Two loci of the insular cortex project to the taste zone of the nucleus of the solitary tract in rats

Abstract Distribution of insular cortical neurons projecting to the taste zone of the solitary tract nucleus (NTS) was examined histologically in rats. Injection of wheat germ agglutinin–conjugated horseradish peroxidase (WGA–HRP) into the taste responsive regions in the NTS resulted in labeling of cells in layer V within almost entire extent of the rostrocaudal axis of the granular and dysgranular areas of the insular cortex (IC) bilaterally with a clear contralateral dominance. The density of the cells was highest in the taste area of the IC [11] and second highest in the IC area around the bregma level, showing a bimodal distribution. After WGA–HRP injection into the IC taste area or the caudal IC, dense or sparse anterograde labeling was seen in the rostral NTS, respectively. The results indicate that not only the IC taste area but also the caudal IC exerts control influences directly upon the NTS taste zone.