title: Prenatal dexamethasone augments the neurobehavioral teratology of chlorpyrifos: significance for maternal stress and preterm labor.
abstract: Glucocorticoids are the consensus treatment given in preterm labor and are also elevated by maternal stress; organophosphate exposures are virtually ubiquitous, so human developmental coexposures to these two agents are common. This study explores how prenatal dexamethasone exposure modifies the neurobehavioral teratology of chlorpyrifos, one of the most widely used organophosphates. We administered dexamethasone to pregnant rats on gestational days 17-19 at a standard therapeutic dose (0.2 mg/kg); offspring were then given chlorpyrifos on postnatal days 1-4, at a dose (1 mg/kg) that produces barely-detectable (<10%) inhibition of brain cholinesterase activity. Dexamethasone did not alter brain chlorpyrifos concentrations, nor did either agent alone or in combination affect brain thyroxine levels. Assessments were carried out from adolescence through adulthood encompassing T-maze alternation, Figure 8 maze (locomotor activity, habituation), novelty-suppressed feeding and novel object recognition tests. For behaviors where chlorpyrifos or dexamethasone individually had small effects, the dual exposure produced larger, significant effects that reflected additivity (locomotor activity, novelty-suppressed feeding, novel object recognition). Where the individual effects were in opposite directions or were restricted to only one agent, we found enhancement of chlorpyrifos' effects by prenatal dexamethasone (habituation). Finally, for behaviors where controls displayed a normal sex difference in performance, the combined treatment either eliminated or reversed the difference (locomotor activity, novel object recognition). Combined exposure to dexamethasone and chlorpyrifos results in a worsened neurobehavioral outcome, providing a proof-of-principle that prenatal glucocorticoids can create a subpopulation with enhanced vulnerability to environmental toxicants.
authors.affiliation: Department of Psychiatry & Behavioral Sciences, Duke University Medical Center, Durham, NC, USA; Department of Pharmacology & Cancer Biology, Duke University Medical Center, Durham, NC, USA; Nicholas School of the Environment, Duke University, Durham, NC, USA. Electronic address: edlevin@duke.edu.
authors.forename: Edward D
authors.initials: ED
authors.lastname: Levin
authors.affiliation: Department of Psychiatry & Behavioral Sciences, Duke University Medical Center, Durham, NC, USA.
authors.forename: Marty
authors.initials: M
authors.lastname: Cauley
authors.affiliation: Department of Psychiatry & Behavioral Sciences, Duke University Medical Center, Durham, NC, USA.
authors.forename: Joshua E
authors.initials: JE
authors.lastname: Johnson
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA.
authors.forename: Ellen M
authors.initials: EM
authors.lastname: Cooper
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Stapleton
authors.affiliation: Nicholas School of the Environment, Duke University, Durham, NC, USA; Pratt School of Engineering, Duke University, Durham, NC, USA.
authors.forename: P Lee
authors.initials: PL
authors.lastname: Ferguson
authors.affiliation: Department of Pharmacology & Cancer Biology, Duke University Medical Center, Durham, NC, USA.
authors.forename: Frederic J
authors.initials: FJ
authors.lastname: Seidler
authors.affiliation: Department of Pharmacology & Cancer Biology, Duke University Medical Center, Durham, NC, USA.
authors.forename: Theodore A
authors.initials: TA
authors.lastname: Slotkin
mesh_terms: D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D001921:Brain / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D004390:Chlorpyrifos / Q000633:toxicity*; D003072:Cognition Disorders / Q000139:chemically induced / Q000175:diagnosis; D003907:Dexamethasone / Q000633:toxicity*; D005260:Female; D005508:Food Deprivation; D005938:Glucocorticoids / Q000633:toxicity*; D007306:Insecticides / Q000633:toxicity*; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D011247:Pregnancy; D047928:Premature Birth / Q000139:chemically induced*; D011297:Prenatal Exposure Delayed Effects / Q000139:chemically induced / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013315:Stress, Psychological / Q000209:etiology*
chemical_list: D005938:Glucocorticoids; D007306:Insecticides; D003907:Dexamethasone; D004390:Chlorpyrifos
keywords: Chlorpyrifos; Dexamethasone; Glucocorticoids; Organophosphate pesticides; Preterm labor; Thyroid hormone