One Special Glomerulus in the Olfactory Bulb of Xenopus laevis Tadpoles Integrates a Broad Range of Amino Acids and Mechanical Stimuli.

The olfactory system senses odors, but not exclusively, as shown over the past years. It also registers other modalities such as temperature and pressure. However, it remains unknown how widespread these sensitivities are across species and how strongly their processing is interconnected with the processing of odors. Here, we present data on the β-glomerulus in the olfactory bulb of Xenopus laevis tadpoles. We show that this glomerulus possesses an unusually broad response pattern to a large number of amino acids. The β-glomerulus uses the classical cAMP-mediated pathway, as suggested by its sensitivity to forskolin. This finding was unexpected because amino acid-sensitive olfactory sensory neurons of Xenopus commonly function in a cAMP-independent manner. Furthermore, we show that the β-glomerulus also reacts to pressure pulses delivered to the olfactory mucosa. These mechanical stimuli induce responses with profiles having typical dose-response and adaptation curves. Finally, whereas the mechanosensitivity in the glomerular layer was observed repeatedly in the β-glomerulus only, mechanosensitive modulation of mitral cells and their postsynaptic neuropils was found on a larger scale. Some mitral cells closely followed the response time course of the β-glomerulus, whereas many others were strongly inhibited by short pressure pulses. In conclusion, our data demonstrate the existence of one glomerulus sensitive to both a large number of amino acids and pressure pulses and show that the processing of pressure pulses is intertwined with odor processing. SIGNIFICANCE STATEMENT: We present a glomerulus in the olfactory bulb (OB) activated by very different stimuli, namely mechanical stimuli to the olfactory mucosa and a large number of amino acids. This unusual sensitivity is conveyed to the second-order neurons in the OB. Pressure sensitivity of olfactory sensory neurons has been shown recently in mice. Along with temperature sensitivity found in the olfactory system of mice and Xenopus laevis tadpoles, a discussion arose about the influence of these modalities on odor coding. Our results suggest that mechanosensitivity may be a general feature in olfactory systems. The pressure and broad amino acid sensitivity is not only focused to one glomerulus, but is also integrated in the odor processing of the OB's network.