The organisation of the axonal reticulum at a ligation, in in vitro incubated bovine splenic nerves

Abstract

From previous studies we concluded that in noradrenergic neurons the axonal reticulum can be considered to be an extension of the Golgi apparatus, directly involved in the condensation and packaging of neurosecretion. But the precise ultrastructure of the organisation of the axonal reticulum in relation to neurosecretory granule formation remained to be elucidaded. This conversion was studied in ligated bovine splenic nerve incubated in vitro for three hours. The ultrastructure of the material accumulating proximally and distally was examined and its nature was determined by phosphotungstic acid staining and immunocytochemistry on glycolmethacrylate sections. Proximal to the ligation predominantly electron-lucent vesicles and tubules were found. Tubules of intermediate electron density appeared in between. The latter, especially in thicker sections, were seen to form complexes with tubules and granules of high electron density. All those elements were shown to be positive for dopamine-β-hydroxylase and cytochrome b561. In the distal part multivesicular bodies accumulated and they were also positive for both enzymes. From these findings it is concluded that the different types of structures accumulating proximally belong to a neurosecretory axonal reticulum. At a block the axonal reticulum is triggered to generate a reticular differentiation, in which granular densities of different size are found. This configuration compares well with that in nerve terminals and strongly suggests that granule formation is basically a local process.