Investigation of the effects of levetiracetam on pain by using in vitro electrophysiologic (patch clamp) and in vivo (hot plate test) methods

INVESTIGATION OF THE EFFECTS OF LEVETIRACETAM ON PAINBY USING IN VITRO ELECTROPHYSIOLOGIC (PATCH CLAMP) ANDIN VIVO (HOT PLATE TEST) METHODSMete OZCANABSTRACTElectrical excitability of plasma membrane and ionic basis of excitability,?membrane biophysics of excitable tissues?, are among to the topics of classicalbiophysics. Altered electrical activity at the level of neuronal membraneexcitability involving voltage-dependent sodium, potassium and calcium channelsmay be underlying cause in variety of pathophysiological conditions includingepilepsy and pain. Understanding and modification of the biophysical propertiesof these ion channels by chemical agents is of importance with respect todevelopment of therapeutic approach against these conditions including anti-nociceptive therapy. Levetiracetam (LEV, ucb L059; C8H14N2O2) is aantiepileptic drug with a unique pharmacologic profile, seizure suppression inepilepsy. The aim of this study was to investigate the possible analgesic actions ofthe novel antiepileptic agent LEV in isolated sensory neurones using whole cellpatch-clamp electrophysiology and in vivo by nociceptive behavioral ?Hot-platetest?.Dorsal root ganglia (DRG) were removed from 1-2 day old neonatal ratsafter decapitation and DRG neurones were isolated by enzymatic and mechanicalprocedures. In current clamp experiments, after establishing whole-cell mode ofthe patch clamp technique, resting membrane potentials were recorded. Effects ofLEV (30, 100 and 300 µM) on membrane potential and action potential (AP)parameters (thresholds, peak amplitude, duration, after potentials, decay time) andpassive membrane properties (input rezistance) were investigated. The effects ofLEV on these parameters was dose dependent; 30 µM LEV had no significanteffect on either parameter while 100 and 300 µM LEV caused hyperpolarizationof the resting membrane potential, and caused a significant increase in meanamplitude of AP after hyperpolarisations and input rezistance (n=7, P<0.05).In in vivo experiments, hot plate analgesimeter was used to determine painthreshold from latency of the nociceptive behavior. LEV (60, 300 and 900 mg/kg)had no significant effect on the pain threshold in normal mouse (n=8, P>0.05).But, much lower doses of LEV (20, 100 and 200 mg/kg) significantly increasedthe pain threshold when diabetic neuropathy was induced (n=15, P<0.05).In conclusion; results obtained by cellular biophysical procedures in invitro experiments and in vivo behavioral tests with agreement suggest that thenovel antiepileptic agent LEV may possess a therapeutic potential for thetreatment of neuropathic pain.Key words: Cellular Electrophysiology, Patch Clamp, Ion Channels,Levetiracetam, Action Potential, Excitability, Pain.