The novel antiepileptic drug, lamotrigine, exerts prodystonic effects in a mutant hamster model of generalized dystonia.

Recent findings of antidystonic effects of NMDA and non-NMDA receptor antagonists in an inbred line of Syrian hamsters with primary generalized dystonia prompted us to investigate the effects of lamotrigine, an inhibitor of veratrine-induced glutamate release, on the severity of dystonia in mutant hamsters. In mutant dystonic hamsters the dystonic attacks which can be induced by mild environmental stimuli or handling are age-dependent with maximum severity between days 30 and 40 of life (maximum period). Thereafter the severity of dystonia slowly declines (post-maximum period) until the susceptibility to induction of dystonia disappears completely at an age of about 70 days. Lamotrigine (5.0, 10.0 or 30.0 mg/kg i.p.) dose dependently decreased the latency to onset of dystonic attacks. Furthermore, at a dose of 30 mg/kg the dystonic attacks were aggravated when lamotrigine was administered during the max and post-max period. Even in mutant hamsters older than 70 days, i.e. after spontaneous remission of dystonia, and in an inbred line of non-dystonic Syrian hamsters with genetic origin similar to the mutant hamsters, lamotrigine (10.0 or 30.0 mg/kg i.p. and 30.0 mg/kg p.o.) provoked dystonic disturbances. In a genetically different outbred line of Syrian hamsters, lamotrigine did not cause dystonic movements. The unexpected finding that lamotrigine exerts prodystonic effects in genetically susceptible hamsters may be due to the lack of selectivity of lamotrigine to block glutamate release. Tentatively, simultaneous inhibition of GABA (gamma-aminobutyric acid) release might be critically involved in the prodystonic activity of lamotrigine.