Nigral modulation of cerebello-thalamo-cortical transmission in the ventral medial thalamic nucleus.

In the rat, the highly active GABAergic neurons of the substantia nigra pars reticulata (SNR) are known to exert a tonic inhibitory influence on cells in the ventral medial thalamic nucleus (VM). Considering that this nucleus is involved in the transfer of cerebellar signals towards motor cortex, we investigated the role played by SNR in that transmission. For this purpose we examined how changes in nigral background activity are reflected in the reactivity of VM cells to their cerebellar input. We report here that a GABA induced nigral pause increases the efficacy of cerebellar afferent volleys in VM, whereas an increase of nigral background by bicuculline, interrupts cerebello-thalamo-cortical transmission. It is concluded that nigrothalamic neurons subserve a permanent gating of cerebello-thalamo-cortical transmission in VM.