Visceral-related area in the rat insular cortex.

The insular cortex interacts with the bulbar autonomic nuclei providing autonomic manifestations accompanying several neurological and psychosomatic disorders. The aim of our study was to identify the sites within the insular cortex, which could be responsible for the gastrointestinal, respiratory and cardiovascular responses. The main methods used were microinjections of HRP into several parts of the bulbar dorsal vagal complex and microstimulation of the insular cortex. It has been found that a compact group of neurons located in the middle level of the rat insular cortex projects directly to the specific "gastric" part of the dorsal vagal complex. Retrograde labelled cell bodies were revealed in the V layer of the disgranular and agranular insular cortex. Microstimulation of the sites within the middle level of the rat insular cortex produced gastric motor responses and a decrease in inspiratory airflow without significant alteration in respiratory cycle duration. More caudal microstimulation produced an increase in respiratory airflow and decreased respiratory cycle duration. These responses were usually accompanied by changes in the level of blood pressure. It is concluded that autonomic representation in the rat insular cortex is organised in a viscerotopic manner. The inhibitory respiratory zone overlaps with the gastrointestinal control area in the middle part of the insular cortex. More caudally, the excitatory respiratory zone overlaps with the cardiovascular area. On the basis of these experimental results and the data of others authors the general scheme of autonomic representation in the rat insular cortex is discussed.