An interneurone of unusual morphology is tuned to the female song frequency in the bushcricket Ancistrura nigrovittata (Orthoptera, Phaneropteridae)

The interneurone AN5-AG7 of the duetting bushcricket Ancistrura nigrovittat a has its soma in the seventh (penultimate) abdominal ganglion, Its major p ostsynaptic arborizations with dense thin branches of smooth appearance are found in the prothoracic ganglion. The branches terminate In the auditory neuropile, predominantly at the same location as those auditory receptors t hat respond best to the female song frequency, Correspondingly, AN5-AG7 res ponds preferentially to frequencies between 24 and 28 kHz, thereby matching the carrier frequency of the female response song quite well. At frequenci es below 24 kHz, AN5-AG7 receives inhibition, which is sometimes seen as cl ear inhibitory postsynaptic potentials, At these frequencies, thresholds of excitatory postsynaptic potentials are considerably lower than spike thres holds, In contrast, above 20kHz, the two thresholds match and they correspo nd to the behavioural threshold, The AN5-AG7 interneurone is more sensitive to soma-contralateral stimuli and it receives predominantly inhibition, bu t also some excitation, from the soma-ipsilateral ear, Response strength is not greatly affected by stimulus duration but shows prominent habituation, This habituation depends only weakly on intensity and frequency. Some AN5- AG7 interneurones show very small graded potentials and no spiking response s to any acoustic stimuli.