Amygdalo-hypothalamic projections in the lizard Podarcis hispanica: a combined anterograde and retrograde tracing study.

Abstract

The cells of origin and terminal fields of the amygdalo-hypothalamic projections in the lizard Podarcis hispanica were determined by using the anterograde and retrograde transport of the tracers, biotinylated dextran amine and horseradish peroxidase. The resulting labeling indicated that there was a small projection to the preoptic hypothalamus, that arose from the vomeronasal amygdaloid nuclei (nucleus sphericus and nucleus of the accessory olfactory tract), and an important projection to the rest of the hypothalamus, that was formed by three components: medial, lateral, and ventral. The medial projection originated mainly in the dorsal amygdaloid division (posterior dorsal ventricular ridge and lateral amygdala) and also in the centromedial amygdaloid division (medial amygdala and bed nucleus of the stria terminalis). It coursed through the stria terminalis and reached mainly the retrochiasmatic area and the ventromedial hypothalamic nucleus. The lateral projection originated in the cortical amygdaloid division (ventral anterior and ventral posterior amygdala). It coursed via the lateral amygdalofugal tract and terminated in the lateral hypothalamic area and the lateral tuberomammillary area. The ventral projection originated in the centromedial amygdaloid division (in the striato-amygdaloid transition area), coursed through the ventral peduncle of the lateral forebrain bundle, and reached the lateral posterior hypothalamic nucleus, continuing caudally to the hindbrain. Such a pattern of the amygdalo-hypothalamic projections has not been described before, and its functional implications in the transfer of multisensory information to the hypothalamus are discussed. The possible homologies with the amygdalo-hypothalamic projections in mammals and other vertebrates are also considered.