Peripheral and Central Target Requirements for Survival of Embryonic Rat Dorsal Root Ganglion Neurons in Slice Cultures

Abstract

Developmental cell death in the nervous system usually is controlled by the availability of target-derived trophic factors. It is well established that dorsal root ganglia (DRG) neurons require the presence of their peripheral target for survival, but because of their central projections, it is possible that the spinal cord also may be required. Before examining this possibility in rat embryos, we first used terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) to determine that thoracic DRG cell death occurred from embryonic day 15 (E15) to E18. To determine the target requirements of DRG neurons, we used organotypic slice cultures of E15 thoracic trunk segments. After peripheral target removal, essentially all DRG neurons disappeared within 5 d. In contrast, after removal of the spinal cord, approximately half of the DRG neurons survived for at least 8 d. Hence, some E15 DRG neurons could survive without the spinal cord. However, those DRG neurons that died after spinal cord ablation apparently required trophic factors from both central and peripheral targets, because the presence of only one of these tissues was not adequate by itself to support this cell group. Addition of neurotrophin-3 (NT-3) to the culture medium rescued some DRG neurons after CNS removal, suggesting a possible role for NT-3 in vivo. In other experiments, cultures were established from older (E16) embryos, and essentially all neurons survived after spinal cord ablation, even without added factors. These and other experiments indicated that ϳ65% of DRG neurons are transiently dependent on the CNS early in development.

A Sensory Neuron Subpopulation with Unique Sequential Survival Dependence on Nerve Growth Factor and Basic Fibroblast Growth Factor during Development

“…Their requirement of NGF better correlates with the period of naturally occurring death, which peaks between E15 and E19, and is over just after birth. This conforms to the more recent notion that NGF is required by embryonic sensory neurons during the period of massive neuronal death, supplied by sources other than the peripheral targets, before their innervation (Coggeshall et al, 1994;Davies, 1997;Wetts and Vaughn, 1998). Accordingly, Trk genes (receptors for neurotrophins) are expressed early in development (Mu et al, 1993).…”

Adult Sensory Neurons Regenerate Axons Through Adult CNS White Matter: Implications for Functional Restoration After SCI

“…1. They do not require the addition of growth factors such as neurotrophins for survival after axotomy, 22 and they survive well suspended in minimal essential tissue culture media. 2.…”