In Vivo Evidence for the Link Between l‐ and d‐Serine Metabolism in Rat Cerebral Cortex

Abstract: To obtain an insight into the metabolic pathways of endogenous d ‐serine in mammalian brains, we have investigated in the infant rat the effects of systemic administration of l ‐serine, d ‐serine, and related amino acids, including glycine and threonine, on the amino acid contents in the cerebral cortex. Intraperitoneal injection of l ‐serine induced a rapid and transient elevation of the levels of l ‐serine itself in the neocortex, with its peak at 3 h post injection, and a delayed and prolonged increase in d ‐serine contents from 1.5 h to at least 24 h thereafter. Similarly, a significant augmentation in cerebral d ‐serine contents was observed 6 h after intraperitoneal administration of glycine, which also elevated the cortical l ‐serine levels. In contrast, l ‐threonine injection affected the concentrations of neither d ‐ nor l ‐serine in the cortex of the pups. d ‐Serine given systemically, in turn, increased the neocortical contents of l ‐serine as well as d ‐serine itself, but failed to alter those of glycine and l ‐threonine. These in vivo data suggest the possible link between metabolic pathways of d ‐ and l ‐serine in the cerebral cortex of the rat.