Involvement of transient receptor potential vanilloid type 1 channels in the pro-convulsant effect of anandamide in pentylenetetrazole-induced seizures.

Anandamide, an endogenous agonist of CB(1) receptors, also activates TRPV1 but at a higher concentration. Studies demonstrate the anticonvulsant activity of anandamide via CB(1) receptors, while its action through TRPV1 is still ambiguous. Thus, the present study investigated the influence of anandamide on pentylenetetrazole-induced seizures in mice pretreated with TRPV1 or CB(1) receptor antagonists. Acute intracerebroventricular administration of low doses of anandamide (10, 20, or 40μg/mouse) produced anticonvulsant effect, while the pro-convulsant effect was evident at high doses (80 or 100μg/mouse). Interestingly, AM251 (2μg/mouse), a CB(1) antagonist pretreatment blocked the anticonvulsant effect, but augmented the pro-convulsant effect. Conversely, in the presence of inactive dose of capsazepine (1μg/mouse), a TRPV1 antagonist, anandamide exhibited significant anticonvulsant effect even at high doses with no change in its anticonvulsant effect. Moreover, mice treated with capsaicin, a TRPV1 agonist (10, or 100μg/mouse) exhibited pro-convulsant activity that was blocked by capsazepine pretreatment. However, capsazepine, per se at doses 10 or 100μg/mouse exhibited anticonvulsant effect. Like anandamide, the agents (AM404 and URB597), which increase its synaptic concentrations produced similar biphasic effects. Thus, these results indicate that anandamide exhibits both pro- and anticonvulsant activities by activating TRPV1 and CB(1) receptor respectively.