Catecholamine fluorescence in the pituitary of the eel, Anguilla anguilla, with special reference to its variation during background adaptation.

In the neuro-intermediate lobe (NIL) of the eel, Anguilla anguilla, a specific formaldehyde-induced fluorescence, indicating a catecholamine (CA) innervation, has been demonstrated in the neural lobe processes. Microspectrofluorimetric analyses and pharmacological treatments indicate noradrenaline or dopamine or both to be responsible for the fluorescence. The fluorescence in the NIL has displayed a definite tendency toward variation during the adaptation to a white and to a black background. The highest amounts of fluorescence were generally found in animals adapted to a black background, especially when adapted for a rather long period, and in animals recently transferred to a white background. The lowest amounts of fluorescence were generally found in animals adapted to a white background. This and the result of injections of CA-depleting drugs suggest that the monoaminergic nerves are active when the animal is on a white background, inhibiting the MSH release directly or indirectly or both, or in co-operation with other factors. Specific green fluorescent structures were also found in other parts of the neural lobe supplying the pars distalis. In some pharmacologically untreated specimens and in animals treated with CA-depleting drugs, the intermedia cells fluoresced. Microspectrofluorimetric analyses indicated that this fluorophore was not a CA.