after its discovery in 1965, naag was disregarded as a neurotransmitter for several reasons. first, neuropeptides were not considered neurotransmitters until years later. second, it did not seem to directly affect membrane potential, so it was classified as a metabolic intermediate. the importance of brain peptides became clearer with the discovery of endogenous opioids. whereas the ability of naag to interact with nmda receptors in a manner relevant to physiology is controversial, its primary receptor was long believed to be the mglur3. its interaction with the mglur3 causes an activation of g proteins that reduce the concentration of the second messengers camp and cgmp in the both nerve cells and glia. this can lead to several changes in the cellular activity, including regulation of gene expression, reduction in the release of transmitter, and inhibition of long-term potentiation. stimulation of the mglur3 by naag has been, however, questioned, finding relevant glutamate contamination in commercially available naag.