Ontogeny of behavior in two inbred lines of selected mice.

The development over 11 ages of 14 reflex responses, 26 behavioral components, jumpiness, and left-right discrimination learning was studied in 2 strains of mice genetically selected for high (SRH) and low (SRL) rearing response frequency. Significant age-dependent differences between the strains were found mainly, but not exclusively, in the behavioral components, e.g., rearing, jumping, scratching, defecating. Two-week-old pups of both strains showed good acquisition and retention in learning tests without shock, but the "jumpy" behavior disturbed performance to a certain degree in the SRH strain. Although less active initially, SRH mice were ahead at later developmental stages. Whether these differences are determined by the gene controlling rearing frequency or by other genes remains undecided.