A COMPARISON OF BEHAVIOR FOLLOWING STIMULATION OF THE ANTERIOR SUBSTANTIA-NIGRA BY DIRECT CHOLINERGIC AGONISTS AND ANTICHOLINESTERASES

Microinjections of carbachol, a muscarinic cholinergic receptor agonis t, into the anterior substantia nigra increase feeding, drinking and s exual behaviour if there is a pre-existing tendency to respond and a l ow baseline rate of behaviour. The present experiment was undertaken t o compare the effects of carbachol with other cholinergic stimulants. Groups of 6-12 satiated rats received 0.5 mul microinjections into the anterior substantia nigra of 0. 1-5.0 mug carbachol, 0. 1-5.0 mug nic otine, 2.5-10.0 mug eserine, and 1.25-5.0 mug or 0. 1-1.0 mug neostigm ine (each dissolved in sterile saline) and the effects on feeding, dri nking, locomotion, grooming, rearing and sniffing were examined. Carba chol, nicotine and low doses of neostigmine stimulated eating in a dos e-dependent manner. The increased feeding following neostigmine was ov er a shorter time-period than following carbachol or nicotine. Neither carbachol nor nicotine had a ny significant effect on behaviour other than eating., The higher doses of neostigmine increased the frequency of sniffing and rearing, but not eating, and no dose of eserine had a clear effect on behaviour. These data are discussed in terms of their relationship to the cholinergic input to substantia nigra which excit es pars compacta dopamine-containing neurones.