Electrical Stimulation Of Sciatic Nerve Research Articles

Body Weight Support Treadmill Training Combined With Sciatic Nerve Electrical Stimulation Ameliorating Motor Function by Enhancing PI3K/Akt Proteins Expression via BDNF/TrkB Signaling Pathway in Rats with Spinal Cord Injury

To investigate the effects of body weight support treadmill training (BWSTT) and sciatic nerve electrical stimulation (SNES) on motor function recovery in spinal cord injury (SCI) rats and its possible mechanism. Modified Allen's method was utilized for T10 incomplete SCI. The Basso-Beattie-Bresnahan (BBB) score and modified Tarlov score were applied to assess motor function. Pathologic alterations of the spinal cord and muscles were observed by hematoxylin and eosin (HE) staining. The positive staining region of collagen fibers was assessed with Masson staining. Immunofluorescence was applied to count the positive cells of brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB). BDNF, TrkB, phosphatidylinositol-3-kinase (PI3K), and protein kinase B (Akt) relative mRNA and protein expressions were evaluated by reverse transcription polymerase chain reaction (RT-PCR) and Western blotting. On the 21st day of the intervention, the motor scores in SNES and BWSTT+ SNES groups were higher than that in SCI group (P < 0.05). Compared with SCI group, mRNA and protein expressions of BDNF/TrkB and PI3K/Akt were more significant on the 21st day of the intervention in SNES and BWSTT+ SNES groups (P < 0.05), but there was no difference in BWSTT group (P > 0.05). This experiment demonstrated that BWSTT combined with SNES contributed to alleviating spinal cord tissue injury, delaying muscle atrophy and improving locomotion. One of the possible mechanisms may be related to the regulation of the BDNF/TrkB signaling pathway, which changes the expression of PI3K/Akt protein. Furthermore, it was discovered that the ultra-early BWSTT may not be conducive to recovery.

End-to-Side vs. Free Graft Nerve Reconstruction-Experimental Study on Rats.

The long history of regeneration nerve research indicates many clinical problems with surgical reconstruction to be resolved. One of the promising surgical techniques in specific clinical conditions is end-to-side neurorrhaphy (ETS), described and then repeated with different efficiency in the 1990s of the twentieth century. There are no reliable data on the quality of recipient nerve regeneration, possible donor nerve damage, and epineural window technique necessary to be performed. This research attempts to evaluate the possible regeneration after end-to-side neurorrhaphy, its quality, potential donor nerve damage, and the influence of epineural windows on regeneration efficiency. Forty-five female Wistar rats were divided into three equal groups, and various surgical technics were applied: A-ETS without epineural window, B-ETS with epineural window, and C-free graft reconstruction. The right peroneal nerve was operated on, and the tibial nerve was selected as a donor. After 24 weeks, the regeneration was evaluated by (1) footprint analysis every two weeks with PFI (peroneal nerve function index), TFI (tibial nerve function index), and SFI (sciatic nerve function index) calculations; (2) the amplitude and latency measurements of motor evoked potentials parameters recorded on both sides of the peroneal and tibial nerves when electroneurography with direct sciatic nerve electrical stimulation and indirect magnetic stimulation were applied; (3) histomorphometry with digital conversion of a transverse semithin nerve section, with axon count, fibers diameter, and calculation of axon area with a semiautomated method were performed. There was no statistically significant difference between the groups investigated in all the parameters. The functional indexes stabilized after eight weeks (PFI) and six weeks (TFI and SFI) and were positively time related. The lower amplitude of tibial nerve potential in groups A and B was proven compared to the non-operated side. Neurophysiological parameters of the peroneal nerve did not differ significantly. Histomorphometry revealed significantly lower diameter and area of axons in operated peroneal nerves compared to non-operated nerves. The axon count was at a normal level in every group. Tibial nerve parameters did not differ from non-operated values. Regeneration of the peroneal nerve after ETS was ascertained to be at the same level as in the case of free graft reconstruction. Peroneal nerves after ETS and free graft reconstruction were ascertained to have a lower diameter and area than non-operated ones. The technique of an epineural window does not influence the regeneration result of the peroneal nerve. The tibial nerve motor evoked potentials were characterized by lower amplitudes in ETS groups, which could indicate axonal impairment.

An Implantable Fiber Biosupercapacitor with High Power Density by Multi‐Strand Twisting Functionalized Fibers

AbstractBiosupercapacitors (BSCs) that can harvest and store chemical energy show great promise for power delivery of biological applications. However, low power density still limits their applications, especially as miniaturized implants. Here, we report an implantable fiber BSC with maximal power density of 22.6 mW cm−2, superior to the previous reports. The fiber BSC was fabricated by integrating anode and cathode fibers of biofuel cell with supercapacitor fibers through multi‐strand twisting. This twisting structure endowed many channels inside and high electrochemical active area for efficient mass diffusion and charge transfer among different fibers, benefiting high power output. The obtained thin and flexible fiber BSC operated stably under deformations and performed high biocompatibility after implantation. Eventually, the fiber BSC was implanted subcutaneously in rats and successfully realized electrical stimulation of sciatic nerve, showing promise as a power source in vivo.

An Implantable Fiber Biosupercapacitor with High Power Density by Multi-Strand Twisting Functionalized Fibers.

Biosupercapacitors (BSCs) that can harvest and store chemical energy show great promise for power delivery of biological applications. However, low power density still limits their applications, especially as miniaturized implants.Here, we report an implantable fiber BSC with maximal power density of 22.6 mW‧cm-2, superior to the previous reports. The fiber BSC was fabricated by integrating anode and cathode fibers of biofuel cell with supercapacitor fibers through multi-strand twisting. This twisting structure endowed many channels inside and high electrochemical active area for efficient mass diffusion and charge transfer among different fibers, benefiting high power output. The obtained thin and flexible fiber BSC operated stably under deformations and performed high biocompatibility after implantation. Eventually, the fiber BSC was implanted subcutaneously in rats and successfully realized electrical stimulation of sciatic nerve, showing promiseas a power source in vivo.

Skeletal muscle-derived extracellular vesicles contribute to post-exercise hypotension

Post-exercise hypotension (PEH) is an immediate reduction in blood pressure (BP) after a single bout of exercise that forms the long-term hypertension amelioration by chronic exercise. The present study aims to explore a novel mechanism of PEH, with a focus of skeletal muscle-derived extracellular vesicles (SkM-EVs). We hypothesize that repetitively contracting-relaxing muscle releases antioxidant-enriched EVs that induce hypotension. Experiments were carried out in 48 male Sprague-Dawley rats. BP was recorded by a Millar catheter inserted into right carotid artery. EVs were isolated from SkM and plasma using ultracentrifugation, and then qualified and quantified using transmission electron microscopy and the ZetaView nanoparticle tracking analyzer. Results: First, in rats undergoing 1-hour of treadmill exercise (15/30/15 m/min for 10/40/10 min), we found an elevated BP during exercise (34.7 ± 5.2 mmHg, p &lt; 0.001; n = 8), followed by a decrease in BP below baseline during the post exercise period (-7.3 ± 1.1 mmHg, p &lt; 0.01). Pretreatment with the EV inhibitor GW4869 (1.5 mg/kg) had no effects on hypertension during exercise, but completely abolished the post-exercise hypotension (1.93 ± 0.64 mmHg, p &lt; 0.001), suggesting a role for SkM-EVs in this response. Bolus i.v. injection of SkM-EVs from exercised rats (400 μg EV protein) induced a dramatic decrease in BP (-16.7 ± 4.4 mmHg; p &lt; 0.01, n = 6/group) in non-exercised rats, which lasted for up to 40 min. Second, 1-hour sciatic nerve electrical stimulation (2.5V, 50Hz, 0.3s/3s)-evoked hindlimb muscle contraction in isoflurane-anesthetized rats induced a biphasic change in BP, with hypertension during the initial 20 min followed by hypotension in the last 40 min. Transection of the sciatic nerve or pretreatment with GW4869 abolished the stimulation-evoked hypertension and hypotension. Bolus i.v. injection of EVs from contracting-muscle significantly reduced BP with a maximal change of -14 ± 3.2 mmHg (p = 0.003; n = 5). Third, mass spectroscopic and western blotting analyses of these EVs identified 827 proteins, including Catalase, GSTMs, PRDXs, EPHX1, HSP90, and many others, which are involved in redox homeostasis and mitochondrial bioenergetics. Finally, using muscle-specific GFP reporter mice (MS-mG), we found increased SkM-EVs in both muscle and plasma following exercise by using flow cytometry. Confocal imaging identified GFP+-particles in the neurons of the rostral ventrolateral medulla (RVLM) of C57BL/6 mice that received an injection of SkM-EVs isolated from the exercised MS-mG mice, suggesting their active uptake across the blood-brain barrier. In summary, the major findings of this study include (1) SkM-EVs are essential for PEH; (2) i.v. administration of SkM-EVs reduced BP; (3) SkM-EVs contain enriched antioxidant enzymes and other cytoprotective proteins. These results suggest a novel mechanism underpinning PEH and provides a potential therapeutic strategy for hypertension. Supported by NIH grant R01HL160820. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Direct Sciatic Nerve Electrical Stimulation for Complex Regional Pain Syndrome Type 1

Foot and leg pain in complex regional pain syndrome (CRPS) presents a challenge even with neuromodulation techniques such as spinal cord stimulation (SCS). We report our experience with a novo technique of direct sciatic nerve electrical stimulation (DISNES) for intractable foot and leg pain in CRPS I. Following Research Ethics Board (REB) approval, data were gathered for 16 patients (10 women and 6 men, age 26-61 years) who had been subjected to ipsilateral DISNES. All 16 patients had failed conventional medical management. As well, seven subjects were previously treated with SCS for CRPS I pain. These subjects reported pain relief in the thigh and leg, however the SCS was unable to alleviate the disabling foot pain despite varied and multiple programming techniques. The remaining nine subjects were treated primarily with DISNES. Evaluation was done using visual analog scale (VAS), Oswestry Disability Index version 2 (ODI), and quality of life (EQ-5D and SF-36) scores done both pre-DISNES and at two follow-ups. VAS scores decreased by 59% at follow-up (F/U) 1 (P=0.00001) and 46% F/U 2. ODI improving by 40% F/U 1 (P=0.0038) and 37% F/U 2. SF-36 scores improved by 69% F/U 1 (P=0.015) and 80% F/U 2. EQ-5D scores improved significantly by F/U 1 (P=0.00030) but insignificantly at F/U 2 (P=0.81). There was also a rapid resolution of autonomic features such as edema, hyperemia, and allodynia (within 7-10 days). Three subjects returned to work post-DISNES. Our study shows that DISNES helps to control the disabling foot pain in CRPS I, thus improving the quality of life, improving ambulation and decreasing disability. DISNES also alleviates autonomic features and dystonia in CRPS I. Further studies are needed to determine long-term efficacy as this study pool is limited in size and follow-up period.

4-Aminopyridine: A Single-Dose Diagnostic Agent to Differentiate Axonal Continuity in Nerve Injuries.

Traumatic peripheral nerve injuries (TPNIs) are increasingly prevalent in battlefield trauma, and the functional recovery with TPNIs depends on axonal continuity. Although the physical examination is the main tool for clinical diagnosis with diagnostic work up, there is no diagnostic tool available to differentiate nerve injuries based on axonal continuity. Therefore, treatment often relies on "watchful waiting," and this leads to muscle weakness and further reduces the chances of functional recovery. 4-aminopyridine (4-AP) is clinically used in multiple sclerosis patients for walking performance improvement. Preliminary results in conscious mice suggested a diagnostic role of 4-AP in distinguishing axonal continuity. In this study, we thought to evaluate the diagnostic potential of 4-AP on the axonal continuity in unawake/sedated animals. Rat sciatic nerve crush and transection injuries were used in this study. Briefly, rats were anesthetized with isoflurane and mechanically ventilated with oxygen-balanced vaporized isoflurane. Sciatic nerve and triceps surae muscles were exposed by blunt dissection, and a stimulating electrode was placed under a sciatic nerve proximal to the crush injury. A force transducer measured muscle tension response to electrical stimulation of sciatic nerve. Muscle response was measured before crush, after crush, and 30 minutes after systemic 4-AP (150 µg/kg) or local (4-AP)-poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (PLGA-PEG) treatment. We found that both crush and transection injuries in sciatic nerve completely abolished muscle response to electrical stimulation. Single dose of systemic 4-AP and local (4-AP)-PLGA-PEG treatment with crush injury significantly restored muscle responses to electrical stimulation after 30 minutes of administration. However, systemic 4-AP treatment had no effect on muscle response after nerve transection. These results clearly demonstrate that 4-AP can restore nerve conduction and produce muscle response within minutes of administration only when there is a nerve continuity, even in the sedated animal. We conclude that 4-AP could be a promising diagnostic agent in differentiating TPNI based on axonal continuity.

Effects of sodium metavanadate on the electrical stimulation of sciatic nerve of toads (Bufo regularis)

Introduction: Vanadium and its compounds have been documented to exert toxic effects on almost all systems in living organisms including cardiovascular, reproductive and nervous systems. In the nervous system however, toxicity assays have been on the brain and its structures with little information on its effects on peripheral nerves. This study was therefore conducted to examine the toxicity of vanadium in the peripheral nervous system. Methods: Vanadium as sodium metavanadate was used in the study. Fifteen toads (Bufo regularis) were randomly distributed into 3 groups (A-C); A served as control and was administered distilled water during the experiment, B were intraperitoneally (i.p.) administered with sodium metavanadate at 3 mg/kg while C were administered with sodium metavanadate at 5 mg/kg i.p. for 7 consecutive days. Nerve conduction was studied in isolated toad sciatic nerve-gastrocnemius muscle preparation following electrical stimulation. The recordings were obtained on a kymograph for each group. Results: The results showed significant (p&lt;0.05) reduction in the peak amplitude of the action potential and an increase in the latency of the onset of the action potential at 5 mg/kg sodium metavanadate. Furthermore, an increased threshold stimulus voltage was also observed in group administered with 5 mg/kg sodium metavanadate. The values of these parameters in the 3 mg/kg sodium metavanadate group were not statistically different from the control group. Significance: The findings of this preliminary study suggest that vanadium at 5 mg/kg may result in decrease speed of impulse conduction which may be as a result of demyelination in the sciatic nerve.

Implantable liquid metal-based flexible neural microelectrode array and its application in recovering animal locomotion functions

With significant advantages in rapidly restoring the nerve function, electrical stimulation of nervous tissue is a crucial treatment of peripheral nerve injuries leading to common movement disorder. However, the currently available stimulating electrodes generally based on rigid conductive materials would cause a potential mechanical mismatch with soft neural tissues which thus reduces long-term effects of electrical stimulation. Here, we proposed and fabricated a flexible neural microelectrode array system based on the liquid metal GaIn alloy (75.5% Ga and 24.5% In by weight) and via printing approach. Such an alloy with a unique low melting point (10.35 °C) owns excellent electrical conductivity and high compliance, which are beneficial to serve as implantable flexible neural electrodes. The flexible neural microelectrode array embeds four liquid metal electrodes and stretchable interconnects in a PDMS membrane (500 µm in thickness) that possess a lower elastic modulus (1.055 MPa), which is similar to neural tissues with elastic moduli in the 0.1–1.5 MPa range. The electrical experiments indicate that the liquid metal interconnects could sustain over 7000 mechanical stretch cycles with resistance approximately staying at 4 Ω. Over the conceptual experiments on animal sciatic nerve electrical stimulation, the dead bullfrog implanted with flexible neural microelectrode array could even rhythmically contract and move its lower limbs under the electrical stimulations from the implant. This demonstrates a highly efficient way for quickly recovering biological nerve functions. Further, the good biocompatibility of the liquid metal material was justified via a series of biological experiments. This liquid metal modality for neural stimulation is expected to play important roles as biologic electrodes to overcome the fundamental mismatch in mechanics between biological tissues and electronic devices in the coming time.

Neuronal Regulation of Schwann Cell Mitochondrial Ca2+ Signaling during Myelination

Schwann cells (SCs) myelinate peripheral neurons to promote the rapid conduction of action potentials, and the process of myelination is known to be regulated by signals from axons to SCs. Given that SC mitochondria are one of the potential regulators of myelination, we investigated whether SC mitochondria are regulated by axonal signaling. Here, we show a purinergic mechanism that sends information from neurons to SC mitochondria during myelination. Our results show that electrical stimulation of rat sciatic nerve increases extracellular ATP levels enough to activate purinergic receptors. Indeed, electrical stimulation of sciatic nerves induces Ca(2+) increases in the cytosol and the mitochondrial matrix of surrounding SCs via purinergic receptor activation. Chronic suppression of this pathway during active myelination suppressed the longitudinal and radial development of myelinating SCs and caused hypomyelination. These results demonstrate a neuron-to-SC mitochondria signaling, which is likely to have an important role in proper myelination.

Differential response of microRNA to contraction in aged and obese mice (1168.4)

Resistance to anabolic stimuli in skeletal muscle occurs within both aging and obese populations. However, the mechanisms responsible for this ‘anabolic resistance’ are unknown. MicroRNA (miRNA), small (20‐24 nucleotides) post‐transcriptional regulators, have recently been shown to play a role in the response of skeletal muscle to anabolic stimulation. We aimed to compare the response of miRNA to an acute bout of contraction via sciatic nerve electrical stimulation (ES) in skeletal muscle within three groups of C57BL/6 mice aged, 24 wks and fed a control (CON, 10% fat/kcal) or high‐fat (FAT, 60% fat/kcal) diet or aged 124 wks (OLD, 10% fat/kcal). The expressions of miRNA that are known (miR‐378, miR‐27a) and putative (miR‐126, miR‐324) regulators of skeletal muscle development were measured by qPCR at baseline (BL) and after ES. Obesity increased the BL expression of miR‐27a and miR‐324, while miR‐27a and mir‐378 expression was increased with age, compared to CON. After contraction, miR‐126 and miR‐378 were decreased in CON, while miR‐27a and miR‐324 were decreased in FAT. However, the only contraction‐induced change in OLD was a decrease of miR‐378 expression back to control levels. These results illustrate the differential responses of miRNA in skeletal muscle as a result of ES within these distinct groups.Grant Funding Source: USDA and NIH/NIA

Spinal LTP induced by sciatic nerve electrical stimulation enhances posterior triangular thalamic nociceptive responses

Long-term potentiation (LTP) can be induced by electrical stimulation and gives rise to an increase in synaptic strength at the first relay. This phenomenon has been associated with learning and memory and also could be the origin of several pathological states elicited by an initial strong painful stimulus, such as some forms of neuropathic pain. We used high-frequency electrical stimulation of the sciatic nerve in anesthetized rats to produce spinal LTP. To evaluate the effect of spinal LTP on the activity of neurons in the posterior triangular nucleus of the thalamus (PoT), we applied an electrical stimulation (40 stimuli; 1ms; 0.5Hz; 1.5mA) to cutaneous tissues at 10-min intervals during at least 3h. In the majority of cases, PoT cells did not respond to cutaneous stimulation before LTP, but 50min after LTP induction PoT cells progressively began responding to the cutaneous stimulation. Furthermore, after 3h of LTP induction, PoT neurons could respond to cutaneous stimulation applied to different paws. Interestingly, the conduction velocities for the receptive field responses from the paw to the PoT cells were compatible with those of Aδ-fibers. Since PoT cells project to the insular cortex, the progressive increase in PoT activity and also the progressive unmasking of somatic receptive fields in response to LTP, place these cells in a key position to detect pain stimuli following central sensitization.

Effects of electrical stimulation of sciatic nerve on synaptic plasticity of spinal dorsal horn, hippocampal CA1 region and spinal c-fos, hippocampal CA1 region expression in neonatal rats

To explore the response to nociceptive stimuli in spinal cord of neonatal rat and observe the electrical stimulation of sciatic nerve on synaptic plasticity of spinal dorsal horn, hippocampal CA1 region and spinal c-fos, hippocampal CA1 region expression in neonatal rats. The rats were divided into neonatal and adult groups. The evoked potentials of left spinal dorsal horn from T13-L1 and right hippocampal CA1 region were recorded. After conditional electric stimulations, the potential amplitudes were recorded. When the incubation period reached 120 min, D-AP5 was added to spinal cord of rats and resulting changes in field potential and c-fos expression were recorded. Long-term potentiation (LTP) in neonatal rats was mainly evoked by A-type nerve fibers whereas LTP in adult rats was mainly evoked by C-type nerve fibers. C-fos expression was significantly increased in superficial, deep layers of spinal dorsal horn, ventral horn and hippocampal CA1 region in neonatal rats. Pain signals change with age.

Effect of electrical stimulation of sciatic nerve on synaptic plasticity of spinal dorsal horn and spinal c-fos expression in neonatal, juvenile and adult rats

To explore the response to nociceptive stimuli in spinal cord of immature rat and observe the electrical stimulation of the sciatic nerve on synaptic plasticity of the spinal dorsal horn and spinal c-fos expression in rats of different ages, MK-801 was added to the spinal cord of rats, and the resulting changes in field potential as well as c-fos expression were recorded. LTP in neonatal rats was mainly evoked by A-type nerve fibers, whereas LTP in juvenile and adult rats was mainly evoked by C-type nerve fibers. C-fos expression was significantly increased in the superficial and deep layers of the spinal dorsal horn and in the ventral horn in neonatal rats indicating that the pain signal changed with age.

AMPK activation attenuates S6K1, 4E-BP1, and eEF2 signaling responses to high-frequency electrically stimulated skeletal muscle contractions

Regulation of protein translation through Akt and the downstream mammalian target of rapamycin (mTOR) pathway is an important component of the cellular response to hypertrophic stimuli. It has been proposed that 5'-AMP-activated protein kinase (AMPK) activation during muscle contraction may limit the hypertrophic response to resistance-type exercise by inhibiting translational signaling. However, experimental manipulation of AMPK activity during such a stimulus has not been attempted. Therefore, we investigated whether AMPK activation can attenuate the downstream signaling response of the Akt/mTOR pathway to electrically stimulated lengthening muscle contractions. Extensor digitorum longus muscles (n = 8/group) were subjected to a 22-min bout of lengthening contractions by high-frequency sciatic nerve electrical stimulation (STIM) in young adult (8 mo) Fischer 344 x Brown Norway male rats. Forty minutes before electrical stimulation, rats were subcutaneously injected with saline or 5-aminoimidazole-4-carboxamide-1-4-ribofuranoside (AICAR; 1 mg/g body wt), an AMPK activator. Stimulated and contralateral resting muscles were removed at 0, 20, and 40 min post-STIM, and AMPK, acetyl CoA carboxylase (ACC), Akt, eukaryotic initiation factor 4E-binding protein (4E-BP1), 70-kDa ribosomal protein S6 kinase (S6K1), and eukaryotic elongation factor 2 (eEF2) phosphorylations were assessed by Western blot. AICAR treatment increased (P < or = 0.05) post-STIM AMPK (Thr172) and ACC phosphorylation (Ser79/221), inhibited post-STIM S6K1 (Thr389) and 4E-BP1 (gel shift) phosphorylation, and elevated post-STIM eEF2 phosphorylation (Thr56). These findings suggest that translational signaling downstream of Akt/mTOR can be inhibited after lengthening contractions when preceded by AMPK activation and that energetic stress may be antagonistic to the hypertrophic translational signaling response to loaded muscle contractions.

Effects of TRPA1 Agonists Mustard Oil and Cinnamaldehyde on Lumbar Spinal Wide-Dynamic Range Neuronal Responses to Innocuous and Noxious Cutaneous Stimuli in Rats

Mustard oil [allyl isothiocyanate (AITC)] and cinnamaldehyde (CA), agonists of the ion channel TRPA1 expressed in sensory neurons, elicit a burning sensation and heat hyperalgesia. We tested whether these phenomena are reflected in the responses of lumbar spinal wide-dynamic range (WDR) neurons recorded in pentobarbital-anesthetized rats. Responses to electrical and graded mechanical and noxious thermal stimulation were tested before and after cutaneous application of AITC or CA. Repetitive application of AITC initially increased the firing rate of 52% of units followed by rapid desensitization that persisted when AITC was reapplied 30 min later. Responses to noxious thermal, but not mechanical, stimuli were significantly enhanced irrespective of whether the neuron was directly activated by AITC. Windup elicited by percutaneous or sciatic nerve electrical stimulation was significantly reduced post-AITC. These results indicate that AITC produced central inhibition and peripheral sensitization of heat nociceptors. CA did not directly excite WDR neurons, and significantly enhanced responses to noxious heat while not affecting windup or responses to skin cooling or mechanical stimulation, indicating a peripheral sensitization of heat nociceptors.

AICAR suppresses p70S6k and eEF2 signaling after eccentric resistance exercise

p70S6k (S6k) and eukaryotic elongation factor 2 (eEF2) are key signaling proteins involved in skeletal muscle hypertrophy and can be inhibited by activation of 5′-AMP-activated protein kinase (AMPK). To study the effect of AMPK activity on S6k and eEF2 signaling after eccentric resistance exercise, EDL muscles (n=8/group) from Fischer344 x Brown Norway male rats were subjected to a 20-min bout of in-vivo eccentric resistance exercise by sciatic nerve electrical stimulation. 40 min prior to exercise, rats received a subcutaneous injection of saline (SAL) or AICAR (AIC; 1 mg/g BW), an AMPK activator. Exercised (EX) and contralateral control (CTR) muscles were removed at 0, 20 and 40 min post-exercise, and phosphorylation of AMPK (Thr172), S6k (Thr389), and eEF2 (Thr56) was assessed by western blot. AMPK phosphorylation was not different in EX vs. CTR at any time-point. With SAL, S6k phosphorylation (indicative of activity) was elevated (p ≤ 0.05) in EX vs. CTR at 0, 20 and 40 min, but AIC attenuated this increase. With SAL, eEF2 phosphorylation (indicative of decreased activity) was suppressed in EX vs. CTR at 20 and 40, but not 0, min. AIC generally increased eEF2 phosphorylation vs. SAL regardless of exercise. In conclusion, eccentric resistance exercise may not stimulate AMPK in fast-twitch muscle. Signaling through S6k and eEF2 appears to be enhanced in response to such exercise. However, this signaling is inhibited by AICAR, suggesting that AMPK could act as a negative regulator of exercise-induced translational signaling. Supported by NIH AG025101 and NIA Animal Allocation Dissertation Support.

The Cerebellum Modulates Rodent Cortical Motor Output after Repetitive Somatosensory Stimulation

To analyze the possible role of the cerebellum in the modulation of cortical motor output associated with repetitive electrical stimulation of the sciatic nerve in the rat. A sustained somatosensory stimulation induces an increase in the intensity of the response of the rodent motor cortex. Wistar rats were anesthetized for surgical preparation using a continuous infusion of chloral hydrate. We analyzed the response evoked by electrical stimulation of the right motor cortex before (basal condition) and after peripheral electrical stimulation of the left sciatic nerve in rats with no cerebellar intervention (n = 6), and in control rats with Ringer's infusion via a microdialysis probe (n = 8) implanted in the left cerebellar nuclei. In addition, we investigated the effects of 1) the administration of ethanol (20 mmol/L) in the left cerebellar nuclei (n = 5); 2) the administration of tetrodotoxin (10 micromol/L), a sodium channel blocker, in the left cerebellar nuclei (n = 5); 3) electrical stimulation by deep cerebellar stimulation (frequency 100 Hz) on the left side (n = 5); or 4) electrical stimulation of the cerebellar nuclei on the right side (100 Hz; n = 6). For peripheral stimulation, all of the animals received 1 hour of electrical stimulation. Trains of stimulation consisted of five stimuli (duration of 1 stimulus, 1 ms) at a rate of 10 Hz. During stimulation of the motor cortex, peak-to-peak amplitudes in responses of the left calf muscle were analyzed. Motor threshold was defined as the lowest intensity eliciting at least 5 of 10 evoked responses with an amplitude greater than 20 muV. The intensity used was 130% of the motor threshold. In the basal condition (before repetitive stimulation), amplitudes of motor responses were similar in the six groups of rats (P = 0.40). In rats without cerebellar intervention, peripheral electrical stimulation was associated with an increase of motor response to 147.4 +/- 8.5% of baseline (P < 0.001). In rats with Ringer's infusion, the motor response increased to 141.6 +/- 7.9% of baseline (P < 0.001). The administration of ethanol in the cerebellum prevented the enhancement of the response ipsilaterally. The mean +/- standard deviation (SD) of motor responses was 105.7 +/- 6.2% of baseline measurements after stimulation of the sciatic nerve (P = 0.36). The same observation was made after the infusion of tetrodotoxin (mean +/- SD of motor responses: 107.1 +/- 7.4% after peripheral stimulation [P = 0.19] and after electrical stimulation of the cerebellum on the left side [mean +/- SD of motor responses, 104.3 +/- 8.5% after peripheral stimulation, P = 0.40]). However, electrical stimulation of cerebellar nuclei on the right side did not impair the modulation of cortical motor output by sciatic nerve stimulation (mean +/- SD of motor responses, 148.4 +/- 5.8% after peripheral stimulation, P < 0.001). Until now, the increase of motor output after peripheral nerve stimulation has been considered as a plasticity directly and solely dependent on cortical structures. We demonstrate that the cerebellum plays a key role in this form of neural plasticity.

Motor nerve blockade potency and toxicity of non‐racemic bupivacaine in rats

Racemic [RS(+/-)] bupivacaine can be associated with severe cardiotoxicity. The S(-) isomer is known to be less neuro- and cardiotoxic, but demonstrates a lower potency to block motor activity than RS(+/-) bupivacaine. Thus, the potency and toxicity of a non-racemic bupivacaine mixture were studied. Gastrocnemic muscle twitches induced by electrical stimulation of sciatic nerves in rats were used to compare the impact by bupivacaine solutions on motor activity. Field stimulation at 1 Hz eliciting ventricular muscle twitches was used to investigate the effects on cardiac contractility. The lethal dose of each local anesthetic agent was determined following drug infusions during general anesthesia in mechanically ventilated rats. Non-racemic (75S:25R) bupivacaine was more potent (P<0.05) than S(-) or R(+) enantiomers to block motor nerve activity. The concentrations of RS(+/-), 75S:25R, R(+) and S(-) bupivacaine to inhibit nerve conduction by 50% were 0.84 (0.37- 2.20), 0.84 (0.47-2.48), 2.68 (0.98-3.42) and 2.11 mM (1.5-4.03), respectively. Pronounced reductions in ventricular muscle twitches were observed with RS(+/-) and R(+) bupivacaine at low concentrations (0.5-4 microM). Lethal doses for 75S:25R (39.9 mg kg(-1)), and S(-) (34.7 mg kg(-1)) were higher (P<0.05) than for R(+) (16.2 mg kg(-1)) and RS(+/-) bupivacaine (18.4 mg kg(-1)), respectively. The potency of S(-) bupivacaine to block the motor activity in the sciatic nerve was enhanced when 25% of the S(-) isomer was replaced by the antipode R(+) bupivacaine. This effect was not associated with increased toxicity.

HIF and VEGF relationships in response to hypoxia and sciatic nerve stimulation in rat gastrocnemius

To determine if hypoxia-inducible factor-1 (HIF-1) may regulate skeletal muscle vascular endothelial growth factor (VEGF) expression in response to exercise or hypoxia, rats underwent 1h sciatic nerve electrical stimulation (ES), hypoxic exposure (H) or combined stimuli. HIF-1alpha protein levels increased six-fold with maximal (8V) ES with or without H. Similar HIF-1alpha increases occurred with sub-maximal (6V and 4V) ES plus H, but not in sub-maximal ES or H alone. VEGF mRNA and protein levels increased three-fold in sub-maximal ES or H alone, six-fold in sub-maximal ES plus H, 6.3-fold with maximal ES, and 6.5-fold after maximal ES plus H. These data suggest: (1) intracellular hypoxia during normoxic exercise may exceed that during 8% oxygen breathing at rest and is more effective in stimulating HIF-1alpha; (2) HIF-1 may be an important regulator of exercise-induced VEGF transcription; and (3) breathing 8% O(2) does not alter HIF-1alpha expression in skeletal muscle, implying that exercise-generated signals contribute to the regulation of HIF-1alpha and/or VEGF.