Resumo

Introduction: Ethanol ingestion during pregnancy is associated with several cognitive and neuroanatomical abnormalities in the offspring. Animal models allow experimental control over dose and period of exposure and a wide range of methods for administering ethanol have been used in studies with animals. One of the most common and validated is the use of liquid diets containing differing amounts of ethanol. The most widely used procedure entails the addition of 68 ml of ethanol for each litre of diet, leading to 35% of ethanol-derived calories (EDC). However, the literature on the effects of small doses of ethanol in animals is scarce. Indeed, the threshold dose for the teratogenic effects of ethanol is uncertain. This study compared the effects of exposure to a standard (35% EDC) and a low dose (10% EDC) of ethanol during pregnancy on the offspring of Wistar rats. Method: 49 pregnant rats (two to three months old) were assigned to one of the four maternal treatments: A35-liquid diet with 35% EDC, A10-liquid diet with 10% EDC, with caloric intake limited by pair-feeding to match that in the A35 group, Control-liquid diet without ethanol with caloric intake limited by pair-feeding to match that in the A35 group and Chow- free access to laboratory chow and water. During pregnancy, the animals were weighed three times a week. The litters were tested for developmental milestones: weight (PND 1-40), negative geotaxis (PND 7-10), grip strength (PND 14 and 17) and locomotor activity (PND 19). Results: The dams treated with liquid diet gained less weight during pregnancy than the ones in the free-feeding Chow group [F(3,44)=4.9, p=0.005]. Group A35 gave birth to 18 stillborn pups, and 19 other pups died during PND 1-7, so only 43% of the pups in this group survived. During postnatal days 1-40 the weight of male pups from the A35 group was lower than all other groups [F(3,37)=5, p=0.005]. During the same period, the weight of A35 female pups was lower than the Chow group [F(3,34)=2.8, p=0.054]. The groups did not differ in the negative geotaxis task (p>0.05). In the grip strength both males [F(3,37)=3.8, p=0.018] and females [F(3,38)=4.6, p=0.007] from the A35 group had a significantly worse performance than Control and Chow groups. The evaluation of the locomotor activity at postnatal day 19 shows that the males from the A35 group walked significantly further than groups A10 and Control [F(3,89)=3.7, p=0.013]. Discussion: The high mortality and the impaired weight gain of the group prenatally treated with the higher dose of ethanol are consistent with earlier studies. Moreover, the deficits in development of muscle strength are consistent with studies that demonstrated similar impairments with other doses of ethanol. Additionally, prenatal exposure to ethanol has been found to reduce somatosensory and motor cortical representation of rats’ forelimbs, which may underlie the verified deficits in reflex development. In the present study, the male offspring of group A35 showed more ambulation, but there are conflicting evidences about the effects of prenatal exposure to ethanol on locomotor activity. The overall results of our study suggest that litters derived from dams treated with a lower amount of ethanol did not present any detectable impairments. These results indicate that the threshold for the teratogenic effects of ethanol lies between 10 and 35% EDC. This study was supported by the Wellcome Trust and CNPq.