Light-dark variation in response to chronic nicotine treatment and the density of hypothalamic α-bungarotoxin receptors

Abstract

Chronic nicotine administration increased locomotor activity during the light, but not the dark, in rats maintained on a 12:12-hr light/dark cycle, but the period and peak of the circadian rhythm (CR) were not affected. In Experiment I, 24 male rats were implanted with battery-operated telemeters and locomotor activity was continuously measured for 10 days before and 10 days after the implantation of osmotic mini-pumps which delivered 0, 0.5, 3.0 or 10 mg/kg/day of (±)-nicotine tartrate. Nicotine increased locomotor activity during the light in a dose-dependent manner. Tolerance to the stimulant effects of nicotine during the light occurred in 5–6 days. To determine if the stimulant properties of nicotine were associated with light as opposed to disruption by the environmental stimuli normally present during the day in our animal facility, a second experiment was conducted in which rats were treated with saline or 10 mg/kg/day (±)-nicotine di(+)hydrate tartrate and maintained on a reversed light/dark cycle. Again nicotine increased activity during the light (21:00–09:00) but not dark (09:00–21:00). In a third experiment, the density of α-bungarotoxin binding sites was found to be significantly decreased when animals were sacrificed at 06:00 in comparison with animals sacrificed at 10:00 and 14:00