Subcortical projections of area 25 (subgenual cortex) of the macaque monkey

In several species, including primates, stimulation studies indicate that t he infralimbic cortex, the most caudal part of the ventromedial prefrontal cortex, functions as a visceral motor region. In addition, recent positron emission tomography studies implicate the subgenual region in depression an d mania. To determine the subcortical projections of this region in primate s, injections of Phaseolus vulgaris leukoagglutinin, biotinylated dextran a mine, or rhodamine-labeled dextran amine were placed in area 25 in three mo nkeys. In contrast to the efferents from area 25 previously described in th e rat, there were no projections to autonomic effector regions, such as the nucleus of the solitary tract, magnocellular neurosecretory cell groups in the hypothalamus, ventrolateral medulla, or intermediolateral column of th e spinal cord. However, projections were shown to a number of structures wi th probable roles in autonomic function and direct connections to some of t he abovementioned autonomic effector regions, including bed nucleus of the stria terminalis, perifornical and anterior hypothalamus, periaqueductal gr ay, and lateral parabrachial nucleus. In addition, there were projections t o several forebrain structures that receive projections from other componen ts of the medial prefrontal network including the medial part of the caudat e nucleus, lateral septum. midline and mediodorsal thalamic nuclei, the lat eral parvocellular part of the basal accessory amygdaloid nucleus, and the magnocellular part of the basal amygdaloid. None of the injections resulted in labeling in the medulla. These connections support the idea of a role f or cortical area 25 in emotional and autonomic responses, albeit less direc t than that described in rodents. (C) 2000 Wiley-Liss, Inc.