Interrelations between lateral, dorsomedial and ventromedial hypothalamic nuclei in the rat:An HRP study

Afferents of the lateral (LH) and ventromedial (VMH) hypothalamic nuclei were studied with the horseradish peroxidase method. The aim was to investigate relations between these two centers presumed to be involved in the regulation of food intake. Special attempts were made to produce HRP injections limited to intranuclear dimensions, which was achieved by iontophoretic delivery of the tracer. The results indicate that LH and VMH do not maintain direct interconnections. Both nuclei, however, appear to have numerous afferents from the dorsomedial hypothalamic nucleus (DMH) in common, which led us to extend our analysis to the DMH. DMH injections of HRP resulted in retrograde labeling of somata in both LH and VMH, suggesting a reciprocal relationship of DMH with these latter nuclei. The possible significance of such a LH-DMH-VMH relationship in the food intake control circuitry is discussed. The other labeling of afferents resulting from HRP injections localized to LH, DMH and VMH is described and discussed as regards their morphological significance. A number of these connections confirm studies using anterograde transport techniques, but others have not been described before, including an extensive projection to the VMH from the mesencephalic peripeduncular nucleus