Effects of D-alpha-aminoadipate on excitation of afferent fibers in the lateral line of Xenopus laevis.

The effects of D-alpha-aminoadipate (D alpha AA) on excitation of afferent nerve fibers in the Xenopus laevis lateral line were studied in vitro. D alpha AA reversibly suppressed spontaneous activity and excitation induced by water motion at concentrations as low as 0.25-0.5 mM. Higher concentrations (up to 10 mM) caused a greater suppression that was rapidly and fully reversible. L-alpha-Aminoadipate at 0.25-1.0 mM had no suppressive effects. Responses elicited by NMDA (1.0-2.0 mM) were the most sensitive to D alpha AA (0.25-0.5 mM), those elicited by L-aspartate and L-glutamate (1.0-2.0 mM) were less sensitive and similar, and those elicited by kainate (5-15 muM) were the least sensitive. The results provide evidence that the transmitter released by hair cells in the Xenopus lateral line interacts postsynaptically with NMDA-preferring receptors and that the transmitter is an excitatory amino acid, possibly L-glutamate or L-aspartate.