Differential subcellular distribution of glutamate and taurine in primary olfactory neurones

Taurine and glutamate are widely distributed amino acids in the mammalian brain, including the olfactory bulb where their functions have not been fully elucidated. This study investigated the precise cellular distribution of taurine and glutamate in the nerve layer and the glomeruli of the olfactory bulb, using semiquantitative immunocytochemistry at the electron microscopic level. The results show that both amino acids are present at higher concentrations in primary olfactory neurones than in the postsynaptic dendrites. Glutamate is also enriched in terminals vs axons of the primary olfactory neurones. This suggests that glutamate acts as a neurotransmitter at the primary synapse in the olfactory system. An opposite concentration gradient is found for taurine, with a higher level of taurine-like immunoreactivity in axons than in terminals of primary olfactory neurones. Further studies are required before conclusions can be drawn about the function of taurine in these neurones.