Optimization of somatic inhibition at critical period onset in mouse visual cortex.

Local GABAergic circuits trigger visual cortical plasticity in early postnatal life. How these diverse connections contribute to critical period onset was investigated by nonstationary fluctuation analysis following laser photo-uncaging of GABA onto discrete sites upon individual pyramidal cells in slices of mouse visual cortex. The GABA(A) receptor number decreased on the soma-proximal dendrite (SPD), but not at the axon initial segment, with age and sensory deprivation. Benzodiazepine sensitivity was also higher on the immature SPD. Too many or too few SPD receptors in immature or dark-reared mice, respectively, were adjusted to critical period levels by benzodiazepine treatment in vivo, which engages ocular dominance plasticity in these animal models. Combining GAD65 deletion with dark rearing from birth confirmed that an intermediate number of SPD receptors enable plasticity. Site-specific optimization of perisomatic GABA response may thus trigger experience-dependent development in visual cortex.