A scanning microfluorimetric study on sympathetic nerve fibres: intraneuronal differences in noradrenaline turnover

The quantitative aspects of formaldehyde induced fluorescence (FIF) of noradrenaline (NA) in sympathetic nerve fibres were studied in whole mount preparations of the iris of the rat. Both "static" and scanning microfluorimetric measurements showed a close linear relationship between the FIF intensity and the NA content after pharmacological treatment (alpha-methyl-p-tyrosine, amphetamine, guanethidine, nialamide). A histogram analysis method is described to study fluorescence changes in different parts of the nerve fibre histogram, in order to evaluate changes in different segments of the nerve fibres characterized by their fluorescence intensity. The method is illustrated by a study on NA turnover. The chemically determined halflife (T 1/2 of NA after alpha-methyl-p-tyrosine (4.3 h) was in close agreement with the T 1/2 estimated microfluorimetrically (4.2 h). However, pronounced differences were found in various parts of the nerve fibre histogram (3.7-6.3 h). We conclude that the turnover of NA is different in various segments of the sympathetic nerve fibres in the rat iris and that the most intensely fluorescent varicosities display the longest T 1/2 and the highest turnover rate of NA.