A Study of the Connections of Nociceptive Substantia Nigra Neurones

Abstract

Of 226 spontaneously active neurons recorded from the substantia nigra (SN) of rats anesthetized with halothane, 112 (50%) were nociceptive. Nociceptive neurons were located in the zona compacta (ZC) and zona reticulata (ZR) compartments of the SN. The collision-test technique showed that approximately equal proportions of nociceptive and non-nociceptive SN neurons project to the thalamus. The majority of nigrostriatal neurons were non-nociceptive. Striatonigral and amygdalonigral afferents are more likely to influence nociceptive than non-nociceptive SN neurons. Experiments were performed to determine whether nociceptive SN neurons were dopaminergic. Examination of spontaneous firing rate, action potential configuration and responses to systemically administered dopaminomimetic agents of histologically identified SN neurons did not allow a reliable distinction to be made between dopaminergic and non-dopaminergic neurons.