Neurotensin Levels in Specific Brain Regions and Hypnotic Sensitivity to Ethanol and Pentobarbital as a Function of Time after Haloperidol Administration in Selectively Bred Rat Lines

Evidence indicates that sensitivity to ethanol is a good predictor of the development of alcoholism. Thus, identification of neuronal processes that regulate ethanol sensitivity has been the subject of much recent research. The present studies were designed to further test the hypothesis that neurotensinergic processes mediate, in part, hypnotic sensitivity to ethanol. Single doses of haloperidol were administered to lines of rats [selectively bred for high and low sensitivity (HAS and LAS, respectively) to hypnotic effects of ethanol] to produce increases in neurotensin (NT) levels in brain regions. At 20 h after administration, haloperidol produced dose-dependent increases in NT immunoreactivity levels in nucleus accumbens (NA) and caudate putamen (CP) in both HAS and LAS lines. Levels of NT in NA and CP returned to control values at 48 h after 4 mg/kg haloperidol. These studies used two measures of hypnotic sensitivity to ethanol: duration of loss of righting reflex (sleep time) and blood ethanol concentration at regain of righting reflex (BECRR). At 20 h, but not 48 h, after haloperidol treatment, both HAS and LAS rats displayed increases in ethanol-induced sleep time with concomitant decreases in BECRR. Pentobarbital-induced sleep time was not increased 20 h after administration of 4 mg/kg haloperidol; however, hypnotic sensitivity to both pentobarbital and ethanol was increased by acute (30-min) pretreatment with 1 mg/kg. These results suggest that NT levels in NA, acting via NT receptors, enhance hypnotic sensitivity to ethanol, but not pentobarbital.