Infrared Neural Stimulation Elicits Distinct Molecular Pathways in Astrocytes Based on Laser Pulse Parameters

Label-free optical stimulation of brain cells with infrared (IR) light provides a powerful tool for spatially targeted neuromodulation. However, lingering questions about the off-target effects of IR stimulation on non-neuronal cells remain sparsely explored. It is shown that rat astroglial cultures are independently sensitive to single pulses of infrared light, evoking calcium signaling and osmoregulatory phenomena in vitro. Recent studies highlight that astrocytes respond differently to electromagnetic and laser stimulation, recruiting different pathways. The impact of three different IR stimulation time courses on astrocyte calcium and water transport dynamics is explored with widefield fluorescence microscopy and pharmacology to fill this gap. Results show that different stimulation methods can evoke astrocyte calcium responses, resulting from distinct biomolecular signaling processes. Notably, swelling and shrinkage are also differently evoked by short-term and long-term stimulation pulses. It is shown that specific IR stimulation can drive selective water and calcium dynamics in astrocytes. The work uniquely reports label-free optical modulation techniques to drive astroglial homeostatic machinery, a crucial process in healthy brain function that lacks tools for spatially precise modulation. More broadly, the results demonstrate the need to consider off-target effects with neuromodulation strategies and how to use such effects to study brain physiology.