Number and size of neurons and synapses in the motor cortex of cats raised in different environmental complexities

In a previous study we have shown that the richness of the environment affects the number of neurons, the size of their nuclei, the number of round‐asymmetrical synapses per neuron, the numerical density (number per unit volume; Nv) of flat‐symmetrical synaptic contacts, their number per neuron and their size in the visual cortex of cats. Of these, the number of flat‐symmetrical synapses per unit volume is particularly affected (there are nearly twice as many per mm3 in the impoverished cortex). Several studies in the rat have shown that environmentally induced changes in cortical thickness occur in the occipital regions but are much smaller or absent in the frontal regions. In order to determine if the cat motor cortex is also resistant to environmental changes, we have estimated the number and size of neurons and of synapses in individual laminae of motor cortex, area 4γ, in six pairs of cats raised either in a colony (EC: enriched condition) or in isolation (IC: impoverished condition).

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