Neural inputs to the prefrontal agranular insular cortex in the rat: horseradish peroxidase study.

The prefrontal cortex, dorsal to the rhinal sulcus of the rat (hereinafter termed the agranular insular cortex) has been examined with the use of the retrograde transport of horseradish peroxidase. Labelled perikarya were seen in the region of the ipsilateral medial forebrain bundle, consistently rostral to the caudal edge of the posterior mammillary nucleus. These cells were interpreted as being the rostral members of the A10 dopaminergic cell group. Labelled cells were also seen in the dorsal raphe nucleus, the ipsilateral pyriform cortex, the contralateral agranular insular cortex, the ipsilateral basolateral amygdaloid nucleus, the ipsilateral locus coeruleus, and the medio-dorsal, ventromedial, and parafascicular thalamic nuclei. Detailed examination of the thalamic input confirmed a differential innervation of the dorsal and ventral regions of the agranular insular cortex. Possible functional correlates of these prefrontal afferents are discussed.