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

Analysing vagus nerve spontaneous activity using finite element modelling

Objective. Finite element modelling has been widely used to understand the effect of stimulation on the nerve fibres. Yet the literature on analysis of spontaneous nerve activity is much scarcer. In this study, we introduce a method based on a finite element model, to analyse spontaneous nerve activity with a typical bipolar electrode recording setup, enabling the identification of spontaneously active fibres. We applied our method to the vagus nerve, which plays a key role in refractory epilepsy. Approach. We developed a 3D model including dynamic action potential propagation, based on the vagus nerve geometry. The impact of key recording parameters – inter-electrode distance and temperature – and uncontrolled parameters – fibre size and position in the nerve – on the ability to discriminate active fibres were quantified. A specific algorithm was implemented to detect and classify action potentials from recordings and tested on six rats in vivo vagus nerve recordings. Main results. Fibre diameters can be discriminated if they are below 3 µm and 7 µm, respectively for inter-electrode distances of 2 mm and 4 mm. The impact of the position of the fibre inside the nerve on fibre diameter discrimination, is limited. The range of active fibres identified by modelling in the vagus nerve of rats is in agreement with ranges found at histology. Significance. The nerve fibre diameter, directly proportional to the action potential propagation velocity, is related to a specific physiological function. Estimating the source fibre diameter is thus essential to interpret neural recordings. Among many possible applications, the present method was developed in the context of a project to improve vagus nerve stimulation therapy for epilepsy

Vagus nerve electroneurogram for seizure detection in rats as possible biomarker for responsive vagus nerve stimulation

info:eu-repo/semantics/publishe

Modulation of seizure threshold by vagus nerve stimulation in an animal model for motor seizures

Objective -  The precise mechanism of action of vagus nerve stimulation (VNS) in suppressing epileptic seizures remains to be elucidated. This study investigates whether VNS modulates cortical excitability by determining the threshold for provoking focal motor seizures by cortical electrical stimulation before and after VNS. Material and methods -  Male Wistar rats (n = 8) were implanted with a cuff-electrode around the left vagus nerve and with stimulation electrodes placed bilaterally on the rat motor cortex. Motor seizure threshold (MST) was assessed for each rat before and immediately after 1 h of VNS with standard stimulation parameters, during two to three sessions on different days. Results -  An overall significant increase of the MST was observed following 1 h of VNS compared to the baseline value (1420 μA and 1072 μA, respectively; P < 0.01). The effect was reproducible over time with an increase in MST in each experimental session. Conclusions -  VNS significantly increases the MST in a cortical stimulation model for motor seizures. These data indicate that VNS is capable of modulating cortical excitability

Increased rat serum corticosterone suggests immunomodulation by stimulation of the vagal nerve

The role of the vagal nerve within the immune system has not been fully elucidated. Vagal afferents connect to several central nervous system structures, including the hypothalamus. We investigated the effect of vagal nerve stimulation (VNS) on serum corticosterone levels in rats. Corticosterone levels were measured following 1 h of high frequency (30 Hz) or low frequency (1 Hz) VNS in awake animals. There was a significant increase (p < 0.05) in serum corticosterone levels following 30 Hz VNS compared to 1 Hz VNS or sham stimulation. These results suggest an immediate effect of VNS on the hypothalamic pituitary-adrenal (HPA) axis and support the role of the vagal nerve in immunomodulation

Increased hippocampal extracellular noradrenalin concentration contributes to the anticonvulsant effect of VNS in the focal pilocarpine rat model for limbic seizures

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