Activation of brain NOP receptors attenuates acute and protracted alcohol withdrawal symptoms in the rat

Abstract

Background: Alcohol withdrawal refers to a cluster of symptoms that may occur from suddenly ceasing the use of alcohol after chronic or prolonged ingestion. These symptoms make alcohol abstinence difficult and increase the risk of relapse in recovering alcoholics. In previous studies, we demonstrated that treatment with Nociceptin/orphanin FQ (N/OFQ) significantly reduces alcohol consumption and attenuates alcohol-seeking behavior induced by environmental conditioning factors or by stress in rats. In this study, we evaluated whether activation of brain NOP receptors may also attenuate alcohol withdrawal signs in rats.

Methods: For this purpose, animals were subjected to a 6-day chronic alcohol intoxication (by intragastric administration), and at 8, 10, and 12 hours following cessation of alcohol exposure, they were treated intracerebroventricularly (ICV) with N/OFQ (0.0, 1.0, and 3.0 μg/rat). Somatic withdrawal signs were scored after ICV treatment. In a subsequent experiment, to evaluate N/OFQ effects on alcohol withdrawal-induced anxiety, another group of rats was subjected to ethanol intoxication and after 1 week was tested for anxiety behavior in the elevated plus maze (EPM). In the last experiment, an additional group of rats was tested for anxiety elicited by acute ethanol intoxication (hangover anxiety). For this purpose, animals received an acute dose (3.0 g/kg) of 20% alcohol and 12 hour later were tested in the EPM following ICV N/OFQ (0.0, 1.0, and 2.0 μg/rat).

Results: Results showed that N/OFQ significantly reduced the expression of somatic withdrawal signs and reversed anxiety-like behaviors associated with both chronic and acute alcohol intoxication. N/OFQ did not affect anxiety scores in nondependent animals.

Conclusions: These findings suggest that the N/OFQ-NOP receptor system may represent a promising target for the development of new treatments to ameliorate alcohol withdrawal symptoms.

Fig. 1

Effect of N/OFQ administration (0.0, 1.0 and 3.0 μg; ICV) on total withdrawal scores. Total withdrawal scores were obtained for each animal by accumulating the score of the four different withdrawal signs (Vocalization, Ventromedial limb retraction, Tail Rigidity, Tremors) for the 3 different time-points monitored (8 h, 10 h and 12 h). N/OFQ was ICV injected 10 min before each observation time-point. Total withdrawal score ranged between 0 and 8. Values represent the (±SEM) of 8 subjects per group. Statistical differences between N/OFQ Vehicle (0.0) and Control (Ctr): ##p<0.01. Statistical differences between Vehicle (0.0) and N/OFQ treated groups (1.0 or 3.0): **p<0.01, *p<0.05.

Fig. 2

Effect of N/OFQ (1.0 and 3.0 μg; ICV) or its vehicle (0.0), on ethanol withdrawal score of: A) Vocalization, B) Tail Rigidity, C) Tail Tremors and D) Ventromedial Limb Retraction (VmLR) measured at 8, 10 and 12 hours following the last ethanol dose. N/OFQ was administered 10 min before each observation time point. Each withdrawal sign was assigned a score of 0–2. Values represent the mean (±SEM) of 8 subjects per group. Statistical differences between N/OFQ Vehicle (0.0) and Control (Ctr): ##p<0.01; #p<0.05. Statistical differences between Vehicle (0.0) and N/OFQ treated groups (1.0 or 3.0): **p<0.01, *p<0.05.

Fig. 3

Effect of ICV treatment with N/OFQ (1.0 and 2.0 μg) or its vehicle (0.0) on postdependent rats and nondependent controls tested in the EPM test one week following withdrawal from ethanol intoxication. A) Percentage of time spent in open arms; B) Percentage of open arm entries; C) Percentage of closed arm entries. Control group (non intoxicated rats) received N/OFQ and alcohol vehicles. Significant differences from vehicle (0.0): ***p<0.001, **p<0.01, *p<0.05.

Fig. 4

Effect of ICV treatment with N/OFQ (1.0 and 2.0 μg) or its vehicle (0.0) on animals treated with a single dose of 3.0 g/kg of 20% alcohol given IP 12 hrs prior to the EPM test. A) Percentage of time spent in the open arms; B) Percentage of open arm entries; C) Percentage of closed arm entries.. Control group (nonintoxicated rats; Ctr) received N/OFQ vehicle. Significant differences from vehicle (0.0): **p<0.01, *p<0.05.