An intracellular HRP study of the rat globus pallidus. I. Responses and light microscopic analysis.

A study of the intracellularly recorded responses of rat globus pallidus neurons to activation of striopallidal fibers was combined with light microscopic examination of the morphology of these same neurons using intracellular horseradish peroxidase. The response to stimulation of caudate-putamen is an inhibitory postsynaptic potential with observed latencies ranging from 5.1 to 9.8 msec. These values correspond to conduction velocities of 0.4 to 0.8 m/second for striopallidal fibers. Comparison with extracellular controls shows no excitatory component to the response. All recovered and analyzed neurons (n = 11) were of the large type of pallidal neuron known from Golgi studies but the addition that two subtypes could be recognized. Large neurons located medially in the nucleus had dendritic fields with large dorsoventral extent (ca. 1 mm) when compared to their mediolateral and rostrocaudal dimensions (ca. 0.4 mm) and these neurons emitted no axon collaterals. Large neurons located laterally in the nucleus had disklike dendritic fields with both dorsoventral and rostrocaudal dimensions being on the order of 1 mm but with a minor axis of approximately 100 micrometers. The axons of these neurons possessed collaterals. As a consequence of their disk-shaped dendritic field, neurons belonging to the laterally placed subgroup and occupying the narrow (ca. 100 micrometers thick) striopallidal border zone known to receive a distinct input from neostriatum have dendrites restricted to that zone.