Somatic sensory regulation of hypothalamic secretion of corticotropin-releasing hormone

Abstract

Response characteristics of 833 neurons in the pericruciate cortex of the cat were studied to find which sent axons into the medullary pyramids. The traditional criteria for classifying cortical neurons as pyramidal tract neurons were examined and found to be adequate. The population behavior of these neurons was then analyzed. The population was found to segregate into two groups on the basis of both antidromic and orthodromic response properties. A group of early-firing neurons was scattered throughout the cortex, but was concentrated at the level of layer V. A second group of later-firing neurons was found in the upper parts of the cortex, concentrated at the level of layer III. Two distinct afferent inputs appeared to underlie the orthodromic group segregation: Both inputs bombarded the early-firing neurons, but only one of them bombarded the late-firing neurons. A similar grouping of these neurons was observed following stimulation of the ipsilateral forepaw and of both hindpaws. The patterns of activity of these neurons are related to certain properties of the reflex corticofugal discharge recordable from the medullary pyramids.