Data on the absence of axon terminals of medial preoptic area neurons in the surface zone of the median eminence.

In order to investigate whether neurons of the medial preoptic area (MPOA) project to the surface zone (zona palisadica) of the median eminence (ME) and proximal part of the pituitary stalk, an electrolytic lesion or a frontal cut was placed in the pre- and suprachiasmatic region of the rat hypothalamus and the mentioned zone examined under the electron microscope. Degenerated nerve profiles were not observed int the zona palisadica following a lesion restricted to the MPOA or after a frontal cut at the posterior border of the MPOA. Altered elements were seen only in those cases in which the posterior part of the suprachiasmatic region was destroyed. The present data indicate that neurons of the MPOA do not terminate in the zona palisadica of the ME but presumably end on the nerve cells of the medial basal hypothalamus.