Morphological and physiological changes in central auditory neurons following unilateral foreleg amputation in larval crickets

Summary1.In view of the surprising recent demonstration that developmentally one-eared female crickets can track sound sources (Huber et al. 1984), we have looked for correlates in the morphological and physiological properties of auditory interneurons of these animals. One foreleg was amputated in the 3rd/4th or penultimate (8/9th) larval instar; in both cases the leg regenerated without developing a functional ear. In the adult stage, these animals were studied first for their phonotactic behavior and then by intracellular recording and staining; three types of auditory interneurons in the prothoracic ganglion were identified: the omega neuron ON1, and the ascending neurons AN1 and AN2.2.Of these three neuron types, those that normally receive excitatory input from the side now deafferented send dendrites across the midline of the ganglion, along specific pathways, to end in the auditory neuropil of the intact side (Figs. 1–4).3.The new connections are functional, as shown by the responses of the neurons to synthesized calling songs presented to the remaining ear. With respect to the copying of chirp structure, threshold curves and intensity characteristics, these neurons respond like cells in intact animals that are presented with the same stimulus on the side ipsilateral to the main input region of the neurons (Figs. 2–4). The implication is that in animals with one ear missing, functional pathways within the central nervous system are reorganized, resulting in better orientation of one-eared animals.