METHYL MERCURY DURING LATE-GESTATION AFFECTS TEMPORARILY THE DEVELOPMENT OF CORTICAL MUSCARINIC RECEPTORS IN RAT OFFSPRING

Pregnant Sprague-Dawley rats were treated by gavage with a single dose of 8 mg/kg of methyl mercury on gestational day 15. Offspring of cont rol and treated rats were killed at 14, 21 and 60 days of age. The bin ding characteristics of muscarinic receptors labelled in cortical memb rane preparation by H-3-L-quinuclidinyl benzilate were studied togethe r with the assessment of mercury level in the same brain area. Further more, the performance in passive avoidance tasks was evaluated in 8 we eks old rats. Perinatal exposure to methyl mercury significantly reduc ed the maximum number of muscarinic receptors (Bmax) in the brain of 1 4 (53%) and 21 day old rats (21%), while this change was no more prese nt in 60 day old rats. This phenomenon seems to be strictly related to the presence of mercury in the cortex since it disappeared with the n ormalization of mercury levels in the brain. Despite the recovery of m uscarinic receptor densities in methyl mercury exposed rats at 8 weeks of age, the avoidance latency was reduced in passive avoidance test a s an indication of learning and memory deficits in these animals. Resu lts from this study indicate that prenatal methyl mercury exposure ind uces latent cognitive dysfunction which does not seem to be related to transient muscarinic receptor alteration found in the early period of postnatal life.