Primate cerebellar granule cells exhibit a tonic GABAAR conductance that is not affected by alcohol: a possible cellular substrate of the low level of response phenotype

Abstract

In many rodent brain regions, alcohol increases vesicular release of GABA, resulting in an increase in the frequency of spontaneous inhibitory postsynaptic currents (sIPSCs) and the magnitude of tonic GABAA receptor (GABAAR) currents. A neglected issue in translating the rodent literature to humans is the possibility that phylogenetic differences alter the actions of alcohol. To address this issue we made voltage-clamp recordings from granule cells (GCs) in cerebellar slices from the non-human primate (NHP), Macaca fascicularis. We found that similar to Sprague Dawley rats (SDRs), NHP GCs exhibit a tonic conductance generated by α6δ subunit containing GABAARs, as evidenced by its blockade by the broad spectrum GABAAR antagonist, GABAzine (10 μM), inhibition by α6 selective antagonist, furosemide (100 μM), and enhancement by THDOC (10–20 nM) and THIP (500 nM). In contrast to SDR GCs, in most NHP GCs (~60%), application of EtOH (25–105 mM) did not increase sIPSC frequency or the tonic GABAAR current. In a minority of cells (~40%), EtOH did increase sIPSC frequency and the tonic current. The relative lack of response to EtOH was associated with reduced expression of neuronal nitric oxide synthase (nNOS), which we recently reported mediates EtOH-induced enhancement of vesicular GABA release in rats. The EtOH-induced increase in tonic GABAAR current was significantly smaller in NHPs than in SDRs, presumably due to less GABA release, because there were no obvious differences in the density of GABAARs or GABA transporters between SDR and NHP GCs. Thus, EtOH does not directly modulate α6δ subunit GABAARs in NHPs. Instead, EtOH enhanced GABAergic transmission is mediated by enhanced GABA release. Further, SDR GC responses to alcohol are only representative of a subpopulation of NHP GCs. This suggests that the impact of EtOH on NHP cerebellar physiology will be reduced compared to SDRs, and will likely have different computational and behavioral consequences.

Prenatal cerebral ischemia triggers dysmaturation of caudate projection neurons

“…Methods for preparation of brain slices and subsequent patch‐clamp recording were similar to our previous reports in rodents and modifications for brain tissue from larger mammals . Upon removal of the brain, the frontal pole (anterior to section 0600 in the online Michigan State University sheep brain atlas: https://www.msu.edu/~brains/brains/sheep/index.html) of one hemisphere of the forebrain was rapidly isolated and immersed in an ice‐cold slurry (0–2°C) of low‐sodium artificial cerebrospinal fluid (aCSF) composed of (in millimolars) 220 sucrose, 3.2 KCl, 1.2 NaH 2 PO 4 , 6.0 MgSO 4 , 10 D‐glucose, 26 NaHCO 3 , and 0.2 CaCl 2 that was bubbled for 30 minutes with 95%O 2 /5% CO 2 .…”

Changes in nonhuman primate brain function following chronic alcohol consumption in previously naïve animals

“…that are a source of uncontrolled variance in clinical populations. Studies of one such model (Grant et al, 2008; Vivian et al, 2001) have demonstrated functional and genomic consequences throughout the brain following 15 months of chronic daily drinking (Acosta et al, 2010; Ariwodola et al, 2003; Budygin et al, 2003; Carden et al, 2006; Cuzon Carlson et al, 2011; Floyd et al, 2004; Grant et al, 2008; Hemby et al, 2006; Mohr et al, 2013; Welsh et al, 2011). Recently, graph theoretical analyses of fMRI data from this model found that chronic heavy drinking altered RS brain network organization (Telesford et al, 2015).…”

Alcohol Suppresses Tonic GABAA Receptor Currents in Cerebellar Granule Cells in the Prairie Vole: A Neural Signature of High‐Alcohol‐Consuming Genotypes

“…Cerebellar granule cells (GCs) are key targets through which EtOH differentially affects cerebellar processing in high‐ and low‐EtOH‐consuming phenotypes (Kaplan et al., ; Mohr et al., ). GCs are the main relay of afferent information through the cerebellar cortex to Purkinje cells (PCs), the primary integrator and sole output of the cerebellar cortex.…”

“…Specifically, while it is well established that EtOH increases the frequency of GC sIPSCs and the magnitude of the GC tonic GABA A R current in low‐EtOH‐consuming Sprague Dawley (SD) rats and DBA/2J (D2) mice (Carta et al., ; Hanchar et al., ; Kaplan et al., ), we recently determined that in high‐EtOH‐consuming C57BL/6J (B6) mice, EtOH has little impact on GC sIPSCs, and actually suppresses GC tonic GABA A R currents (Kaplan et al., ). EtOH has intermediate impact on GC sIPSCs and tonic GABA A R currents in rodents and non human primates that exhibit intermediate EtOH consumption phenotypes (Kaplan et al., ; Mohr et al., ). Importantly, with respect to cerebellar contributions to the LLR and EtOH consumption, B6 mice are significantly less sensitive to EtOH‐induced disruption of rotarod performance when compared to D2 mice (Gallaher et al., ).…”

“…In an effort to understand the molecular underpinnings of genetic variation in GC GABA A R current sensitivity to EtOH, we determined that the net effect of EtOH on the magnitude and polarity of the tonic GABA A R current is dictated by 2 genetically regulated mechanisms: (i) the degree of neuronal nitric oxide synthase (nNOS) expression in the GC layer determines the magnitude by which EtOH enhances presynaptic vesicular GABA release to increase tonic GABA A R currents in GCs, whereas (ii) low GC protein kinase C (PKC) activity enables EtOH to postsynaptically inhibit the extrasynaptic α 6 δ‐containing GABA A Rs that mediate the tonic GABA A R current (Kaplan et al., ; Mohr et al., ). Thus, low‐EtOH‐consuming SD rats have high levels of expression of nNOS and high GC PKC activity, whereas the high‐EtOH‐consuming, behaviorally insensitive B6 mice have low nNOS expression and low GC PKC activity that, together, promote EtOH‐induced suppression of tonic GABA A R inhibition of GCs.…”