title: Efferent projections of the basolateral amygdala in the opossum, Didelphis virginiana.
abstract: The autoradiographic anterograde axonal transport technique was used to study efferent projections of the opossum basolateral amygdala. All nuclei of the basolateral amygdala send topographically organized fibers to the bed nucleus of the stria terminalis (BST) via the stria terminalis (ST). Injections into rostrolateral portions of the basal nuclei label fibers that surround the commissural bundle of the ST, cross the midline by passing along the outer aspect of the anterior commissure, and terminate primarily in the contralateral BST, anterior subdivision of the basolateral nucleus (BLa), ventral putamen, and olfactory cortex. Each of the basal nuclei project ipsilaterally to the anterior amygdaloid area, substantia innominata and topographically to the ventral part of the striatum and adjacent olfactory tubercle. The posterior subdivision of the basolateral nucleus (BLp), but not the basomedial nucleus (BM), projects to the ventromedial hypothalamic nucleus. BLa and BLp have projections to the nucleus of the lateral olfactory tract and also send fibers to the central nucleus, as does the lateral nucleus (L). The lateral nucleus also has a strong projection to BM and both nuclei project to the amygdalo-hippocampal area. BLa and BLp send axons to the ventral subiculum and ventral lateral entorhinal area whereas L projects only to the latter area. The lateral nucleus and BLp project to the perirhinal cortex and the posterior agranular insular area. The BLa sends efferents to the anterior agranular insular area. Rostrally this projection is continuous with a projection to the entire frontal cortex located rostral and medial to the orbital sulcus. All of the nuclei of the basolateral amygdala project to areas on the medial wall of the frontal lobe that appear to correspond to the prelimbic and infralimbic areas of other mammals. Despite the great phylogenetic distance separating the opossum from placental mammals, the projections of the opossum basolateral amygdala are very similar to those seen in other mammals. The unique frontal projections of the opossum BLa to the dorsolateral prefrontal cortex appear to be related to the distinctive organization of the mediodorsal thalamic nucleus and prefrontal cortex in this species.
mesh_terms: D000679:Amygdala / Q000166:cytology*; D000818:Animals; D001345:Autoradiography; D004027:Diencephalon / Q000166:cytology*; D005260:Female; D008032:Limbic System / Q000166:cytology; D008297:Male; D009434:Neural Pathways / Q000166:cytology; D009893:Opossums / Q000033:anatomy & histology*; D013687:Telencephalon / Q000166:cytology*