Vagal and sciatic nerve stimulation have complex, time-dependent effects on chemically-induced seizures: a controlled...

Area of Science:

• Neuroscience
• Epilepsy Research
• Autonomic Nervous System

Background:

• Previous studies on vagus nerve stimulation (VNS) for seizures lacked controls and statistical rigor.
• The impact of VNS-induced hemodynamic changes on seizure activity was overlooked.

Purpose of the Study:

• To investigate the effects of periodic left vagus nerve stimulation (LVNS) on chemically-induced seizures in rats.
• To compare LVNS with control groups (no stimulation, sciatic nerve stimulation, and atropine-pretreated LVNS).
• To assess the role of hemodynamic depression and cortical activation in seizure modulation by nerve stimulation.

Main Methods:

• Chemically-induced seizures in rats were monitored during periodic LVNS (30s on/120s off for 130 min).
• Control groups included no stimulation (NoS), left sciatic nerve stimulation (LSNS), and LVNS after methyl atropine (MA-LVNS).
• Seizure probability (P(s)) was statistically analyzed, alongside cortical rhythm and hemodynamic parameters (bradycardia, hypoxemia).

Main Results:

• Seizure probability (P(s)) differed significantly across groups (P<0.01). LSNS showed the highest P(s), MA-LVNS the lowest.
• LVNS exhibited intermediate P(s), demonstrating both seizure suppression and precipitation, with a small net anti-seizure effect compared to NoS.
• LVNS and MA-LVNS did not alter cortical rhythms ('activation'), unlike LSNS which increased synchrony and P(s). LVNS induced bradycardia and hypoxemia.

Conclusions:

• Cranial and peripheral nerve stimulation exert complex, time-varying effects on cerebral excitability.
• Low-frequency LSNS facilitated seizures, while LVNS had a dual effect (suppression/precipitation).
• The limited anti-seizure effect of LVNS may be partly attributed to hemodynamic depression, suggesting minimal direct anti-seizure efficacy without such effects.