M.C. Carrasco

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.

Effects of early spatial training on water maze performance: a longitudinal study in mice.

The aim of the present study is to establish whether in mice the effects of an early experience in the Morris water maze are maintained after a long period. A longitudinal study was performed in which mice of two different strains (NMRI and C57) received spatial training at 2 months of age and their performance was re-evaluated 8 and 16 months later. In both strains, results showed a beneficial effect of prior experience on this spatial memory task even 8 months after the initial training. At 18 months of age, performance of C57 mice that were trained at 2 months of age for the first time was similar to those who received their first training at 10 months of age. These findings suggest that the beneficial effect of previous training could be limited by time. In addition, water maze performance of 18 month-old C57 mice did not differ from their earlier performance when they were 10 months of age, which would indicate that experience in this task could prevent some of the age-related spatial learning deficits observed in mice.

Previous training in the water maze: differential effects in NMRI and C57BL mice.

It has been shown that acquisition rates in the water maze vary across strains of mice, although the differential effects of previous experience in this spatial task have been scarcely evaluated. The aim of the present study was to evaluate the effects of training in the water maze at an early age (2 months) in two strains of mice (NMRI and C57BL) using a longitudinal study. Mice with or without previous training were tested when they were 6 months, and retested when 10 months old. The results showed that trained NMRI mice performed better than all the other groups, both at test and retest, indicating that previous training had more beneficial effects in NMRI than in C57BL mice. These results demonstrate that the effects of an early training in the water maze may be influenced by the characteristics of the strain of mice. It could have implications in longitudinal studies evaluating effects of pharmacological or behavioral manipulations.

Time estimation and aging: a comparison between young and elderly adults.

Studies about effects of aging on the estimation of short temporal intervals are not conclusive. The aim of the present research was to evaluate age-related differences in the reproduction of a short interval (10 s) using a computerized method. The sample comprised thirteen young adults (M = 26.15 years) and twelve elderly adults (M = 79.1 years). Three parameters of time estimation were measured: estimated time, absolute error, and standard deviation. Results showed that time estimates performed by elderly participants were shorter than those of younger ones, although there were no significant differences between the two age groups in the percentage of absolute errors or standard deviations. These findings could be explained by changes in the rate of the internal clock or to an interaction between more general changes in cognitive processes.

Differential sensitivity to the effects of nicotine and bupropion in adolescent and adult male OF1 mice during social interaction tests

Few studies have compared the action of both nicotine (NIC) and bupropion (BUP), an antidepressant used to treat NIC dependence, on social and aggressive behavior at different ages. This study aims to determine whether these drugs produce differential effects in adolescent (postnatal day: 36-37) and adult (postnatal day: 65-66) mice that have been housed individually for 2 weeks in order to induce aggressive behavior. Mice received BUP (40, 20, or 10 mg/kg), NIC (1, 0.5, and 0.25 mg/kg as base), or vehicle earlier to a social interaction test. BUP (40 mg/kg) decreased social investigation and increased nonsocial exploration in both adolescent and adult mice. The same effects were also observed in adult mice administered with a lower dose of the same drug (20 mg/kg). In adolescents, NIC (1 mg/kg) decreased social investigation, but this effect did not reach statistical significance in adults. In conclusion, a differential sensitivity to the effects of NIC or BUP emerged in some of the behavioral categories when the two age groups were compared.

Effects of lobeline on spatial learning in C57BL mice

In the present study, the effect of lobeline on water maze performance in C57BL/6J mice have been evaluated. In the first experiment, subjects were 2-month old mice to which lobeline (3.5 and 7 mg/kg) had been administered SC along 5 days 15 min before daily training in the water maze. Results showed that lobeline did not have effects on the acquisition of the task. In the second experiment, effects of lobeline were compared in 2, 6 and 20-month old mice. In this experiment the drug was administered daily five days prior to the beginning of the task and during the five days of acquisition. Results indicated that 20-month old mice learned the spatial task more slowly than 2 and 6-month old mice and that lobeline treatment did not have a significant effect on this rate of learning.

Differential effects of bupropion on acquisition and performance of an active avoidance task in male mice.

Bupropion is an antidepressant drug that is known to aid smoking cessation, although little experimental evidence exists about its actions on active avoidance learning tasks. Our aim was to evaluate the effects of this drug on two-way active avoidance conditioning. In this study, NMRI mice received bupropion (10, 20 and 40mg/kg) or saline before a daily training session (learning phase, days 1-4) in the active avoidance task. Performance was evaluated on the fifth day (retention phase): in each bupropion-treated group half of the mice continued with the same dose of bupropion, and the other half received saline. Among the vehicle-treated mice, different sub-groups were challenged with different doses of bupropion. Results indicated that mice treated with 10 and 20mg/kg bupropion exhibited more number of avoidances during acquisition. The response latency confirmed this learning improvement, since this parameter decreased after bupropion administration. No differences between groups were observed in the retention phase. In conclusion, our data show that bupropion influences the learning process during active avoidance conditioning, suggesting that this drug can improve the control of emotional responses.