Reinnervation of the rat musculocutaneous nerve stump after its direct reconnection with the C5 spinal cord segment by the nerve graft following avulsion of the ventral spinal roots: a comparison of intrathecal administration of brain-derived neurotrophic factor and Cerebrolysin

Experimental model based on the C5 ventral root avulsion was used to evaluate the efficacy of brain-derived neurotrophic factor (BDNF) and Cerebrolysin treatment on motor neuron maintenance and survival resulted in the functional reinnervation of the nerve stump. In contrast to vehicle, BDNF treatment reduced the loss and atrophy of motor neurons and enhanced the regrowth axon sprouts into the distal stump of musculocutaneous nerve. However, the axon diameter of the myelinated fibers was smaller than those of control rats. The morphometric results were related to a low score in behavioral test similar to vehicle-treated rats. Cerebrolysin treatment greatly protected the motor neurons against cell death. Moreover, morphometric features of myelinated axons were better than those of rats treated with vehicle or BDNF. The mean score of grooming test suggested better results of the functional motor reinnervation than after BDNF administration. The majority of rescued motor neurons regenerating their axons through nerve graft in both BDNF- and Cerebrolysin-treated rats expressed choline acetyltransferase immunostaining. The results demonstrate that BDNF has more modest effects in preventing the death of motor neurons and functional recovery of injured motor nerve after root avulsion than Cerebrolysin.

Convergence of nociceptive information from temporomandibular joint and tooth pulp afferents on C1 spinal neurons in the rat

The aim of the present study was to test the hypothesis that there is a convergence of afferent inputs from the temporomandibular joint (TMJ) on C1 spinal neurons responding to electrical stimulation of the tooth pulp (TP). In 14 pentobarbital anesthetized rats, the extracellular single unit activity of 31 C1 spinal neurons and the amplitude in a digastric muscle electromyogram (n = 31) increased proportionally during 1.0-3.5 times the threshold for the jaw-opening reflex (JOR). Of 31 C1 spinal neurons responsive to TP afferents, 28 (approximately 90%) were also excited by electrical stimulation of the ipsilateral TMJ capsule. All neurons tested were divided into three categories of nociceptive specific, wide dynamic range and non-responsive as to their responsiveness to mechanical stimuli (pin prick and touch) of the somatic receptive field (skin of the face, neck, jaw and upper forearm) and TMJ capsule. Nineteen (68%) of 28 C1 spinal neurons received nociceptive information from C fibers of the TMJ capsule. These results suggest that there is a convergence of noxious information from the TMJ and TP afferents on the same C1 spinal neurons, which importantly contribute to pain perception from the TMJ region.

Effects of spinal and peripheral nerve lesions on the intersegmental synchronization of the spontaneous activity of dorsal horn neurons in the cat lumbosacral spinal cord

In the anesthetized and paralyzed cat, spontaneous negative cord dorsum potentials (nCDPs) appeared synchronously in the L3 to S1 segments, both ipsi- and contralaterally. The acute section of both the intact sural and the superficial peroneal nerve increased the variability of the spontaneous nCDPs without affecting their intersegmental coupling. On the other hand, the synchronization between the spontaneous nCDPs recorded in segments L5-L6 was strongly reduced following an interposed lesion of the left (ipsilateral) dorsolateral spinal quadrant and it was almost completely abolished by an additional lesion of the contralateral dorsolateral quadrant at the same level. Our observations support the existence of a system of spontaneously active dorsal horn neurons that is bilaterally distributed along the lumbosacral segments and affects, in a synchronized and organized manner, impulse transmission along many reflex pathways, including those mediating presynaptic inhibition.

A Direct Comparison of Whole Cell Patch and Sharp Electrodes by Simultaneous Recording From Single Spinal Neurons in Frog Tadpoles

High-impedance, sharp intracellular electrodes were compared with whole cell patch electrodes by recording from single spinal neurons in immobilized frog tadpoles. A range of neuron properties were examined using sharp or patch test electrodes while making simultaneous recordings with a second control patch electrode. Overall, test patch electrodes did not significantly alter the activity recorded by the control electrode, and recordings from the two electrodes were essentially identical. In contrast, sharp electrode recordings differed from initial control patch recordings. In some cases, differences were due to real changes in neuron properties: the resting membrane potential became less negative and the neuron input resistance ( Ri) fell; this fall was larger for neurons with a higher Ri. In other cases, the control patch electrode revealed that differences were due to the recording properties of the sharp electrode: tip potentials were larger and more variable; resting potentials appeared to be more negative; and spike amplitude was attenuated. However, sharp electrode penetration did not, in most cases, significantly alter the pattern of neuron firing in response to injected current or the normal pattern of activity following sensory stimulation or during fictive swimming. We conclude that sharp electrodes introduce a significant leak to the membrane of tadpole spinal neurons compared with patch electrodes but that this does not change the fundamental firing characteristics or activity of the neurons.

Membrane-associated prostaglandin E synthase-1 is required for neuropathic pain

It is widely accepted that prostaglandin (PG) E2 is the principal pro-inflammatory prostanoid and plays an important role in inflammatory pain. However whether PGE2 is involved in neuropathic pain remains unknown. PGE2 is produced from arachidonic acid via PGH2 by at least three PGE synthases (PGES), cytosolic PGES (cPGES), and membrane-associated PGES (mPGES)-1 and -2. In the present study, to clarify the involvement of PGE2 and identify PGES mediating neuropathic pain, we applied a neuropathic pain model prepared by L5 spinal nerve transection to mPGES-1 knockout (mPGES-1-/-) mice. Whereas they retained normal nociceptive responses, mPGES-1-/- mice did not exhibit mechanical allodynia and thermal hyperalgesia over a week. These results demonstrate that PGE2 produced by mPGES-1 is involved in neuropathic pain.

Peri-sciatic administration of indomethacin early after nerve injury can attenuate the development of tactile allodynia in a rat model of L5 single spinal nerve injury

To clarify the role of cyclooxygenase in the peripheral nerve on the development of neuropathic pain, we investigated the effects of peri-sciatic administration of indomethacin on the development of allodynia in a model of L5 single spinal nerve injury. Peri-sciatic administration of indomethacin (1 mg/kg) was performed 3, 24, or 72 h after nerve injury (n=6/each). In rats with indomethacin 3 or 24 h after nerve injury, ipsi-lateral paw withdrawal thresholds 7-35 days after nerve injury were significantly higher compared with those in the control group (n=6: without peri-sciatic treatment) (P<0.05). However, such efficacy was no longer apparent when indomethacin was administered 72 h after nerve injury. These results suggest that peri-sciatic administration of indomethacin early (less than 24 h) after nerve injury can attenuate the development of allodynia.

[New monitoring method for the pudental nerve during surgery: cases of intraoperative monitoring for lumbo-sacral lipomeningocele]

We carried out intraoperative monitoring of the pudental nerve while separating vertebral spinal tumors from the spinal cord in five patients, including four infants. Although monitoring using a manometer or needle electrodes has been reported, monitoring done with disk electrodes to ascertain the compound muscle action potential (CMAP) of the external sphincter muscle has not been yet attempted. Prior to the surgical procedure, we locate a point suitable for CAMP recording of the muscle. In our recent study, we determined that maximum action potentials were recorded in the part with the greatest depth from the individual anal verge. Therefore, the depth of the anal canal was preoperatively measured for the manometry method, and sphincter electrodes currently on the market were refigured to suit the infant's anal canal. After the two procedures described above, we were able to preserve the pudental nerves intraoperatively. The postoperative neurological findings of all five patients were unchanged. We introduce here this new method of intraoperative monitoring for preserving the pudental nerve.

Plasticity of spinal nicotinic acetylcholine receptors following spinal nerve ligation

The nicotinic cholinergic system is known to be important in the processing of nociceptive information. In the spinal cord, nicotinic receptors are expressed on primary afferent terminals, inhibitory interneurons and descending noradrenergic and serotoninergic fibers. Following peripheral nerve injury, the expression of numerous receptors involved in nociceptive processing is altered in the superficial dorsal horn of the spinal cord. However, the expression of nicotinic acetylcholine receptor subunits in the lumbar spinal cord following peripheral nerve injury has not been investigated. We examined the expression of the alpha3, alpha4, alpha5, alpha7, beta2, beta3 and beta4 nicotinic subunits in the spinal cord of normal and spinal nerve ligated rats using immunocytochemistry. Two nicotinic subunits were found to have an increased expression following spinal nerve ligation. The number of cells expressing the alpha3 subunit in the dorsal horn increased bilaterally following spinal nerve injury. Also, the number of alpha5 immunoreactive fibers increased significantly ipsilateral to ligation. The expression of the alpha4, alpha7, beta2, beta3 and beta4 subunits was unchanged. We propose that the increased expression of the alpha3 and alpha5 nicotinic subunits may contribute to the mechanical hypersensitivity observed following spinal nerve ligation.

Developmental-dependent action of microtubule depolymerization on the function and structure of synaptic glycine receptor clusters in spinal neurons

Microtubules have been proposed to interact with gephyrin/glycine receptors (GlyRs) in synaptic aggregates. However, the consequence of microtubule disruption on the structure of postsynaptic GlyR/gephyrin clusters is controversial and possible alterations in function are largely unknown. In this study, we have examined the physiological and morphological properties of GlyR/gephyrin clusters after colchicine treatment in cultured spinal neurons during development. In immature neurons (5-7 DIV), disruption of microtubules resulted in a 33 +/- 4% decrease in the peak amplitude and a 72 +/- 15% reduction in the frequency of spontaneous glycinergic miniature postsynaptic currents (mIPSCs) recorded in whole cell mode. However, similar colchicine treatments resulted in smaller effects on 10-12 DIV neurons and no effect on mature neurons (15-17 DIV). The decrease in glycinergic mIPSC amplitude and frequency reflects postsynaptic actions of colchicine, since postsynaptic stabilization of microtubules with GTP prevented both actions and similar reductions in mIPSC frequency were obtained by modifying the Cl(-) driving force to obtain parallel reductions in mIPSC amplitude. Confocal microscopy revealed that colchicine reduced the average length and immunofluorescence intensity of synaptic gephyrin/GlyR clusters in immature (approximately 30%) and intermediate (approximately 15%) neurons, but not in mature clusters. Thus the structural and functional changes of postsynaptic gephyrin/GlyR clusters after colchicine treatment were tightly correlated. Finally, RT-PCR, kinetic analysis and picrotoxin blockade of glycinergic mIPSCs indicated a reorganization of the postsynaptic region from containing both alpha2beta and alpha1beta GlyRs in immature neurons to only alpha1beta GlyRs in mature neurons. Microtubule disruption preferentially affected postsynaptic sites containing alpha2beta-containing synaptic receptors.

Defining eupnea

To describe a pattern of rhythmic activity as "breathing" or "respiration" inevitably leads to the conclusion that this rhythmic activity is "normal" or "eupneic". Initially, it must be noted that, by strictest definition, "eupnea" can only be applied to "breathing" in an unanesthetized preparation. Any experimental perturbation, including anesthesia, changes eupnea, primarily by reducing the frequency of "breathing". However, a "eupneic pattern", in terms of the pattern of airflow of individual breaths, remains. Also remaining are patterns of neural and neuronal activities which are characteristic of individual breaths of eupnea. In this commentary, we consider these patterns of activities, which define a eupneic pattern and contrast these with patterns during apneusis and gasping. It has long been recognized that these three different patterns of "respiratory activity", eupnea, apneusis and gasping, can be generated in preparations in which all of the central nervous system has been removed, exclusive of the brainstem and spinal cord.

Cholecystokinin fails to block the spinal inhibitory effects of nociceptin in sham operated and neuropathic rats

Cholecystokinin (CCK) has a number of roles in the central nervous system and can reduce the analgesic effect of activation of mu (micro), delta (delta) and kappa (kappa) opioid receptors. CCK has been proposed to be a major reason for reduced effects of morphine after nerve injury. This study examines if CCK modulates the effect of the Opioid Receptor Like-1 (ORL1) agonist, nociceptin on dorsal horn neurone activity in vivo in the spinal nerve ligation model of neuropathic pain compared with sham-operated and naive rats. In naive and neuropathic rats nociceptin alone inhibited the C-fibre evoked response, post-discharge, wind-up and input, while in sham operated rats nociceptin did not cause any inhibition but by contrast caused a facilitation of post-discharge and wind-up. CCK alone had no significant effect, although did cause slight facilitation in the three groups. In the presence of CCK the inhibitory effect of nocieceptin was blocked in naive animals, but in contrast the inhibitory effect of nociceptin was enhanced by CCK in sham and neuropathic rats. These results emphasize the differences between ORL1 and other opioid receptors. This loss of the inhibitory effect of CCK on nociceptin after nerve injury may be of clinical interest in the treatment of neuropathic pain.

Ontogeny of central CO2 chemoreception: chemosensitivity in the ventral medulla of developing bullfrogs

Sites of central CO2 chemosensitivity were investigated in isolated brain stems from Rana catesbeiana tadpoles and frogs. Respiratory neurograms were made from cranial nerve (CN) 7 and spinal nerve 2. Superfusion of the brain stem with hypercapnic artificial cerebrospinal fluid elicited increased fictive lung ventilation. The effect of focal perfusion of hypercapnic artificial cerebrospinal fluid on discrete areas of the ventral medulla was assessed. Sites of chemosensitivity, which are active continuously throughout development, were identified adjacent to CN 5 and CN 10 on the ventral surface of the medulla. In early- and middle-stage tadpoles and frogs, unilateral stimulation within either site was sufficient to elicit the hypercapnic response, but simultaneous stimulation within both sites was required in late-stage tadpoles. The chemosensitive sites were individually disrupted by unilateral application of 1 mg/ml protease, and the sensitivity to bath application or focal perfusion of hypercapnia was reassessed. Protease lesions at CN 10 abolished the entire hypercapnic response, but lesions at CN 5 affected only the hypercapnic response originating from the CN 5 site. Neurons within the chemosensitive sites were also destroyed by unilateral application of 1 mM kainic acid, and the sensitivity to bath or focal application of hypercapnia was reassessed. Kainic acid lesions within either site abolished the hypercapnic response. Using a vital dye, we determined that kainic acid destroyed neurons by only within 100 microm of the ventral medullary surface. Thus, regardless of developmental stage, neurons necessary for CO2 sensitivity are located in the ventral medulla adjacent to CN 5 and 10.

Oral administration of B vitamins increases the antiallodynic effect of gabapentin in the rat

The purpose of this study was to assess the possible synergistic interaction between gabapentin and B-vitamins (100:100:1 of vitamin B1, B6 and B12, respectively) in a neuropathic pain model in the rat. Neuropathic pain was induced by ligation of the left L5 and L6 spinal nerves of female Wistar rats. Tactile allodynia was determined by measuring paw withdrawal in response to probing with a series of calibrated von Frey filaments. Gabapentin (30-300 mg/kg), B-vitamins (75-600 mg/kg), or a combination of gabapentin and B-vitamins were administered orally and the antiallodynic effect was determined. Isobolographic analyses were used to define the nature of the functional interactions between gabapentin and B-vitamins in a fixed-dose ratio (0.5:0.5). Gabapentin (ED30 23.0+/-5.3 mg/kg), B-vitamins (ED30 524.0+/-97.0 mg/kg), or a fixed-dose ratio combination of gabapentin-B vitamins combinations dose-dependently reduced tactile allodynia. The theoretical ED30 value for the combination estimated from the isobologram was 273.5+/-48.6 mg/kg. This value was significantly higher than the experimental ED30 value which was 18.7+/-1.7 mg/kg. Results indicate that systemic administration of gabapentin and B vitamins can interact synergistically to reduce neuropathic pain in the rat and suggest the use of this combination to relieve neuropathy in humans.

Antinociceptive synergy between dexamethasone and the B vitamin complex in a neuropathic pain model in the rat

The combination of dexamethasone and B-vitamins is widely used in Mexico to treat neuropathic pain in human beings. However, so far there is no evidence in preclinical models about the efficacy of this combination. The purpose of this study was to assess the possible synergistic interaction between dexamethasone and the B-vitamin complex in a neuropathic pain model in the rat. Neuropathic pain was induced by ligation of the left L5 and L6 spinal nerves in female Wistar rats. Tactile allodynia was determined by measuring paw withdrawal in response to probing with a series of calibrated von Frey filaments. Dexamethasone (4-32 mg/kg), B-vitamins (75-600 mg/kg), or a combination of dexamethasone and B-vitamins (100:100:1 of vitamin B1, B6 and B12, respectively) was administered subcutaneously and the antiallodynic effect was determined. Isobolographic analyses were used to define the nature of the functional interactions between dexamethasone and B-vitamins (0.5:0.5). Dexamethasone (ED30 5.4+/-1.2 mg/kg), B-vitamins (ED30 181.1+/-2.6 mg/kg), and fixed-dose ratio dexamethasone-B-vitamins combinations dose-dependently reduced tactile allodynia in the rat. Theoretical ED30 value for the combination estimated from the isobologram was 128.2+/-5.8 mg/kg. This value was significantly higher than experimental ED30 value which was 21.8+/-2.3 mg/kg. Results indicate that subcutaneous administration of dexamethasone and B-vitamins interacted synergistically to reduce tactile allodynia in the rat and suggest the use of this combination to reduce neuropathic pain in humans.

Clinical examination versus routine and paraspinal electromyographic studies in predicting the site of lesion in brachial plexus injury

PURPOSE

To study the role of clinical examination, routine electromyography (EMG), and paraspinal EMG individually and in combination to predict the site of lesion in brachial plexus injury.

METHODS

Forty cases of brachial plexus injury were evaluated clinically. They then were subjected to routine and paraspinal EMG. All of them underwent surgical exploration and the intraoperative findings were correlated.

RESULTS

The combination of clinical examination, routine EMG, and paraspinal EMG was able to localize the site of the lesion in 80% of patients in both intra- and extraforaminal injury and in 67% in those with a combination type of lesion. The individual parameter predictability was less; paraspinal EMG had the highest individual predictability (67%).

CONCLUSIONS

EMG of the paraspinal muscles helps differentiate between root avulsion and distal rupture. It is useful in the planning for surgery, especially when the lesions are evaluated in combination with clinical examination and routine EMG.

Effect of diclofenac on the antiallodynic activity of vitamin B12 in a neuropathic pain model in the rat

B vitamins have been used as analgesic drugs to treat pain disorders associated with their deficiency. More recently it has been claimed that B vitamins are useful to relieve different pain states as carpal tunnel, migraine and premenstrual tension. In Latin America, B vitamins are commonly used to treat neuropathic pain; however, there is no data to support this indication. In the present work we assessed the possible analgesic activity of vitamin B12 alone and combined with diclofenac in a neuropathic pain model in the rat. Neuropathic pain was induced by ligation of the left L5 and L6 spinal nerves of female Wistar rats. Tactile allodynia was determined by measuring paw withdrawal in response to probing with a series of calibrated von Frey filaments. Vitamin B12 (0.75-6 mg/kg), but not diclofenac (1-10 mg/kg), reduced in a dose-dependent manner tactile allodynia induced by spinal nerve ligation. Diclofenac (3.2 mg/kg) was not able to further increase vitamin B12-induced antiallodynia. Results indicate that vitamin B12, but not diclofenac, produces antiallodynic effects in the rat and suggest that this vitamin could be a potential treatment for neuropathic pain in humans.

Rapid modulation of cortical proprioceptive activity induced by transient cutaneous deafferentation: neurophysiological evidence of short-term plasticity across different somatosensory modalities in humans

Single cell recording in non-human primates shows plastic changes of cortical somatic representations across different types of somatic inputs originating from the same peripheral territory. In humans, muscle afferents from first dorsal interosseus are supplied by the ulnar nerve while the cutaneous territory overlying this muscle is supplied by the radial nerve. This peculiar anatomical nervous distribution allowed us to devise an experimental model which provided a unique opportunity to assess, in humans with a non-invasive technique, the functional relationships between cutaneous and muscle afferent inputs originating from the same peripheral territory. We recorded spinal, brainstem and cortical somatosensory potentials evoked by stimulation of muscle afferents of the right first dorsal interosseus before, during and after anaesthetic block of the sensitive branch of the ipsilateral radial nerve. Amplitude of parietal N20 and P27 and frontal N30 somatosensory evoked potential components showed an increase of amplitudes with more profound anaesthesia. Amplitudes returned to pre-anaesthetic values several minutes after anaesthesia. By contrast, spinal N13 and brainstem P14 potentials did not change throughout the experiment. Results show, for the first time in humans, that a transient cutaneous deafferentation may induce rapid modulation of cortical activity evoked by stimulation of muscle afferents originating in the anaesthetic territory.

The effect of treatment with BRX-220, a co-inducer of heat shock proteins, on sensory fibers of the rat following peripheral nerve injury

In this study, we examined the effect BRX-220, a co-inducer of heat shock proteins, in injury-induced peripheral neuropathy. Following sciatic nerve injury in adult rats and treatment with BRX-220, the following features of the sensory system were studied: (a) expression of calcitonin gene-related peptide (CGRP); (b) binding of isolectin B4 (IB4) in dorsal root ganglia (DRG) and spinal cord; (c) stimulation-evoked release of substance P (SP) in an in vitro spinal cord preparation and (d) nociceptive responses of partially denervated rats. BRX-220 partially reverses axotomy-induced changes in the sensory system. In vehicle-treated rats there is a decrease in IB4 binding and CGRP expression in injured neurones, while in BRX-220-treated rats these markers were better preserved. Thus, 7.0 +/- 0.6% of injured DRG neurones bound IB4 in vehicle-treated rats compared to 14.4 +/- 0.9% in BRX-220-treated animals. Similarly, 4.5 +/- 0.5% of DRG neurones expressed CGRP in the vehicle-treated group, whereas 9.0 +/- 0.3% were positive in the BRX-220-treated group. BRX-220 also partially restored SP release from spinal cord sections to electrical stimulation of primary sensory neurones. Behavioural tests carried out on partially denervated animals showed that BRX-220 treatment did not prevent the emergence of mechanical or thermal hyperalgesia. However, oral treatment for 4 weeks lead to reduced pain-related behaviour suggesting either slowly developing analgesic actions or enhancement of recovery processes. Thus, the morphological improvement seen in sensory neurone markers was accompanied by restored functional activity. Therefore, treatment with BRX-220 promotes restoration of morphological and functional properties in the sensory system following peripheral nerve injury.

Decreased L5 spinal nerve ligation nociceptive behavior following L4 spinal nerve transection

This study used the escape/avoidance paradigm to explore the role of the L4 spinal nerve in L5 ligation nociception. Unlike L5-ligated controls, L5-ligated/L4-transected animals had normal mechanical withdrawal threshold and did not escape/avoid mechanical stimulation of the afflicted paw. The result from the escape/avoidance paradigm, which does not rely on a reflexive withdrawal response, directly supports the hypothesis that the L4 spinal nerve contributes to L5 ligation neuropathic pain.

Effect of electromyostimulation training on soleus and gastrocnemii H- and T-reflex properties

When muscle is artificially activated, as with electromyostimulation (EMS), action potentials are evoked in both intramuscular nerve branches and cutaneous receptors, therefore activating spinal motoneurons reflexively. Maximal soleus and gastrocnemii H- and T-reflex and the respective mechanical output were thus quantified to examine possible neural adaptations induced at the spinal level by EMS resistance training. Eight subjects completed 16 sessions of isometric EMS (75 Hz) over a 4-week period. Maximal soleus and gastrocnemii M wave (M(max)), H reflex (H(max)) and T reflex (T(max)) were compared between before and after training, together with the corresponding plantar flexor peak twitch torque. No significant changes were observed for electromechanical properties of H(max) reflex following EMS. On the other hand, peak twitch torque produced by T(max), but not by equal-amplitude H reflex, significantly increased as a result of training (+21%, P<0.05). These changes were associated with a trend towards a significant increase for normalized gastrocnemii (+21%, P=0.07) but not soleus T(max) reflex. It is concluded that, contrary to results previously obtained after voluntary physical training, EMS training of the plantar flexor muscles did not affect alpha motoneuron excitability and/or presynaptic inhibition, as indicated by H-reflex results. On the other hand, in the absence of change in a control group, T(max) electromechanical findings indicated that: (1). equal-amplitude H- and T-reflex adapted differently to EMS resistance training; and (2). EMS had an effect on gastrocnemii but not on soleus muscle, perhaps because of the differences in respective motor unit characteristics (e.g., axon diameter).

Afferent fibers of the pudendal nerve modulate sympathetic neurons controlling the bladder neck

AIMS

Pudendal nerve stimulation is known to have a potential modulative effect on bladder function. However, even if its efficiency has been established for various neurogenic and non-neurogenic bladder dysfunctions, the underlying neuronal mechanism, and the involved pathways in humans remain unknown. In this prospective study we focused on the effects of pudendal nerve stimulation in complete spinal cord injured patients to identify neuromodulative processes that occur on spinal level.

METHODS

Twenty complete spinal male presenting with upper motor neuron lesion and neurogenic incontinence underwent pudendal nerve stimulation. Bladder, bladder neck (BN), and external urethral sphincter (EUS) pressures were continuously recorded with a three channel microtip pressure transducer catheter. Fifty six pudendal stimulations using biphasic rectangular impulses (0.2 ms, 10 Hz) with intensities up to 100 mA were applied to the dorsal penile nerve. In six patients, 18 stimulations were repeated after intravenous (i.v.) administration of 7 mg phentolamine.

RESULTS

Mean BN and EUS pressure increased during stimulation significantly (P < 0.001). The latencies to the EUS responses range between 27 and 41 ms and those to the BN responses between 188 and 412 ms. Phentolamine decreased initial BN pressure and reduced the pressure rise during stimulation significantly (P < 0.05).

CONCLUSIONS

Pudendal nerve stimulation evoked somatic responses in the EUS and autonomic responses in the smooth muscle sphincter controlling the BN. Longer latencies of the BN responses and the sensitivity to the alpha-blocking agent phentolamine suggest that sympathetic alpha-adrenergic fibers are involved. Somatic afferent fibers of the pudendal nerve are supposed to project on sympathetic thoracolumbar neurons to the BN and modulate their function. This neuromodulative effect works exclusively at the spinal level and appears to be at least partly responsible for BN competence and at least continence.

Spinal neuronal responses to urinary bladder stimulation in rats with corticosterone or aldosterone onto the amygdala

Elevating glucocorticoids in the amygdala produces colorectal hypersensitivity through activation of lumbosacral spinal neurons. The aim of this study was to determine if descending modulation from the amygdala affects spinal processing of input from urinary bladder afferents. Fischer-344 rats received cholesterol (inactive control)-, corticosterone-, or aldosterone-containing micropellets placed stereotaxically on the dorsal margin of the left and right amygdala (n = 10 for each group). Seven days after amygdaloid implantation, extracellular potentials of single L6-S1 spinal neurons were examined for the responses to graded (0.5-2.0 ml, 20 s) urinary bladder distension (UBD). Spontaneous activity of neurons with excitatory responses to UBD in aldosterone-implanted rats [11.0 +/- 1.7 (SE) imp/s], but not in corticosterone-implanted rats, was higher than in the cholesterol-implanted group (6.6 +/- 1.1 imp/s, P < 0.05). Noxious UBD (1.5 ml) produced a greater excitatory response (21.6 +/- 2.6 imp/s) in aldosterone-implanted rats compared with cholesterol- or corticosterone-implanted rats (15.1 +/- 1.5 and 13.6 +/- 1.4 imp/s; P < 0.05). In contrast, the duration of excitatory responses to UBD in corticosterone-implanted rats (38.5 +/- 3.4 imp/s) was significantly longer than those in the aldosterone or control groups (26.8 +/- 1.8 and 24.7 +/- 1.5 imp/s). Neurons with low thresholds for excitatory responses to UBD were seen more frequently in aldosterone-implanted rats than in corticosterone or cholesterol treated rats (74 vs. 44% and 39%, P < 0.05). No difference in somatic field properties of spinal neurons responsive or nonresponsive to UBD was found among the three groups. These findings suggest that both mineralocorticoid- and glucocorticoid-mediated mechanisms in the amygdala are involved in descending modulation to lumbosacral spinal neurons receiving inputs from the urinary bladder; and this mechanism may play a role in the activation and maintenance of primary central sensitization to noxious visceral stimuli.

Spinal interleukin-6 (IL-6) inhibits nociceptive transmission following neuropathy

Interleukin-6 (IL-6) is a neuropoietic cytokine which is dramatically upregulated following peripheral nerve injury at the site of injury, in the dorsal root ganglion (DRG) and in the spinal cord. The functional effects of IL-6 in nociception in normal conditions and following nerve injury are unclear. Thus the aim of this study was to assess the effect of spinal IL-6 administration on nociceptive transmission in naive, sham-operated and neuropathic (spinal nerve ligation, SNL) rats using in vivo electrophysiology to elucidate the possible role of IL-6 in neuropathic pain. In anaesthetised rats, extracellular recordings were made from individual convergent dorsal horn neurones following electrical and natural (mechanical and thermal) stimulation of peripheral receptive fields. Exogenous spinal IL-6 (100-500 ng) had no significant effect on electrically evoked neuronal responses in naive rats. In contrast, following neuropathy, spinal IL-6 produced a dose-related inhibition of the electrically evoked C-fibre, initial C-fibre and measures of neuronal hyperexcitability (post discharge and wind-up). In addition, spinal IL-6 markedly inhibited mechanical neuronal responses in neuropathic rats. Higher doses of spinal IL-6 also inhibited, to a lesser degree, the initial C-fibre, post discharge and wind-up responses in sham-operated rats. These studies show that following nerve injury the actions of the cytokine alter so that spinal administration of IL-6 elicits anti-nociceptive effects not observed under normal conditions. Moreover, the inhibitory effects of IL-6 on C-fibre activity and neuronal hyperexcitability, suggest IL-6 to be a potential modulator of neuropathic pain.

Reference values of F wave parameters in healthy subjects

OBJECTIVE AND METHODS

A large reference value database for F wave parameters was constructed with data from 121 to 196 healthy subjects; the age range of the subjects was 14-95 years. We studied the following parameters: minimum F wave latency (FMINLAT), mean F wave latency (FMEANLAT), maximum F wave latency (FMAXLAT), number of F waves/20 stimuli (FNUMBER) and F wave dispersion (FDISP=FMAXLAT-FMINLAT). The median, ulnar, peroneal and tibial nerves were studied.

RESULTS

Height explains almost half of the FMINLAT variability. The F wave latency increases with height in the arms by 0.2 ms/cm and in legs 0.4 ms/cm. The effect of age on F wave latency in the arms is relatively small, only 0.03 ms/year; and in the legs age increases the FMINLAT by 0.1 ms/year. Gender does not affect FMINLAT in a systematic way. The peroneal nerve has slightly longer FMINLAT than the tibial nerve, while the FNUMBER is higher in the tibial nerve than the peroneal nerve. The differences between the ulnar and median nerve are slight. There is a very high correlation between all 3 latency parameters (FMINLAT, FMAXLAT and FMEANLAT), but no correlation between FDISP and FNUMBER and the other parameters. Side to side comparisons reveals no significant differences in any of the parameters except for the median nerve FMINLAT and FMEANLAT, which is 0.2 ms longer on the right than left. If side difference of more than 2 standard deviation is taken as the upper limit for normal, the side difference in arms is 1.4 ms and in legs 3 ms. In repeated studies the interexaminer variability is small; the correlation coefficient between the different F parameters is high (P>0.6 in arms and P>0.7 in legs). In the arms the upper limit for a significant difference of FMINLAT on repeated studies in the median nerve is 1.0 and 1.7 ms for the ulnar nerve. In the legs, FMINLAT for the peroneal nerve is 2.6 ms and for the tibial nerve is 2.1 ms.

CONCLUSIONS

This large reference value database can be used not only to evaluate single measurements in relation with height and age, but also to compare right and left side and changes over time at repeated studies.

Intraspinal adenosine induces spinal cord norepinephrine release in spinal nerve-ligated rats but not in normal or sham controls

BACKGROUND

Intrathecal adenosine is antinociceptive under conditions of central sensitization, but not in response to acute stimuli in normals. The reasons for this selective circumstance of action remain unclear, but some evidence links adenosine's antinociceptive effects to release of norepinephrine by terminals in the spinal cord. The purpose of this study was to test whether spinal adenosine induces norepinephrine release selectively in settings of hypersensitivity.

METHODS

Rats randomly assigned to spinal nerve ligation, sham operation, or no operation were anesthetized. A microdialysis fiber was implanted in the spinal cord dorsal horn at the L5-L6 level and perfused with artificial cerebrospinal fluid. After washout and a baseline sample period, adenosine at various concentrations was infused through the fiber for 150 min, and samples were collected every 15 min.

RESULTS

In ligated, but not in sham or normal animals, adenosine perfusion increased norepinephrine in spinal cord microdialysates in a concentration-dependent manner. The effects of adenosine plateaued after 75 min and remained stable until the end of the experiment. Intravenous injection of selective adenosine A1 and A2 receptor antagonists revealed that adenosine's effect on spinal norepinephrine release was A1 receptor mediated.

CONCLUSIONS

This is the first study to provide direct evidence that adenosine is able to release norepinephrine in spinal cord dorsal horns in living animals. However, this effect was only seen in animals after spinal nerve ligation. These data are consistent with behavioral studies demonstrating that adenosine's antinociceptive effects in rats after spinal nerve ligation is totally dependent on intact spinal noradrenergic terminals and can be blocked by spinal alpha 2-adrenergic receptor antagonists.

In vivo and in vitro effects of peripheral galanin on nociceptive transmission in naive and neuropathic states

Galanin is widely distributed in the nervous system and is consistently upregulated in both dorsal root ganglion and spinal neurones by peripheral nerve injury. This study investigates the peripheral effects of galanin on nociceptive neurones using in vitro and in vivo electrophysiological techniques in naive and neuropathic rats. Using an in vitro skin-nerve preparation recording from single nociceptive fibres, galanin (1 microM) significantly inhibited firing induced by noxious heat in 65% of fibres examined. In the remaining 35% of fibres, galanin (1 microM) induced a facilitation of the responses to noxious heat. To examine the effect of peripheral galanin in vivo, extracellular recordings from convergent dorsal horn neurones were made in anaesthetised naive sham-operated and spinal nerve-ligated (SNL) rats. Injection of galanin (0.1-10 microg) into hindpaw receptive fields inhibited responses to innocuous mechanical, noxious mechanical and noxious heat stimuli in a proportion of neurones in each animal group and facilitated the remaining neurones. However, a higher proportion of neurones (80-90%) was inhibited by peripheral galanin administration in SNL rats compared with naive (45-55%) and sham (70-80%) rats. These results show that galanin can have both excitatory and inhibitory effects on peripheral sensory neurones, perhaps reflecting differential receptor activation, and that the proportion of these receptors may change following peripheral neuropathy.

Efferent control of different visceral pelvic organs by spinal and supraspinal centres

A growing number of patients with pelvic organ dysfunction and failing response to standard treatment concepts are referred to special neuro-urology services. New therapeutic options are available, such as unilateral and bilateral sacral nerve stimulation, and the use of different neurotoxins for the overactive bladder. However, a lack of knowledge and understanding in central innervation and modulation of pelvic organ function prevents a striking progress in this clinical area. A concept of efferent innervation of pelvic organs based on experimental animal studies, using the retrograde, transneuronal and self-amplifying tracer Pseudorabiesvirus, is discussed in a clinical context.

Changes in the gene expression of six subtypes of P2X receptors in rat dorsal root ganglion after spinal nerve ligation

Increased purinergic sensitivity of injured sensory neurons suggests the possible involvement of purinoceptors for the generation of pain after nerve injury. To identify the purinoceptors that are involved, the changes in mRNA levels of 6 subtype purinoceptors were examined in the dorsal root ganglia (DRG) of the normal rat and after spinal nerve ligation, using RNase protection assay (RPA). In addition, the P2X(2) containing neurons were examined in the L5 DRG, using an immunohistochemical method. The relative amounts of mRNAs for the six purinoceptor subtypes were in the order of P2X(3)>>P2X(4)>P2X(6)>P2X(5) approximately P2X(2)>P2X(1) in the normal lumbar DRG. After nerve injury, the mRNA of P2X(5) was increased, those of P2X(3) and P2X(6) were decreased, and those of P2X(2) and P2X(4) were unchanged. Immunohistochemical studies, however, showed 23% of the total DRG neurons are P2X(2) positive in the normal L5 DRG, but that increased to 73% after nerve ligation. These data suggest that not only transcriptional but also posttranscriptional changes of multiple purinoceptors might be involved in the enhancement of purinergic sensitivity in injured sensory neurons.

Evoked potentials elicited by stimulation of the lateral and anterior femoral cutaneous nerves in meralgia paresthetica

Seventy-five consecutive patients with clinical symptoms and signs of meralgia paresthetica underwent bilateral somatosensory evoked potential (SEP) studies involving stimulation of skin areas innervated by the lateral and anterior femoral cutaneous nerves of the thighs. The most common abnormality was an absolute lateral femoral cutaneous SEP latency > 40 ms in 35 patients (47%), followed by an absent response in 14 patients (19%), an absolute latency < 40 ms but amplitude reduction > 50% compared with the contralateral response in 8 patients (11%), and an absolute latency < 40 ms but > 5 ms interside latency difference in 5 patients (7%). Anterior femoral cutaneous SEPs were of value in distinguishing meralgia paresthetica from a proximal lumbar radiculopathy in an additional 4 patients and confirming bilateral meralgia paresthetica in 10 patients.

Further insights into post-exercise effects on H-reflexes and motor evoked potentials of the flexor carpi radialis muscles

The present study investigated the relative contribution of the cortical and spinal mechanisms for post-exercise excitability changes in human motoneurons. Seven healthy right-handed adults with no known neuromuscular disabilities performed an isometric voluntary wrist flexion at submaximum continuous exertion. After the subjects continued muscle contraction until volitional fatigue, the H-reflexes induced by an electric stimulation and motor evoked potentials (MEPs) induced by a transcranial magnetic stimulation (TMS) from a flexor carpi radialis (FCR) muscle were recorded 7 times every 20 s. The H-reflex was used to assess excitability changes at the spinal level, and the MEP was used to study excitability changes at the cortical level. Hreflexes showed a depression (30% of control value) soon after the cessation of wrist flexion and recovered with time thereafter. On the other hand, an early (short latency) MEP showed facilitation immediately after the cessation of wrist flexion (50% of control value) and thereafter decreased. A possible mechanism for the contradictory results of the 2 tests, in spite of focusing on the same motoneuron pool, might be the different test potential sizes between them. In addition, a late (long latency) MEP response appeared with increasing exercise. With regard to the occurrence of late MEP response, a central mechanism may be proposed to explain the origin-that is, neural pathways with a high threshold that do not participate under normal circumstances might respond to an emergency level of muscle exercise, probably reflecting central effects of fatigue.

Extensive somatosensory innervation in infants with obstetric brachial palsy

In the pre-operative screening of infants with obstetric brachial palsy (OBP), the results of routine electromyography are often overly optimistic when compared to the peri-operative findings. This prompted us to include investigation of the sensory innervation of these infants using the N20 (the first cortical response to a peripheral stimulation) of the somatosensory evoked potentials (SSEP). Three to seven months after birth, SSEP were recorded at the skull after stimulation of the thumb and middle finger in infants with obstetric rupture of the upper trunk or avulsion of roots C5, C6, or C7, and in whom no clinical improvement of motor function was observed in the biceps brachii and deltoid muscles. In most infants, a normal N20 could be evoked, indicating the existence of peripheral sensory pathways. From the thumb, these sensory pathways would necessarily bypass the upper trunk and dorsal roots of spinal nerves C5 and C6, and from the middle finger bypass the middle trunk and dorsal root C7, before extending into the dorsal column and projecting toward the thalamus and cerebral cortex. These data suggest that in infancy the segmental sensory innervation of the hand is more diverse than is described in most textbooks.

[Changes in mechano-receptive properties of Abeta-fiber induced by antidromical electrical stimulation of the cutaneous nerve from adjacent spinal segment]

The purpose of the present study was to observe whether primary afferent Abeta-fiber is involved in the information transmission between peripheral terminals of adjacent dermatomes. The dorsal cutaneous nerve branches of spinal nerves from T(8) to T(12) segments were cut proximally. One peripheral stump end of the cut nerves was dissected into a few filaments for the examination of mechanoreceptive properties of single Abeta-fibers and their discharges were observed while the other end was stimulated antidromically. Fifty Abeta-units were recorded in forty-two intact rats. After an electrical stimulation (0.45 mA, 0.1 ms, 20 Hz, for 10 s) was delivered to the stimulated nerve, the size of the receptive field of 60.6% (n=33) Abeta-fibers extended. The mean area of receptive fields of all examined units enlarged from 8.94+/-6.51 mm(2) to 20.34+/-16.17 mm(2) (P<0.01) and the shapes of the receptive fields of 81.8% (n=20) units changed from a dot, round or ellipse with its long axis in parallel with the longitudinal axis of the body to an oblique ellipse with the longitudinal axis of the body. The mechanoreceptive threshold of 68.0% (n=50) units decreased with a reduction in mean threshold from 2.37+/-1.24 to 2.29+/-1.24 mN (P<0.05). The duration of these changes in mechano-receptive properties increased from 52.23+/-9.27 to 56.93+/-15.76 min. Meanwhile, increasing discharge was found in 50.0% (n=50) units but lasted only for 1.52+/-0.46 min. The changes in mechanoreceptive properties appeared simultaneously with discharge changes but had longer duration than that of discharge change (P<0.01). Discharges changes usually appeared in those units with the changes in mechanoreceptive properties following an antidromical electrical stimulation of adjacent spinal segment. These results suggest that low-threshold mechanoreceptive Abeta-fibers are affected by antidromical electrical stimulation of the cutaneous nerve from an adjacent spinal segment, indicating that information transmission occurs between the two endings of peripheral afferent nerves from adjacent spinal segments without any involvement of the central nervous system, and that Abeta-fibers are involved in the process of information transmission between peripheral terminals from adjacent spinal segments.

A case of trigeminal-vagal neuralgia relieved by peripheral self-stimulation

A case of simultaneous trigeminal and vagoglossopharyngeal neuralgia is described. No microvascular compression was seen at the trigeminal complex while the origin of vagoglossopharyngeal pain could have been due either to Chiari malformation or microvascular compression of the IX-X nerve complex. Decompressive surgery was ineffective. The patient could completely block his facial painful fits by strongly pinching the anterior axillary fold. This case militates against peripheral theories of facial neuralgias, including microvascular compression and ganglion ignition focus theories, and supports a central origin thereof.

Examination of the variations of lateral femoral cutaneous nerves: report of two cases

The origins, courses and relations of lateral femoral cutaneous nerves (LFCNs) were examined bilaterally in 28 cadavers, and the variations were observed in two. On the right side of one cadaver, the ventral rami of the first and second lumbar spinal nerves were united and then this nerve was divided into four branches. From medial to lateral, these branches were the obturator nerve, the femoral nerve, the medially located LFCN and the laterally located LFCN. On the left side of another cadaver, there were three LFCNs. All of these nerves pierced the psoas major muscle anterolaterally. Two of these nerves, which pierced the psoas major muscle more proximally than the third, united with each other by a communicating branch anterior to the iliacus muscle. These types of variations are very important, especially in the presence of paresthesias or pain in the anterior thigh, lateral thigh and gluteal region. In these cases, surgeons must always remember the possible variations of the LFCN during surgical procedures in order to prevent injury and the occurrence of meralgia paresthetica.

Sartorius muscle afferents influence the amplitude and timing of flexor activity in walking decerebrate cats

Recent investigations have demonstrated that afferent signals from hindlimb flexor muscles can strongly influence flexor burst activity during walking and during fictive locomotion in decerebrate cats. We have reported previously that modifying afferent feedback from the sartorius (Sart) muscles by assisting or resisting hip flexion has a marked effect on the magnitude and duration of activity in iliopsoas (IP) as well as the sartorius muscles. The objective of the present investigation was to identify the afferents responsible for these effects by examining, in walking decerebrate cats, the influence of electrically stimulating sartorius afferents on burst activity in the IP and tibialis anterior (TA) muscles. Stimulation of the sartorius nerve at group I strength resulted in an increase in the duration of IP and TA bursts and an increase in the magnitude of IP bursts. The effect on burst durations was only observed at stimulus strengths of 1.6 T and higher. At lower stimulus strengths, there was a strong excitatory effect on IP bursts but no effect on TA bursts. Stimulation of the sartorius nerve at group II strength yielded variable results. When group II stimulation was delivered repeatedly during a walking sequence, the initial response was usually a strong inhibition of burst activity in IP and TA followed by a progressive reduction in inhibition and the emergence in IP of an excitatory response. This observation, together with findings of previous studies, suggests the existence of parallel excitatory and inhibitory pathways from sartorius group II afferents to flexor motoneurons. Taken together, these results support an earlier speculation that feedback from large afferents from the sartorius muscles has a strong influence on the generation of flexor burst activity in walking cats.

Anatomical study of lumbar spine innervation

To precisely evaluate low back pain, identification of the detailed innervation of the lumbar spine is necessary. On twenty-five sides of adult cadavers we investigated various patterns of rami communicantes (RC) and their relationship to the psoas major muscle (PM). In ten sides, we focused our dissection on the minute nerve supply of the anterior (ALL) and posterior longitudinal ligaments (PLL), vertebral bodies and the intervertebral discs (IVD). According to the mode of piercing PM, two types of RC were observed: superficial oblique rami (SOR) and deep transverse rami (DTR). SOR ran obliquely between superficial heads of PM, connecting sympathetic trunk (ST) and T12-L2 (3) spinal nerves non-segmentally. DTR ran segmentally close to the vertebral bodies and were situated deep to the PM slips. On the lateral side of the lumbar spine, the vertebral bodies and IVD received branches from DTR and ventral rami segmentally, as well as branches from the sympathetic trunk (ST) and, in the upper lumbar region, SOR non-segmentally. On the anterior aspect of the lumbar spine, ALL received branches from ST and splanchnic nerves non-segmentally. Within the vertebral canal, the posterior aspect of IVD and PLL received the sinu-vertebral nerves originating from DTR. These findings suggest the coexistence of two different types of innervation: one originating directly from the spinal nerve segmentally, and one reaching vertebral structures via the sympathetic nerves non-segmentally. Therefore, sympathetic nerves are likely involved in the proprioception of the spinal column.

VR1, but not P2X(3), increases in the spared L4 DRG in rats with L5 spinal nerve ligation

We investigated the expression of two candidate transducers of noxious stimuli in peripheral tissues, the vanilloid receptor subtype 1 (VR1) and the P2X(3), a subunit of the ionotropic P2X receptor for ATP, in spared L4 DRG neurons following L5 spinal nerve ligation, a neuropathic pain model. VR1 mRNA expression increased in the small- and medium-sized DRG neurons from the first to 28th day after injury, and this up-regulation corresponded well with the development and maintenance of thermal hyperalgesia of the hind paw. The increase in VR1-immunoreactive (ir) neurons was confirmed at the third day after surgery. In contrast, there was no change in expression of P2X(3) mRNA over 4 weeks after ligation, or in the percentage of P2X(3)-ir neurons observed 3 days after surgery. Our data suggests that increased VR1 in the spared L4 DRG may contribute to the exaggerated heat response observed in this neuropathic pain model. Taken together with the previous reports that P2X(3) expression increases in the spared DRG neurons in other neuropathic pain models, there appears to be differences in the phenotypic changes and pathomechanisms of the various neuropathic pain models.

Group II mGluR receptor agonists are effective in persistent and neuropathic pain models in rats

The involvement of Group II metabotropic receptors in acute and persistent pain states was evaluated in several in vivo models of pain with selective and potent Group II metabotropic glutamate (mGlu) 2,3 agonists. LY354740, LY379268 and LY389795 attenuated late-phase paw-licking pain behavior in a dose-dependent manner in the formalin model of persistent pain. Effects occurred in the absence of overt neuromuscular deficits as measured by performance in the rotorod test for ataxia. The effects of LY354740 and LY379268 were also stereoselective. The order of potency of the agonists was LY389795>LY379268>LY354740. The attenuation of licking behavior by LY379268 (3 mg/kg) in the formalin model was reversed by a potent and selective mGlu2,3 receptor antagonist, LY341495 (1 mg/kg). In the L5/L6 spinal nerve ligation model of neuropathic pain in rats, LY379268 significantly reversed mechanical allodynia behavior in a dose-related manner. In contrast, LY379268 had no significant effects on the tail flick test or paw withdrawal test of acute thermal nociceptive function. These results support the involvement of Group II mGlu2,3 receptors in persistent pain mechanisms and suggest the potential utility of selective Group II mGlu agonists for the treatment of persistent pain.

Reduced basal release of serotonin from the ventrobasal thalamus of the rat in a model of neuropathic pain

Drugs that inhibit reuptake of monoamines are frequently used to treat pain syndromes, e.g. neuropathy or fibromyalgia, where mechanical allodynia is present. Several lines of evidence suggest the involvement of supraspinal sites of action of these drugs. However, a direct study of supraspinal serotonin (5-HT) or norepinephrine (NE) release in an animal model in which allodynia is expressed, e.g. neuropathy, has not been done. The ventrobasal (VB) thalamus and the hypothalamus are major supraspinal projection regions for spinal neurons that transmit nociceptive information and are innervated by monoaminergic fibers. This study determined if peripheral neuropathy would induce changes in extracellular monoamines in VB thalamus and hypothalamus. Male Sprague-Dawley rats had spinal nerve roots L5 and L6 tightly ligated (neuropathic rats; NP) or sham (SHAM) surgery; contralateral and ipsilateral VB thalamus and contralateral hypothalamus were dialyzed with modified artificial cerebral spinal fluid (aCSF), with and without fluoxetine. NP rats had significantly decreased 5-HT content in dialysates of the contralateral VB thalamus compared with SHAM rats with (82% decrease) or without (63% decrease) fluoxetine in the perfusion medium over the 180 min of the study. There were no differences in the ipsilateral VB thalamus. In contrast, release of 5-HT was unchanged in the hypothalamic dialysates of SHAM vs. NP rats. NE release was not different in dialysates of either the VB thalamus or hypothalamus of SHAM vs. NP rats. Synthesis of 5-HT, as assessed by accumulation of 5-hydroxytrytophan after treatment with an L-amino acid decarboxylase inhibitor, was not different between NP and SHAM rats in VB thalamic and hypothalamic brain tissue. This study is the first to demonstrate changes in monoamine release supraspinally in NP rats. The differential effect between VB thalamus and hypothalamus suggests that a terminal field change may be involved. Putative mechanisms for mediating this change include alterations of GABA-ergic systems and/or plasticity related to alterations in N-methyl-D-aspartate receptor activation and nitric oxide release related to afferent hyperactivity induced by neuropathic pain.

Analgesic profile of intrathecal P2X(3) antisense oligonucleotide treatment in chronic inflammatory and neuropathic pain states in rats

Extracellular adenosine triphosphate (ATP), acting at P2X ionotropic receptors, is implicated in numerous sensory processes. Exogenous ATP has been shown to be algogenic in both animals and humans. Research focus has been directed towards the P2X(3) receptor, as it is preferentially expressed on nociceptive C-fibers and its implication in pain processing is supported by an altered nociceptive phenotype in P2X(3) knock-out mice. In order to further characterize the role of P2X(3) receptor activation in nociception, we evaluated the effects of continuous intrathecal administration of P2X(3) antisense oligonucleotides for 7 days in the rat. P2X(3) receptor antisense oligonucleotide treatment significantly decreased nociceptive behaviors observed after injection of complete Freund's adjuvant (CFA), formalin or alphabeta-methylene ATP into the rat's hind paw. The anti-hyperalgesic effects of the antisense treatment in the CFA model of inflammatory pain were dose related. Similar effects were observed with two distinct P2X(3) antisense oligonucleotides. These behavioral effects were significantly correlated with a decrease in P2X(3) receptor protein expression in the dorsal root ganglia (DRG). In contrast, a decrease in P2X(3) receptor protein expression in the DRG did not affect nociceptive behavior in the carrageenan model of acute thermal hyperalgesia. P2X(3) receptor antisense oligonucleotide treatment also significantly reduced mechanical allodynia observed after spinal nerve ligation. Overall, the present data demonstrate that activation of P2X(3) receptors contribute to the expression of chronic inflammatory and neuropathic pain states and that relief form these forms of chronic pain might be achieved by selective blockade of P2X(3 )receptor expression or activation.

Segmental regulation pattern of body surface temperature in the rat hindlimb

Body surface zones or 'thermatomes', whose temperature is regulated by a single spinal segment, were investigated by thermography in the rat hindlimb. First, the spatial relation between the dermatome delineated by dye extravasation and the corresponding thermatome was investigated in rats pretreated with intravenous application of Evans blue. Electrical stimulation of the spinal nerves and sympathetic trunk segments at L3 and L5 induced a distal dominant temperature decrease. In contrast, Evans blue extravasation appeared in the medial (in L3) and lateral (in L5) paw only by electrical stimulation of the spinal nerves. Second, thermatomes L1-L5 were determined in other rats. Electrical stimulation of the sympathetic trunk segments L1-L6 produced a temperature decrease in the abdomen, hindlimb, and tail. However, the hindlimb temperature was regulated mainly by L2-L5 levels, particularly by L4 and L5. The abdomen was regulated uniformly by L1-L6, and the tail by L6. It was demonstrated that thermatomes are manifested differently from the corresponding dermatomes in the rat hindlimb.

Nerve injury induces plasticity that results in spinal inhibitory effects of galanin

Galanin is a 29-amino-acid neuropeptide that has been implicated in the processes of nociception. This study examines the effect of exogenous galanin on dorsal horn neurone activity in vivo in the spinal nerve ligation (SNL) model of neuropathic pain. SNL rats but not naive or sham-operated rats exhibited behaviour indicative of allodynia. In anaesthetized rats, extracellular recordings were made from individual convergent dorsal horn neurones following stimulation of peripheral receptive fields electrically or with natural (innocuous mechanical, noxious mechanical and noxious thermal) stimuli. Spinal administration of galanin (0.5-50 microg) caused a slight facilitation of the neuronal responses to natural and electrical stimuli in naive rats and up to a 65% inhibition of neuronal responses in sham-operated rats following 50 microg galanin. In contrast, there was a marked inhibition of up to 80% of responses to both natural and electrical stimuli in SNL rats following spinal galanin administration. These results suggest that following peripheral nerve injury, there is plasticity in the levels of galanin and/or its receptors at spinal cord level so that the effect of exogenous galanin favours inhibitory function.

Combined systemic administration of morphine and magnesium sulfate attenuates pain-related behavior in mononeuropathic rats

The response to opioids is reduced in neuropathic pain states. We examined the effect of the combination of morphine (0.1 mg/kg) and magnesium sulfate (125 mg/kg) on behavioral signs of neuropathic pain in spinal nerve ligated rats. Administered alone, neither drug produced any effect, but the combination exerted a significant anti-allodynic effect, which was partially reversed by naloxone. These results suggest that combining low doses of magnesium sulfate with opiates might be an alternative in treating neuropathic pain, with reduced risk of side effects.

High intensity magnetic stimulation over the lumbosacral spine evokes antinociception in rats

OBJECTIVES

High intensity magnetic stimulation (MS) applied over the skin can painlessly depolarize superficial and deep nerves and we aimed to evaluate the effectiveness of MS of spinal nerves in evoking a potent analgesic response.

METHODS

The MS was administered to adult male Sprague-Dawley rats using a Cadwell MES-10 high-speed magnetic stimulator. A Peltier device and von Frey fibers were used to determine heat and mechanical nociceptive responses of the rats.

RESULTS

A brief (5 min) course of MS over the rat's lumbosacral spine produced a long-lasting (30-40 min) and robust (80-90% maximum possible effect) hindpaw antinociceptive effect to both mechanical and heat stimuli. Spinal cord transected rats had intact hindpaw nociceptive withdrawal responses, but transection eliminated MS evoked antinociception, indicating a critical extrasegmental component in the mechanism of MS antinociceptive action. The opiate receptor antagonist naloxone (5 mg/kg, i.p.) completely blocked MS evoked antinociception, demonstrating an opioidergic mechanism for MS antinociception. The alpha(2) adrenoceptor antagonist atipamezole (5 mg/kg, i.p.) slightly reduced the MS antinociceptive response to heat and had no effect on MS antinociception for mechanical stimuli.

CONCLUSIONS

These data indicate that MS can evoke a robust, long-lasting antinociceptive effect, which requires an intact supraspinal pathway and is opioidergic mediated.