Infrared neurostimulation in ex-vivo rat sciatic nerve using 1470 nm wavelength.

OBJECTIVE: To design and implement a setup for ex-vivo optical stimulation for exploring the effect of several key parameters (optical power and pulse duration), activation features (threshold, spatial selectivity) and recovery characteristics (repeated stimuli) in peripheral nerves. APPROACH: A nerve chamber allowing ex-vivo electrical and optical stimulation was designed and built. A 1470 nm light source was chosen to stimulate the nerve. A photodiode module was implemented for synchronization of the electrical and optical channels. MAIN RESULTS: Compound Neural Action Potentials (CNAPs) were successfully generated with infrared light pulses of 200-2000 µs duration and power in the range of 3-10 W. These parameters determine a radiant exposure for stimulation in the range 1.59-4.78 J/cm2. Recruitment curves were obtained by increasing durations at a constant power level. Neural activation threshold is reached at a mean radiant exposure of 3.16 ± 0.68 J/cm2 and mean pulse energy of 3.79 ± 0.72 mJ. Repetition rates of 2-10 Hz have been explored. In 8 out of 10 sciatic nerves, repeated light stimuli induced a sensitisation effect in that the CNAP amplitude progressively grows, representing an increasing number of recruited fibres. In 2 out of 10 sciatic nerves, CNAPs were composed of a succession of peaks corresponding to different conduction velocities. SIGNIFICANCE: The reported sensitisation effect could shed light on the mechanism underlying Infrared NeuroStimulation (INS). Our results suggest that, in sharp contrast with electrical stimuli, optical pulses could recruit slow fibres early on. This more physiological order of recruitment opens the perspective for specific neuromodulation of fibre population who remained poorly accessible until now. Short high-power light pulses at wavelengths below 1.5 µm offer interesting perspectives for neurostimulation

Chronic Setup System for Continuous Monitoring of Epileptic Rats

This work presents a setup for chronic monitoring of spontaneous epileptic seizures in rats under kainic acid. The system allows to record the vagus nerve electroneurogram at 40 kS/s and the electroencephalogram at 250 S/s using an USB-6212 multifunction I/O-device. The system includes a video channel (20 fps) controlled by a Raspberry Pi 4 Model B. A slipring allows the rat to move freely. Quick cage cleaning is possible through a movable base. The chronic setup was tested on a Wistar rat after status epilepticus induction, using kainic acid. The system appears to be robust and reliable enough to record status epilepticus, making it suitable for more extended experiments in epileptic rats

Micro Cuff Electrode Manufacture for Vagus Nerve Monitoring in Rats

This work describes the fabrication of a lab-made cuff electrode intended for rat vagus nerve electroneurography. The cuff electrode is built around 50 µm platinum wires contacts in tripolar configuration, 4mm contact spacing. The body is made of silicone rubber and four surgical threads. In vivo validation allowed to record respiration and cardiac related activity from the vagus nerve. The results show that our electrodes are a suitable low-cost alternative for our preclinical studies