Rat medial frontal cortex: a visceral motor region with a direct projection to the solitary nucleus.

Pressure injections of the neuroanatomical tracer wheat germ agglutinin conjugated with HRP (WGA-HRP) were made into either the dorsal medulla or the medial frontal cortex of the rat. Following the brainstem injections, retrogradely labeled neurons were found in the paraventricular nucleus of the hypothalamus, central nucleus of the amygdala, insular cortex and in the infralimbic, prelimbic and anterior cingulate regions of the medial frontal cortex. The infralimbic labeling consisted of a dense band of neurons and was bilateral. Cells in the prelimbic and anterior cingulate regions were less densely packed. Following injections of WGA-HRP into the medial frontal cortex anterograde labeling in the dorsal medulla was confined to the solitary nucleus (NTS). Label was found throughout the rostro-caudal extent of the NTS and was bilateral although heavier contralaterally. The projection from the medial frontal cortex to the solitary nucleus suggests that this area of cortex may function primarily as a visceral 'motor' cortical region that may play a role in regulating autonomic activities.