In mammals, neurons are accompanied by numerous cell types, including microglia, oligodendrocytes, and astrocytes. These cells work cohesively to stabilize the neuronal microenvironments and ensure cellular functionality is unperturbed. Studies involving infrared neural stimulation (INS) have been focused on neuronal-type cellular responses, while the effects on non-neuronal cells have been largely unexplored. Astrocytes, in particular, play a key role in maintaining extracellular ion and neurotransmitter concentrations, maintaining osmotic balance, preserving synaptic connectivity, and in mediating neurovascular coupling responses in the brain. Previous work has speculated whether astrocytes are affected by INS in the brain. Here, we characterize the effect of INS on astrocytes using calcium dynamics in response to varying optical parameters and explore whether astrocytic response is driven by neuronal activity or directly by transient thermal energy deposition. Using video-rate calcium-fluorescence multiphoton imaging and nonlinear microscopy of cultured cells, we found that calcium activity in astrocytes is sensitive to infrared light independent of neuronal presence. These cells exhibited similar time-dependent behavior as reported in previous in vivo studies. Success in eliciting calcium responses from a cell, as well as response amplitude, appears to correlate with radiant exposure. The duration and shape of such responses are variable from cell to cell, with some responses aligning with previous observations. Our results suggest that collateral activation of non-neuronal cells, particularly in astrocytes, may play a role when applying INS in vivo.
Wilson R. Adams, Manqing Wang, Ana I. Borrachero-Conejo, Emanuela Saracino, Roberto Zamboni, Valentina Benfenati, E. Duco Jansen, and Anita Mahadevan-Jansen, "Excitability of astrocyte in vitro with infrared neural stimulation (Conference Presentation)," Proc. SPIE 10482, Optogenetics and Optical Manipulation 2018, 104820D (Presented at SPIE BiOS: January 27, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291246.5751488244001.
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