Hemispheric asymmetries in spontaneous firing characteristics of substantia nigra pars reticulata neurons following a unilateral 6-hydroxydopamine lesion of the rat nigrostriatal pathway.

Single unit activity of substantia nigra pars reticulata (SNR) neurons was recorded bilaterally in rats subjected to unilateral 6-hydroxydopamine lesions of the ascending mesostriatal dopaminergic pathway, resulting in an almost complete loss of dopaminergic neurons in the ipsilateral SN pars compacta. Firing rate and firing pattern of SNR neurons in lesioned rats were compared with respective data from sham-lesioned rats and naive controls. In lesioned rats, the mean firing rate of SNR neurons at the lesioned side was significantly reduced and there was an increase in the occurrence of bursting activity. In contrast, firing rate in the contralateral SNR was significantly increased without change in the frequency of bursting neurons. This asymmetrical change in spontaneous firing characteristics of SNR neurons following the lesion could be involved in the complex behavioral changes seen in this model of Parkinson's disease.