HANDLING DURING SUCKLING ALTERS RAT BEHAVIOR BUT DOES NOT REVERSE THEDELETERIOUS EFFECTS OF UNDERNUTRITION ON NALTREXONE-INDUCED INHIBITION OF EXPLORATORY ACTIVITY

The effects of undernutrition during suckling, early environmental sti mulation and naltrexone administration on the locomotor activity test were investigated in adult rats. Young rats were undernourished from d elivery until weaning (23 days) by feeding their dams a diet containin g 7% casein diet. Mothers of well-nourished rats were fed a 25% casein diet. After weaning, both groups of rats received standard lab chow. From day 2 to day 8 after delivery the animals were stimulated by bein g placed individually in plastic containers for 4 minutes. From day 12 to 19 the litters were removed from their home cages and placed for 1 0 min in plastic cages. Exploratory behavior was assessed using a bioc ompartmentalized open field The number of crossings from one compartme nt to the other and the number of rearings were recorded Undernourishe d animals crossed less frequently than control animals and presented a higher latency to the first crossing response. Early handling increas ed the total number of rearing responses regardless of nutritional tre atment. Naltrexone administration caused a dose-dependent reduction in the number of rearing responses only in the well-nourished group.