Ex vivo Infrared Nerve Stimulation on the Rat Sciatic Nerve: Challenges and Pitfalls

Infrared nerve stimulation (INS) offers millisecond-scale, electrical artifact-free activation of peripheral nerves, yet rat ex vivo studies remain scarce. We present an INS setup utilizing a lens system for free-beam focus for rat sciatic nerves partially submerged in a nerve bath, making re-wetting of the tissue in existing ex vivo INS setups redundant. Excised sciatic nerve preparations were illuminated at 1470 nm, delivering pulse trains from 100 - 2000 s at 5 Hz with radiant exposures up to 25.7 J/cm2. Compound action potentials (CAPs) were recorded with tungsten hook electrodes. Nerve activity could be recorded up to 200 minutes after excision, though persistent nerve excitability remained comparable to existing ex vivo studies as a yet to be optimized parameter. Peak CAP amplitudes ranged from 3.9 - 36.9 {micro}V with latencies averaged at 3.4 ms. Activation thresholds spanned 1.75 - 13.05 J/cm2. Additionally, potential pitfalls for INS setups and ways to resolve them were investigated, with two artifact types highly relevant to ex vivo INS being identified: A photo-thermal expansion artifact and a photovoltaic artifact with thermo-capacitive coupling. The observations confirm that CAPs can be evoked via INS in an ex vivo preparation of the rat sciatic nerve. The presented platform supports 3R principles and offers a robust basis for introduction of pharmacological investigations with INS.