COOPER, R.L.*; BHATT, D.; BHATT, D.; VIELE, K; Univ of KY, Lexington; Univ of KY, Lexington; Univ of KY, Lexington; Univ of KY, Lexington: Pre- & Post-synaptic Actions of Kainate: Negative Feedback at Glutamate-ergic Nerve Terminals in Drosophila

Glutamate receptors within the mammalian CNS are of prime interest since they are the major receptor type used. Invertebrate models served and still do a vital role in characterizing glutamate receptor function. Considering that Drosophila melanogaster is a true model organism with a known genome and successful rapid induction of mutations for various studies, it is important to understand the pharmacological and physiological function within this model synaptic neuromuscular preparation. There are 5 glutamate postsynaptic receptors subtypes at the Drosophila NMJ and they were deemed to be most similar to the kainate/AMPA class for vertebrates by sequence data. This lead to the receptors being labeled kainate type without pharmacological testing. We show the responses are primarily of a quisqualate subtype and not a kainate or a AMPA subtype since the muscle is not depolarized by kainate or AMPA at 1 mM. In fact, kainate might block the glutamate receptors since the excitatory postsynaptic potential (EPSP) is reduced in the presence of kainate (40% for 1 mM and 500uM but about 20% for 100uM). The reduction in the EPSP amplitude occurred without any significant change in resting membrane potential; thus, kainate did not depolarize the muscle as observed for application of glutamate or quisqualate. (NSF-IBN-0131459, RLC, KV; REU-NSF, DB)