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Rodnyy AY, Kondaurova EM, Tsybko AS, Popova NK, Kudlay DA, Naumenko VS. The brain serotonin system in autism. Rev Neurosci 2024; 35:1-20. [PMID: 37415576 DOI: 10.1515/revneuro-2023-0055] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 06/10/2023] [Indexed: 07/08/2023]
Abstract
Autism spectrum disorders (ASDs) are among the most common neurodevelopmental diseases. These disorders are characterized by lack of social interaction, by repetitive behavior, and often anxiety and learning disabilities. The brain serotonin (5-HT) system is known to be crucially implicated in a wide range of physiological functions and in the control of different kinds of normal and pathological behavior. A growing number of studies indicate the involvement of the brain 5-HT system in the mechanisms underlying both ASD development and ASD-related behavioral disorders. There are some review papers describing the role of separate key players of the 5-HT system in an ASD and/or autistic-like behavior. In this review, we summarize existing data on the participation of all members of the brain 5-HT system, namely, 5-HT transporter, tryptophan hydroxylase 2, MAOA, and 5-HT receptors, in autism in human and various animal models. Additionally, we describe the most recent studies involving modern techniques for in vivo regulation of gene expression that are aimed at identifying exact roles of 5-HT receptors, MAOA, and 5-HT transporter in the mechanisms underlying autistic-like behavior. Altogether, results of multiple research articles show that the brain 5-HT system intimately partakes in the control of some types of ASD-related behavior, and that specific changes in a function of a certain 5-HT receptor, transporter, and/or enzyme may normalize this aberrant behavior. These data give hope that some of clinically used 5-HT-related drugs have potential for ASD treatment.
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Affiliation(s)
- Alexander Ya Rodnyy
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of Russian Academy of Sciences, Akad. Lavrentyeva Ave. 10, Novosibirsk 630090, Russia
| | - Elena M Kondaurova
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of Russian Academy of Sciences, Akad. Lavrentyeva Ave. 10, Novosibirsk 630090, Russia
| | - Anton S Tsybko
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of Russian Academy of Sciences, Akad. Lavrentyeva Ave. 10, Novosibirsk 630090, Russia
| | - Nina K Popova
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of Russian Academy of Sciences, Akad. Lavrentyeva Ave. 10, Novosibirsk 630090, Russia
| | - Dmitry A Kudlay
- NRC Institute of Immunology FMBA of Russia, Kashirskoe Highway 24, Moscow 115522, Russia
- Sechenov's University, 8-2 Trubetskaya Str., Moscow 119991, Russia
| | - Vladimir S Naumenko
- Federal Research Center Institute of Cytology and Genetics, Siberian Branch of Russian Academy of Sciences, Akad. Lavrentyeva Ave. 10, Novosibirsk 630090, Russia
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On the role of serotonin 5-HT 1A receptor in autistic-like behavior: сross talk of 5-HT and BDNF systems. Behav Brain Res 2023; 438:114168. [PMID: 36280010 DOI: 10.1016/j.bbr.2022.114168] [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: 08/17/2022] [Revised: 10/11/2022] [Accepted: 10/17/2022] [Indexed: 12/05/2022]
Abstract
Autism spectrum disorders (ASDs) are some of the most common neurodevelopmental disorders; however, the mechanisms underlying ASDs are still poorly understood. Serotonin (5-HT) and brain-derived neurotrophic factor (BDNF) are known as key players in brain and behavioral plasticity and interact with each other. 5-HT1A receptor is a principal regulator of the brain 5-HT system, which modulates normal and pathological behavior. Here we investigated effects of adeno-associated-virus-based 5-HT1A receptor overexpression in the hippocampus of BTBR mice (which are a model of autism) on various types of behavior and on the expression of 5-HT7 receptor, proBDNF, mature BDNF, and BDNF receptors (TrkB and p75NTR). The 5-HT1A receptor overexpression in BTBR mice reduced stereotyped behavior in the marble-burying test and extended the time spent in the center in the open field test. Meanwhile, this overexpression failed to affect social behavior in the three-chambered test, immobility time in the tail suspension test, locomotor activity in the open field test, and associative learning within the "operant wall" paradigm. The 5-HT1A receptor overexpression in the hippocampus raised hippocampal 5-HT7 receptor mRNA and protein levels. Additionally, the 5-HT1A receptor overexpression lowered both mRNA and protein levels of TrkB receptor but failed to affect proBDNF, mature BDNF, and p75NTR receptor expression in the hippocampus of BTBR mice. Thus, obtained results suggest the involvement of the 5-HT and BDNF systems' interaction mediated by 5-HT1A and TrkB receptors in the mechanisms underlying autistic-like behavior in BTBR mice.
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McCarthy W, Huq SN, Allen K, Scally L, Petri A, Wujek M, Sachs BD. Chronic, but not sub-chronic, stress increases binge-like alcohol consumption in male and female c57BL6 mice. Front Behav Neurosci 2022; 16:958342. [PMID: 36204485 PMCID: PMC9530781 DOI: 10.3389/fnbeh.2022.958342] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 08/15/2022] [Indexed: 12/03/2022] Open
Abstract
Stress is known to contribute to mental illness and alcohol use disorders, which are highly prevalent and lead to considerable disability. These stress-related disorders are characterized by significant sex differences, which remain poorly understood. Preclinical research comparing the effects of stress in males and females has the potential to provide new insights into the neurobiology of these conditions. The current study compared the effects of chronic and sub-chronic exposure to variable environmental stressors on binge-like alcohol consumption using the drinking-in-the-dark model in male and female c57BL6 mice. The results reveal that chronic, but not sub-chronic, exposure to variable stress increases alcohol intake in both sexes. Stress-induced alterations in gene expression were also compared in the nucleus accumbens, a brain region widely known to play a key role in stress susceptibility and reward processing. Real-time PCR data indicate that chronic, but not sub-chronic, environmental stress leads to downregulation of adenosine 2A (A2A) receptor mRNA. By contrast, sub-chronic stress increased CREB expression, while chronic stress did not. Several sex differences in the effects of stress on gene expression were also noted. Our results demonstrate that reductions in A2A receptor mRNA in the nucleus accumbens are associated with the increased binge drinking of chronically stressed animals, but future work will be required to determine the functional importance of this gene expression change. Continuing to define the molecular alterations associated with stress-induced increases in alcohol intake has the potential to provide insights into the development and progression of stress-related disorders.
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Sivasangari K, Rajan KE. Standardized Bacopa monnieri Extract Ameliorates Learning and Memory Impairments through Synaptic Protein, Neurogranin, Pro-and Mature BDNF Signaling, and HPA Axis in Prenatally Stressed Rat Offspring. Antioxidants (Basel) 2020; 9:antiox9121229. [PMID: 33291595 PMCID: PMC7761874 DOI: 10.3390/antiox9121229] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2020] [Revised: 11/19/2020] [Accepted: 11/24/2020] [Indexed: 01/10/2023] Open
Abstract
Prenatal stress (PNS) influences offspring neurodevelopment, inducing anxiety-like behavior and memory deficits. We investigated whether pretreatment of Bacopa monnieri extract (CDRI-08/BME) ameliorates PNS-induced changes in signaling molecules, and changes in the behavior of Wistar rat offspring. Pregnant rats were randomly assigned into control (CON)/prenatal stress (PNS)/PNS and exposed to BME treatment (PNS + BME). Dams were exposed to stress by placing them in a social defeat cage, where they observed social defeat from gestational day (GD)-16–18. Pregnant rats in the PNS + BME group were given BME treatment from GD-10 to their offspring’s postnatal day (PND)-23, and to their offspring from PND-15 to -30. PNS led to anxiety-like behavior; impaired memory; increased the level of corticosterone (CORT), adrenocorticotropic hormone, glucocorticoid receptor, pro-apoptotic Casepase-3, and 5-HT2C receptor; decreased anti-apoptotic Bcl-2, synaptic proteins (synaptophysin, synaptotagmin-1), 5-HT1A, receptor, phosphorylation of calmodulin-dependent protein kinase II/neurogranin, N-methyl-D-aspartate receptors (2A,2B), postsynaptic density protein 95; and conversion of pro and mature brain derived neurotropic factor in their offspring. The antioxidant property of BME possibly inhibiting the PNS-induced changes in observed molecules, anxiety-like behavior, and memory deficits. The observed results suggest that pretreatment of BME could be an effective coping strategy to prevent PNS-induced behavioral impairments in their offspring.
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Qi CC, Wang QJ, Ma XZ, Chen HC, Gao LP, Yin J, Jing YH. Interaction of basolateral amygdala, ventral hippocampus and medial prefrontal cortex regulates the consolidation and extinction of social fear. Behav Brain Funct 2018; 14:7. [PMID: 29554926 PMCID: PMC5858134 DOI: 10.1186/s12993-018-0139-6] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Accepted: 03/14/2018] [Indexed: 11/13/2022] Open
Abstract
Background Following a social defeat, the balanced establishment and extinction of aversive information is a beneficial strategy for individual survival. Abnormal establishment or extinction is implicated in the development of mental disorders. This study investigated the time course of the establishment and extinction of aversive information from acute social defeat and the temporal responsiveness of the basolateral amygdala (BLA), ventral hippocampus (vHIP) and medial prefrontal cortex (mPFC) in this process. Methods Mouse models of acute social defeat were established by using the resident–intruder paradigm. To evaluate the engram of social defeat, the intruder mice were placed into the novel context at designated time to test the social behavior. Furthermore, responses of BLA, vHIP and mPFC were investigated by analyzing the expression of immediate early genes, such as zif268, arc, and c-fos. Results The results showed after an aggressive attack, aversive memory was maintained for approximately 7 days before gradually diminishing. The establishment and maintenance of aversive stimulation were consistently accompanied by BLA activity. By contrast, vHIP and mPFC response was inhibited from this process. Additionally, injecting muscimol (Mus), a GABA receptor agonist, into the BLA alleviated the freezing behavior and social fear and avoidance. Simultaneously, Mus treatment decreased the zif268 and arc expression in BLA, but it increased their expression in vHIP. Conclusion Our data support and extend earlier findings that implicate BLA, vHIP and mPFC in social defeat. The time courses of the establishment and extinction of social defeat are particularly consistent with the contrasting BLA and vHIP responses involved in this process.![]() Electronic supplementary material The online version of this article (10.1186/s12993-018-0139-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Chu-Chu Qi
- Institute of Anatomy and Histology & Embryology, Neuroscience, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China
| | - Qing-Jun Wang
- Institute of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China
| | - Xue-Zhu Ma
- Institute of Anatomy and Histology & Embryology, Neuroscience, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China
| | - Hai-Chao Chen
- Institute of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China
| | - Li-Ping Gao
- Institute of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China
| | - Jie Yin
- Institute of Anatomy and Histology & Embryology, Neuroscience, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China
| | - Yu-Hong Jing
- Institute of Anatomy and Histology & Embryology, Neuroscience, School of Basic Medical Sciences, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China. .,Key Laboratory of Preclinical Study for New Drugs of Gansu Province, Lanzhou University, No. 199 of Donggang West Road, Lanzhou, 730000, Gansu, People's Republic of China.
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Padurariu M, Antioch I, Balmus I, Ciobica A, El-Lethey HS, Kamel MM. Describing some behavioural animal models of anxiety and their mechanistics with special reference to oxidative stress and oxytocin relevance. Int J Vet Sci Med 2017; 5:98-104. [PMID: 30255057 PMCID: PMC6137856 DOI: 10.1016/j.ijvsm.2017.08.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 08/14/2017] [Accepted: 08/29/2017] [Indexed: 12/14/2022] Open
Abstract
It is now generally accepted that animal studies are playing an important role in the understanding of anxiety disorders, since they contribute to the current knowledge regarding the mechanisms and possible therapeutic approaches in anxiety. In the present review we will detail some essential aspects of behavioral animal models of anxiety related to social defeat paradigm, elevated plus maze, elevated zero or T maze, light/dark box, social interaction test or tests based on predator models, considering the latest theories and methodological approaches in this area of research, as well as our previous studies focusing on anxiety manifestations in a variety of species including rats, zebrafish, dogs and pigs. Moreover, in this context, we will focus on the recent theories concerning oxidative stress, as well as importance of oxytocin administration (especially the intranasal route). This could be important considering that these two factors are currently being investigated as possible mechanisms (oxidative stress status) and related therapeutic target (both intranasal oxytocin and antioxidants) in the pathology of the anxiety disorders.
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Affiliation(s)
- Manuela Padurariu
- “Grigore T. Popa” University of Medicine and Pharmacy, 16, Universitatii Street, 700115 Iasi, Romania
| | - Iulia Antioch
- “Alexandru Ioan Cuza” University, 11, Carol I, 700506 Iaşi, Romania
| | - Ioana Balmus
- “Alexandru Ioan Cuza” University, 11, Carol I, 700506 Iaşi, Romania
| | - Alin Ciobica
- Department of Research, Faculty of Biology, “Alexandru Ioan Cuza” University, 11, Carol I, 700506 Iaşi, Romania
- Center of Biomedical Research of the Romanian Academy, Iasi Branch, Romania
- The Academy of the Romanian Scientists, Bucharest, Splaiul Independentei 54, 050094, Romania
| | - Heba S. El-Lethey
- Department of Animal Hygiene and Management, Faculty of Veterinary Medicine, Cairo University, Cairo, Egypt
| | - Mervat M. Kamel
- Department of Animal Hygiene and Management, Faculty of Veterinary Medicine, Cairo University, Cairo, Egypt
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Cooper MA, Seddighi S, Barnes AK, Grizzell JA, Dulka BN, Clinard CT. Dominance status alters restraint-induced neural activity in brain regions controlling stress vulnerability. Physiol Behav 2017; 179:153-161. [PMID: 28606772 PMCID: PMC5581240 DOI: 10.1016/j.physbeh.2017.06.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Revised: 05/18/2017] [Accepted: 06/07/2017] [Indexed: 01/29/2023]
Abstract
Understanding the cellular mechanisms that control resistance and vulnerability to stress is an important step toward identifying novel targets for the prevention and treatment of stress-related mental illness. In Syrian hamsters, dominant and subordinate animals exhibit different behavioral and physiological responses to social defeat stress, with dominants showing stress resistance and subordinates showing stress vulnerability. We previously found that dominant and subordinate hamsters show different levels of defeat-induced neural activity in brain regions that modulate coping with stress, although the extent to which status-dependent differences in stress vulnerability generalize to non-social stressors is unknown. In this study, dominant, subordinate, and control male Syrian hamsters were exposed to acute physical restraint for 30min and restraint-induced c-Fos immunoreactivity was quantified in select brain regions. Subordinate animals showed less restraint-induced c-Fos immunoreactivity in the infralimbic (IL), prelimbic (PL), and ventral medial amygdala (vMeA) compared to dominants, which is consistent with the status-dependent effects of social defeat stress. Subordinate animals did not show increased c-Fos immunoreactivity in the rostroventral dorsal raphe nucleus (rvDRN), which is in contrast to the effects of social defeat stress. These findings indicate that status-dependent changes in neural activity generalize from one stressor to another in a brain region-dependent manner. These findings further suggest that while some neural circuits may support a generalized form of stress resistance, others may provide resistance to specific stressors.
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Affiliation(s)
- Matthew A Cooper
- Department of Psychology, NeuroNET Research Center, University of Tennessee, Knoxville, TN 37996-0900, United States.
| | - Sahba Seddighi
- Department of Psychology, NeuroNET Research Center, University of Tennessee, Knoxville, TN 37996-0900, United States
| | - Abigail K Barnes
- Department of Psychology, NeuroNET Research Center, University of Tennessee, Knoxville, TN 37996-0900, United States
| | - J Alex Grizzell
- Department of Psychology, NeuroNET Research Center, University of Tennessee, Knoxville, TN 37996-0900, United States
| | - Brooke N Dulka
- Department of Psychology, NeuroNET Research Center, University of Tennessee, Knoxville, TN 37996-0900, United States
| | - Catherine T Clinard
- Department of Psychology, NeuroNET Research Center, University of Tennessee, Knoxville, TN 37996-0900, United States
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Burleson CA, Pedersen RW, Seddighi S, DeBusk LE, Burghardt GM, Cooper MA. Social play in juvenile hamsters alters dendritic morphology in the medial prefrontal cortex and attenuates effects of social stress in adulthood. Behav Neurosci 2016; 130:437-47. [PMID: 27176563 DOI: 10.1037/bne0000148] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Social play is a fundamental aspect of behavioral development in many species. Social play deprivation in rats alters dendritic morphology in the ventromedial prefrontal cortex (vmPFC) and we have shown that this brain region regulates responses to social defeat stress in Syrian hamsters. In this study, we tested whether play deprivation during the juvenile period disrupts dendritic morphology in the prefrontal cortex and potentiates the effects of social defeat stress. At weaning, male hamsters were either group-housed with peers or pair-housed with their mother, with whom they do not play. In adulthood, animals received acute social defeat stress or no-defeat control treatment. The hamsters were then tested for a conditioned defeat response in a social interaction test with a novel intruder, and were also tested for social avoidance of a familiar opponent. Brains were collected for Golgi-Cox staining and analysis of dendritic morphology in the infralimbic (IL), prelimbic (PL), and orbitofrontal cortex (OFC). Play-deprived animals showed an increased conditioned defeat response and elevated avoidance of a familiar opponent compared with play-exposed animals. Furthermore, play-deprived animals showed increased total length and branch points in apical dendrites of pyramidal neurons in the IL and PL cortices, but not in the OFC. These findings suggest that social play deprivation in juvenile hamsters disrupts neuronal development in the vmPFC and increases vulnerability to the effects of social stress in adulthood. Overall, these results suggest that social play is necessary for the natural dendritic pruning process during adolescence and promotes coping with stress in adulthood. (PsycINFO Database Record
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Cooper MA, Clinard CT, Morrison KE. Neurobiological mechanisms supporting experience-dependent resistance to social stress. Neuroscience 2015; 291:1-14. [PMID: 25677096 PMCID: PMC4369454 DOI: 10.1016/j.neuroscience.2015.01.072] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Revised: 01/28/2015] [Accepted: 01/30/2015] [Indexed: 11/16/2022]
Abstract
Humans and other animals show a remarkable capacity for resilience following traumatic, stressful events. Resilience is thought to be an active process related to coping with stress, although the cellular and molecular mechanisms that support active coping and stress resistance remain poorly understood. In this review, we focus on the neurobiological mechanisms by which environmental and social experiences promote stress resistance. In male Syrian hamsters, exposure to a brief social defeat stressor leads to increased avoidance of novel opponents, which we call conditioned defeat. Also, hamsters that have achieved dominant social status show reduced conditioned defeat as well as cellular and molecular changes in the neural circuits controlling the conditioned defeat response. We propose that experience-dependent neural plasticity occurs in the prelimbic (PL) cortex, infralimbic (IL) cortex, and ventral medial amygdala (vMeA) during the maintenance of dominance relationships, and that adaptations in these neural circuits support stress resistance in dominant individuals. Overall, behavioral treatments that promote success in competitive interactions may represent valuable interventions for instilling resilience.
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Affiliation(s)
- M A Cooper
- Department of Psychology, University of Tennessee, Knoxville, TN, 37996, USA.
| | - C T Clinard
- Department of Psychology, University of Tennessee, Knoxville, TN, 37996, USA
| | - K E Morrison
- Department of Animal Biology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA
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Activation of 5-HT2a receptors in the basolateral amygdala promotes defeat-induced anxiety and the acquisition of conditioned defeat in Syrian hamsters. Neuropharmacology 2014; 90:102-12. [PMID: 25458113 DOI: 10.1016/j.neuropharm.2014.11.016] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2014] [Revised: 11/11/2014] [Accepted: 11/22/2014] [Indexed: 01/14/2023]
Abstract
Conditioned defeat is a model in Syrian hamsters (Mesocricetus auratus) in which normal territorial aggression is replaced by increased submissive and defensive behavior following acute social defeat. The conditioned defeat response involves both a fear-related memory for a specific opponent as well as anxiety-like behavior indicated by avoidance of novel conspecifics. We have previously shown that systemic injection of a 5-HT2a receptor antagonist reduces the acquisition of conditioned defeat. Because neural activity in the basolateral amygdala (BLA) is critical for the acquisition of conditioned defeat and BLA 5-HT2a receptors can modulate anxiety but have a limited effect on emotional memories, we investigated whether 5-HT2a receptor modulation alters defeat-induced anxiety but not defeat-related memories. We injected the 5-HT2a receptor antagonist MDL 11,939 (0 mM, 1.7 mM or 17 mM) or the 5-HT2a receptor agonist TCB-2 (0 mM, 8 mM or 80 mM) into the BLA prior to social defeat. We found that injection of MDL 11,939 into the BLA impaired acquisition of the conditioned defeat response and blocked defeat-induced anxiety in the open field, but did not significantly impair avoidance of former opponents in the Y-maze. Furthermore, we found that injection of TCB-2 into the BLA increased the acquisition of conditioned defeat and increased anxiety-like behavior in the open field, but did not alter avoidance of former opponents. Our data suggest that 5-HT2a receptor signaling in the BLA is both necessary and sufficient for the development of conditioned defeat, likely via modulation of defeat-induced anxiety.
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