Auditory processing of descending neurons in the prothorax of a bush-cricket

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Auditory processing and song recognition in bush-crickets has gained increasing interest during the last twenty years. The species Ancistrura nigrovittata has been studied from their acoustic behavior (the male sings, the female replies, both perform phonotaxis) to the neuronal basis of that behavior on the level of sensory neurons and interneurons on various levels. A. nigrovittata is of special interest due to three features: (i) males and females produce songs with different carrier frequencies, (ii) males and females produce songs of different temporal patterns and (iii) the male song has two components, from which one serves as identifier for the species and the second as trigger for the short, reflex-like female reply. Several local prothoracic neurons, ascending neurons to the brain and brain neurons have been studied so far. One group of auditory neurons with a descending axon from the prothorax to posterior ganglia (DN) has been widely ignored in A. nigrovittata due to its small processes in the prothoracic ganglion making intracellular recordings difficult. A previous study on local neurons (DUM) has shown that recording from the soma is a promising alternative in such a situation. Preliminary studies have demonstrated, that it is possible to record and stain DN with success from their soma and have suggested the existence of at least seven different DN types on each side. The purpose of the project is to characterize descending neurons by their morphology and responses to acoustic stimuli. This should identify potentially relevant neurons for song recognition. Among these might be a neuron tuned to the male song, which might elicit the female reply song, which is produced reflex like by the mesothoracic wings and is too fast to loop via the brain. Others obviously respond to low frequencies and vibration, as described for other bush-cricket species. It would be interesting to know, whether these respond selectively to the conspecific song pattern and, therefore, might be relevant for close distance communication. Even others seem to respond well to ultrasound – their specific properties might help to understand their potential role. Experiments with blocking inhibition should demonstrate, whether sharpening of tuning occurs as described for other auditory neurons as well, but not for descending neurons. This is suggested by the observation of IPSP-like negative deflections of the membrane potential.