sirolimus and methylatropine

Exposure to organophosphorous (OP) nerve agents such as soman inhibits the critical enzyme acetylcholinesterase (AChE) leading to excessive acetylcholine accumulation in synapses, resulting in cholinergic crisis, status epilepticus and brain damage in survivors. The hippocampus is profoundly damaged after soman exposure leading to long-term memory deficits. We have previously shown that treatment with three sequential doses of alpha-linolenic acid, an essential omega-3 polyunsaturated fatty acid, increases brain plasticity in naïve animals. However, the effects of this dosing schedule administered after a brain insult and the underlying molecular mechanisms in the hippocampus are unknown. We now show that injection of three sequential doses of alpha-linolenic acid after soman exposure increases the endogenous expression of mature BDNF, activates Akt and the mammalian target of rapamycin complex 1 (mTORC1), increases neurogenesis in the subgranular zone of the dentate gyrus, increases retention latency in the passive avoidance task and increases animal survival. In sharp contrast, while soman exposure also increases mature BDNF, this increase did not activate downstream signaling pathways or neurogenesis. Administration of the inhibitor of mTORC1, rapamycin, blocked the alpha-linolenic acid-induced neurogenesis and the enhanced retention latency but did not affect animal survival. Our results suggest that alpha-linolenic acid induces a long-lasting neurorestorative effect that involves activation of mTORC1 possibly via a BDNF-TrkB-mediated mechanism.

Topics: alpha-Linolenic Acid; Animals; Antigens, Nuclear; Atropine Derivatives; Avoidance Learning; Brain Damage, Chronic; Brain-Derived Neurotrophic Factor; Diazepam; DNA Replication; Doublecortin Domain Proteins; Electroshock; Exploratory Behavior; Hippocampus; Male; Mechanistic Target of Rapamycin Complex 1; Microtubule-Associated Proteins; Multiprotein Complexes; Nerve Tissue Proteins; Neurogenesis; Neuropeptides; Neuroprotective Agents; Neurotoxins; Oximes; Proto-Oncogene Proteins c-akt; Pyridinium Compounds; Rats; Rats, Sprague-Dawley; Receptor, trkB; Signal Transduction; Sirolimus; Soman; Status Epilepticus; TOR Serine-Threonine Kinases

Dentate granule cell axon (mossy fiber) sprouting is a common abnormality in patients with temporal lobe epilepsy. Mossy fiber sprouting creates an aberrant positive-feedback network among granule cells that does not normally exist. Its role in epileptogenesis is unclear and controversial. If it were possible to block mossy fiber sprouting from developing after epileptogenic treatments, its potential role in the pathogenesis of epilepsy could be tested. Previous attempts to block mossy fiber sprouting have been unsuccessful. The present study targeted the mammalian target of rapamycin (mTOR) signaling pathway, which regulates cell growth and is blocked by rapamycin. Rapamycin was focally, continuously, and unilaterally infused into the dorsal hippocampus for prolonged periods beginning within hours after rats sustained pilocarpine-induced status epilepticus. Infusion for 1 month reduced aberrant Timm staining (a marker of mossy fibers) in the granule cell layer and molecular layer. Infusion for 2 months inhibited mossy fiber sprouting more. However, after rapamycin infusion ceased, aberrant Timm staining developed and approached untreated levels. When onset of infusion began after mossy fiber sprouting had developed for 2 months, rapamycin did not reverse aberrant Timm staining. These findings suggest that inhibition of the mTOR signaling pathway suppressed development of mossy fiber sprouting. However, suppression required continual treatment, and rapamycin treatment did not reverse already established axon reorganization.

Topics: Animals; Anticonvulsants; Atropine Derivatives; Axons; Dentate Gyrus; Disease Models, Animal; Epilepsy, Temporal Lobe; Immunohistochemistry; Infusions, Parenteral; Injections, Intraperitoneal; Male; Mossy Fibers, Hippocampal; Muscarinic Agonists; Neural Inhibition; Neurons; Parasympatholytics; Pilocarpine; Protein Kinases; Rats; Rats, Sprague-Dawley; Signal Transduction; Sirolimus; Staining and Labeling; Status Epilepticus; Time Factors; TOR Serine-Threonine Kinases