Cholinergic involvement in lateral hypothalamic rewarding brain stimulation.

Rats were implanted with stimulating electrodes in the lateral hypothalamus, and cannulae for chemical injections in the ventral tegmentum. Injections of atropine, a muscarinic antagonist, increased thresholds for self-stimulation in a dose-dependent fashion, without slowing bar pressing rates. Thresholds increased less for a self-stimulation site contralateral to the atropine injection. In a conditioned place preference test, the rats preferred compartments in which they received carbachol, a cholinergic agonist. Muscarinic receptors in ventral tegmentum therefore seem critical for medial forebrain bundle (MFB) reward. The possible cholinergic cells of origin are discussed.