Enhanced long-term depression in schizophrenia-associated TCF4 transgenic mice is NMDA receptor-mediated

Enhanced expression of transcription factor 4 (TCF4), driven by the schizophrenia-risk-associated single-nucleotide polymorphism rs9960767, has been linked to disturbances in neuronal plasticity and synaptic pruning. Previous studies using classical glass-electrode recordings showed that Tcf4 gain-of-function (Tcf4tg) mice exhibit enhanced long-term depression (LTD) in the hippocampus, a form of synaptic weakening that is critically involved in circuit refinement and has been implicated in the cognitive deficits observed in schizophrenia. The present study aimed to validate this LTD phenotype using a high-throughput three-dimensional multi-electrode array (MEA) platform and to pharmacologically dissect the underlying glutamatergic mechanisms.

Hippocampal slices were prepared from 4- to 6-week-old Tcf4tg mice and wild-type littermates in sucrose-based cutting solution, recovered in artificial cerebrospinal fluid, and positioned on 3D MEA chips (interelectrode distance 100 µm) under continuous perfusion and temperature control. LTD was induced by low-frequency stimulation (1 Hz for 15 min) of the Schaffer collateral–CA1 pathway. Field excitatory postsynaptic potentials (fEPSPs) were recorded continuously, and LTD magnitude was quantified as the post-induction / pre-induction fEPSP slope ratio (mean ± SD) 25–30 min after induction. Data were analysed using Wilcoxon rank sum test with statistical significance set at p < 0.05. To evaluate receptor contributions, parallel experiments included bath application of the competitive N-methyl-D-aspartate (NMDA) receptor antagonist (R)-CPP (10 µM), or the combined group I metabotropic glutamate receptor antagonists LY367385 (100 µM, mGluR1a-selective) and MPEP (40 µM, mGluR5-selective).

MEA recordings confirmed significantly enhanced LTD in Tcf4tg versus wild-type slices under control conditions (Tcf4tg: 0.58 ± 0.04, n=10; wild-type: 0.69 ± 0.04, n=10; p<0.05). Blockade of NMDA receptors with (R)-CPP produced robust inhibition of LTD induction in both genotypes (Tcf4tg: 0.79 ± 0.06, n=11, p<0.01 versus untreated Tcf4tg; wild-type: 0.84 ± 0.05, n=11, p<0.05 versus untreated wild-type). Importantly, the genotype difference observed under control conditions was fully eliminated in the presence of (R)-CPP (p=0.69). In contrast, simultaneous inhibition of mGluR1a and mGluR5 with LY367385 and MPEP attenuated LTD in both genotypes (Tcf4tg: 0.69 ± 0.04, n=11, p<0.05; wild-type: 0.82 ± 0.04, n=10, p<0.05), yet a significant difference between genotypes persisted (p<0.05), comparable in magnitude to that seen in untreated slices.

In conclusion, these electrophysiological findings validate the enhanced LTD phenotype in Tcf4 transgenic mice using an advanced MEA recording platform and establish that this augmentation is primarily mediated by NMDA receptor-dependent mechanisms. The complete rescue of the phenotype by NMDA receptor antagonism, contrasted with only partial normalisation by group I metabotropic glutamate receptor blockade, indicates that alterations in NMDA receptor signalling or closely associated intracellular cascades represent the dominant driver of TCF4-mediated plasticity disturbances. Given the established genetic association of TCF4 overexpression with schizophrenia risk, these data suggest that dysregulated NMDA receptor-dependent synaptic depression is a plausible contributor to the synaptic and cognitive pathophysiology of the disorder. NMDA receptor-related pathways therefore represent promising molecular targets for pharmacological strategies aimed at restoring synaptic homeostasis in TCF4-associated schizophrenia. Further studies are warranted to determine whether these mechanisms can be therapeutically modulated without compromising physiological plasticity.

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