The Trophic Effect Of Endogenous NGF From Cat Spared Dorsal Root Ganglion On Ganglionic Neurons

Nerve growth factor (NGF) is a target-derived factor responsible for the survival, growth and differentiation of a subpopulation of sensory neurons in dorsal root ganglion ( DRG ) during embryonic development. NGF down-expressed significantly in target in adulthood. After partial deafferentation of spinal cord of adult cat, the expression of NGF in dorsal horn, which is the target area of dorsal root afferent fibers, up-regulated. It was thought to play an important role in inducing the spared root to collaterally sprout. Meanwhile, the expression of both of NGF and NGFmRNA in spared DRG up-regulted. It suggests that the endogenous NGF from spared DRG may take part in stimulating the spared root collateral sprouting.In order to probe the effect of endogenous NGF from normal DRG and spared DRG (rhizotomy of unilateral L1, L3, L5, L7 dorsal root), the present study was involved in the basic data of the neuronal number and the percentage of NGF as well as its' functional receptor trkA possitive neuron oflumbar DRG for adult cat; the expressional change of NGF within spared DRG and its'act mode; the effect of endogenous NGF from spared DRG on neurons inside the DRG, using H.E staining, immunohistochemistry single and double labeling, ELISA, cell culture methods. The results obtained were as follows:1. For adult male cat, there was no significant difference ( P>0.05 ) in the mean neuronal number of DRG between two sides in each lubmar segment. Two sides could be ipsilateral or control side.2. Comparing the neuronal number of every segment, the most one is L6 DRG and the least one is L7 DRG ( P<0.05 ) , the others have no significant difference ( P>0.05 ).3. There were some NGF-expression neurons and trkA-expression neurons in lumbar DRG of adult male cat. It suggests that endogenous NGF from DRG may act on a subpopulation of neurons inside the DRG. The percentage of positive neuron was similar in each segment ( P. >0.05 ).4. Some DRG neurons express both NGF and trkA, but some neurons and satellite cells express NGF only. This means endogenous NGF carried out function by endocrine and paracrine modes between neurons, neuron and satellite cell.5. The rhizotomy of partial dorsal roots resulting in up-expression of both NGF and trkA within spared DRG, suggests that the effect , mediated by trkA, of NGF may be improved in spared DRG.6. The numbers of survival neuron and neurite of spared DRG group were much more than those of control and anti-NGF antibody block groups, so was the neurite length ( P<0.05 ). This demonstrates the endogenous NGF from normal DRG play a role in maintaining the survival of DRG neuron and stimulating the out-growth of neurite. This kind of effect was significantly improved within spared DRG.In conclusion, taking the modes of endocrine and paracrine, mediated by trkA, the endogenous NGF from DRG play an important role in maintaining the survival of DRG neuron of adult male cat and stimulating the out-growth of neurite. This kind of effect was significantly improved within spared DRG after rhizotomy of partial dorsal roots. This maybe one of the factors which induce the collateral sprouting of spared dorsal root in spinal cord.