Most integral membrane proteins are modified post-translationally by addition of oligosaccharide chains of varying length and composition. For ionotropic glutamate receptors, this serves as a key mechanism to facility folding of these complex structures in the endoplasmic reticulum. We discovered recently that the chemical composition of the attached oligosaccharides have the potential to impact receptor gating directly and thereby represent an unexpected and novel source of functional diversity controlled by post-translationally mechanisms. Moreover, certain sugar isoforms serve as binding sites for a family of allosteric modulatory proteins known as galectins, which have poorly defined roles in CNS function. Because galectins are secreted by cancer cells, including gliomas, we speculate that they could alter neuronal function in peritumoral areas in the CNS, which would be consistent with the known network hyperexcitability and propensity to act as seizure foci. More generally, the relevance of galectins to normal and pathological CNS function is not well characterized and is an area of our current research efforts.