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Soutar CN, Grenier P, Patel A, Kabitsis PP, Olmstead MC, Bailey CDC, Dringenberg HC. Brain-Generated 17β-Estradiol Modulates Long-Term Synaptic Plasticity in the Primary Auditory Cortex of Adult Male Rats. Cereb Cortex 2021; 32:2140-2155. [PMID: 34628498 DOI: 10.1093/cercor/bhab345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Neuron-derived 17β-estradiol (E2) alters synaptic transmission and plasticity in brain regions with endocrine and non-endocrine functions. Investigations into a modulatory role of E2 in synaptic activity and plasticity have mainly focused on the rodent hippocampal formation. In songbirds, E2 is synthesized by auditory forebrain neurons and promotes auditory signal processing and memory for salient acoustic stimuli; however, the modulatory effects of E2 on memory-related synaptic plasticity mechanisms have not been directly examined in the auditory forebrain. We investigated the effects of bidirectional E2 manipulations on synaptic transmission and long-term potentiation (LTP) in the rat primary auditory cortex (A1). Immunohistochemistry revealed widespread neuronal expression of the E2 biosynthetic enzyme aromatase in multiple regions of the rat sensory and association neocortex, including A1. In A1, E2 application reduced the threshold for in vivo LTP induction at layer IV synapses, whereas pharmacological suppression of E2 production by aromatase inhibition abolished LTP induction at layer II/III synapses. In acute A1 slices, glutamate and γ-aminobutyric acid (GABA) receptor-mediated currents were sensitive to E2 manipulations in a layer-specific manner. These findings demonstrate that locally synthesized E2 modulates synaptic transmission and plasticity in A1 and suggest potential mechanisms by which E2 contributes to auditory signal processing and memory.
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Affiliation(s)
- Chloe N Soutar
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Patrick Grenier
- Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Ashutosh Patel
- Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Pauline P Kabitsis
- Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Mary C Olmstead
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada.,Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Craig D C Bailey
- Department of Biomedical Sciences, Ontario Veterinary College, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Hans C Dringenberg
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada.,Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada
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Lee KKY, Soutar CN, Dringenberg HC. Gating of long-term potentiation (LTP) in the thalamocortical auditory system of rats by serotonergic (5-HT) receptors. Brain Res 2018; 1683:1-11. [PMID: 29325855 DOI: 10.1016/j.brainres.2018.01.004] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Revised: 11/24/2017] [Accepted: 01/02/2018] [Indexed: 01/01/2023]
Abstract
The neuromodulator serotonin (5-hydroxytryptamine, 5-HT) plays an important role in controlling the induction threshold and maintenance of long-term potentiation (LTP) in the visual cortex and hippocampus of rodents. Serotonergic fibers also innervate the rodent primary auditory cortex (A1), but the regulation of A1 plasticity by 5-HT receptors (5-HTRs) is largely uncharted. Thus, we examined the role of several, predominant 5-HT receptor classes (5-HT1ARs, 5-HT2Rs, and 5-HT3Rs) in gating in vivo LTP induction at A1 synapses of adult, urethane-anesthetized rats. Theta-burst stimulation (TBS) applied to the medial geniculate nucleus resulted in successful LTP induction of field postsynaptic potentials (fPSPs) generated by excitation of thalamocortical and intracortical A1 synapses. Local application (by reverse microdialysis in A1) of the broad-acting 5-HTR antagonist methiothepin suppressed LTP at both thalamocortical and intracortical synapses. In fact, rather than LTP, TBS elicited long-term depression during methiothepin application, an effect that was mimicked by the selective 5-HT2R antagonist ketanserin, but not the 5-HT1AR blocker WAY 100635. Interestingly, antagonism of 5-HT3Rs by granisetron selectively blocked LTP at thalamocortical, but not intracortical A1 synapses. Further, in the absence of TBS, granisetron application resulted in a pronounced increase in fPSP amplitude, suggesting that 5-HT3Rs play an important role in regulating baseline (non-potentiated) transmission at A1 synapses. Together, these results indicate that activation of 5-HT2Rs and 5-HT3Rs, but not 5-HT1ARs, exerts a clear, facilitating effect on LTP induction at A1 synapses, allowing 5-HT to act as a powerful regulator of long-term plasticity induction in the fully matured A1 of mammalian species.
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Affiliation(s)
- Karen K Y Lee
- Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Chloe N Soutar
- Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada
| | - Hans C Dringenberg
- Department of Psychology, Queen's University, Kingston, Ontario K7L 3N6, Canada; Centre for Neuroscience Studies, Queen's University, Kingston, Ontario K7L 3N6, Canada.
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Potential Role of Synaptic Activity to Inhibit LTD Induction in Rat Visual Cortex. Neural Plast 2017; 2016:1401935. [PMID: 28050286 PMCID: PMC5168486 DOI: 10.1155/2016/1401935] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2016] [Revised: 09/08/2016] [Accepted: 10/05/2016] [Indexed: 12/31/2022] Open
Abstract
Long-term depression (LTD), a widely studied form of activity-dependent synaptic plasticity, is typically induced by prolonged low-frequency stimulation (LFS). Interestingly, LFS is highly effective in eliciting LTD in vitro, but much less so under in vivo conditions; the reasons for the resistance of the intact brain to express LTD are not well understood. We examined if levels of background electrocorticographic (ECoG) activity influence LTD induction in the thalamocortical visual system of rats under very deep urethane anesthesia, inducing a brain state of reduced spontaneous cortical activity. Under these conditions, LFS applied to the lateral geniculate nucleus resulted in LTD of field postsynaptic potentials (fPSPs) recorded in the primary visual cortex (V1). Pairing LFS with stimulation of the brainstem (pedunculopontine) reticular formation resulted in the appearance of faster, more complex activity in V1 and prevented LTD induction, an effect that did not require muscarinic or nicotinic receptors. Reticular stimulation alone (without LFS) had no effect on cortical fPSPs. These results show that excitation of the brainstem activating system blocks the induction of LTD in V1. Thus, higher levels of neural activity may inhibit depression at cortical synapses, a hypothesis that could explain discrepancies regarding LTD induction in previous in vivo and in vitro work.
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Intskirveli I, Joshi A, Vizcarra-Chacón BJ, Metherate R. Spectral breadth and laminar distribution of thalamocortical inputs to A1. J Neurophysiol 2016; 115:2083-94. [PMID: 26888102 DOI: 10.1152/jn.00887.2015] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Accepted: 02/15/2016] [Indexed: 11/22/2022] Open
Abstract
The GABAergic agonist muscimol is used to inactivate brain regions in order to reveal afferent inputs in isolation. However, muscimol's use in primary auditory cortex (A1) has been questioned on the grounds that it may unintentionally suppress thalamocortical inputs. We tested whether muscimol can preferentially suppress cortical, but not thalamocortical, circuits in urethane-anesthetized mice. We recorded tone-evoked current source density profiles to determine frequency receptive fields (RFs) for three current sinks: the "layer 4" sink (fastest onset, middle-layer sink) and current sinks 100 μm above ("layer 2/3") and 300 μm below ("layer 5/6") the main input. We first determined effects of muscimol dose (0.01-1 mM) on the characteristic frequency (CF) tone-evoked layer 4 sink. An "ideal" dose (100 μM) had no effect on CF-evoked sink onset latency or initial response but reduced peak amplitude by >80%, implying inhibition of intracortical, but not thalamocortical, activity. We extended the analysis to current sinks in layers 2/3 and 5/6 and for all three sinks determined RF breadth (quarter-octave steps, 20 dB above CF threshold). Muscimol reduced RF breadth 42% in layer 2/3 (from 2.4 ± 0.14 to 1.4 ± 0.11 octaves), 14% in layer 4 (2.2 ± 0.12 to 1.9 ± 0.10 octaves), and not at all in layer 5/6 (1.8 ± 0.10 to 1.7 ± 0.12 octaves). The results provide an estimate of the laminar and spectral extent of thalamocortical projections and support the hypothesis that intracortical pathways contribute to spectral integration in A1.
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Affiliation(s)
- Irakli Intskirveli
- Department of Neurobiology and Behavior and Center for Hearing Research, University of California, Irvine, California
| | - Anar Joshi
- Department of Neurobiology and Behavior and Center for Hearing Research, University of California, Irvine, California
| | | | - Raju Metherate
- Department of Neurobiology and Behavior and Center for Hearing Research, University of California, Irvine, California
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Effects of Patterned Sound Deprivation on Short- and Long-Term Plasticity in the Rat Thalamocortical Auditory System In Vivo. Neural Plast 2016; 2016:3407135. [PMID: 26881106 PMCID: PMC4736309 DOI: 10.1155/2016/3407135] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2015] [Revised: 10/28/2015] [Accepted: 10/29/2015] [Indexed: 11/17/2022] Open
Abstract
Postnatal sensory experience plays a significant role in the maturation and synaptic stabilization of sensory cortices, such as the primary auditory cortex (A1). Here, we examined the effects of patterned sound deprivation (by rearing in continuous white noise, WN) during early postnatal life on short- and long-term plasticity of adult male rats using an in vivo preparation (urethane anesthesia). Relative to age-matched control animals reared under unaltered sound conditions, rats raised in WN (from postnatal day 5 to 50–60) showed greater levels of long-term potentiation (LTP) of field potentials in A1 induced by theta-burst stimulation (TBS) of the medial geniculate nucleus (MGN). In contrast, analyses of short-term plasticity using paired-pulse stimulation (interstimulus intervals of 25–1000 ms) did not reveal any significant effects of WN rearing. However, LTP induction resulted in a significant enhancement of paired-pulse depression (PPD) for both rearing conditions. We conclude that patterned sound deprivation during early postnatal life results in the maintenance of heightened, juvenile-like long-term plasticity (LTP) into adulthood. Further, the enhanced PPD following LTP induction provides novel evidence that presynaptic mechanisms contribute to thalamocortical LTP in A1 under in vivo conditions.
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Abstract
This review covers the spatial and temporal rules governing induction of hippocampal long-term potentiation (LTP) by theta-burst stimulation. Induction of LTP in field CA1 by high frequency stimulation bursts that resemble the burst discharges (complex-spikes) of hippocampal pyramidal neurons involves a multiple-step mechanism. A single burst is insufficient for LTP induction because it evokes both excitatory and inhibitory currents that partially cancel and limit postsynaptic depolarization. Bursts repeated at the frequency (~5 Hz) of the endogenous theta rhythm induce maximal LTP, primarily because this frequency disables feed-forward inhibition and allows sufficient postsynaptic depolarization to activate voltage-sensitive NMDA receptors. The disinhibitory process, referred to as "priming", involves presynaptic GABA autoreceptors that inhibit GABA release. Activation of NMDA receptors allows a calcium flux into dendritic spines that serves as the proximal trigger for LTP. We include new data showing that theta-burst stimulation is more efficient than other forms of stimulation for LTP induction. In addition, we demonstrate that associative interactions between synapses activated during theta-bursts are limited to major dendritic domains since such interactions occur within apical or basal dendritic trees but not between them. We review evidence that recordings of electrophysiological responses during theta burst stimulation can help to determine if experimental manipulations that affect LTP do so by affecting events antecedent to the induction process, such as NMDA receptor activation, or downstream signaling cascades that result from postsynaptic calcium fluxes. Finally, we argue that theta-burst LTP represents a minimal model for stable, non-decremental LTP that is more sensitive to a variety of experimental manipulations than is LTP induced by other stimulation paradigms. This article is part of a Special Issue entitled SI: Brain and Memory.
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Affiliation(s)
- John Larson
- Psychiatric Institute, Department of Psychiatry, University of Illinois College of Medicine, Chicago, IL 60612, United States.
| | - Erin Munkácsy
- Barshop Institute for Longevity and Aging Studies, Department of Cell and Structural Biology, University of Texas Health Science Center at San Antonio, San Antonio, TX 78245, United States
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Dringenberg HC, Branfield Day LR, Choi DH. Chronic fluoxetine treatment suppresses plasticity (long-term potentiation) in the mature rodent primary auditory cortex in vivo. Neural Plast 2014; 2014:571285. [PMID: 24719772 PMCID: PMC3956292 DOI: 10.1155/2014/571285] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2013] [Revised: 01/12/2014] [Accepted: 01/13/2014] [Indexed: 01/13/2023] Open
Abstract
Several recent studies have provided evidence that chronic treatment with the selective serotonin reuptake inhibitor (SSRI) fluoxetine can facilitate synaptic plasticity (e.g., ocular dominance shifts) in the adult central nervous system. Here, we assessed whether fluoxetine enhances long-term potentiation (LTP) in the thalamocortical auditory system of mature rats, a developmentally regulated form of plasticity that shows a characteristic decline during postnatal life. Adult rats were chronically treated with fluoxetine (administered in the drinking water, 0.2 mg/mL, four weeks of treatment). Electrophysiological assessments were conducted using an anesthetized (urethane) in vivo preparation, with LTP of field potentials in the primary auditory cortex (A1) induced by theta-burst stimulation of the medial geniculate nucleus. We find that, compared to water-treated control animals, fluoxetine-treated rats did not express higher levels of LTP and, in fact, exhibited reduced levels of potentiation at presumed intracortical A1 synapses. Bioactivity of fluoxetine was confirmed by a reduction of weight gain and fluid intake during the four-week treatment period. We conclude that chronic fluoxetine treatment fails to enhance LTP in the mature rodent thalamocortical auditory system, results that bring into question the notion that SSRIs act as general facilitators of synaptic plasticity in the mammalian forebrain.
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Affiliation(s)
- Hans C. Dringenberg
- Department of Psychology, Queen's University, Kingston, ON, Canada K7L 3N6
- Center for Neuroscience Studies, Queen's University, Kingston, ON, Canada K7L 3N6
| | | | - Deanna H. Choi
- Department of Psychology, Queen's University, Kingston, ON, Canada K7L 3N6
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Brozoski T, Odintsov B, Bauer C. Gamma-aminobutyric acid and glutamic acid levels in the auditory pathway of rats with chronic tinnitus: a direct determination using high resolution point-resolved proton magnetic resonance spectroscopy (H-MRS). Front Syst Neurosci 2012; 6:9. [PMID: 22383901 PMCID: PMC3285819 DOI: 10.3389/fnsys.2012.00009] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2011] [Accepted: 02/08/2012] [Indexed: 12/02/2022] Open
Abstract
Damage to the auditory system following high-level sound exposure reduces afferent input. Homeostatic mechanisms appear to compensate for the loss. Overcompensation may produce the sensation of sound without an objective physical correlate, i.e., tinnitus. Several potential compensatory neural processes have been identified, such as increased spontaneous activity. The cellular mechanisms enabling such compensatory processes may involve down-regulation of inhibitory neurotransmission mediated by γ-amino butyric acid (GABA), and/or up-regulation of excitatory neurotransmission, mediated by glutamic acid (Glu). Because central processing systems are integrated and well-regulated, compensatory changes in one system may produce reactive changes in others. Some or all may be relevant to tinnitus. To examine the roles of GABA and Glu in tinnitus, high resolution point-resolved proton magnetic resonance spectroscopy (1H-MRS) was used to quantify their levels in the dorsal cochlear nucleus (DCN), inferior colliculus (IC), medial geniculate body (MGB), and primary auditory cortex (A1) of rats. Chronic tinnitus was produced by a single high-level unilateral exposure to noise, and was measured using a psychophysical procedure sensitive to tinnitus. Decreased GABA levels were evident only in the MGB, with the greatest decrease, relative to unexposed controls, obtained in the contralateral MGB. Small GABA increases may have been present bilaterally in A1 and in the contralateral DCN. Although Glu levels showed considerable variation, Glu was moderately and bilaterally elevated both in the DCN and in A1. In the MGB Glu was increased ipsilaterally but decreased contralaterally. These bidirectional and region-specific alterations in GABA and Glu may reflect large-scale changes in inhibitory and excitatory equilibrium accompanying chronic tinnitus. The present results also suggest that targeting both neurotransmitter systems may be optimal in developing more effective therapeutics.
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Affiliation(s)
- Thomas Brozoski
- Division of Otolaryngology, Southern Illinois University School of Medicine, Springfield IL, USA
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