Functional development of guanine nucleotide binding protein (Gs) and catalytic subunit from embryonic day 17 to postnatal day 28 in whole rat brain homogenates, expressed as percentage of day 28 values. Basal rate of cAMP formation represents the unstimulated level. Sodium fluoride (NaF) and forskolin, believed to activate the Gs and catalytic subunit, respectively, show increasing stimulatory effects through development, roughly in parallel with the basal level. (Data from ref. 48)