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.