[3H]MK-801 binding in immature and mature chicken forebrain.

Previous studies have shown that the rate of calcium uptake stimulated by N-methyl-D-aspartate (NMDA) increased during the maturation phase of synapse development in chicken forebrain. To investigate whether this change in function is due to a change in the properties of NMDA receptor associated ion channels, we measured the binding of [3H]MK-801 (a ligand which binds to the NMDA receptor associated ion channel) to membranes from immature and mature chicken brain. The binding properties of MK-801 in chicken brain were similar to those in mammalian brain. There was no significant difference in any of the binding parameters measured at the two ages, i.e. KD, Bmax and optimal glutamate concentration for and maximal enhancement by glutamate of MK-801 binding. These results suggest that there is no change in the NMDA operated ion-channels during maturation. Thus the maturational change in NMDA receptor function could be due to: a change in the agonist portion of the NMDA receptor, a change in the regulation of the receptor/ionophore complex, perhaps by the postsynaptic density whose structure and composition changes during the same period, or a change in the number of voltage-sensitive calcium channels recruited as a result of NMDA receptor activation.