Bioelectric activity is required for regional specificity of sensory ganglion projections to spinal cord explants cultured in vitro.

Chronic blockade of spontaneous nerve impulses by means of tetrodotoxin leads to abnormally diffuse afferent projections into spinal cord cross-sections cultured for two to six weeks in vitro. In addition, even untreated explants which show a low level of spontaneous cord discharges failed to develop the normal degree of dorsal pathway selectivity. It is therefore concluded that centrally generated neuronal activity may play an important role in eliminating 'exuberant' connections which, during early development, are transiently present in this part of the nervous system.

Regional specificity of functional sensory connections in developing spinal cord cultures varies with the incidence of spontaneous bioelectric activity.

Cultured spinal cord explants in which little spontaneous bioelectric activity was present showed, when monitored using sensory ganglion-evoked monosynaptic action potentials, diffuse innervation by ingrowing afferent fibers at 3-4 weeks in vitro. In contrast, highly active cultures of the same age showed a strong tendency for functional sensory connections to be made within the dorsal half of the cord. Regional specificity was present in mature cultures (4-5 weeks in vitro), however, even when their spontaneous activity level was low. The results support earlier results using tetrodotoxin, and make it appear likely that centrally generated neuronal discharges can influence the topography of afferent terminals within the developing spinal cord.