Neuropeptide tyrosine (NPY)‐like immunoreactivity in adrenal chromaffin cells and intraadrenal nerve fibers of rats

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Abstract
The present peroxidase‐antiperoxidase immunohistochemical study demonstrated that approximately 50% of the total chromaffin cells of the rat adrenal medulla exhibited NPY‐like immunoreactivity. The immunoreactive material was localized in the core of the chromaffin granules as well as diffusely in the cytoplasm. By combination of immunohistochemistry with noradrenaline‐fluorescence microscopy, all NPY‐immunoreactive chromaffin cells are nonfluorescent, indicating that all NPY‐chromaffin cells co‐store adrenaline. A comparison of two consecutive sections, each of which was processed for the immunostaining with anti‐NPY and anti‐Met‐Enk‐Arg‐Gly‐Leu antisera, respectively, indicated that NPY and preproenke‐phalin A and its derivatives coexist in approximately one‐fifth of the total NPY‐immunoreactive cells.In addition to the NPY‐immunoreactive cells, a plexus of NPY‐immunoreactive nerve fibers with varicosities was found in the subcapsular regions of the adrenal gland. The nerve fibers were often associated with small blood vessels and extended into the zona glomerulosa. Single NPY‐immunoreactive fibers were sparsely distributed in the deeper regions of the cortex and in the medulla. Ganglion cells in the adrenal gland were not seen exhibiting intensely positive NPY‐like immunoreactivity. The NPY‐immunoreactive nerve fibers contained abundant small clear vesicles mixed with a few small and large granular vesicles. The immunoreactive material appeared on the granular cores as well as in the axoplasm. The NPY fibers were closely apposed to smooth muscle cells and pericytes of small blood vessels in the cortex. They were sometimes seen in close apposition to the fenestrated endothelial cells with a common basal lamina intervening. The NPY fibers also made synaptic contacts with both cortical and chromaffin cells.