THE ORGANIZATION OF THE AXONAL RETICULUM AT A LIGATION, IN IN-VITRO INCUBATED BOVINE SPLENIC NERVES

From previous studies we concluded that in noradrenergic neurons the a xonal reticulum can be considered to be an extension of the Golgi appa ratus, directly involved in the condensation and packaging of neurosec retion. But the precise ultrastructure of the organisation of the axon al reticulum in relation to neurosecretory granule formation remained to be elucidaded. This conversion was studied in ligated bovine spleni c nerve incubated in vitro for three hours. The ultrastructure of the material accumulating proximally and distally was examined and its nat ure was determined by phosphstungstic acid staining and immunocytochem istry on glycolmethacrylate sections. Proximal to the ligation predomi nantly electron-lucent vesicles and tubules were found. Tubules of int ermediate electron density appeared in between. The latter, especially in thicker sections, were seen to form complexes with tubules and gra nules of high electron density. All those elements were shown to be po sitive for dopamine-P-hydroxylase and cytochrome b561. In the distal p art multivesicular bodies accumulated and they were also positive for both enzymes. From these findings it is concluded that the different t ypes of structures accumulating proximally belong to a neurosecretory axonal reticulum. At a block the axonal reticulum is triggered to gene rate a reticular differentiation, in which granular densities of diffe rent size are found. This configuration compares well with that in ner ve terminals and strongly suggests that granule formation is basically a local process.