Chronic dizocilpine (MK-801) reversibly delays GABAA receptor maturation in cerebellar granule neurons in vitro

Abstract: We investigated the effect of chronically blocking NMDA receptor stimulation to examine changes in GABAA receptor expression and pharmacology in cerebellar granule cells at different stages of maturation. We have previously shown that NMDA-selective glutamate receptor stimulation alters GABAA receptor pharmacology in cerebellar granule neurons in vitro by altering the levels of selective subunits. When NMDA receptor stimulation is blocked with MK-801 during the first week in vitro, a decrease in the α1, γ2S, and γ2L receptor subunit mRNAs occurred. When present only during the second week, changes were limited to the α1 and γ2L mRNAs. Finally, if MK-801 was present during the first week and removed during the second week, these changes reversed. Whole-cell voltage-clamp recordings showed that treatment with MK-801 during either the first or second week increased the EC50 of the receptors for GABA and attenuated the potentiation mediated by flunitrazepam. Last, these properties were reversed if MK-801 was removed after the first week in vitro. Our results suggest that MK-801 reversibly inhibits GABAA receptor maturation by modulating receptor subunit expression and that the altered pharmacological responses appear to be dominated by changes in the levels of allosteric modulation mediated by the γ2 receptor subunit.