Locomotor Activity Studies in Mice

Thirty-two male mice with a C57BL/6J genetic background and body weight 22–25 g were purchased from the Charles River Laboratories (Raleigh, NC). After arrival, they were group housed (4 per cage) in the animal facility under a reversed 12 h light-dark cycle (light on at 7:00 PM) with free access to food and water, and allowed to acclimate to the new environment for 7 days prior to initiating the experiment. All procedures were in accordance with the “Principles of Laboratory Animal Care” outlined by National Institute of Health (NIH publication 86-23, 1996).

Locomotor activity tests were conducted in open-field chambers (43 × 43 × 30 cm) (Accuscan Instruments, Inc., Columbus, OH, USA). Before testing, the mice were habituated to the locomotor chamber (2 h/day for 3 consecutive days), and then were randomly divided into 4 groups (n=8 per group) to examine the effects of cocaine, (R)-modafinil [(R)-2], compounds 4 and and 11b on locomotor activity, respectively. On habituation days, the animals were moved to the test room, acclimated there for about 30 min, and then placed in their assigned locomotor chambers. On test day 1, each group of mice was first placed in the locomotor chambers for 1 h habituation, and then they received either vehicle (25% of 2-hydroxypropyl-β-cyclodextrin) or one dose of the corresponding test compound. The animals were then immediately placed into the test chambers. Their locomotor activities were recorded every 10 min for 2 h. Each animal was tested 3 times with 3 different doses, with the inter-test interval of 3–5 days. The order of the drug doses was counter-balanced.

The locomotor behavioral data are expressed as means (±S.E.M.). The traveled distance (cm) every 10 min (Fig. 5) was used to evaluate the locomotor effects of each test compound in mice. Two-way ANOVA with repeated measures over time was used to evaluate the statistical significance of the changes in locomotor activity after each drug administration. Post-hoc Fisher’s least significant difference was used for multiple comparisons. p<0.05 was considered statistically significant.