Embryonic exposure to thimerosal, an organomercury compound, causes abnormal early development of serotonergic neurons

► We found small clusters of serotonergic neurons in the dorsal area of caudal raphe. ► Dramatic increase in the number of serotonergic neurons after exposure to thimerosal. ► Embryonic exposure to thimerosal affects early development of serotonergic neurons.