Morphological features of physiologically identified hypothalamic neurons as revealed by intracellular marking.

In the in vitro slice preparation intracellular recordings and injections of procion yellow (PY) were made in neurons of the hypothalamus. Of these neurons, one medial preoptic-anterior hypothalamus (MPO-AH) and four arcuate-ventromedial hypothalamus (ARC-VM) neurons were driven by electrical stimulation of the median eminence area (ME). Two other MPO-AH and five other ARC-VM neurons were driven by stimulation of the stria terminalis (ST). On the basis of the PY injections two morphologically distinct cell types were delineated: a larger multipolar cell type with a polygonal perikaryon was found with equal frequency in the MPO-AH and the ARC-VM. A smaller fusiform cell type was encountered mainly in the ARC-VM. On the secondary dendrites of both cell types spine-like appendages were seldom seen, but dendritic swellings were common. Some of the dendrites projected to capillaries in both areas and presumably contacted them. The axons were usually tortuous and could only be traced a short distance.