Effects of chronic suppression of bioelectric activity on the development of sensory ganglion evoked responses in spinal cord explants.

Dorsal root ganglion (DRG) afferent terminals were identified, using electrophysiological techniques, within fetal mouse spinal cord cross-sections cultured in vitro. Afferent distribution patterns were monitored in explants grown for 3 to 6 weeks either in a serum-supplemented or in a serum-free, chemically defined medium (CDM). Bioelectrically active control explants from both series were compared with explants which had been reversibly silenced by chronic exposure to tetrodotoxin (TTX). The control (serum-grown) cultures showed a significant dorsal cord innervation preference, whereas in the corresponding TTX series there was an equal dorsoventral distribution. In the CDM series the mean number of DRG evoked responses was lower at first in TTX-grown than in control cultures, but with age in vitro there was a rise in excitability to normal levels. Spontaneous neuronal activity was abnormally low in cultures (serum as well as CDM-grown) which had been exposed to TTX. It is concluded that bioelectric activity may be an important factor in the proper regulation of synaptic connectivity and functional responsiveness in the developing spinal cord.