Decrease of locomotor activity by injections of carbachol into the anterior hypothalamic/preoptic area of the rat.

Cholinergic elements in forebrain structures are implicated in locomotion but their role is still unclear. In the present study, the effects of intracerebrally injected carbachol or atropine on spontaneous locomotion and rearing activity were investigated. Effective injection sites were found in the area between frontal planes 5.3 and 6.3 mm from interaural plane and between the ventricle wall and lateral plane 1.1 mm from the midline which corresponds to the medial anterior hypothalamic/preoptic area. Injections of 1.0 micrograms of carbachol into this area decreased locomotor activity and rearing to one-third of the control level during the first 5 min of recording. These reductions of locomotion and rearing were dose-dependent and reversed by 1.5 microgram of atropine. Atropine alone, at this dose, had no effect on locomotion but higher doses (20.0-60.0 micrograms) of atropine produced a dose-dependent increase of locomotion. A comparison of the injection sites with recent maps of the cholinergic system indicates that muscarinic cholinoceptive, presumably non-cholinergic, cells throughout the medial AH/POA might be associated with a decrease of locomotor activity caused by intracerebral injections of carbachol.