Effect of auditory deafferentation on the synaptic connectivity of a pair of identified interneurons in adult field crickets

Abstract

In adult crickets, Teleogryllus oceanicus, unilateral auditory deafferentation causes the medial dendrites of an afferent‐deprived, identified auditory interneuron (Int‐1) in the prothoracic ganglion to sprout and form new functional connections in the contralateral auditory neuropil. The establishment of these new functional connections by the deafferented Int‐1, however, does not appear to affect the physiological responses of Int‐1's homolog on the intact side of the prothoracic ganglion which also innervates this auditory neuropil. Thus it appears that the sprouting dendrites of the deafferented Int‐1 are not functionally competing with those of the intact Int‐1 for synaptic connections in the remaining auditory neuropil following unilateral deaferentation in adult crickets. Moreover, we demonstrate that auditory function is restored to the afferent‐deprived Int‐1 within 4–6 days following deafferentation, when few branches of Int‐1's medial dendrites can be seen to have spouted. The strength of the physiological responses and extent of dendritic sprouting in the deafferented Int‐1 progressively increase with time following deafferentation. By 28 days following deafferentation, most of the normal physiological responses of Int‐1 to auditory stimuli have been restored in the deafferented Int‐1, and the medial dendrites of the deafferented Int‐1 have clearly sprouted and grown across into the contralateral auditory afferent field. The strength of the physiological responses of the deafferented Int‐1 to auditory stimuli and extent of dendritic sprouting in the deafferented Int‐1 are greater in crickets deafferented as juveniles than as adults. Thus, neuronal plasticity persists in Int‐1 following sensory deprivation from the earliest juvenile stages through adulthood.