The inhibitory input from the substantia nigra to the mediodorsal nucleus neurons projecting to the prefrontal cortex in the cat

The effects of stimulation of the substantia nigra pars reticulata (SNr) on the neurons of the mediodorsal nucleus (MD) projecting to the prefrontal cortex (PF) were studied in cats. The MD neurons projecting to the ventral part of the PF tended to be located in the ventral part of the MD, while those projecting to the dorsal part of the PF in the dorsal part. Spontaneous discharges of 30/57 tested MD neurons were suppressed by SNr stimulation at a latency ranging from 2 to 15 ms. The latency of the suppression corresponded well to that of antidromic responses of SNr neurons elicited by MD stimulation (from 1.4 to 14.0 ms). Intracellular recordings in a few MD neurons showed IPSP by SNr stimulation. The SNr is considered to exert an inhibitory effect on the MD neurons projecting to the PF.