From parents to offspring: spontaneous variations of phenotype influence descendants' behavior

Spontaneous variations of behavioral phenotype towards/away from salient stimuli can even occur within a mice inbred C57BL/6J strain. By using the Approaching/Avoiding (A/A) Y-Maze Test it has been demonstrated that in males the A/A behavior is normally distributed, allowing to evidence three different phenotypes: avoiding, mice that reacted with withdrawing responses to the conflicting stimuli (appetitive food in aversive environment), balancing, mice that reacted with balanced responses to the conflicting stimuli, and approaching, mice that reacted with advancing responses to the conflicting stimuli. Starting from the evaluation of the same distribution also in the C57BL/6J females, AV/BA/AP animals of both sexes were selected. The aim of the study was to investigate the differences in parenting style linked to the different maternal and paternal phenotypes and to assess if such differences can influence the behavioral phenotype of offspring. To this aim males and females of the three phenotypes were tested in the Open Field Test with novel object (OF) and Elevated Plus Maze (EPM) and then mated, to assemble parenting couples of double (both AV or AP mother and father), single (one AV or AP parent and the other BA parent) and control (both BA mother and father) composition. The different couples obtained were kept in exclusive relationship throughout pregnancy, delivery and even up to the weaning of offspring. The influence of the phenotype on parenting style was assessed by undisturbed parental care 30-min observation at pup post-natal day (pnd) 3. Male and female offspring was tested in the A/A Y-Maze (pnd 35-38), OF and EPM (pnd 55-60). Results indicate that offspring behavior varied according to maternal/paternal phenotype as well as to parental care, with significant differences between males and females.