YAGER, D.D.; Univ. of Maryland, College Park: Information transformation by an auditory interneuron in the high-speed bat evasion of a praying mantis.

Many praying mantises have sensitive ultrasonic hearing. Afferent neurons carry information from the single, midline ear to the metathoracic gangion. There they connect to several bilaterally symmetrical pairs of auditory interneurons. One of these, 501-T3, produces a distinctive pattern of action potentials in response to ultrasonic pulses: an initial burst of 3-6 spikes at 700-800 spikes/s followed by a pause of 10-20 and then tonic firing at a low rate. The interneuron shows a strong response decrement with repeated stimulation, and it cannot follow stimulus repetition rates above 50-60 pps. Because 501-T3 is a major part of a high-speed bat evasion system, it is especially interesting to ask what forces shape the neural response of 501-T3. It could be that it is faithfully relaying the spike pattern of the afferents. However, the tympanal afferents have no initial, high-rate burst of spikes and no pauses; the overall response is strictly tonic. Adaptation is slight, and the tympanal afferents can accurately follow pulse repetition rates of >200 pps. Therefore, 501-T3�s response is highly transformed. The distinctive pause after the initial burst of spikes could result from factors intrinsic to the interneuron or from inhibition. We used microinjection of GABA and glycine antagonists into the neuropile near 501-T3 to look for evidence of inhibition. The glycine antagonist strychnine had no effect on the 501-T3 firing pattern. However, picrotoxin increased overall firing in 501-T3 and reduced or eliminated the pause suggesting a strong GABAergic inhibitory influence. Supported by NIH/NIDCD Grant DC01382.