Microspectrofluorimetric study of monoamines in the hypothalamus of Scyliorhinus stellaris L.

In a combined fluorescence histochemical and microspectrofluorimetrical study, the distribution, morphology and amino content of the hypothalamic circumventricular organs of an elasmobranch (Scyliorhinus stellaris) have been investigated. In the walls of the third ventricle, two aminergic circumventricular organs, viz. the preoptic recess organ and organon vasculosum hypothalami, were found to display an intense blue-green fluorescence. The emission maximum was registered at about 490 nm and the excitation spectra, conducted from 240 nm to 460 nm at neutral pH, displayed a main peak at 410 nm, with additional peaks at about 320 nm and 260 nm, values that are indicative of catecholamines. In neutral state, the quotient of the excitation peak ratio values 410/260 nm exceeded 1, thus determining the differentiation between noradrenaline and adrenaline, excluding the latter as a secondary monoamine. Recordings of hydrochloric acid (HCl)-treated sections showed a hypsochromic shift of the main excitation peak from 410 nm to 370 nm and a concurrent increase of the peak at 320 nm, with the mean peak ratio 370/320 nm being 0.98, pointing to the presence of dopamine. The fading curves indicated a photodecomposition of less than 20%, both in neutral and acidified sections, which is typical of dopamine. It can therefore be deduced that the blue-green fluorescent cells in the hypothalamic circumventricular organs of the dogfish contained mainly dopamine. Some cells expressed a yellowish fluorescence, showing rapid photodecomposition characteristic of indolethylamine fluorophores, pointing to the presence of 5-hydroxytryptamine (5-HT).