Cholinergic stimulation of substantia nigra: effects on feeding,drinking and sexual behaviour in the male rat

Previous studies have shown that cholinergic stimulation of the substantia nigra increases food intake but not other activities. The present experiments were undertaken to determine whether or not activities other than feeding could be stimulated if conditions were appropriate. Microinjections of the cholinergic agonist carbachol (0.5 µg/0.5 µl each side) bilaterally into substantia nigra increased the consumption of dry spaghetti, and, in subsequent tests, changed sexual behaviour in male rats. Ejaculation, mount and intromission latencies were unaffected but intromission frequency (though not mount frequency) was reduced following cholinergic stimulation (experiment 1). In a second experiment, an increase in the consumption of 2.0% saccharin solution and lab chow was stimulated by intranigral carbachol while the intake of tap water, and locomotion, gnawing, grooming, rearing and sniffing were all unaffected. These data indicate that cholinergic stimulation of substantia nigra can affect activity for which there is a pre-existing tendency, regardless of its form. A possible role for nigral acetylcholine in the control of pars compacta dopamine containing neurones is discussed.