Strain dependent effects of ketamine on locomotor activity and antinociception in mice.

The effects of ketamine (12.5, 25 and 50 mg/kg) on locomotor activity and response to nociceptive stimuli were investigated in the inbred strains of mice: BALB/c (BALB), C57BL/6 (C57) and DBA/2 (DBA). In the BALB and in the C57 mice ketamine exerted activity stimulating effects, which were already present at doses lower than those inducing antinociception. Locomotor depressent effects were evident in the DBA mice following the administration of doses higher than those necessary to induce analgesia. It is suggested that: (1) ketamine affects locomotor activity and response to painful stimuli through different mechanisms, (2) the brain regional and biochemical differences reported for the strains considered may account for their different responses to ketamine administtation.