GABA, taurine and hypotaurine in developing mouse brain.

The cerebral concentrations and synaptosomal uptake of taurine and hypotaurine, two putative neuromodulators, were compared with those of GABA, an established neurotransmitter, in developing mice starting from the birth until 3 months of age. The taurine and hypotaurine contents of blood serum and the sodium-independent binding of GABA and taurine to synaptic membranes were also monitored. In the brain the maximum concentration level was reached for taurine at one week, for hypotaurine at 3 weeks, and for GABA at 4 weeks of age. In the serum the hypotaurine content was maximal in the youngest mice (1-week-old) and the taurine concentration during the three first weeks of life. The uptakes of GABA, taurine and hypotaurine were also high during the first three weeks of age, subsequently declining to a constant level. GABA binding to brain membranes was highest at 2 weeks of age. Taurine binding was also higher in the immature than in the adult brain. These developmental alterations suggest that GABA, taurine and hypotaurine are already functionally active in the brain in early postnatal life.