Oxytocin blocks enhanced motivation for alcohol in alcohol dependence and blocks alcohol effects on GABAergic transmission in the central amygdala

Abstract

Oxytocin administration has been reported to decrease consumption, withdrawal, and drug-seeking associated with several drugs of abuse and thus represents a promising pharmacological approach to treat drug addiction. We used an established rat model of alcohol dependence to investigate oxytocin's effects on dependence-induced alcohol drinking, enhanced motivation for alcohol, and altered GABAergic transmission in the central nucleus of the amygdala (CeA). Intraperitoneal oxytocin administration blocked escalated alcohol drinking and the enhanced motivation for alcohol in alcohol-dependent but not nondependent rats. Intranasal oxytocin delivery fully replicated these effects. Intraperitoneal administration had minor but significant effects of reducing locomotion and intake of non-alcoholic palatable solutions, whereas intranasal oxytocin administration did not. In dependent rats, intracerebroventricular administration of oxytocin or the oxytocin receptor agonist PF-06655075, which does not cross the blood-brain barrier (i.e., it would not diffuse to the periphery), but not systemic administration of PF-06655075 (i.e., it would not reach the brain), decreased alcohol drinking. Administration of a peripherally restricted oxytocin receptor antagonist did not reverse the effect of intranasal oxytocin on alcohol drinking. Ex vivo electrophysiological recordings from CeA neurons indicated that oxytocin decreases evoked GABA transmission in nondependent but not in dependent rats, whereas oxytocin decreased the amplitude of spontaneous GABAergic responses in both groups. Oxytocin blocked the facilitatory effects of acute alcohol on GABA release in the CeA of dependent but not nondependent rats. Together, these results provide converging evidence that oxytocin specifically and selectively blocks the enhanced motivation for alcohol drinking that develops in alcohol dependence likely via a central mechanism that may result from altered oxytocin effects on CeA GABA transmission in alcohol dependence. Neuroadaptations in endogenous oxytocin signaling may provide a mechanism to further our understanding of alcohol use disorder.

Fig 1. Effect of intraperitoneal and intranasal oxytocin on alcohol intake (FR1) and motivation (PR).

(A) Effect of intraperitoneal oxytocin on alcohol reinforcers earned by dependent and nondependent rats in 30-min alcohol self-administration sessions. (B) Effect of intraperitoneal oxytocin on breakpoint for alcohol on a PR schedule of reinforcement. (C) Effect of intranasal oxytocin on alcohol reinforcers earned by dependent and nondependent rats in 30-min alcohol self-administration sessions. (D) Effect of intranasal oxytocin on breakpoint for alcohol on a PR schedule of reinforcement. ^#Significant difference between dependent and nondependent rats (p < 0.05). *Significantly different from groups’ respective control condition (0 mg/kg; p < 0.05). EtOH, ethanol; FR1, fixed ratio 1; IN, intranasal; IP, intraperitoneal; PR, progressive ratio.

Fig 2. Effects of intraperitoneal and intranasal oxytocin administration on locomotion, grooming, motor coordination and consumption of nonalcoholic palatable solutions.

Effect of intraperitoneal (0.25 mg/kg) and intranasal (1 mg/kg) oxytocin on (A) spontaneous locomotion measured in a 5-min test in an open field. The inset panel shows grooming behavior during the test collapsed across dependent and nondependent rats; (B) motor coordination measured in latency to fall in an accelerating rotarod test; (C) consumption of palatable nonalcoholic solutions assessed in rats trained on an FR1 schedule to respond for access to sweet/noncaloric 0.1% saccharin or caloric/nonsweet 5% maltodextrin. *Significantly different from saline (p < 0.05). Dep, dependent; FR1, fixed-ratio 1; IN, intranasal; IP, intraperitoneal; NonDep, nondependent.

Fig 3. Central versus peripheral mediation of OXT’s effect on alcohol intake.

(A) Effect of intracerebroventricular infusion of OXT on alcohol reinforcers earned by dependent rats in 30-min alcohol self-administration sessions. (B) Effect of peripheral administration (intraperitoneal) of the OXT receptor antagonist L-371,257 that does not cross the blood-brain barrier on the ability of intranasal OXT to reduce alcohol reinforcers earned by dependent rats in 30-min alcohol self-administration sessions. (C) Effect of central (intracerebroventricular) administration of the OXT receptor agonist (PF-06655075, a long-acting, large molecule that does not cross the blood-brain barrier), on reinforcers earned by dependent rats in 30-min alcohol self-administration sessions. (D) Effect of systemic (subcutaneous) administration of PF-06655075 on reinforcers earned by dependent rats in 30-min alcohol self-administration sessions. *Significantly different from baseline or VEH condition (both in the case of panel C) (p < 0.05). OXT, oxytocin; VEH, vehicle.

Fig 4. Oxytocin decreases locally evoked CeA GABAergic signaling and blunts alcohol effects.

(A) Representative eIPSPs recorded from CeA neurons of nondependent (upper) and dependent (lower) rats before (baseline) and during acute application of oxytocin (500 nM), oxytocin with alcohol (44 mM), and alcohol alone. (B) Effect of 3 concentrations of oxytocin (100, 500, and 1,000 nM) on eIPSP amplitudes in CeA neurons from alcohol-nondependent and -dependent rats. Higher concentrations of oxytocin (500 and 1,000 nM) decreased eIPSP amplitudes in nondependent but not in dependent rats. (C) Oxytocin blunted the alcohol-induced enhancement of eIPSP in neurons from both alcohol-nondependent and alcohol-dependent rats. *Significant effect of drug compared to baseline (p < 0.05). ^#Significant difference between groups (p < 0.05). CeA, central nucleus of the amygdala; eIPSP, evoked inhibitory postsynaptic potential; EtOH, ethanol; OT, oxytocin.

Fig 5. Oxytocin decreases postsynaptic CeA spontaneous GABAergic transmission and blocks presynaptic alcohol effects.

(A, Top) Representative GABA_A-mediated sIPSCs of CeA neurons from nondependent and dependent rats prior to (baseline) and during application of oxytocin (500 nM). (A, Bottom) Oxytocin decreased sIPSC amplitude from baseline in CeA neurons from both nondependent and dependent rats and caused a small increase from baseline in sIPSC rise time in nondependent rats. However, there were no significant differences between neurons from nondependent and dependent rats across these measures. (B, Top) Representative GABA_A-mediated mIPSCs of CeA neurons from nondependent and dependent rats with TTX and during application of oxytocin (500 nM). (B, Bottom) Oxytocin had no effect on mIPSC frequency, amplitude, or kinetics in CeA neurons from both nondependent and dependent rats. (C) Representative sIPSCs of CeA neurons from nondependent (Left) and dependent (Right) rats before and during application of alcohol (44 mM), oxytocin (500 nM), and oxytocin with alcohol. (D) In the neurons that received oxytocin and oxytocin with alcohol, oxytocin had no significant effect on sIPSC frequency from baseline in either nondependent or dependent rats. However, alcohol with oxytocin significantly increased sIPSC frequency from oxytocin alone only in nondependent rats. (E) In these same neurons, oxytocin decreased amplitude of sIPSCs from baseline in dependent rats but with no significant effects of drug or alcohol history. (F) Oxytocin and coapplication of oxytocin with alcohol increased rise time from baseline in neurons from nondependent rats only, with no significant effects of drug or alcohol history. (G) Alcohol with oxytocin increased sIPSC decay times from oxytocin alone only in nondependent rats. (H) Alcohol alone increased frequency of sIPSCs from baseline in both nondependent and dependent rats but with no significant effects of drug or alcohol history when compared to alcohol with oxytocin. Alcohol had no effect on amplitude (I), rise times (J), or decay times (K) in nondependent or dependent rats, but the alcohol with oxytocin increase in rise times in nondependent rats was significantly different from the effect of alcohol alone (J). (L) Representative sIPSCs of CeA neurons from dependent rats with the oxytocin receptor antagonist OTA (100 nM), during oxytocin (500 nM), and during subsequent coapplication of oxytocin with 44 mM alcohol. (M) OTA blocked oxytocin’s effects on sIPSC amplitude and subsequent alcohol application increased sIPSC frequency. *Significantly different from baseline or control condition (p < 0.05). ^#Significant difference between groups (p < 0.05). Amp, amplitude; CeA, central nucleus of the amygdala; EtOH, ethanol; Freq, frequency; mIPSC, miniature inhibitory postsynaptic current; OT, oxytocin; OTA, desGly-NH2-d(CH2)5[D-Tyr2,Thr4]OVT; sIPSC, spontaneous inhibitory postsynaptic current; TTX, tetrodotoxin.