Phaseolus vulgaris leuco-agglutinin tracing of intrahypothalamic connections of the lateral, ventromedial, dorsomedial and paraventricular hypothalamic nuclei in the rat
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Abstract
Intrahypothalamic connections of the lateral (LHA), ventromedial (VMH), dorsomedial
(DMH) and paraventricular (PVN) hypothalamic nuclei were studied with anterograde
transport of iontophoretically injected Phaseolus vulgaris leuco-agglutinin and the
immunocytochemical detection of labeled structures. The LHA was found to give rise
to a minor projection in the VMH, whereas the VMH in reverse maintains few connections
with the ventromedial part of the tuberal LHA. Tracer deposits in both the LHA and
VMH resulted in anterograde terminal labeling in the DMH. The DMH, in turn, donates
a small number of projections to the LHA and VMH. The main projection of the DMH is
aimed at the parvocellular paraventricular nucleus. Direct outflow pathways from the
VMH to the PVN were not found, but lectin injections in the LHA on the other hand
gave rise to terminal labeling in both the parvocellular and magnocellular divisions
of the PVN. The PVN in turn was found to give only minor reciprocal projections to
the LHA, DMH and VMH. These findings indicate that the main stream of connections
in the hypothalamus runs from the LHA and VMH to the DMH, and from the DMH to the
PVN. The identified circuitry patterns were discussed with respect to the role of
the hypothalamus in the control of homeostasis and metabolic regulation, and more
specifically in relation to the modulation of the hormone release from the pancreas
and adrenal glands.