Critical periods for chlorpyrifos-induced developmental neurotoxicity: alterations in adenylyl cyclase signaling in adult rat brain regions after gestational or neonatal exposure.

Abstract

Developmental exposure to chlorpyrifos (CPF) alters the function of a wide variety of neural systems. In the present study we evaluated the effects in adulthood of CPF exposure of rats during different developmental windows, using the adenylyl cyclase (AC) signaling cascade, which mediates the cellular responses to numerous neurotransmitters. Animals were exposed on gestational days (GD) 9-12 or 17-20 or on postnatal days (PN) 1-4 or 11-14 and assessed at PN60. In addition to basal AC activity, we evaluated the responses to direct AC stimulants (forskolin, Mn 2+ ) and to isoproterenol, which activates signaling through β-adrenoceptors coupled to stimulatory G-proteins. CPF exposure in any of the four periods elicited significant changes in AC signaling in a wide variety of brain regions in adulthood. In general, GD9-12 was the least sensitive stage, requiring doses above the threshold for impaired maternal weight gain, whereas effects were obtained at subtoxic doses for all other regimens. Most of the effects were heterologous, involving signaling elements downstream from the receptors, and thus shared by multiple stimulants; superimposed on this basic pattern, there were also selective alterations in receptor-mediated responses, in G-protein function, and in AC expression and subtypes. Exposures conducted at GD17-20 and later all produced sex-selective alterations. These results suggest that developmental exposure to CPF elicits long-lasting alterations in cell-signaling cascades that are shared by multiple neurotransmitter and hormonal inputs; the resultant abnormalities of synaptic communication are thus likely to occur in widespread neural circuits and their corresponding behaviors. Key words: adenylyl cyclase, β-adrenoceptor, brain development, chlorpyrifos, organophosphate insecticides.

Comparative developmental neurotoxicity of organophosphates in vivo: Transcriptional responses of pathways for brain cell development, cell signaling, cytotoxicity and neurotransmitter systems

“…It is therefore of critical importance that both CPF and DZN produced major changes in gene expression related to the various PKAs and their modulators expressed in the developing brain. In general, these showed overall upregulation, possibly in reaction to the general impairment of AC signaling as noted in previous work with CPF exposure [17,64,100,106,114]. Here, too, CPF and DZN showed many basic similarities in gene expression patterns but also a few notable differences, particularly with the higher dose of DZN: loss of the prkaa1 stimulation seen with the other two treatments, and suppression of prkar2a.…”

“…One notable distinction was seen for grk1, which encodes the receptor kinase that uncouples G-proteins from their ability to signal through α-subunits: DZN had a much greater effect than CPF, suggesting a greater potential impact on receptor coupling capabilities and therefore on the efficiency of receptor signaling in general. As deficiencies in GPCR function have already been clearly established for CPF [17,64,106,114], we expect that this might be an even greater problem with DZN exposure. The specificity of these actions was demonstrated further by the relative sparsity of effects on the genes encoding the β and γ subunits of the heterotrimeric G-proteins, which showed only sporadic differences of generally smaller magnitude.…”

“…The adverse effects of CPF on brain development prominently feature mechanisms centered around cell signaling cascades that control the expression and function of nuclear transcription factors required for neural cell differentiation [17,22,36,47,64,65,83,100,106]. Among the best studied is the pathway connecting GPCRs to the generation of cAMP and the downstream effectors controlled by cAMP, such as PKA and the transcription factors AP-1, Sp1 and CREB.…”

Prenatal Nicotine Exposure Alters the Responses to Subsequent Nicotine Administration and Withdrawal in Adolescence: Serotonin Receptors and Cell Signaling

“…All of the assay methodologies used in this study have appeared in previous papers (Aldridge et al, 2003;Meyer et al, 2003Meyer et al, , 2004a, so only brief descriptions will be provided here. Tissues were thawed and homogenized (Polytron, Brinkmann Instruments, Westbury, NY, USA) in ice-cold 50 mM Tris (pH 7.4), and the homogenates were sedimented at 40 000 g for 15 min.…”

“…Third, we probed the AC response to 5HT receptor-mediated activation by determining the ratio of activity with 5HT to that without 5HT, evaluated in samples stimulated with forskolin, an approach that enables detection of potential inhibitory or excitatory actions (Aldridge et al, 2003(Aldridge et al, , 2004Chow et al, 2000;Slotkin et al, 1999;Xu et al, 2002). The concentrations of all the agents used here have been found previously to be optimal for effects on AC (Aldridge et al, 2003;Meyer et al, 2003Meyer et al, , 2004a.…”