STIMULATION PULSE NUMBER CRITICALLY SHAPES ITBS-INDUCED EXCITATORY SYNAPTIC PLASTICITY IN MOUSE ORGANOTYPIC TISSUE CULTURES

Repetitive transcranial magnetic stimulation (rTMS) is widely used to modulate cortical excitability in both clinical and experimental settings, yet the stimulation parameters that critically determine synaptic plasticity remain incompletely defined. Previous work demonstrated that 10 Hz repetitive magnetic stimulation (rMS) reliably induces excitatory synaptic plasticity in organotypic entorhino-hippocampal tissue cultures prepared from the mouse brain. Whether clinically established patterned protocols such as intermittent theta-burst stimulation (iTBS) engage comparable plasticity mechanisms in this preclinical model is not well established. Here, we examined the impact of stimulation pulse number on iTBS-induced synaptic plasticity. Using whole-cell patch-clamp recordings from CA1 pyramidal neurons in mouse organotypic tissue cultures, we found that iTBS with 600 pulses (iTBS600), a commonly used clinical protocol, under our experimental conditions, did not produce detectable changes at excitatory synapses. In contrast, when the burst pattern was kept constant while increasing the total number of pulses to 900 (iTBS900), robust potentiation of excitatory synapses was observed. These results identify stimulation pulse number as a critical determinant of iTBS-induced excitatory synaptic plasticity in vitro. They demonstrate that patterned stimulation alone is insufficient to induce plasticity unless an effective stimulation dose is reached. Our findings emphasize stimulation dose, i.e., pulse number, as a key variable for mechanistic studies of rTMS-induced plasticity and underscore the need for careful parameter selection when translating patterned rTMS protocols across experimental and clinical contexts.