippocampus' influence on the HPA axis, and mechanisms by which antidepressants may reverse chronic stress-induced 5-HT and neurogenic changes. Although data are as yet equivocal, antidepressant modulation of 5-HT neurotransmission may well serve as one of the factors that could drive neurogenesis-dependent antidepressant effects through these stress regulation-related mechanisms.
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Affiliation(s)
- Ian Mahar
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, Verdun, QC, Canada; Integrated Program in Neuroscience, McGill University, Montreal, QC, Canada.
| | | | - Naguib Mechawar
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, Verdun, QC, Canada; Integrated Program in Neuroscience, McGill University, Montreal, QC, Canada; Department of Psychiatry, McGill University, Montreal, QC, Canada
| | - José N Nobrega
- Behavioural Neurobiology Laboratory, Centre for Addiction and Mental Health, Toronto, ON, Canada; Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON, Canada; Department of Psychiatry, University of Toronto, Toronto, ON, Canada; Department of Psychology, University of Toronto, Toronto, ON, Canada
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26
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Neurogenesis along the septo-temporal axis of the hippocampus: Are depression and the action of antidepressants region-specific? Neuroscience 2013; 252:234-52. [DOI: 10.1016/j.neuroscience.2013.08.017] [Citation(s) in RCA: 166] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Revised: 07/01/2013] [Accepted: 08/12/2013] [Indexed: 01/25/2023]
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27
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Tanti A, Westphal WP, Girault V, Brizard B, Devers S, Leguisquet AM, Surget A, Belzung C. Region-dependent and stage-specific effects of stress, environmental enrichment, and antidepressant treatment on hippocampal neurogenesis. Hippocampus 2013; 23:797-811. [DOI: 10.1002/hipo.22134] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/05/2013] [Indexed: 11/11/2022]
Affiliation(s)
- Arnaud Tanti
- INSERM UMR930; Tours France
- Université François Rabelais; Tours France
| | | | - Virginie Girault
- INSERM UMR930; Tours France
- Université François Rabelais; Tours France
| | - Bruno Brizard
- INSERM UMR930; Tours France
- Université François Rabelais; Tours France
| | - Severine Devers
- INSERM UMR930; Tours France
- Université François Rabelais; Tours France
| | | | - Alexandre Surget
- INSERM UMR930; Tours France
- Université François Rabelais; Tours France
| | - Catherine Belzung
- INSERM UMR930; Tours France
- Université François Rabelais; Tours France
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SMARCA3, a chromatin-remodeling factor, is required for p11-dependent antidepressant action. Cell 2013; 152:831-43. [PMID: 23415230 DOI: 10.1016/j.cell.2013.01.014] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2012] [Revised: 09/14/2012] [Accepted: 01/08/2013] [Indexed: 02/02/2023]
Abstract
p11, through unknown mechanisms, is required for behavioral and cellular responses to selective serotonin reuptake inhibitors (SSRIs). We show that SMARCA3, a chromatin-remodeling factor, is a target for the p11/annexin A2 heterotetrameric complex. Determination of the crystal structure indicates that SMARCA3 peptide binds to a hydrophobic pocket in the heterotetramer. Formation of this complex increases the DNA-binding affinity of SMARCA3 and its localization to the nuclear matrix fraction. In the dentate gyrus, both p11 and SMARCA3 are highly enriched in hilar mossy cells and basket cells. The SSRI fluoxetine induces expression of p11 in both cell types and increases the amount of the ternary complex of p11/annexin A2/SMARCA3. SSRI-induced neurogenesis and behavioral responses are abolished by constitutive knockout of SMARCA3. Our studies indicate a central role for a chromatin-remodeling factor in the SSRI/p11 signaling pathway and suggest an approach to the development of improved antidepressant therapies. PAPERCLIP:
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Dougherty KA, Nicholson DA, Diaz L, Buss EW, Neuman KM, Chetkovich DM, Johnston D. Differential expression of HCN subunits alters voltage-dependent gating of h-channels in CA1 pyramidal neurons from dorsal and ventral hippocampus. J Neurophysiol 2013; 109:1940-53. [PMID: 23324324 PMCID: PMC3628004 DOI: 10.1152/jn.00010.2013] [Citation(s) in RCA: 70] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 01/12/2013] [Indexed: 12/23/2022] Open
Abstract
The rodent hippocampus can be divided into dorsal (DHC) and ventral (VHC) domains on the basis of behavioral, anatomical, and biochemical differences. Recently, we reported that CA1 pyramidal neurons from the VHC were intrinsically more excitable than DHC neurons, but the specific ionic conductances contributing to this difference were not determined. Here we investigated the hyperpolarization-activated current (I(h)) and the expression of HCN1 and HCN2 channel subunits in CA1 pyramidal neurons from the DHC and VHC. Measurement of Ih with cell-attached patches revealed a significant depolarizing shift in the V(1/2) of activation for dendritic h-channels in VHC neurons (but not DHC neurons), and ultrastructural immunolocalization of HCN1 and HCN2 channels revealed a significantly larger HCN1-to-HCN2 ratio for VHC neurons (but not DHC neurons). These observations suggest that a shift in the expression of HCN1 and HCN2 channels drives functional changes in I(h) for VHC neurons (but not DHC neurons) and could thereby significantly alter the capacity for dendritic integration of these neurons.
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Affiliation(s)
- Kelly A Dougherty
- Center for Learning and Memory, The University of Texas at Austin, Austin, TX 78712, USA.
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Wang ME, Fraize NP, Yin L, Yuan RK, Petsagourakis D, Wann EG, Muzzio IA. Differential roles of the dorsal and ventral hippocampus in predator odor contextual fear conditioning. Hippocampus 2013; 23:451-66. [PMID: 23460388 DOI: 10.1002/hipo.22105] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/11/2013] [Indexed: 01/15/2023]
Abstract
The study of fear memory is important for understanding various anxiety disorders in which patients experience persistent recollections of traumatic events. These memories often involve associations of contextual cues with aversive events; consequently, Pavlovian classical conditioning is commonly used to study contextual fear learning. The use of predator odor as a fearful stimulus in contextual fear conditioning has become increasingly important as an animal model of anxiety disorders. Innate fear responses to predator odors are well characterized and reliable; however, attempts to use these odors as unconditioned stimuli in fear conditioning paradigms have proven inconsistent. Here we characterize a contextual fear conditioning paradigm using coyote urine as the unconditioned stimulus. We found that contextual conditioning induced by exposure to coyote urine produces long-term freezing, a stereotypic response to fear observed in mice. This paradigm is context-specific and parallels shock-induced contextual conditioning in that it is responsive to extinction training and manipulations of predator odor intensity. Region-specific lesions of the dorsal and ventral hippocampus indicate that both areas are independently required for the long-term expression of learned fear. These results in conjunction with c-fos immunostaining data suggest that while both the dorsal and ventral hippocampus are required for forming a contextual representation, the ventral region also modulates defensive behaviors associated with predators. This study provides information about the individual contributions of the dorsal and ventral hippocampus to ethologically relevant fear learning.
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Affiliation(s)
- Melissa E Wang
- Neuroscience Graduate Group, Department of Psychology, University of Pennsylvania, Philadelphia, PA, USA
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Bambico FR, Belzung C. Novel insights into depression and antidepressants: a synergy between synaptogenesis and neurogenesis? Curr Top Behav Neurosci 2013; 15:243-291. [PMID: 23271325 DOI: 10.1007/7854_2012_234] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Major depressive disorder has been associated with manifold pathophysiological changes. These include metabolic abnormalities in discreet brain areas; modifications in the level of stress hormones, neurotransmitters, and neurotrophic factors; impaired spinogenesis and synaptogenesis in crucial brain areas, such as the prefrontal cortex and the hippocampus; and impaired neurogenesis in the hippocampus. Antidepressant therapy facilitates remission by reversing most of these disturbances, indicating that these dysfunctions may participate causally in depressive symptomatology. However, few attempts have been made to integrate these different pathophysiologies into one model. The present chapter endeavors (1) to review the extant literature in the field, with particular focus on the role of neurogenesis and synaptogenesis in depression; (2) and to suggest a possible interplay between these two processes, as well as, describe the ways by which improving both neurogenesis and synaptogenesis may enable effective recovery by acting on a larger neuronal network.
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Affiliation(s)
- Francis Rodriguez Bambico
- Behavioural Neurobiology Laboratory, Research Neuroimaging Division, Center for Addiction and Mental Health, University of Toronto, 250 College Street, Toronto, ON, M5T 1R8, Canada,
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Differential environmental regulation of neurogenesis along the septo-temporal axis of the hippocampus. Neuropharmacology 2012; 63:374-84. [DOI: 10.1016/j.neuropharm.2012.04.022] [Citation(s) in RCA: 122] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 04/16/2012] [Accepted: 04/19/2012] [Indexed: 01/06/2023]
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Ventral hippocampal molecular pathways and impaired neurogenesis associated with 5-HT1A and 5-HT1B receptors disruption in mice. Neurosci Lett 2012; 521:20-5. [DOI: 10.1016/j.neulet.2012.05.046] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 05/10/2012] [Accepted: 05/12/2012] [Indexed: 02/06/2023]
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Mikroulis AV, Psarropoulou C. Endogenous ACh effects on NMDA-induced interictal-like discharges along the septotemporal hippocampal axis of adult rats and their modulation by an early life generalized seizure. Epilepsia 2012; 53:879-87. [DOI: 10.1111/j.1528-1167.2012.03440.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Liang JC, Wagner AD, Preston AR. Content representation in the human medial temporal lobe. ACTA ACUST UNITED AC 2012; 23:80-96. [PMID: 22275474 DOI: 10.1093/cercor/bhr379] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Current theories of medial temporal lobe (MTL) function focus on event content as an important organizational principle that differentiates MTL subregions. Perirhinal and parahippocampal cortices may play content-specific roles in memory, whereas hippocampal processing is alternately hypothesized to be content specific or content general. Despite anatomical evidence for content-specific MTL pathways, empirical data for content-based MTL subregional dissociations are mixed. Here, we combined functional magnetic resonance imaging with multiple statistical approaches to characterize MTL subregional responses to different classes of novel event content (faces, scenes, spoken words, sounds, visual words). Univariate analyses revealed that responses to novel faces and scenes were distributed across the anterior-posterior axis of MTL cortex, with face responses distributed more anteriorly than scene responses. Moreover, multivariate pattern analyses of perirhinal and parahippocampal data revealed spatially organized representational codes for multiple content classes, including nonpreferred visual and auditory stimuli. In contrast, anterior hippocampal responses were content general, with less accurate overall pattern classification relative to MTL cortex. Finally, posterior hippocampal activation patterns consistently discriminated scenes more accurately than other forms of content. Collectively, our findings indicate differential contributions of MTL subregions to event representation via a distributed code along the anterior-posterior axis of MTL that depends on the nature of event content.
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Affiliation(s)
- Jackson C Liang
- Department of Psychology, Center for Learning and Memory, Institute for Neuroscience, University of Texas at Austin, Austin, TX 78712, USA
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Mahar I, Tan S, Davoli MA, Dominguez-Lopez S, Qiang C, Rachalski A, Turecki G, Mechawar N. Subchronic peripheral neuregulin-1 increases ventral hippocampal neurogenesis and induces antidepressant-like effects. PLoS One 2011; 6:e26610. [PMID: 22028923 PMCID: PMC3197569 DOI: 10.1371/journal.pone.0026610] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2011] [Accepted: 09/29/2011] [Indexed: 02/07/2023] Open
Abstract
Background Adult hippocampal neurogenesis has been implicated in the mechanism of antidepressant action, and neurotrophic factors can mediate the neurogenic changes underlying these effects. The neurotrophic factor neuregulin-1 (NRG1) is involved in many aspects of brain development, from cell fate determination to neuronal maturation. However, nothing is known about the influence of NRG1 on neurodevelopmental processes occurring in the mature hippocampus. Methods Adult male mice were given subcutaneous NRG1 or saline to assess dentate gyrus proliferation and neurogenesis, as well as cell fate determination. Mice also underwent behavioral testing. Expression of ErbB3 and ErbB4 NRG1 receptors in newborn dentate gyrus cells was assessed at various time points between birth and maturity. The phenotype of ErbB-expressing progenitor cells was also characterized with cell type-specific markers. Results The current study shows that subchronic peripheral NRG1β administration selectively increased cell proliferation (by 71%) and neurogenesis (by 50%) in the caudal dentate gyrus within the ventral hippocampus. This pro-proliferative effect did not alter neuronal fate, and may have been mediated by ErbB3 receptors, which were expressed by newborn dentate gyrus cells from cell division to maturity and colocalized with SOX2 in the subgranular zone. Furthermore, four weeks after cessation of subchronic treatment, animals displayed robust antidepressant-like behavior in the absence of changes in locomotor activity, whereas acute treatment did not produce antidepressant effects. Conclusions These results show that neuregulin-1β has pro-proliferative, neurogenic and antidepressant properties, further highlight the importance of peripheral neurotrophic factors in neurogenesis and mood, and support the role of hippocampal neurogenesis in mediating antidepressant effects.
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Affiliation(s)
- Ian Mahar
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
- Department of Neurology and Neurosurgery, McGill University, Montréal, Québec, Canada
| | - Stephanie Tan
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
| | - Maria Antonietta Davoli
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
| | | | - Calvin Qiang
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
| | - Adeline Rachalski
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
| | - Gustavo Turecki
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
- Department of Psychiatry and McGill University, Montréal, Québec, Canada
- Department of Neurology and Neurosurgery, McGill University, Montréal, Québec, Canada
| | - Naguib Mechawar
- McGill Group for Suicide Studies, Douglas Mental Health University Institute, McGill University, Verdun, Québec, Canada
- Department of Psychiatry and McGill University, Montréal, Québec, Canada
- Department of Neurology and Neurosurgery, McGill University, Montréal, Québec, Canada
- * E-mail:
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Yin HS, Tien TW, Li L, Yang YH, Lai CC. Amphetamine differentially modifies the expression of monoaminergic and GABAergic synaptic boutons and processes in lateral habenula, dorsal and ventral hippocampal formation. Neurotoxicology 2011; 33:235-45. [PMID: 22001174 DOI: 10.1016/j.neuro.2011.10.001] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2011] [Revised: 09/04/2011] [Accepted: 10/02/2011] [Indexed: 11/16/2022]
Abstract
The habenular complex is thought to be associated with cognitive functions and indirectly connected with the hippocampal formation (HF). Thus the responses of the monoaminergic and GABAergic neurons were examined in both structures to the psychostimulant, amphetamine (Amph). Immunocytochemical analysis was performed on brain sections prepared from adult mice treated with a single or multiple (2 doses/day, 7 doses in total) injections of saline or Amph, 5mg/kg. The synaptic boutons were verified by immuno-electron microscopy specific for parvalbumin (PV), glutamic acid decarboxylase(67) (GAD(67)), aromatic amino acid decarboxylase (AADC) or dopamine-β-hydroxylase (DBH). In the lateral part of the lateral habenula (LHb), at 4h post-acute Amph, the densities of PV-positive boutons/processes and DBH-boutons were decreased by approximate 75% and 72% respectively, compared with corresponding saline-controls; however, at 4h post-repeated Amph exposure, PV was increased by 244%, and DBH unaltered. In the dorsal HF (DHF), at 4h post-repeated Amph exposure, GAD(67)-boutons and PV resembled controls in CA1 and CA3 pyramidal cell layers, whereas in the granule cell layer of dentate gyrus (DG), PV was increased by 112%, and GAD(67) unchanged. As shown by biochemical methods, at 4h post-repeated Amph, the decreased level of DHF GABA probably correlates with the immunocytochemical changes. In the ventral HF (VHF), at 4h post-repeated Amph treatment, PV and the enzymes of CA1 and DG were unaltered, while CA3 PV was decreased by 63%, and AADC-boutons increased 55%. Double immuno-electron microscopy revealed synaptic contacts between PV and GAD(67) containing presynaptic or postsynaptic elements, and between PV or GAD(67) and DBH or AADC. This ultrastructural evidence may support the functional significance of the Amph-induced differential changes, which could reflect Amph toxicity and distinct characteristics of the LHb, DHF and VHF.
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Affiliation(s)
- Hsiang-Shu Yin
- Department of Anatomy and Cell Biology, College of Medicine, National Taiwan University, Taipei, Taiwan, ROC.
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Penley SC, Hinman JR, Sabolek HR, Escabí MA, Markus EJ, Chrobak JJ. Theta and gamma coherence across the septotemporal axis during distinct behavioral states. Hippocampus 2011; 22:1164-75. [PMID: 21748821 DOI: 10.1002/hipo.20962] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/04/2011] [Indexed: 11/05/2022]
Abstract
Theta (4-12 Hz) and gamma (40-100 Hz) field potentials represent the interaction of synchronized synaptic input onto distinct neuronal populations within the hippocampal formation. Theta is quite prominent during exploratory activity, locomotion, and REM sleep. Although it is generally acknowledged that theta is coherent throughout most of the hippocampus, there is significant variability in theta, as well as gamma, coherence across lamina at any particular septotemporal level of the hippocampus. Larger differences in theta coherence are observed across the septotemporal (long) axis. We have reported that during REM sleep there is a decrease in theta coherence across the long axis that varies with the topography of CA3/mossy cell input rather than the topography of the prominent entorhinal input. On the basis of differences in the rat's behavior as well as the activity of neuromodulatory inputs (e.g., noradrenergic and serotonergic), we hypothesized that theta coherence across the long axis would be greater during locomotion than REM sleep and exhibit a pattern more consistent with the topography of entorhinal inputs. We examined theta and gamma coherence indices at different septotemporal and laminar sites during distinct theta states: locomotion during maze running, REM sleep, following acute treatment with a θ-inducing cholinomimetic (physostigmine) and for comparison during slow-wave sleep. The results demonstrate a generally consistent pattern of theta and gamma coherence across the septotemporal axis of the hippocampus that is quite indifferent to sensory input and overt behavior. These results are discussed with regards to the neurobiological mechanisms that generate theta and gamma and the growing body of evidence linking theta and gamma indices to memory and other cognitive functions.
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Affiliation(s)
- Stephanie C Penley
- Department of Psychology, University of Connecticut, Storrs, Connecticut 06269, USA
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Hinman JR, Penley SC, Long LL, Escabí MA, Chrobak JJ. Septotemporal variation in dynamics of theta: speed and habituation. J Neurophysiol 2011; 105:2675-86. [DOI: 10.1152/jn.00837.2010] [Citation(s) in RCA: 91] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Theta (6–12 Hz) field potentials and the synchronization (coherence) of these potentials present neural network indices of hippocampal physiology. Theta signals within the hippocampal formation may reflect alterations in sensorimotor integration, the flow of sensory input, and/or distinct cognitive operations. While the power and coherence of theta signals vary across lamina within the septal hippocampus, limited information is available about variation in these indices across the septotemporal (long) or areal axis. The present study examined the relationship of locomotor speed to theta indices at CA1 and dentate gyrus (DG) sites across the septotemporal axis as well as in the entorhinal cortex. Our findings demonstrate the dominant relationship of speed to theta indices at septal sites. This relationship diminished systematically with distance from the septal pole of the hippocampus at both CA1 and DG sites. While theta power at entorhinal sites varied in relation to speed, there were no differences across the areal axis of the entorhinal cortex. Locomotor speed was also related to changes in theta coherence along the septotemporal axis as well as between the hippocampus and entorhinal cortex. In addition to the speed-related variation, we observed a decrease in theta power at more temporal hippocampal sites over repeated behavioral testing within a single day that was not observed at septal sites. The results outline a dynamic and distributed pattern of network activity across the septotemporal axis of the hippocampus in relation to locomotor speed and recent past experience.
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Affiliation(s)
| | | | | | - Monty A. Escabí
- Departments of 1Psychology,
- Biomedical Engineering, and
- Electrical and Computer Engineering, University of Connecticut, Storrs, Connecticut
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Christensen T, Bisgaard C, Nielsen H, Wiborg O. Transcriptome differentiation along the dorso–ventral axis in laser-captured microdissected rat hippocampal granular cell layer. Neuroscience 2010; 170:731-41. [DOI: 10.1016/j.neuroscience.2010.07.016] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2010] [Revised: 07/02/2010] [Accepted: 07/06/2010] [Indexed: 12/31/2022]
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Female rats learn trace memories better than male rats and consequently retain a greater proportion of new neurons in their hippocampi. Proc Natl Acad Sci U S A 2009; 106:2927-32. [PMID: 19188598 DOI: 10.1073/pnas.0809650106] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Learning increases the survival of new cells that are generated in the hippocampal formation before the training experience, especially if the animal learns to associate stimuli across time [Gould E, Beylin A, Tanapat P, Reeves A, Shors TJ (1999) Nat Neurosci 2:260-265]. All relevant studies have been conducted on male rats, despite evidence for sex differences in this type of learning. In the present study, we asked whether sex differences in learning influence the survival of neurons generated in the adult hippocampus. Male and female adult rats were injected with one dose of bromodeoxyuridine (BrdU; 200 mg/kg), to label one population of dividing cells. One week later, half of the animals were trained with a temporal learning task of trace eyeblink conditioning, while the other half were not trained. Animals were killed 1 day after training (12 days after the BrdU injection). Hippocampal tissue was stained for BrdU and a marker of immature neurons, doublecortin. Both sexes learned to emit the conditioned eyeblink response during the trace interval. As a consequence, more new neurons remained in their hippocampi than in sex-matched controls. In individual animals, the number of surviving cells correlated positively with asymptotic performance; those that expressed more learned responses retained more new neurons. However, animals that learned very well retained even more new cells if they required many trials to do so. Because females emitted more learned responses than males did, they retained nearly twice as many new cells per unit volume of tissue. This effect was most evident in the ventral region of the hippocampal formation. Thus, sex differences in learning alter the anatomical structure of the hippocampus. As a result, male and female brains continue to differentiate in adulthood.
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Thompson CL, Pathak SD, Jeromin A, Ng LL, MacPherson CR, Mortrud MT, Cusick A, Riley ZL, Sunkin SM, Bernard A, Puchalski RB, Gage FH, Jones AR, Bajic VB, Hawrylycz MJ, Lein ES. Genomic Anatomy of the Hippocampus. Neuron 2008; 60:1010-21. [DOI: 10.1016/j.neuron.2008.12.008] [Citation(s) in RCA: 303] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2007] [Revised: 07/03/2008] [Accepted: 12/08/2008] [Indexed: 11/16/2022]
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Abstract
The development of new treatments for depression is predicated upon identification of neural substrates and mechanisms that underlie its etiology and pathophysiology. The heterogeneity of depression indicates that its origin may lie in dysfunction of multiple brain regions. Here we evaluate adult hippocampal neurogenesis as a candidate mechanism for the etiology of depression and as a substrate for antidepressant action. Current evidence indicates that adult hippocampal neurogenesis may not be a major contributor to the development of depression, but may be required for some of the behavioral effects of antidepressants. We next revisit the functional differentiation of the hippocampus along the septo-temporal axis within the context of adult hippocampal neurogenesis and suggest that neurogenesis in the ventral dentate gyrus may be preferentially involved in regulation of emotion. Finally, we speculate on how increased adult hippocampal neurogenesis may modulate dentate gyrus function to confer the behavioral effects of antidepressants.
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Affiliation(s)
- Amar Sahay
- Department of Neuroscience, Division of Integrative Neuroscience, Columbia University, 1051 Riverside Drive, Box 87, PI Annex, Room 767B, New York, New York 10032, USA.
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Bisgaard CF, Jayatissa MN, Enghild JJ, Sanchéz C, Artemychyn R, Wiborg O. Proteomic investigation of the ventral rat hippocampus links DRP-2 to escitalopram treatment resistance and SNAP to stress resilience in the chronic mild stress model of depression. J Mol Neurosci 2007; 32:132-44. [PMID: 17873297 DOI: 10.1007/s12031-007-0025-4] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2007] [Revised: 11/30/1999] [Accepted: 02/22/2007] [Indexed: 02/06/2023]
Abstract
The development of depression as well as recovery from depression is most likely accompanied by a change in protein expression profiles. The purpose of the present study was to quantitatively investigate global protein expression differences independent of any hypothesis describing depression etiology and recovery. Thus two-dimensional differential in-gel electrophoresis was employed to compare the ventral hippocampal proteomes between different treatment groups in the chronic mild stress (CMS) model of depression. The CMS paradigm induces anhedonic behaviour, which is a major symptom of depression, by exposing rats to a series of mild stressors for 7 weeks, with antidepressant treatment during the last 4 weeks. In the CMS model, animals were split into six different groups at the end of treatment; unchallenged control escitalopram (n = 12), unchallenged control vehicle (n = 12), CMS vehicle (n = 12), CMS escitalopram responders (n = 11), CMS escitalopram non-responders (n = 13) and CMS resilient (stress resistant) (n = 12). Protein levels in the ventral rat hippocampus were compared between the groups to provide putative markers of anhedonia, escitalopram resistance, and stress resilience. Twenty-eight candidate protein spots were selected, of which 13 were successfully identified using tandem mass spectrometry. DRP-2 (dihydropyrimidinase-related protein-2) was a potential marker for escitalopram resistance, whereas alpha-SNAP and beta-SNAP were associated with stress resilience. Furthermore, several molecular chaperones and cytoskeleton organisers were identified as being differentially expressed. Our data indicate that neuronal adaptation is an essential element of depression etiology and recovery, suggesting the involvement of cellular plasticity in the underlying molecular mechanism.
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Affiliation(s)
- Christina F Bisgaard
- Center for Basic Psychiatric Research, Aarhus Psychiatric University Hospital, Skovagervej 2, Risskov, Denmark
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Jayatissa MN, Bisgaard C, Tingström A, Papp M, Wiborg O. Hippocampal cytogenesis correlates to escitalopram-mediated recovery in a chronic mild stress rat model of depression. Neuropsychopharmacology 2006; 31:2395-404. [PMID: 16482085 DOI: 10.1038/sj.npp.1301041] [Citation(s) in RCA: 274] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
From clinical studies it is known that recurrent depressive episodes associate with a reduced hippocampal volume. Conversely, preclinical studies have shown that chronic antidepressant treatment increases hippocampal neurogenesis. Consequently, it has been suggested that a deficit in hippocampal neurogenesis is implicated in the pathophysiology of depression. To study a potential correlation between recovery and hippocampal cytogenesis, we established the chronic mild stress (CMS) rat model of depression. When rats are subjected to CMS, several depressive symptoms develop, including the major symptom anhedonia. Rats were exposed to stress for 2 weeks and subsequently to stress in combination with antidepressant treatment for 4 consecutive weeks. The behavioral deficit measured in anhedonic animals is a reduced intake of a sucrose solution. Prior to perfusion animals were injected with bromodeoxyuridine (BrdU), a marker of proliferating cells. Brains were sectioned horizontally and newborn cells positive for BrdU were counted in the dentate gyrus and tracked in a dorsoventral direction.CMS significantly decreased sucrose consumption and cytogenesis in the ventral part of the hippocampal formation. During exposure to the antidepressant escitalopram, given as intraperitoneally dosages of either 5 or 10 mg/kg/day, animals distributed in a bimodal fashion into a group, which recovered (increase in sucrose consumption), and a subgroup, which refracted treatment (no increase in sucrose consumption). Chronic treatment with escitalopram reversed the CMS-induced decrease in cytogenesis in the dentate gyrus of the ventral hippocampal formation, but in recovered animals only. Our data show a correlation between recovery from anhedonia, as measured by cessation of behavioral deficits in the CMS model, and an increase in cytogenesis in the dentate gyrus of the ventral hippocampal formation.
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Affiliation(s)
- Magdalena N Jayatissa
- Centre for Basic Psychiatric Research, Aarhus Psychiatric University Hospital, Aarhus, Denmark
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Sotiriou E, Papatheodoropoulos C, Angelatou F. Differential expression of gamma-aminobutyric acid--a receptor subunits in rat dorsal and ventral hippocampus. J Neurosci Res 2006; 82:690-700. [PMID: 16273537 DOI: 10.1002/jnr.20670] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Recent data demonstrate weaker gamma-aminobutyric acid (GABA)-ergic inhibition in ventral (VH) compared with dorsal (DH) hippocampus. Therefore, we examined possible differences regarding the GABAA receptors between VH and DH as follows: 1) the expression of the GABAA receptor subunits (alpha1/2/4/5, beta1/2/3, gamma2, delta) mRNA and protein and 2) the quantitative distribution and kinetic parameters of [3H] muscimol (GABAA receptor agonist) binding. VH compared with DH showed: 1) lower levels for alpha1, beta2, gamma2 but higher levels for alpha2 and beta1 subunits in CA1, CA2, and CA3, the differences being more pronounced in CA1 region; in the CA1 region, the mRNA levels of alpha5 were higher, whereas those of alpha4 subunit were slightly lower; in dentate gyrus, the mRNA levels of alpha4, beta3, and delta subunits were significantly lower, presumably suggesting a lower expression of the alpha4/beta3/delta receptor subtype; and 2) lower levels of [3H]muscimol binding, with the lowest value observed in CA1, apparently resulting from weaker binding affinity, insofar as the KD values were higher in VH, whereas the Bmax values were similar between DH and VH. The differences in the subunit expression and the lower affinity of GABAA receptor binding observed predominantly in the CA1 region of VH suggest that the alpha1/beta2/gamma2 GABAA receptor subtype dominates in DH, and the alpha2/beta1/gamma2 subtype prevails in VH. This could underlie the lower GABAA-mediated inhibition observed in VH and, to some extent, explain 1) the higher liability of VH for epileptic activity and 2) the differential involvement of DH and VH in cognitive and emotional processes.
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Affiliation(s)
- Evangelos Sotiriou
- Physiology Department, Medical School, University of Patras, Patras, Greece
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Trivedi MA, Coover GD. Neurotoxic lesions of the dorsal and ventral hippocampus impair acquisition and expression of trace-conditioned fear-potentiated startle in rats. Behav Brain Res 2006; 168:289-98. [PMID: 16413066 DOI: 10.1016/j.bbr.2005.11.029] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2005] [Revised: 11/18/2005] [Accepted: 11/18/2005] [Indexed: 10/25/2022]
Abstract
Pavlovian delay conditioning, in which a conditioned stimulus (CS) and unconditioned stimulus (US) co-terminate, is thought to reflect non-declarative memory. In contrast, trace conditioning, in which the CS and US are temporally separate, is thought to reflect declarative memory. Hippocampal lesions impair acquisition and expression of trace conditioning measured by the conditioned freezing and eyeblink responses, while having little effect on the acquisition of delay conditioning. Recent evidence suggests that lesions of the ventral hippocampus (VH) impair conditioned fear under conditions in which dorsal hippocampal (DH) lesions have little effect. In the present study, we examined the time-course of fear expression after delay and trace conditioning using the fear-potentiated startle (FPS) reflex, and the effects of pre- and post-training lesions to the VH and DH on trace-conditioned FPS. We found that both delay- and trace-conditioned rats displayed significant FPS near the end of the CS relative to the unpaired control group. In contrast, trace-conditioned rats displayed significant FPS throughout the duration of the trace interval, whereas FPS decayed rapidly to baseline after CS offset in delay-conditioned rats. In experiment 2, both DH and VH lesions were found to significantly reduce the overall magnitude of FPS compared to the control group, however, no differences were found between the DH and VH groups. These findings support a role for both the DH and VH in trace fear conditioning, and suggest that the greater effect of VH lesions on conditioned fear might be specific to certain measures of fear.
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Affiliation(s)
- Mehul A Trivedi
- Department of Psychology, Northern Illinois University, DeKalb, IL 60115, USA.
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Weible AP, O'Reilly JA, Weiss C, Disterhoft JF. Comparisons of dorsal and ventral hippocampus cornu ammonis region 1 pyramidal neuron activity during trace eye-blink conditioning in the rabbit. Neuroscience 2006; 141:1123-37. [PMID: 16753261 DOI: 10.1016/j.neuroscience.2006.04.065] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2006] [Revised: 04/26/2006] [Accepted: 04/28/2006] [Indexed: 11/23/2022]
Abstract
Previous studies demonstrating a critical role of the hippocampus during trace eye-blink conditioning have focused primarily upon the dorsal portion of the structure. However, evidence suggests that a functional differentiation exists along the septotemporal axis of the hippocampus. In the present study, the activity of 2588 single cornu ammonis region 1 pyramidal neurons of the dorsal hippocampus and ventral hippocampus were recorded during trace and pseudo-eye-blink conditioning of the rabbit. Learning-related increases in dorsal hippocampus neuron firing rates were observed immediately prior to behavioral criterion, and increased over the course of training. Activation of dorsal hippocampus neurons during trace conditioning was also greater than that of ventral hippocampus neurons, including during the trace interval, in well-trained animals. An unexpected difference in the patterns of learning-related activity between hemispheres was also observed. Neurons of the dorsal hippocampus ipsilateral and contralateral to the trained eye, exhibiting significant increases in firing rate [rate increasing neurons], demonstrated the greatest magnitude of activation early and late in training, respectively. Rate increasing neurons of the dorsal hippocampus also exhibited a greater diversity of response profiles, with 69% of dorsal hippocampus rate increasing neurons exhibiting significant increases in firing rate during the conditioned stimulus and/or trace intervals, compared with only 8% of ventral hippocampus rate increasing neurons (the remainder of which were significantly responsive during only the unconditioned stimulus and/or post-unconditioned stimulus intervals). Only modest learning-related activation of ventral hippocampus neurons was observed, reflected as an increase in conditioning stimulus-elicited rate increasing neuron response magnitudes over the course of training. No differences in firing rate between dorsal hippocampus and ventral hippocampus neurons during a 1-day pre-training habituation session were observed. Thus, dorsal hippocampus activation is more robust, suggesting a more substantial role for these neurons in the processing of temporal information during trace eye-blink conditioning.
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Affiliation(s)
- A P Weible
- Department of Physiology, Northwestern University Institute for Neuroscience, Northwestern University Feinberg School of Medicine, 303 East Chicago Avenue, Chicago, IL 60611, USA.
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Strange BA, Hurlemann R, Duggins A, Heinze HJ, Dolan RJ. Dissociating intentional learning from relative novelty responses in the medial temporal lobe. Neuroimage 2005; 25:51-62. [PMID: 15734343 DOI: 10.1016/j.neuroimage.2004.12.014] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2004] [Revised: 11/11/2004] [Accepted: 12/08/2004] [Indexed: 11/20/2022] Open
Abstract
The establishment of a role for medial temporal lobe (MTL) structures in episodic memory has led to an investigative focus on the specific contributions and interactions between constituent MTL regions, including the hippocampus and surrounding medial temporal cortices. By dissociating an intentional stimulus-category learning condition from a passive viewing condition, we demonstrate, using fMRI, that novelty- and familiarity-driven responses in human anterior and posterior hippocampus, respectively, only occur during intentional learning. With increasing familiarity of stimulus-category associations, there is a shift in neuronal responses from anterior to posterior hippocampal regions. This anterior/posterior response gradient may reflect a weighting of functional hippocampal architecture related to encoding of novel and retrieval of familiar information. By contrast, perirhinal cortex is engaged by novel stimuli irrespective of task, highlighting this region as a component of a generic familiarity discrimination system. By introducing distinct stimulus types, we further demonstrate that these MTL responses are independent of stimulus complexity. Different patterns of activity for intentional learning vs. passive viewing indicate that intentional encoding/retrieval of stimulus-category associations and automatic novelty/familiarity assessment of stimuli are processed in anatomically dissociable neuronal ensembles within the MTL memory system.
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Affiliation(s)
- Bryan A Strange
- Wellcome Department of Imaging Neuroscience, Functional Imaging Laboratory, Institute of Neurology, 12 Queen Square, London, WC1N 3BG, UK.
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Bjarkam CR, Sørensen JC, Geneser FA. Distribution and morphology of serotonin-immunoreactive axons in the hippocampal region of the New Zealand white rabbit. I. Area dentata and hippocampus. Hippocampus 2003; 13:21-37. [PMID: 12625454 DOI: 10.1002/hipo.10042] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
This study provides a detailed light microscopic description of the morphology and distribution of immunohistochemically stained serotonergic axons in the hippocampal region of the New Zealand white rabbit. The serotonergic axons were segregated morphologically into three types: beaded fibers, fine fibers, and stem-axons, respectively. Beaded fibers were thin serotonergic axons with large varicosities, whereas thin axons with small fusiform or granular varicosities were called fine fibers. Finally, thick straight non-varicose axons were called stem-axons. Beaded fibers often formed large conglomerates with numerous boutons (pericellular arrays) in close apposition to the cell-rich layers in the hippocampal region, e.g., the granular and hilar cell layers of the dentate area and the pyramidal cell layer ventrally in CA3. The pericellular arrays in these layers were often encountered in relation to small calbindin-D2BK-positive cells, as shown by immunohistochemical double staining for serotonin and calbindin-D28K. The beaded and fine serotonergic fibers displayed a specific innervation pattern in the hippocampal region and were encountered predominantly within the terminal field of the perforant path, e.g., the stratum moleculare hippocampi and the outer two-thirds of the dentate molecular layer. These fibers were also frequently seen in the deep part of the stratum oriens and the alveus, forming a dense plexus in relation to large multipolar calbindin-D28K-positive cells and their basal extensions. Stem-axons were primarily seen in the fimbria and alveus. This innervation pattern was present throughout the entire hippocampal formation, but there were considerable septotemporal differences in the density of the serotonergic innervation. A high density of innervation prevailed in the ventral/temporal part of the hippocampal formation, whereas the dorsal/septal part received only a moderate to weak serotonergic innervation. These results suggest that the serotonergic system could modulate the internal hippocampal circuitry by way of its innervation in the terminal field of the perforant path, the hilus fasciae dentatae, and ventrally in the zone closely apposed to the mossy fiber layer and the pyramidal cells of CA3. This modulation could be of a dual nature, mediated directly by single serotonergic fibers traversing the hippocampal layers or indirectly by the pericellular arrays and their close relation to the calbindin-D28K-positive cells. The marked septotemporal differences in innervation density point toward a difference between the ventral and dorsal parts of the hippocampal formation with respect to serotonergic function and need for serotonergic modulation.
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Affiliation(s)
- Carsten R Bjarkam
- Department of Neurobiology, Institute of Anatomy, University of Aarhus, Denmark.
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