Transcriptional analysis of rat piriform cortex following exposure to the organophosphonate anticholinesterase sarin and induction of seizures

Abstract

BackgroundOrganophosphorus nerve agents irreversibly inhibit acetylcholinesterase, causing a toxic buildup of acetylcholine at muscarinic and nicotinic receptors. Current medical countermeasures to nerve agent intoxication increase survival if administered within a short period of time following exposure but may not fully prevent neurological damage. Therefore, there is a need to discover drug treatments that are effective when administered after the onset of seizures and secondary responses that lead to brain injury.MethodsTo determine potential therapeutic targets for such treatments, we analyzed gene expression changes in the rat piriform cortex following sarin (O-isopropyl methylphosphonofluoridate)-induced seizure. Male Sprague-Dawley rats were challenged with 1 × LD50 sarin and subsequently treated with atropine sulfate, 2-pyridine aldoxime methylchloride (2-PAM), and the anticonvulsant diazepam. Control animals received an equivalent volume of vehicle and drug treatments. The piriform cortex, a brain region particularly sensitive to neural damage from sarin-induced seizures, was extracted at 0.25, 1, 3, 6, and 24 h after seizure onset, and total RNA was processed for microarray analysis. Principal component analysis identified sarin-induced seizure occurrence and time point following seizure onset as major sources of variability within the dataset. Based on these variables, the dataset was filtered and analysis of variance was used to determine genes significantly changed in seizing animals at each time point. The calculated p-value and geometric fold change for each probeset identifier were subsequently used for gene ontology analysis to identify canonical pathways, biological functions, and networks of genes significantly affected by sarin-induced seizure over the 24-h time course.ResultsA multitude of biological functions and pathways were identified as being significantly altered following sarin-induced seizure. Inflammatory response and signaling pathways associated with inflammation were among the most significantly altered across the five time points examined.ConclusionsThis analysis of gene expression changes in the rat brain following sarin-induced seizure and the molecular pathways involved in sarin-induced neurodegeneration will facilitate the identification of potential therapeutic targets for the development of effective neuroprotectants to treat nerve agent exposure.

Neuroprotective mechanisms activated in non-seizing rats exposed to sarin

“…1a). The extensive activation of inflammatory responses in the seizing rats, in particular by neurotoxic and pro-inflammatory cytokines, such as Il-1β, Tnf-α, and Il-6, was observed in all brain regions (Spradling et al, 2011a(Spradling et al, , 2011b, consistent with findings from previous studies (Chapman et al, 2006;Dhote et al, 2007;Dillman et al, 2009;Johnson and Kan, 2010;Svensson et al, 2001Svensson et al, , 2005Williams et al, 2003).…”

“…We determined the differentially expressed genes (DEGs) from the data of Spradling et al (2011b), using a false discovery rate (FDR)-corrected p-value cutoff of 0.05 for each of the five studied brain regions (amygdala, hippocampus, piriform cortex, septum, and thalamus) and at each time point (0.25 h, 1 h, 3 h, 6 h, and 24 h). The determination of the DEGs from each cohort of seizing and non-seizing rats employed separate control groups due to differences in countermeasure administration.…”

“…Furthermore, pretreatment of the thalamus can protect against seizures originating from the piriform cortex (Cassidy and Gale, 1998). In the study by Spradling et al (2011b), the thalamus was identified as a brain region with a unique molecular response to nerve agent-induced seizures (Spradling et al, 2011a).…”

“…To understand the mechanism of seizures, previous studies (Spradling et al, 2011a(Spradling et al, , 2011b have analyzed the transcriptomic responses in five nerve agent-sensitive brain regions (Aroniadou-Anderjaska et al, 2009;Myhrer, 2007;Myhrer et al, 2007) at different time intervals (0.25 h, 1 h, 3 h, 6 h, and 24 h) in rats following sarin-induced seizures. In these experiments, approximately half of the rats exposed to a 1 Â LD 50 (median lethal dose) concentration of sarin developed seizures (Fig.…”

Assessment of Potential Long Term Health Effects on Army Human Test Subjects of Relevant Biological and Chemical Agents, Drugs, Medications and Substances

“…High arsenic levels in drinking water (>100μg/L) increased the risk of peripheral artery disease, coronary heart disease, stroke, and carotid atherosclerosis in studies conducted in Chile, 177 Taiwan, 178 Inner Mongolia, 179,180 Bangladesh, 181,182 and Pakistan. 183,184 The prospective cohort study from Bangladesh also examined the lower threshold of arsenic concentrations of arsenic in water and found that concentrations above 12 μg/L were associated with an increased hazard of CVD mortality.…”