Prodromal changes in cortical neuron physiology before amyloid pathology in a mild model of Alzheimer's disease.

The heterozygous NLGF mouse is considered a mild model of Alzheimer’s disease (AD), closely reflecting the gradual progression observed in humans, compared to more aggressive homozygous models (APP/PS1, 5xFAD, NLGF). Using whole-cell patch-clamp recordings, we examined neocortical neuron properties during prodromal (P40-P90; pre-plaque) and early-symptomatic (P200) stages. Following plaque emergence (P200), NLGF+ neurons exhibited a depolarized resting membrane potential, enhanced hyperpolarization-activated currents (Ih), and increased action potential firing. Recordings of spontaneous inputs revealed reduced EPSC amplitude, elevated EPSC frequency, and heightened susceptibility to 4-aminopyridine (4-AP, 100 µM)-induced epileptiform activity. This hyperexcitability was more effectively suppressed by gap junction blockade with carbenoxolone (CBX, 50 µM), suggesting strengthened electrical coupling in AD mice. Calcium imaging in primary cortical cultures showed elevated spontaneous activity in NLGF+ neurons. NMR-based metabolomic profiling of whole-brain tissue showed no consistent genotype-dependent differences in neurotransmitter or amino acid levels (glutamate, GABA, choline, glycine, adenosine, etc.). Together, these results identify increased sensitivity to 4-AP and CBX as early functional signatures of circuit dysfunction in this mild AD model, highlighting potential biomarkers and therapeutic targets that emerge prior to irreversible amyloid pathology. Notably, at the earliest pre-plaque stage (P40-90), there is an elevated baseline EPSC frequency, and susceptibility to 4-AP-induced epileptiform activity.