Intracellular response of neurons of the caudate nucleus and putamen to intrastriatal stimulation in cat.

The purpose of this research was to determine if the different functional areas of the striatum, as defined by corticostriate connections, have excitatory and/or inhibitory interconnections. In cats anesthetized with barbiturates, an intracellular recording electrode was angled at 45 degrees such that it (1) crossed all functional areas of the striatum in a single pass and (2) traversed perpendicular to intrastriatal axonal bundles and their terminal fields. > 95% of the neurons recorded intracellularly in the head of the caudate (Cd) nucleus responded to stimulation of the rostromedial striatum (limbic area) producing an initial excitatory response in all cases. Membrane hyperpolarization and inhibition followed the initial excitatory response in approximately half of the responsive neurons. As the recording electrode approached the stimulating electrode, latencies to response onset decreased and amplitudes of the initial excitatory responses increased. Stimulation of a single site produced responses in neurons found in all functional areas of the Cd nucleus. Based on the known topography of afferents to the striatum, these results cannot be explained by stimulation of fibers en passant. Therefore, we conclude that the limbic striatum is connected to other functional areas of the Cd nucleus by intrinsic excitatory and inhibitory circuits. We speculate that intrinsic circuits are a hidden layer of organization providing connectional plasticity by which the influence of an input on striatal neurons may be expanded or contracted beyond the anatomical limits of the afferent terminal field.