The hypothalamic 'tuberoinfundibular' system of the rat as demonstrated by horseradish peroxidase (HRP) microiontophoresis.

Microiontophoresis of horseradish peroxidase (20%) into the median eminence of the rat has allowed visualization of perikarya and axon projections of the tuberoinfundibular system after retrograde transport. Cells projecting to the median eminence were found in the periventricular regions of the hypothalamus and were particularly pronounced in dorsal portions of the rostral arcuate nucleus, the medial division of the paraventricular nucleus, and within the anterior periventricular nucleus. Labeling of perikarya within the ventromedial nucleus was rarely found. No labeling by HRP was found within cells of the dorsomedial, anterior, suprachiasmatic, preoptic, lateral hypothalamic nuclei or within the septal and amygdaloid nuclei. Axons from identifiably cells were located within the periventricular neuropil and contained within the baso-lateral portions of the hypothalamic-hypophysial tract.