Risdiplam improves subjective swallowing quality in non-ambulatory adult patients with 5q-spinal muscular atrophy despite advanced motor impairment.

BACKGROUND: 5q-associated spinal muscular atrophy (SMA) is characterized by the progressive loss of motor neurons with consecutive weakness and atrophy of the limb, respiratory, and bulbar muscles. While trunk and limb motor function improve or stabilize in adults with SMA under nusinersen and risdiplam treatment, the efficacy on bulbar function in this age group of patients remains uncertain. However, it is important to assess bulbar dysfunction, which frequently occurs in the disease course and is associated with increased morbidity and mortality. METHODS: Bulbar function was evaluated prospectively in 25 non-ambulatory adults with type 2 and 3 SMA before and 4 and 12 months after risdiplam treatment initiation using the Sydney Swallow Questionnaire (SSQ) and the bulbar subscore of the Amyotrophic Lateral Sclerosis Functional Rating Scale Revised (b-ALSFRS-R). Extremity function was assessed using the Hammersmith Functional Motor Scale Expanded (HFMSE) and Revised Upper Limb Module (RULM). RESULTS: Subjective swallowing quality, measured with the SSQ, improved after 12 months of therapy with risdiplam. For the b-ALSFRS-R, a non-significant trend towards improvement was observed. The RULM score improved after 12 months of risdiplam therapy, but not the HFMSE score. HFMSE and RULM scores did not correlate with the SSQ but the b-ALSFRS-R score at baseline. CONCLUSIONS: The improvement in subjective swallowing quality under risdiplam treatment, despite an advanced disease stage with severe motor deficits, strengthens the importance of a standardized bulbar assessment in addition to established motor scores. This may reveal relevant treatment effects and help individualize treatment decisions in the future.

Biomarkers in 5q-associated spinal muscular atrophy-a narrative review.

5q-associated spinal muscular atrophy (SMA) is a rare genetic disease caused by mutations in the SMN1 gene, resulting in a loss of functional SMN protein and consecutive degeneration of motor neurons in the ventral horn. The disease is clinically characterized by proximal paralysis and secondary skeletal muscle atrophy. New disease-modifying drugs driving SMN gene expression have been developed in the past decade and have revolutionized SMA treatment. The rise of treatment options led to a concomitant need of biomarkers for therapeutic guidance and an improved disease monitoring. Intensive efforts have been undertaken to develop suitable markers, and numerous candidate biomarkers for diagnostic, prognostic, and predictive values have been identified. The most promising markers include appliance-based measures such as electrophysiological and imaging-based indices as well as molecular markers including SMN-related proteins and markers of neurodegeneration and skeletal muscle integrity. However, none of the proposed biomarkers have been validated for the clinical routine yet. In this narrative review, we discuss the most promising candidate biomarkers for SMA and expand the discussion by addressing the largely unfolded potential of muscle integrity markers, especially in the context of upcoming muscle-targeting therapies. While the discussed candidate biomarkers hold potential as either diagnostic (e.g., SMN-related biomarkers), prognostic (e.g., markers of neurodegeneration, imaging-based markers), predictive (e.g., electrophysiological markers) or response markers (e.g., muscle integrity markers), no single measure seems to be suitable to cover all biomarker categories. Hence, a combination of different biomarkers and clinical assessments appears to be the most expedient solution at the time.

Objective measurement of oral function in adults with spinal muscular atrophy.

BACKGROUND: Impairment of bulbar function in adult individuals with spinal muscular atrophy (SMA) usually is not assessed by established motor scores. Measurements of oral function including quantitative muscle and endurance tests are able to detect subtle changes. The aim of this study was to systematically evaluate the measurement of maximum bite force and endurance, maximum tongue pressure and endurance, as well as maximum mouth opening in adult individuals with SMA types 2 and 3. METHODS: Data from oral function tests in 43 individuals were analyzed. Differences in oral function between individuals with different SMA types and numbers of SMN2 copies were tested. Spearman´s rho correlations among oral function measures themselves as well as with established clinical outcome scales were analyzed. RESULTS: The absolute maximum measures of oral function (maximum bite force, maximum tongue pressure, maximum mouth opening) were able to discriminate between individuals with different SMA types, individuals with a different number of SMN2 copies and with different walking abilities. The pairwise correlations of the absolute maximum measures of oral function were fair to moderate in size; the same was true for their correlations with the established motor scores. All correlations assessing endurance measures of oral function were weaker and statistically insignificant. CONCLUSIONS: Among the oral function tests maximum tongue pressure and maximum mouth opening are particulary promising as clinical and sensitive outcome measures for clinical trials. Oral function tests may supplement existing motor scores, in particular concerning specific questions about bulbar function or in severely affected non-ambulatory individuals where mild (treatment-related) changes would otherwise remain undetected. Trial registration DRKS, DRKS00015842. Registered 30 July 2019, https://drks.de/search/de/trial/DRKS00015842.

[Gene-based treatment in spinal muscular atrophy]. / Genetisch basierte Therapien bei spinaler Muskelatrophie.

BACKGROUND: The 5q-associated spinal muscular atrophy (SMA) affects ~ 80-120 newborns annually. The disease is characterized by progressive paresis involving the bulbar and respiratory musculatures. The phenotypes are very heterogeneous ranging from severe courses with early death in the first years of life to loss of gait in older age. OBJECTIVE: There are now an increasing number of causally targeted therapies available that can either directly interfere with the transcription of the gene causing the disease or replace the homozygous loss of the SMN1 gene. This work aims to elucidate the current state of therapy in different groups of patients with SMA. MATERIAL AND METHODS: Presentation of clinical trials and basic studies with a focus on patients with disease onset in adulthood. RESULTS: The clinical studies all show improvement or stabilization of motor function; however, in individual cases, the burden of the therapy for severely immobilized patients must be considered in addition to the efficacy in the treatment decision. Even if the drugs show a good safety profile, observations on the long-term efficacy and safety of the new substance classes are still lacking. CONCLUSION: The study landscape shows a good efficacy of the currently approved therapies across all degrees of severity and age groups. Due to the lack of comparative studies, the decision on the appropriate therapy should therefore be made according to an individual risk-benefit assessment.

Minimal clinically important differences in functional motor scores in adults with spinal muscular atrophy.

BACKGROUND AND PURPOSE: In patients with spinal muscular atrophy (SMA), functional disease scores are frequently used to evaluate the course of the disease and the efficacy of treatment. The aim of the present study was to propose minimal clinically important difference (MCID) values for motor scores in order to estimate the degree of change within a functional score that can be considered clinically meaningful. METHODS: To estimate the MCID, distribution-based approaches were used. For each assessment [Revised Upper Limb Module (RULM), Hammersmith Functional Motor Scale Expanded (HFMSE) and 6-min walk test (6MWT)] and subgroup (SMA type 2, SMA type 3, ambulatory and non-ambulatory), the following MCID values based on a cohort of 51 adults with SMA were calculated: standard error of measurement (SEm), one-half of standard deviation (1/2 SD) and one-third of standard deviation (1/3 SD) of patients' baseline scores. RESULTS: For the overall cohort, the SEm, 1/2 SD and 1/3 SD MCID values were 2.9, 6.4 and 4.3 for the RULM and 4.3, 10.6 and 7.0 for the HFMSE, respectively. Subgroup analysis led to generally lower standard deviations and consecutively lower MCID values due to the significantly different motor functions of the groups. The respective MCID values for the 6MWT were 55.5 m, 71.1 m and 47.8 m. CONCLUSIONS: Our data provide MCID values for functional motor scores commonly used in adults with SMA in order to distinguish statistical effects from 'real' changes. A complementary systematic consensus process could help to further adjust the MCID values we propose.

Measuring Outcomes in Adults with Spinal Muscular Atrophy - Challenges and Future Directions - Meeting Report.

Spinal muscular atrophy (SMA) is a progressive autosomal recessive motor neuron disease which affects 1 in 6,000-10,000 live births, caused by loss of the survival motor neuron 1 gene (SMN1). A major focus of therapeutic developments has been on increasing the full-length SMN protein by increasing the inclusion of exon 7 in SMN2 transcripts, enhancing SMN2 gene expression, stabilizing the SMN protein or replacing the SMN1 gene.In June 2017, FDA and EMA have approved the antisense oligonucleotide Nusinersen as the first treatment for all SMA subtypes without age restriction. While prominent treatment effects have been observed in the earlier stages of the disease and in patients up to 15 years of age, there is only limited data from clinical trials in adult SMA patients. First real-world data from neuromuscular clinical centers suggest a therapeutic benefit of nusinersen with a favourable safety profile also in adult SMA patients: in several cases, relevant improvements of motor function is achieved, which might lead to enhanced autonomy in daily life activities and improved quality of life. Systematic follow-up of the motor status with validated instruments is crucial for an adequate monitoring of the therapeutic effects but most of the widely used scales and scores have been developed and evaluated for the pediatric population only. International neuromuscular experts have met in Frankfurt/Main, Germany in May 2019 to discuss relevant aspects of the diagnostic pathway and patient management in adult SMA. The recommendations and challenges in this patient population are discussed.

Radiation exposure of image-guided intrathecal administration of nusinersen to adult patients with spinal muscular atrophy.

PURPOSE: To examine diagnostic reference levels (DRL) and achievable doses (AD) of image-guided and size-specific dose estimates (SSDE) and organ and effective doses of CT-guided intrathecal nusinersen administration to adult patients with spinal muscular atrophy (SMA). METHODS: This study involved a total of 60 image-guided intrathecal nusinersen treatments between August 2017 and June 2018. Patient cohort comprised 14 adult patients with the following SMA types: type 2 (n = 9) and type 3 (n = 5) with a mean age of 33.6 years (age range 25-57 years). DRL, AD, SSDE, organ, and effective doses were assessed with a dose-monitoring program based on the Monte Carlo simulation techniques. RESULTS: DRL and AD for computed tomography are summarised as follows: in terms of CT-dose index (CTDIvol), DRL 56.4 mGy and AD 36.7 mGy; in terms of dose-length product (DLP), DRL 233.1 mGy cm and AD 120.1 mGy cm. DRL and AD for fluoroscopic guidance were distributed as follows: in terms of dose-area product (DAP), DRL 239.1 µGy m2 and AD 135.2 mGy cm2. Mean SSDE was 9.2 mGy. Mean effective dose of the CT-guided injections was 2.5 mSv (median 2.0 mSv, IQR 1.3-3.2 mSv). Highest organ doses in the primary beam of radiation were the small intestine 12.9 mSv, large intestine 9.5 mSv, and ovaries 3.6 mSv. CONCLUSION: Radiation exposure of SMA patients measured as DRLs is generally not higher compared with patients without SMA despite severe anatomical hazards. Dose monitoring data may allow clinicians to stratify radiation risk, identify organs at risk, and adopt measures for specific radiation dose reduction.

Intrathecal Resiniferatoxin Modulates TRPV1 in DRG Neurons and Reduces TNF-Induced Pain-Related Behavior.

Transient receptor potential vanilloid-1 (TRPV1) is a nonselective cation channel, predominantly expressed in sensory neurons. TRPV1 is known to play an important role in the pathogenesis of inflammatory and neuropathic pain states. Previous studies suggest interactions between tumor necrosis factor- (TNF-) alpha and TRPV1, resulting in a modulation of ion channel function and protein expression in sensory neurons. We examined the effect of intrathecal administration of the ultrapotent TRPV1 agonist resiniferatoxin (RTX) on TNF-induced pain-associated behavior of rats using von Frey and hot plate behavioral testing. Intrathecal injection of TNF induces mechanical allodynia (2 and 20 ng/kg) and thermal hyperalgesia (200 ng) 24 h after administration. The additional intrathecal administration of RTX (1.9 µg/kg) alleviates TNF-induced mechanical allodynia and thermal hyperalgesia 24 h after injection. In addition, TNF increases the TRPV1 protein level and number of TRPV1-expressing neurons. Both effects could be abolished by the administration of RTX. These results suggest that the involvement of TRPV1 in TNF-induced pain offers new TRPV1-based experimental therapeutic approaches and demonstrates the analgesic potential of RTX in inflammatory pain diseases.

Early platelet and leukocyte decline in patients with neuroinflammatory disorders after intravenous immunoglobulins.

BACKGROUND AND PURPOSE: Intravenous immunoglobulins (IVIGs) are a common therapy in patients with neuroinflammatory disorders, especially chronic inflammatory demyelinating polyradiculoneuropathy or Guillain-Barré syndrome. Hematological toxicities upon IVIG infusion are a known side effect and still an important subject of investigation. METHODS: Laboratory results and data for clinical efficacy and tolerability of 62 patients with neuroinflammatory disorders treated with IVIG (0.4 g/kg bodyweight per day over 5 days) at the Department of Neurology, University of Duisburg-Essen, Germany, were retrospectively analyzed. Blood samples were taken before and 1 day after IVIG administration. RESULTS: In pre-treated and first-time treated patients, there was a significant decrease in white blood cell count (WBC) (8.10 ± 2.85/nl to 5.61 ± 2.50/nl, P < 0.001, n = 57) and platelets (255 ± 72/nl to 215 ± 66/nl, P < 0.001, n = 57). Mild hemolysis of red blood cells was found in patients who received IVIG for the first time (red blood cell count 4.61 ± 0.67/pl to 4.28 ± 0.52/pl, hemoglobin 13.7 ± 1.7 g/l to 13.0 ± 1.7 g/l, P < 0.001, n = 40). Hemolysis was associated with less tolerability of IVIG treatment and clinical efficacy was accompanied with a higher decline of WBC (not significant). CONCLUSIONS: Next to mild hemolysis, a significant decrease in WBC and platelets can be detected early after high dose IVIGs in patients with neuroinflammatory disorders. Changes in blood counts may be possible markers for clinical efficacy and tolerability. Patients with low blood counts in advance should be particularly closely monitored whilst on IVIG treatment.

Modulation of Voltage-Gated Sodium Channels by Activation of Tumor Necrosis Factor Receptor-1 and Receptor-2 in Small DRG Neurons of Rats.

Tumor necrosis factor- (TNF-) α is a proinflammatory cytokine involved in the development and maintenance of inflammatory and neuropathic pain. Its effects are mediated by two receptors, TNF receptor-1 (TNFR-1) and TNF receptor-2 (TNFR-2). These receptors play a crucial role in the sensitization of voltage-gated sodium channels (VGSCs), a key mechanism in the pathogenesis of chronic pain. Using the whole-cell patch-clamp technique, we examined the influence of TNFR-1 and TNFR-2 on VGSCs and TTX-resistant NaV1.8 channels in isolated rat dorsal root ganglion neurons by using selective TNFR agonists. The TNFR-1 agonist R32W (10 pg/mL) caused an increase in the VGSC current (I(Na(V))) by 27.2 ± 5.1%, while the TNFR-2 agonist D145 (10 pg/mL) increased the current by 44.9 ± 2.6%. This effect was dose dependent. Treating isolated NaV1.8 with R32W (100 pg/mL) resulted in an increase in I(NaV(1.8)) by 18.9 ± 1.6%, while treatment with D145 (100 pg/mL) increased the current by 14.5 ± 3.7%. Based on the current-voltage relationship, 10 pg of R32W or D145 led to an increase in I(Na(V)) in a bell-shaped, voltage-dependent manner with a maximum effect at -30 mV. The effects of TNFR activation on VGSCs promote excitation in primary afferent neurons and this might explain the sensitization mechanisms associated with neuropathic and inflammatory pain.

Icilin reduces voltage-gated calcium channel currents in naïve and injured DRG neurons in the rat spinal nerve ligation model.

Recently, the transient receptor potential (TRP) channels TRPM8 and TRPA1 have been identified as molecular sensors for cold, and it has been suggested that they play a crucial role in allodynia by modulating voltage-gated calcium channel currents (ICa(V)). The aim of this study was to analyze the modulation of ICa(V) by the TRPM8-agonist icilin in vitro and to investigate the analgesic effect of icilin in a neuropathic pain model in vivo. Whole cell patch-clamp recordings were performed on isolated naïve and injured rat dorsal root ganglia (DRG) neurons, and the analgesic efficacy of icilin applied topically to the paws or intrathecally was tested in rats after spinal nerve ligation (SNL). ICa(V) (depolarization from -80 to 0mV) in naïve DRG neurons was reduced dose dependently (0.002-200µM) by icilin (18-80%). Subtype isolation of calcium channels show a marked reduction of L-type channel currents compared to N-type channel currents. The effects of icilin on ICa(V) were not significantly different in non-injured and SNL-injured DRG neurons. In vivo, neither topical (10-200µM) nor intrathecal application of icilin (0.1nM to 1µM) affected tactile allodynia or thermal hyperalgesia after SNL, but it increases cold allodynia 6h after application. We conclude that the icilin-induced modulation of ICa(V) in DRG neurons is unlikely to mediate analgesic effects or contribute directly to the pathogenesis of cold allodynia in the rat SNL model, but it is a potential mechanism for the analgesic effects of icilin in other pain models.

Analgesic ineffectiveness of lacosamide after spinal nerve ligation and its sodium channel activity in injured neurons.

BACKGROUND: Lacosamide is a novel anti-epileptic drug that enhances the slow- and not fast-inactivating state of voltage-gated sodium channels. Lacosamide has demonstrated analgesic efficacy in several animal studies but preclinical studies on neuropathic pain models are rare, and recent clinical trials showed no superior analgesic effects. METHODS: Here, we examine whether an acute or chronic administration of lacosamide (3-60 mg/kg, i.p.) attenuates pain behaviour induced by spinal nerve ligation (SNL). To validate the inhibitory efficacy of lacosamide on voltage-gated sodium channels, sodium currents in naïve and SNL-injured dorsal root ganglion (DRG) neurons were recorded using whole-cell patch clamping. RESULTS: Lacosamide only marginally attenuated thermal hyperalgesia, but not tactile allodynia when applied once 7 or 14 days after SNL and showed no analgesic effect when applied daily for 19 days. In naïve neurons, 100 µmol/L lacosamide inhibited sodium channel currents by 58% and enhanced the slow inactivation (87% for lacosamide vs. 47% for control). In contrast, lacosamide inhibited sodium currents in injured DRG neurons by only 15%, while the effects on slow inactivation were diminished. Isolated currents from the NaV 1.8 channel subtype were only marginally changed by lacosamide. CONCLUSION: The reduced effectiveness of lacosamide on voltage-gated sodium channel currents in injured DRG neurons may contribute to the reduced analgesic effect observed for the SNL model.

Additive inhibitory effects of calcitonin and capsaicin on voltage activated calcium channel currents in nociceptive neurones of rat.

Calcitonin, a peptide hormone expressed in C-cells of the thyreoid gland, as well as capsaicin, isolated from chili, both, modify intracellular signalling in nociceptive neurones. The pathways triggered by the activation of either of these receptors results in a modulation of the intracellular calcium ([Ca(2+)](i)) concentration. While the regulation of [Ca(2+)](i) depends on many factors, voltage activated calcium channels (VACCs) are a major gate for the calcium entry into neurones. Here we describe the changes of voltage gated calcium channel currents (I(Ca(V))) induced by calcitonin and/or capsaicin. Currents were recorded using adequate solutions and voltage protocols with the whole cell patch-clamp technique. When the channels were opened by a depolarisation to 0 mV, both substances reduce the peak I(Ca(V)) (calcitonin (10nM): 29.3 ± 3.9%; capsaicin (0.5 µM): 41.1 ± 7.7%). While the effect of calcitonin was voltage dependent, capsaicin shifted the largest current to the more hyperpolarizing range (peak current from -10 to -20 mV). A subsequent co-application of either of the two substances (with a pre-application of either 3 min or 60 min) results in an additive reduction of the currents, and prevents the capsaicin-induced shift of the current-voltage relation. Therefore, we hypothesize, that the activation of either of the two receptors reduces I(Ca(V)) by different cellular binding sites of the channel protein triggering channel opening. These findings may be useful to understand cellular mechanisms of pain modulation and might help to find better treatments for neuropathic pain.

Evoked pain behavior and spinal glia activation is dependent on tumor necrosis factor receptor 1 and 2 in a mouse model of bone cancer pain.

Bone-cancer-related pain is one of the most disabling factors in patients suffering from primary bone cancer or bone metastases. Recent studies point toward an important role of proinflammatory cytokines, example tumor necrosis factor-alpha (TNF), for tumor growth and bone-cancer-associated pain. Mechanisms by which TNF, through its receptor subtypes, TNF receptor 1 (TNFR1) and -2 (TNFR2), elicits altered sensation and pain behavior, are still incompletely understood. To look for a potential role of TNF in bone cancer pain, cancer-related pain was analyzed in fibrosarcoma-bearing C57Bl/6J wild type mice after systemic antagonism of TNF. To further clarify the role of TNF receptor (TNFR) in bone-cancer pain, naive and fibrosarcoma-bearing C57Bl/ 6J wild type and transgenic mice with a deficiency of TNFR1 (TNFR1ko), TNFR2 (TNFR2ko), and TNFR1+2 (TNFR1+2ko) were compared regarding cancer-related pain and hyperalgesia, tumor growth, osteoclast activation, and spinal astrogliosis. Systemic antagonism of TNF significantly alleviated tactile hypersensitivity and spontaneous bone-cancer-related pain behavior. Most interestingly, combined deletion of the TNFR1 and TNFR2, but not of either gene alone, almost completely inhibited the development of tactile hypersensitivity, whereas spontaneous pain behavior was transiently increased. Accordingly, spinal astrogliosis was markedly reduced, whereas tumor growth was significantly increased in TNFR1+2ko mice. In contrast, deletion of the TNFR1 or TNFR2 gene alone did not change tumor growth or spinal astrogliosis. Our findings suggest that the combined absence of TNFR1 and TNFR2 is necessary for the attenuation of cancer-related tactile hypersensitivity and concomitant spinal astrogliosis, whereas tumor growth seems to be inhibited by combined TNFR activation. These findings support the hypothesis of cytokine-dependent pain development in cancer pain. Differential targeting of TNFR activation could be an interesting strategy in bone-cancer-related pain conditions.

A High CSF Signal on FLAIR: It Is Not Always Blood.

We describe a patient with progressive neurologic deficit due to middle cerebral branch occlusion. Temporary partial balloon occlusion of the abdominal aorta led to an increased signal in the subarachnoid space on fluid-attenuated inversion recovery images with no evidence of subarachnoid hemorrhage. After spontaneous recanalization, the increased signal of the subarachnoid space returned to normal. We assume that signal changes in the subarachnoid space were due to a temporary increase in blood volume in the superficial brain vessels.

Sensitization of voltage activated calcium channel currents for capsaicin in nociceptive neurons by tumor-necrosis-factor-alpha.

It is known that application of tumor-necrosis-factor-alpha (TNF-alpha) sensitizes neuronal calcium channels for heat stimuli in rat models of neuropathic pain. This study examines whether TNF-alpha modulates the capsaicin-induced effects after transient receptor potential vanilloid (TRPV)-1 receptor activation on voltage activated calcium channel currents (I(Ca(V))). TRPV-1 receptors are activated by heat and play an important role in the pathogenesis of thermal hyperalgesia in neuropathic pain syndromes, while voltage activated channels are essential for transmission of neuronal signals. Eliciting I(Ca(V)) in DRG neurons of rats by a depolarization from the resting potential to 0 mV, TNF-alpha (100 ng/ml) reduces I(Ca(V)) by 16.9+/-2.2%, while capsaicin (0.1 microM) decreases currents by 27+/-4.3%. Pre-application of TNF-alpha (100 ng/ml) for 24h results in a sensitization of I(Ca(V)) to capsaicin (0.1 microM) with a reduction of 42.8+/-4.4% mediated by TRPV-1. While L-type (36.6+/-5.2%) and P/Q-type currents (35.6+/-4.1%) are also sensitized by TRPV-1 activation, N-type channel currents are most sensitive (74.5+/-7.3%). The capsaicin-induced shift towards the hyperpolarizing voltage range does not occur when TNF-alpha is applied. Summarizing, TNF-alpha sensitizes nociceptive neurons for capsaicin.

Selective stimulation of either tumor necrosis factor receptor differentially induces pain behavior in vivo and ectopic activity in sensory neurons in vitro.

Recent studies suggest that tumor necrosis factor-alpha (TNF) sensitizes primary afferent neurons, and thus facilitates neuropathic pain. Here, we separately examined the roles of tumor necrosis factor receptor (TNFR) 1 and 2 by parallel in vivo and in vitro paradigms using proteins that selectively activate TNFR1 or TNFR2 (R1 and R2). In vivo, intrathecally injected R1, but not R2 slightly reduced mechanical and thermal withdrawal thresholds in rats, whereas co-injection resulted in robust, at least additive pain-associated behavior. In vitro, the electrophysiological responses of dorsal root ganglia (DRG) from rats with spinal nerve ligation were measured utilizing single-fiber recordings of teased dorsal root filaments. In naïve DRG, only R1 (10-1000 pg/ml) induced firing in Ass- and Adelta-fibers, whereas R2 had no effect. In injured DRG, both R1 and R2 at significantly lower concentrations (1 pg/ml) increased discharge rates of Adelta-fibers. Most interesting, in adjacent uninjured DRG, R2 and not R1, increased ectopic activity in both Ass- and Adelta-fibers. We conclude that TNFR1 may be predominantly involved in the excitation of sensory neurons and induction of pain behavior in the absence of nerve injury, TNFR2 may contribute in the presence of TNFR1 activation. Importantly, the effects of individually applied R1 and R2 on injured and adjacent uninjured fibers imply that the role of TNFR2 in the excitation of sensory neurons increases after injury.

Feedback mechanisms in the regulation of intracellular calcium ([Ca2+]i) in the peripheral nociceptive system: role of TRPV-1 and pain related receptors.

Multimodal stimuli like heat, cold, bacterial or mechanical events are able to elicit pain, which is necessary to guarantee survival. However, the control of pain is of major clinical importance. The perception and transduction of pain is differentially modulated in the peripheral and central nervous system (CNS): while peripheral structures modulate these signals, the perception of pain occurs in the CNS. In recent years major advances have been made in the understanding of the processes which are involved in pain sensation. For the peripheral pain reception, the importance of specific pain receptors of the transition receptor pore (TRP)-family (e.g. the TRPV-1 receptor) has been analyzed. These receptors/channels are localized at the cell membrane of nociceptive neurones as well as in membranes of intracellular calcium stores like the endoplasmic reticulum. While the associated channel conducts different ions, a major proportion is calcium. Therefore, this review focuses on (1) the modulations of intracellular calcium ([Ca2+]i) initiated by the activation of pain receptors and (2) the consequences of [Ca2+]i changes for the processing of pain signals at the peripheral side. The possible interference of TRPV-1 induced [Ca2+]i modulations to the function of other membrane receptors and channels, like voltage gated calcium, sodium or potassium channels, or co-expressed CB1-receptors will be discussed. The latter interactions are of specific interest since the analgetic properties of endo- and exo-cannabinoids are mediated by CB1 receptors and their activation significantly modulates the calcium induced release of pain related transmitters. Furthermore, multiple cross links between different pain modulating intracellular pathways and their dependence on [Ca2+]i modulations will be illuminated. Overall, this review will summarize new insights resulting in the understanding of the prominent influence of [Ca2+]i for processes which are involved in pain sensation.