Novel attempts to optimize vagus nerve stimulation parameters on serotonin neuronal firing activity in the rat brain.
BACKGROUND
Vagus nerve stimulation (VNS) is indicated for treatment-resistant epilepsy and depression. Electrophysiologic recordings in the rat brain have shown that VNS promptly increases the firing rate of NE neurons and subsequently that of 5-HT neurons. Thus far, it appears that the standard stimulation parameters currently used in depressed patients produce an optimal activation of 5-HT neurons.


OBJECTIVE
This study was therefore aimed at investigating additional alterations of stimulation parameters to optimize VNS efficacy to further increase 5-HT neuronal activity.


METHODS
Rats were implanted with a VNS device and stimulated for 14 days using standard (0.25 mA/20 Hz/500 microseconds/30 seconds ON-5 minutes OFF, continuously) or various stimulation parameters: extension of the OFF period (30 seconds ON every 10 to 30 minutes), the OFF and ON periods, discontinuous stimulation (12 hours per day using standard parameters), and burst stimulation modes. Rat dorsal raphe 5-HT neurons were recorded under chloral hydrate anesthesia.


RESULTS
Both 12-hour stimulation periods for 14 days, and the 30-second stimulation every 10 or 15 minutes significantly increased the firing activity of 5-HT neurons to the same extent as standard parameters while the 30-minute intervals were ineffective. Stimulations in a burst mode and the pseudo-one-pulse stimulations also significantly increased 5-HT neuronal activity.


CONCLUSIONS
These results indicate that less stimulation is sufficient to achieve the same VNS efficacy on 5-HT neuronal firing. These data may be relevant for patients using VNS because these new parameters could minimize or prevent side effects and increase battery life of the stimulator.
University of Ottawa Institute of Mental Health Research, Ottawa, Ontario, Canada. Electronic address: stella.manta@rohcg.on.ca.
Stella
S
Manta
University of Ottawa Institute of Mental Health Research, Ottawa, Ontario, Canada.
Mostafa
M
El Mansari
University of Ottawa Institute of Mental Health Research, Ottawa, Ontario, Canada; Department of Cellular and Molecular Medecine, Ottawa, Ontario, Canada.
Pierre
P
Blier
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation / Q000379:methods*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D059326:Serotonergic Neurons / Q000502:physiology*; D012701:Serotonin / Q000378:metabolism*; D014630:Vagus Nerve / Q000502:physiology*
D012701:Serotonin