The use of fetal mouse spinal cord-dorsal root ganglion explants to study the factors underlying selective connections in vitro.

Dorsal root ganglion (DRG) afferents selectively project to dorsal spinal cord (SC) explants when grown in a medium containing serum or a serum-free medium (CDM) containing galactose compounds. SC-DRG explants grown in CDM retain their gross morphological characteristics over several months in vitro, greatly facilitating the mapping of the sensory afferents within given regions of the cord explant. Explants grown in CDM without the addition of galactose show no such selective preference for dorsal cord, and terminate equally throughout the cord. This lack of selectivity also occurs in galactose-grown SC-DRG provided tetrodotoxin (TTX) is added to the medium sufficient to block all recordable spontaneous bioelectric activity (SBA), viz., action potential discharges and slow waves. Gangliosides are galactose-containing compounds found in neural membranes which may be involved in cell-cell recognition/adhesion. The addition of a mixture of gangliosides to the CDM results in the preferential restriction of the sensory afferents within the dorsal cord regions even in the presence of TTX. It is concluded that gangliosides may be able to compensate for the absence of SBA during periods of development associated with the formation of selective interneuronal connections.