title: Chronic lead exposure alters presynaptic calcium regulation and synaptic facilitation in Drosophila larvae.
abstract: Prolonged exposure to inorganic lead (Pb(2+)) during development has been shown to influence activity-dependent synaptic plasticity in the mammalian brain, possibly by altering the regulation of intracellular Ca(2+) concentration ([Ca(2+)](i)). To explore this possibility, we studied the effect of Pb(2+) exposure on [Ca(2+)](i) regulation and synaptic facilitation at the neuromuscular junction of larval Drosophila. Wild-type Drosophila (CS) were raised from egg stages through the third larval instar in media containing either 0 microM, 100 microM or 250 microM Pb(2+) and identified motor terminals were examined in late third-instar larvae. To compare resting [Ca(2+)](i) and the changes in [Ca(2+)](i) produced by impulse activity, the motor terminals were loaded with a Ca(2+) indicator, either Oregon Green 488 BAPTA-1 (OGB-1) or fura-2 conjugated to a dextran. We found that rearing in Pb(2+) did not significantly change the resting [Ca(2+)](i) nor the Ca(2+) transient produced in synaptic boutons by single action potentials (APs); however, the Ca(2+) transients produced by 10 Hz and 20 Hz AP trains were larger in Pb(2+)-exposed boutons and decayed more slowly. For larvae raised in 250 microM Pb(2+), the increase in [Ca(2+)](i) during an AP train (20 Hz) was 29% greater than in control larvae and the [Ca(2+)](i) decay tau was 69% greater. These differences appear to result from reduced activity of the plasma membrane Ca(2+) ATPase (PMCA), which extrudes Ca(2+) from these synaptic terminals. These findings are consistent with studies in mammals showing a Pb(2+)-dependent reduction in PMCA activity. We also observed a Pb(2+)-dependent enhancement of synaptic facilitation at these larval neuromuscular synapses. Facilitation of EPSP amplitude during AP trains (20 Hz) was 55% greater in Pb(2+)-reared larvae than in controls. These results showed that Pb(2+) exposure produced changes in the regulation of [Ca(2+)](i) during impulse activity, which could affect various aspects of nervous system development. At the mature synapse, this altered [Ca(2+)](i) regulation produced changes in synaptic facilitation that are likely to influence the function of neural networks.
authors.affiliation: Department of Biological Sciences, University at Albany, SUNY, Albany, NY 12222, USA.
authors.forename: T
authors.initials: T
authors.lastname: He
authors.forename: H V B
authors.initials: HV
authors.lastname: Hirsch
authors.forename: D M
authors.initials: DM
authors.lastname: Ruden
authors.forename: G A
authors.initials: GA
authors.lastname: Lnenicka
mesh_terms: D000818:Animals; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004330:Drosophila; D004558:Electric Stimulation / Q000379:methods; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects; D005260:Female; D007814:Larva / Q000166:cytology* / Q000254:growth & development / Q000378:metabolism; D007854:Lead / Q000494:pharmacology*; D008297:Male; D009469:Neuromuscular Junction / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000187:drug effects*
chemical_list: D007854:Lead; D002118:Calcium