Distribution of chromogranins A and B and secretogranin II (secretoneurin) in rat pelvic neurons and vas deferens.

The family of chromogranins/secretogranin peptides comprises three major subtypes: chromogranin A, chromogranin B and secretogranin II. We have characterized these proteins in rat vas deferens and pelvic ganglia by using two approaches. Firstly, extracts of rat vas deferens were subjected to molecular sieve chromatography followed by radioimmunoassay. The results indicate that, in the peripheral nerves of this organ, chromogranin B and secretogranin II are processed to small peptides, i.e. PE-11 and secretoneuron, respectively. Secondly, we investigated the localization of each of these peptides in the rat pelvic ganglia and vas deferens. Comparisons with the distribution of tyrosine hydroxylase, choline acetyltransferase, vesicular acetylcholine transporter and SV2 were carried out in double labelling studies. All tyrosine hydroxylase-positive neurons contained neuropeptide Y, but many neuropeptide Y-containing neurons were negative for tyrosine hydroxylase. In the pelvic ganglia, chromogranin A was widely localized in the neuropeptide-positive neurons and 65% of chromogranin A-containing neurons were positive for tyrosine hydroxylase, suggesting their adrenergic nature. However, in nerve terminals of the vas deferens, chromogranin A was present at very low, or undetectable, levels. The chromogranin B-derived peptide PE-11, on the other hand, was absent from the large-sized, tyrosine hydroxylase-positive neurons, but present in some small-sized neurons that were choline acetyltransferase/vesicular acetylcholine transporter-positive and tyrosine hydroxylase-negative. In the vas deferens, PE-11 was present with intense immunoreactivity in nerve terminals of the lamina propria beneath the epithelium, but it was very sparse in the muscular layer and co-localized with vesicular acetylcholine transporter-like immunoreactivity, suggesting a cholinergic nature. The secretogranin II-derived peptide secretoneurin was distributed with strong immunoreactivity in the somata of pelvic ganglion neurons, 72% of which also contained tyrosine hydroxylase, as well as in nerve terminals in the muscular layer and the lamina propria of the vas deferens. Most, if not all, secretoneurin-positive terminals in the pelvic ganglia and the vas deferens were positive for choline acetyltransferase/vesicular acetylcholine transporter-like immunoreactivity. Retrograde tracing with FluoroGold demonstrated that the majority of FluoroGold-labelled neurons in the pelvic ganglia were positive for either chromogranin A or secretoneurin. The present study indicates that chromogranins A and B and secretogranin II are proteolytically processed to a high degree in the nerves of the rat vas deferens. Furthermore, they are heterogeneously localized in subsets of neurons of the pelvic ganglia and in different sets of nerve terminals in the vas deferens, suggesting that each of these peptides may play distinct roles in neurons of the autonomic nervous system to the vas deferens.