Sigma-receptors: implication for the control of neuronal activity of nigral dopamine-containing neurons

Using extracellular single unit recording techniques, we analyzed the significance of sigma-receptors in the neuronal control of dopamine (DA) neurons in the zona compacta of the substantia nigra. Administration of racemic trans-9-methoxy-4-benzyl-1,2,3,4,4a,5,6,10b-octahydrobenzo[f]quinoline (HW 173), a drug displaying high and specific affinity for sigma-receptors, was not associated with any change in the firing rate of DA neurons. Furthermore, pretreatment with the drug did not affect the dose-response curve for the inhibitory effects of the DA receptor agonist apomorphine or the mixed DA agonist/sigma-receptor ligand (+)-3-(3-hydroxyphenyl)-N-1-propyl)piperidine ((+)-3-PPP). In contrast to the effects of HW 173 on the DA cell firing rate, the firing pattern of the DA cells was significantly changed by the drug. The data suggest that sigma-receptors do not play a pivotal role in the control of the firing rate of DA neurons in the substantia nigra. Rather, they may have a function in the regulation of the firing pattern of these neurons.