On the presence of extraneuronal catecholamine in the iris of the rat: a scanning microfluorimetric study

Formaldehyde-induced fluorescence (FIF) of noradrenalin (NA) was studied in histochemical preparations of the rat iris. With the aid of a two-dimensional microfluorimetric scanning method, quantitative information was obtained from neuronal and non-neuronal elements selectively. Spectral analysis and fluorimetric studies showed the existence of extraneuronal NA in the iris of untreated rats. Surgical and pharmacological (reserpine, amphetamine, imipramine, nialamide) manipulation of sympathetic neurotransmission-induced changes in extraneuronal fluorescence, which did not parallel changes in fluorescence of neuronal elements. A positive relationship was found between changes in extraneuronal fluorescence and the postsynaptic effect (pupil diameter). We hypothesize that extraneuronal catecholamine (CA) fluorescence is a histochemical parameter for synaptic neurotransmission.