GABA_A receptor composition in the rat. Figure illustrates changes of expression of alpha1 subunit mRNA during postnatal development of the rat. Expression gradually increases with postnatal (P) age (in days) in most areas of the brain. Note a peak of expression at postnatal day 21 (P21) of expression in most brain areas and subsequent decrease to adult values. Red color symbolizes very high expression, yellow and orange high and moderate expression and violet the low expression. Black color represents background level.