σ-Receptors: Implication for the control of neuronal activity of nigral dopamine-containing neurons

Abstract

Using extracellular single unit recording techniques, we analyzed the significance of σ-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 σ-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/σ-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 σ-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.