van Essen et al. Mefloquine induced motor deficits In all performance tasks the variation was more closely examined The training process in these animals was slowed down substantially, with the coefficient of variation (CV). The resulting CVs were not but they revealed no impaired general motor performance (Kistler significantly different either (unpublished observations). Taken et al., 2002; Van Der Giessen et al., 2008) similar to our findings in together, these results show that mefloquine has no influence on humans. The lack of effect of mefloquine on general performance these three different IO-related performance tasks. is most likely due to the specific function of Cx36 within the IO. Blocking Cx36 by mefloquine does not affect the performance, it -yeIlbkn IdnocItInogn Is dtcefa In Iuqolfemen resu makes the performance only unadjustable. In order to affect these To investigate whether the use of mefloquine leads to motor learn- performances other mechanisms within the IO need to be altered ing deficits in humans, we tested mefloquine users and control (Rondi-Reig et al., 1997; Welsh, 1998). participants (i.e., no mefloquine use) using an eye-blink condition- With regard to our experimental design, the question arises ing task (Figure 4A). whether a single dose of mefloquine is capable of altering brain Compared to the control participants, mefloquine users showed functions. Mefloquine has no problem crossing the blood–brain a significant lower number CRs that were acquired during training barrier (Baudry et al., 1997) and there is evidence that mefloquine and after training (Figures 4B,C, p = 0.02, control participants: can accumulate in the brain (Barraud de Lagerie et al., 2004). This n = 11 and mefloquine users: n = 8, t test). The percentage of CRs is, for instance, supported by the observation of a higher risk of was on average 74.0 ± 4.7% in the control group and 46.8 ± 11.0% neuropsychiatric adverse events in the first days after first meflo- in the group of mefloquine users. The learning curves of the meflo- quine intake (Schlagenhauf et al., 1996, 2003; van Riemsdijk et al., quine group and the control group are plotted in Figure 4D. Before 2002), suggesting a direct effect of mefloquine on the brain. Some the task started, it was confirmed that volunteers did not respond of these neuropsychiatric adverse events were also observed in our to the tone and did respond to the US with an UR. Therefore, in mefloquine using participants (Table 1). Furthermore, the reported block 0 no conditioned blinking has been observed. In blocks 1, 2, IC50 of mefloquine for Cx36 is 0.3 Mμ ( Cruikshank et al., 2004) and 4, 5, and 6 the number of CRs was significantly lower in the group this is much smaller than the mefloquine blood level concentration of mefloquine users compared to the control group (respectively achieved with one dosage of 250 mg mefloquine (Pennie et al., p = 0.03, 0.01, 0.01, 0.04, and 0.03, t test), whereas blocks 3, 7, and 1993), indicating that the level of mefloquine in the brain is high 8 did not reveal significantly difference (respectively p = 0.14, 0.14, enough to alter brain functions. and 0.08, t test). Curve fitting the data of both groups resulted Of course, one could argue that the altered brain function in well-associated learning curves (Rc2ontrol = 0.98, p < 0.01 and associated with mefloquine might be caused by mechanisms Rm2efloquine = 0.87, p < 0.01). The fitted learning curve generated two other than interference with Cx36 gap junction coupling. learning coefficients: a and b. The learning coefficient a represents However, the IC50 values for mefloquine inhibiting ATP-sensitive learning capacity, whereas the learning coefficient b represents learn- potassium channels (IC50 = 3 μM), L-type calcium channels ing speed. The coefficients a and b of the learning curves were both (IC50 ≈ 10 μM), delayed rectifier channels (IC 50 = 1 μM), and significantly different between the control group and the group volume- (IC50 = 1 μM) and calcium-activated chloride chan - of mefloquine users (control: a = 84.7 ± 0.7 and b = 1.53 ± 0.05 nels (IC50 = 3 μM) are all higher than those required for Cx36 vs mefloquine: a = 70.8 ± 7.2 and b = 3.96 ± 0.71, both p < 0.05, t blockade (Coker et al., 2000; Gribble et al., 2000; Maertens et al., test). Mefloquine users learned this task 2.6 times slower than the 2000; Kang et al., 2001). So far, Cx36 gap junctions are the most participants that did not use mefloquine and their learning capacity mefloquine-sensitive molecules in the brain and the mefloquine was also reduced by 16% compared to the non-users. The average blocking effect in the IO will lead to motor learning deficit (Van onset latency of the CRs was similar in the mefloquine group and Der Giessen et al., 2008). control group (control: 877 ± 14.8 ms vs mefloquine: 906 ± 16.6 ms, Finally, one could also suggest that the present findings might be p = 0.23, t test). UR onset across groups did not differ either (con- explained by a confounding involvement of other Cx36 containing trol: 1062 ± 6.1 ms vs mefloquine: 1075 ± 4.5 ms, p = 0.13, t test), brain areas apart from the IO. Despite the fact that for all the tasks excluding that possible deficits in reflex pathways can contribute used in this study the involvement of the IO is necessary (Rondi- to the observed reduced motor learning. Conclusively, these data Reig et al., 1997; Xu et al., 2006; Van Der Giessen et al., 2008), we show that the use of mefloquine affects motor learning. cannot directly exclude a possible role of other Cx36 containing brain areas. It is, though, noteworthy that an altered attention due to IdIucsno mefloquine might have affected the dart throwing and the rhythm In this study we investigated the possibility that mefloquine induces perception task; it cannot explain the results on eye-blink and eye- deficits in olivocerebellar related behaviors in young and healthy volun- blink conditioning tasks, because not being aware of the stimuli teers.We show that mefloquine has no effect on dart throwing,rhythm does not prevent eye blinking or eye-blink conditioning (Smith perception and reflex blinking, but has an effect on the conditioning et al., 2005). Thus, the most likely explanation for our results is the of eye-blink responses to a tone (associative learning). In this learning- selective blocking of Cx36 gap junctions in the IO. dependent motor task, mefloquine users were impaired in their learn- The demonstration that mefloquine, a marketed anti-malarial ing speed as well as in their learning capacity.Mefloquine reduced their drug, imposes a deficit in motor learning capabilities in man might learning speed by 2.6 times and their learning capacity by 16%. come as a surprise in the field of adverse events of malaria prophy- Animal studies in which mefloquine was injected in the IO and laxis and treatment. Although this adverse effect is not defined on studies on Cx36-deficient mice have shown comparable motor direct clinical grounds (i.e., people do not report the adverse effect learning problems (Frisch et al., 2005; Van Der Giessen et al., 2008). reduced motor learning as a result of mefloquine usage), it can have Frontiers in Neuroscience | Neuropharmacology November 2010 | Volume 4 | Article 191 | 6