Nerve growth factor counteracts the neurophysiological and neurochemical effects of chronic sciatic nerve section

The sciatic nerve was sectioned unilaterally in rats and nerve growth factor (NGF) applied locally to the nerve stump for the following 10-14 days using an indwelling osmotic pump. The aim of the experiment was to test whether NGF had any effect on the previously reported neurophysiological and neurochemical events that occur central to a peripheral nerve lesion. The method of application allowed the sciatic nerve on the other side to be used as a control. Primary afferent depolarization fell, as expected, to 13% of its control value after chronic nerve section but if NGF was administered it fell to only 43.5% of control. Chronic nerve section is also known to result in expansion of the receptive fields of deafferented dorsal horn cells. NGF treatment reduced the number of such large receptive fields by 50%. The normal depletion of fluoride resistant acid phosphatase from the cut nerve terminals in the dorsal horn did not occur following NGF treatment. Radioimmunoassay of substance P revealed that the 30% reduction in dorsal horn levels that follows chronic sciatic nerve section did not occur when NGF was applied and that the accompanying 60% decrease in dorsal root ganglion levels was changed to a 64% increase by NGF. The results show that chronic NGF treatment of a cut sciatic nerve does partially reverse the central changes that normally follow deafferentation.