Evidence for connections between a discrete hypothalamic dorsochiasmatic area and the supraoptic and paraventricular...

In order to check the existence of direct or indirect connections between the hypothalamic supraoptic (SON) and paraventricular (PVN) nuclei, four retrograde traces were iontophoretically injected into these nuclei. The small injection sites were restricted to parts of the SON and PVN, enabling the identification of afferent neurons localized in their immediate vicinity. The tracer injections into any of these hypothalamic nuclei resulted in conspicuous labeling of cells gathered dorsally to the optic chiasma and the optic tract. This neuronal population was tentatively called dorsochiasmatic area. Double retrograde tracers injections into the ipsilateral SON and PVN gave evidence for some neurons containing both tracers in this dorsochiasmatic area. Otherwise, labeled parvocellular neurons were occasionally found in one PVN, after injecting retrograde tracer into either the ipsilateral SON or the contralateral PVN. As few connections exist between the four magnocellular nuclei, the dorsochiasmatic area connected with both the ipsilateral SON and PVN could play an important role in regulating the oxytocin and/or vasopressin systems.