L-[3H]Carnosine binding in the olfactory bulb. II. Biochemical and biological studies.

During the first 10 days after peripheral deafferentation of the mouse olfactory bulb stereoselective binding of L-[3H]carnosine declines markedly. The initial phase of this decline is due to a decrease in binding site stereoselectivity, which is then followed by a loss of assayable binding sites. The specificity of inhibition of L-[3H]carnosine binding by various peptides is also altered after denervation. Competitive inhibitors of carnosine binding become less potent after denervation, while analogues which are not competitive inhibitors remain equipotent before and after denervation. Several carnosine analogues that are normally poor inhibitors become more potent after denervation. Treatment of bulb membranes with trypsin, RNase and hyaluronidase, but not DNase or collagenase, resulted in significant alterations in carnosine binding. L-, but not D-carnosine, protected the binding site from trypsin digestion, and induced additional binding in bulb membranes in a dose-and temperature-dependent fashion. Preincubation of membranes with L-carnosine also led to the induction of additional carnosine binding in membranes from cerebral cortex, cerebellum and deafferentated bulbs but not from muscle. Bulbs from newborn mice contain about one-half of the adult levels of binding and no significant sex differences in carnosine binding were detected in bulbs from adult rats. L-[3H]carnosine binding was two-fold higher in the anterior compared to the posterior portion of the bulb, but there were no significant differences in binding of opiate, GABA, alpha-adrenergic, muscarinic cholinergic, benzodiazepine of glutamic acid receptor ligands.