Axon morphology and intrinsic cellular properties determine repetitive transcranial magnetic stimulation threshold for plasticity

• Published in: Frontiers in cellular neuroscience Vol. 18; p. 1374555
• Main Authors: Galanis, Christos, Neuhaus, Lena, Hananeia, Nicholas, Turi, Zsolt, Jedlicka, Peter, Vlachos, Andreas
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Research Foundation 03.04.2024; Frontiers Media S.A
• Subjects: Animal welfare; axons; Brain; Cell activation; Cellular Neuroscience; Computational neuroscience; Electric fields; excitation; Glucose; Hippocampus; inhibition; Magnetic fields; Mathematical models; Molecular modelling; Morphology; Neural networks; Neuroplasticity; Penicillin; Pyramidal cells; Standardization; Structure-function relationships; Sucrose; Synaptic plasticity; Synaptic strength; Transcranial magnetic stimulation; whole-cell patch-clamp recordings; Switzerland; organotypic tissue cultures; axons; morphology; excitation; whole-cell patch-clamp recordings; inhibition; synaptic plasticity
• ISSN: 1662-5102; 1662-5102
• DOI: 10.3389/fncel.2024.1374555

Repetitive transcranial magnetic stimulation (rTMS) is a widely used therapeutic tool in neurology and psychiatry, but its cellular and molecular mechanisms are not fully understood. Standardizing stimulus parameters, specifically electric field strength, is crucial in experimental and clinical settings. It enables meaningful comparisons across studies and facilitates the translation of findings into clinical practice. However, the impact of biophysical properties inherent to the stimulated neurons and networks on the outcome of rTMS protocols remains not well understood. Consequently, achieving standardization of biological effects across different brain regions and subjects poses a significant challenge. This study compared the effects of 10 Hz repetitive magnetic stimulation (rMS) in entorhino-hippocampal tissue cultures from mice and rats, providing insights into the impact of the same stimulation protocol on similar neuronal networks under standardized conditions. We observed the previously described plastic changes in excitatory and inhibitory synaptic strength of CA1 pyramidal neurons in both mouse and rat tissue cultures, but a higher stimulation intensity was required for the induction of rMS-induced synaptic plasticity in rat tissue cultures. Through systematic comparison of neuronal structural and functional properties and computational modeling, we found that morphological parameters of CA1 pyramidal neurons alone are insufficient to explain the observed differences between the groups. Although morphologies of mouse and rat CA1 neurons showed no significant differences, simulations confirmed that axon morphologies significantly influence individual cell activation thresholds. Notably, differences in intrinsic cellular properties were sufficient to account for the 10% higher intensity required for the induction of synaptic plasticity in the rat tissue cultures. These findings demonstrate the critical importance of axon morphology and intrinsic cellular properties in predicting the plasticity effects of rTMS, carrying valuable implications for the development of computer models aimed at predicting and standardizing the biological effects of rTMS.