Fig. 1.

The Effect of Different Doses of Amphetamine (amph, Top Panel) and MK-801 (MK, Bottom Panel) on Locomotor Activity of C57BL/6 Mice (M. van den Buuse, unpublished data). Both drugs showed little effect at the lowest dose, markedly increase locomotor distance moved at the middle dose, but induced low scores at the highest dose, presumably because of the induction of stereotyped responses which disrupted ambulatory activity. Depending on the dose of the drug, an increase of locomotor distance moved displayed by a genetically modified mouse model could either mean hypersensitivity or hyposensitivity to the treatment. Locomotor distance moved was assessed using automated photocell cages (see van den Buuse et al¹⁷⁵ for details). Doses indicated are in milligram per kilogram. There were 8–20 mice per group, and data are expressed as mean ± standard error of the mean.