Peripheral and striatal influences on nigral dopamine cells: Mediation by reticulata neurons

It is reported here that the excitation of DA cells by muscimol is potentiated by the removal of striato-nigral pathway mediated inhibitory influences on DA cells as well as by pretreatment with the dopamine receptor blocker haloperidol.

Abstract

We have previously reported that a neuron exists within the zona reticulata (ZR) of the substantia nigra which exerts an inhibitory influence on zona compacta dopaminergic (DA) cells. Furthermore, this ZR neuron is much more sensitive to the inhibitory effects of GABA agonists than are the DA cells. Thus, low doses of GABA agonists (such as muscimol) appear to induce an increase in DA cell rate by preferentially inhibiting this inhibitory ZR neuron [11]. We report here that the excitation of DA cells by muscimol is potentiated by the removal of striato-nigral pathway mediated inhibitory influences on DA cells as well as by pretreatment with the dopamine receptor blocker haloperidol. In addition, we have found that the population of ZR neurons studied are excited by noxious stimuli (e.g. foot pinch), which in turn induces an inhibition of DA cell firing rate.