Development and plasticity of the inhibitory neocortical circuitry with an emphasis on the rodent barrel field cortex: a review.

The present paper reviews current knowledge of the development and plasticity of the inhibitory gamma-aminobutyric acid (GABA) containing circuitry of the cerebral neocortex, in particular, the rat somatosensory barrel field cortex. Recent studies reveal a delayed and protracted maturation of the inhibitory compared with the excitatory cortical system, both at the neuronal and synaptic levels. This characteristic developmental pattern leaves a longer time window during which behaviourally relevant activity coming from the periphery can influence the organization of the GABA system. Indeed, sensory deprivation experiments confirm the involvement of the GABA system in phenomena of experience-dependent cortical plasticity. Changing the pattern and level of afferent activity of in the rat somatosensory system during development by removing vibrissae results in a significant decrease in the number of GABA neurons and synapses in the thalamocortical recipient layer IV. Particularly affected are GABA synapses contacting dendritic spines, the number of which decreases by almost two-thirds. The involvement of the GABA system in events of experience-dependent plasticity contributes to the adequate functioning of the cerebral cortex in the conditions of constantly changing environment and varying individual experience.