Developmental milestones and behavior of infant rats: The role of sensory input from whiskers.

Developmental milestones are behavioral and physical skills which are considered as markers of neurodevelopment. In rodents, sensory input from whiskers plays a crucial role in development of brain functions. Development of whisker system in rats includes the early period of passive whisker touch (PN1-8) before the onset of coordinated whisker movements which underlie active sensing. Inasmuch as transitioning from passive to active sensing requires a strong sensorimotor integration, we assume that the effect of whisker deprivation during the period of passive touch is unfavorable for neurodevelopment, but deprivation after the onset of active sensing might elicit less harmful effect due to compensatory neuroplalstic changes. Here we examined the effect of complete whisker trimming (WT) in WAG/Rij rats during PN1-8 and PN9-16 (active sensing) on achieving developmental milestones (e.g., eyelid opening, walking, self-grooming, rearing activity, physical maturation of forelimbs), locomotor activity and body weight. Control groups underwent sham trimming during the same periods. WT during PN1-8 caused a delay in achieving all investigated milestones, but WT during PN9-16 delayed only self-grooming. Both WT/sham trimming during PN9-16 caused a delay in explorative behavior, but accelerated self-grooming. These changes are likely to link with the effect of manipulations during PN9-16 in previously unhandled pups, but not specifically with WT. In general, developmental milestones appeared to be an informative tool to access neurodevelopment in rat pups and might have a translational value for studying developmental disorders during early life.