Co-administration of monosialoganglioside and skeletal muscle cells on dorsal root ganglion neuronal phenotypes in vitro. 
The neuropeptide-immunoreactive (IR) and neurofilament-IR neurons are two major phenotypical classes in dorsal root ganglion (DRG).  Targets of neuronal innervation play a vital role in regulating the survival and differentiation of innervating neurotrophin-responsive neurons.  Monosialoganglioside (GM1) has been considered to have a neurotrophic factor-like activity.  Both GM1 and target skeletal muscle (SKM) cells are essential for the maintenance of the function of neurons.  However, whether target SKM cells and GM1, alone or associated, generate neuropeptide or neurofilament expression remains unclear.  The aim of the present study is to investigate the effects of GM1 or/and SKM on DRG neuronal phenotypes.  DRG neurons containing the neuropeptide substance P (SP) and neurofilament 200 (NF-200) were quantified using immunofluorescent labeling in cultures of DRG, which was dissected out at times before (at embryonic days 12.5, E12.5) and after (at E19.5) sensory neurons contact peripheral targets in vivo.  DRG neurons were cultured in absence or presence of GM1 or/and SKM cells.  In this experiment, we found that: (1) GM1 promoted expression of SP and NF-200 in E12.5 DRG cultures; (2) SKM cells promoted expression of NF-200 but not SP in E12.5 DRG cultures; (3) GM1 and target SKM cells had additive effects on expression of SP and NF-200 in E12.5 DRG cultures; and (4) SKM or/and GM1 did not have effects on expression of SP and NF-200 in E19.5 DRG cultures.  These results suggested that GM1 could influence DRG, two major neuronal phenotypes, before sensory neurons contact peripheral targets in vivo.  Target SKM cells could only influence neurofilament-expressed neuronal phenotype before sensory neurons contact peripheral targets in vivo.  GM1 and SKM cells had the additive effects on two major DRG neuronal classes, which express neuropeptide or neurofilament when DRG cells were harvested before sensory neurons contact peripheral targets in vivo.  These results offered new clues for a better understanding of the association of GM1 or/and SKM with neuronal phenotypes.