Effects of co-administration of anticonvulsant and putative anticonvulsiveagents and sub-/suprathreshold doses of L-Dopa upon motor behaviour of MPTP-treated mice

The effects of co-administration of the dopamine precursor, L-Dopa, with an ticonvulsant and putative anticonvulsive agents upon the motor activity of hypoactive MPTP-treated C57 BL/6 mice were measured in six experiments. In each case, MPTP (2 x 40 mg/kg, s.c., separated by a 24-hr interval) was adm inistered four to six weeks prior to behavioural testing. Thus, the effects of these agents combined with either a single acute, subthreshold dose (5 mg/kg, s.c.) of L-Dopa, or, with chronically-administered, suprathreshold d oses (20 mg/kg, s.c.) of L-Dopa were studied. In the former, lamotrigine, F CE 26743 and L-Deprenyl, injected 60 min before subthreshold L-Dopa (5 mg/k g), each induced an antiparkinsonian action in MPTP-treated mice that consi sted of dose-specific, as opposed to dose-related, elevations of locomotion and rearing behaviour. In the latter, lamotrigine (all three measures of a ctivity at 3 mg/kg), FCE 26743 (locomotion and total activity at 3; rearing at 1 and 3 mg/kg) and L-Deprenyl (locomotion and total activity at 1 and 3 mg/kg), but not phenytoin (neither at 1 nor 3 mg/kg), reinstated the motor activity-stimulating effects of the threshold dose of L-Dopa (20 mg/kg) in L-Dopa-tolerant, MPTP-treated mice. Neurochemical analyses confirmed sever e DA depletions in MPTP-treated mice. Since neither lamotrigine, FCE 26743 nor L-Deprenyl, nor subthreshold L-Dopa, by themselves increased the motor behaviour of MPTP-treated mice, a a synergistic effect of the coadministrat ion is concluded. Further, since the suprathreshold dose of L-Dopa by itsel f failed to stimulate motor activity in the MPTP mice following chronic (25 daily injections) administrations of the compound, it is suggested that a restorative effect, in combination with lamotrigine, FCE 26743 or L-Depreny l was evidenced. The potential therapeutic benefits of anticonvulsant or pu tative anticonvulsive compounds for parkinsonian symptoms are discussed.