Prenatal drug exposures sensitize noradrenergic circuits to subsequent disruption by chlorpyrifos

Persistent proteomic changes in glutamatergic and GABAergic signaling in the amygdala of adolescent rats exposed to chlorpyrifos as juveniles

Chlorpyrifos (CPF) remains one of the most widely used organophosphorus insecticides (OPs) despite the concerns about its developmental neurotoxicity. Developmental exposure to CPF has long-lasting negative impacts, including abnormal emotional behaviors. These negative impacts are observed at exposure levels do not cause inhibition of acetylcholinesterase, the canonical target of OPs. Exposure to CPF at these levels inhibits the endocannabinoid metabolizing enzyme fatty acid amide hydrolase (FAAH) but it is not clear what the persistent effects of this inhibition are. To investigate this, male rat pups were exposed orally to either corn oil, 0.75 mg/kg CPF, or 0.02 mg/kg PF-04457845 (PF; a specific inhibitor of FAAH) daily from postnatal day 10 (PND10) - PND16. This dosage of CPF does not inhibit brain cholinesterase activity but inhibits FAAH activity. On PND38 (adolescence), the protein expression in the amygdala was determined using a label-free shotgun proteomic approach. The analysis of control vs CPF and control vs PF led to the identification of 44 and 142 differentially regulated proteins, respectively. Gene ontology enrichment analysis revealed that most of the proteins with altered expression in both CPF and PF treatment groups were localized in the synapse-related regions, such as presynaptic membrane, postsynaptic density, and synaptic vesicle. The different biological processes affected by both treatment groups included persistent synaptic potentiation, glutamate receptor signaling, protein phosphorylation, and chemical synaptic transmission. These results also indicated disturbances in the balance between glutamatergic (↓ Glutamate AMPA receptor 2, ↓ Excitatory amino acid transporter 2, and ↑ vesicular glutamate transporter 2) and GABAergic signaling (↑ GABA transporter 3 and ↑ glutamate decarboxylase 2). This imbalance could play a role in the abnormal emotional behavior that we have previously reported. These results suggest that there is a similar pattern of expression between CPF and PF, and both these chemicals can persistently alter emotional behavior as a consequence of inhibition of FAAH.

Does growth impairment underlie the adverse effects of dexamethasone on development of noradrenergic systems?

Glucocorticoids are given in preterm labor to prevent respiratory distress but these agents evoke neurobehavioral deficits in association with reduced brain region volumes. To determine whether the neurodevelopmental effects are distinct from growth impairment, we gave developing rats dexamethasone at doses below or within the therapeutic range (0.05, 0.2 or 0.8 mg/kg) at different stages: gestational days (GD) 17-19, postnatal days (PN) 1-3 or PN7-9. In adolescence and adulthood, we assessed the impact on noradrenergic systems in multiple brain regions, comparing the effects to those on somatic growth or on brain region growth. Somatic growth was reduced with exposure in all three stages, with greater sensitivity for the postnatal regimens; brain region growth was impaired to a lesser extent. Norepinephrine content and concentration were reduced depending on the treatment regimen, with a rank order of deficits of PN7-9 > PN1-3 > GD17-19. However, brain growth impairment did not parallel reduced norepinephrine content in magnitude, dose threshold, sex or regional selectivity, or temporal pattern, and even when corrected for reduced brain region weights (norepinephrine per g tissue), the dexamethasone-exposed animals showed subnormal values. Regression analysis showed that somatic growth impairment accounted for an insubstantial amount of the reduction in norepinephrine content, and brain growth impairment accounted for only 12%, whereas specific effects on norepinephrine accounted for most of the effect. The adverse effects of dexamethasone on noradrenergic system development are not simply related to impaired somatic or brain region growth, but rather include specific targeting of neurodifferentiation.

Neurotransmitter changes in rat brain regions following glyphosate exposure

The effects of glyphosate oral exposure (35, 75, 150 and 800mg/kg bw, 6 days) on brain region monoamine levels of male Wistar rats were examined. Glyphosate-treated rats (35, 75, 150 and 800mg/kg bw, 6 days), had no visible injury, i.e., no clinical signs of dysfunction were observed. After last dose of glyphosate, serotonin (5-HT), dopamine (DA) and norepinephrine (NE) and its metabolites levels were determined in the brain regions striatum, hippocampus, prefrontal, cortex, hypothalamus and midbrain, by HPLC. Glyphosate caused statistically significant changes in the 5-HT and its metabolite 5-hydroxy-3-indolacetic acid (5-HIAA), DA and its metabolites 3,4-hydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and NE and its metabolite 3-metoxy-4-hydroxyphenylethyleneglycol (MHPG) levels in a brain regional- and dose-related manner. Moreover, glyphosate, dose-dependent, evoked a statistically significant increase in 5-HT turnover in striatum and hypothalamus and in DA turnover in prefrontal cortex and hippocampus, and a statistically significant decrease in NE turnover in prefrontal cortex and hypothalamus. The present findings indicate that glyphosate significantly altered central nervous system (CNS) monoaminergic neurotransmitters in a brain regional- and dose-related manner, effects that may contribute to the overall spectrum of neurotoxicity caused by this herbicide.