Morphological characteristics and electrophysiological responses of visceral nociceptive neurons in somatosensory cerebral cortex of cat.

The morphology of intracellular neurobiotin-labeled cortical neurons activated by noxious visceral stimuli in cat was reported. The electrophysiologic properties of 851 neurons and structure of 52 neurons of representative area of the greater splanchnic nerve (GSN) in the primary somatosensory cortex were described. The neurons responding to stimulation of GSN with strong intensity were referred to as viscero-nociceptive neurons (VNNs). Patterns of the responses of VNNs in SI area were excitatory, inhibitory and mixed. According to latency of discharge clusters in response, the VNNs could be classified into two kinds. The neurons only showing long latency were called specific VNNs; those having discharge clusters with both long and short latency induced by stimulus were nonspecific VNNs. Following acquisition of electrophysiological data, neurobiotin was injected into some cells by electrophoresis and their structure and location in the cerebral cortex were studied. The results provided some findings about morphological and electrophysiological characteristics of VNNs in SI area. It is thought that VNNs have more complicated morphology in the dendritic construction and axon distribution than nonvisceral nociceptive neurons (NVNNs). Most of the excitatory VNNs showed pyramidal shape and most of the inhibitory VNNs had stellate shape in camera lucida drawing. The architecture of the nonspecific VNNs might be different from specific VNNs in dendritic distribution.