Olfactory bulbectomy increases met-enkephalin- and neuropeptide-Y-like immunoreactivity in rat limbic structures

Bilateral olfactory bulbectomy (OBX) in rats produces a well-characterized syndrome of behavioral, physiological, and neurochemical changes identical to those seen in depression. Previous experiments using in situ hybridization histochemistry have demonstrated that OBX increases prepro-neuropeptide-Y (NPY) and prepro-enkephalin (ENK) mRNA levels in limbic structures. The present experiments determined whether increases in peptide immunoreactivity occur in conjunction with increases in mRNA levels following OBX. In situ hybridization analyses in olfactory bulbectomized and sham-operated rats revealed increased prepro-ENK mRNA in the piriform cortex (PIR) and olfactory tubercles (OTs) of bulbectomized rats. Prepro-NPY mRNA levels were significantly increased in the PIR of bulbectomized rats as comapred to controls. Radioimmunoassays (RIAs) revealed significant elevations in ENK-like immunoreactivity in the OTs following OBX. NPY-like immunoreactivity was significantly elevated in the PIR following OBX. These data reveal that OBX-induced increases in ENK-like immunoreactivity occur concomitantly with increases in prepro-ENK mRNA, and NPY-like immunoreactivity occur concomitantly with increases in prepro-NPY mRNA.