Ultrastructural localization of neuropeptide Y-immunoreactivity in the axonal reticulum elements, accumulating...

The detection of dopamine-beta-hydroxylase and cytochrome B561 on the membranes of the axonal reticulum demonstrated that in sympathetic neurons the different compartments of the axonal reticulum participate in the formation of neurosecretory vesicles. In the present study we tried to reveal that the components of the vesicular content are also channeled along the axonal reticulum, by examining whether neuropeptide Y could be localized in elements of the axonal reticulum. Therefore 6 h transected rat sciatic nerve was embedded in glycolmethacrylate and an immunogold labeling was performed. Counterstaining with phosphotungstic acid at low pH selectively contrasted the accumulated axonal reticulum elements and associated granules. In the non-myelinated axons gold labeling was localized on granules and on tubular and granular profiles, demonstrating the presence of neuropeptide Y in the accumulated axonal reticulum elements. This indicates that neuropeptides are indeed transported via the axonal reticulum to the nerve ending and suggests that the accumulation of large dense-cored vesicles at a block is mainly due to local new formation rather than down transport.