Connections of the corticomedial amygdala in the golden hamster. I. Efferents of the “vomeronasal amygdala”

Abstract

The medial (M) an posteromedial cortical (C3) amygdaloid nuclei and the nucleus of the accessory olfactory tract (NAOT) are designated the "vomeronasal amygdala" because they are the only components of the amygdala to receive a direct projection from the accessory olfactory bulb (AOB). The efferents of M and C3 were traced after injections of 3H-proline into the amygdala in male golden hamsters. Frozen sections of the brains were processed for autoradiography. The efferents of the "vomeronasal amygdala" are largely to areas which are primary and secondary terminal areas along the vomeronasal pathway, although the efferents from C3 and M terminate in different layers in these areas than do the projections from the vomeronasal nerve or the AOB. Specifically, C3 projects ipsilaterally to the internal granule cell layer of the AOB, the cellular layer of NAOT, and layer Ib of M. Additional fibers from C3 terminate in a retrocommissural component of the bed nucleus of the strain terminalis (BNST) bilaterally, and in the cellular layers of the contralateral C3. The medial nucleus projects to the cellular layer of the ipsilateral NAOT, layer Ib of C3, and bilaterally to the medial component of BNST. Projections from M to non-vomeronasal areas terminate in the medial preoptic area-anterior hypothalamic junction, ventromedial nucleus of the hypothalamus, ventral premammillary nucleus and possibly in the ventral subiculum. These results demonstrate reciprocal connections between primary and secondary vomeronasal areas between the secondary areas themselves. They suggest that M, but not C3, projects to areas outside this vomeronasal network. The medial amygdaloid nucleus is therefore an important link between the vomeronasal organ and areas of the brain not receiving direct vomeronasal input.

The main and the accessory olfactory systems interact in the control of mate recognition and sexual behavior

“…While main and accessory olfactory systems exhibit segregated pathways at the level of the first olfactory relays, the two systems converge downstream at several levels, including the cortical-medial amygdala [33,53,54,75,77,93,107]. Indeed, electrical stimulations of both the MOB and vomeronasal organ induce electrophysiological activation of this structure [61,77].…”

Sexual dimorphism and developmental expression of signal‐transduction machinery in the vomeronasal organ

“…In several classes of vertebrates, chemical sensory perception is mediated by sensory neurons at two anatomically distinct locations: the main olfactory epithelium (MOE) and the vomeronasal organ (VNO; Winan and Scalia, 1970;Broadwell, 1975;Scalia and Winan, 1975;Kevetter and Winan, 1981;Shepherd, 1988). Although they are of similar embryonic and neuronal origin (Cuschieri and Bannister, 1975), the two olfactory systems appear to diverge in function.…”

Castration reversibly alters levels of cholecystokinin immunoreactivity within cells of three interconnected sexually dimorphic forebrain nuclei in the rat.

“…Such direct effects of gonadal steroids on CCK-positive cells in the MPNc may be complemented by steroid-induced neural activity of cells within the BSTe and MeAp, which in turn may be relayed to the MPNc via direct axonal projections from both regions. Although electrophysiological (36) and anatomical (37,38) results suggest that cells in the region of the MeAp [which receives an input from the accessory olfactory bulb (17) (5) G14 (4) G14+T ( Proc. Natl.…”