The stability of motor activity in rats

Individual differences in motor activity were investigated in two groups of male rats. One group contained non-homozygotic and the second homozygotic rats. In both groups the individual differences were similar and very pronounced. Starting from the age of about 3 months the level of motor activity in individual animals remained relatively stable until the age of at least 6 1/2 months. The results may be useful for certain behavioural investigations and for long-term pharmacological studies and bioassays.