Splanchnic nerve activation of single cells in the cat's postcruciate motorsensory cortex

Abstract

Single neurons were recorded extracellularly in the forepaw posteruciate region, area 4 gamma, in chloralose-anesthetized cats. Several features of cellular behavior in response to skin and splanchnic nerve stimuli are described. First, in agreement with earlier work, the motor cortex receives bilateral, long-latency splanchnic input which depends primarily on A-delta afferents. Second, this input divides almost perfectly between the neuron populations delineated by Towe et al. on the basis of somatic responsiveness: sa (small-field) cells in this tissue do not receive splanchnic input, and m (wide-field) cells do. These data strengthen Towe's claim that the sa m dichotomy is fundamental and may offer a reliable identification routine for the two populations. Third, visceral input may be included as one of several long-latency excitation modes for cortical m neurons which do not involve the local sa cells: The body surface away from the contralateral topographic focus, the visual system, and the auditory system. Reasons are presented for assuming these diverse afferent systems to be based on A-delta fibers. Fourth, most pyramidal tract and some nonpyramidal tract neurons almost certainly receive splanchnic input, a finding which strengthens the notion of considerable intimacy between somatic and visceral control processes. Fifth, the common recruitment order previously shown for m neurons in response to stimmulation of skin areas other than the topographic focus obtains for their responsiveness to splanchnic stimulation as well. Finally, the suggestion is made that the several components of the wide-field input system to m neurons may have a major nociceptive function.