Time dependent effects produced in chicks after prenatal injection of methylmercury

Methylmercury dicyandiamide (0.05 to 10 mg/kg eff) injected into the volk sac of fertilized chicken eggs prior to incubation produced a dose related decrease in the percentage of chicks hatched (90-57% of control). With dosage fixed at 0.5 or 5.0 mg/kg egg and injections made on Days 0, 7 or 14 of incubation, hatches were 90, 68 and 75%, respectively, for the low dose and 63, 13 and 18% for the high dose. In contrast to results obtained from chicks hatched from eggs injected on Day 0 of incubation, chicks hatched from eggs injected with 0.5 or 5.0 mg MMD/kg on Day 7 or 14 were not different from controls in a detour learning situation. Administration of 14-C methylmercury revealed maximal brain radiolabel in embryos injected on Day 0 to be 10% that seen with eggs injected on Day 7 but twice that seen with eggs injected on Day 14. We tentatively conclude that a period of maximal sensitivity to the behavior effects exists prior to Day 7 and that the mechanisms of embryolethality is different from that producing the functional deficits.