AF64 depletes hypothalamic high-affinity choline uptake and disrupts the circadian rhythm of locomotor activity without altering the density of nicotinic acetylcholine receptors

Abstract

Ethylcholine aziridinium ion (AF64) was synthesized from acetylethycholine mustard hydrochloride and 5 nmol was infused into the third ventricle of rats. Seven days after AF64 treatment, sodium dependent high-affinity choline (HACU) uptake was decreased by 54% in the hypothalamus. The density of hypothalamic (−)-[ 3H]nicotine binding sites and [α- 125I]bungarotoxin sites in AF64-treated animals did not differ significantly from controls. A second experiment was performed to elucidate the effect of AF64 treatment on HACU and determine the effect of AF64 on entrained circadian rhythms. Animals were infused with artificial CSF or 5 nmol AF64. Locomotor activity and body temperature were recorded for 3 weeks before and 3 weeks after treatment. Ten of 14 AF64-treated animals showed a decrease in the ratio of dark cycle:light cycle locomotor activity. The decrease in dark-cycle activity was correlated with a disruption of a predominant circadian rhytm. The circadian rhythm (CR) of core body temperature was disrupted only transiently, but the CR of locomotor activity remained disrupted for the duration of the experiment in several AF64-treated animals. HACU was decreased by 48% in animals with disrupted rhythms in comparison with controls but was not significantly decreased in AF64-treated animals with normal dark-cycle activity and circadian activity. These data suggest that the AF64-treated animal may be a good model for studying the role of acetylcholine in maintaining the integrity of certain circadian rhythms.