Why clozapine plus d-cycloserine backfires: excess extrasynaptic glutamate signalling in a rat NMDA hypofunction model
- In rats given prolonged MK-801 to mimic NMDA receptor hypofunction, the orbitofrontal cortex showed blunted stimulated glutamate and D-serine release, fewer GluN2A/GluN2B subunits, higher resting extracellular levels, and anhedonia-like behaviour.
- Clozapine or d-cycloserine alone rescued the behaviour and stimulated release without shifting resting levels or subunit expression.
- Together they pushed resting levels and receptor expression further up and worsened behaviour; adding memantine reversed this.
💡 Points Based on the abstract
The combination liability is the finding to chase here, more than the rescue. Resting extracellular glutamate rising while evoked release falls is a signal-to-noise problem, and it argues for caution with any NMDA co-agonist stacked on an antipsychotic. Still missing are a dose-response for the pair and evidence that memantine's benefit survives chronic dosing, since MK-801 rats are a blunt schizophrenia proxy.