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Updated: Mar 31, 2026
Vagus Nerve Stimulation as a Tool to Induce Plasticity in Pathways Relevant for Extinction Learning
Published on: August 21, 2015
Modulation of Hippocampal Activity by Vagus Nerve Stimulation in Freely Moving Rats
Lars Emil Larsen1, Wytse Jan Wadman2, Pieter van Mierlo3
1Laboratory for Clinical and Experimental Neurophysiology, Neurobiology and Neuropsychology (LCEN3), De Pintelaan 185, Blok B, Ghent University, BE-9000 Ghent, Belgium.
Background:
Vagus Nerve Stimulation (VNS) has seizure-suppressing effects but the underlying mechanism is not fully understood. To further elucidate the mechanisms underlying VNS-induced seizure suppression at a neurophysiological level, the present study examined effects of VNS on hippocampal excitability using dentate gyrus evoked potentials (EPs) and hippocampal electroencephalography (EEG).
Methods:
Male Sprague-Dawley rats were implanted with a VNS electrode around the left vagus nerve. A bipolar stimulation electrode was implanted in the left perforant path and a bipolar recording electrode was implanted in the left dentate gyrus for EEG and dentate field EP recording. Following recovery, VNS was applied in freely moving animals, using a duty cycle of 7 s on/18 s off, 30 Hz frequency, 250 µs pulse width, and an intensity of either 0 (SHAM), 25 µA or 1000 µA, while continuously monitoring EEG and dentate field EPs.
Results:
VNS at 1000 µA modulated dentate field EPs by decreasing the field excitatory post-synaptic potential (fEPSP) slope and increasing the latency and amplitude of the population spike. It additionally influenced hippocampal EEG by slowing theta rhythm from 7 Hz to 5 Hz and reducing theta peak and gamma band power. No effects were observed in the SHAM or 25 µA VNS conditions.
Conclusion:
VNS modulated hippocampal excitability of freely moving rats in a complex way. It decreased synaptic efficacy, reflected by decreased fEPSP slope and EEG power, but it simultaneously facilitated dentate granule cell discharge indicating depolarization of dentate granule cells.
