Effects of general anesthesia, neodecortication and spreading depression upon somatic evoked responses in caudate and entopeduncular nuclei, and their electrophysiological correlates in cats.

The electrophysiological relationship among an afferent somatic input (radial nerve), the caudate and the entopeduncular nuclei was studied in intact animals under chloralose anesthesia and in decorticated ones. The results confirm the hypothesis that the cerebral cortex is not essential to record somatic evoked responses in both nuclei, nor for the reciprocal responses in these nuclei when one of them is stimulated, suggesting the existence of direct somatic projections to these nuclei from the subcortical structures. On the other hand, the spreading depression by microinjection of KCl 3M into the CN does not modify the ERs in EPN, but the spreading depression in EPN does modify the CN response. Thus, the somatic projection to EPN seems to course directly from the thalamus or the reticular formation but not through the CN. The results suggest a reciprocal influence of the outflow structure (EPN) upon the higher level (CN), in which the inferior structure is modifying the excitability of the higher one.