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

In several species, including primates, stimulation studies indicate that the 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 and mania. To determine the subcortical projections of this region in primates, injections of Phaseolus vulgaris leukoagglutinin, biotinylated dextran amine, or rhodamine-labeled dextran amine were placed in area 25 in three monkeys. In contrast to the efferents from area 25 previously described in the 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 the spinal cord. However, projections were shown to a number of structures with probable roles in autonomic function and direct connections to some of the abovementioned autonomic effector regions, including bed nucleus of the stria terminalis, perifornical and anterior hypothalamus, periaqueductal gray, and lateral parabrachial nucleus. In addition, there were projections to several forebrain structures that receive projections from other components of the medial prefrontal network including the medial part of the caudate nucleus, lateral septum, midline and mediodorsal thalamic nuclei, the lateral 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 for cortical area 25 in emotional and autonomic responses, albeit less direct than that described in rodents. Copyright 2000 Wiley-Liss, Inc.