An electrophysiological assessment of taste coding and salt transduction mechanisms from rat geniculate ganglion neurons

The present research focused on determining how the peripheral taste system distinguishes among the variety of chemical stimuli found in nature with special emphasis on salt taste. The use of improved surgical sampling procedures and controlled stimulation variables has allowed a clearer categorization of individual neurons. Extracellular recordings in the geniculate ganglion identified 5 different groups of neurons: sucrose-specialist, NaCl-specialist, NaCl-generalist, HCl-generalist and QHCl-generalist neurons. These neural channels can be equated to human's five basic taste qualities.; There are practical implications of salt taste (e.g. fluid balance, blood pressure regulation) and a variety of salts can be distinguished by taste. The present research explored the coding and receptor transduction mechanisms underlying NaCl, KCl and NH₄Cl discrimination. NaCl-specialist neurons responded selectively to NaCl, while NH₄Cl differentially activated HCl-generalist neurons. These three salts might be discriminated based on the relative activity evoked in NaCl-specialist and HCl-generalist neurons.; A blocker of epithelial Na+ channels, amiloride, reduced selectively responses to NaCl solutions in NaCl-specialist neurons. Another blocker that targets Na+/H+ exchanger proteins, DMA, reduced responses to both NaCl and KCl in NaCl-specialist neurons. The differential activation of NaCl-specialists by these salts can be explained by the expression of Na+ channels exclusively on the membranes of receptor cells that synapse with this neuron group. The generalist neuron types apparently utilize salt transduction mechanisms that differ from those used by NaCl-specialists. The K+ channel blocker 4-aminopyradine was without consistent effects.; Taken altogether, the chemical sensitivity profile of individual neurons represents best the different taste qualities, which may rely on specific receptive elements.