IMMUNOHISTOCYTOCHEMICAL DISTRIBUTION OF AMINE-CONTAINING NEURONS RELATED TO CIRCUMVENTRICULAR ORGANS IN THE FROG BRAIN

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Abstract
The circumventricular organs of the frog R. catesbeiana were studied at the light microscopic EM levels with antisera against catecholamine-synthesizing enzymes (tyrosine hydroxylase: TH, dopamine-.beta.-hydroxylase: DBH, phenylethanolamine-N-methyltransferase:PNMT) and serotonin (5-hydroxytryptamine; 5-HT). The presence of 3 groups of neuronal vesicles in the liquor-contacting neurons which are either TH or 5-HT-positive is shown for the 1st time. The neurons contacting the preoptic recess liquor were TH-positive but DBH-negative. Amounts of TH-immunoreactive product were localized not only in the cytoplasm but also in the granules (90-100, 120-150, and 170-200 nm in diameter). Evidently, dopamine (DA) synthesis occurs in the cytoplasm as well as in cored vesicles. A few 5-HT-positive, TH-negative serotonergic neurons were scattered in the preoptic recess organ. In the paraventricular organ, subependymal liquor-contacting neurons were serotonergic. In immunoelectron microscopy, 5-HT-immunoreactivity was localized both in the cytoplasm and in the cored vesicles (90-120, 130-170, and 200-210 nm in diameter). In the medullospinal liquor-contacting neurons, the 4th ventricular organ, TH-positive and DBH-positive, but PNMT-negative and 5-HT-negative reactions were observed in the granules (70-80, 90-100, and 110-130 nm in diameter). Noradrenaline [norepinephrine] (NA) seemed also to be present in the cored vesicles. Cored vesicles therefore may contain DA and 5-HT besides NA.