The efferent connections of the anterior hypothalamic area of the rat, cat and monkey.

The general morphology and topographic relations of the anterior hypothalamic area (AHA) in the rat, cat and squirrel monkey have been described, and its efferent connections analyzed autoradiographically, after small injections of 3H-labeled amino acids into, or around, the area. In all three species the AHA is rather poorly separated from the surrounding preoptic and hypothalamic areas and nuclei but shows three distinct cellular condensations, located rostrally, centrally, and posterodorsally. Closely associated with the AHA are the retrochiasmatic area, the anterior periventricular nucleus and the scattered neurons usually referred to as the accessory supraoptic nucleus. The AHA has primarily short connections to the adjoining medial preoptic area, the lateral hypothalamic area, the periventricular nucleus, the dorsomedial nucleus, and to the "capsule" of the ventromedial nucleus. However, it also has certain more distant projections, rostrally to a narrow zone centered in the ventral part of the lateral septal nucleus, and caudally to the dorsal premammillary nuclei, the posterior hypothalamic area and the central gray. There is some evidence to suggest that the various subdivisions of the AHA have different efferent connections. Thus the posterodorsal cell condensation appears to give rise to the bilateral projection to the dorsal premammillary nuclei, while the projections to the septum, the posterior hypothalamic area and the central gray seem to have their origin in the central condensation. Similarly, the retrochiasmatic area sends its efferents through the ventral supraoptic commissure to the amygdala, the anterior periventricular nucleus contributes to the periventricular fiber system and to the external lamina of the median eminence, and the accessory supraoptic neurons project to the internal lamina of the median eminence.