Behavioural and neurochemical changes in offspring of rats exposed to methyl mercury during gestation.

On day 8 of gestation, pregnant Sprague-Dawley rats were intubated with 8 mg/kg of methyl mercury (MM). At 15 days of age, stereotyped sniffing was elicited by a challenge dose of apomorphine (1 mg/kg) only in pups prenatally exposed to MM; furthermore, at 22 days of age, the stereotyped behaviour induced by apomorphine (0.5-1 mg/kg) was significantly potentiated in MM-pretreated animals. Neurochemical data showed that at 22 days of age there was a significant increase of 3H-spiroperidol binding sites in striatal membranes of MM-pretreated rats. At 40 and 60 days of age, these behavioural and neurochemical changes were absent. On the other hand, prenatal exposure to MM influenced neither the effects of a challenge dose of clonidine (0.025 mg/kg) on locomotor activity nor the affinity and the density of alpha-2 adreno-receptors in cortex of 15, 22, 40 and 60 day old rats. The behavioural alterations in the response to apomorphine presumably result from an enhancement of dopamine binding sites induced by MM. Finally, our data further confirm that prenatal MM induces long lasting behavioural alterations which can be accurately displayed by using passive avoidance procedures.