Journal of Neuroscience, Vol 13, 2230-2236, Copyright © 1993 by Society for Neuroscience
Short-term changes in the numerical density of synapses in the intermediate and medial hyperstriatum ventrale following one-trial passive avoidance training in the chick
TP Doubell and MG Stewart
Brain and Behaviour Research Group, Department of Biology, Open University, Walton Hall, Milton Keynes, United Kingdom.
Previous ultrastructural studies using stereological counting techniques,
based on assumptions regarding shape, size, and orientation of synapses,
have suggested synaptic remodeling occurred at least 24 hr after one-trial
passive avoidance training in day-old chicks. The present study estimates
the mean synaptic density (Nv syn) in a region of the chick forebrain known
to be involved in memory formation, the intermediate and medial
hyperstriatum ventrale (IMHV), 1 and 24 hr following one-trial passive
avoidance training. A stereological technique, the "disector," that makes
no assumptions about size, shape, and orientation of synapses was used in
the synaptic analyses. The density of axospinous synapses increased by
approximately 77% at 1 hr posttraining in the right IMHV of chicks
(M-trained) that learned to avoid a bitter-tasting bead, compared to those
(W-trained controls) that peck a water-coated bead. A measure of the
postsynaptic density size, the mean projected height of synapses (H), was
57% smaller 1 hr posttraining in the right IMHV of M-trained chicks. These
differences were not found at 24 hr posttraining. We suggest that
structural modification of synapses may be a key part of the processes
involved in short-term memory formation.
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