Inhibition of amphetamine-induced locomotor activity by injection of carbachol into the anterior hypothalamic/preoptic area: pharmacological and electrophysiological studies in the rat.
The effects of carbachol injected into the anterior hypothalamic/preoptic area on locomotion initiated by intra-accumbens injections of amphetamine were investigated. Changes of locomotion following intracerebral injections were measured in an automated activity box and the mean firing rate (m.f.r.) from neurons in the mesencephalic locomotor region (MLR) recorded in parallel acute electrophysiological experiments. Amphetamine (20.0 micrograms) injected to the nucleus accumbens caused a 2.5-fold increase in locomotion of rats. Subsequently, injections of carbachol (0.5 or 1.0 microgram) into the hypothalamic/preoptic area reduced the amphetamine-induced locomotion. These effects were stronger with ipsilateral than with contralateral injections and were reversed by pretreating the hypothalamic/preoptic area with 1.5 micrograms of atropine before carbachol injection. In electrophysiological experiments, injecting carbachol into the hypothalamic/preoptic area reduced the m.f.r. of MLR neurons from 8.3 +/- 0.7 to 4.1 +/- 0.5 per s and reduced the m.f.r. of 13 of 17 MLR neurons recorded continuously before and after injection. In contrast, injecting amphetamine into the nucleus accumbens increased the m.f.r. of units from 8.3 +/- 0.7 to 12.8 +/- 1.0 per s and increased the m.f.r. of 11 of 12 MLR neurons recorded continuously before and after injection. These results suggest that the hypothalamic/preoptic area contains muscarinic cholinoceptive areas which reduce locomotor activity by direct or indirect effects on the MLR.
D000661:Amphetamine / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D004347:Drug Interactions; D004594:Electrophysiology; D007032:Hypothalamus, Anterior / Q000502:physiology*; D007267:Injections; D008297:Male; D008636:Mesencephalon / Q000166:cytology / Q000502:physiology; D009043:Motor Activity / Q000187:drug effects*; D009474:Neurons / Q000502:physiology; D011301:Preoptic Area / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D002217:Carbachol; D000661:Amphetamine