Taurine is important in neural tissue function as a neuromodulator or neurotransmitter. Taurine is also involved in the structural integrity of the retina, at least, because a deficiency causes this tissue to degenerate. The concentration of taurine in brain is very high in the fetus and the newborn compared to the adult, the decrease taking place slowly over the period of weaning. The purpose of this study is to examine the origin, mechanism of accumulation, and function of the high taurine concentrations found in fetal and newborn neural tissue of the subhuman primate. The Rhesus monkey has been shown to be similar to the human in many aspects of sulfur amino acid metabolism during development whereas lower animals exhibit marked differences from the human. The amount of taurine transferred to the brain and other tissues of the fetus and newborn will be determined by using radioactive taurine tracer. We shall assess the contribution via the placenta before birth, and the contribution via the mother's milk after birth. We will also study the distribution of taurine, both labelled and unlabelled in subcellular fractions of brain at various stages of development and attempt to distinguish any differences which may exist in such distributions between taurine supplied prenatally and postnatally. The specific functions of taurine will be investigated in selected neural tissue using biochemical measurements of its rate of synthesis, rate of turnover, rate of uptake, localization within specific organelles and effects on other biochemical reactions and cellular structures. The results of feeding the developing Rhesus monkey a diet containing no taurine (equivalent to the commercial formulas currently available for feeding human infants) will be examined. We shall investigate the severity of any taurine deficiency produced by assessing both chemical changes and pathologic changes. We hope to be able to assess whether or not there are any irreversible changes or damage caused by feeding such a diet and to apply this knowledge to help assess the possibility of imminent of long-term neurological dysfunction or mental retardation occurring in human infants fed such a formula.