Pentylenetetrazol-induced seizure-like behavior and neural hyperactivity in the medicinal leech

This study examined the capacity of a known pro-epileptic drug, pentylenetetrazol (PTZ), to elicit seizure-like activity in the medicinal leech, Hirudo verbana. During in vivo experiments, PTZ elicited increased motor activity in a concentration-dependent manner with the highest concentration (10 mM) eliciting episodes of highly uncoordinated exploratory and swimming behavior. Co-application of the anti-epileptic drug, phenytoin, failed to reduce the absolute amount of PTZ-induced motor behavior, but was able to prevent expression of abnormal exploratory and swimming behaviors. During in vitro experiments in which extracellular recordings of connective nerve activity were made, bath application of 1 μM PTZ in Mg(2+)-free saline elicited a significant increase in spontaneous activity. This PTZ-induced increase in activity was completely inhibited by phenytoin. Interestingly, PTZ-induced hyperactivity was also blocked by co-application of the endocannabinoid 2-arachidonoyl glycerol and the selective serotonin re-uptake inhibitor (SSRI) fluoxetine. These findings suggest that the leech can be a useful system in which to study potential anti-epileptic treatments.