NEUROPEPTIDE TYROSINE IS EXPRESSED IN ENSHEATHING CELLS AROUND THE OLFACTORY NERVES IN THE RAT OLFACTORY-BULB

The olfactory bulbs of young and adult normal rats and of colchicine-t reated rats and of some other species were analysed for the presence o f neuropeptide Y and neuropeptide Y messenger RNA, using immunohistoch emistry at the light- and electron-microscopic levels and with in situ hybridization. In the rat and mouse, but not in monkey and guinea-pig , neuropeptide Y-like immunoreactivity and neuropeptide Y messenger RN A were observed in ensheathing cells in the olfactory nerve layer of t he olfactory bulb and within nerve bundles in the olfactory mucosa. Do uble staining experiments revealed that neuropeptide Y-like immunoreac tivity was often present in a restricted compartment, mainly the Golgi apparatus, of S-100 protein-positive ensheathing cells. After colchic ine treatment a different distribution of neuropeptide Y-like immunore activity and neuropeptide Y messenger RNA was observed. Thus, in the o uter olfactory nerve layer both neuropeptide Y-like immunoreactivity a nd neuropeptide Y messenger RNA disappeared, whereas in the inner part messenger RNA levels remained high and neuropeptide Y-like immunoreac tivity was observed in many granule-like structures distributed diffus ely in the cytoplasm. The present findings suggest that neuropeptide Y may be involved in the control of regeneration, growth and/or guiding of the axons of the olfactory sensory neurons, the only mammalian neu rons known to have a continuous renewal and growth during adult life.