GABA-induced Inhibition Research Articles

Non-invasive ultrasonic modulation of visual evoked response by GABA delivery through the blood brain barrier

GABA is an inhibitory neurotransmitter that is maintained outside the brain by the blood brain barrier in normal condition. In this paper we demonstrate the feasibility of modulating brain activity in the visual cortex of non-human primates by transiently permeabilizing the blood brain barrier (BBB) using focused ultrasound (FUS) coupled with ultrasound contrast agents (UCA), followed by intra-venous injection of GABA. The visual evoked potentials exhibited a significant and GABA-dose-depend decrease in activity. The effect of the sonication only (with and without UCA) was also investigated and was shown to decrease the activity 8.7 times less than the GABA-induced inhibition enabled by BBB permeabilization. Finally, the UCA harmonic response was monitored during sonication to estimate the level of stable cavitation (a signature of the effectiveness of BBB permeabilization) and to avoid damage due to inertial cavitation (the sonication was automatically shut down when this condition was detected). Our results extend the promise of the exploration and treatment of the brain using non-invasive, controllable, repeatable, and reversible neuromodulation.

Commentary: GABA Depolarizes Immature Neurons and Inhibits Network Activity in the Neonatal Neocortex In vivo.

Commentary: GABA Depolarizes Immature Neurons and Inhibits Network Activity in the Neonatal Neocortex In vivo.

Depolarization-induced depression of inhibitory transmission in cerebellar Purkinje cells

Several forms of depolarization-induced plasticity in inhibitory transmission have been reported to occur in cerebellar Purkinje cells (PCs), namely depolarization-induced suppression of inhibition (DSI), depolarization-induced potentiation of inhibition (DPI), and rebound potentiation (RP). Here, we describe another form of synaptic plasticity for gamma-amino butyric acid (GABA)ergic transmission in PCs. Immediately following depolarization trains in a PC, evoked inhibitory postsynaptic currents (eIPSCs) changed their direction from outward to inward currents under a recording condition in which eIPSCs were elicited as an outward current. Subsequently, the eIPSC amplitude remained depressed (depolarization-induced depression of inhibition [DDI]) for more than 20 min under the blockade of cannabinoid and N-methyl-D-aspartic acid (NMDA) receptor-mediated DSI and DPI, respectively. This DDI was completely abolished by intracellular infusion of the fast Ca2+-chelating agent BAPTA and by inhibition of Ca2+/calmodulin-dependent protein kinase II (CaMKII). Furthermore, DDI was strongly suppressed by calcium-activated chloride channel (CaCC) blockers, while an inhibitor of cation-chloride cotransporters (CCCs) partially blocked DDI during the early phase. Exogenous GABA-induced inhibition of spontaneous spike activity was attenuated in ∼50% of the PCs by climbing fiber stimulation-induced depolarization. These results suggest that activation of both CaCCs and CCCs was necessary for alteration of [Cl-]i after activation of CaMKII following elevation of [Ca2+]i in PCs. DDI may provide another mechanism for regulation of inhibitory inputs to PCs within the neuronal networks of the cerebellar cortex.

Enhancement of asynchronous release from fast-spiking interneuron in human and rat epileptic neocortex.

Author SummaryThe balance between excitation and inhibition in the cerebral cortex is important for multiple brain functions. Down-regulation of GABA-induced inhibition disrupts this balance and may lead to epileptic seizures. Asynchronous release of GABA is known to occur at certain GABAergic synapses and represents release of inhibitory neurotransmitter that is not precisely timed to presynaptic action potentials. Whether asynchronous release is subject to change after the induction of epilepsy remains unclear. In this study, using simultaneous recordings from inhibitory fast-spiking neurons and excitatory pyramidal cells, we found that asynchronous release occurred at the output synapses of fast-spiking neurons in both human and rat neocortex. The occurrence of asynchronous release depended on the level of residual calcium at the presynaptic terminals but not on postsynaptic spiking. Further experiments using cortical tissue derived from human patients with intractable epilepsy and from a rat model of the disorder revealed an elevation of asynchronous release in epileptic cortex, possibly resulting from an increase in action potential amplitude of fast-spiking neurons and changes in calcium dynamics in their axon terminals. Taken together, these results demonstrate that asynchronous release is a fundamental property shared by neocortical fast-spiking neurons regardless of species, and the enhancement of asynchronous release in epileptic tissue suggests a role for it in regulating epileptic activities.

Use of naloxone in the treatment of benzodiazepine poisoning

We read with interest the recent article by Solhi et al., studying the use of naloxone in benzodiazepine poisoning treatment and the comments by Jang et al. It is an interesting topic and we would like to express our thoughts on these comments and concerns based on the literature review. Jang et al. had a concern: ‘Since naloxone is a known antidote for opioid toxicity, it is very important to exclude their presence to validate the data obtained’. This is a good point to make this article better. However, this might not affect the final conclusion in this study based on the results. First, a number of studies show that the prevalence of current benzodiazepine use in methadone-maintenance treatment populations varies between 24.9% and 50.6%. However, prevalence data suggest that most benzodiazepine users do not take illegal drugs. In the study by Solhi et al., after a naloxone injection, 80%–100% of the patients, varying by type of benzodiazepine, significantly improved the main signs and symptoms such as lethargy, weakness, and ataxia, while there was no improvement in the control groups. It is unlikely that 80%–100% of the patients in this study were using illegal drug or synthetic opioids. In another word, there must be few, if not all, patients without any illegal drug or synthetic opioid use, whose symptoms and clinical signs were improved by naloxone, but not by control treatments. Second, animal studies provide direct evidence that naloxone antagonizes gamma-aminobutyric acid (GABA)/benzodiazepine receptor functions. Electrophysiological data show that GABA-induced inhibition of neuronal firing in the brain of rat can be antagonized by naloxone. Furthermore, in experimental animals, naloxone antagonizes various benzodiazepine-induced behaviors, for example, hyperdipsia, hyperphagia, anticonflict effects, and anxiolytic-like effects. These data suggest the direct interaction of naloxone with GABA/benzodiazepine receptor functions. In summary, this study provides useful information on the treatment of benzodiazepine poisoning by naloxone. The nature of the mechanism involved, which needs further study, might involve its interaction with GABA receptors.

Modulation of in vivo GABA-evoked responses by nitric oxide-active compounds in the globus pallidus of rat

Nitric oxide (NO) is a gaseous molecule acting as a messenger in both the peripheral and the central nervous systems. NO affects synaptic activity by modulating neurotransmitter release and/or receptor function. We previously observed that NO-active compounds modify the bioelectric activity of basal ganglia (BG) units. In this study, we applied microiontophoresis to extracellular in vivo recordings to investigate the effect of NO-active compounds on GABA-evoked responses in the globus pallidus (GP) of anesthetized rats. The changes induced by NO-active drugs on the GABA-induced inhibition were used as indicators of NO modulation. The response to GABA release was tested on recorded GP neurons before and during the administration of S-nitroso-glutathione (SNOG, a NO donor) and/or Nω-nitro-L: -arginine methyl ester (L: -NAME), an inhibitor of nitric oxide synthase (NOS); furthermore, SNOG and L: -NAME were tested at different ejection currents in order to highlight the possibility of a current-dependent effect in the nitrergic modulation of GABA transmission. In general, during SNOG ejection the magnitude of GABA-evoked responses was reduced, whereas the administration of L: -NAME produced the opposite effect. The results suggest that NO-active drugs modulate the response of GP neurons to GABA transmission; the effects induced by SNOG and L: -NAME were strictly related to the ejection currents. Then, the modulation of GABAergic transmission by NO could represent a mechanism to finely regulate the GP neurons activity with important consequences on the overall BG function.

Analysis of GABA-induced inhibition of spontaneous firing in chick accessory lobe neurons

It has been hypothesized that chick accessory lobes (ALs) contain functional neurons and act as a sensory organ of equilibrium. It was reported that neurons located in an outer layer of ALs showed γ-aminobutyric acid (GABA)- and glutamic acid decarboxylase (GAD)-like immunoreactivity more strongly than centrally located neurons, which were surrounded by the GAD-immunoreactive terminals. We investigated effects of GABA on the electrical activity of AL neurons. About 50% of embryonic AL neurons exhibited spontaneous firing. In the on-cell recording, GABA, muscimol, and GABA in combination with CGP35348 inhibited this firing. In whole-cell voltage clamp recordings, GABA and muscimol evoked a transient current. The mean reversal potential of GABA-evoked currents was close to the theoretical reversal potential of Cl⁻. These results indicate that GABA exerts the inhibitory effect on the firing through the activation of GABA(A) receptors. In addition, the intracellular concentration of Cl⁻ was estimated to be about 16 mM in measurements with the gramicidin-perforated configuration, indicating the physiological reversal potential of the GABA current was about -60 mV. In conclusion, AL neurons have an intrinsic mechanism to evoke the spontaneous firing, which can be arrested by the inhibitory mechanism through the activation of the GABA(A) receptors.

The cerebellar GABA AR α6-R100Q polymorphism alters ligand binding in outbred Sprague–Dawley rats in a similar manner as in selectively bred AT and ANT rats

The alcohol-tolerant AT and alcohol-nontolerant ANT rat lines have been selectively bred for innate sensitivity to ethanol-induced motor impairment. The cerebellar GABA A receptor (GABA AR) α6 subunit alleles α6-100R and α6-100Q are segregated in the AT and ANT rats, respectively. This α6 polymorphism might explain various differences in pharmacological properties and density of GABA ARs between the rat lines. In the present study, we have used nonselected outbred Sprague–Dawley rats homozygous for the α6-100RR (RR) and α6-100QQ (QQ) genotypes to show that these RR and QQ rats display similar differences between genotypes as AT and ANT rat lines. The genotypes differed in their affinity for [ 3H]Ro 15-4513 and classic benzodiazepines (BZs) to cerebellar “diazepam-insensitive” (DZ-IS) binding sites, in density of cerebellar [ 3H]muscimol binding and in the antagonizing effect of furosemide on GABA-induced inhibition of [ 3H]EBOB binding. The results suggest the involvement of α6-R100Q polymorphism in these line differences and in the differences previously found between AT and ANT rats. In addition, the α6-R100Q polymorphism induces striking differences in [ 3H]Ro 15-4513 binding kinetics to recombinant α6β3γ2s receptors and cerebellar DZ-IS sites. Association of [ 3H]Ro 15-4513 binding was ∼10-fold faster and dissociation was ∼3–4-fold faster in DZ-IS α6βγ2 receptors containing the α6-100Q allele, with a resulting change of ∼2.5-fold in equilibrium dissociation constant ( K D). The results indicate that in addition to the central role of the homologous α6-100R/Q (α1-101H) residue in BZ binding and efficacy, this critical BZ binding site residue has a major impact on BZ binding kinetics.

GABAA- and AMPA-like receptors modulate the activity of an identified neuron within the central pattern generator of the pond snail Lymnaea stagnalis

To examine the neurochemistry underlying the firing of the RPeD1 neuron in the respiratory central pattern generator of the pond snail, Lymnaea stagnalis, we examined electrophysiologically and pharmacologically either "active" or "silent" preparations by intracellular recording and pharmacology. GABA inhibited electrical firing by hyperpolarizing RPeD1, while picrotoxin, an antagonist of GABA(A) receptors, excited silent cells and reversed GABA-induced inhibition. Action potential activity was terminated by 1 mM glutamate (Glu) while silent cells were depolarized by the GluR agonists, AMPA, and NMDA. Kainate exerted a complex triphasic effect on membrane potential. However, only bath application of AMPA desensitized the firing. These data indicate that GABA inhibits RPeD1 via activation of GABA(A) receptors, while Glu stimulates the neuron by activating AMPA-sensitive GluRs.

γ-Aminobutyric Acid Inhibits Synergistic Interleukin-6 Release but Not Transcriptional Activation in Astrocytoma Cells

Objective: A decline in the inhibitory neurotransmitter γ-aminobutyric acid (GABA) may enhance cytokine release in Alzheimer’s disease (AD) resulting in neuroinflammation. We investigated the GABA-mediated suppression of the synergistic release of interleukin (IL)-6 due to interleukin 1-β (IL-1β) and tumor necrosis factor-α (TNF-α). Methods: Rat C6 astrocytoma cells were treated with IL-1β and TNF-α in the absence and presence of GABA. Activation of p38, degradation of IĸB-α and total cellular IL-6 were determined by Western blot analysis. IL-6 release and gene expression were measured by ELISA and RT-PCR, respectively. Results: Although p38 and nuclear factor (NF)-ĸB are essential for the synergistic release of IL-6, GABA did not affect either p38 phosphorylation or IĸB-α degradation. Additionally, GABA suppressed IL-6 release but did not alter cytokine-driven synergistic increases in IL-6 gene expression. Western blot analysis revealed that co-treatments with IL-1β and TNF-α resulted in an increase in intracellular IL-6 that was prevented by GABA. Conclusion: GABA-induced inhibition of IL-6 release appears to coincide with a reduction in cellular IL-6. The GABA-induced suppression of IL-6 release may include inhibition of IL-6 gene translation.

γ-Aminobutyric acid in the lateral septal area is involved in mediation of the inhibition of hypothalamic angiotensin II-sensitive neurons induced by blood pressure increases in rats

Previously, we have demonstrated that intravenous phenylephrine-induced increases in blood pressure inhibit angiotensin II-sensitive neurons via γ-aminobutyric acid (GABA) inputs in the anterior hypothalamic area (AHA). The lateral septal area (LSV) is also demonstrated to be involved in mediation of the baroreceptor reflex. To investigate central mechanisms involved in mediating the baroreceptor reflex, we examined whether GABA in the LSV is involved in mediation of the phenylephrine-induced inhibition of AHA angiotensin II-sensitive neurons. Microinjection of GABA into the LSV inhibited angiotensin II-sensitive neurons in the AHA of rats. The LSV GABA-induced inhibition of AHA neurons was abolished by pressure application of bicuculline onto the same AHA neurons. Intravenous injection of phenylephrine also inhibited AHA angiotensin II-sensitive neurons and the phenylephrine-induced inhibition of AHA neurons was abolished by microinjection of the GABAA receptor antagonist bicuculline into the LSV. In contrast, the LSV microinjection of bicuculline did not affect the inhibition of firing of AHA neurons induced by GABA pressure-applied in the AHA. These findings suggest that intravenous phenylephrine inhibits AHA angiotensin II-sensitive neurons via release of GABA in the LSV.

GABAergic mechanisms in regulating the activity state of substantia nigra pars reticulata neurons

Substantia nigra reticulata is the major output structure of the basal ganglia involved in somatosensory integration and organization of movement. While previous work in vitro and in anesthetized animal preparations suggests that these neurons are autoactive and points to GABA as a primary input regulating their activity, single-unit recording coupled with iontophoresis was used in awake, unrestrained rats to further clarify the role of tonic and phasic GABA input in maintenance and fluctuations of substantia nigra reticulata neuronal activity under physiologically relevant conditions. In contrast to glutamate, which was virtually ineffective at stimulating substantia nigra reticulata neurons in awake rats, all substantia nigra reticulata neurons tested were inhibited by iontophoretic GABA and strongly excited by bicuculline, a GABA-A receptor blocker. The GABA-induced inhibition had short onset and offset latencies, a fading response pattern (a rapid decrease in rate followed by its relative restoration), and was independent of basal discharge rate. The bicuculline-induced excitation was inversely related to discharge rate and current (dose)-dependent in individual units. However, the average discharge rate during bicuculline applications at different currents increased to a similar plateau (∼60 impulses/s), which was about twice the mean basal rates. The excitatory effects of bicuculline were phasically inhibited or completely blocked by brief GABA applications and generally mimicked by gabazine, another selective GABA antagonist. These data as well as neuronal inhibitions induced by nipecotic acid, a selective GABA uptake inhibitor, suggest that substantia nigra reticulata neurons in awake, quietly resting conditions are under tonic, GABA-mediated inhibition. Therefore, because of inherent autoactivity and specifics of afferent inputs, substantia nigra reticulata neurons are very sensitive to phasic alterations in GABA input, which appears to be the primary factor determining fluctuations in their activity states under physiological conditions. While these cells are relatively insensitive to direct activation by glutamate, and resistant to a continuous increase in GABA input, they appear to be very sensitive to a diminished GABA input, which may release them from tonic inhibition and determine their functional hyperactivity.

Role of GABA B receptors in GABA and baclofen-induced inhibition of adult rat cerebellar interpositus nucleus neurons in vitro

Previous studies suggested that the postsynaptic GABA B receptors of deep cerebellar nuclear neurons of adult rats were not activated by selective GABA B receptor agonist baclofen or endogenous GABA released by cerebellar cortical Purkinje cells, although the receptors have been demonstrated to exist in the deep cerebellar nuclei. In this study, cerebellar slices of adult rats were prepared for testing effects of GABA, baclofen and muscimol (selective GABA A receptor agonist) on cerebellar interpositus nucleus (IN) neurons. Perfusing slices with GABA (10–1000 μM), baclofen (1–30 μM) and muscimol (1–100 μM) respectively produced a dose-dependent inhibitory response on the IN neurons ( n = 39, 62 and 50), which was not blocked by low-Ca 2+/high-Mg 2+ medium ( n = 5, 6 and 6), supporting a direct postsynaptic action of these GABAergic agonists. Moreover, both selective GABA B receptor antagonist CGP35348 and selective GABA A receptor antagonist bicuculline were capable of partially blocking the inhibitory response of IN neurons to GABA ( n = 14 and 11), suggesting that the GABA-induced inhibition may contain two components, a GABA B receptors-mediated component and a GABA A receptors-mediated one. Further experiments revealed that not only muscimol ( n = 50) but also baclofen ( n = 62) suppressed IN cells’ activity. The baclofen-induced inhibition was selectively blocked by CGP35348 ( n = 12) but not by bicuculline ( n = 8), whereas the muscimol-induced inhibition was selectively antagonized by bicuculline ( n = 8) instead of CGP35348 ( n = 9). These results indicate that GABA B receptors in the IN neurons can be activated not only by GABA but also by baclofen, suggesting that besides GABA A receptors, GABA B receptors may also be involved in mediating the inhibitory effect of GABA on cerebellar IN neurons of adult rats.

Alpha 2- and beta-adrenoceptors differentially modulate GABA A- and GABA B-mediated inhibition of red nucleus neuronal firing

In mesencephalic red nucleus (RN), GABA-induced inhibition of neuronal firing is modulated by noradrenaline acting on α 2- and β-adrenoceptors. Since both GABA A and GABA B receptors are present in the rat RN, we have recorded the firing activity of RN neurons in vivo from anaesthetized rats to study how GABA A- and GABA B-mediated effects are modulated by either α 2- or β-adrenoceptor activation. Both the GABA A agonist isoguvacine and the GABA B agonist baclofen depressed the firing of RN neurons. During simultaneous application of clonidine, an α 2-adrenoceptor agonist, half of the isoguvacine- and baclofen-mediated responses were modified: isoguvacine-mediated inhibition was enhanced by 97% without any change in effect duration, whereas baclofen responses were either increased or slightly reduced in the same number of cases. Application of isoprenaline, a β-adrenoceptor agonist, increased isoguvacine effect in 66% of neurons without modifying effect duration; the amount of increase (43%) was significantly lower than that induced by clonidine. On the other hand, in the presence of isoprenaline, baclofen response was reduced in 72% of neurons with respect to both the amount (52%) and the duration (34%) of effect. Taken together, these results indicate that α 2-adrenoceptors mainly enhance GABA A-induced inhibition and induce mixed effects on GABA B response; on the other side, β-adrenoceptors exert an opposite modulation on GABA effects, respectively, enhancing and depressing GABA A- and GABA B-mediated responses.

Role of GABA A and GABA B receptors in GABA-induced inhibition of rat red nucleus neurons

We investigated GABA receptor subtypes mediating GABA-induced inhibition of red nucleus (RN) neuronal firing recorded extracellularly from anaesthetized rats. GABA response was mimicked by the GABA A agonists muscimol and isoguvacine in all cases and was partially blocked by the GABA A antagonist bicuculline. The GABA B agonist baclofen induced a long-lasting inhibition in 84% of cells. Neurons responding to either GABA A or GABA B agonists were equally distributed within the RN. The GABA C receptor agonist cis-amino-crotonic acid (CACA) did not modify RN neuronal firing; at high doses CACA occasionally induced inhibition abolished by bicuculline and thus mediated by GABA A receptors. We conclude that the inhibitory effects of GABA in the RN are mediated by both GABA A and GABA B receptors, whereas GABA C receptors are not involved.

Withdrawal properties of a neuroactive steroid: implications for GABA(A) receptor gene regulation in the brain and anxiety behavior.

Early work in the field established that the 5 alpha-reduced metabolite of progesterone 3 alpha-OH-5 alpha-pregnan-20-one (allopregnanolone or 3 alpha,5 alpha-THP) is a potent positive modulator of the GABA(A) receptor (GABAR), the receptor mediating the effects of the primary inhibitory transmitter in the brain. This steroid acts in a manner similar to sedative drugs, such as the barbiturates, both in terms of potentiating GABA-induced inhibition in vitro and in behavioral assays, by reducing anxiety and seizure susceptibility. Because sedative compounds exhibit withdrawal properties that result in behavioral hyperexcitability, our laboratory has more recently investigated the effect of prolonged application and rapid removal (i.e. 'withdrawal') of this steroid, administered in vivo to female rats. Withdrawal from 3 alpha,5 alpha-THP produces a state of increased anxiety and lowered seizure threshold, similar to withdrawal from other GABA-modulatory drugs such as the benzodiazepines and alcohol. Hormone withdrawal also produced increases in the alpha 4-containing GABAR, an effect correlated with insensitivity of the GABAR to modulation by the benzodiazepine class of tranquilizers, as would normally occur under control conditions. In addition, changes in intrinsic channel properties, including a marked acceleration in the decay rate was also observed as a result of declining levels of 3 alpha,5 alpha-THP. Such a change would result in less inhibitory total current, and the resulting increase in neuronal excitability could then underlie the observed behavioral excitability following hormone withdrawal. These results suggest that actions of this steroid on a traditional transmitter receptor in the brain lead to alterations in GABAR subunit composition that result in changes in the intrinsic channel properties of the receptor and behavioral excitability. These results may have implications for endogenous fluctuations in this hormone which may accompany premenstrual dysphoric disorder.

Biochemical approaches to study interaction of calcium channels with RGS12 in primary neuronal cultures

Regulation of the timing of voltage-dependent calcium channel activity is traditionally thought to involve heterotrimeric G-protein-signaling pathways. However, it is now being realized that these complex timing events are controlled by interactions between components of several signaling pathways and the cytoskeletal structure that serves as a scaffold element for interactions between the signaling components and the effector, the calcium channel, γ-Aminobutyric acid type B (GABA B ) receptors inhibit N-type calcium channels through Gα o -mediated activation of a tyrosine kinase pathway. Data from author's laboratory suggest that the timing of GABA-induced inhibition is a complex process that involves several signals. The α (pore-forming) subunit of the calcium channel is tyrosine phosphorylated by Src kinase. This phosphorylation makes the channel a target for the binding of a GTPase-activating protein, RGS 12. The phosphotyrosine-binding (PTB) domain of RGS12 binds to the tyrosine-phosphorylated channel, altering the kinetics of the termination of the response. This chapter describes the biochemical protocols used to determine the phosphorylation of the channel and its interaction with RGSl2.

GABAergic modulation of neurons in the nucleus of the solitary tract with ascending projections to the subfornical organ in the rat

Twenty-five neurons in the region of the nucleus of the solitary tract (NTS) were antidromically activated by electrical stimulation of the subfornical organ (SFO) in male rats under urethane anesthesia. Microiontophoretically applied bicuculline, a γ-aminobutyric acid (GABA) A antagonist, but not phaclofen, a GABA B antagonist, attenuated the post-antidromic inhibitory response evoked by SFO stimulation of approximately two-third ( n=17) of identified neurons, indicating the existence of recurrent inhibitory systems through GABA A receptors. Iontophoretically applied GABA decreased the spontaneous activity of all identified neurons, and the GABA-induced inhibition was prevented by simultaneously applied bicuculline, but not by phaclofen. Activation of peripheral baroreceptors, achieved by rising arterial blood pressure with an intravenous infusions of phenylepherine, suppressed the activity of the majority ( n=20) of identified neurons. The inhibitory response of identified neurons ( n=7) to baroreceptor activation was partially antagonized by iontophoretically applied bicuculline, but not by phaclofen. These results imply that GABAergic mechanisms may modulate the baroreceptor reflex acting on GABA A receptors of NTS neurons with ascending projections to the SFO in the region of the NTS.

Chronic Ethanol Consumption Alters Recovery of Spontaneously Active Medial Septal/Diagonal Band of Broca Neurons From GABA‐Microiontophoresis

Acute ethanol administration increases GABA-mediated inhibition in a variety of cerebral cortical preparations. Furthermore, chronic ethanol administration blunts ethanol-induced increases in GABA-mediated inhibition and alters GABA A receptor subunit mRNA and peptide expression in the cerebral cortex. The sedative hypnotic effects of ethanol are believed to be modulated by GABA-induced inhibition in medial septum/diagonal band of Broca (MS/DB) neurons, a brain region where acute ethanol administration increases GABA-mediated inhibition of spontaneously active neurons. Chronic ethanol administration produces tolerance to the sedative effects of ethanol. However, it is unknown if chronic ethanol consumption produces alterations in GABA-mediated inhibition in the MS/DB in a manner similar to that found in the cerebral cortex. Animals either consumed ethanol chronically for 14 days via a liquid diet or were pair-fed an equicaloric dextrose-containing control diet. Spontaneously active MS/DB neurons were recorded using multibarrel glass micropipettes while the effect of GABA-microiontophoresis was investigated. The total amount of GABA-mediated inhibition at four ejection currents was analyzed, as was the recovery to spontaneous neural firing rates following GABA inhibition. In a separate group of animals, the medial septum was microdissected, and the relative expression of GABA A receptor alpha1 and alpha4 subunit peptide were analyzed via Western blot analysis. Chronic ethanol consumption altered recovery of spontaneous neural activity of MS/DB neurons following GABA-microiontophoresis compared to premicroiontophoresis levels. Specifically, the recovery of spontaneous neural activity of MS/DB neurons recorded from animals that chronically consumed ethanol was slower following GABA-microiontophoresis compared to neurons recorded from control animals. This effect was temporary and reversible. Furthermore, the alteration in recovery of spontaneous neural activity was not due to changes in the total amount of inhibition produced by GABA. Finally, there was no significant change in GABA A receptor alpha1 and alpha4 subunit peptide levels in the MS/DB. Chronic ethanol consumption alters the frequency of spontaneous MS/DB neural activity following GABA microiontophoresis compared to premicroiontophoresis levels. These data suggest that the kinetics of GABA A receptors in the MS/DB are altered by chronic ethanol consumption independent of changes in the total amount of inhibition or alterations in GABA A receptor alpha1 and alpha4 subunit peptide expression.

Chronic Ethanol Consumption Alters Recovery of Spontaneously Active Medial Septal/Diagonal Band of Broca Neurons From GABA-Microiontophoresis

Background: Acute ethanol administration increases GABA-mediated inhibition in a variety of cerebral cortical preparations. Furthermore, chronic ethanol administration blunts ethanol-induced increases in GABA-mediated inhibition and alters GABAA receptor subunit mRNA and peptide expression in the cerebral cortex. The sedative hypnotic effects of ethanol are believed to be modulated by GABA-induced inhibition in medial septum/diagonal band of Broca (MS/DB) neurons, a brain region where acute ethanol administration increases GABA-mediated inhibition of spontaneously active neurons. Chronic ethanol administration produces tolerance to the sedative effects of ethanol. However, it is unknown if chronic ethanol consumption produces alterations in GABA-mediated inhibition in the MS/DB in a manner similar to that found in the cerebral cortex. Methods: Animals either consumed ethanol chronically for 14 days via a liquid diet or were pair-fed an equicaloric dextrose-containing control diet. Spontaneously active MS/DB neurons were recorded using multibarrel glass micropipettes while the effect of GABA-microiontophoresis was investigated. The total amount of GABA-mediated inhibition at four ejection currents was analyzed, as was the recovery to spontaneous neural firing rates following GABA inhibition. In a separate group of animals, the medial septum was microdissected, and the relative expression of GABAA receptor α1 and α4 subunit peptide were analyzed via Western blot analysis. Results: Chronic ethanol consumption altered recovery of spontaneous neural activity of MS/DB neurons following GABA-microiontophoresis compared to premicroiontophoresis levels. Specifically, the recovery of spontaneous neural activity of MS/DB neurons recorded from animals that chronically consumed ethanol was slower following GABA-microiontophoresis compared to neurons recorded from control animals. This effect was temporary and reversible. Furthermore, the alteration in recovery of spontaneous neural activity was not due to changes in the total amount of inhibition produced by GABA. Finally, there was no significant change in GABAA receptor α1 and α4 subunit peptide levels in the MS/DB. Conclusions: Chronic ethanol consumption alters the frequency of spontaneous MS/DB neural activity following GABA microiontophoresis compared to premicroiontophoresis levels. These data suggest that the kinetics of GABAA receptors in the MS/DB are altered by chronic ethanol consumption independent of changes in the total amount of inhibition or alterations in GABAA receptor α1 and α4 subunit peptide expression.