Taurine (2-aminoethane sulfonic acid) and carnosine (β-alanyl-L-histidine) are found in large quantities in the olfactory epithelium and bulb. Taurine is a structurally simple amino acid, and has been reported to have several putative roles, such as neurotransmitter, neuromodulator, neurogrowth factor and to function in membrane stabilization. Carnosine, on the other hand, has been suggested as a putative neurotransmitter in the olfactory system. We have succeeded in visualizing taurine-and carnosine-like immunoreactivities (LI) in the human olfactory mucosa, and also carnosine-LI in the human olfactory bulb. For this investigation, we collected specimens of the human olfactory bulb by autopsy and from the olfactory mucosa by biopsy, and compared localization of taurine-and carnosine-LI in several cases. By means of biopsy using Nakano's forceps, samples of olfactory mucosa were obtained from 5 cases: a 17 year old female, 23 year old male, 46 year old male, 47 year old male, and a 57 year old male. The olfactory bulb of a 1 month old male was collected at autopsy. These specimens were processed for immunohistochemical study according to the peroxidase-antiperoxidase (PAP) method. In the olfactory epithelium, taurine-LI was demonstrated in some primary olfactory neurons, and in basal cells. Carnosine-LI was observed only in primary olfactory neurons, i.e, dendrites, vesicles and axonal bundles of olfactory receptor cells, but not in basal cells. In the olfactory bulb, the olfactory nerve layer and the glomelular layer showed carnosine-LI positive reactions. Therefore, taurine and carnosine may possibly coexist in some olfactory neurons. Olfactory receptor cells are classified as sensory neurons. Considerable evidence indicates that they are continually replaced throughout adult life by proliferative basal cells. Taurine in the basal cells and the olfactory receptor cells may play certain roles in cell growth and differentiation. Nerve growth functions of taurine have already been reported in certain portions of the central nervous system. The existence of carnosine in the nerve terminals of the olfactory bulb supports the concept that this peptide is a putative neurotransmitter in olfactory neurons. The pattern of taurine staining demonstrated in our study is highly compatible with this theory.
