Chronic ethanol exposure decreases CB₁receptor function at GABAergic synapses in the rat central amygdala

Abstract

The endogenous cannabinoids (eCBs) influence the acute response to ethanol and the development of tolerance, dependence and relapse. Chronic alcohol exposure alters eCB levels and type 1 cannabinoid receptor (CB 1 ) expression and function in brain regions associated with addiction. CB 1 inhibits GABA release, and GABAergic dysregulation in the central nucleus of the amygdala (CeA) is critical in the transition to alcohol dependence. We investigated possible disruptions in CB 1 signaling of rat CeA GABAergic transmission following intermittent ethanol exposure. In the CeA of alcohol-naïve rats, CB 1 agonist WIN 55,212-2 (WIN) decreased the frequency of spontaneous and miniature GABA A receptor-mediated inhibitory postsynaptic currents (s/ mIPSCs). This effect was prevented by CB 1 antagonism, but not type 2 cannabinoid receptor (CB 2 ) antagonism. After 2-3 weeks of intermittent ethanol exposure, these WIN inhibitory effects were attenuated, suggesting ethanol-induced impairments in CB 1 function.The CB 1 antagonist AM251 revealed a tonic eCB/CB 1 control of GABAergic transmission in the alcohol-naïve CeA that was occluded by calcium chelation in the postsynaptic cell. Chronic ethanol exposure abolished this tonic CB 1 influence on mIPSC, but not sIPSC, frequency. Finally, acute ethanol increased CeA GABA release in both naïve and ethanol exposed rats. Although CB 1 activation prevented this effect, the AM251-and ethanol-induced GABA release were additive, ruling out a direct participation of CB 1 signaling in the ethanol effect. Collectively, these observations demonstrate an important CB 1 influence on CeA GABAergic transmission and indicate that the CeA is particularly sensitive to alcohol-induced disruptions of CB 1 signaling.

Involvement of Activated Brain Stress Responsive Systems in Excessive and “Relapse” Alcohol Drinking in Rodent Models: Implications for Therapeutics

“…After chronic alcohol exposure and protracted withdrawal, however, there may be an eCB/CB1 signaling deficiency, which could also increase alcohol intake via the negative reinforcement mechanism. This notion is supported by several findings: [1] there is down-regulation of CB1 expression and function observed during protracted alcohol withdrawal in rats [Mitrirattanakul et al, 2007;Varodayan et al, 2016]; [2] in human imaging studies, decreased CB1 availability is observed in heavy-drinking alcoholics that persists into abstinence [Hirvonen et al, 2013;Ceccarini et al, 2014]; and [3] a lowered plasma AEA level is found in alcohol dependent patients during recent abstinence [Mangieri et al, 2009]. …”

Acute and chronic ethanol exposure differentially regulate CB1 receptor function at glutamatergic synapses in the rat basolateral amygdala

“…Thus, relatively small reductions in CB1 expression at glutamatergic terminals might have a much more dramatic impact on receptor function relative to GABAergic terminals which express relatively high levels of the receptor. A more prolonged CIE exposure may be potentially required before reductions in GABAergic CB1 expression sufficient to impair CB1 function of this terminal population occur [60]. …”

P/Q-type voltage-gated calcium channels mediate the ethanol and CRF sensitivity of central amygdala GABAergic synapses

“…Rats were anesthetized (3–5% isoflurane) and decapitated, and the brains placed in oxygenated (95% O 2 /5% CO 2 ), cold high-sucrose solution (pH 7.3–7.4; in mM): 206.0 sucrose; 2.5 KCl; 0.5 CaCl 2 ; 7.0 MgCl 2 ; 1.2 NaH 2 PO 4 ; 26.0 NaHCO 3 ; 5.0 glucose; 5.0 HEPES, as previously described (Herman et al, 2013; Herman and Roberto, 2016; Roberto et al, 2010b; Varodayan et al, 2016). The brains were coronally sliced (300 μm) and the tissue incubated (30 min at 37 °C, then 30 min at room temperature) in oxygenated artificial cerebrospinal fluid (aCSF; in mM): 130.0 NaCl; 3.5 KCl; 2 CaCl 2 ; 1.25 NaH 2 PO 4 ; 1.5 MgSO 4 ; 24 NaHCO 3 ; 10 glucose.…”