Lamotrigine blocks NMDA receptor-initiated arachidonic acid signalling in rat brain: implications for its efficacy in bipolar disorder.
When administered chronically to rats, drugs that are effective in bipolar disorder—lithium and the anticonvulsants, valproic acid and carbamazepine—have been shown to downregulate the expression of certain enzymes involved in brain arachidonic acid (AA) release and cyclooxygenase (COX)-mediated metabolism. Phase II clinical trials with the anticonvulsant topiramate [2,3:4,5-bis-O-(1-methylethylidene)-beta-d-fructopyranose sulfamate] suggest that this drug may also be effective for bipolar disorder. To see if topiramate has effects similar to those of the other three drugs, we administered topiramate to rats for 14 days at 20 mg/kg, p.o. twice daily. Compared with p.o. vehicle, topiramate treatment did not significantly affect the brain activity or protein level of cytosolic phospholipase A2, secretory PLA2, or Ca2+-independent iPLA2. Additionally, brain protein levels of COX-1, COX-2, 5-lipoxygenase, and cytochrome P450 epoxygenase were unchanged. These results suggest that topiramate does not modify expression of the enzymes involved in brain AA metabolism that have been shown to be targeted by lithium, valproic acid, or carbamazepine. If topiramate proves effective in bipolar disorder, it may not act by modulating brain AA metabolism. In view of the proven anticonvulsant effect of topiramate, our results also suggest that the AA cascade is not involved in the antiseizure properties of the drug.