Localization of glutamatergic/aspartatergic neurons projecting to the hypothalamic paraventricular nucleus studied by retrograde transport of [H-3]D-aspartate autoradiography

Morphological and functional data indicate that glutamatergic innervation o f the hypothalamic paraventricular nucleus plays an important role in the c ontrol of this prominent cell group. Sources of this neural input are unkno wn. The present investigations were aimed at studying this question. The re trograde tracer [H-3]D-aspartate, which is selectively taken up by the term inals of neurons that use glutamate or aspartate as a neurotransmitter, and is retrogradely transported to their perikarya, was injected into the para ventricular nucleus. The brain was examined for labelled neurons visualized by autoradiography. Labelled neurons were detected in the paraventricular nucleus itself in several hypothalamic areas including medial and lateral p reoptic area, suprachiasmatic nucleus, anterior hypothalamic area, ventrome dial nucleus, dorsomedial nucleus, lateral hypothalamic area, posterior par t of arcuate nucleus, ventral premammillary nucleus and supramammillary nuc leus. Outside the hypothalamus labelled neurons were found in the thalamic paraventricular nucleus and in certain telencephalic regions including late ral septum, bed nucleus of the stria terminalis and amygdala. All of them a re known to project to the hypothalamic paraventricular nucleus. We failed to detect labelled neurons in the lower brainstem. From these findings we conclude that firstly, there are glutamatergic/aspar tatergic interneurons in the paraventricular nucleus; secondly, all intrahy pothalamic and telencephalic, but not lower brainstem afferents to this nuc leus contain glutamatergic/aspartatergic fibres; and thirdly, the glutamate rgic/aspartatergic innervation of this heterogeneous cell group is extremel y complex. (C) 2000 IBRO. Published by Elsevier Science Ltd. All rights res erved.