Changes in multiunit activity of nigral neurons induced by cholinergic and dopaminergic stimulation of the caudate...

The effects of stimulation of the caudate cholinergic and dopaminergic receptors on multiunit activity in the ipsilateral substantia nigra were studied in cats locally anesthetized, paralyzed and artificially respired. Cholinergic stimulation by intracaudate microinjections of 10 micrograms of carbachol diminished multiunit activity by 36% in the ventral substantia nigra (SN) and increased activity by 48% in the dorsal SN. This effect was abolished after electrolytic lesion of the ipsilateral striatonigral pathway. Opposite responses were observed following intracaudate administration of 20 micrograms of dopamine or 20 micrograms of D-amphetamine. Multiunit activity in the ventral SN increased by 36% and 34%, respectively, while the activity in the dorsal SN was reduced by 56% and 53%, respectively. Similar results were obtained in response to systemic administration of D-amphetamine. Extracaudate microinjections of carbachol and dopamine left multiunit activity in the SN unaffected. In conclusion, our results indicate an opposite action of caudate cholinergic and dopaminergic receptors on multiunit activity in the SN of the cat.