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McNeill JK, Walton JC, Ryu V, Albers HE. The Excitatory Effects of GABA within the Suprachiasmatic Nucleus: Regulation of Na-K-2Cl Cotransporters (NKCCs) by Environmental Lighting Conditions. J Biol Rhythms 2020; 35:275-286. [PMID: 32406304 DOI: 10.1177/0748730420924271] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The suprachiasmatic nucleus (SCN) contains a pacemaker that generates circadian rhythms and entrains them with the 24-h light-dark cycle (LD). The SCN is composed of 16,000 to 20,000 heterogeneous neurons in bilaterally paired nuclei. γ-amino butyric acid (GABA) is the primary neurochemical signal within the SCN and plays a key role in regulating circadian function. While GABA is the primary inhibitory neurotransmitter in the brain, there is now evidence that GABA can also exert excitatory effects in the adult brain. Cation chloride cotransporters determine the effects of GABA on chloride equilibrium, thereby determining whether GABA produces hyperpolarizing or depolarizing actions following activation of GABAA receptors. The activity of Na-K-2Cl cotransporter1 (NKCC1), the most prevalent chloride influx cotransporter isoform in the brain, plays a critical role in determining whether GABA has depolarizing effects. In the present study, we tested the hypothesis that NKCC1 protein expression in the SCN is regulated by environmental lighting and displays daily and circadian changes in the intact circadian system of the Syrian hamster. In hamsters housed in constant light (LL), the overall NKCC1 immunoreactivity (NKCC1-ir) in the SCN was significantly greater than in hamsters housed in LD or constant darkness (DD), although NKCC1 protein levels in the SCN were not different between hamsters housed in LD and DD. In hamsters housed in LD cycles, no differences in NKCC1-ir within the SCN were observed over the 24-h cycle. NKCC1 protein in the SCN was found to vary significantly over the circadian cycle in hamsters housed in free-running conditions. Overall, NKCC1 protein was greater in the ventral SCN than in the dorsal SCN, although no significant differences were observed across lighting conditions or time of day in either subregion. These data support the hypothesis that NKCC1 protein expression can be regulated by environmental lighting and circadian mechanisms within the SCN.
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Affiliation(s)
- John K McNeill
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia
| | - James C Walton
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia
| | - Vitaly Ryu
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia
| | - H Elliott Albers
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, Georgia
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Abstract
Over 90% of neurons within the suprachiasmatic nucleus (SCN) express γ-aminobutyric acid (GABA). Although GABA is primarily an inhibitory neurotransmitter, in vitro studies suggest that the activation of GABAA receptors (GABAAR) elicits excitation in the adult SCN. The ratio of excitatory to inhibitory responses to GABA depends on the balance of chloride influx by Na+-K+-Cl- cotransporter 1 (NKCC1) and chloride efflux by K+-Cl- cotransporters (KCCs). Excitatory responses to GABA can be blocked by inhibition of the inward chloride cotransporter, NKCC1, with the loop diuretic bumetanide. Here we investigated the role of NKCC1 activity in phase shifting the circadian pacemaker in response to photic and nonphotic signals in male Syrian hamsters housed in constant darkness. In the early subjective night (CT 13.5), injection of bumetanide into the SCN reduced light-induced phase delays. However, during the late subjective night (CT 19), bumetanide administration did not alter light-induced phase advances. Injection of bumetanide during the subjective day (CT 6) did not alter the phase of free-running circadian rhythms but attenuated phase advances induced by injection of the GABAAR agonist muscimol into the SCN. These data support the hypothesis that the excitatory effects of endogenously released GABA contribute to the ability of light to induce phase delays, thereby contributing to the most important function of the circadian system, its entrainment with the day-night cycle. Further, the finding that bumetanide inhibits the phase-advancing effects of muscimol during the subjective day supports the hypothesis that the excitatory responses to GABA also contribute to the ability of nonphotic stimuli to phase shift the circadian pacemaker.
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Affiliation(s)
- John K McNeill
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - James C Walton
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - H Elliott Albers
- Neuroscience Institute and Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
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Albers HE, Walton JC, Gamble KL, McNeill JK, Hummer DL. The dynamics of GABA signaling: Revelations from the circadian pacemaker in the suprachiasmatic nucleus. Front Neuroendocrinol 2017; 44:35-82. [PMID: 27894927 PMCID: PMC5225159 DOI: 10.1016/j.yfrne.2016.11.003] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/30/2016] [Revised: 10/16/2016] [Accepted: 11/22/2016] [Indexed: 12/31/2022]
Abstract
Virtually every neuron within the suprachiasmatic nucleus (SCN) communicates via GABAergic signaling. The extracellular levels of GABA within the SCN are determined by a complex interaction of synthesis and transport, as well as synaptic and non-synaptic release. The response to GABA is mediated by GABAA receptors that respond to both phasic and tonic GABA release and that can produce excitatory as well as inhibitory cellular responses. GABA also influences circadian control through the exclusively inhibitory effects of GABAB receptors. Both GABA and neuropeptide signaling occur within the SCN, although the functional consequences of the interactions of these signals are not well understood. This review considers the role of GABA in the circadian pacemaker, in the mechanisms responsible for the generation of circadian rhythms, in the ability of non-photic stimuli to reset the phase of the pacemaker, and in the ability of the day-night cycle to entrain the pacemaker.
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Affiliation(s)
- H Elliott Albers
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States.
| | - James C Walton
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Karen L Gamble
- Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35294, United States
| | - John K McNeill
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Neuroscience Institute, Georgia State University, Atlanta, GA 30302, United States
| | - Daniel L Hummer
- Center for Behavioral Neuroscience, Atlanta, GA 30302, United States; Department of Psychology, Morehouse College, Atlanta, GA 30314, United States
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Hummer DL, Ehlen JC, Larkin TE, McNeill JK, Pamplin JR, Walker CA, Walker PV, Dhanraj DR, Albers HE. Sustained activation of GABAA receptors in the suprachiasmatic nucleus mediates light-induced phase delays of the circadian clock: a novel function of ionotropic receptors. Eur J Neurosci 2015; 42:1830-8. [PMID: 25865743 DOI: 10.1111/ejn.12918] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Revised: 03/16/2015] [Accepted: 04/07/2015] [Indexed: 01/16/2023]
Abstract
The suprachiasmatic nucleus (SCN) contains a circadian clock that generates endogenous rhythmicity and entrains that rhythmicity with the day-night cycle. The neurochemical events that transduce photic input within the SCN and mediate entrainment by resetting the molecular clock have yet to be defined. Because GABA is contained in nearly all SCN neurons we tested the hypothesis that GABA serves as this signal in studies employing Syrian hamsters (Mesocricetus auratus). Activation of GABAA receptors was found to be necessary and sufficient for light to induce phase delays of the clock. Remarkably, the sustained activation of GABAA receptors for more than three consecutive hours was necessary to phase-delay the clock. The duration of GABAA receptor activation required to induce phase delays would not have been predicted by either the prevalent theory of circadian entrainment or by expectations regarding the duration of ionotropic receptor activation necessary to produce functional responses. Taken together, these data identify a novel neurochemical mechanism essential for phase-delaying the 'master' circadian clock within the SCN as well as identifying an unprecedented action of an amino acid neurotransmitter involving the sustained activation of ionotropic receptors.
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Affiliation(s)
- Daniel L Hummer
- Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA.,Department of Psychology, Morehouse College, Atlanta, GA, USA
| | - J Christopher Ehlen
- Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA.,Neuroscience Institute, Georgia State University, Atlanta, GA, USA.,Neuroscience Institute, Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, USA
| | - Tony E Larkin
- Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA.,Department of Psychology, Morehouse College, Atlanta, GA, USA.,Neuroscience Institute, Georgia State University, Atlanta, GA, USA
| | - John K McNeill
- Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA.,Neuroscience Institute, Georgia State University, Atlanta, GA, USA
| | - John R Pamplin
- Department of Psychology, Morehouse College, Atlanta, GA, USA
| | - Colton A Walker
- Department of Psychology, Morehouse College, Atlanta, GA, USA
| | | | - Daryl R Dhanraj
- Department of Psychology, Morehouse College, Atlanta, GA, USA
| | - H Elliott Albers
- Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA.,Neuroscience Institute, Georgia State University, Atlanta, GA, USA
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Song Z, McCann KE, McNeill JK, Larkin TE, Huhman KL, Albers HE. Oxytocin induces social communication by activating arginine-vasopressin V1a receptors and not oxytocin receptors. Psychoneuroendocrinology 2014; 50:14-9. [PMID: 25173438 PMCID: PMC4252597 DOI: 10.1016/j.psyneuen.2014.08.005] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/26/2014] [Revised: 08/01/2014] [Accepted: 08/02/2014] [Indexed: 11/28/2022]
Abstract
Arginine-vasopressin (AVP) and oxytocin (OT) and their receptors are very similar in structure. As a result, at least some of the effects of these peptides may be the result of crosstalk between their canonical receptors. The present study investigated this hypothesis by determining whether the induction of flank marking, a form of social communication in Syrian hamsters, by OT is mediated by the OT receptor or the AVP V1a receptor. Intracerebroventricular (ICV) injections of OT or AVP induced flank marking in a dose-dependent manner although the effects of AVP were approximately 100 times greater than those of OT. Injections of highly selective V1a receptor agonists but not OT receptor agonists induced flank marking, and V1a receptor antagonists but not OT receptor antagonists significantly inhibited the ability of OT to induce flank marking. Lastly, injection of alpha-melanocyte-stimulating hormone (α-MSH), a peptide that stimulates OT but not AVP release, significantly increased odor-induced flank marking, and these effects were blocked by a V1a receptor antagonist. These data demonstrate that OT induces flank marking by activating AVP V1a and not OT receptors, suggesting that the V1a receptor should be considered to be an OT receptor as well as an AVP receptor.
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Affiliation(s)
- Zhimin Song
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - Katharine E McCann
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - John K McNeill
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - Tony E Larkin
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - Kim L Huhman
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA
| | - H Elliott Albers
- Neuroscience Institute, Center for Behavioral Neuroscience, Georgia State University, Atlanta, GA, USA.
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