VISUALIZATION OF LOCAL NEURAL CIRCUIT DISRUPTION DURING MALIGNANT BRAIN TUMOR PROGRESSION USING TWO-PHOTON OPTOGENETICS​​​​​

Malignant brain tumors are highly invasive and therapy-resistant diseases with poor prognosis, frequently recurring even after surgical resection and adjuvant treatments. Beyond direct tissue invasion, tumor cells aberrantly interact with surrounding neurons, inducing neuronal hyperexcitability that may further promote tumor growth (Venkataramani et al, Neuro Oncol, 2021). However, the mechanism by which malignant tumors affect the integrity of local neural circuits in vivo remains poorly understood.
Here, we have combined in vivo two-photon calcium imaging with two-photon optogenetics to quantitatively assess local neural connectivity during malignant brain tumor progression (Yoshioka M. et al., Neurophotonics, 2024). This approach has enabled single-cell optical stimulation of defined neurons while simultaneously monitoring activity responses in surrounding neuronal populations, allowing the functional evaluation of local circuit integrity in the living brain.
In C57BL/6J mice, cortical neurons were transduced with adeno-associated viruses expressing GCaMP6s and the channel rhodopsin variant C1V1. Malignant brain tumors were generated by intracortical implantation of cultured tumor cells. Identical neuronal populations adjacent to the tumor site were examined before and after tumor implantation. Target neurons were optically stimulated using a 1064-nm near-infrared laser, while calcium responses in the surrounding neurons were recorded via 920-nm two-photon excitation. Functional connectivity was quantified based on the synchrony between the optically stimulated neurons and neighboring cells.
Following tumor development, significant alterations in local connectivity were observed, indicating functional disruption of peritumoral neural circuits. These findings have demonstrated that malignant brain tumor progression induces abnormal local neural network function and provide new insights into neuron–tumor interactions.