A sensory neuron subpopulation with unique sequential survival dependence on NGF and bFGF during development

CRISTIAN ACOSTA; ANDRÉS FÁBREGA; DANIEL MASCÓ; HÉCTOR LÓPEZ

JOURNAL OF NEUROSCIENCE

SOC NEUROSCIENCE

Lugar: Washington; Año: 2001 vol. 21 p. 8873 - 8885

0270-6474

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 DiIC18 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.