Xenopus oocytes were injected with mRNA from adult or neonatal rat spinal cord, or from adult cerebral cortex, and examined electrophysiologically to measure currents elicited by various receptor agonists. The mRNAs induced the oocytes to acquire similar types of amino acid receptors, albeit with different potencies. In oocytes injected with adult cord mRNA the responses to kainate and gamma-aminobutyrate were much smaller, whilst the currents elicited by glycine and beta-alanine were markedly larger, than those in oocytes injected with cortex mRNA. For these receptors, the expressional potency of neonatal spinal cord mRNA is similar to that of the adult cord mRNA, except for a lower sensitivity to beta-alanine.