Development of responses of globus pallidus and entopeduncular nucleus neurons to stimulation of the caudate nucleus and precruciate cortex

Extracellular recordings were made from neurons in the globus pallidus and entopeduncular nucleus (GP-ENTO) of anesthetized kittens of 2 to 177 days of age and from four adult cats. Stimulation of the striatum and the precruciate cortex produced responses in GP-ENTO neurons of the youngest kittens tested (2 days of age). In kittens of 1 to 10 days, about 70% of the GP-ENTO neurons responded to either caudate or cortical stimulation with a purely excitatory response (i.e., an evoked action potential). With increasing age the frequency of occurrence of this type of response decreased and the occurrence of inhibitory responses or of sequences of excitation followed by inhibition increased. In addition to these changes in the form of the evoked responses, other response parameters exhibited age-dependent alterations. Latency to response decreased with age and the ability of GP-ENTO neurons to follow repetitive stimuli increased as the kittens became older. These findings suggest that although GP-ENTO neurons are functional as early as 2 days postnatally in the kitten, subsequent maturation of the responsiveness of these neurons continues for several postnatal months.