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Pittman DW, McGinnis MM, Liddy C, Richardson LM, Ellison ZT, Baird JP. Further disentangling the motivational processes underlying benzodiazepine hyperphagia. Pharmacol Biochem Behav 2022; 218:173426. [PMID: 35810922 DOI: 10.1016/j.pbb.2022.173426] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/08/2021] [Revised: 06/29/2022] [Accepted: 06/30/2022] [Indexed: 01/05/2023]
Abstract
In addition to their well-known anxiolytic functions, benzodiazepines produce hyperphagia. Previously, we reported that the benzodiazepine, chlordiazepoxide (CDP), increased consumption of both normally-preferred and normally-avoided taste stimuli during long-term (1 h) tests, primarily through changes in licking microstructure patterns associated with hedonic taste evaluation, whereas there was little effect on licking microstructure measures associated with post-ingestive feedback. In this study, we further examined the hedonic and motivational specificity of CDP effects on ingestive behavior. We tested brief access (15 s) licking responses for tastants spanning all taste qualities after treatment with either CDP (5 or 10 mg/kg) or the non-benzodiazepine anxiolytic, buspirone (1.5 or 3 mg/kg). A between-subjects, counterbalanced design compared the CDP or buspirone effects on licking responses for water and a range of weak to strong concentrations of NaCl, Q-HCl, citric acid, MSG, saccharin, and capsaicin under water-restricted (23 h) conditions; and sucrose, saccharin, and MSG under water-replete conditions. In a dose dependent manner, CDP increased licking for taste stimuli that were normally-avoided after saline treatment, with a notable exception observed for the trigeminal stimulus, capsaicin, which was not affected at any concentration or drug dose, suggesting a taste-specific effect of CDP on orosensory processing. Under water-replete conditions, CDP dose-dependently increased licking to normally-accepted concentrations of sucrose, saccharin, and MSG. There was no effect of either drug on licks for water under either water-restricted or water-replete conditions. Buspirone slowed oromotor coordination by increasing brief interlick intervals, but it did not affect licking for any concentrations of the tastants. Overall, these results indicate that benzodiazepines selectively enhance the hedonic acceptance of gustatory orosensory stimuli, independent of general anxiolytic or oromotor coordination effects, or physiological states such as thirst.
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Affiliation(s)
- David W Pittman
- Department of Psychology, Wofford College, 429 North Church Street, Spartanburg, SC 29303-3663, USA.
| | - Molly M McGinnis
- Department of Psychology, Wofford College, 429 North Church Street, Spartanburg, SC 29303-3663, USA
| | - Caroline Liddy
- Department of Psychology, Wofford College, 429 North Church Street, Spartanburg, SC 29303-3663, USA
| | - Lindsey M Richardson
- Department of Psychology, Wofford College, 429 North Church Street, Spartanburg, SC 29303-3663, USA
| | - Zachary T Ellison
- Department of Psychology, Wofford College, 429 North Church Street, Spartanburg, SC 29303-3663, USA
| | - John-Paul Baird
- Department of Psychology, Amherst College, P.O. Box 5000, Amherst, MA 01002-5000, USA
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Enhancing GABAergic Tone in the Rostral Nucleus of the Solitary Tract Reconfigures Sensorimotor Neural Activity. J Neurosci 2021; 41:489-501. [PMID: 33234608 DOI: 10.1523/jneurosci.0388-20.2020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 11/11/2020] [Accepted: 11/15/2020] [Indexed: 11/21/2022] Open
Abstract
Recent work has shown that most cells in the rostral, gustatory portion of the nucleus tractus solitarius (rNTS) in awake, freely licking rats show lick-related firing. However, the relationship between taste-related and lick-related activity in rNTS remains unclear. Here, we tested whether GABA-derived inhibitory activity regulates the balance of lick- and taste-driven neuronal activity. Combinatorial viral tools were used to restrict the expression of channelrhodopsin 2-enhanced yellow fluorescent protein to GAD1+ GABAergic neurons. Viral infusions were bilateral in rNTS. A fiber-optic fiber attached to a bundle of drivable microwires was later implanted into the rNTS. After recovery, water-deprived rats were presented with taste stimuli in an experimental chamber. Trials were five consecutive taste licks [NaCl, KCl, NH4Cl, sucrose, monosodium glutamate/inosine-5'-monophosphate, citric acid, quinine, or artificial saliva (AS)] separated by five AS rinse licks on a variable ratio 5 schedule. Each taste lick triggered a 1 s train of laser light (25 Hz; 473 nm; 8-10 mW) in a random half of the trials. In all, 113 cells were recorded in the rNTS, 50 cells responded to one or more taste stimuli without GABA enhancement. Selective changes in response magnitude (spike count) within cells shifted across-unit patterns but preserved interstimulus relationships. Cells where enhanced GABAergic tone increased lick coherence conveyed more information distinguishing basic taste qualities and different salts than other cells. In addition, GABA activation significantly amplified the amount of information that discriminated palatable versus unpalatable tastants. By dynamically regulating lick coherence and remodeling the across-unit response patterns to taste, enhancing GABAergic tone in rNTS reconfigures the neural activity reflecting sensation and movement.
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Chen Z, Travers SP, Travers JB. Inhibitory modulation of optogenetically identified neuron subtypes in the rostral solitary nucleus. J Neurophysiol 2016; 116:391-403. [PMID: 27146980 DOI: 10.1152/jn.00168.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Accepted: 04/27/2016] [Indexed: 12/27/2022] Open
Abstract
Inhibition is presumed to play an important role in gustatory processing in the rostral nucleus of the solitary tract (rNST). One source of inhibition, GABA, is abundant within the nucleus and comes both from local, intrasolitary sources and from outside the nucleus. In addition to the receptor-mediated effects of GABA on rNST neurons, the hyperpolarization-sensitive currents, Ih and IA, have the potential to further modulate afferent signals. To elucidate the effects of GABAergic modulation on solitary tract (ST)-evoked responses in phenotypically defined rNST neurons and to define the presence of IA and Ih in the same cells, we combined in vitro recording and optogenetics in a transgenic mouse model. This mouse expresses channelrhodopsin 2 (ChR2) in GAD65-expressing GABAergic neurons throughout the rNST. GABA positive (GABA+) neurons differed from GABA negative (GABA-) neurons in their response to membrane depolarization and ST stimulation. GABA+ neurons had lower thresholds to direct membrane depolarization compared with GABA- neurons, but GABA- neurons responded more faithfully to ST stimulation. Both IA and Ih were present in subsets of GABA+ and GABA- neurons. Interestingly, GABA+ neurons with Ih were more responsive to afferent stimulation than inhibitory neurons devoid of these currents, whereas GABA- neurons with IA were more subject to inhibitory modulation. These results suggest that the voltage-gated channels underlying IA and Ih play an important role in modulating rNST output through a circuit of feedforward inhibition.
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Affiliation(s)
- Z Chen
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, Ohio
| | - S P Travers
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, Ohio
| | - J B Travers
- Division of Biosciences, College of Dentistry, The Ohio State University, Columbus, Ohio
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Central connectivity of the chorda tympani afferent terminals in the rat rostral nucleus of the solitary tract. Brain Struct Funct 2014; 221:1125-37. [PMID: 25503820 DOI: 10.1007/s00429-014-0959-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2014] [Accepted: 12/06/2014] [Indexed: 10/24/2022]
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Huang W, Chen JX, Li YM, Lu YC, Wu XJ. Structures and connections of enkephalin- and γ-aminobutyric acid-immunoreactive profiles in the gustatory region of the nucleus tractus solitarius: a light and electron microscopic study. Neurol Sci 2010; 32:53-8. [DOI: 10.1007/s10072-010-0387-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2009] [Accepted: 07/17/2010] [Indexed: 10/19/2022]
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Terminal field specificity of forebrain efferent axons to brainstem gustatory nuclei. Brain Res 2008; 1248:76-85. [PMID: 19028464 DOI: 10.1016/j.brainres.2008.10.075] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Revised: 10/28/2008] [Accepted: 10/28/2008] [Indexed: 11/22/2022]
Abstract
Rostral forebrain structures like the gustatory cortex (GC), bed nucleus of the stria terminalis (BNST), central nucleus of the amygdala (CeA), and lateral hypothalamus (LH) send projections to the nucleus of solitary tract (NST) and the parabrachial nucleus (PBN) that modulate taste-elicited responses. However, the proportion of forebrain-induced excitatory and inhibitory effects often differs when taste cell recording changes from the NST to the PBN. The present study investigated whether this descending influence originates from a shared or distinct population of forebrain neurons. Under electrophysiological guidance, the retrograde tracers fast blue (FB) and fluorogold (FG) or green (GFB) and red (RFB) fluorescent latex microbeads were injected iontophoretically or by pressure pulses (10 ms at 20 psi) into the taste-responsive regions of the NST and the ipsilateral PBN in six rats. Seven days later, the animals were euthanized and tissue sections containing the LH, CeA, BNST, and GC were processed for co-localization of FB and FG or GFB and RFB. The results showed that the CeA is the major source of input to the NST (82.3+/-7.6 cells/section) and the PBN (76.7+/-11.5), compared to the BNST (31.8+/-4.5; 37.0+/-4.8), the LH (35.0+/-5.4; 33.6+/-5.7), and the GC (27.5+/-4.0; 29.0+/-4.6). Of the total number of retrogradely labeled cells, the incidence of tracer co-localization was 17+/-3% in the GC, 17+/-2% in the CeA, 15+/-3% in the BNST and 16+/-1% in the LH. Thus, irrespective of forebrain source the majority of descending input to the gustatory NST and PBN originates from distinct neuronal populations. This arrangement provides an anatomical substrate for differential modulation of taste processing in the first and second central relays of the ascending gustatory system.
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Lundy RF. Gustatory hedonic value: potential function for forebrain control of brainstem taste processing. Neurosci Biobehav Rev 2008; 32:1601-6. [PMID: 18675299 DOI: 10.1016/j.neubiorev.2008.07.002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2008] [Revised: 05/29/2008] [Accepted: 07/07/2008] [Indexed: 10/21/2022]
Abstract
Among well-nourished populations, eating beyond homeostatic needs when presented with caloric-dense palatable food evidences the assertion that an increasing proportion of consumption is driven by pleasure, not just by the need for calories. This presents a major health crisis because the affective component of foods constitutes a behavioral risk factor that promotes over consumption [Sorensen, L.B., Moller, P., Flint, A., Martens, M., Raben, A., 2003. Effect of sensory perception of foods on appetite and food intake: a review of studies on humans. Int. J. Obes. Relat. Metab. Disord. 27, 1152-1166; Yeomans, M.R., Blundell, J.E., Leshem, M., 2004. Palatability: response to nutritional need or need-free stimulation of appetite? Br. J. Nutr. 92 (Suppl. 1), S3-S14]. Overweight or obese individuals have an increased risk of developing hypertension, stroke, heart disease, chronic musculoskeletal problems, type-2 diabetes, and certain types of cancers [Hill, J.O., Catenacci, V., Wyatt, H.R., 2005. Obesity: overview of an epidemic. Psychiatr. Clin. N. Am. 28, 1-23, vii]. The etiology of obesity is complex involving genetic, metabolic, and behavioral factors, but ultimately results from long-term energy imbalance. Evidence indicates that learned and some forms of unlearned control of ingestive behavior driven by palatability (i.e. hedonic value) are critically dependent on reciprocal interactions between brainstem gustatory nuclei and the ventral forebrain. This review discusses the current understanding of centrifugal control of taste processing in subcortical gustatory nuclei and the potential role of such modulation in hedonic responding.
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Affiliation(s)
- Robert F Lundy
- University of Louisville School of Medicine, Department of Anatomical Sciences and Neurobiology, 500 South Preston Street, Louisville, KY 40292, United States.
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Bradley R. rNST Circuits. Front Neurosci 2006. [DOI: 10.1201/9781420005974.ch7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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N/A, 闫 剑, 施 京, 杨 雪. N/A. Shijie Huaren Xiaohua Zazhi 2006; 14:1906-1911. [DOI: 10.11569/wcjd.v14.i19.1906] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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Fong AY, Stornetta RL, Foley CM, Potts JT. Immunohistochemical localization of GAD67-expressing neurons and processes in the rat brainstem: subregional distribution in the nucleus tractus solitarius. J Comp Neurol 2006; 493:274-90. [PMID: 16255028 DOI: 10.1002/cne.20758] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The role of gamma-aminobutyric acid (GABA) in homeostatic control in the brainstem, in particular, in the nucleus tractus solitarius (NTS), is well established. However, to date, there is no detailed description of the distribution of GABAergic neurons within the NTS. The goal of the current study was to reexamine the efficacy of immunohistochemical localization of glutamic acid decarboxylase (GAD) protein, specifically the 67-kDa isoform (GAD67), as a marker for GABAergic neurons in the medulla and to provide a detailed map of GAD67-immunoreactive (-ir) cells within rat NTS by using a recently developed mouse monoclonal antibody. We describe a distribution of GAD67-ir cells in the medulla similar to that reported previously from in situ hybridization study. GAD67-ir cells were localized in regions known to contain high GABA content, including the ventrolateral medulla, raphe nuclei, and area postrema, but were absent from all motor nuclei, although dense terminal labeling was discerned in these regions. In the NTS, GAD67-ir was localized in all subregions. Semiquantitative analysis of the GAD67-ir distribution in the NTS revealed greater numbers of GAD67-ir cells medial to the solitary tract. Finally, dense GAD67 terminal labeling was found in the medial, central, intermediate, commissural, and subpostremal subregions, whereas sparse labeling was observed in the ventral subregion. Our findings support the use of immunohistochemistry for GAD67 as a marker for the localization of GABAergic cells and terminal processes in the rat brainstem. Furthermore, the reported heterogeneous distribution of GAD67-ir in the NTS suggests differential inhibitory modulation of sensory processing.
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Affiliation(s)
- Angelina Y Fong
- Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA
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Dynamic coding of taste stimuli in the brainstem: effects of brief pulses of taste stimuli on subsequent taste responses. J Neurosci 2003. [PMID: 14523091 DOI: 10.1523/jneurosci.23-26-08893.2003] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Recent studies have suggested that the response profiles of taste-responsive cells in the brainstem may be modulated by inhibitory interactions, potentially originating from activity in peripheral taste nerves. This idea was explored by testing the hypothesis that brief (100 msec) pulses of taste stimuli would alter the responses to subsequently presented tastants in the nucleus of the solitary tract (NTS) of urethane-anesthetized rats. Pulses of taste stimuli, called prepulses, were followed by a 3 sec presentation of the same or different taste stimulus. The prepulse-stimulus interval was either 1 or 5 sec, during which the tongue was rinsed with distilled water. Taste stimuli consisted of 0.1 m NaCl, 0.5 m sucrose, 0.01 m quinine HCl, and 0.01 m HCl. Taste prepulses suppressed (or enhanced) subsequent taste responses in 30 of 49 (61%) units when the prepulse-stimulus interval was 1 sec but were ineffective when this interval was 5 sec. Most commonly, NaCl or HCl prepulses attenuated the response to quinine. Control experiments showed that these effects were not attributable to adaptation, mixture effects, or response variability. In 19 (39%) of the units tested, effects of prepulses were large enough to change the order of effectiveness of the taste stimuli. Taste responses in these cells were "dynamically tuned" in that the magnitude of response was a function of the taste stimulus that immediately preceded it. Dynamic tuning may be the result of inhibitory interactions within the NTS; cells that show dynamic tuning may have a unique function in taste coding.
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King MS. Distribution of immunoreactive GABA and glutamate receptors in the gustatory portion of the nucleus of the solitary tract in rat. Brain Res Bull 2003; 60:241-54. [PMID: 12754086 DOI: 10.1016/s0361-9230(03)00034-0] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The distribution of glutamate (GLU) and gamma-aminobutyric acid (GABA) receptors within the gustatory portion of the rat nucleus of the solitary tract (gNST) was investigated using immunohistochemical, histological and neural tract tracing techniques. Numerous somata throughout the gNST were immunoreactive for alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) and N-methyl-D-aspartate (NMDA) receptors, while few were labeled for kainate receptors. AMPA and NMDA receptors were particularly abundant in the rostral central (RC) subdivision of the gNST, which receives most of the primary afferent input from the oral cavity and contains most of the gNST neurons that project to the parabrachial nuclei (PBN). This finding supports electrophysiological evidence that AMPA and NMDA receptors are involved in responses to orosensory input and indicates that their action may influence ascending taste signals as well. Compared to the ionotropic GLU receptors, few cell bodies were immunoreactive for metabotropic GLU receptors. Somata immunoreactive for GABA(A) and GABA(B) receptors were located throughout the nucleus. The densest neuropil labeling was for GABA(A) receptors in the ventral (V) subnucleus, the gNST subdivision that sends output to brainstem oromotor centers. The distributions of immunolabeling for GLU and GABA receptors imply that different functional roles may exist for specific receptors within this nucleus.
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Affiliation(s)
- Michael S King
- Unit 8264, Biology Department, Stetson University, DeLand, FL 32723, USA.
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Heck WL, Basaraba AM, Slusarczyk A, Schweitzer L. Early GABA(A) receptor clustering during the development of the rostral nucleus of the solitary tract. J Anat 2003; 202:387-96. [PMID: 12739616 PMCID: PMC1571086 DOI: 10.1046/j.1469-7580.2003.00169.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
While there is an abundance of gamma-aminobutyric acid (GABA) in the gustatory zone of the nucleus of the solitary tract of the perinatal rat, we know that GABAergic synapse formation is not complete until well after birth. Our recent results have shown that GABA(B) receptors are present at birth in the cells of the nucleus; however, they do not redistribute and cluster at synaptic sites until after PND10. The present study examined the time course of appearance and redistribution of GABA(A) receptors in the nucleus. GABA(A) receptors were also present at birth. However, in comparison to GABA(B) receptors, GABA(A) receptors underwent an earlier translocation to synaptic sites. Extrasynaptic label, for example, of GABA(A) receptors was non-existent compared to GABA(B) receptors at PND10 and well-defined clusters of GABA(A) receptors could be seen as early as PND1. We propose that while GABA(A), receptors may play an early neurotransmitter role at the synapse, GABA(B) receptors may play a non-transmitter neurotrophic role.
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Affiliation(s)
- W L Heck
- Department of Biology, University of North Carolina-Chapel Hill, Chapel Hill, NC 27599, USA
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Grabauskas G, Bradley RM. Frequency-dependent properties of inhibitory synapses in the rostral nucleus of the solitary tract. J Neurophysiol 2003; 89:199-211. [PMID: 12522172 DOI: 10.1152/jn.00963.2001] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To explore the parameters that define the characteristics of either inhibitory postsynaptic potentials (IPSP) or currents (IPSC) in the gustatory nucleus of the solitary tract (rNST), whole cell patch-clamp recordings were made in horizontal brain stem slices of newborn rats. Neurons were labeled with biocytin to confirm both their location and morphology. IPSPs or IPSCs were evoked by delivering either single, paired-pulse, or tetanic stimulus shocks (0.1-ms duration) via a bipolar stimulating electrode placed on the rNST. Pure IPSP/IPSCs were isolated by the use of glutamate receptor antagonists. For 83% of the single-stimulus-evoked IPSCs, the decay time course was fitted with two exponentials having average time constants of 38 and 181 ms, respectively, while the remainder could be fitted with one exponential of 59 ms. Paired-pulse stimulation resulted in summation of the amplitude of the conditioning and test-stimulus-evoked IPSCs. The decay time course of the test-stimulus-evoked IPSC was slower when compared to the decay time of the conditioning stimulus IPSC. Repeated stimulation resulted in an increase in the decay time of the IPSP/Cs where each consecutive stimulus contributed to prolongation of the decay time constant. Most of the IPSP/Cs resulting from a 1-s >/= 30-Hz tetanic stimulus exhibited an S-shaped decay time course where the amplitude of the IPSP/Cs after termination of the stimulus was initially sustained before starting to decay back to the resting membrane potential. Elevation of extracellular Ca(2+) concentration 10 mM resulted in an increase in the amplitude and decay time of single-stimulus shock-evoked IPSP/Cs. The benzodiazepine GABA(A) receptor modulator diazepam increased the decay time of single-stimulus shock-evoked IPSCs. However, application of diazepam did not affect the decay time of tetanic-stimulation-evoked IPSP/Cs. These results suggest that the decay time of single-stimulus-evoked IPSCs is defined either by receptor kinetics or neurotransmitter clearance from the synaptic cleft or both, while the decay time course of the tetanic stimulus evoked IPSP/Cs is defined by neurotransmitter diffusion from the synaptic cleft. During repetitive stimulation, neurotransmitter accumulates in the synaptic cleft prolonging the decay time constant of the IPSCs. High-frequency stimulation elevates the GABA concentration in the synaptic cleft, which then oversaturates the postsynaptic receptors, and, as a consequence, after termination of the tetanic stimulus, the amplitude of IPSP/Cs is sustained resulting in an S shaped decay time course. This activity-dependent plasticity at GABAergic synapses in the rNST is potentially important in the encoding of taste responses because the dynamic range of stimulus frequencies that result in synaptic plasticity (0-70 Hz) corresponds to the breadth of frequencies that travels via afferent gustatory nerve fibers in response to taste stimuli.
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Affiliation(s)
- Gintautas Grabauskas
- Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor 48109, USA.
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Sharp AA, Finger TE. GABAergic modulation of primary gustatory afferent synaptic efficacy. JOURNAL OF NEUROBIOLOGY 2002; 52:133-43. [PMID: 12124751 DOI: 10.1002/neu.10073] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Modulation of synaptic transmission at the primary sensory afferent synapse is well documented for the somatosensory and olfactory systems. The present study was undertaken to test whether GABA impacts on transmission of gustatory information at the primary afferent synapse. In goldfish, the vagal gustatory input terminates in a laminated structure, the vagal lobes, whose sensory layers are homologous to the mammalian nucleus of the solitary tract. We relied on immunoreactivity for the GABA-transporter, GAT-1, to determine the distribution of GABAergic synapses in the vagal lobe. Immunocytochemistry showed dense, punctate GAT-1 immunoreactivity coincident with the layers of termination of primary afferent fibers. The laminar nature and polarized dendritic structure of the vagal lobe make it amenable to an in vitro slice preparation to study early synaptic events in the transmission of gustatory input. Electrical stimulation of the gustatory nerves in vitro produces synaptic field potentials (fEPSPs) predominantly mediated by ionotropic glutamate receptors. Bath application of either the GABA(A) receptor agonist muscimol or the GABA(B) receptor agonist baclofen caused a nearly complete suppression of the primary fEPSP. Coapplication of the appropriate GABA(A) or GABA(B) receptor antagonist bicuculline or CGP-55845 significantly reversed the effects of the agonists. These data indicate that GABAergic terminals situated in proximity to primary gustatory afferent terminals can modulate primary afferent input via both GABA(A) and GABA(B) receptors. The mechanism of action of GABA(B) receptors suggests a presynaptic locus of action for that receptor.
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Affiliation(s)
- Andrew A Sharp
- Department of Cellular and Structural Biology, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA
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Heck WL, Slusarczyk A, Basaraba AM, Schweitzer L. Subcellular localization of GABA receptors in the central nervous system using post-embedding immunohistochemistry. BRAIN RESEARCH. BRAIN RESEARCH PROTOCOLS 2002; 9:173-80. [PMID: 12113777 DOI: 10.1016/s1385-299x(02)00143-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The following detailed protocol can be applied to demonstrate the localization of GABA receptors in CNS neurons at the ultrastructural level. While others have investigated receptors at the electron microscopic level using immunocytochemical techniques, the appearance of the tissue is usually poor and analyses of the distribution of receptors is limited. The methodology described in this paper allows for optimal preservation of the tissue while retaining immunogenicity. It does this, in part, by utilizing a balanced salt solution washout in conjunction with fixation. When the ionic composition of a fixative solution differs from extracellular fluids, like in most fixation protocols for electron microscopy, ultrastructural changes may occur in the tissue. Balanced salt solutions, like the Tyrode solution used here, helps maintain the normal extracellular environment allowing the fixing agent to reach sufficient concentration to bring about permanent and more optimal fixation even when reduced amounts of glutaraldehyde are required to preserve antigenicity. Therefore, unlike many protocols for post-embedding immunoelectronmicroscopy, this method allows for superior preservation of tissue ultrastructure compared to results previously published by others.
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Affiliation(s)
- Wendy L Heck
- Department of Biology and Cell/Molecular Physiology, University of North Carolina--Chapel Hill, Chapel Hill, NC 27599, USA
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Heck WL, Renehan WE, Schweitzer L. Redistribution and increased specificity of GABA(B) receptors during development of the rostral nucleus of the solitary tract. Int J Dev Neurosci 2001; 19:503-15. [PMID: 11470380 DOI: 10.1016/s0736-5748(01)00031-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Recent results show that there is an abundance of gamma-aminobutyric acid (GABA) before GABAergic synapses have formed in the gustatory zone of the nucleus of the solitary tract. These results suggest that a non-synaptic, developmental function may exist for GABA prior to synaptogenesis. However, GABA exerts its physiological effect via its receptors, the development of which is a largely unknown process. The developmental expression of one of the GABA receptors in the young nucleus of the solitary tract is the focus of this study. The development of GABA(B) receptors was investigated by light and electron microscopy. The results suggest that before the development of GABAergic synapses, GABA(B) receptors are diffusely distributed. When GABAergic synapses form, the receptors become clustered. Quantitative postembedding immunohistochemical studies at the electron microscopic level show that extrasynaptic labeling for GABA(B) receptors decreases during development, but synaptic labeling increases. Increased specificity of neurotransmitter receptors at synapses has been shown in other systems during development, including other central nervous system structures, but this may be the first demonstration of the phenomenon using quantitative electron microscopy.
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Affiliation(s)
- W L Heck
- Department of Anatomical Sciences and Neurobiology, School of Medicine, University of Louisville, Louisville, KY 40292, USA
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Brown M, Renehan WE, Schweitzer L. Changes in GABA-immunoreactivity during development of the rostral subdivision of the nucleus of the solitary tract. Neuroscience 2001; 100:849-59. [PMID: 11036219 DOI: 10.1016/s0306-4522(00)00355-9] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
GABA plays an important role in the processing of gustatory information in the rostral nucleus of the solitary tract. The following study used post-embedment immunohistochemistry in the rat brainstem to localize GABA at both the light and electron microscopic levels to characterize the developmental distribution of GABA and synaptogenesis of GABA-immunoreactive terminals in the rostral nucleus of the solitary tract. During the first postnatal week, GABA is present in the rostral nucleus of the solitary tract, but less of it is synaptic than any time later in development. Of the few synaptic terminals present at postnatal day 1, less than 20% are GABA-immunoreactive. This proportion more than doubles to reach adult levels by postnatal day 10. By weaning (postnatal day 20), GABA-immunoreactive cells are found in nearly the same density as in the adult. Development continues after weaning and is characterized by a disproportionate loss of non-GABA-containing cells. Finally, one previously identified subtype of GABA-immunoreactive terminal matures very late during the postweaning phase of development. The study provides the first analysis of the development of GABA-related circuitry in the rostral nucleus of the solitary tract using anatomical methods. These data provide the background with which to view the emerging physiology of developing taste neurons.
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Affiliation(s)
- M Brown
- Anatomical Sciences and Neurobiology, University of Louisville School of Medicine, Louisville, KY 40292, USA
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Saha S, Sieghart W, Fritschy JM, McWilliam PN, Batten TF. Gamma-aminobutyric acid receptor (GABA(A)) subunits in rat nucleus tractus solitarii (NTS) revealed by polymerase chain reaction (PCR) and immunohistochemistry. Mol Cell Neurosci 2001; 17:241-57. [PMID: 11161482 DOI: 10.1006/mcne.2000.0919] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Expression of mRNAs encoding seven GABA(A) receptor subunits (alpha1, alpha2, alpha3, alpha5, beta2, beta3, gamma2) in the nucleus tractus solitarii (NTS) of rat medulla oblongata was examined by reverse transcription-polymerase chain reaction (RT-PCR). All subunit mRNAs, except alpha5, were clearly detected. Band densities produced by alpha1, alpha3, beta3, and gamma2 subunits were greater than those corresponding to beta2 and alpha2 transcripts. The localization of these subunits in tissue sections through NTS was examined by immunohistochemistry. The differential patterns of immunoreactivity in neuronal somata and dendrites of NTS neurons were generally in agreement with the PCR results, confirming that mRNA expression is correlated with receptor protein synthesis. At ultrastructural level, alpha1, alpha3, beta2/3, and gamma2 subunits were localized in both cytoplasmic and subsynaptic sites, the latter often apposed to GABA immunoreactive synapses. These results suggest that ionotropic receptors comprising the alpha1, alpha3, beta2/3, and gamma2 may mediate inhibitory GABA responses in the NTS.
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Affiliation(s)
- S Saha
- Institute for Cardiovascular Research, University of Leeds, Leeds, LS2 9JT, United Kingdom
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