Chromogranin A in the olfactory system of the rat

The olfactory bulb of the rat contains chromogranin A at a similar
level as the adrenal gland or the hypophysis as revealed by
immunoblots. Olfactory chromogranin A also displays the same size
as chromogranin A of endocrine cells. In the hippocampus and other
brain regions, we could not detect chromogranin A by
immunoblotting. In contrast, chromogranin A messenger ribonucleic
acid (using S1 nuclease protection assays) was observed in all
brain regions examined, including the olfactory bulb. By in situ
hybridization histochemistry with a complementary ribonucleic acid
probe (280 nucleotides), and by immunocytochemistry, chromogranin A
synthesis could be localized to cell bodies of the mitral cell
layer, of the external plexiform layer and of the periglomerular
region of the olfactory bulb. Immunocytochemically, chromogranin A
was also detected in the central projection areas of mitral and
tufted cells in the primary olfactory cortex and the anterior
amygdaloid area but not in the olfactory glomeruli, where the
incoming olfactory nerve fibers of the primary olfactory neurons
establish synaptic contacts. Taken together the data show that
chromogranin A, following biosynthesis in the perikarya of the
mitral and tufted cells, is specifically transported into their
axonal terminals but not into their primary dendrites. We propose
that the rat olfactory system could serve as a model for the study
of chromogranin A regulation and function in neurons.