Comparison of the neuritogenic activity of cyclic nucleotides and skeletal muscle-conditioned medium on ciliary ganglia in vitro.
The parasympathetic ciliary ganglion (CG) of the embryonic chick in vitro, is unresponsive to Nerve Growth Factor and has been reported to form neurites only in response to neurotrophic factors derived from striated muscle or optic tissues. We investigated a possible role of cyclic adenosine-3',5'-monophosphate (cAMP) in the neurotrophic activity of skeletal muscle-conditioned medium (SCM) on CG explants. We showed that treatment with cAMP or dibutyryl cAMP stimulated neuritogenesis of CG explants in a dose-dependent fashion. SCM and cyclic nucleotide stimulation produced distinctly different types of neuritic growth. The growth cones of SCM-stimulated neurites were observed consistently to contact other cells or processes whereas nucleotide-stimulated neurites were not associated with other cells. These observations suggested that the two neuritogenic agents do not act through identical mechanisms, a conclusion supported by experiments demonstrating that stimulation of the CG with dibutyryl cAMP enhanced ornithine decarboxylase (ODC) activity relative to controls, whereas stimulation with SCM had no effect on ODC activity. We conclude that although cAMP does exhibit neuritogenic activity on the CG in vitro, it does not appear to be involved directly in the neurite formation elicited by SCM. It is feasible that the two types of neuritic growth which we described are representative of the two populations of CG neurons. Because only one of these neuronal populations innervates striated muscle in vivo, SCM and cAMP might act on different neurons.
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D002478:Cells, Cultured; D002642:Chick Embryo; D003470:Culture Media; D000242:Cyclic AMP / Q000494:pharmacology*; D005726:Ganglia, Parasympathetic / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D009132:Muscles / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009955:Ornithine Decarboxylase / Q000378:metabolism
D003470:Culture Media; D003994:Bucladesine; D000242:Cyclic AMP; D009955:Ornithine Decarboxylase