Ontogeny and interdependence of genetically selected behaviors in rats: avoidance response and open field

Ontogeny and interdependence of genetically selected avoidance and open-field behaviors were investigated in six genetic lines, involving 1,018 animals, and three developmental models (longitudinal, cross sectional, and generational). In selected lines, behaviors varied with age, depending upon the genetic selection; in the control (random bred) line, no such effects were found. Between the lines selected for high (RHA) and low (RLA) rates of two-way-active avoidance, ontogenetic differences in the selected behavior emerged as the animals grew older, whereas between the lines selected for high (MR) and low (MNR) frequency of open-field defecation, the differences in the selected behavior were present at all stages of development. In unconditioned escape response to footshock, which shows an inverse relation to avoidance response in the RHA and RLA lines, and in general activity (number of sections crossed in an open field), which shows inverse relation to defecation in the MNR and MR lines, the differences were present at all stages. The relation between avoidance response and open-field defecation (emotional reactivity) was not linear but suggestive of curvilinear inverted-U-function.