NT-3 Increases Amplitude of EPSPs Produced by Axotomized Group Ia
Afferents.
JB Munson, RD Johnson and LM Mendell.
Department of Neuroscience, College of Medicine and Brain Institute,
University of Florida, Gainesville, Florida 32610.
APStracts 4:0030N, 1997.
ABSTRACT
In adult cats we tested the hypothesis that neurotrophin-3 (NT-3) can rescue
the central synapses made by muscle afferents from the effects of peripheral
axotomy. The medial gastrocnemius (MG) muscle nerve in cats was axotomized and
capped or axotomized and the distal end provided with saline or NT-3 by mini-
osmotic pump. Four to five weeks later monosynaptic EPSPs elicited by
electrical stimulation of the axotomized MG nerve were recorded in intact
lateral gastrocnemius/soleus (LGS) motoneurons. The axotomized MG afferents
without NT-3 treatment generated EPSPs averaging half the amplitude of those
generated by normal intact MG afferents. Axotomized MG afferents treated with
NT-3 elicited EPSPs averaging 2.5 times normal amplitude and 5 times the
amplitude of those from afferents axotomized but not treated. The very large
EPSPs generated by NT-3-treated afferents remained as susceptible to
depression during high-frequency stimulation (32 shocks at 167 HZ) as those
elicited by untreated axotomized afferents. The arrival of the afferent volley
of the cord dorsum potential and the onset of EPSPs were both delayed by
axotomy of the group Ia afferents and were both restored by exposure to NT-3.
This suggests that the calibre and thus the conduction velocity of group Ia
afferents are also controlled by NT-3. We conclude that the neurotrophin NT-3
has a continuing role in the maintenance of physiological function of muscle
afferents in adult mammals.
Received 24 October 1996; accepted in final form 10 January 1997.
APS Manuscript Number J842-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 5 February 1997