Ontogenetic Exposure of Rats to Pre- and Post-Natal Manganese Enhances Behavioral Impairments Produced by Perinatal 6-Hydroxydopamine

Abstract

Rats lesioned shortly after birth with 6-hydroxydopamine (6-OHDA; 134μg icv) represent a near-ideal model of severe Parkinson's disease because of the near-total destruction of nigrostriatal dopaminergic fibers. The element manganese, an essential cofactor for many enzymatic reactions, itself in toxic amount, replicates some clinical features similar to those of Parkinson's disease. The aim of this study was to examine the effect of neonatal manganese exposure on 6-OHDA modeling of Parkinson's disease in rats. Manganese (MnCl(2)·4H(2)O) 10,000ppm was included in the drinking water of pregnant Wistar rats from the time of conception until the 21st day after delivery, the age when neonatal rats were weaned. Control rats consumed tap water. Other groups of neonatal rat pups, on the 3rd day after birth, were pretreated with desipramine (20mg/kg ip 1h) prior to bilateral icv administration of 6-OHDA (30, 60, or 137μg) or its vehicle saline-ascorbic (0.1%) (control). At 2months after birth, in rats lesioned with 30, 60, or 134μg 6-OHDA, endogenous striatal dopamine (DA) content was reduced, respectively, by 66, 92, and 98% (HPLC/ED), while co-exposure of these groups to perinatal manganese did not magnify the DA depletion. However, there was prominent enhancement of DA D(1) agonist (i.e., SKF 38393)-induced oral activity in the group of rats exposed perinatally to manganese and also treated neonatally with the 30mg/kg dose of 6-OHDA. The 30mg/kg 6-OHDA group, demonstrating cataleptogenic responses to SCH 23390 (0.5mg/kg) and haloperidol (0.5mg/kg ip), developed resistance if co-exposed to perinatal manganese. In the group exposed to manganese and lesioned with the 60mg/kg dose of 6-OHDA, there was a reduction in D(2) agonist (i.e., quinpirole, 0.1mg/kg)-induced yawning. The series of findings demonstrate that ontogenetic exposure to manganese results in an enhancement of behavioral toxicity to a moderate dose of 6-OHDA, despite the fact that there is no enhanced depletion of striatal DA depletion by the manganese treatment.