title: 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.
abstract: 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.
authors: Brain and Behaviour Research Group, Department of Biology, Open University, Walton Hall, Milton Keynes, United Kingdom.
authors: T P
authors: TP
authors: Doubell
authors: M G
authors: MG
authors: Stewart
mesh_terms: D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D001362:Avoidance Learning / Q000502:physiology*; D002645:Chickens; D016548:Prosencephalon / Q000648:ultrastructure*; D013569:Synapses / Q000648:ultrastructure*; D013997:Time Factors