In cardiac medicine, VNS has proven to promote cardioprotective and anti-fibrillatory effects, thus providing a promising therapeutic approach for non-pharmacological treatment of various cardiac pathological conditions, such as ventricular arrhythmias 15, atrial fibrillation 13 and heart failure 16, 17. Therefore, vagus nerve stimulation (VNS) has been considered to be a promising therapeutic approach to treat diverse pathological conditions, such as epilepsy 5, 6, 7, 8, depression 9, and cardiac diseases 10, 11, 12, 13, 14 by restoring the vagal tone to a physiological level. There is growing evidence showing that various pathological conditions are associated with and affected by autonomic imbalances that manifest as dominance of the sympathetic over the parasympathetic activity 1, 2, 3, 4. Overall, the viability of this ex-vivo model to study the acute cardiac effects of VNS was demonstrated. The charges needed for a 10-bpm HR reduction, normalized to the physiological threshold were 1.78 ± 0.8 and 1.22 ± 0.1, in-vivo and ex-vivo, respectively. The charges required to reduce HR by 5 bpm were 9 ± 6 ♜ and 549 ± 370 ♜, ex-vivo and in-vivo, respectively. Overall, the nerve remained excitable for about 5 h ex-vivo. In the ex-vivo isolated heart, the baseline HR was about 20 bpm lower than in-vivo (158 ± 11 bpm vs 181 ± 19 bpm). The results were compared to a series of in-vivo experiments rabbits (n = 5). The excitability was quantified as the charge needed for a 10-bpm HR reduction. The general nerve excitability was assessed through the ability to evoke a heart rate (HR) reduction of at least 5 bpm (physiological threshold). The feasibility to evoke chronotropic responses through electrical stimulation ex-vivo was studied in innervated isolated rabbit hearts (n = 6). Therefore, an ex-vivo Langendorff-perfused rabbit heart with intact vagal innervation is proposed to study VNS in absence of cofounding anesthetic or autonomic influences. The cardiac responses to vagus nerve stimulation (VNS) are still not fully understood, partly due to uncontrollable confounders in the in-vivo experimental condition.
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