Electrophysiological Properties of Caudate Neurons Following Substantia nigra, Motor Cortex, and Amygdaloid Nuclear Complex Stimulation of the Rat

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Abstract
Extracellular single unit activities were recorded from the caudate nucleus (CN) in rat anesthetized with urethane. The present study is related to a selected population of CN neurons, only cells that exhibited spontaneous activity being investigated. A wide range of spontaneous firing was observed (0.1–15 spikes/sec). The majority of the units responded to electrical stimulation of substantia nigra (SN), motor cortex (MC), and amygdaloid complex (Amyg), 72, 70 and 65%, respectively; both decreased and increased firing rates were obtained following the three central stimulations. The majority of the responsive neurons (87%) showed significant alteration of their spontaneous firing rates following each of the three stimuli applied, i.e., there was a high degree of convergence. If a cell responded to one particular stimulation by an increase in discharge rate, the same cell would not necessarily respond to the other two stimuli in the same direction of change. Time locked action potentials were observed only following Amyg stimulation in 32% of the CN neuronal population. In the present study the population of units which exhibit spontaneous activity demonstrate polysynaptic connections with MC and SN. The possibility of mono, oligo- and polysynaptic connections from Amyg to CN is discussed. It is suggested that the connection between Amyg and CN provides a route through which the limbic system may influence somatic motor activity.