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

Abstract

We characterized a subpopulation of dorsal root ganglion (DRG) sensory neurons that were previously identified as preferential targets of enkephalins. This group, termed P-neurons after their "pear" shape, sequentially required nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) for survival in vitro during different developmental stages. Embryonic P-neurons required NGF, but not bFGF. NGF continued to promote their survival, although less potently, up to postnatal day 2 (P2). Conversely, at P5, they needed bFGF but not NGF, with either factor having similar effects at P2. This trophic switch was unique to that DRG neuronal group. In addition, neither neurotrophin-3 (NT-3) nor brain-derived neurotrophic factor influenced their survival during embryonic and postnatal stages, respectively. The expression of NGF (Trk-A) and bFGF (flg) receptors paralleled the switch in trophic requirement. No single P-neuron appeared to coexpress both Trk-A and flg. In contrast, all of them coexpressed flg and substance P, providing a specific marker of these cells. Immunosuppression of bFGF in newborn animals greatly reduced their number, suggesting that the factor was required in vivo. bFGF was present in the DRG and spinal cord, as well as in skeletal muscle, the peripheral projection site of P-neurons, as revealed by tracer DiIC(18)3. The lack of requirement of NT-3 for survival and immunoreactivity for the neurofilament of 200 kDa distinguished them from muscle proprioceptors, suggesting that they are likely to be unmyelinated muscle fibers. Collectively, their properties indicate that P-neurons constitute a distinct subpopulation of sensory neurons for which the function may be modulated by enkephalins.

In vitro comparison of motor and sensory neuron outgrowth in a 3D collagen matrix

“…Embryonic neurons have a higher intrinsic capacity to grow than adult neurons, and adult neurons need trophic factor support to survive (Montoya et al, 2009). In contrast, spinal cord explants from P7 rats can be maintained for relatively long-term on media without additional growth factors (Acosta et al, 2001;Guzman-Lenis et al, 2009a;Lowry et al, 2001;Rakowicz et al, 2002). Moreover, some intrinsic promoters of regeneration (as cAMP levels or integrin expression) are already normalized to the adult levels at this postnatal time (Domeniconi and Filbin, 2005;Lemons et al, 2008).…”

Angiopoietin-1 promotes neurite outgrowth from dorsal root ganglion cells positive for Tie-2 receptor

“…nerve growth factor (NGF), brain-derived growth factor, neurotrophins 3 and 4, and acidic and basic fibroblast growth factor (Ernforns et al 1995;Baird 1994;Kerkes et al 1994) among which NGF represents the most familiar molecule (Levi-Montalcini 1987). NGF supports not only the survival of approximally 80% of dorsal root ganglion (DRG) neurons during the embryonic and the early postnatal periods (Minichiello et al 1995;Baudet et al 2000;Acosta et al 2001), but also axonal elongation of neuronal subpopulations in DRG explants (Edstrom and Ekstrom 2003). In vitro, both the survival and the elongation of neurites are dependent on NGF binding to the p75 neurotrophin receptor (p75NTR) of low affinity or to the trkA receptor of high affinity.…”

Bacterial lipopolysaccharide regulates nociceptin expression in sensory neurons

“…Sensory neurons from DRG of embryonic, newborn, and adult CD‐1 mice were isolated as described previously (Acosta and Lopez, 1999; Acosta et al, 2001). Briefly, DRG were enzymatically dissociated by incubation for 15–45 min (depending on age) with 0.25% trypsin and 1.25% collagenase at 37°C (Worthington, Lakewood, NJ).…”

“…Purified P60 DRG neurons were plated in 200‐μl video microscopy chambers (Acosta et al, 2001) and incubated with nerve growth factor (NGF). After 24 hr, the cells were washed and exposed for 30 min at 37°C to 1 μg/ml LPS serotype 055:B5 tagged with Alexa‐568 (Molecular Probes, Eugene, OR) alone or in combination with 50ng/ml recombinant lipid‐binding protein (Biometec, Greifswald, Germany).…”