[show abstract][hide abstract] ABSTRACT: The neurotrophin Nerve Growth factor (NGF) is known to influence the phenotype of mature nociceptors, for example by altering synthesis of neuropeptides, and changes in NGF levels have been implicated in the pathophysiology of chronic pain conditions such as neuropathic pain. We have tested the hypothesis that after partial nerve injury, NGF accumulates within the skin and causes 'pro-nociceptive' phenotypic changes in the remaining population of sensory nerve fibres, which could underpin the development of neuropathic pain.
Eleven days after chronic constriction injury of the rat mental nerve the intra-epidermal nerve fibre density of the chin skin from had reduced from 11.6 +/- 4.9 fibres/mm to 1.0 +/- 0.4 fibres/mm; this slowly recovered to 2.4 +/- 2.0 fibres/mm on day 14 and 4.0 +/- 0.8 fibres/mm on day 21. Cold hyperalgesia in the ipsilateral lower lip was detectable 11 days after chronic constriction injury post-injury, although at this time skin [NGF] did not differ between sides. At 14 days post-injury, there was a significantly greater [NGF] ipsilaterally compared to contralaterally (ipsilateral = 111 +/- 23 pg/mg, contralateral = 69 +/- 13 pg/mg), but there was no behavioural evidence of neuropathic pain at this time-point. By 21 days post-injury, skin [NGF] was elevated bilaterally and there was a significant increase in the proportion of TrkA-positive (the high-affinity NGF receptor) intra-epidermal nerve fibres that were immunolabelled for the neuropeptide Calcitonin Gene-related peptide.
The temporal mismatch in behaviour, skin [NGF] and phenotypic changes in sensory nerve fibres indicate that increased [NGF] does not cause hyperalgesia after partial mental nerve injury, although it may contribute to the altered neurochemistry of cutaneous nerve fibres.
[show abstract][hide abstract] ABSTRACT: Voltage-gated sodium channels Nav1.8 and Nav1.9 are expressed preferentially in small diameter sensory neurons, and are thought to play a role in the generation of ectopic activity in neuronal cell bodies and/or their axons following peripheral nerve injury. The expression of Nav1.8 and Nav1.9 has been quantified in human lingual nerves that have been previously injured inadvertently during lower third molar removal, and any correlation between the expression of these ion channels and the presence or absence of dysaesthesia investigated.
Immunohistochemical processing and quantitative image analysis revealed that Nav1.8 and Nav1.9 were expressed in human lingual nerve neuromas from patients with or without symptoms of dysaesthesia. The level of Nav1.8 expression was significantly higher in patients reporting pain compared with no pain, and a significant positive correlation was observed between levels of Nav1.8 expression and VAS scores for the symptom of tingling. No significant differences were recorded in the level of expression of Nav1.9 between patients with or without pain.
These results demonstrate that Nav1.8 and Nav1.9 are present in human lingual nerve neuromas, with significant correlations between the level of expression of Nav1.8 and symptoms of pain. These data provide further evidence that changes in expression of Nav1.8 are important in the development and/or maintenance of nerve injury-induced pain, and suggest that Nav1.8 may be a potential therapeutic target.
[show abstract][hide abstract] ABSTRACT: BACKGROUND: Calcitonin gene-related peptide (CGRP) is a powerful pro-inflammatory mediator thought to play a significant role in the development of inflammation and pain. We investigated the role of CGRP in trigeminal inflammatory pain by determining the ability of a monoclonal antibody to CGRP to modify central Fos expression in response to stimulation of the inflamed ferret tooth pulp. We also assessed the effect of the antibody on pulpal inflammation. METHODS: 10 adult ferrets were prepared under anaesthesia to allow stimulation of the upper and lower left canine pulps, recording from the digastric muscle and intravenous injections at subsequent experiments. In all animals, pulpal inflammation was induced by introducing human caries into a deep buccal cavity. 4 days later animals were treated intravenously with either CGRP antibody (n=5) or vehicle (n=5). After a further 2 days animals were re-anaesthetised and the tooth pulps stimulated at 10times jaw-opening reflex threshold. Brainstems and tooth pulps were processed immunohistochemically for Fos and the common leucocyte marker CD45, respectively. RESULTS: Fos was expressed in ipsilateral trigeminal subnuclei caudalis (Vc) and oralis (Vo). Significantly fewer Fos-positive nuclei were present within Vc of CGRP antibody-treated animals (p=0.003 vs vehicle-treated). Mean percentage area of staining for CD45 was significantly less in antibody-treated animals (p=0.04 vs vehicle-treated). CONCLUSIONS: This is the first direct evidence that sequestration of CGRP has anti-inflammatory and putative analgesic effects. Previous studies using this Fos model have demonstrated that it is able to predict clinical analgesic efficacy. Thus these data indicate that this antibody may have analgesic effects in dental pain and other types of inflammatory-mediated transmission, and suggest that this is in part due to peripheral anti-inflammatory effects.
[show abstract][hide abstract] ABSTRACT: Currently there is a great interest in the development of nerve guide conduits to improve regeneration of injured peripheral nerves. In this study we tested simple polyethylene-glycol (PEG) conduit repair against graft repair in thy-1-YFP-H mice; a transgenic strain with a subset of axons labelled with yellow fluorescent protein.
Under anaesthesia the common fibular nerve in 10 mice was exposed and a 3mm section removed. The gap was repaired with PEG conduit or nerve graft taken from a wild-type littermate. After 3-weeks recovery mice were re-anaesthetised and the nerve fixed in situ with 4% formaldehyde. The repaired nerve was excised mounted whole on a slide and coverslipped using Vectashield. Images of nerves were acquired using Image ProPlus.
No significant differences were detected between the two groups in the three methods of analysis used. Both groups saw axon numbers of ~150% compared to the pre-repair axon numbers at 0.5mm into the repair, this number proceeded to fall at each subsequent interval to ~62% at the distal stump 4.0mm into the repair. The proportion of axons at the repair start represented at the distal stump was 34% in conduit repairs and 37% in. Axons increased in length by 16% in conduits and 22% grafts over the initial 1.5mm of the repair.
In conclusion, PEG conduits are able to support nerve regeneration across a 3mm gap at similar levels to nerve grafts. These results will help to assess the impact of adding internal structure and/or exogenous regeneration enhancing molecules in future conduit studies.
[show abstract][hide abstract] ABSTRACT: Aim:
The formation of scar tissue following nerve injury has been shown to adversely affect nerve regeneration. The aim of this study was to utilise the fluorescent labelling of axons in thy-1-YFP-H mice to analyse the effects of mannose-6-phosphate (M6P), a potential scar reducing agent that affects TGF-β activation, on nerve regeneration following injury.
Under anaesthesia (isoflurane 4%), the common fibular (CF) nerve of twenty 9–11 week-old thy-1-YFP-H mice was exposed and a small section of nerve removed to create a gap (2.5 mm) between the proximal and distal ends. A graft taken from a wild-type (WT) littermate, pre-soaked for 30 minutes in a solution of M6P (n=10) or vehicle (PBS; n=10), was positioned in this gap and fixed in place using fibrin glue.
After 2 weeks' recovery, the animals were re-anaesthetised (fluanisone 0.8 ml/kg and midazolam 4 mg/kg, ip) and the nerve fixed in situ (4% paraformaldehyde, 30 min). The nerve and graft were removed, positioned on a microscope slide and coverslipped using Vectashield.
Images were taken from the nerve using fluorescent structured illumination microscopy and reconstructed using Adobe Photoshop. These were used to calculate the sprouting index at 0.5-mm intervals along the nerve, to assess the proportion of axons at the start of the graft that had successfully regenerated through the graft, and the lengths of axons regenerating through the graft.
No significant differences in axon sprouting were found between M6P and vehicle grafts at any point along the graft length, with maximal sprouting occurring at 1.0mm post-graft in both groups (169.4% ± 19.8% [SEM] for M6P; 177.2% ± 26.9% for vehicle). There were also no significant differences in the proportion of axons regenerating through the graft in either group (23.8% ± 2.9% for M6P; 21.9% ± 3.7% for vehicle). However, the average length of axons regenerating through the graft was significantly different, with M6P treated graft axons reaching 3.5mm from the graft starting point along a shorter path than vehicle treated graft axons (increases of 9.33% ± 0.58% SEM and 12.27% ± 0.60% SEM for M6P and vehicle grafts respectively, p<0.05, Mann-Whitney U test).
Application of M6P appears to reduce the disruption of regenerating axons and may therefore facilitate quicker recovery; this is likely to result from reduced scar tissue formation in M6P grafts in the early stages of recovery. However the overall recovery does not appear to be improved as similar proportions of axons in M6P and vehicle grafts were found to have successfully regenerated through the graft.
Supported by Renovo Group plc and the MRC.
[show abstract][hide abstract] ABSTRACT: The development of ectopic neural discharge at a site of peripheral nerve injury is thought to contribute to the initiation of sensory disturbances and pain. We have previously shown that this discharge can be initiated or increased by the neuropeptide calcitonin gene-related peptide (CGRP). We have now studied a potential therapeutic approach to reducing the discharge by evaluating the effect of a systemically administered monoclonal antibody to CGRP on injury-induced activity in the lingual nerve. In 16 anaesthetised adult ferrets the left lingual nerve was sectioned. One day after the injury, the animals received a subcutaneous injection of either a monoclonal antibody to CGRP or a vehicle control. Three days after the injury, under a second anaesthetic, single-unit electrophysiological recordings were made from central to the injury site (469 and 391 units were analysed in antibody and vehicle groups, respectively), and the proportion of units that were spontaneously active was determined. In the vehicle-treated animals 6.4±2.7 [SEM]% of the units were spontaneously active, with conduction velocities of 8.8-40.8m/s and discharge frequencies of 0.03-2.7Hz. In the monoclonal antibody-treated animals 5.7±2.0% of the units were spontaneously active, with conduction velocities of 13.9-38.8m/s and discharge frequencies of 0.07-1.8Hz. There was no significant difference between these two groups (for spontaneous activity and conduction velocity: p>0.05, Student's t-test; for discharge frequency: p>0.05, Mann-Whitney test), suggesting that the spontaneous activity initiated by a nerve injury cannot be modulated by administration of a monoclonal antibody to CGRP.
[show abstract][hide abstract] ABSTRACT: In this study we have determined the amount of Nerve Growth Factor (NGF) and the innervation density of the glabrous hindpaw skin of diabetic rats (n=4) and controls (n=3). The proportion of intra-epidermal nerve fibres (IENF) expressing the high affinity NGF receptor (trkA) and calcitonin gene-related peptide (CGRP) were also determined. Four weeks after induction of diabetes by intraperitoneal streptozotocin injection skin was analyzed for: (i) NGF content using ELISA and (ii) the innervation density of peptidergic afferents that also expressed trkA using immunocytochemistry. NGF levels were approximately three-fold higher in diabetic skin compared to controls (diabetic: 134.7±24.0 (SD) pgml(-1), control: 42.7±21.5pgml(-1), p=0.002). As expected there was a significant reduction in IENF density in diabetic skin (2.7±1.3 fibresmm(-1)) compared to controls (6.9±1.5 fibresmm(-1); p=0.01). In diabetic rats there was no significant difference in the proportion of trkA-labelled IENF (diabetic 74±21%; control 83±15%, p=0.6), but significantly more trkA-positive IENF were also labelled by CGRP antibodies in diabetic skin compared to controls (diabetic 89±22%; control 38±2%, p=0.03). These data suggest that in diabetes the upregulation of cutaneous NGF may 'over-troph' the surviving axons, increasing CGRP labelling, which may be important in the aetiology of painful diabetic neuropathy.
[show abstract][hide abstract] ABSTRACT: Objectives: Nerve injury represents a significant clinical problem, giving rise to substantial disability including chronic pain. Animal models have been developed to investigate and improve nerve regeneration. Many of these employ electrophysiological or behavioural approaches; however, our objective is to develop an in vivo model of peripheral nerve injury and repair that allows visual analysis of axonal regeneration, using genetically modified mice (thy-1-YFP-H [thy-1]) which express yellow fluorescent protein (YFP) in a subset of axons.
Methods: Under anaesthesia (isoflurane 4%), the common fibular (CF) nerve of 9–11 week-old thy-1 mice was exposed and a small section of nerve removed to create a gap (2.5 mm) between the proximal and distal ends. A graft taken from a wild-type (WT) littermate was positioned in this gap and fixed in place using fibrin glue.
After 2 weeks’ recovery, the animals were re-anaesthetised (fluanisone 0.8 ml/kg and midazolam 4 mg/kg, ip) and the nerve fixed in situ (4% paraformaldehyde, 30 min). The nerve and graft were removed, positioned on a microscope slide and coverslipped using Vectashield.
Images were taken from the nerve using fluorescent structured illumination microscopy and reconstructed using Adobe Photoshop. These were used to calculate the sprouting index at 0.5-mm intervals along the nerve and to assess the distance travelled through the graft by each axon.
Results: The CF nerve had a mean pre-graft YFP-axon count of 40 (± 1.46 SEM). The sprouting index was maximal at 1 mm (mean value 2.29 ± 0.09). Individual axons could be traced through the graft and the percentage of axons reaching each 0.5-mm interval could be calculated.
Conclusions: This method allows visual analysis of in vivo axon regeneration through a graft. Future studies will use this technique to assess the effects of molecules that may enhance nerve regeneration.
Funded by MRC
[show abstract][hide abstract] ABSTRACT: Microsurgical repair of transected peripheral nerves is compromised by the formation of scar tissue and the development of a neuroma, thereby limiting the success of regeneration. The aim of this study was to quantify histomorphometrically the structural changes in neural tissue that result from repair, and determine the effect of mannose-6-phosphate (M6P), a scar-reducing agent previously shown to enhance regeneration. In anaesthetised C57-black-6 mice, the left sciatic nerve was sectioned and repaired using four epineurial sutures. Either 100 μL of 600 mm M6P (five animals) or 100 μL of phosphate-buffered saline (placebo controls, five animals) was injected into and around the nerve repair site. A further group acted as sham-operated controls. After recovery for 6 weeks, the nerve was harvested for analysis using light and electron microscopy. Analysis revealed that when compared with sham controls, myelinated axons had smaller diameters both proximal and distal to the repair. Myelinated axon counts, axonal density and size all decreased across the repair site. There were normal numbers and densities of non-myelinated axons both proximal and distal to the repair. However, there were more Remak bundles distal to the repair site, and fewer non-myelinated axons per Remak bundle. Application of M6P did not affect any of these parameters.
Journal of Anatomy 08/2011; 219(5):638-45. · 2.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have determined the effect of applying Mannose-6-Phosphate (M6P), a scar reducing agent, to a site of sciatic nerve repair. In anaesthetised C57-Black-6 mice, the left sciatic nerve was sectioned and repaired using 4 epineurial sutures. Either 100 μl of 600 mM Mannose-6-Phosphate (29 animals), or 100 μl of phosphate buffered saline as a placebo control (29 animals), was injected into and around the nerve repair site. A further group acted as sham-operated controls. After 6 or 12 weeks of recovery the extent of regeneration was assessed electrophysiologically and the percentage area of collagen staining at the repair site was analysed using picrosirius red and image analysis. Gait analysis was undertaken pre-operatively and at 1, 3, 6, 9 and 12 weeks postoperatively, to assess functional recovery. At 6 weeks the compound action potentials recorded from the regenerated nerves in the M6P group were significantly larger than in the placebo controls (P=0.015), and the conduction velocities were significantly faster (P=0.005), but there were no significant differences between these groups at 12 weeks. Gait analysis suggested better early functional recovery in the M6P group. In both repair groups there was a significant reduction in collagen staining between 6 and 12 weeks, suggestive of scar remodelling. We conclude that the normal scar remodelling process aids long term recovery in repaired nerves. Administration of 600 mM M6P to the nerve repair site enhances nerve regeneration and functional recovery in the early stages, and may lead to improved outcomes.
Brain research 06/2011; 1394:40-8. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: We have investigated the effect of three potential scar-reducing agents applied at a sciatic nerve repair site in C57-black-6 mice. Under anaesthesia the nerve was transected, repaired using four epineurial sutures, and 100 μl of either triamcinolone acetonide (1 mg/100 μl), an interleukin-10 peptide fragment (125 ng/100 μl or 500 ng/100 μl) or mannose-6-phosphate (M6P, 200 mM or 600 mM) was injected into and around the nerve. After 6 weeks the extent of regeneration was assessed electrophysiologically by determining the ratio of the compound action potential (CAP) modulus evoked by electrical stimulation of the nerve 2 mm distal or proximal to the repair site. The conduction velocity of the fastest components in the CAP was also calculated. The percentage area of collagen staining (PAS) at the repair site was analysed using Picrosirius Red and image analysis. Comparisons were made with a placebo group (100 μl of phosphate buffered saline) and sham-operated controls. The median CAP modulus ratio in the 600 mM M6P group was 0.44, which was significantly higher than in the placebo group (0.24, P=0.012: Kruskal-Wallis test). Conduction velocities were also faster in the 600 mM M6P group (median 30 m s(-1)) than in the placebo group (median 27.8 m s(-1); P=0.0197: Kruskal-Wallis test). None of the other treated groups were significantly different from the placebo, and all had significantly lower CAP ratios than the sham controls (P<0.05). All repair groups had a significantly higher PAS for collagen than sham controls. We conclude that the administration of 600 mM mannose-6-phosphate to a nerve repair site enhances axonal regeneration.
[show abstract][hide abstract] ABSTRACT: Activity-induced neuronal plasticity is partly facilitated by the expression of the immediate-early gene c-fos and the resulting transcription factor Fos. Expression of Fos is associated with nociceptive afferent activation, but a detailed stimulation-transcription pathway for Fos expression has not yet been determined in the trigeminal system. This study utilized a novel in vitro model to determine whether Fos expression can be induced in trigeminal subnucleus caudalis by NMDA or neurokinin-1 receptor activation, and whether inhibition of intracellular kinases has any effect on Fos expression induced by activation of these receptors. Brainstems of male Wistar rats were excised and maintained in artificial cerebrospinal fluid at 37°C. NMDA or the specific neurokinin-1 receptor agonist [Sar(9),Met(O(2))(11)]-SP was applied. These agonists were subsequently tested in the presence of the protein kinase A inhibitor Rp-cAMP or protein kinase C inhibitor chelerythrine chloride. In all experiments the sodium channel blocker tetrodotoxin was used to prevent indirect neuronal activation. Brainstems were processed immunocytochemically for Fos expression, and positive cells were counted in the trigeminal subnucleus caudalis. NMDA and [Sar(9),Met(O(2))(11)]-SP significantly increased Fos expression, but these increases could be prevented by chelerythrine chloride. Rp-cAMP had no effect on Fos induced by NMDA but caused a significant reduction in Fos induced by [Sar(9),Met(O(2))(11)]-SP. These data demonstrate that in trigeminal subnucleus caudalis activation of either NK1 or NMDA receptors alone induces Fos expression; protein kinases A and C are involved in NK1R-induced Fos while protein kinase A is not required for NMDA receptor-induced Fos.
Brain research 10/2010; 1368:19-27. · 2.46 Impact Factor
[show abstract][hide abstract] ABSTRACT: The TRPA1 receptor is a member of the ankyrin family and is found in both spinal and trigeminal neurones. There is evidence to suggest that this receptor may be a sensor of noxious thermal stimuli in normal animals. After nerve injury, TRPA1 shows increased expression in uninjured axons, and has been implicated in the development and maintenance of hyperalgesia. We examined expression of TRPA1 in lingual nerve neuromas and investigated any potential correlation with the presence or absence of symptoms of dysaesthesia. Thirteen neuroma-in-continuity specimens were obtained from patients undergoing repair of a lingual nerve that had previously been damaged during lower third molar removal. Visual analogue scales (VAS) were used to record the degree of pain, tingling and discomfort. Tissue was processed for indirect immunofluorescence and the percentage area of PGP 9.5-immunoreactive neuronal tissue also labelled for TRPA1 was quantified. No significant difference between levels of TRPA1 in neuromas from patients with or without symptoms of dysaesthesia and no relationship between TRPA1 expression and VAS scores for pain, tingling or discomfort were observed. TRPA1 expression and the time after initial injury that the specimen was obtained also showed no correlation. These data show that TRPA1 is expressed in lingual nerve neuromas, but, it appears that, at this site, TRPA1 does not play a principal role in the development of neuropathic pain.
[show abstract][hide abstract] ABSTRACT: Recent evidence suggests that the purinoceptor P2X7 may be involved in the development of dysesthesia following nerve injury, therefore, the aim of the present study was to investigate whether a correlation exists between the level of P2X7 receptor expression in damaged human lingual nerves and the severity of the patients' symptoms.
Neuroma-in-continuity specimens were obtained from patients undergoing surgical repair of the damaged lingual nerve. Specimens were categorized preoperatively according to the presence or absence of dysesthesia, and visual analog scales scores were used to record the degree of pain, tingling, and discomfort. Indirect immunofluorescence using antibodies raised against S-100 (a Schwann cell marker) and P2X7 was employed to quantify the percentage area of S-100 positive cells that also expressed P2X7.
P2X7 was found to be expressed in Schwann cells of lingual nerve neuromas. No significant difference was found between the level of P2X7 expression in patients with or without symptoms of dysesthesia, and no relationship was observed between P2X7 expression and VAS scores for pain, tingling, or discomfort. No correlation was found between P2X7 expression and the time between initial injury and nerve repair.
These data show that P2X7 is expressed in human lingual nerve neuromas from patients with and without dysesthesia. It therefore appears that the level of P2X7 expression at the injury site may not be linked to the maintenance of neuropathic pain after lingual nerve injury.
Journal of orofacial pain 02/2009; 23(1):65-72. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: To investigate the presence of proteinase-activated receptor 2 (PAR2) in the human tooth pulp and to determine whether there are any changes in receptor expression with caries and pain.
Forty-four mandibular first permanent molars were collected from children (n = 36, mean age 9.96 years +/- 2.11) requiring dental extractions under general anesthesia. Teeth were categorized as either intact (n = 22) or carious (n = 22). Carious teeth were further subdivided into asymptomatic (n = 10) and painful (n = 12). The coronal pulp was removed and processed for indirect immunofluorescence by using antibodies raised against PAR2 and double labeled with either a neuronal marker (protein gene product 9.5) or both a smooth muscle cell (aSMA) and endothelial (UEIL) marker, in order to examine PAR2 presence in both neuronal and vascular tissue. In addition, hemotoxylin and eosin staining was performed to identify pulpal fibroblasts.
PAR2 expression was found to be present in pulpal nerve fibers, vascular tissue, and pulpal fibroblasts. PAR2 neuronal expression was not affected by the presence of caries (P > .05) but was significantly less in carious painful teeth than in carious asymptomatic teeth (P < .05). No changes in vascular PAR2 expression were found (P > .05); however, the number of PAR2-labeled fibroblast-like cells per mm2 was significantly greater in carious teeth (P < .05).
These findings indicate that PAR2 receptors and changes in their level of expression may have relevance and clinical importance in nociception.
Journal of orofacial pain 01/2009; 23(3):265-74. · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: Abnormal neural activity generated at a site of nerve injury is thought to contribute to the development of dysaesthesia. Vanilloid receptor 1 (TRPV1), a transducer of noxious stimuli, may be involved in the initiation of this abnormal activity and could provide a useful therapeutic target. We investigated the effect of a specific TRPV1 antagonist (SB-750364) on injury-induced discharge in the lingual nerve. In 12 anaesthetised adult ferrets the left lingual nerve was sectioned and animals were allowed to recover for 3-7 days. In terminal experiments under general anaesthesia, the nerve was re-exposed and electrophysiological recordings made from spontaneously active axons in fine filaments dissected from the nerve central to both the injury site and the junction with the chorda tympani. SB-750364 was infused via the cephalic vein in order to achieve three increasing but stable systemic blood levels of the compound (0.3, 1.0 and 3.0 microM). Twenty-eight spontaneously active units were studied, with discharge frequencies ranging from 0.02 to 4.9 Hz. There was a significant reduction in spontaneous activity in 17 units (61%) at 1.0 microM or less of SB-750364 (p<0.01; Friedman test with Dunn's multiple comparisons). A further 4 units (14%) showed a significant reduction in activity at 3.0 microM (p<0.01). In the remaining 7 units (25%) the discharge was unaffected (p>0.05). These data show that the TRPV1 antagonist SB-750364 can reduce the level of spontaneous activity initiated in some axons following lingual nerve injury.
[show abstract][hide abstract] ABSTRACT: We have investigated a possible role for the ATP receptor subunit P2X(3), in the development of neuropathic pain following injury to a peripheral branch of the trigeminal nerve. In nine anaesthetised adult ferrets the left lingual nerve was sectioned and recovery permitted for 3 days, 3 weeks or 3 months (3 ferrets per group). A retrograde tracer, fluorogold, was applied to the nerve to allow identification of cell bodies in the trigeminal ganglion with axons in the injured nerve. Indirect immunofluorescence for P2X(3) and image analysis was used to quantify the percentage area of staining at the site of injury. Additionally, the proportion of fluorogold-positive cells that expressed P2X(3) was determined and compared with expression in non-fluorogold containing cells in another part of the ganglion. Comparisons were made with results from control animals that only received the tracer injection. After lingual nerve injury there was no significant change in P2X(3) expression at the site of nerve injury or within cell bodies linked to either injured (lingual) or uninjured (ophthalmic) axons, at any of the time periods investigated. Overall, this study suggests that P2X(3) expression at these sites is not involved in the development of neuropathic pain following lingual nerve injury.
[show abstract][hide abstract] ABSTRACT: We have developed a model to study central changes following inflammation of the tooth pulp in the ferret and have examined Fos expression in the trigeminal nucleus following stimulation of non-inflamed and inflamed tooth pulps. The aim of this study was to establish the ability of this model to predict analgesic efficacy in clinical studies of inflammatory pain. We addressed this by assessing the effects of the neurokinin-1 receptor antagonist GR205171A and ibuprofen on Fos expression following stimulation of the inflamed pulp and comparing this with known analgesic efficacy. Adult ferrets were prepared under anaesthesia to allow tooth pulp stimulation, recording from the digastric muscle and intravenous injections at a subsequent experiment. In some animals pulpal inflammation was induced, by introducing human caries into a deep buccal cavity. After 5 days, animals were reanaesthetised, treated with vehicle, GR205171A or ibuprofen and the teeth were stimulated at ten times the threshold of the jaw-opening reflex. Stimulation of all tooth pulps induced ipsilateral Fos in trigeminal subnuclei caudalis and oralis. GR205171A had no significant effect on Fos expression in the trigeminal nucleus of animals with either non-inflamed or inflamed tooth pulps. Ibuprofen reduced Fos expression in the trigeminal nucleus and this effect was most marked in animals with pulpal inflammation. These results differ from those previously described using a range of other animal models, but agree with known clinical efficacy of neurokinin-1 receptor antagonists and ibuprofen. Therefore this model is likely to be of use in accurately predicting the analgesic efficacy of novel compounds.
European journal of pain (London, England) 05/2008; 12(3):385-94. · 3.37 Impact Factor
[show abstract][hide abstract] ABSTRACT: This was to compare the pulpal expression of the transient receptor potential ion channel (TRPV1), a noxious heat receptor, in sound and hypomineralised human first permanent molars. The rationale for the investigation was to gain further insight into pulpal changes in hypomineralised teeth and the possible biological mechanisms underlying thermal hypersensitivity.
This was a laboratory study using a quantitative immuncocytochemical approach.
The experimental material comprised 17 sound and 18 hypomineralised molars (10 with intact enamel and 8 with enamel loss), obtained from children requiring dental extractions under general anaesthesia. Coronal pulps were removed and processed for indirect immunofluorescence using antibodies raised against TRPV1 and either the general neuronal marker, protein gene-product 9.5 or alpha smooth muscle actin in conjunction with Ulex europaeus agglutinin 1 lectin to fully label the pulp vasculature. Computerised image analysis was used to quantify the expression of TRPV1 in both pulpal nerves and blood vessels within different regions of the pulp including the pulp horn, subodontoblastic plexus and mid-coronal region.
Mean neuronal and vascular TRPV1 expression was significantly greater in some pulpal regions of hypomineralised teeth (both with and without enamel loss) than for sound samples (p<0.05, ANOVA).
Increased TRPV1 expression within the pulps of hypomineralised teeth may be indicative of an underlying pulpal inflammation and may help to explain the heat sensitivity experienced by some patients with this condition. However, future lines of enquiry should seek to correlate patient symptoms and responses to controlled hot and cold stimuli with pulpal expression of a variety of thermal receptors to gain further insight into dental pain mechanisms.
European Archives of Paediatric Dentistry. Official Journal of the European Academy of Paediatric Dentistry. 01/2008; 8(4):184-8.