Vagus Nerve Stimulation Exerts Disease-Modifying Effects in Epileptic Rats by Enhancing Hippocampal Adenosine Signalling

Objectives Vagus nerve stimulation (VNS) is an established neuromodulatory therapy for refractory epilepsy, but its disease-modifying mechanisms remain unclear. Adenosine is an endogenous anticonvulsant and a key regulator of epileptogenesis, and adenosine kinase (ADK) controls extracellular adenosine availability. This study investigated whether VNS modifies epilepsy progression by regulating hippocampal adenosine signalling. Methods A pilocarpine-induced rat model of temporal lobe epilepsy was used. Animals were assigned to control, pilocarpine, VNS-treated, VNS 4-4W (4 weeks of active VNS followed by 4 weeks without stimulation), and sham groups. Spontaneous recurrent seizures (SRS) were monitored using video-electroencephalography, and spatial learning and memory were assessed using the Morris water maze. Hippocampal extracellular adenosine dynamics were measured in vivo using the GRABAdo1.0 sensor combined with fibre photometry. ADK and adenosine A1 receptor (A1R) expression levels were evaluated by immunostaining and Western blotting. Results Acute VNS induced a rapid increase in hippocampal extracellular adenosine levels. In pilocarpine-treated rats, active VNS significantly reduced the frequency and duration of SRS and improved spatial learning and memory compared with time-matched epileptic rats that did not receive active stimulation. These beneficial effects persisted after a 4-week stimulation-free period. VNS also suppressed hippocampal ADK overexpression and restored A1R expression. Furthermore, pharmacological blockade of A1Rs with DPCPX reversed the antiseizure effect of VNS. Conclusions VNS exerts disease-modifying effects in epileptic rats by enhancing hippocampal adenosine signalling. These effects are associated with VNS-evoked adenosine release, inhibition of ADK overexpression, and restoration of A1R-mediated anticonvulsant signalling.