Effect of nucleus accumbens shell infusions of ganaxolone or gaboxadol on ethanol consumption in mice

Abstract

Rationale: Allopregnanolone (ALLO) is an endogenous neuroactive steroid thought to alter the reinforcement value of alcohol (ethanol) due to its actions as a positive modulator of the GABAA receptor (GABAAR). Extrasynaptic GABAARs may be a particularly sensitive target of ethanol and neuroactive steroids. Previous work showed that systemic injections of an ALLO analog, ganaxolone (GAN), or an extrasynaptic GABAAR agonist (gaboxadol; THIP) decreased ethanol intake in male mice with limited access to ethanol.

Objectives: The present studies tested whether activation of GABAARs in the nucleus accumbens (NAc) shell by GAN or THIP was sufficient to reduce ethanol intake. C57BL/6J male mice had 2-h access to 10 % ethanol (10E) and water, and 10E intake was measured following site-specific infusions of GAN or THIP.

Results: Decreases in limited-access 10E consumption were observed following site-specific bilateral infusions of either drug into the NAc shell. Significant changes in intake were absent when the drugs were infused in a region dorsal to the target site (GAN) or into the lateral ventricle (THIP). Locomotor data confirmed that the decreases in intake were not due to a sedative effect of the drugs.

Conclusions: These data demonstrate the sufficiency of GABAAR activation by a positive allosteric modulator or an agonist with selectivity for extrasynaptic GABAARs to decrease ethanol consumption in mice. Importantly, more refined GABAAR-active targets that decrease ethanol intake may enhance our understanding and ability to treat alcohol use disorders.

Figure 1

Effect of bilateral intra-nucleus accumbens (NAc) shell infusions of ganaxolone (GAN) on 10% ethanol (10E) intake. A) Squares depict injector tip locations for mice (n = 15) used in the drinking studies for GAN infused into the NAc shell. B) A sample photomicrograph of a mouse that received a bilateral NAc shell infusion of GAN. C) Effect of NAc shell GAN on total 2-hour 10E intake, D) average bout frequency, and E) 10E licks split into 20-minute bins. F) Horizontal locomotor activity (cm) following a NAc shell infusion of 0 or 500 ng GAN across 20-minute bins, subtracting out cm moved on a baseline day. The inset depicts total 2-hour activity. Values represent mean ± SEM. + p ≤ 0.10, * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001 relative to 0 ng.

Figure 2

Effect of dorsal control infusions of ganaxolone (GAN) on 10% ethanol (10E) intake. A) Squares depict injector tip locations for mice (n = 9) used in the drinking studies for dorsal controls infused with GAN. B) A sample photomicrograph of a mouse that received a bilateral infusion of GAN dorsal to the NAc shell. C) Effect of GAN into regions dorsal to the nucleus accumbens shell (NAc) on total 2-hour 10E intake and D) average bout frequency.

Figure 3

Effect of intra-NAc GAN, with one injector placed in the NAc shell and one in the NAc core on 10% ethanol (10E) intake. A) Squares depict injector tip locations for mice (n = 9) that received GAN prior to the drinking studies, where one injector terminated in the NAc shell and one in the NAc core. B) A sample photomicrograph of a mouse that received a bilateral infusion of GAN with one injector located in the core and one injector located in the shell. C) Effect of GAN into the NAc core + shell on total 2-hour 10E intake, D) average bout frequency, E) latency to first bout, and F) latency to first lick. Values represent mean ± SEM. + p ≤ 0.10, * p ≤ 0.05 relative to 0 ng.

Figure 4

Effect of intra-NAc shell infusions of THIP on 10% ethanol (10E) intake. A) Squares depict injector tip locations for mice (n = 9) used in the drinking studies for nucleus accumbens (NAc) shell infusions with THIP. B) A sample photomicrograph of a mouse that received a bilateral NAc shell infusion of THIP. C) Effect of NAc shell THIP on total 2-hour 10E intake, D) average bout frequency, and E) 10E licks split into 20-minute bins. F) Horizontal locomotor activity (cm) following a NAc shell infusion of 0 or 500 ng THIP, subtracting out cm moved on a baseline day. The inset depicts total 2-hour activity. Values represent mean ± SEM for each dose. + p ≤ 0.10, * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001 relative to 0 ng.