Axoplasmic transport of carnosine (β-alanyl-L-histidine) in the mouse olfactory pathway.

Carnosine in the chemoreceptor neurons of the olfactory epithelium can be labeled in vivo by intranasal irrigation with either(14)C-β-alanine or(14)C-L-histidine. This newly synthesized carnosine (but not the precursor amino acids) is translocated to the olfactory bulb, where the olfactory chemoreceptor axons synapse with the dendrites of mitral cells and other second-order neurons. Labeled carnosine arrives in the bulb several hours after intranasal administration of precursor. Similar arrival time is seen for macromolecules after intranasal administration of [(3)H]L-fucose, [(14)C]L-proline, or [(14)C]L-histidine. Macromolecules labeled with [(3)H]uridine take much longer to reach the bulb. Carnosine is also labeled after [(3)H]uridine administration. No labeling of macromolecules is observed after administration of 1-[(14)C]-β-alanine. Oral administration of the same dose of [(14)C]-β-alanine gives almost no labeled carnosine in bulb or epithelium. This method has permitted us to estimate that the half-life of labeled carnosine in both the bulb and epithelium is about 20 h. This method provides a means of selectively prelabeling the olfactory chemoreceptor neurons in the olfactory epithelium and their synapses in the olfactory bulb prior to cellular and subcellular separation procedures, and may also enable us to monitor the influences of olfactory stimulation on synthesis and transport of carnosine.