Stimulation Of Sciatic Nerve Research Articles

Temporal clustering analysis of cerebral blood flow activation maps measured by laser speckle contrast imaging

Temporal and spatial orchestration of neurovascular coupling in brain neuronal activity is crucial for comprehending the mechanism of functional cerebral metabolism and pathophysiology. Laser speckle contrast imaging (LSCI) through a thinned skull over the somatosensory cortex is utilized to map the spatiotemporal characteristics of local cerebral blood flow (CBF) in anesthetized rats during sciatic nerve stimulation. The time course of signals from all spatial loci among the massive dataset is hard to analyze, especially for the thousands of images, each of which composes millions of pixels. We introduce a temporal clustering analysis (TCA) method, which is proven as an efficient method to analyze functional magnetic resonance imaging (fMRI) data in the temporal domain. The timing and location of CBF activation shows that contralateral hindlimb sensory cortical microflow is activated to increase promptly in less than 1 s after the onset of 2-s electrical stimulation and is evolved in different discrete regions. This pattern is similar but slightly elaborated from the results obtained from laser Doppler flowmetry (LDF) and fMRI. We present this combination to investigate interacting brain regions, which might lead to a better understanding of the nature of brain parcellation and effective connectivity.

Reverse End-to-Side Neurotization

The authors describe a reverse end-to-side neurorrhaphy model in which the proximal end of a donor nerve is sutured to an epineurial window in the side of a recipient nerve. If effective, this technique would have useful applications in nerve reconstructive surgery. Female Sprague-Dawley rats were divided into three groups (n = 9). In Group A, the peroneal nerve was transected and directly repaired in standard end-to-end fashion. In Group B, the tibial nerve was transected and the proximal end was sutured to the side of the intact peroneal nerve through an epineurial window. In Group C, the tibial nerve was also transected and the proximal end sutured to the side of the intact peroneal nerve, but the peroneal nerve was then cut proximally. After 12 weeks, contractile forces of the extensor digitorum communis (EDC) were measured, following stimulation of the proximal sciatic nerve on all experimental (and normal) hind limbs. For Group B, the peroneal nerve was transected proximal to the repair site just prior to stimulation. Group B animals did not demonstrate any measurable contractions. No statistically significant differences were found between Groups A and C. This demonstrated the successful neurotization of a denervated muscle using a reverse end-to-side neurorrhaphy model.

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.

Tooth-pulp-evoked rostral spinal trigeminal nucleus neuron activity is inhibited by conditioning sciatic nerve stimulation in the rat: possible role of 5-HT 3 receptor mediated GABAergic inhibition

The purpose of the present study was to determine whether modulation of the trigeminal spinal nucleus oralis (TSNO) neurons related to tooth-pulp (TP)-evoked jaw-opening reflex (JOR) after electrical stimulation of the sciatic nerve (SN) is mediated by the descending serotonergic (5-HT 3) inhibitory system activated by inhibitory GABAergic interneurons. In 30 anesthetized rats, the activity of TSNO neurons (87.5%, 35/40) and all digastric muscle electromyograms (dEMG, n = 30) in response to TP stimulation (at an intensity of 3.5 times the threshold for JOR) were inhibited by conditioning stimulation of the SN (5.0 mA × 0.5 ms, 1 Hz, conditioning-test intervals; 50 ms). The inhibitory effects were significantly attenuated after intravenous administration of the 5-HT 3 receptor antagonist ICS 205-930 ( n = 6). Using multibarrel electrodes, iontophoretic application of ICS 205-930 into the TSNO significantly reduced the SN stimulation-induced inhibition of TP-evoked TSNO neuronal excitation ( n = 6), and in the same neurons, iontophoretic application of the GABA A receptor antagonist bicuculline into the TSNO greatly inhibited their effect. On the other hand, we found the expression of 5-HT 3 receptor immunoreactive neurons in the TSNO. These results suggest that SN stimulation may activate the descending serotonergic (5-HT 3) inhibitory system through activation of inhibitory GABAergic interneurons, which inhibit excitatory responses of the TSNO neurons to TP stimulation.

α2-Adrenoceptors Do Not Mediate Reflex Mydriasis in Rabbits

The aim of this study was to identify receptors that mediate reflex mydriasis in pentobarbital-anesthetized rabbits, in which the cervical sympathetic nerve was sectioned unilaterally. Voltage-response curves of pupillary dilation were generated bilaterally by stimulation of the sciatic nerve. Evoked mydriatic responses were mediated mainly by efferent parasympathetic innervation, and, to a lesser extent, by sympathetic innervation. The alpha-adrenergic antagonist, phenoxybenzamine (0.3 mg/kg, intravenously (i.v.)), antagonized mydriasis of the neurally intact eye, but not that on the sympathectomized side. The alpha2-adrenergic antagonist, RS 79948 (0.3 mg/kg, i.v.), potentiated mydriasis of the normal eye, but was without either a potentiating or inhibitory effect on the mydriasis of the sympathectomized eye. In addition, the dopamine-receptor antagonist, haloperidol (1 mg/kg, i.v.), inhibited evoked mydriasis of the sympathectomized eye. These results suggest that, unlike some other species (cats and rats), alpha2-adrenoceptors do not mediate reflex mydriasis elicited by sciatic-nerve stimulation in the rabbit, and support the previous finding in humans that dopamine receptors may mediate this response.

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.

Development of GABAergic and glycinergic transmission in the neonatal rat dorsal horn.

Cutaneous spinal sensory transmission appears to lack inhibitory control in the newborn spinal cord, but the properties of GABAergic and glycinergic synapses in the neonatal dorsal horn have not been characterized. Whole-cell patch-clamp recordings from rat superficial dorsal horn neurons in spinal cord slices at postnatal day 0 (P0) to P2, P6-P7, and P13-P14 revealed an age-dependent increase in the frequency of spontaneous IPSCs, which were abolished by the GABA(A) receptor (GABA(A)R) antagonist bicuculline between P0 and P7 but not at P14. GABA(A)R-mediated miniature IPSCs (mIPSCs), but not glycinergic mIPSCs, were present at birth, and GABA mIPSCs remained more frequent than glycine mIPSCs at all ages. Sciatic nerve stimulation resulted in IPSCs with both GABAergic and glycinergic components, although a larger contribution arose from GABA(A) receptors at all ages. In gramicidin perforated patch-clamp recordings, exogenous GABA applications produced depolarization in 40% of neurons at P0-P2, but the reversal potential of GABA-evoked currents (E(GABA)) was consistently more negative than action potential threshold at this age. By P6-P7, GABA evoked only membrane hyperpolarization. The GABA(B)R agonist baclofen elicited an outward current in all neurons with peak amplitudes observed by P6-P7 and abolished sciatic nerve-evoked monosynaptic glutamatergic EPSCs in all groups. The results show considerable postnatal development of inhibitory processing in the dorsal horn with GABAergic mechanisms initially dominant over glycinergic events. GABA(A)R-mediated depolarizations during the first postnatal week are likely to be important for the maturation of spinal networks but do not provide a major excitatory drive to the newborn dorsal horn.

The effects of adrenalectomy in blood flow adjustments produced by sciatic nerve stimulation in rats

Sciatic nerve stimulation (SNS) produces hypertension, tachycardia, vasodilatation in the stimulated limb and vasoconstriction in the limb contralateral to the stimulation site. These autonomic adjustments represent an equivalent of the cardiovascular responses described as features of defense-alerting reactions. However, while the muscle vasodilatation observed in rats during stimulation of hypothalamic sites involved in defense reactions has been referred to as a general, non-selective increase in blood flow, previous studies conducted on cats have demonstrated that high-intensity cutaneus stimulation produces vasodilatation in the stimulated limb and vasoconstriction in the other limbs. In anesthetized rats, the effects of SNS in the muscle vascular territory of the contralateral limb, as well as the participation of circulating catecholamines in these adjustments continued to be unknown. Therefore, in the present study we investigated the blood flow adjustments elicited by SNS in the stimulated and in the contralateral hind limbs before and after bilateral adrenalectomy. In urethane-anesthetized, paralyzed, and artificially ventilated rats, SNS (800–1000 μA, 1 ms, 100 Hz, 10 s) produced hypertension, tachycardia, vasodilatation in the stimulated hindlimb and vasoconstriction in the contralateral hindlimb. After bilateral adrenalectomy the pressor responses to SNS were abolished, the vasodilatation in the stimulated limb was greater and the vasoconstriction in the contralateral limb was replaced by vasodilatation. These results suggest that the vasodilatation in the stimulated limb does not depend on circulating catecholamines.

Pharmacological studies of 8-OH-DPAT-induced pupillary dilation in anesthetized rats

Serotonin (5-HT) 1A receptor agonists have been reported to produce mydriasis in mice, and miosis in rabbits and humans. However, the underlying mechanisms for this action are unclear. This study was undertaken in an attempt to explore the mechanism by which 5-HT 1A receptors are involved in the modulation of pupillary size in pentobarbital-anesthetized rats. Intravenous administration of the 5-HT 1A receptor agonist, (2 R)-(+)-8-hydroxy-2-(di- n-propylamino)tetralin hydrobromide (8-OH-DPAT; 0.003–3 mg/kg), elicited dose-dependent pupillary dilation, which was not affected by section of the preganglionic cervical sympathetic nerve. 8-OH-DPAT-elicited mydriatic responses were attenuated by the selective 5-HT 1A receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]- N-2-pyridinylcyclohexanecarboxamide maleate (WAY 100635; 0.3–1 mg/kg, i.v.), as well as by the selective α 2-adrenoceptor antagonist, (8 aR,12 aS,13 aS)-5,8,8 a,9,10,11,12,12 a,13,13 a-dechydro-3-methoxy-12-(ethylsulfonyl)-6 H-isoquino[2,1- g][1,6]naphthyridine hydrochloride (RS 79948; 0.3 mg/kg, i.v.), but not by the selective α 1-adrenoceptor antagonist, prazosin (0.3 mg/kg, i.v.). Mydriatic responses elicited by the α 2-adrenoceptor agonist, guanabenz (0.003–0.3 mg/kg, i.v.), were not antagonized by WAY 100635 (0.3–1 mg/kg, i.v.). To determine whether central nervous system (CNS) 5-HT 1A receptors, like α 2-adrenoceptors, are involved in reflex mydriasis, voltage response curves of pupillary dilation were constructed by stimulation of the sciatic nerve in anesthetized rats. WAY 100635 (1 mg/kg, i.v.) did not antagonize the evoked reflex mydriasis, which, however, was blocked by RS 79948 (0.3 mg/kg, i.v.). Taken together, these results suggest that 8-OH-DPAT produces pupillary dilation in anesthetized rats by stimulating CNS 5-HT 1A receptors, which in turn trigger the release of norepinephrine, presumably from the locus coeruleus. The latter reduces parasympathetic neuronal tone to the iris sphincter muscle by stimulation of postsynaptic α 2-adrenoceptors within the Edinger-Westphal nucleus. Unlike α 2-adrenoceptors, 5-HT 1A receptors in the CNS do not mediate reflex mydriasis evoked by sciatic nerve stimulation.

Interaction between repetitive stimulation of the sciatic nerve and functional ablation of cerebellar nucleus interpositus in the rat

It is established that cerebellar nuclei exert a significant effect on the excitability of spinal neurons. However, their output is heterogeneous. Conditioning trains of dentate nucleus stimuli are known to modify the post-synaptic potentials evoked in motoneurons by stimulation of group Ia and Ib afferents in appropriate peripheral nerves. The role of the interpositus nucleus in the modulation of the excitability of rat spinal cord remains unclear. We investigated the interactions between tetrodotoxin (TTX)-induced inactivation of the interpositus cerebellar nuclei and repetitive electrical stimulation of the ipsilateral sciatic nerve (proximal segment) in the anesthetized rat. TTX (10 microM) was administered in cerebellar nuclei by the technique of microdialysis (coordinates of the extremity of the guide related to bregma: AP: -11.6, L: +2.3, V: -4.6). Peripheral stimulation consisted of trains of electric stimuli at a rate of 10 Hz, which were repeated every second during 1 hour. Stimulus intensity was adjusted to produce constant somatosensory evoked potentials. H-reflex, F-wave and M responses of the plantaris muscles were analysed ipsilaterally. H-reflex recruitment curve, Hmax/Mmax ratios, F-wave persistence and mean F/mean M ratios were studied. Functional blockade of cerebellar interpositus nucleus reduced the slope of H-reflex recruitment curve without affecting the Hmax/Mmax ratio, and depressed both F-waves persistence and mean F/mean M ratios. Concomitant repetitive stimulation of the sciatic nerve counteracted the depression of the H-reflex recruitment curve, without interacting with F-waves depression. Our results (1) show that TTX-sensitive sodium channels in cerebellar nucleus interpositus modulate the H-reflex recruitment, and (2) reveal an interaction between TTX-sensitive sodium channels in cerebellar nuclei and afferent repetitive activity not described so far.

Effects of desflurane on spinal somatosensory-evoked potentials and conductive spinal cord evoked potential.

Spinal somatosensory-evoked potential (interspinous-space-recorded evoked potentials after peripheral nerve or dermatomal stimulation) and conductive spinal cord evoked potential (interspinous-space-recorded evoked potentials after spinal cord stimulation) were analyzed in rats under different concentrations of the anesthetic desflurane. To investigate and compare the effects of a new volatile anesthetic, desflurane, on the common intraoperative neuromonitoring models. Intraoperative evoked potentials are sensitive to most anesthetics. Interpretation of the data becomes complicated because of a suppression effect caused by the anesthesia. Desflurane has become a valuable anesthetic in neurosurgery because of its pharmacokinetic advantages. Fifteen rats were placed under general anesthesia, and vital signs were closely monitored. Needle recording electrodes were placed stereotactically into the thoracolumbar interspinous ligament; dermatomal somatosensory-evoked potential by L5 dermatome, mixed-nerve somatosensory-evoked potential by sciatic nerve stimulation, and spinal cord evoked potential of the same recording electrodes elicited by C2-C3 interspinous stimulation were obtained. The effects of desflurane were examined at end-tidal concentrations of 6% (1.05 minimal alveolar concentration), 9% (1.57 minimal alveolar concentration), and 12% (2.10 minimal alveolar concentration). Amplitude decreased and latency was delayed in all three kinds of potentials, and the more so with higher concentrations. Comparing 9% with 6% desflurane, the amplitude in dermatomal somatosensory-evoked potential, mixed-nerve somatosensory-evoked potential, and spinal cord evoked potential decreased to 84.3%, 88.9%, and 70.8%, respectively, values with no statistically significant difference. However, at 12%, again compared with 6%, the amplitude decreased further to 64.4%, 70.3%, 41.8%, respectively; mixed-nerve somatosensory-evoked potential and dermatomal somatosensory-evoked potential were significantly more preserved than spinal cord evoked potential (P = 0.04). The concentration of desflurane alters the amplitude of somatosensory-evoked potential and spinal cord evoked potential, and, to a lesser degree, delays the latency; spinal cord evoked potential is more liable to be suppressed than somatosensory-evoked potential. The dose-dependent suppression effect on amplitude should be considered when interpreting changes during surgery. Furthermore, the potential benefit of somatosensory-evoked potential elicited by direct major nerve stimulation should be considered because of its large amplitude and higher resistance, even with a greater concentration of volatile anesthetics.

Blood flow activation in rat somatosensory cortex under sciatic nerve stimulation revealed by laser speckle imaging*

Abstract In many functional neuroimaging research the change of local cerebral blood flow (CBF) induced by sensory stimulation is regarded as an indicator of the change in cortical neuronal activity although a precise and full spatio-temporal description of local CBF response coupled to neural activity has still not been laid out. Using the laser speckle imaging technique a relatively large exposed area in somatosensory cortex of rat was imaged for the observation of the variations of CBF during sciatic nerve stimulation. The results showed that cerebral blood flow activation was spatially localized and discretely distributed in the targeted microvasculature. Individual arteries, veins and capillaries in different diameters were activated with the time going. The response pattern of CBF related to the function of brainactivity and energy metabolism is delineated exactly.

Functional and electrophysiological characterization of photochemical graded spinal cord injury in the rat.

This study characterizes by functional and electrophysiological methods changes following photochemically induced injuries to the spinal cord in adult rats. The spinal cord was exposed by laminectomy and bathed with 1.5% rose bengal solution for 10 min (T12-L1 vertebrae). The excess dye was removed by saline rinse and the spinal cord was irradiated with "cold" light for 0, 1, 2.5, 5, and 10 min in different groups of rats. During the first 15 days postlesion, locomotion activity, pain sensibility, motor and somatosensory evoked potentials, and motor and nerve action potentials were evaluated. Graded locomotor and nociceptive recovery was observed in irradiated rats depending on the photoinduction time. At 15 days, the amplitude of motor and sensory evoked potentials was significantly lower in irradiated groups with respect to control rats. The amplitude of compound muscle action potentials and of reflex H wave after sciatic nerve stimulation decreased significantly in irradiated animals with respect to control rats, while the latency did not show significant differences. In irradiated groups, significant differences were seen between pre- and postoperative values for most functional and electrophysiological parameters analyzed. A significant negative relationship was found between the area of cystic cavity of the spinal cord and the functional and electrophysiological impairment.

Effects of hypothyroidism on the skeletal muscle blood flow response to contractions.

Hypothyroidism is associated with impaired blood flow to skeletal muscle under whole body exercise conditions. It is unclear whether poor cardiac and/or vascular function account for blunted muscle blood flow. Our experiment isolated a small group of hindlimb muscles and simulated exercise via tetanic contractions. We hypothesized that muscle blood flow would be attenuated in hypothyroid rats (HYPO) compared with euthyroid rats (EUT). Rats were made hypothyroid by mixing propylthiouracil in their drinking water (2.35 x 10-3 mol/l). Treatment efficacy was evidenced by lower serum T3 concentrations and resting heart rates in HYPO (both P<0.05). In the experimental preparation, isometric contractions of the lower right hindlimb muscles at a rate of 30 tetani/min were induced via sciatic nerve stimulation. Regional blood flows were determined by the radiolabelled microsphere method at three time points: rest, 2 min of contractions and 10 min of contractions. Muscle blood flow generally increased from rest ( approximately 5-10 ml/min per 100 g) through contractions for both groups. Further, blood flow during contractions did not differ between groups for any muscle (eg. red section of gastrocnemius muscle; EUT, 59.9 +/- 14.1; HYPO, 61.1 +/- 15.0; NS between groups). These findings indicate that hypothyroidism does not significantly impair skeletal muscle blood flow when only a small muscle mass is contracting. Our findings suggest that impaired blood flow under whole body exercise is accounted for by inadequate cardiac function rather than abnormal vascular function.

Exercise pressor reflex in decerebrate and anesthetized rats.

I investigated whether muscular contraction evokes cardiorespiratory increases (exercise pressor reflex) in alpha-chloralose- and chloral hydrate-anesthetized and precollicular, midcollicular, and postcollicular decerebrated rats. Mean arterial pressure (MAP), heart rate (HR), and minute ventilation (Ve) were recorded before and during 1-min sciatic nerve stimulation, which induced static contraction of the triceps surae muscles, and during 1-min stretch of the calcaneal tendon, which selectively stimulated mechanosensitive receptors in the muscles. Anesthetized rats showed various patterns of MAP response to both stimuli, i.e., biphasic, depressor, pressor, and no response. Sciatic nerve stimulation to muscle in precollicular decerebrated rats always evoked spontaneous running, so the exercise pressor reflex was not determined from these preparations. None of the postcollicular decerebrated rats showed a MAP response or spontaneous running. Midcollicular decerebrated rats consistently showed biphasic blood pressure response to both stimulations. The increases in MAP, HR, and Ve were related to the tension developed. The static contractions in midcollicular decerebrated rats (381 +/- 65 g developed tension) significantly increased MAP, HR, and Ve from 103 +/- 12 to 119 +/- 24 mmHg, from 386 +/- 30 to 406 +/- 83 beats/min, and from 122 +/- 7 to 133 +/- 25 ml/min, respectively. After paralysis, sciatic nerve stimulation had no effect on MAP, HR, or Ve. These results indicate that the midcollicular decerebrated rat can be a model for the study of the exercise pressor reflex.

Blood flow activation in rat somatosensory cortex under sciatic nerve stimulation revealed by laser speckle imaging

Blood flow activation in rat somatosensory cortex under sciatic nerve stimulation revealed by laser speckle imaging

Heterogeneous synaptic inputs from the ventrolateral periaqueductal gray matter to neurons responding to somatosensory stimuli in the rostral ventromedial medulla of rats

The ventrolateral cell column of the midbrain periaqueductal gray matter (vl-PAG) plays a major role in the attenuation of pain behaviour. It is established that this effect is exerted via modulation of neuronal activities in the rostral ventromedial medulla (RVM). Until recently it has been generally accepted that the vl-PAG exerts its modulatory effects upon RVM neurons through a direct monosynaptic pathway. However, recent data suggest that an additional indirect, di- or polysynaptic pathway may also exist. Using in vivo intracellular recordings we tested this hypothesis, by studying synaptic responses of somatosensory receptive RVM neurons evoked by electric stimulation of the vl-PAG in rats. RVM neurons were regarded as somatosensory receptive if they responded to electrical stimulation of the sciatic nerve. Most of the recorded RVM cells were excited by vl-PAG stimulation. Some of them responded with a short onset latency (3.6±0.9 ms) corresponding to monosynaptic excitation. All of these neurons were also excited by sciatic nerve stimulation at nociceptive intensities. In contrast to this, another proportion of the recorded RVM neurons responded with a four times longer (14.8±3 ms) onset latency to the vl-PAG stimulation, corresponding to polysynaptic modulation. All of these neurons were inhibited by sciatic nerve stimulation. The findings show that RVM neurons receive heterogeneous monosynaptic and polysynaptic inputs from the vl-PAG. The results also suggest that the monosynaptic and polysynaptic pathways modulate the activity of functionally distinct groups of RVM neurons.

Eccentric contraction injury in dystrophic canine muscle

Childers MK, Okamura CS, Bogan DJ, Bogan JR, Petroski GF, McDonald K, Kornegay JN. Eccentric contraction injury in dystrophic canine muscle. Arch Phys Med Rehabil 2002;83:1572-8. Objective: To test the hypothesis that eccentric contractions induce greater injury in dystrophic compared with normal canine muscle. Design: Blinded cohort study. Setting: Animal laboratory. Animals: Ten dogs with a homologue to Duchenne muscular dystrophy (Golden retriever muscular dystrophy [GRMD]) and 10 normal littermates. Interventions: Contractions induced in tibiotarsal flexors and extensors by sciatic nerve stimulation. Because more powerful extensors overrode flexors, eccentric contractions occurred in flexors. Concentric contractions were induced in contralateral flexors by peroneal nerve stimulation. Main Outcome Measure: Tibiotarsal flexion force 3 days after contractions. Muscle was examined for injury (esterase activity, Evans blue dye penetration) and regeneration (embryonic myosin isoform expression). Results: Mean force deficit after eccentric flexor contractions was 43.3%±25.7% in GRMD dogs compared with 25.0%±18.4% in controls (P=.04, Wilcoxon rank-sum test). Concentric contractions induced force deficits in GRMD but not normal dogs; however, the difference between the 2 groups was not significant (P=.08, Wilcoxon rank-sum test). After concentric contractions in controls, force decrements correlated with esterase activity measured by area (r=.794, P=.006) and intensity (r=.697, P=.025, Spearman rank correlation). No other significant correlation was detected between force and biopsy data. Conclusions: Force data support the hypothesis that eccentric contractions induce greater injury in dystrophic compared with normal canine muscle. Phenotypic features of the dystrophic canine model used here are similar to those of humans with Duchenne's. © 2002 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation

Posterior subgluteal approach to block the sciatic nerve: description of the technique and initial clinical experiences.

A new posterior approach to the sciatic nerve in the subgluteal region was developed. We describe our clinical experiences on 135 consecutive patients. All blocks were performed with a nerve stimulator (stimulation frequency 2 Hz; intensity from 1 reduced to < or = 0.5 mA before application). A line was drawn from the greater trochanter to the ischial tuberosity of the femur; then, from the mid-point of this line, a second line was drawn perpendicularly and extended caudally for 4 cm: the end of this line represented the entry point of the needle. Sciatic stimulation was elicited at < or = 0.5 mA; then ropivacaine 0.75% 20 mL was injected. An independent observer recorded the time from needle insertion to successful sciatic nerve stimulation (performance time), the depth of appropriate sciatic stimulation and the number of needle redirections, as well as the quality of nerve block, the discomfort during the procedure and patient acceptance. The performance time was 41 +/- 25 s (mean +/- SD) and the mean (SD) depth at which the sciatic nerve stimulation was found was 45 +/- 10 mm. The median (range) number of needle redirections required to find the proper sciatic stimulation was 2 (1-5). The tibial response was observed in 77 patients (57%), while the common peroneal response was observed in 58 patients (43%). The degree of discomfort reported was very low and only 16 patients (12%) reported severe pain during placement of the block. The onset time (mean +/- SD) of sensory and motor block was 7 +/- 4 and 17 +/- 13 min respectively, and the surgical procedure was completed with only the peripheral nerve block in 127 patients (94%). The same anaesthesia procedure was acceptable by 127 patients (94%) and only eight patients (6%) would prefer a different anaesthesia technique in the future. The study demonstrated that the sciatic nerve can be easily blocked using this new posterior subgluteal approach, suggesting that it represents a safe and effective alternative to block the sciatic nerve at a proximal level, with the potential for reducing the discomfort experienced by the patient during block placement.

Cardiovascular responses during stimulation of hindlimb skeletal muscle nerves in anaesthetized rats.

1. Cardiovascular responses during static skeletal muscle contraction in anaesthetized rats appear to be contradictory. The present study attempted to explain such variations by stimulating different peripheral nerves supplying the hindlimb skeletal muscles using anaesthetized Sprague-Dawley rats. 2. Muscle contractions were evoked by a 30 s stimulation of the sciatic, tibial, peroneal nerves or the sciatic nerve with transected peroneal branch at threefold the motor threshold, 0.1 msec duration and 40 Hz frequency. 3. Contractions during stimulation of the tibial or the sciatic nerve with severed peroneal branch evoked similar increases in arterial pressure and heart rate. Following stimulation of the tibial nerve, blood pressure, heart rate and muscle tension increased by 23 +/- 3 mmHg, 31 +/- 5 b.p.m. and 789 +/- 34 g, respectively. For the sciatic nerve with transected peroneal branch, increases the respective increases were 27 +/- 5 mmHg, 32 +/- 6 b.p.m. and 802 +/- 43 g. In contrast, peroneal nerve stimulation produced depressor and bradycardic responses of -22 +/- 5 mmHg and -40 +/- 9 b.p.m., respectively. Interestingly, intact sciatic nerve stimulation elicited pressor, depressor or no responses (average being -10 +/- 8 mmHg), along with a consistent increase in heart rate of 24 +/- 7 b.p.m. 4. The results demonstrate that static muscle contraction following stimulation of the tibial or sciatic nerve with transected peroneal branch, elicits consistent increases in blood pressure and heart rate. Furthermore, stimulation of the peroneal nerve elicits a depressor response, while stimulation of the intact sciatic nerve evokes variable cardiovascular responses. Overall, anaesthetized rats can be excellent models to study the variable cardiovascular responses during activation of group III and/or group IV muscle afferents.