Competitive interactions between supernumerary and normal sensory neurons
in the cockroach are mediated through a change in quantal content and not
quantal size.
Sosa, Maria A. and Jonathan M. Blagburn.
Institute of Neurobiology and Department of Physiology, University of
Puerto Rico, 201 Blvd. del Valle, Old San Juan, PR 00901.
APStracts 2:0171N, 1995.
Summary and Conclusions
1. The final steps in synapse formation and stabilization involve the
adjustment of strength of connections through competitive interactions between
neurons contacting a common target. The mechanisms underlying this
competition-driven adjustment of synaptic strength are not well understood. We
have studied one aspect of this phenomenon using the cercal sensory system of
first instar cockroach nymphs. 2. Quantal analysis of excitatory postsynaptic
potentials (EPSPs) recorded at the synapse between the lateral filiform hair
sensory neuron (L) and giant interneuron 3 (GI3) was carried out to determine
whether the reduction in EPSP amplitude observed in the presence of an
additional sensory neuron ("Space Invader Neuron", SIN) was due to pre- or
postsynaptic changes. 3. Mean quantal content, not quantal size, was reduced
at the L-GI3 synapse in the presence of SIN. Fitting binomial distributions to
the EPSP amplitude histograms gave estimates of n and p. The reduction in
quantal content is associated with a decrease in the binomial parameter n and
not p, suggesting that there is a decrease in the number of contacts, release
sites or quanta available for release, rather than a change in probability of
release.
Received 15 March 1994; accepted in final form 25 May 1995.
APS Manuscript Number J173-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 June 1995.