Talampanel reduces the level of motoneuronal calcium in transgenic mutant SOD1 mice only if applied presymptomatically

Abstract

We tested the efficacy of treatment with talampanel in a mutant SOD1 mouse model of ALS by measuring intracellular calcium levels and loss of spinal motor neurons. We intended to mimic the clinical study; hence, treatment was started when the clinical symptoms were already present. The data were compared with the results of similar treatment started at a presymptomatic stage. Transgenic and wild-type mice were treated either with talampanel or with vehicle, starting in presymptomatic or symptomatic stages. The density of motor neurons was determined by the physical disector, and their intracellular calcium level was assayed electron microscopically. Results showed that motor neurons in the SOD1 mice exhibited an elevated calcium level, which could be reduced, but not restored, with talampanel only when the treatment was started presymptomatically. Treatment in either presymptomatic or symptomatic stages failed to rescue the motor neurons. We conclude that talampanel reduces motoneuronal calcium in a mouse model of ALS, but its efficacy declines as the disease progresses, suggesting that medication initiation in the earlier stages of the disease might be more effective.

Figure 1

Increased calcium level in the lumbar motor neurons of mutant SOD1 Tg mice. An increased number of electron-dense deposits (EDDs; arrows) is noted, reflecting the distribution of calcium in the motor neurons in the talampanel-treated (A) and the vehicle-treated (B) mutant SOD1 Tg mice at the age of 19 weeks. Motor neurons from the wild-type mice at the same age contain fewer deposits, regardless of whether they were treated with talampanel (C) or with vehicle only (D). Besides the increased number of EDDs in the mutant SOD1 Tg animals, mitochondrial degeneration with clusters of EDDs (asterisk) was frequently seen. In the wild-type animals, regardless of the treatment, no structural alterations were present. Mit: mitochondrion, Go: Golgi complex. Bar: 500 nm.

Figure 2

Effects of talampanel treatment on the calcium level of lumbar motor neurons of mutant SOD1 Tg mice. The volume occupied by electron-dense deposits (EDDs), reflecting tissue calcium, relative to the perikaryal volume was determined in mutant SOD1 Tg (mSODl-Tg) and wild-type (wt) animals after talampanel (Ta) or vehicle (Ve) treatment at 12 (A) and 19 (B) weeks of age. Talampanel had a significant effect in reducing the calcium level only at the age of 12 weeks (asterisk; p = 0.01, two-way ANOVA with Duncan post hoc comparison). Data are shown as means ± SEM.

Figure 3

Effects of talampanel treatment on the number of lumbar motor neurons in mutant SOD1 Tg mice. Relative to the vehicle-only treatment (Ve), talampanel treatment (Ta) did not exert a significant effect either in the mutant SOD1 Tg (mSOD 1-Tg), or in the wild-type (wt) mice in the presymptomatic (A) or a later stage of the disease (B). Regardless of the treatment, lower cell numbers were counted at 19 weeks of age than at 12 weeks of age in the mutant SOD1 Tg animals. Data are shown as means ± SEM.