Distribution of Rab3a in rat nervous system: comparison with other synaptic vesicle proteins and neuropeptides

In the present study we have investigated the distribution of Rab3a in rat peripheral nervous system and compared it with the distribution of other synaptic vesicle proteins (synaptophysin, synapsin I), neuropeptides (CGRP, SP, NPY) and tyrosine hydroxylase (TH). Rab3a immunoreactivity (-IR) was always colocalized with synaptophysin-IR and synapsin I-IR in nerve terminals of the spinal cord and peripheral nerve endings. In many cases, Rab3a-IR was also present in the same axons and terminals as peptides. In crushed sciatic nerve axons, Rab3a was colocalized, proximal to the crush, with synaptophysin-IR, synapsin I-IR, CGRP-IR, and TH-IR, but only partially co-localized with NPY-IR and SP-IR. In the area distal to the crush, Rab3a-IR was very weakly positive in a few thin axons, while larger amount of synaptophysin, CGRP, NPY and SP immunoreactivities were detected. The subcellular distribution of peptides and Rab3a differed in that peptides were observed mainly in large granular structures, while Rab3a-IR was observed mainly as diffuse, finely granular immunoreactivity, in addition to a few exceptional large granules present in some axons. The results demonstrate that Rab3a is widely distributed in different types of neurons, i.e. motor, sensory, autonomic adrenergic and cholinergic neurons, and colocalized with other synaptic vesicle proteins, suggesting that Rab3a may play an essential role in neuronal function. Furthermore, Rab3a is present in many peptide containing axons and terminals, but with an apparently different subcellular distribution, being affiliated mostly with small synaptic vesicles and only occasionally with large vesicles, that may represent peptide contained vesicles.