Limited changes in handedness and morphine reactivity in CD-1 mice after pre- and postnatal ozone exposure

Outbred CD-1 mice were either not exposed (control group) or exposed to ozo ne (O-3) (0.3, 0.6, or 0.9 ppm), during foetal and neonatal life until the time of weaning (postnatal day (PND) 26). On PND 70 the subjects were teste d for handedness using a paw preference task assessing both the animals' ca pability to reach a food pellet in a feeding tube and the individual prefer ence for the use of one of the other forepaw. O-3 exposure did not affect t he animals' capability to learn the task but caused changes in handedness. Specifically, females exposed to the intermediate O-3 concentration showed a reduced preference for the right paw than both their same-sex controls an d 0.6 ppm males. On PND 100, mice underwent a hot plate test after IP treat ment by either saline or morphine HCl (10 mg/kg). The results were generall y in the direction of reduced drug sensitivity after exposure to the highes t concentration. The evidence for this effect was more robust in the case o f an organised avoidance response (wall-rearing) than in the case of a refl exive response (limb withdrawal); in the case of the former, latency data s howed an effect on both males and females while frequency data showed an ef fect only in females. Overall, the O-3 effects are suggestive of subtle CNS changes affecting mouse behavioural responses.