Connections of the hypothalamus and preoptic area with nuclei of the amygdaloid body in the rat; HRP retrograde transport study.

Horseradish peroxidase (HRP) was injected into various nuclei of the amygdala in 50 rats. The retrograde axonal transport of HRP showed various connections arising from the hypothalamic nuclei and the basal forebrain. Neurons of the magnocellular preoptic nucleus send out amygdalopetal axons to all amygdaloid nuclei except the lateral nucleus. The amygdalopetal projections emerge from the large neurons situated dorsally in the most lateral preoptic area (probably substantia innominata) and terminate in the basal dorsal and the central amygdaloid nuclei. Neurons in the lateral division of the hypothalamus (the lateral hypothalamic area proper and the perifarnical region) send out axons which terminate in the medial and central nuclei and in the posterior part of the cortical amygdaloid nucleus. Axons emerging from the ventromedial hypothalamic nucleus end mainly in the medial nucleus and in the central amygdaloid nucleus. Amygdalopetal fibers arising from neurons of the ventral premammillary and dorsal hypothalamic nuclei reach the medial amygdaloid nucleus and perhaps a few of them end in the posterior part of the cortical amygdaloid nucleus. Neurons of the bed nucleus of the stria terminalis project to the medial, the posterior part of the cortical and probably to the basal dorsal amygdaloid nuclei.