title: Waterborne lead exposure affects brain endocannabinoid content in male but not female fathead minnows (Pimephales promelas).
abstract: There are several similarities between the behavioral and neurochemical effects of lead (Pb2+) and the cannabinoids. Both Pb2+ exposure and cannabinoid treatment decrease exploratory behavior. Pb2+-induced hyperactivity has been observed in rats and fish. By comparison, cannabinoids increase locomotor activity at higher doses in rats. Moreover, Pb2+ exposure produces learning and memory impairments as do the cannabinoids. Many of the behavioral effects of Pb2+ are thought to be due, in part, to the ability of Pb2+ to either inhibit or mimic the actions of calcium (Ca2+). At low concentrations, Pb2+ enhances basal release of neurotransmitter from presynaptic terminals by increasing intracellular free Ca2+ concentrations. Pb2+ also decreases evoked neurotransmitter release due to blockade of voltage-gated Ca2+ channels. Interestingly, the endocannabinoids (eCBs) including N-arachidonylethanolamine (AEA) and 2-arachidonylglycerol (2-AG) are synthesized in response to increases in intracellular Ca2+ and activate the CB1 receptor that inhibits voltage-gated Ca2+ channels. We tested the hypothesis that waterborne Pb2+ exposure significantly affects whole-brain eCB content in adult male and female fathead minnows (Pimephales promelas). Waterborne Pb2+ exposure (1.0 ppm) resulted in a time-dependent accumulation of Pb2+ in bone in both males and females. Brain AEA and 2-AG content were significantly greater in females compared to males. Pb2+ exposure increased brain AEA content in males at 7 and 14 days of exposure and increased brain 2-AG content at 14 days. Pb2+ exposure had no effect on either brain AEA or 2-AG content in females at any of the time points examined. As eCBs serve as activity-dependent retrograde inhibitors of neurotransmitter release, the increase in brain eCB content would accentuate Pb2+-induced decreases in evoked neurotransmitter release in male but not female fathead minnows.
authors.affiliation: Department of Pharmacology and Toxicology, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA. drademac@mcw.edu
authors.forename: David J
authors.initials: DJ
authors.lastname: Rademacher
authors.forename: Daniel N
authors.initials: DN
authors.lastname: Weber
authors.forename: Cecilia J
authors.initials: CJ
authors.lastname: Hillard
mesh_terms: D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D001842:Bone and Bones / Q000737:chemistry; D001923:Brain Chemistry / Q000187:drug effects*; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism*; D002853:Chromatography, Liquid; D003530:Cyprinidae / Q000378:metabolism*; D063388:Endocannabinoids; D005260:Female; D005989:Glycerides / Q000378:metabolism; D007854:Lead / Q000032:analysis / Q000633:toxicity*; D008297:Male; D013058:Mass Spectrometry; D012727:Sex Characteristics; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*
chemical_list: D001095:Arachidonic Acids; D063385:Cannabinoid Receptor Modulators; D063388:Endocannabinoids; D005989:Glycerides; D014874:Water Pollutants, Chemical; D007854:Lead; C094503:glyceryl 2-arachidonate