CASCADE PROJECTIONS FROM SOMATOSENSORY CORTEX TO THE RAT BASOLATERAL AMYGDALA VIA THE PARIETAL INSULAR CORTEX

The pathways by which somatosensory information could be relayed from the cortex to the amygdaloid complex were investigated by using the an terograde axonal transport of biocytin following cortical microinjecti ons. Injections of biocytin into head and limb areas of secondary soma tosensory cortex (S2) produced heavy labeling of fibers and terminals in granular and dysgranular parietal insular cortex from bregma to 3.8 mm behind bregma but only extremely sparse labeling in the lateral an d basolateral amygdaloid nuclei. Biocytin injections into granular par ietal insular cortex produced a heavy labeling of the subjacent dysgra nular parietal insular cortex, but only sparse labeling in the basolat eral amygdala. Biocytin injections into dysgranular parietal insular c ortex resulted in heavy labeling of the subjacent agranular parietal i nsular cortex and strong labeling of fibers and terminals in the dorsa l part of lateral nucleus, with moderate labeling of fibers in the ant erior and posterior basolateral nuclei, and the central nucleus. Injec tions into S2 labeled the ventroposterior medial, ventroposterior late ral and posterior thalamic nuclei; injections in rostral granular and dysgranular parietal insular cortex labeled the ventral posterior and parvicellular part of ventroposterior lateral thalamic nuclei; and inj ections in middle to caudal dysgranular parietal insular cortex labele d only the posterior nucleus. These results suggest that whereas somat osensory cortex projects only very sparsely to the amygdala, somatosen sory-related inputs to the amygdala arise in the dysgranular parietal insular cortex. The association of dysgranular parietal insular cortex with the posterior thalamus suggests it may relay nociceptive informa tion to the amygdala. (C) 1998 Wiley-Liss, Inc.