NMDA-MEDIATED FACILITATION IN THE ECHO-DELAY TUNED AREAS OF THE AUDITORY-CORTEX OF THE MOUSTACHED BAT

We recorded the responses of single delay-tuned neurons in the dorsal fringe (DF) area and the FM-FM area of the auditory cortex of the must ached bat using multi-barreled carbon-fiber electrodes. An iontophoret ic application of N-methyl-D-aspartate (NMDA) or kainate (ICA) to a DF neuron evoked a burst of discharges from the neuron. The burst of dis charges evoked by NMDA was always smaller than that evoked by KA. Simu ltaneous application of D-2-amino-5-phosphonovalerate (APV) with NMDA and KA abolished the NMDA-evoked but not the KA-evoked discharges. APV did not evoke any significant changes in the auditory responses of 43 out of the 47 delay-tuned neurons studied in the DF area, and in all 20 neurons studied in the FM-FM area. In the remaining four DF neurons , however, APV either increased the initial discharges of their audito ry response or decreased the late discharges of their response. These results indicate that in the majority of neurons in the DF and FM-FM a reas NMDA receptors do not play a significant role in the processing o f target-distance information, and that their facilitative auditory re sponses are basically created by synaptic interactions occurring in th e subcortical auditory nuclei.