Type 7 Adenylyl Cyclase is Involved in the Ethanol and CRF Sensitivity of GABAergic Synapses in Mouse Central Amygdala

Abstract

The GABAergic system in the central amygdala (CeA) plays a major role in ethanol dependence and in the anxiogenic response to ethanol withdrawal. Previously, we found that both ethanol and corticotropin releasing factor (CRF) increase GABAergic transmission in mouse and rat CeA neurons, in part by enhancing the release of GABA via activation of presynaptic CRF1 receptors. CRF1 receptors are coupled to the enzyme adenylyl cyclase (AC), which produces the second messenger cyclic AMP. There are nine isoforms of AC, but we recently found that CRF1 receptors in the pituitary were coupled to the Type 7 AC (AC7). Therefore, using an in vitro electrophysiological approach in brain slices, here we have investigated a possible role of the AC7 signaling pathway in ethanol and CRF effects on CeA GABAergic synapses of genetically modified mice with diminished brain Adcy7 activity (HET) compared to their littermate male wild-type (WT) mice. We found no significant differences in basal membrane properties, mean baseline amplitude of evoked GABAA receptor-mediated inhibitory postsynaptic potentials (IPSPs), or paired-pulse facilitation (PPF) of GABAA-IPSPs between HET and WT mice. In CeA neurons of WT mice, ethanol superfusion significantly augmented (by 39%) GABAA-IPSPs and decreased PPF (by 25%), suggesting increased presynaptic GABA release. However, these effects were absent in HET mice. CRF superfusion also significantly augmented IPSPs (by 38%) and decreased PPF (by 23%) in WT CeA neurons, and still elicited a significant but smaller (by 13%) increase of IPSP amplitude, but no effect on PPF, in HET mice. These electrophysiological data suggest that AC7 plays an important role in ethanol and CRF modulation of presynaptic GABA release in CeA and thus may underlie ethanol-related behaviors such as anxiety and dependence.

Innate immune factors modulate ethanol interaction with GABAergic transmission in mouse central amygdala

“…However, because we have previously shown that application of 44 mM ethanol always augments PPF in outbred rodents (Bajo et al, 2008; Cruz et al, 2011; Roberto et al, 2003; Roberto et al, 2004a; Roberto et al, 2004b), we tested whether the lack of ethanol effect on PPF in CD 14 KO CeA might result from the inclusion of higher doses, which do not generate PPF. When the effects of 44 mM ethanol were analyzed separately by two-way repeated measures ANOVA, we found a significant ethanol application × mouse strain interaction (F(1,17) = 5.6; p < 0.05) with no main effects of mouse strain or ethanol application.…”

“…Overall, these findings indicate that both TLR4 and the GABAergic system, and their cellular interactions in the CeA, may play an important role in ethanol drinking. However, little is known about the cellular aspects of TLR4 activation on neurophysiology and GABAergic transmission or on ethanol-induced potentiation of GABAergic transmission in the CeA (Bajo et al, 2008; Cruz et al, 2011; Roberto et al, 2012; Roberto et al, 2003; Roberto et al, 2004b). Therefore, in the present study we explored these issues using electrophysiological methods in CeA slices from CD14 KO mice, with exogenous administration of LPS and the TLR4 antagonist (+)-naloxone to activate and inhibit TLR4, respectively.…”

Ghrelin Increases GABAergic Transmission and Interacts with Ethanol Actions in the Rat Central Nucleus of the Amygdala

“…Our previous studies showed that the adenylate cyclase pathway is one of the second messenger pathways engaged by ethanol and CRF receptor activation (Cruz et al, 2011;Cruz et al, 2012). We speculate that the adenylate cyclase pathway may represent a common signaling pathway targeted in the same directions by ghrelin and ethanol in regulating GABAergic transmission, thus playing an essential role in their interactions.…”

The Central Amygdala and Alcohol: Role of -Aminobutyric Acid, Glutamate, and Neuropeptides

“…Although the molecular mechanism(s) for alcohol effects have yet to be identified, we showed that activation of adenylyl cylase (AC) and/or protein kinase C (PKC) mediate GABAergic transmission in CeA synapses (Bajo et al 2008;Cruz et al 2011). In CeA slices of mice lacking PKC1 or pretreated with a PKC1 antagonist, the ability of acute alcohol to augment IPSCs is impaired (Bajo et al 2008), suggesting that PKC1 facilitates alcohol-elicited vesicular GABA release.…”