Primary somatosensory cortex in rats with pain-related behaviours due to a peripheral mononeuropathy after moderate ligation of one sciatic nerve: neuronal responsivity to somatic stimulation

Single-unit recordings were made under moderate gaseous anaesthesia in the hindpaw representation area of the two primary somatosensory motor cortices (SmI) of rats (n = 58) rendered mononeuropathic by four loose ligatures placed around one common sciatic nerve 2-3 weeks beforehand. The rats exhibited clear hyperalgesia and allodynia from the paw with the ligated sciatic nerve, to both mechanical and thermal stimuli. From the tested neuronal population (n = 640), about the same proportion could be activated by somatic stimuli in each cortex: 165/362 (45%) in the cortex contralateral to the ligated sciatic nerve (Cc), 105/278 (37%) in the cortex ipsilateral to the ligated sciatic nerve (Ci). Neurones driven by light touch, exhibited RFs strictly contralateral to the recording sites. Their proportion and response characteristics were similar regardless of recording side. However, the number of neurones with RFs in the sciatic nerve territory was above 95% in the Ci, and was dramatically reduced to 43% in the Cc. By contrast, the number of neurones with RFs supplied by the saphenous nerve reached 57% on this side. Although the RF size of all the neurones appeared roughly normal, there were fewer Cc than Ci neurones with RFs located on the paw itself and with RFs of extremely small size in the sciatic nerve territory. The proportion of neurones responding to a joint stimulus was significantly higher in the Cc than in the Ci. The neuronal responses to joint stimuli of the paw with the ligated sciatic nerve were significantly more sustained than those recorded in the Ci and elicited from the normal paw. The proportion of neurones driven by mechanical stimulation which gave rise to nociceptive reactions in freely moving animals, i.e. "nociceptive" neurones, was comparable in each cortex. However, half of the Cc neurones exhibited paroxysmal discharges occurring without intentional stimulation and of long duration (1 min to several minutes). Only 66% of Cc but 93% of Ci "nociceptive" neurones were exclusively activated by pinch. The remaining Cc neurones were also activated by applying moderate pressure to the paw with the ligated nerve. Pinch responses from the paw with the ligated nerve were often more intense and of longer duration than responses elicited from the intact paw. The "nociceptive" Cc neurones were especially sensitive to thermal stimuli of 39-44 degrees C when the stimuli were applied to the paw with the ligated nerve. They also responded vigorously to a 10 degrees C stimulus applied to this paw.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

Magnetic fields stimulate peripheral nerve regeneration in hypophysectiomized rats

The effect of a sinusoidal 50 Hz magnetic field, 0.4 mT on regeneration of the rat sciatic nerve was studied. The sciatic nerve of intact and hypophysectomized rats was crushed and regeneration was evaluated by the pinch test and by immunocytochemical staining for neurofilaments. The animals were exposed to the magnetic field for 3-6 days, between a pair of Helmholtz coils. Hypophysectomy of the rats resulted in an impaired regeneration. However, the magnetic field exposure stimulated regeneration in both the intact and hypophysectomized animals. The results imply that the pituitary gland is not involved in magnetic field induced stimulation of nerve regeneration.

Residual effects of tracer in sequential double label deoxyglucose studies

The validity of sequential double label deoxyglucose (DG) determinations of local metabolic rate for glucose (IMRglc) was examined by quantifying the degree of trapping of residual first DG tracer during the second experimental period. One sciatic nerve was repetitively stimulated for 25 min, beginning either at the time of the DG injection or 25 min later. IMRglc in the ipsilateral dorsal horn of the lumbar spinal cord was found to be 105% and 56%, respectively, greater than that of the contralateral unstimulated side. Attempts to lower the body burden of radioactive DG by exchange blood transfusion failed to reduce this delayed effect. These data indicate that residual effects of the first tracer could obscure possible differences in IMRglc between two sequential experimental states.

Expression of the pro-opiomelanocortin gene in dorsal root ganglia, spinal cord and sciatic nerve after sciatic nerve crush in the rat

Neuropeptides related to alpha-melanocyte-stimulating hormone (alpha-MSH) stimulate nerve outgrowth following peripheral nerve injury and may play an important physiological role in peripheral nerve regeneration. The mechanism of action underlying the neurotrophic effect of pharmacologically administered alpha-MSH is unknown. Here we investigate the hypothesis that reexpression of the proopiomelanocortin (POMC) gene, the prohormone of alpha-MSH/adrenocorticotropic hormone (ACTH)-like peptides, is part of the endogenous repertoire of peripheral nerve responses following injury. The effect of sciatic nerve crush on the expression of POMC mRNA between 0.5 h and 14 days after crush was investigated using polymerase chain reaction (PCR) and Northern blot analysis. The presence of a POMC transcript in dorsal root ganglia (DRG), spinal cord and in the sciatic nerve at the crush site could be demonstrated in both control and lesioned animals by PCR using primers located in exon 1 and 3 of the POMC gene. Minute quantities of two POMC transcripts (1200 nt and 800 nt) could be detected by Northern blot analysis of total RNA prepared from DRG, spinal cord and the sciatic nerve of control animals and of animals subjected to nerve crush. POMC mRNA expression was, however, not increased following nerve crush. Probes specific for exons 1 and 2 or specific for exon 3 of the POMC gene were employed to demonstrate that the 800 nt transcript represents the truncated POMC mRNA previously shown to be present in extra-pituitary tissue. The larger 1200 nt transcript comigrates with the full length POMC mRNA expressed in the pituitary gland. The present results demonstrate the expression of small amounts of POMC mRNA in all compartments of the sciatic nerve. The absence of an induction of POMC expression in response to nerve crush suggests that the stimulating effect of exogenously applied alpha-MSH does not mimic a POMC derived neurotrophic peptide induced in the nerve following nerve injury.

Evidence of a neurogenic component during IgE-mediated inflammation in mouse skin

IgE-mediated inflammation was measured in mouse footpads that lacked sciatic innervation. Mice were passively sensitized with a monoclonal antibody, IgE anti-dinitrophenol, or were immunized for specific IgE production. Antigen-induced swelling in the denervated footpads was reduced 23-39% when compared to sham or untreated controls. Reduced IgE-mediated swelling responses were attributed to the loss of a mast cell-nerve interaction and not to blood vessel sensitivity to vasoamines. Furthermore, electrical stimulation of the distal segment of the sciatic nerve completely restored IgE-mediated inflammation. These data provide in vivo evidence that peripheral nerves participate in cutaneous IgE-mediated swelling reactions with the net effect of increasing inflammation.

P15 in tibial nerve SEPs as an example of the junctional potential

Tibial nerve stimulation at the ankle elicited a stationary, dipolar potential P15/N15 over the buttock with a reference electrode at the contralateral greater trochanter (GTc). P15 was distributed in the rostral and contralateral region and N15 in the caudal and ipsilateral region. The derivation from the contralateral iliac crest to the ipsilateral greater trochanter (ICc-GTi) registered a large P15 (= P15-N15) potential which was well free from artifacts. The Cz'-contralateral knee lead, which had been employed in previous studies, registered a smaller P15 of poor quality. Sequential bipolar recording along the course of the sciatic nerve indicated that P15 was generated around the greater sciatic foramen. Comparison with a simulation study suggested that P15 is a junctional potential which is generated when the sciatic nerve enters the bone at the greater sciatic foramen. P15 is expected to be a useful tool to evaluate the proximal segment of the tibial nerve.

The effect of nizatidine on neuromuscular transmission

The effect of the H2-receptor antagonist, nizatidine, on neuromuscular transmission was investigated using sciatic nerve-gastrocnemius muscle preparations of rat in vivo. Nizatidine, administered by i.v. injection, potentiates the neuromuscular blockade induced by d-tubocurarine, pancuronium and the aminoglycoside antibiotic, kanamycin. Moreover, the drug alone is capable of producing a blockade on preparations stimulated at high frequency. The neuromuscular blockade induced by nizatidine is reversed by 4-aminopyridine but not by dimaprit.

[An experimental study on elongation injury of peripheral nerve]

The sciatic nerve of rabbits was indirectly elongated by lengthening the femur to clarify the pathology of elongation injury of the peripheral nerve. Electrophysiologic and morphologic changes and the blood flow in the nerve due to nerve elongation were evaluated in this model. No significant changes were observed when the nerve was elongated by 5.01%. Conduction disturbances, however, developed and the blood flow in the nerve was markedly reduced by sustained 11.8% elongation. In the latter case, the blood-nerve barrier was disrupted after 6-12 hours, endoneurial edema was observed after 48 hours, and extensive degeneration of nerve fibers was noted after 5 days. When the nerve was returned to the original length after 11.8% elongation for 2 hours, degeneration of the nerve fibers followed only partially. These findings suggest that circulatory impairments as well as mechanical damages are closely involved in elongation injury of peripheral nerves. The results also indicate that the duration of elongation plays an important role in determining the severity of elongation injury of peripheral nerves.

Axonal transport of class II and III beta-tubulin: evidence that the slow component wave represents the movement of only a small fraction of the tubulin in mature motor axons

Pulse-labeling studies demonstrate that tubulin synthesized in the neuron cell body (soma) moves somatofugally within the axon (at a rate of several millimeters per day) as a well-defined wave corresponding to the slow component of axonal transport. A major goal of the present study was to determine what proportion of the tubulin in mature motor axons is transported in this wave. Lumbar motor neurons in 9-wk-old rats were labeled by injecting [35S]methionine into the spinal cord 2 wk after motor axons were injured (axotomized) by crushing the sciatic nerve. Immunoprecipitation with mAbs which recognize either class II or III beta-tubulin were used to analyze the distributions of radioactivity in these isotypes in intact and axotomized motor fibers 5 d after labeling. We found that both isotypes were associated with the slow component wave, and that the leading edge of this wave was enriched in the class III isotype. Axotomy resulted in significant increases in the labeling and transport rates of both isotypes. Immunohistochemical examination of peripheral nerve fibers demonstrated that nearly all of the class II and III beta-tubulin in nerve fibers is located within axons. Although the amounts of radioactivity per millimeter of nerve in class II and III beta-tubulin were significantly greater in axotomized than in control nerves (with increases of +160% and +58%, respectively), immunoassay revealed no differences in the amounts of these isotypes in axotomized and control motor fibers. We consider several explanations for this paradox; these include the possibility that the total tubulin content is relatively insensitive to changes in the amount of tubulin transported in the slow component wave because this wave represents the movement of only a small fraction of the tubulin in these motor fibers.

Neonatal sciatic nerve section results in thiamine monophosphate but not substance P or calcitonin gene-related peptide depletion from the terminal field in the dorsal horn of the rat: the role of collateral sprouting

The expression of substance P, calcitonin gene-related peptide (CGRP) and thiamine monophosphatase in the sciatic nerve terminal field of the lumbar dorsal horn of the rat was examined following neonatal sciatic nerve section and ligation. The total terminal field from L3 to L5 was mapped from semi-serial sections on the treated side and compared to equivalent maps on the contralateral intact side. To obtain a detailed time course of events, data were obtained 4, 7, 10, 15-20 and 40-60 days after sciatic nerve section. At 4-7 days thiamine monophosphate was depleted from the cut nerve terminals resulting in a gap in dorsal horn thiamine monophosphate stain similar to that seen after adult nerve section. In contrast, substance P and CGRP-containing terminals showed only a transient fall in expression in the first week following nerve section and then staining was no different from that seen on the control side. The depletion of peptides normally observed after adult nerve section did not occur. This phenomenon was only observed if the sciatic nerve was cut at birth. Nerve section at 10 days of age resulted in the same pattern of peptide depletion as is observed in the adult. A week after neonatal sciatic nerve section, thiamine monophosphate-containing nerve terminals from nearby intact nerves begin to sprout into the sciatic nerve territory in the dorsal horn. This, together with some recovery of thiamine monophosphate from the remaining sciatic terminals themselves, results in a slow filling in of the gap in the thiamine monophosphate stain. Resection of the cut sciatic nerve, together with adjacent intact nerves, re-establishes the depletion. Substance P and CGRP terminals from nearby intact nerves also sprout into the deafferented sciatic field and this can be demonstrated by the larger than normal area of depletion following section of these nerves when adult. Furthermore, resection of the neonatally cut sciatic nerve when adult also causes some depletion of substance P and CGRP within the sciatic field, indicating a degree of recovery or up-regulation of peptides in surviving cut afferents. However, even after resection of the cut sciatic nerve and nearby intact nerves, substance P and CGRP staining remained in the terminal region. We conclude that while central collateral sprouting does take place in both substance P and CGRP-containing afferents following peripheral nerve section, it cannot account for the lack of depletion of peptides observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Force-velocity shifts with repetitive isometric and isotonic contractions of canine gastrocnemius in situ

The force-velocity (F-V) relationships of canine gastrocnemius-plantaris muscles at optimal muscle length in situ were studied before and after 10 min of repetitive isometric or isotonic tetanic contractions induced by electrical stimulation of the sciatic nerve (200-ms trains, 50 impulses/s, 1 contraction/s). F-V relationships and maximal velocity of shortening (Vmax) were determined by curve fitting with the Hill equation. Mean Vmax before fatigue was 3.8 +/- 0.2 (SE) average fiber lengths/s; mean maximal isometric tension (Po) was 508 +/- 15 g/g. With a significant decrease of force development during isometric contractions (-27 +/- 4%, P < 0.01, n = 5), Vmax was unchanged. However, with repetitive isotonic contractions at a low load (P/Po = 0.25, n = 5), a significant decrease in Vmax was observed (-21 +/- 2%, P < 0.01), whereas Po was unchanged. Isotonic contractions at an intermediate load (P/Po = 0.5, n = 4) resulted in significant decreases in both Vmax (-26 +/- 6%, P < 0.05) and Po (-12 +/- 2%, P < 0.01). These results show that repeated contractions of canine skeletal muscle produce specific changes in the F-V relationship that are dependent on the type of contractions being performed and indicate that decreases in other contractile properties, such as velocity development and shortening, can occur independently of changes in isometric tension.

The formation of a 'pseudo-nerve' in silicone chambers in the absence of regenerating axons

The formation of a regenerate between sciatic nerve segments or stumps inserted into Y-tunnelled silicone chambers was studied under conditions where regenerating axons were prevented from entering the chamber. This was accomplished by using an isolated segment of the nerve as a proximal insert. After one week, a cellular regenerate spanned the proximal and distal inserts. The size of the regenerate increased if circulation was preserved in the distal inserts. At four weeks, a perineurium-like sheath surrounded the regenerate and longitudinally oriented Schwann cell columns could be observed throughout the regenerate. A similar 'pseudo-nerve' formed towards a piece of distally inserted tendon. Thus, the information required for the formation of a nerve-like structure is inherent to the non-neuronal cells entering the chamber. Schwann cells, in contrast to regenerating axons, do not exhibit preferential growth towards nervous tissue.

Collateral reinnervation and expansive regenerative reinnervation by sensory axons into "foreign" denervated skin: an immunohistochemical study in the rat

Immunohistochemistry has been used to study, the capacity of different types of sensory axons in the saphenous nerve to extend into denervated glabrous skin territory after a chronic sciatic nerve lesion. In this study, the extension of the intact or regenerating thin peptidergic and coarse saphenous nerve fibres in adult and neonatal rats was determined. Substance P (SP) and calcitonin gene-related peptide (CGRP) antibodies were used as markers for thin axons and neurofilament (NF) antibodies for coarse axons. In addition, S-100 protein (S-100) antibodies, which primarily stain Schwann cells associated with myelinated axons, as well as innervated lamellated cells of Meissner corpuscles, were used. After a chronic sciatic nerve lesion in adult rats, thin dermal and epidermal SP-immunoreactive (IR) and CGRP-IR saphenous nerve fibres were present in an area lateral to that normally innervated by the saphenous nerve in the foot sole. In neonatally lesioned animals, thin dermal and epidermal SP-IR and CGRP-IR, as well as coarse dermal NF-IR fibres and S-100-IR cells, all of which derived from the saphenous nerve, were found in the sciatic nerve territory. In addition, some dermal SP-IR and CGRP-IR fibres were transiently present in the lateral part of the foot sole. After chronic sciatic nerve lesion and a concomitant crush injury of the saphenous nerve in adults or neonatals, thin dermal and epidermal SP-IR and CGRP-IR fibres, as well as coarse dermal NF-IR fibres and S-100-IR cells, were found in the innervation area normally occupied by the sciatic nerve. After a sciatic nerve cut and a concomitant crush injury of the saphenous nerve in adult rats, the SP-IR and CGRP-IR fibres, as well as the NF-IR fibres and S-100-IR cells were restricted to the medial part of this area. After a sciatic nerve cut and a concomitant crush injury of the saphenous nerve in neonatal rats, a few thin dermal SP-IR and CGRP-IR fibres were found in the lateral part of the foot sole as well. The findings of the present study together with those of previous morphological studies indicate that intact thin axons from the saphenous nerve, including those exhibiting peptide immunoreactivity, but not coarse saphenous axons, are capable of extending into "foreign" denervated glabrous skin after chronic sciatic nerve injuries. In neonatally sciatic-nerve-injured animals, both groups of axons spread from the intact saphenous nerve into the sciatic nerve territory.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of selective neurotoxic lesion of lumbosacral serotonergic and noradrenergic systems on autotomy behaviour in rats

Male rats underwent unilateral ligation and transection of the sciatic and saphenous nerves 2, 7 or 14 days after being injected intrathecally (at the thoracolumbar junction) with 6-hydroxydopamine (6-OHDA), 5,6-dihydroxytryptamine (5,6-DHT) or vehicle, and the development of autotomy was monitored. The effects of both neurotoxins on cervicothoracic (C5-T1) and lumbosacral (L1-S1) norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) spinal cord levels were analysed by HPLC in separate groups of rats. 6-OHDA treatment (20 micrograms/10 microliters) produced a rapid (from day 2) and significant (90-95%) fall in NE content only at L1-S1. 5,6-DHT administration (20 micrograms/10 microliters) produced a gradual (68%, 90% and 94%, at 2, 7 and 14 days, respectively) and selective depletion of 5-HT only at L1-S1. DA levels remained essentially unchanged after both neurotoxins. No differences in monoamine levels were detected among groups injected with vehicle. The main effects of neurotoxins on autotomy were: (1) a significant delay in the onset of autotomy in the rats injected with 6-OHDA 2 days before neurectomy; (2) a trend to autotomize earlier and more severely in the rats injected with 5,6-DHT 7 days before neurectomy and (3) an almost complete suppression of autotomy in the rats injected with 5,6-DHT 14 days before neurectomy. These results revealed that the expression of autotomy in rats can be modulated by interfering with spinal cord serotonergic activity and suggest new possible avenues for the treatment of certain specific pain diseases, such a phantom limb pain, by using selective agents capable of activating or blocking spinal cord serotonergic receptor subtypes.

Further evidence for myelinated as well as unmyelinated fibre damage in a rat model of neuropathic pain

A mononeuropathy, produced by ligation of the sciatic nerve in rats, has recently been proposed as an animal model of experimental pain and pain-related disorders (hyperalgesia and allodynia). We investigated quantitatively the morphological changes in myelinated and unmyelinated fibres of the sciatic nerves 2 weeks after ligation in rats exhibiting allodynia to thermal stimulation. There was a marked reduction in the number of large myelinated fibres distal to the ligature (711 +/- 34 compared with 5315 +/- 230 in normal nerves). We also found a significant loss of small myelinated fibres (2429 +/- 109 compared with 3197 +/- 308 in normal nerves), the remaining fibres of this type showing pathological properties. Finally, ultrastructural evidence of damage to unmyelinated fibres was found. The typical pattern of large clusters of normal unmyelinated axons was no longer present within most regions of the nerve. There was a significant reduction in the size of the unmyelinated fibres (0.41 micron +/- 0.15 compared with 0.71 micron +/- 0.08 in normal nerves), together with a twofold increase in their number per cluster. Hypotheses about the mechanism of thermal allodynia in this pain model therefore must take into account the fact that all fibre classes show pathological changes.

Regulation of opioid binding sites in the superficial dorsal horn of the rat spinal cord following loose ligation of the sciatic nerve: comparison with sciatic nerve section and lumbar dorsal rhizotomy

The aim of the present study was to quantify time-related modifications in mu and delta opioid binding sites in the superficial layers (laminae I and II) of the L4 lumbar segment in a rat model of mononeuropathy induced by loose ligation of the sciatic nerve. We have shown a 28% (P < 0.01) and 24% (P < 0.01) decrease in ipsi/contralateral side binding ratios for tritiated (Tyr*-D-Ala-Gly-NMe-Phe-Gly-ol) ([3H]DAMGO) and tritiated (Tyr*-D-Thr-Gly-Phe-Leu-Thr) ([3H]DTLET) respectively, at two weeks postlesion which correspond to the delay of maximal hyperalgesia and of maximal alteration of fine diameter primary afferent fibers. In contrast, no change in [3H]U.69593 specific binding could be detected at this postlesion delay. For longer survival delays (four, eight and 15 weeks postlesion), mu and delta binding ratios return towards control values (approximately equal to 1), probably reflecting the occurrence of a long-term neuroplasticity (i.e. a new equilibrium in the metabolism of primary neurons, or collateral sprouting from intact primary afferents) following loose nerve ligation. In addition, a comparison of the results obtained in this model with those measured after sciatic nerve section and lumbar dorsal rhizotomy was performed in order to compare the degree of loss in opioid binding sites in these three types of lesion. The section of the sciatic nerve induced at eight days postlesion an 18% (P < 0.01) and 28% (P < 0.01) decrease in binding ratio for [3H]DAMGO and [3H]DTLET, respectively. At two weeks postlesion the loss was 24% (P < 0.01) for the two ligands, and at longer delays (four and 12 weeks), a progressive recovery in binding ratio was observed. Thus, it appears that both sciatic nerve lesions we have studied result in mu and delta binding modifications which have similar intensity and similar time course from two to 12-15 weeks postlesion. In contrast, the unilateral rhizotomy of nine consecutive dorsal roots (T13-S2), which is known to induce a massive degeneration of fine diameter primary afferent fibers, is followed by a dramatic decrease in binding ratios for [3H]DAMGO (53%, P < 0.001) and [3H]DTLET (45%, P < 0.001) at two weeks postlesion. These data suggest that the more deprived the dorsal horn is of fine diameter primary afferent fibers, the more dramatic is the opioid binding loss in the ipsilateral side as compared to the contralateral side.(ABSTRACT TRUNCATED AT 400 WORDS)

Muscarinic cholinergic receptor binding in rat hindlimb somatosensory cortex following partial deafferentation by sciatic nerve transection

Peripheral nerve injury or amputation leads to extensive changes within the central representations of the mammalian body surface. The mechanisms responsible for post-traumatic reorganization of these maps in adults may also, at least partly, underlie a more general feature of the somatosensory system--the capacity for stimulus-dependent plasticity. Acetylcholine has been implicated in both of these processes. We studied the binding of the ligands [3H]QNB and [3H]pirenzepine in rat hindlimb somatosensory cortex from 1 to 14 days following sciatic nerve transection. Although the [3H]QNB binding was not different from normal levels in tissue homogenates of the affected somatosensory cortex, differences were demonstrated when binding was measured on a layer-by-layer basis. [3H]QNB binding was changed only in certain layers, at certain times. The predominant effects appeared to be a decrease in binding in the middle layers from 4 to 14 days after the transection. Combining the [3H]QNB data with data obtained from the more M1-selective ligand [3H]pirenzepine suggested that complex changes occur among several muscarinic receptors, including receptors with non-M1 subtype characteristics. Moreover, unilateral nerve transection affects the hindlimb somatosensory regions in both hemispheres.

Traumatic degeneration of transected myelinated fibers of the mouse sciatic nerve

Traumatic degeneration of myelinated fibers was studied by electron microscopy over 5 days following transection of mouse sciatic nerve. Special attention was paid to the mechanism which separates the degenerating part, while preserving the viable part of the axon. Immediately after transection, the opened end of the proximal stump revealed extensive subcellular changes including the disorganization of neurofilaments, and disruption of mitochondria and axonal endoplasmic reticulum (SER). Subsequently, vesicles of round and tubular profiles filled up the whole area of the stump end, and proximal to it appeared a neurofilament-predominant area characterized by randomly oriented neurofilaments and normally appearing mitochondria and SER. Characteristic membranous demarcations occurred in early periods at the border between the vesicle accumulation and the neurofilament-predominant areas, and later also within these areas. The demarcation membranes formed both by invagination of the surface plasma membrane and, probably, by fusion of the large vesicles. These became prominent with time, dividing the axoplasm into compartments of varying sizes, which gradually underwent degeneration and were liberated from the parent axon. Occurrence of autophagic vacuoles was characteristic of the degenerating portions of the parent axon. Thus, by the function of demarcation membranes, the parent axon to be preserved could remain membrane-bound, while the degenerating parts were shed off.

Prilocaine in lumbosacral plexus block--general efficacy and comparison of nerve stimulation amplitude

The significance of the threshold amperage of peripheral nerve stimulation (PNS) for the efficacy and latency of sciatic block is shown in a controlled randomized study of stimulation amplitude. In all cases the block was complete within a short time when the threshold amperage was 0.3 mA or less. Incomplete motor and sensory blocks occurred with higher stimulation amplitudes of 0.5 and 1.0 mA. In view of these results a prospective study of the clinical efficacy of 852 combined sciatic/3-in-1 blocks using prilocaine, and performed by means of peripheral nerve stimulation was carried out. No CNS or cardiovascular complications, no problems resulting from methaemoglobinaemia and, above all, no nervous lesions were observed. The limiting factor for surgery of the lower limb with this method of anaesthesia is the tolerance of the femoral tourniquet which depends mainly on the efficacy of the 3-in-1 block. Ninety-one per cent of the combined blockades were primarily successful when there was no tourniquet at all, and 87% when the tourniquet was placed on the lower leg. In the course of surgery with a femoral pneumatic tourniquet, only 55% of the blocks did not require supplement when 20 ml of 1% prilocaine was used for the 3-in-1 block, while 72% and 74% were efficacious with 30 ml and 35 ml, respectively. The efficacy of the sciatic block proved to be extremely high (> 95%), its success depending on the dosage of the local anaesthetic and correct execution of the peripheral nerve stimulation.

Is early vascularization of nerve grafts necessary?

Revascularization and regeneration through vascularized and non-vascularized nerve grafts were compared on optimal and adverse graft beds in 76 rabbit sciatic nerves. A delay in revascularization of more than 14 days was found to occur in 30 mm long, non-vascularized nerve grafts placed on completely avascular graft graft beds. However, over a period of 44 weeks, this prolonged ischaemia did not adversely affect nerve regeneration. The vascularized nerve grafts did not differ significantly with respect to the rate of regeneration, motor conduction velocity, fibre diameter and thickness of myelin sheath. In rabbits, the provision of early vascularity does not appear to confer superior regeneration through nerve grafts. The clinical use of vascularized nerve grafts is discussed in the light of these results.

[Changes due to age in the regenerating axons of the adult rat]

Muscle reinnervation after nerve crush was observed in rats at different ages with a combined technique that simultaneously demonstrates nerve endings and endplates. At early times of reinnervation the amount of sprouting was higher in older rats than in younger rats; according to this finding an enhanced number of polyinnervated endplates was found in older rats. A similar enhancement of sprouting and polyinnervation was observed during muscle reinnervation of vitamin E deficient rats, supporting the proposed analogy between vitamin E deficiency and aging.

Observations on the development of transplanted embryonic ventral horn neurones grafted into adult rat spinal cord and connected to skeletal muscle implants via a peripheral nerve

Embryonic spinal cord grafts from 12-day-old rat embryos were placed into the lumbar spinal cord of adult rats depleted of sciatic motoneurones by a neonatal nerve injury. A soleus muscle was removed from the leg and implanted paravertebrally, the proximal end of its nerve connected to the graft site. Fluorescent retrograde tracers injected into the soleus implant, 37-64 days postoperatively, labelled neurones that had grown axons to the muscle. Approximately one-fifth of retrogradely labelled neurons were within the graft; however, the majority were found within the host spinal cord close to the graft. These included large neurons within the motoneurone-depleted dorsolateral ventral horn. In control experiments a muscle and nerve were implanted but no embryonic tissue grafted. Significantly fewer neurones were labelled. In some animals, one tracer was injected into the soleus muscle whilst another was applied to the cut sciatic nerve ipsilateral to the graft site. No neurones were found to project axons to both targets. In animals that received grafts prelabelled with bromodeoxyuridine (BrDU) some neurones were found to be both BrDU positive and retrogradely labelled from the soleus implant. These were most frequently within the motoneuron-depleted ventral horn ipsilateral to the graft. Thus, grafted neurones may migrate to an appropriate location within the host neuropil. Acetylcholinesterase (AChE) histochemistry showed the graft site contained immature but AChE-positive neurones. Some regions of host ventral horn contained unusually few AChE-positive nerve fibres and occasional large AChE-positive neurones, some of which were also retrogradely labelled from the implanted muscle. Studies of implanted soleus 21-90 days after transplantation showed that muscle fibres, after initial degeneration, regenerated displaying differing phenotypes, presumably under the influence of new motor innervation.

Low-threshold, short-latency cutaneous reflexes during fictive locomotion in the "semi-chronic" spinal cat

Low-threshold, short-latency cutaneous reflexes evoked in ipsilateral hindlimb motor nerves were examined during fictive locomotion. Locomotion in 11 anaemically decerebrated spinal animals (1-3 weeks after transection at T13-L1) was induced by administration of clonidine, L-dopa and nialamide; by administration of the latter two drugs only; or by exteroceptive stimulation in the absence of any drugs. The caudal and lateral cutaneous sural, caudal cutaneous femoral, saphenous and superficial peroneal nerves were stimulated at low threshold (1.5-3 T). Pooled results from all combinations of cutaneous nerves stimulated and muscle nerves recorded show that the initial response was excitatory in 40 of 50 triceps surae and 17 of 20 semitendinosus (St) electroneurograms (ENGs). These excitatory responses occurred at latencies that ranged from 5 to 15 ms and tended to be maximal during the motor nerve's active period in the step cycle (i.e. they were modulated in a phase-dependent manner). Only three inhibitory responses (9-12 ms earliest latency) were encountered in total: in two St ENGs of one animal and in one lateral gastrocnemius-soleus ENG of a different animal. In two animals a "second" excitatory response (15-25 ms latency) was sometimes recorded in triceps surae and St nerves and, interestingly, could be modulated out of phase with the early response. Weak short-latency excitatory reflexes were also found in contralateral St ENGs when examined. Finally, among medial gastrocnemius, lateral gastrocnemius and soleus nerves, excitatory responses due to stimulation of any particular cutaneous nerve tended to be modulated similarly but were of consistently different amplitude among the three. This finding, together with the general observation that excitatory reflexes produced by stimulation of a particular cutaneous nerve were modulated similarly in extensors (or flexors) of different animals, suggests that spinal circuits generating locomotion may indeed exert a stereotypic control over interneurons in specific cutaneous reflex pathways to motoneurons. The results are primarily discussed in terms of the existing evidence for short-latency excitatory cutaneous reflexes in extensors in a variety of locomotive and non-locomotive preparations.

Enhanced synthesis of brain-derived neurotrophic factor in the lesioned peripheral nerve: different mechanisms are responsible for the regulation of BDNF and NGF mRNA

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are molecules which regulate the development and maintenance of specific functions in different populations of peripheral and central neurons, amongst them sensory neurons of neural crest and placode origin. Under physiological conditions NGF is synthesized by peripheral target tissues, whereas BDNF synthesis is highest in the CNS. This situation changes dramatically after lesion of peripheral nerves. As previously shown, there is a marked rapid increase in NGF mRNA in the nonneuronal cells of the damaged nerve. The prolonged elevation of NGF mRNA levels is related to the immigration of activated macrophages, interleukin-1 being the most essential mediator of this effect. Here we show that transsection of the rat sciatic nerve also leads to a very marked increase in BDNF mRNA, the final levels being even ten times higher than those of NGF mRNA. However, the time-course and spatial pattern of BDNF mRNA expression are distinctly different. There is a continuous slow increase of BDNF mRNA starting after day 3 post-lesion and reaching maximal levels 3-4 wk later. These distinct differences suggest different mechanisms of regulation of NGF and BDNF synthesis in non-neuronal cells of the nerve. This was substantiated by the demonstration of differential regulation of these mRNAs in organ culture of rat sciatic nerve and Schwann cell culture. Furthermore, using bioassays and specific antibodies we showed that cultured Schwann cells are a rich source of BDNF- and ciliary neurotrophic factor (CNTF)-like neurotrophic activity in addition to NGF. Antisera raised against a BDNF-peptide demonstrated BDNF-immunoreactivity in pure cultured Schwann cells, but not in fibroblasts derived from sciatic nerve.