Taste aversion learning and perinatal methylmercury exposure in mice.

Since a report by Spyker et al.,1) a number of studies have shown various behavioral changes after perinatal exposure to methylmercury in open field tests,2) shock avoidance learning') and operant learning.4) Taste aversion learning is considered a useful examination in behavioral teratology.5) It requires no special behavioral equipments and seems to be less affected by motor dysfunction than other behavioral examinaitons. However, there is no investigation on the effects of perinatal methylmercury exposure on taste aversion learning. Nulliparous CFW mice of 8 week old were mated for one night with the male mice of the same strain and the same age. On day 10 of gestation, pregnant mice were treated with one of the following doses of methylmercury chloride in saline solution by s.c. injectons. Sizes of doses were 13.5, 6.0, 4.0 and 0 (control for methylmercury treatment) mg Hg/kg. In the morning of the day of delivery, numbers of pups of each dam were checked. Body weight of pups was measured on the following day. Mean body weight and its standard deviation of pups for Groups 13.5, 6.0, 4.0 and 0 were 1.47±0.25, 1.85±0.19, 1.82±0.18 and 1.90±0.17 g, respectively. Group 13.5 was significantly lighter than the other three groups by Mann-Whitney test (U(26, 19) = 60.5, U(26, 30) =111 and U(26, 29) = 68.5, for 6.0, 4.0 and 0, respectively; p<0.01). In Group 13.5, 20 mice of 46 neonates deceased before the body weight measurement. At 21 day old of weaning survival rates of offspring for Groups 13.5, 6.0, 4.0 and 0 were 45.7, 94.7, 86.7 and 82.8%, respectively. Group 13.5 was significantly different from other three groups by the chi-square test (p<0.05, for all comparisons). They were housed individually thereafter.