Effects of d-α-aminoadipate on excitation of afferent fibers in the lateral line of Xenopus laevis

Abstract

The effects of d-α-aminoadipate (DαAA) on excitation of afferent nerve fibers in the Xenopus laevis lateral line were studied in vitro. DαAA 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-α-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 DαAA (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 μM) 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 of l-aspartate.