Effect of Sciatic Nerve Transection on acetylcholinesterase activity in spinal cord and skeletal muscles of the bullfrog Lithobates catesbeianus / Efeito da Secção do Nervo Isquiático sobre a atividade da acetilcolinesterase em medula espinal e músculos esqueléticos da rã-touro Lithobates catesbeianus

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.

Resumo A transecção do nervo isquiático (SNT), um modelo para estudar dor neuropática, simula os sintomas clínicos do "membro fantasma", uma condição dolorosa que ocorre nos humanos após amputação ou secção completa da medula espinal. Essa condição muda a atividade da acetilcolinesterase (AChE), a enzima responsável pela rápida hidrólise da acetilcolina liberada nas sinapses colinérgicas, em alguns tecidos de vertebrados. Em medula espinal de rã Rana pipiens, a atividade da AChE não foi significativamente alterada nos primeiros dias após a secção da raiz ventral, outro modelo para o estudo da dor neuropática. Uma questão ainda não respondida é se a SNT diminui a atividade da AChE na medula espinal de rã Lithobates catesbeianus, uma espécie que vem sendo usada como modelo em estudos da dor neuropática induzida por SNT. Como cada modelo animal é criado a partir de metodologia específica, e seus resultados tendem a variar com pequenas mudanças na metodologia de indução da dor, o presente estudo avaliou a atividade da AChE em medula espinal lombossacral de rã-touro Lithobates catesbeianus, adultos, machos, 3 e 10 dias após a completa SNT. Como há diferenças temporais na maturação de placas motoras em músculos esqueléticos de ratos, nosso estudo ainda demonstrou, na rã-touro, os efeitos da SNT sobre a atividade da AChE nos músculos esqueléticos tibial posticus, um músculo postural, e gastrocnêmio, um músculo frequentemente usado em estudos do sistema motor. A atividade da AChE não mudou significativamente na medula espinal aos 3 e 10 dias após a SNT. Nos músculos, a atividade não alterou significativamente aos 3 dias após a lesão, mas reduziu de forma significativa aos 10 dias após a SNT. Aos 10 dias, a diminuição foi 18% no músculo tibial posticus e 20% no gastrocnêmio. No momento, nós não temos explicação para essa mudança na atividade da AChE. Embora temporalmente diferente, o sentido da mudança é similar ao que é descrito em ratos. Esta similaridade torna a rã-touro um modelo válido para se estudar questões ainda não respondidas da SNT sobre a AChE.

Effect of Sciatic Nerve Transection on acetylcholinesterase activity in spinal cord and skeletal muscles of the bullfrog Lithobates catesbeianus.

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.

Bradykinin B1 antagonism inhibits oxidative stress and restores Na+K+ ATPase activity in diabetic rat peripheral nervous system.

Diabetic peripheral neuropathy is one the most common complications of diabetes mellitus and frequently results in clinically significant morbidities such as pain, foot ulcers and amputations. The diabetic condition progresses from early functional changes to late, poorly reversible structural changes. The chronic hyperglycemia measured alongside diabetes development is associated with significant damage and failure of various organs. In the present study diabetes was induced in male Wistar rats by a single dose of streptozotocin (STZ) and the association between the BKB1-R and the oxidative stress and Na+-K+ ATPase activity in nervous tissues was analysed. The results showed that the resulting hyperglycemia induced a reduction of the neuronal electrical function integrity and increased oxidative stress in the sciatic nerve homogenates of 30 days diabetic rats. Malondialdehyde (MDA) used as a marker of oxidative stress was elevated whereas Biological Antioxidant Potential (BAP), glutathion (GSH) levels and superoxide dismutase (SOD) activity were decreased. Treatment of the rats 3 days before the end of the 4 week period with the BKB1 antagonist R-954 restored the neuronal activity and significantly attenuated the oxidative stress as shown by the level of the various markers returning close to levels found in control rats. Our results suggest that the BKB1-R subtype is overexpressed in sciatic nerve during the STZ-induced diabetes development as evidenced by inhibitory effects of the BKB1-R antagonist R-954. The beneficial role of BKB1-R antagonist R-954 for the treatment of diabetic neuropathy is also suggested.

Localization and irregular distribution of Na,K-ATPase in myelin sheath from rat sciatic nerve.

Sodium, potassium adenosine triphosphatase (Na,K-ATPase) is a membrane-bound enzyme that maintains the Na(+) and K(+) gradients used in the nervous system for generation and transmission of bioelectricity. Recently, its activity has also been demonstrated during nerve regeneration. The present study was undertaken to investigate the ultrastructural localization and distribution of Na,K-ATPase in peripheral nerve fibers. Small blocks of the sciatic nerves of male Wistar rats weighing 250-300g were excised, divided into two groups, and incubated with and without substrate, the para-nitrophenyl phosphate (pNPP). The material was processed for transmission electron microscopy, and the ultra-thin sections were examined in a Philips CM 100 electron microscope. The deposits of reaction product were localized mainly on the axolemma, on axoplasmic profiles, and irregularly dispersed on the myelin sheath, but not in the unmyelinated axons. In the axonal membrane, the precipitates were regularly distributed on the cytoplasmic side. These results together with published data warrant further studies for the diagnosis and treatment of neuropathies with compromised Na,K-ATPase activity.

Expression of neuronal isoform of nitric oxide synthase in spinal neurons of neonatal rats after sciatic nerve transection.

Motoneuron death induced by sciatic nerve transection in neonatal rats has been related to induction of the neuronal isoform of nitric oxide synthase (nNOS), a diaphorase of which one of the cofactors is nicotinamide adenine dinucleotide phosphate (NADPH). We transected the sciatic nerve of neonatal rats (P2) and examined nNOS expression by immunostaining in neurons of the sciatic pool and of other spinal levels on the 5th day after surgery. No correspondence was observed between the surviving motoneurons and nNOS positive cells. The appearance and distribution of nNOS positive neurons at all spinal levels and laminae were similar to those of adult animals. These results are at variance with previous studies which showed correlation between motoneuron loss after axotomy and number of NADPH-diaphorase positive motoneurons after sciatic transection.

Mapeamento fascicular de nervos periféricos por método histoquímico da acetilcolinesterase / Fascicular mapping of peripheral nerves by histochemical method of the acetylcholinesterase

Os autores realizaram estudo sobre o mapeamento fascicular de nervos periféricos baseado na histoquímica enzimática da acetilcolinesterase presentes em fibras que conduzem estímulos motores. O experimento foi realizado em nervos ciáticos de ratos. Seis ratos foram submetidos a lesao dos nervos ciáticos e tiveram segmentos do coto distal retirados no primeiro, terceiro, quinto e sétimo dias após a lesao. Esses segmentos foram congelados, cortados e submetidos à histoquímica enzimática da acetilcolinesterase. A contagem de fibras coradas obedeceu a critérios de histomorfometria. Observou-se que o número de fibras coradas sofre diminuiçao no decorrer do tempo após a lesao. A análise estatística demonstrou que o índice de fibras coradas obedece a funçao linear decrescente em que o número de fibras coradas é zero a partir do sétimo dia após a lesao.

Quantitative assay of Schieff and PAS reactivity during nerve degeneration in rats.

Quantative histochemical analysis of nerve degeneration in rats from zero to 192 hours was studied utilizing both Schiff reagent and PAS reaction. In addition, amylase digestion prior to PAS staining and aniline blockade of Schiff reactivity were employed. The staining intensity of all the reaction was measured histophotometrically and the mean optical density (OD) was determined for the following time intervals: 0, 24, 48, 96, and 192 hours.