Capsaicin protects neuromuscular junctions from the inhibitory effects of botulinum neurotoxin A

Within 24 hrs after injecting botulinum neurotoxin A (BoNT/A) into the hindlimb, mice lost the toe spread reflex and developed progressive muscle weakness. At the same time, the compound muscle action potential amplitude decreased. Injection of capsaicin before BoNT/A significantly reduced these affects and protected the muscle twitch tension of the Extensor digitorum longus (EDL) nerve muscle preparation. Acute in vitro exposure of isolated nerve muscle preparations, as well as Neuro 2a cells, to capsaicin prevented uptake of Alexa 647 BoNT/A. Motor nerve endings as well as Neuro 2a cells express the capsaicin receptor, a transient receptor potential channel of the vanilloid family (TRPV1). Capsaicin as well as disruption of clathrin coated pits (CCPs) reduced Neuro 2a cell uptake of BoNT/A. FM1-43 uptake indicated that exocytosis persists for BoNT/A treated Neuro 2a cells pretreated with capsaicin. Pre-injection of wortmannin (WMN), a PI3Kinase inhibitor, also protected mice from the paralytic effects of BoNT/A. When applied alone, either WMN or capsaicin selectively reduced stimulus-evoked transmitter release from motor nerve endings. We hypothesize that TRPV1 activation reduces PI(4,5)P2 level within the membrane. This prevents CCP formation and uptake of BoNT/A

Lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNF[alfa]) blunt the response of Neuropeptide Y/Agouti-related peptide (NPY/AgRP) glucose inhibited (GI) neurons to decreased glucose

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Motor unit number estimate as a predictor of motor dysfunction in an animal model of type 1 diabetes

Peripheral neuropathy is a common complication of diabetes that leads to severe morbidity. In this study, we investigated the sensitivity of motor unit number estimate (MUNE) to detect early motor axon dysfunction in streptozotocin (STZ)-treated mice. We compared the findings with in vitro changes in the morphology and electrophysiology of the neuromuscular junction. Adult Thy1-YFP and Swiss Webster mice were made diabetic following three interdaily intraperitoneal STZ injections. Splay testing and rotarod performance assessed motor activity for 6 wk. Electromyography was carried out in the same time course, and compound muscle action potential (CMAP) amplitude, latency, and MUNE were estimated. Two-electrode voltage clamp was used to calculate quantal content (QC) of evoked transmitter release. We found that an early reduction in MUNE was evident before a detectable decline of motor activity. CMAP amplitude was not altered. MUNE decrease accompanied a drop of end-plate current amplitude and QC. We also observed small axonal loss, sprouting of nerve endings, and fragmentation of acetylcholine receptor clusters at the motor end plate. Our results suggest an early remodeling of motor units through the course of diabetic neuropathy, which can be readily detected by the MUNE technique. The early detection of MUNE anomalies is significant because it suggests that molecular changes associated with pathology and leading to neurodegeneration might already be occurring at this stage. Therefore, trials of interventions to prevent motor axon dysfunction in diabetic neuropathy should be administered at early stages of the disorder