Intracellular analysis of synaptic potentials in rat neostriatum following stimulation of the cerebral cortex, thalamus, and substantia nigra.

Intracellular recordings were obtained from neostriatal neurons of unparalyzed male hooded rats anesthetized with urethane. Electrical stimulation of the cerebral cortex (Cx), centromedian-parafascicular area of the thalamus (CMP), and the substantia nigra (SN) elicited monosynaptic excitatory postsynaptic potentials (EPSPs) in neostriatal neurons. Response latencies were, on the average, 3.7 msec, 3.3 msec, and 3.8 msec, for Cx, CMP and SN stimulation, respectively. Over 85% of recorded neurons showed convergence of inputs from all three stimulation sites. The SN induced EPSP sometimes had two components, with the second component beginning 10-15 msec after the first. EPSPs from all three stimulation sites were often followed by inhibitory postsynaptic potentials (IPSPs) lasting from 50-250 msec. Double shock experiments indicated that SN induced EPSPs could be reduced in amplitude by 20-80% when preceded by conditioning stimulation to Cx, CMP or SN. In contrast, the EPSP elicited by Cx stimulation were unaffected by conditioning stimulation. Some recorded neurons were morphologically identified by means of intracellular injection of horseradish peroxidase. All were "medium spiny" neurons. The results of the present study agree well with those of previous studies of cat caudate neurons, and extend them to rat neostriatal neurons.