Picrotoxin eliminates frequency selectivity of an auditory interneuron in a bushcricket.
AN1, an auditory interneuron in the bushcricket Ancistrura nigrovittata, is narrowly tuned to the male song frequency ( approximately 15 kHz). It receives pronounced inhibitory input at frequencies below and, more prominently, above this fundamental frequency. It is also subject to side-dependent inhibition producing asymmetric response functions for left- and right-side stimulation. In addition, intensity-response functions of AN1 peak as stimulus intensities increase. Application of the GABAA channel-blocker picrotoxin eliminates all subthreshold inhibitory postsynaptic potentials, revealing underlying excitation that is particularly obvious in the high-frequency range. Excitatory thresholds close to the song frequency remain unchanged by picrotoxin. Thus a specifically tuned neuron is shown to become broadly tuned after elimination of frequency-dependent inhibition. Although average maximum response strength is increased by 150% after picrotoxin application, at male song frequencies a slight reduction of the responses is still present at high intensities. Side-dependent inhibition remains largely unaffected by picrotoxin, suggesting that side- and frequency-dependent inhibitions are caused by different transmitters from different neurons.
Stumpner
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A
I. Zoologisches Institut, D-37073 Gottingen, Germany.
D000818:Animals; D001306:Auditory Pathways / Q000502:physiology*; D001369:Axons / Q000502:physiology; D005260:Female; D018756:GABA Antagonists / Q000494:pharmacology*; D006135:Gryllidae / Q000187:drug effects* / Q000502:physiology; D007395:Interneurons / Q000187:drug effects* / Q000502:physiology; D008297:Male; D010852:Picrotoxin / Q000494:pharmacology*; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000502:physiology
D018756:GABA Antagonists; D010852:Picrotoxin; D011963:Receptors, GABA-A