Abstract
Sciatic nerve transection (SNT), a model for studying neuropathic pain, mimics the clinical symptoms of "phantom limb", a pain condition that arises in humans after amputation or transverse spinal lesions. In some vertebrate tissues, this condition decreases acetylcholinesterase (AChE) activity, the enzyme responsible for fast hydrolysis of released acetylcholine in cholinergic synapses. In spinal cord of frog Rana pipiens, this enzyme's activity was not significantly changed in the first days following ventral root transection, another model for studying neuropathic pain. An answerable question is whether SNT decreases AChE activity in spinal cord of frog Lithobates catesbeianus, a species that has been used as a model for studying SNT-induced neuropathic pain. Since each animal model has been created with a specific methodology, and the findings tend to vary widely with slight changes in the method used to induce pain, our study assessed AChE activity 3 and 10 days after complete SNT in lumbosacral spinal cord of adult male bullfrog Lithobates catesbeianus. Because there are time scale differences of motor endplate maturation in rat skeletal muscles, our study also measured the AChE activity in bullfrog tibial posticus (a postural muscle) and gastrocnemius (a typical skeletal muscle that is frequently used to study the motor system) muscles. AChE activity did not show significant changes 3 and 10 days following SNT in spinal cord. Also, no significant change occurred in AChE activity in tibial posticus and gastrocnemius muscles at day 3. However, a significant decrease was found at day 10, with reductions of 18% and 20% in tibial posticus and gastrocnemius, respectively. At present we cannot explain this change in AChE activity. While temporally different, the direction of the change was similar to that described for rats. This similarity indicates that bullfrog is a valid model for investigating AChE activity following SNT.
Highlights
Contractile muscle activity is controlled by the motor neuron-muscle system
AChE activity did not show significant changes (P=0.063 for tibial posticus muscle; P=0.069 for gastrocnemius muscle) at day 3 (Figures 2, 3), but in tibial posticus and gastrocnemius muscles it was decreased by 16% and 10%, respectively, as compared to sham groups
The reduction was of about 18% and 20% in tibial posticus muscle and gastrocnemius muscles, respectively, as compared to sham groups (Figures 2, 3)
Summary
Contractile muscle activity is controlled by the motor neuron-muscle system In this system, acetylcholine (Ach) released from the presynaptic nerve ending binds to its receptors in the postsynaptic membrane and causes its depolarization. Acetylcholine (Ach) released from the presynaptic nerve ending binds to its receptors in the postsynaptic membrane and causes its depolarization This triggers an action potential and the muscle fibers contract. According to Bartolini et al (2011), strategies to induce analgesia involving cholinergic mechanisms have been used for a long time, but in the modern times cholinergic-induced analgesia lost its importance due to numerous side effects. A reemergence of this therapeutic approach may happen from our improved understanding of the mechanisms through which this form of analgesia can be induced without aversive effects
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