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At least 199 records · Page 11Linked to original sources
PubMed1975

[On decrease in spike height of nerve action potential. A comparison between sciatic nerve and ENM (author's transl)].

Employing ENM and a sciatic nerve removed from bullfrog, configuration of decrease of spike under various experimental conditions was studied. The amplitude of the membrane potential change in excitation was also recorded simultaneously with the decrease of spike in ENM (electric nerve model). Both on the nerve and ENM, with decrease of the resting potential, the amplitude of the spike and the amplitude of the change of the membrane potential were decreased. On the nerve and ENM, the decrease in spike amplitudes was induced by an elevation of the niveau and by a lowering of the top. However, the amplitude of the change of membrane potential of ENM was reduced only from the base of the spike due to an elevation of the niveau, with the top remained at a constant level. These decreases of the spike amplitude and the change of the membrane potential in nerve were consistent with that the electric constitution was the same for nerve and ENM, which is the experimental equivalent circut of the nerve fiber devised by the authors.

Action Potentials↗
PubMed1979

Effects of nerve impulses on threshold of frog sciatic nerve fibres.

1. The firing thresholds of single myelinated fibres of frog sciatic nerves were monitored as a function of impulse activity in the fibre. The threshold was given by the number of coulombs in current pulses that excited a particular fibre half the time when delivered to the whole nerve. Threshold was tracked by a device that incrementally decreased the number of coulombs in the current pulse whenever the fibre responded and increased the pulse if it did not respond. 2. There was a pattern to the after-oscillations of threshold following activity. The fibres were briefly refractory, transiently superexcitable for about 1-1.5 sec and then entered a phase of raised threshold or 'depression' that lasted for many minutes. 3. Activity produced little change in the threshold curve during the refractory period. Strong depressions following prolonged activity prevented the threshold from returning to the base-line level within the time associated with the refractory period for the same fibre at rest. 4. After an impulse, superexcitability reached a maximum within 7-20 msec. This peak was larger as the number of impulses in a preceding burst increased and as the intervals between the impulses became briefer. Each successive impulse of a burst contributed less to the growth of superexcitability, and after the burst had 6-10 impulses additional impulses contributed nothing. 5. The depression phase was marked by the interaction between build-up, which depended on the activity rate, and recovery, which required as long as an hour or more for the threshold to be completely restored to resting level. These two mechanisms, one causing build-up and the other recovery, led to formation of dynamic equilibria. The threshold level at equilibrium increased monotonically with the activity rate. 6. The processes associated with superexcitability interact with those producing depression. In active fibres showing raised thresholds, impulses are followed by a relative superexcitability that persists for at least as long as an absolute superexcitability (with threshold below the resting level) can be measured in the same fibre at rest. 7. The duration of the superexcitable phase interpreted as a relative change in excitability was roughly the same regardless of the level of depression. 8. The magnitude of the oscillation in threshold was give to ten times larger than the grey region (the range of stimuli for which response is probabilistic). It is concluded that at regions of low conduction safety such as axonal branches, where weak forces can influence whether an impulse will pass, such pronounced and long-lasting after-effects of firing can be expected to modulate conduction of nerve impulses.

Action Potentials↗
PubMed1994

Gait-stance duration as a measure of injury and recovery in the rat sciatic nerve model.

The rat sciatic nerve is a well-established animal model for the study of peripheral nerve crush injury. Footprint analysis is the most widely used non-invasive method of measuring functional recovery after injury in this model. However, this method has significant limitations due to inability to obtain clear reproducible prints, especially when the injury is severe, and variation of these prints with gait velocity. In the case of contracture or toe loss, footprint analysis is unreliable. We describe a new technique, gait-stance duration, which is capable of non-invasively quantitating functional recovery in the rat model. This method is not dependent on accurate foot positioning during gait. It utilizes video recording of the animal walking and measures the time each hind foot is in contact with the floor by counting the number of frames that pass. By pairing consecutive steps, it minimizes variation due to changes in velocity and, by calculating a ratio of injured/uninjured hind feet, comparisons to normal gait can be made. This method shows recovery patterns similar to footprint analysis with small inter-animal variability. We believe it has significant advantages over footprint analysis for the measurement of functional recovery in the crushed sciatic nerve rat model.

Animals↗
PubMed2001

The difference in E-cadherin expression between nonvascularized and vascularized nerve grafts: study in the rat sciatic nerve model.

BACKGROUND: We investigated the expression of E-cadherin during nerve regeneration after nonvascularized and vascularized nerve grafts. MATERIALS AND METHODS: We used the rat sciatic nerve model. E-cadherin expression was detected by Western blot analysis and immunofluorescent staining with anti E-cadherin monoclonal antibody. The level of E-cadherin expression was calculated as the amount relative to that of E-cadherin expression of normal control nerve. Furthermore, repair of the neural tissue structure was examined by toluidine blue staining. RESULTS: In both cases, the level of E-cadherin expression decreased at first, and then gradually increased. The maximum level was 1.61 +/- 0.066-fold in the nonvascularized nerve graft and 2.254 +/- 0.071-fold in the vascularized nerve graft. From the 1st to the 16th postoperative weeks, the level of E-cadherin expression in the vascularized nerve graft was significantly higher than that in the nonvascularized nerve graft. In the immunofluorescent staining, E-cadherin expression was almost negative or decreased immediately after the operation, but the degree of expression was gradually increased in Schwann cells. The degree of E-cadherin expression in the vascularized nerve graft was greater than that in the nonvascularized nerve graft. In toluidine blue staining, the velocity of tissue repair was more rapid in the vascularized nerve graft than in the nonvascularized graft. CONCLUSION: These results demonstrate that the E-cadherin expression of grafted nerve was increased during the nerve regeneration, and the expression was mainly observed in Schwann cells. Because the level of E-cadherin expression was significantly higher in the vascularized nerve graft than in the nonvascularized nerve graft, the level of E-cadherin expression may affect the rapidity of nerve regeneration.

Animals↗
PubMed1992

Effects of age and size on development of allodynia in a chronic pain model produced by sciatic nerve ligation in rats.

Sciatic nerve constriction injury in rats has been used by various investigators as a model of chronic pain exhibiting allodynia and hyperalgesia. Although rats ranging between 200 and 350 g (40-70 days old) at the time of operation have been used by various investigators, the effect of rat age and weight on the model has not been previously studied. We noted that a group of older rats failed to develop all the characteristics of the model and designed the present study to determine the effect of age and weight on the development of allodynia and hyperalgesia. Three groups of rats varying in age (54, 71, and 107 days) and weight (220-250 g, 270-350 g, and 370-470 g) with the experimental lesion were tested for hyperalgesia, cold allodynia, and tactile allodynia. We found that although the degree of hyperalgesia of all groups was the same, the oldest group had significantly longer response latencies to allodynia tests than the younger 2 groups. Responses to the cold test were no different than control in the oldest group. The results of the present study demonstrate that larger, older rats fail to develop allodynia after sciatic nerve ligation.

Aging↗
PubMed1980

Study of evolution of nerve damage in leprosy. Part III--Sciatic nerve lesions in mice inoculated with M. leprae with nerve conduction velocity correlates.

Non-immunosuppressed Swiss mice inoculated with 5000 M. leprae in each hind foot pad were subjected to nerve conduction velocity studies followed by light and electron microscopy and fibre tease of both sciatic nerves at sequential time intervals from the 4th to the 24th month. The conduction velocity was standardized for basal temperature of 35 degrees C and uninoculated mice were used as controls. Progressive changes were noted in conduction velocity from the 6th post inoculation month and correlated with the ultrastructural changes which were first observed at the 4th month. Fibre teasing showed predominent segmental demyelination.

Animals↗
PubMed1987

Peripheral nerve as an osmometer: role of endoneurial capillaries in frog sciatic nerve.

The sciatic nerve of the frog was perfused in vivo with isotonic Ringer solution followed by Ringer made hypertonic by addition of sucrose or of NaCl. Nerve diameter and endoneurial hydrostatic pressure fell during hypertonic Ringer perfusion. Using a model that describes the elastic and osmotic properties of the nerve, sigma sLp, the product of the osmotic reflection coefficient at endoneurial capillaries for s equals sucrose or NaCl (which approximates 1), and of capillary hydraulic conductivity, was found to equal 73 X 10(-13) cm3 X s-1 X dyn-1. The nerve is elastic. It has a compliance K of 3.7 X 10(-5) cm2 X mmHg-1, corresponding to a modulus of elasticity E of the perineurium equal to 1.2 X 10(6) dyn X cm-2. The results indicate that the nerve behaves as an osmometer during vascular perfusion, due to the low permeability of endoneurial capillaries to small solutes such as NaCl and sucrose. A low capillary hydraulic conductivity limits bulk water flow between blood and nerve, and a low compliance limits nerve swelling and edema.

Animals↗
PubMed1997

Correlation between evoked motor response of the sciatic nerve and sensory blockade.

BACKGROUND: Incomplete sensory blockade of the foot after sciatic nerve block in the popliteal fossa may be related to the motor response that was elicited when the block was performed. We investigated the appropriate motor response when a nerve stimulator is used in sciatic nerve block at the popliteal fossa. METHODS: Six volunteers classified as American Society of Anesthesiologists' physical status I underwent 24 sciatic nerve blocks. Each volunteer had four sciatic nerve blocks. During each block, the needle was placed to evoke one of the following motor responses of the foot: eversion, inversion, plantar flexion, or dorsiflexion. Forty milliliters 1.5% lidocaine was injected after the motor response was elicited at < 1 mA intensity. Sensory blockade of the areas of the foot innervated by the posterior tibial, deep peroneal, superficial peroneal, and sural nerves was checked in a blinded manner. Motor blockade was graded on a three-point scale. The width of the sciatic nerve and the orientation of the tibial and common peroneal nerves were also examined in 10 cadavers. RESULTS: A significantly greater number of posterior tibial, deep peroneal, superficial peroneal, and sural nerves were blocked when inversion or dorsiflexion was seen before injection than after eversion or plantar flexion (P < 0.05). Motor blockade of the foot was significantly greater after inversion. Anatomically, the tibial and common peroneal nerves may be separate from each other throughout their course. The sciatic nerve ranged from 0.9-1.5 cm in width and was divided into the tibial and common peroneal nerves at 8 +/- 3 (range, 4-13) cm above the popliteal crease. CONCLUSIONS: Inversion is the motor response that best predicts complete sensory blockade of the foot. Incomplete blockade of the sciatic nerve may be a result of the size of the sciatic nerve, to separate fascial coverings of the tibial and common peroneal nerves, or to blockade of either the tibial or common peroneal nerves after branching from the sciatic nerve.

Adult↗
PubMedDate not supplied

Reevaluation of the sciatic nerve block.

BACKGROUND AND OBJECTIVES: Sciatic nerve blocks are perceived as unreliable, technically demanding, and uncomfortable. With strict criteria to define success rates, we designed a study to examine the efficacy of two techniques of sciatic nerve block. METHODS: All blocks were performed by a novice in sedated patients using an insulated needle and a nerve stimulator. RESULTS: Overall success with both techniques was 87.5%. One transient neurologic deficit attributed to the sciatic nerve block was observed; otherwise, the technique provided satisfactory anesthesia without complications. CONCLUSIONS: Patient acceptance was excellent.

Adult↗
PubMed1999

Missile injuries of the sciatic nerve.

Missile injuries of the sciatic nerve are not common in civil practice. We analysed a war series of 55 cases operated on in a period from 1991 to 1995. Nerve continuity was preserved at least partially in 76.4% of cases, but only 13.3% of cases had preserved some nerve function. Surgical results were analysed in 45 cases followed for more than two years. The rates of useful functional recovery were 86.7% for tibial division, 53.3% for peroneal division and 86.7% for the sciatic nerve complex. On the basis of the obtained results we were able to make the following conclusions: (1) missile injuries to the sciatic nerve are characterised by partially preserved nerve continuity and complete functional loss in the majority of cases, (2) surgery should be performed 3 to 6 months after injury, (3) reconstruction of tibial division is the major goal of surgical repair, (4) the extent and severity of nerve damage and the type of surgical procedure are the main prognostic factors and (5) failures of surgical repair are usually related to nerve grafting at gluteal level.

Adolescent↗
PubMed1985

Release of substance P from peripheral nerve terminals following electrical stimulation of the sciatic nerve.

Substance P is a putative mediator of neurogenic inflammation, where it is postulated to be released from nerve terminals in the skin in response to noxious and electrical stimulation. To demonstrate release of substance P from cutaneous nerve terminals a blister model has been established. Electrical stimulation of the sciatic nerve for 20 min at 50 V, 15 Hz, 0.5 ms, resulted in a significant increase in substance P-like immunoreactivity (SPLI) in blister fluid, which was abolished after neonatal pretreatment of rats with capsaicin. There was no increase of SPLI, following stimulation of the sciatic nerve at 4 V. There was a corresponding decrease in skin SPLI following nerve stimulation at 50 V. Characterization of blister fluid SPLI after stimulation at 50 V demonstrated a peak of immunoreactivity, which co-eluted with synthetic substance P and SPLI from rat skin. These results confirm the hypothesis that electrical stimulation results in release of substance P from nerve terminals in the skin, and therefore fulfils an important criterion of its role as a mediator of neurogenic inflammation.

Animals↗
PubMed2005

Does the site of injection distal to the greater trochanter make a difference in lateral sciatic nerve blockade?

UNLABELLED: The two components of the sciatic nerve become more distant from one another in their course down the lower limb. This may have clinical implications if a small volume of local anesthetic is used with a single injection technique. In this prospective, randomized, double-blind study, we compared two different injection sites, 20 cm and 30 cm distal to the greater trochanter, in terms of onset time and success rate of sciatic nerve blockade after a single injection of 20 mL of 1.5% mepivacaine. Fifty patients undergoing foot surgery were randomly allocated to receive a lateral sciatic nerve blockade using one of 2 levels: 20 cm distal to the greater trochanter (group proximal; n = 25) and 30 cm distal to the greater trochanter (group distal; n = 25). Twenty milliliters of 1.5% mepivacaine was injected after a flexion plantar response was obtained at <0.5 mA. Time required for onset of sensory and motor blockade of the foot was recorded. Success rate was defined as complete sensory and motor blockade in all sciatic nerve distributions associated with a pain-free surgery. Onset of complete sensory and motor blockade was faster in group proximal (12 +/- 7 min and 15 +/- 8 min, respectively) compared with group distal (19 +/- 9 min and 23 +/- 9 min; P < 0.05). Group proximal also had a more frequent success rate compared with group distal (88% versus 56%, respectively; P < 0.05). It is concluded that in lateral sciatic nerve blockade, a more proximal approach to the sciatic nerve predicts a shorter onset time and more frequent success than a more distal injection site when a single injection and a small volume of local anesthetic is used. IMPLICATIONS: In lateral sciatic nerve blockade, a more proximal approach to the sciatic nerve provides shorter onset times and more frequent success than a more distal injection site when a single injection of 20 mL of mepivacaine 1.5% is used.

Adolescent↗
PubMed1997

Differential expression of galanin immunoreactivities in the primary sensory neurons following partial and complete sciatic nerve injuries.

Neuropeptide expression in primary sensory neurons is highly plastic in response to peripheral nerve axotomy. While neuropeptide changes following complete sciatic nerve injury have been extensively studied, much less is known about the effects of partial sciatic nerve injuries on neuropeptide plasticity. Galanin. a possible endogenous analgesic peptide, was up-regulated in primary sensory neurons following complete sciatic nerve injury. We investigated the effects of partial sciatic nerve injuries on galanin expression in primary sensory neurons, and compared this effect with that after complete sciatic nerve injury. Complete transection, partial transection and chronic constriction injury were made, respectively, on the sciatic nerves of three groups of rats at high thigh level. Animals were allowed to survive for four and 14 days before being killed. L4 and L5 dorsal root ganglia, L4 5 spinal cord and lower brainstem were processed for galanin immunocytochemical staining. After all three types of sciatic nerve injuries, galanin-immunoreactive neurons were significantly increased in the ipsilateral dorsal root ganglia, and galanin-immunoreactive axonal fibres were dramatically increased in the superficial laminae of the dorsal horn and the gracile nuclei, compared to the contralateral side. However, in partial injury models, the percentages of galanin-immunoreactive dorsal root ganglion neurons were significantly higher than in complete nerve transection. Size frequency distribution analysis detected that more medium- and large-size galanin-immunoreactive dorsal root ganglion neurons were present after partial nerve transection and constriction injury than after complete nerve transection. Using a combined approach of retrograde tracing of flurorescent dyes and galanin immunostaining, we found that a partial transection increased the proportions of galanin-immunoreactive neurons among both axotomized and non-axotomized neurons. Galanin-immunoreactive axonal fibres were not only detected in the superficial laminae, but also in the deeper laminae of the dorsal horn of partial injury animals. Furthermore, more galanin-immunoreactive axonal fibres were observed in the ipsilateral gracile nuclei of partially injured rats than in completely injured rats. We conclude that partial sciatic nerve injuries induced greater galanin up-regulation in medium- and large-size dorsal root ganglion neurons than complete sciatic nerve injury. Galanin expression in primary sensory neurons seems to be differentially regulated following partial and complete sciatic nerve injuries.

Animals↗