Forebrain connections of the rat paraventricular thalamic nucleus as demonstrated using the carbocyanide dye DiI.

The anatomical connections of the rat paraventricular thalamic nucleus (PaVT) have been studied using the fluorescent dye DiI. The fact that this compound is able to dissolve and to diffuse in plasma membranes in formalin-fixed tissues (Godement et al., 1987) allowed us to depose precisely tiny quantities of DiI on the PaVT, in order to study its neuronal connections. Ventralward, the forebrain projections of the PaVT were directed to the reuniens nucleus of the thalamus, the dorso-medial hypothalamic region, the zona incerta and the lateral hypothalamic area. In the rostral direction, the PaVT appeared to innervate mainly the medial preoptic area, the bed nucleus of the stria terminalis (particularly the ventral and medial regions) and the medial septum. The forebrain afferent connections of the PaVT were found to originate mainly in the lateral and periventricular hypothalamic area, the medial preoptic area, the bed nucleus of the stria terminalis and the medial septum where the fluorescent nerve cell bodies appeared particularly numerous. From these results, it is concluded that DiI is a useful tool for demonstrating the neuroanatomical connections of small brain nuclei, as well as for post-mortem neuropathological studies.