Journal of Neuroscience, Vol 7, 236-243, Copyright © 1987 by Society for Neuroscience
Ultrastructural evidence related to presynaptic inhibition of primary muscle afferents in Clarke's column of the cat
B Walmsley, E Wieniawa-Narkiewicz and MJ Nicol
As part of an investigation on excitatory synaptic transmission in the
mammalian CNS, we have examined ultrastructural details of the synaptic
connection between primary afferent fibers and dorsal spinocerebellar tract
(DSCT) neurons in Clarke's column of the cat spinal cord. Single primary
muscle afferents (group Ia and Ib) and DSCT neurons were identified and
stained intracellularly with HRP. The terminations of these afferent fibers
were examined in serial sections under the EM. Five of 6 Ib boutons and 1
of 14 Ia boutons were contacted by small presynaptic boutons. An example
was illustrated in which only 1 out of 7 boutons arising from the same Ia
fiber and contacting the same postsynaptic DSCT neuron was contacted by a
presynaptic bouton. It is likely that the presynaptic contacts are
responsible for presynaptic inhibition of synaptic transmission between
primary afferents and DSCT neurons. We have proposed that the observed
differences in presynaptic contacts from bouton to bouton may be one of the
causes of a nonuniformity in the probability of transmitter release between
release sites at this connection.