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Synaptogenesis and Fos expression in the motor cortex of the adult rat after motor skill learning - PubMed

  • ️Mon Jan 01 1996

Synaptogenesis and Fos expression in the motor cortex of the adult rat after motor skill learning

J A Kleim et al. J Neurosci. 1996.

Abstract

Recent work has suggested that changes in synapse number as well as changes in the expression of the Fos protein may occur within the motor cortex in association with motor learning. The number of synapses per neuron and the percentage of Fos-positive neurons within layer II/III of the rat motor cortex was measured after training on a complex motor learning task. Adult female rats were allocated randomly to either an acrobatic condition (AC), a motor control condition (MC), or an inactive control condition (IC). AC animals were trained to traverse a complex series of obstacles, and each AC animal was pair matched with an MC animal that traversed an obstacle-free runway. IC animals received no motor training. Animals from each condition were killed at various points during training, and unbiased stereological techniques were used to estimate the number of synapses per neuron and the percentage of Fos-positive cells within layer II/III of the motor cortex. AC animals exhibited an overall increase in the number of synapses per neuron in comparison to MC and IC animals at later stages of training. AC animals also had a significantly higher overall percentage of Fos-positive cells in comparison to both controls, with a trend for the increase to be greater during the acquisition versus the maintenance phase. These data suggest that Fos may be involved in the biochemical processes underlying skill acquisition and that motor learning, as opposed to motor activity, leads to increases in synapse number in the motor cortex.

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Figures

Fig. 1.
Fig. 1.

Two serial electron micrographs (11,000×) taken within layer II/III of the motor cortex. Synapse density was determined using the physical disector method. Synapses, within an unbiased counting frame, present in the reference section but not the lookup section (arrows), were counted.

Fig. 2.
Fig. 2.

Photomicrographs of three focal planes through a section of motor cortex labeled immunohistochemically with the Fos antibody and counterstained with the Pyronin Y Nissl stain. An unbiased counting frame was positioned randomly across layer II/III of the motor cortex, and at each position a focal plane was passed slowly through the section. Fos-positive cells were identified as having a black immunoprecipitate within the cell nucleus. The total number of cells, both Fos-positive (+) and -negative (−), were counted, and the percentage of Fos-positive cells was determined.

Fig. 3.
Fig. 3.

Performance on the acrobatic task (± SEM) for all animals. The mean time/trial/task decreased significantly as training progressed. Numbers indicate days on which animals from each of the three conditions were killed.

Fig. 4.
Fig. 4.

Mean number of synapses per neuron (± SEM) within layer II/III of the motor cortex during training as determined by dividing synapse density per cubic millimeter by neuronal density per cubic millimeter. Animals killed on day 1 or 2 (AC,n = 9; MC, n = 9;IC, n = 10) were considered to be in the acquisition phase, and animals killed on day 5, 10, or 20 (AC, n = 13; MC,n = 15; IC, n = 13) were considered to be in the maintenance phase. Asterisk, AC animals (n = 22) had overall significantly more synapses per neuron than both the MC (n = 24) and IC (n = 23) animals (Student–Neuman–Keuls test;p < 0.05); double asterisk, AC animals during the maintenance phase had significantly more synapses per neuron than all other conditions in either phase (Student–Neuman–Keuls test;p < 0.05).

Fig. 5.
Fig. 5.

Percentage of Fos-positive cells (± SEM) in all three conditions at five different points during training.Asterisk, AC animals (n = 25) had a significantly greater percentage of Fos-positive cells than both the MC (n = 25) and IC (n = 24) groups. No significant differences were found across the acquisition and maintenance phases of training.

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