NEONATAL LATERALIZATION OF BEHAVIOR AND BRAIN DOPAMINERGIC ASYMMETRY

Behavioral lateralization has previously been reported in adult animal s. This work presents a study of behavioral laterality and spontaneous alternation behavior in 156 neonatal rats (39 litters with two males and two females per fitter). The initial tail and head lateral movemen ts (axis body-tail or head higher than 30 degrees) were recorded after neonatal rats were gently placed along a straight line drawn on a gla ss surface. This test was repeated 10 times. A leftward population lat eralization was found for tail movement while head movement was rightw ard. The alternation behavior was lower (10-25%) than that previously reported for adult rats (80-90%) and than that expected if movement wa s made at random (50%). Males were more lateralized than females for h ead and tail movements. No sex differences were observed for behaviora l alternation. In 2-day-old rats (10 litters with one male and one fem ale per litter), the right brain side had a higher content in dopamine (mesencephalon) and DOPAC (proencephalon) than the left brain side. T hus, we concluded that behavioral and biochemical asymmetries in anima ls are conditioned by phenomena present during prenatal or early neona tal (first hours after birth) life and that spontaneous alternation be havior is not present during the earlier stages of postnatal developme nt.