Monoaminergic systems of the hypothalamus of ten amphibian species: a histofluorescence study.

The morphological features and distribution of monoamine (MA) containing neurons in the hypothalamus of ten amphibian species have been studied using two histofluorescence methods. Three hypothalamic MA containing nuclei were demonstrated in all species: preoptic recess organ (PRO), paraventricular organ (PVO) and nucleus infundibularis dorsalis (NID), all three composed of liquor-contacting (LC) and accompanying MA neurons. The PRO, more developed in anuran species, shows LC neurons of variable morphology among species which are arranged in layers bordering the preoptic recess. In anurans the PRO extends into the walls of the unpair telencephalic ventricle. The PVO, well developed in all amphibians studied, has bipolar LC neurons with sometimes branched apical dendrites and basal axons. The NID is fairly well developed and better delimited from the PVO in urodeles than in anurans. MA containing fibres of the hypothalamus are specially abundant in the lateral forebrain bundle and the lateral area of the PVO.