Neuroplasticity and phonotaxis in monaural adult female crickets (Gryllus bimaculatus de Geer)

Summary One foreleg was amputated at mid-femur in adultGryllus bimaculatus females. In phonotaxis tests these monaural crickets show course deviations and circling towards the intact side (Fig. 1). Mean course stability is best at 60 and 70 dB (Fig. 2). Here it differs significantly from a threshold value for orientated walking in females operated on the day of adult moult, but not in those operated two weeks later. The orientational performance improves with the interval between amputation and test (Fig. 3).Centripetal cobalt backfills reveal degeneration of tympanal nerve fibers on the amputated side (Fig. 4B, C). The mean number of intact afferents crossing the midline of the prothoracic ganglion is increased in monaural versus binaural crickets. Maximum transmidline extension is not correlated with the period of deafferentation (Fig. 5).Intracellular recording and staining of prothoracic auditory interneurons shows some axonal sprouts in ON1i (intact side) and ON2, but no significant physiological changes (Figs. 6A, D; 8A, C, E, G). Apart from axonal sprouts ON1a (amputated side) may show a few dendritic sprouts into the intact auditory neuropil (Figs. 6C, 7). Excitation in some ON1a-cells reveals functional contacts to intact auditory afferents (via crossing dendrites or possibly crossing afferents, Figs. 6e, 7, 8F). Morphological and associated physiological changes start early in AN2a (amputated side). The degree of crossing dendrites and contralateral excitation increases with postoperative age (Figs. 8H, 9).