RESPONSIVENESS OF POSTERIOR HYPOTHALAMIC NEURONS TO STRIATAL AND PERIPHERAL STIMULI

The effects of the ipsilateral or contralateral caudate nucleus or globus pallidus stimulation on the spontaneous activity of single cells in the posterior hypothalamus, and their responsiveness to photic, acoustic, and sciatic stimuli were studied in cats. All responses were statistically analyzed as to changes in the rate and pattern of firing following stimulation. The firing of most units was inhibited by the caudate and globus pallidus. The ipsilateral caudate stimulation, which was more effective, caused a strong early inhibition which diminished gradually, while globus pallidus caused a sustained inhibition in firing durng the whole 2000 msec after stimulation. The ipsilateral caudate stimulation also caused significant changes in the pattern of firing of the units. The analysis of the relationship between the effects of striatal stimuli and sensory responsiveness of the single cells, has demonstrated that the caudate affected mainly units which were facilitated by peripheral stimuli, while no such pattern was observed in units affected by the globus pallidus. These and other differences in responsiveness suggest that the caudate and globus pallidus may affect to a certain extent two different populations of hypothalamic neurons. The interaction between the striatum and sensory stimuli, which by themselves were mainly facilitatory, produced mostly a decrease in the rate of firing, indicating the predominance of the central influence. Bilateral lesions of the globus pallidus or midbrain reticular formation reduced the percentage of units responsive to caudate stimulation; however, they have increased the number of cells facilitated by the central stimulus. The present results demonstrate the effects of the straitum on the electrical activity of hypothalamic units and the role played by extrahypothalamic structures. © 1968.