Journal of Neuroscience, Vol 6, 2012-2018, Copyright © 1986 by Society for Neuroscience
Effects of nerve growth factor on the survival and synaptic function of Ia sensory neurons axotomized in neonatal rats
Y Miyata, Y Kashihara, S Homma and M Kuno
Sensory neurons with small diameters (A delta and C cells) are known to be
responsive to exogenous NGF even at postnatal stages. We have examined
whether large Group Ia sensory neurons (A alpha cells) arising from muscle
spindles are also responsive to NGF in neonatal rats. For this purpose,
monosynaptic excitatory postsynaptic potentials (EPSPs) were evoked in
spinal motoneurons by Group Ia muscle afferent volleys. When a muscle nerve
was crushed on the day after birth, the monosynaptic EPSPs elicited by
afferent volleys from the muscle were depressed within several weeks. This
synaptic depression was partially reversed by daily treatment with NGF. NGF
treatment also enhanced the EPSPs evoked by stimulation of intact muscle
nerves, but this effect was less marked than that on the EPSPs produced by
stimulation of the previously crushed muscle nerve. Exogenous NGF was
effective for the EPSPs when the treatment began on the day after birth but
not when the treatment began 4 d after birth. Following crush of a muscle
nerve on the day after birth, about 45% of the sensory neurons derived from
the muscle were lost. The cell death of small sensory neurons was prevented
by daily treatment with NGF, whereas the NGF treatment was ineffective in
preventing the cell death of large sensory neurons. The results indicate
that Group Ia sensory neurons are responsive to NGF during early postnatal
life.