Motor activity in group-housed and isolated mice with short and long attack latencies: Effects of scopolamine

Methylthioninium chloride reverses cognitive deficits induced by scopolamine: comparison with rivastigmine

RATIONALE

The cholinergic system is involved in cognition as well as in age-related cognitive decline and Alzheimer disease (AD). Cholinergic enhancers ameliorate AD symptoms and represent the main current therapy for AD. MTC (Methylthioninium chloride), an antioxidant with metabolism-enhancing properties may be a novel candidate with pro-cognitive capacities.

OBJECTIVES

This study was performed: (1) to assess the pro-cognitive efficacy of MTC and establish its dose-response; (2) to compare the efficacy of MTC with rivastigmine and (3) to determine the potential for combination therapy by co-administration of MTC and rivastigmine.

METHODS

Spatial cognition of female NMRI mice was tested in a reference memory water maze task. Subjects received intra-peritoneal injections of scopolamine (0.5 mg/kg) followed by vehicle, and/or MTC and/or rivastigmine (0.15-4 mg/kg MTC; 0.1-0.5 mg/kg rivastigmine) in mono or combination treatment.

RESULTS

Scopolamine treatment prevented spatial learning in NMRI female mice and the deficit was reversed by both rivastigmine and MTC in a dose-dependent manner. Mono-therapy with high doses of rivastigmine (>0.5 mg/kg) caused severe side effects but MTC was safe up to 4 mg/kg. Co-administration of sub-effective doses of both drugs acted synergistically in reversing learning deficits and scopolamine-induced memory impairments.

CONCLUSIONS

In our model, MTC reversed the spatial learning impairment. When combined with the ChEI rivastigmine, the effect of MTC appeared to be amplified indicating that combination therapy could potentially improve not only symptoms but also contribute beneficially to neuronal metabolism by minimising side effects at lower doses.

Effects of housing and nicotine on shuttle-box avoidance in male NMRI mice

The present study aimed to evaluate whether housing condition could interact with nicotine administration in influencing the acquisition of a two-way active avoidance task. Male NMRI mice were either group- or individually housed for 30 days and, after this period, evaluated both in the actimeter and, 24h later, in the elevated plus-maze. On the basis of the percentage of time spent in the open arms of the plus-maze, both group- and individually housed mice were sub-classified into three groups with high, moderate or low anxiety baseline levels. Effects of nicotine on the acquisition of the two-way active avoidance task was assessed in each of these groups of mice using an automated shuttle-box. Mice were treated with nicotine (0.35 mg/kg) or vehicle before each daily training session in the shuttle-box (30 trials) over 5 days. The results showed that motor activity counts were significantly higher in individually housed mice than in group-housed counterparts. The factor "anxiety" in the active avoidance test did not reach statistical significance but the factor "housing" did. The number of avoidances was higher in individually housed than in group-housed mice. Separate analyses performed for individually and group-housed animals indicated that group-housed nicotine-treated mice displayed fewer number of avoidances than saline-treated counterparts. It was concluded that housing condition may be a useful variable in evaluating the effects of nicotine on learning tasks. Indeed, the two-way active avoidance task seems to be sensitive to housing condition.

Spatial learning in male mice with different levels of aggressiveness: effects of housing conditions and nicotine administration

The main aim of the present investigation was to evaluate the possible modulation of spatial learning ability by housing conditions and level of aggressiveness in mice, also testing whether differences in locomotion and anxiety could influence this relationship. Additionally, we have examined effects of nicotine in the acquisition and retention of a spatial learning task in groups of mice differing in these variables. NMRI male mice were either group-housed or individually housed for 30 days and then classified into mice with short (SAL) and long (LAL) attack latency after a pre-screening agonistic encounter. Locomotor activity and baseline levels of anxiety of these groups were evaluated in the actimeter and elevated plus-maze. Results indicated that SAL and LAL individually housed mice displayed higher locomotion activity than LAL group-housed mice. In the plus-maze test, SAL and LAL individually housed mice showed more total and open arm entries than group-housed LAL mice, confirming the hyperactivity of individually housed mice and suggesting that isolation had no clear anxiolytic or anxiogenic actions. In the water-maze, we compared the performance of individually housed SAL, individually housed LAL mice, and group-housed LAL mice treated with nicotine (0.35 and 0.175 mg/kg) or vehicle. Nicotine did not improve acquisition in group-housed mice and even impaired it in individually housed mice. Retention of platform position was better in vehicle-treated individually housed mice in comparison with vehicle-treated group-housed mice. The present study demonstrates that housing conditions but not level of aggressiveness modify spontaneous locomotor activity and behaviors displayed on the elevated plus-maze test, and can also influence retention of a spatial learning task.