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

Microinjections of carbachol, a muscarinic cholinergic receptor agonist, into the anterior substantia nigra increase feeding, drinking and sexual behaviour if there is a pre-existing tendency to respond and a low baseline rate of behaviour. The present experiment was undertaken to 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 nicotine, 2.5-10.0 mug eserine, and 1.25-5.0 mug or 0. 1-1.0 mug neostigmine (each dissolved in sterile saline) and the effects on feeding, drinking, locomotion, grooming, rearing and sniffing were examined. Carbachol, nicotine and low doses of neostigmine stimulated eating in a dose-dependent manner. The increased feeding following neostigmine was over 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 excites pars compacta dopamine-containing neurones.