ORGANIZATION OF CATECHOLAMINERGIC SYSTEMS IN THE HYPOTHALAMUS OF 2 ELASMOBRANCH SPECIES, RAJA-UNDULATA AND SCYLIORHINUS-CANICULA - A HISTOFLUORESCENCE AND IMMUNOHISTOCHEMICAL STUDY

We examined the organization of catecholaminergic neurons in the hypot halamus of the painted ray, Raja undulata, and the small-spotted dogfi sh, Scyliorhinus canicula, with the use of formaldehyde-induced fluore scence (FIF) methods and tyrosine hydroxylase (TH) immunohistochemistr y. In both species we identified distinct populations of catecholamine -containing neurons differing in a) their immunoreactivity to antibodi es against the enzyme tyrosine hydroxylase (TH), b) their fluorescence in response to FIF methods for the detection of catecholamines, and c ) their relationship with the third ventricle. One population is made up of FIF-positive and TH-negative neurons (most of which are CSF [cer ebrospinal fluid]-contacting) and located in two circumventricular org ans, the preoptic recess organ and the organon vasculosum hypothalami. Another population comprises TH-immunoreactive (TH-IR), FIF negative neurons that are located in the suprachiasmatic nucleus and the poster ior tuberculum and are not related to the third ventricle recesses. A third population of TH-IR, CSF-contacting neurons is also present in t he organon vasculosum hypothalami. The existence of three catecholamin ergic populations suggests differences in the metabolism of catecholam ines and/or different functions. The circumventricular neurons are not associated with the hypophysis and appear to accumulate catecholamine (dopamine) obtained from exogenous sources. In both Raja and Scyliorh inus the neurointermediate lobe is innervated by TH-IR fibres originat ing from dopamine-synthesizing neurons of the second catecholaminergic population.