180 Brain Research, 322 (1984) 180-183 Elsevicr BRE 20459 In vivo chronic lead exposure alters pH]nitrendipine binding in rat striatum R. A. RIUS, L. LUCCHI, S. GOVONI and M. TRABUCCHP Institute of Pharmacology and Pharmacognosy, University of Milan, Milan and IChair of Toxicology, II University of Rome, Rome (Italy) (Accepted June 26th, 1984) Key words: lead exposure - - calcium antagonist binding-- striatal membranes The effect of lead as a neurotoxic agent has been associated with alterations in calcium metabolism. On this line, the present study shows that lead alters the characteristics of [3H]nitrendipine ([3H]NDP) binding to rat striatal membranes. In vitro, lead shares the ac- tion of calcium in enhancing [3H]NDP binding although it is more potent on a molar basis. In vivo, lead exposure through drinking wa- ter enhances [3H]NDP binding to crude synaptosomal membrane preparations. This effect is lost when membranes are washed with EDTA-EGTA, indicating that the increased binding is due to the persistence of lead in the brain of treated rats. Lead poisoning is associated with a wide account of symptoms pointing out brain impairment3,9.15; in fact, lead intoxication modifies various neurochemical parameters indicating an alteration of the functional state of cholinergic 17,2°, noradrenergiO 22 GABAer- gic 13,19 and dopaminergic neurotransmission 6. The effect of lead on neurotransmitters may be at least partially due to an interaction with calcium in the mechanisms regulating release, uptake and metabo- lism of neurotransmitters at neuronal level. In partic- ular, in vitro data on striatal synaptosomes show that lead potentiates calcium-dependent dopamine re- lease. In addition, it has been shown that lead may decrease the affinity of brain mitochondria for calci- um 2,4, leading to an accumulation of free intracellular calcium, which is harmful for the cell 23. Calcium entry is a regulated process', in particular, calcium channel opening (either voltage-dependent or receptor-operated ~6) modulates the influx of calci- um into the cell. The availability of labelled organic calcium entry blockers made possible the study of calcium channels in different tissues including the brain ~2.1s. In the present investigation the effect of lead on [3H]NDP binding was studied both by adding this ion in vitro and after chronic in vivo exposure of the animals through the drinking water. Pregnant Sprague-Dawley rats (Charles River, Calco, Italy) were used in our study. Animals at day 16 of pregnancy were caged individually and housed at constant temperature (22 °C) and humidity (50%). They were exposed to a light cycle of 12 h a day (from 07.00 to 19.00 h) and had free access to food and water. Mothers were given a lead acetate solution (2.5 g/l; 1360 ppm lead) or sodium acetate as control in their drinking water. The offspring were reduced to 10 animals/litter after birth. At 21 days of age the young rats were separated from their mothers and divided by sex. They received the same drinking solution which had been supplied to the mothers. Lead-treated rats showed no significantly different growing rate with respect to the age-matched con- trois. At 6 weeks of age the animals were killed by de- capitation. Brains were quickly removed, striatal tis- sues dissected and frozen on dry-ice. Tissue was ho- mogenized using an Ultra-Turrax homogenizer (set- ting 2, 10 s) in 20 vols. of 0.32 M sucrose. The result- ing homogenate was centrifuged at 1000 g for 10 min. Supernatant was centrifuged again at 48,000 g for 15 min. The pellet was treated as follows: (A) resus- pended in 25 vols. of 50 mM Tris-HCl pH 7.4 and then centrifuged as before and used; or (B) exten- sively washed with EDTA (10 mM)-EGTA (10 raM) Correspondence: R. A. Rius, Institute of Pharmacology and Pharmacognosy, University of Milan, Via Andrea del Sarto 21, 20129 Milano, Italy. 0006-8993/84/$03.00 © 1984 Elsevier Science Publishers B.V.