Sulfur Amino Acid Metabolism in the Developing Rhesus Monkey Brain: Subcellular Studies of Taurine, Cysteinesulfinic Acid Decarboxylase, γ‐Aminobutyric Acid, and Glutamic Acid Decarboxylase

Abstract

Taurine, cysteinesulfinic acid decarboxylase (CSAD), glutamate, gamma-aminobutyric acid (GABA), and glutamic acid decarboxylase (GAD) were measured in subcellular fractions prepared from occipital lobe of fetal and neonatal rhesus monkeys. In addition, the distribution of [35S]taurine in subcellular fractions was determined after administration to the fetus via the mother, to the neonate via administration to the mother prior to birth, and directly to the neonate at various times after birth. CSAD, glutamate, GABA, and GAD all were found to be low or unmeasurable in early fetal life and to increase during late fetal and early neonatal life to reach values found in the mother. Taurine was present in large amounts in early fetal life and decreased slowly during neonatal life, arriving at amounts found in the mother not until after 150 days of age. Significant amounts of taurine, CSAD, GABA, and GAD were associated with nerve ending components with some indication that the proportion of brain taurine found in these organelles increases during development. All subcellular pools of taurine were rapidly labeled by exogenously administered [35S]taurine. The subcellular distribution of all the components measured was compatible with the neurotransmitter or putative neurotransmitter functions of glutamate, GABA, and taurine. The large amount of these three amino acids exceeds that required for such function. The excess of glutamate and GABA may be used as a source of energy. The function of the excess of taurine is still not clear, although circumstantial evidence favors an important role in the development and maturation of the CNS.

Functional Expression and Subcellular Localization of the Taurine Transporter TauT in Murine Neural Precursors

“…Taurine levels are markedly high in the immature brain as compared with the adult brain [Rassin et al, 1981;Sturman, 1993;Miller et al, 2000]. This decline is a consistent feature observed among species, regardless of their differences in taurine concentration.…”

“…No evidence of mRNA for cysteine dioxygenase or cysteine sulfinate decarboxylase is found in glia or neurons of the developing rodent brain [Rassin et al, 1981;Fujita et al, 2006]. Only in differentiated astrocytes, some cysteine sulfinate decarboxylase activity has been detected [Reymond et al, 1996].…”

Polarized glucose transporters and mRNA expression properties in newly developed rat syncytiotrophoblast cell lines, TR‐TBTs

“…Therefore, the demand for GABA by fetus may increase from the second to the third trimester. In fact, it has been reported that the GABA concentration is low or unmeasurable during early fetal life and increases during late fetal development and early neonatal life to reach values found in the mother; it may also be used in development of the fetal central nervous system (Rassin et al, 1981). It has been reported that, in rat, there are four GABA transporters, GAT‐1 ∼ 3 for neuronal and glial cell types, and BGT‐1 for the kidney type (Borden, 1996).…”

The Differential Effects of GABA‐Transaminase Inactivation in the Chick Retina and Brain

“…In contrast, the activity of the retinal enzyme did not decrease at all. The interpretation of these results is interesting in light of the current debate as to whether cysteinesulfinate decarboxylase is an en-zyme separate from glutamate decarboxylase (Rassin et al, 1981). Our experiments show that in the retina the two enzymatic activities are very likely distinct.…”