Summary

Neurons can be categorized in terms of where their axons project: within the central nervous system, within the peripheral nervous system, or through both central and peripheral environments. Examples of these categories are cerebellar neurons, sympathetic neurons, and dorsal root ganglion (DRG) neurons, respectively. When explants containing one type of neuron were placed between cryosections of neonatal or adult sciatic nerve and neonatal spinal cord, the neurites exhibited a strong preference for the substrates that they would normally encounter in vivo: cerebellar neurites generally extended only on spinal cord, sympathetic neurites on sciatic nerve, and DRG neurites on both. Neurite growth from DRG neurons has been shown to be stimulated by neurotrophins. To determine whether neurotrophins might also affect the substrate preferences of neurites, DRG were placed between cryosections of neonatal spinal cord and adult sciatic nerve and cultured for 36 to 48 hours in the presence of various neurotrophins. While DRG cultured in NGF-containing media exhibited neurite growth over both spinal cord and sciatic nerve substrates, in the absence of neurotrophins DRG neurites were found almost exclusively on the CNS cryosection. To determine whether these neurotrophin-dependent neurite patterns resulted from the selective survival of subpopulations of DRG neurons with distinct neurite growth characteristics, a type of rescue experiment was performed: DRG cultured in neurotrophin-free medium were fed with NGF-containing medium after 36 hours in vitro and neurite growth examined 24 hours later; most DRG exhibited extensive neurite growth on both peripheral and central nervous system substrates.(ABSTRACT TRUNCATED AT 250 WORDS)