Effects of -[alpha]-aminoadipate on excitation of afferent fibers in the lateral line of Xenopus laevis

Abstract

The effects of -[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. -[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 -aspartate and -glutamate (1.0-2.0 mM) were less sensitive and similar, and those elicited by kainate (5-15 [mu]M) 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 -glutamate of -aspartate.