QUANTITATIVE MICROFLUORIMETRIC AND NEUROCHEMICAL STUDIES ON DEGENERATING ADRENERGIC NERVES

Abstract

The short term effects on noradrenaline (NA) uptake-storage mechanisms and nerve density of the adrenergic nerves in mouse and rat iris following ganglionectomy have been investigated. Uptake-storage mechanisms were studied by measuring ³H-NA uptake-retention and endogenous NA content and nerve density (number of nerve terminals) by using formaldehyde fluorescence histochemical technique in combination with scanning microfluorimetry. ³H-NA uptake-retention, endogenous NA and nerve density in mouse iris were almost unaffected up to 10 hr after ganglionectomy, whereas between 10 and 16 hr there was a drastic and an approximately similar reduction of all of the parameters studies down to about 20-30% of control. The same pattern of changes were observed in rat iris, except that the onset of the changes in NA uptake-storage were delayed about 2 hr, possibly related to the length of the neuron. Although all of the parameters determined showed approximately the same time-course, the results obtained indicate that the function of the storage mechanism is lost somewhat prior to that of the axonal "membrane pump" uptake mechanism. The very close correlation between the nerve density and the ³H-NA uptake shows that ³H-NA uptake is a good index for the relative number of adrenergic nerve terminals. The results presented support the view that the NA uptake-storage mechanisms are intact up to a certain time-point after ganglionectomy, when these functions are rapidly lost with a concomitant disappearance of the transmitter stores. The onset of these changes are somewhat varying for different terminal systems. The ganglionectomy does not have any acute effects on the uptake-storage mechanisms except for those related to the disruption of the nervous impulse flow. The present results also indicate that axotomy and isolation of the iris for in vitro incubation do not have any effects on the NA uptake-storage mechanisms.