Increase in medial palisade zone dopamine activity after long-term castration in the male rat.

The catecholamine (CA) content was measured in nerve terminals of the median eminence (ME) in normal, castrated and adrenalectomized male rats using quantitative microfluorimetry. CA turnover was determined by rates of CA disappearance after tyrosine hydroxylase inhibition. Noradrenaline (NA) levels and turnover in the subependymal layer (SEL) were unchanged 4 weeks after respective surgeries. Dopamine (DA) levels but not turnover in the lateral palisade zone (LPZ) were increased by castration. DA levels and turnover rates were significantly increased in the medial palisade zone (MPZ) by castration, whereas adrenalectomy selectively decreased MPZ CA levels without affecting the turnover rates. These results were discussed in relation to the concept of a medial and a lateral tuberoinfundibular DA pathway innervating different neuroendocrine structures in the rat ME.