Organization of Multisynaptic Circuits Within and Between the Medial and Central Extended Amygdala

摘要

The central and medial extended amygdala comprises the central (CEA) and medial nuclei of the amygdala (MEA), respectively, together with anatomically connected regions of the bed nucleus of the stria terminalis (BST). To reveal direct and multisynaptic connections within the central and medial extended amygdala, monosynaptic and transneuronal viral tracing experiments were performed in adult male rats. In the first set of experiments, a cocktail of anterograde and retrograde tracers was iontophoretically delivered into the medial CEA (CEAm), anterodorsal MEA (MEAad), or posterodorsal MEA (MEApd), revealing direct, topographically-organized projections between distinct amygdalar and BST subnuclei. In the second set of experiments, the retrograde transneuronal tracer pseudorabies virus (PRV) was microinjected into the CEAm or MEAad. After 48 hr survival, there were no significant differences between monosynaptic and PRV cases in the subnuclear distribution or proportions of retrogradely-labeled BST neurons. However, after 60 hr survival, CEAm-injected cases displayed an increased proportion of labeled neurons within the anteromedial group of BST subnuclei (amgBST) and within the posterior BST, which do not directly innervate the CEA. MEApd-injected 60 hr cases displayed a significantly increased proportion of retrograde labeling in the amgBST compared to monosynaptic and 48 hr cases, whereas MEAad-injected cases displayed no proportional changes over time. Thus, multisynaptic circuits within the medial extended amygdala overlap the direct connections comprising this anatomical unit, whereas the multisynaptic boundaries of the central extended amygdala extend into BST subnuclei previously identified as part of the medial extended amygdala.