† These authors contributed equally to this manuscriptThe rotorod is commonly used to assess motor ability in mice. We examined a number of inbred strains to determine whether there is genetic variability in rotorod performance and motor learning. Mice received three trials per day for three days in a modified accelerating rotorod paradigm, and active rotation performance was calculated for each day. Male and female 129S1/SvImJ, A/J, BALB/cByJ, C3H/HeJ, C57BL/6J, CBA/J, DBA/2J and FVB/NJ mice were tested. Strain and sex differences were observed in motor performance. Motor learning also differed across strains, as some strains showed an improvement in performance over the three days while other strains did not. In certain strains the weight and body length of the mouse correlated with rotorod performance. The role of vision in motor performance on the rotorod was assessed by a comparison of C3H/HeJ mice (with retinal degeneration) and congenic C3A.BLiA-Pde6b + (Pdeb+) mice (without retinal degeneration). The sight-impaired C3H mice stayed on the rotorod longer than did their sighted Pdeb+ partners, although both strains improved across days. Thus, we have demonstrated a genetic component in rotorod performance, and we have shown that factors other than inherent motor ability can contribute to rotorod performance in mice.

Most knockout (KO) mice are produced with embryonic stem cells derived from a 129 strain. Because most KO strains are backcrossed to B6 yet retain a portion of their genome from 129, especially around the ablated target locus, phenotypes previously attributed to the ablated locus may be due to passenger 129 genes. Thus, the authors decided to test several 129 substrains for their behavioral characteristics. Seven 129 substrains were put through a battery of tasks to determine their behavioral profiles. Differences were found in anxiety-related behaviors in the zero-maze, habituation to the open field, and cued fear conditioning. All strains successfully performed the rotorod task. The behavioral differences observed may have important implications for the interpretation of data and show divergence of behavioral performance in these 129 substrains.

No abstract

The increasing use of methylphenidate hydrochloride (MPH) in children led us to examine the effects of MPH administration in developing mice. Male CD-1 mice were administered MPH (40 mg/kg, subcutaneously) or saline daily from postnatal days 26-32. The mice were then tested from postnatal days 33-37 for locomotion and exploration in the open field, anxiety in the elevated plus maze, and learning in the Morris water maze. The results indicate that MPH-pretreated mice were more exploratory and less fearful in the open field, entering more center squares than saline controls. MPH-pretreated mice also exhibited less anxiety, spending more time in the open arm and exhibiting more head dips in the elevated plus maze than controls. There was no significant difference between MPH and saline-treated mice in the time taken to find the visible or hidden platform in the water maze task. The results indicate that treatment with MPH has significant effects on later behavior, reducing fear and anxiety, and increasing exploration, but no effect on performance in a spatial learning task.