Mouse Trigeminal Neurons Respond to Kokumi Substances

Abstract

Using in vivo confocal Ca2+ imaging, we investigated whether oral application of kokumi substances elicits responses in trigeminal somatosensory ganglion neurons of the mouse. Our results show that 100 μM γEVG (γ-Glu-Val-Gly), a potent kokumi stimulus, evokes responses in a very small fraction (0.6%) of neurons in area V3 (oral sensory field) of the trigeminal ganglion. By comparison, cooled artificial saliva elicited thermal-evoked responses in >7% of V3 trigeminal ganglion neurons. γEVG-evoked responses were small and quite variable, with latencies ranging from 2 to over 200 s. Co-application of the calcium-sensing receptor (CaSR) inhibitor NPS-2143 significantly decreased γEVG-evoked activity. Furthermore, we show that four additional kokumi substances evoked responses in mouse trigeminal ganglion neurons. All neurons responding to kokumi compounds were small cells, with mean diameters below 20 μm. In summary, our data show that certain physiological and pharmacological properties of responses to kokumi compounds can be recorded from sensory neurons in the trigeminal ganglion of living mice. Thus, sensory neurons in the somatosensory trigeminal ganglia may transmit signals from the oral cavity to the central nervous system to generate the texture perceptions that are part of the enigmatic sensations evoked by kokumi substances.