Taurine action on mitral cell activity in the frog olfactory bulb in vivo

Taurine (TAU) is a free amino acid that is particularly abundant in the olfactory bulb. In the frog, TAU is located in the terminations of the primary olfactory axons and in the granular cell layer. TAU action seems to be associated with gamma amino butyric acid (GABA), the main inhibitory neurotransmitter involved in the processing of the sensory signal. The present study was designed to assess the action of TAU in vivo during the olfactory network's stimulation by odors. It was performed by recording the single-unit activity of mitral cells, the main bulbar output neurons. TAU effects were tested on both their spontaneous and odor-induced firing activity. Interactions between TAU and GABA were examined by analyzing TAU effects under the selective blocking action of GABA(A) or GABA(B) antagonists. TAU was found to suppress the spontaneous firing of mitral cells, mainly without altering their odor response properties. By testing GABA antagonists, we further show that TAU action is associated with GABAergic inhibitory mechanisms mainly via GABA(B) receptors. Thus, TAU action clearly reduces background activity in favor of the emergence of the odor-induced activity in the same manner as GABA action does via GABA(B) receptors. As a conclusion, we propose that, in the frog olfactory bulb, the joint actions of TAU and GABA may favor the processing of the primary sensory information by increasing the signal to noise ratio.