Unilateral lesion of the nigrostriatal pathway induces a transient decrease of firing rate with no change in the firing pattern of neurons of the parafascicular nucleus in the rat

Electrophysiological recordings of thalamic parafascicular nucleus neurons were done in normal rats and in three groups of rats at different time inte rvals after injection of 6-hydroxydopamine into the pars compacta of substa ntia nigra. In normal rats, parafascicular neurons exhibited low firing rat es (3.88 +/- 0.80 spikes/s). Concerning the pattern, 59% of the units disch arged irregularly and 41% exhibited bursty pattern. In rats with 6-hydroxyd opamine lesions, the firing rate decreased significantly during the first w eek post-lesion(1.15 +/- 0.36 spikes/s, Pt 0.01). During the second week, t he firing rate was slightly, but not significantly, lower (2.59 +/- 0.41 sp ikes/s, P > 0.05) than that of normal rats to return to the basal level thr ee weeks post-lesion (3.66 +/- 0.41 spikes/s, P > 0.05). In these three gro ups of 6-hydroxydopamine-lesioned rats, the firing pattern showed no change when compared to control animals. These results show that the lesion of ni gral dopaminergic neurons induced a transient decrease of the firing rate o f parafascicular neurons with no change in the firing pattern demonstrating the absence of a stable influence of the dopaminergic system on the sponta neous activity of parafascicular neurons. (C) 2000 IBRO. Published by Elsev ier Science Ltd. All rights reserved.