Nicholas Jones

A Gain-of-Function Mutation in TRPA1 Causes Familial Episodic Pain Syndrome

Summary Human monogenic pain syndromes have provided important insights into the molecular mechanisms that underlie normal and pathological pain states. We describe an autosomal-dominant familial episodic pain syndrome characterized by episodes of debilitating upper body pain, triggered by fasting and physical stress. Linkage and haplotype analysis mapped this phenotype to a 25 cM region on chromosome 8q12–8q13. Candidate gene sequencing identified a point mutation (N855S) in the S4 transmembrane segment of TRPA1, a key sensor for environmental irritants. The mutant channel showed a normal pharmacological profile but altered biophysical properties, with a 5-fold increase in inward current on activation at normal resting potentials. Quantitative sensory testing demonstrated normal baseline sensory thresholds but an enhanced secondary hyperalgesia to punctate stimuli on treatment with mustard oil. TRPA1 antagonists inhibit the mutant channel, promising a useful therapy for this disorder. Our findings provide evidence that variation in the TRPA1 gene can alter pain perception in humans. Video Abstract

Acid-induced pain and its modulation in humans.

Despite the discovery of ion channels that are activated by protons, we still know relatively little about the signaling of acid pain. We used a novel technique, iontophoresis of protons, to investigate acid-induced pain in human volunteers. We found that transdermal iontophoresis of protons consistently caused moderate pain that was dose-dependent. A marked desensitization occurred with persistent stimulation, with a time constant of ∼3 min. Recovery from desensitization occurred slowly, over many hours. Acid-induced pain was significantly augmented in skin sensitized by acute topical application of capsaicin. However, skin desensitized by repeated capsaicin application showed no significant reduction in acid-induced pain, suggesting that both capsaicin-sensitive and insensitive sensory neurons contribute to acid pain. Furthermore, topical application of non-steroidal anti-inflammatory drugs (NSAIDs) significantly attenuated acid-evoked pain but did not affect the heat pain threshold, suggesting a specific interaction between NSAIDs and peripheral acid sensors. Subcutaneous injection of amiloride (1 mm) also significantly inhibited the pain induced by iontophoresis of acid, suggesting an involvement of acid-sensing ion channel (ASIC) receptors. Conversely, iontophoresis of acid over a wide range of skin temperatures from 4 to 40°C produced only minor changes in the induced pain. Together these data suggest a prominent role for ASIC channels and only a minor role for transient receptor potential vanilloid receptor-1 as mediators of cutaneous acid-induced pain.

Modulation of acid-sensing ion channel activity by nitric oxide.

Acid-sensing ion channels (ASICs) are a class of ion channels activated by extracellular protons and are believed to mediate the pain caused by tissue acidosis. Although ASICs have been widely studied, little is known about their regulation by inflammatory mediators. Here, we provide evidence that nitric oxide (NO) potentiates the activity of ASICs. Whole-cell patch-clamp recordings were performed on neonatal rat cultured dorsal root ganglion neurons and on ASIC isoforms expressed in CHO cells. The NO donor S-nitroso-N-acetylpenicillamine (SNAP) potentiates proton-gated currents in DRG neurons and proton-gated currents in CHO cells expressing each of the acid-sensitive ASIC subunits. Modulators of the cGMP/PKG pathway had no effect on the potentiation, but in excised patches from CHO cells expressing ASIC2a, the potentiation could be reversed by externally applied reducing agents. NO therefore has a direct external effect on the ASIC ion channel, probably through oxidization of cysteine residues. Complementary psychophysiological studies were performed using iontophoresis of acidic solutions through the skin of human volunteers. Topical application of the NO donor glyceryl trinitrate significantly increased acid-evoked pain but did not affect heat or mechanical pain thresholds. ASICs may therefore play an important role in the pain associated with metabolic stress and inflammation, where both tissue acidosis and a high level of NO are present.

Mapping the central effects of ketamine in the rat using pharmacological MRI

RationaleKetamine induces, in both humans and rodents, behaviours analogous to some of the symptoms of schizophrenia.ObjectivesTo utilise pharmacological magnetic resonance imaging (phMRI) techniques that identify changes in blood-oxygenation-level-dependent (BOLD) contrast to determine the temporal and spatial neuronal activation profile of ketamine in the rat brain.MethodTo obtain a pharmacodynamic profile of the drug, we assessed changes in locomotor activity after vehicle and 10 and 25xa0mg/kg ketamine. Separate animals were then anaesthetised and placed in a 4.7-T magnetic resonance (MR) system before receiving the same doses of ketamine during serial MR image acquisition. Subsequent statistical parametric mapping of the main effect of the drug was then undertaken to identify changes in BOLD contrast. Levels of γ-aminobutyric acid (GABA) and dopamine (DA) in brain areas showing localised changes in BOLD contrast were then assessed via microdialysis.ResultsBoth doses of ketamine produced increases in BOLD image contrast in frontal, hippocampal, cortical and limbic areas. A further investigation of the release of DA and its metabolites in the nucleus accumbens, both in anaesthesised and freely moving rats, corroborated these findings. However, an investigation of GABA and DA levels in the ventral pallidum gave no indication of changes in activity.ConclusionsKetamine produced localised dose-dependent alterations in BOLD MR signal, which correlate with the pharmacodynamic profile of the drug. These results can be, at least, partially substantiated with complementary techniques but consideration must be given to the input function applied to the MR signal and the use of anaesthesia during phMRI experimentation.

Identification and quantification of phosphodiesterase 4 subtypes in CD4 and CD8 lymphocytes from healthy and asthmatic subjects

In the present study, for the first time, PDE4 subtypes were identified and semi‐quantified in both CD4 and CD8 lymphocytes from healthy and asthmatic individuals. CD4 and CD8 lymphocytes from healthy and mild asymptomatic asthmatic subjects (receiving β‐agonist therapy only) were isolated from peripheral venous blood using appropriate antibody coated paramagnetic beads. PDE4 subtypes and β‐actin were identified by digoxigenin (DIG)‐labelling reverse transcriptase‐polymerase chain reaction and semi‐quantified by DIG‐detection enzyme‐linked immunosorbance assay. In CD4 and CD8 lymphocytes PDE4A, PDE4B and PDE4D were detected, with no significant differences observed between healthy and asthmatic groups. In CD8 lymphocytes, enzyme subtype expression was lower and showed more intersubject variability. In functional studies investigating the effects of various PDE inhibitors on PHA‐induced proliferation of mononuclear cells from healthy and asthmatic subjects, CDP840 (0.03–10u2003μM), rolipram (0.1–10u2003μM) and theophylline (10u2003μM–1u2003mM) inhibited PHA‐induced proliferation of mononuclear cells from healthy and asthmatic subjects in a concentration‐dependent manner, although no significant difference was observed between the groups investigated. In additional studies, total monocyte cyclic AMP PDE activity was investigated in cells isolated from asthmatic subjects both prior to and 24u2003h after allergen challenge. Total monocyte cyclic AMP PDE activity remained unaffected following challenge of asthmatic subjects with either house dust mite or cat dander and was inhibited in a concentration‐dependent manner by rolipram (0.01–100u2003μM) both before and after allergen challenge.

Examining the neural targets of the AMPA receptor potentiator LY404187 in the rat brain using pharmacological magnetic resonance imaging

RationaleDrugs that enhance α-amino-3-hydroxy-5-methyl-4-isoxazolepropanoic acid (AMPA) receptor-mediated glutamatergic transmission, such as the AMPA receptor potentiator LY404187, may form treatment strategies for disorders of cognition, learning and memory.ObjectivesPharmacological magnetic resonance imaging (phMRI) uses blood oxygenation level dependent (BOLD) contrast as a marker of neuronal activity and allows dynamic non-invasive in vivo imaging of the effects of CNS-active compounds. This study used phMRI to examine the effects of LY404187 in the rat brain.MethodGroups of Sprague Dawley rats (n=7) were anaesthetised and placed in a 4.7 Tesla superconducting magnet before receiving an acute dose of LY404187 (0.5xa0mg/kg s.c.), either alone or after pretreatment with the selective AMPA/kainate antagonist LY293558 (15xa0mg/kg s.c.), or LY293558 alone (15xa0mg/kg s.c.). Brain images were acquired for each subject every minute for 180xa0min. These volumes were extensively pre-processed before being analysed for changes in BOLD contrast.ResultsLY404187 produced significant increases in BOLD contrast in brain regions including the hippocampus, lateral and medial habenulae and superior and inferior colliculi. These changes were blocked by LY293558. When administered alone, LY293558 caused widespread decreases in BOLD contrast.ConclusionsThe known actions of LY404187 suggest the observed BOLD signal increases reflect increases in excitatory neurotransmission. The decreases in signal following LY293558 alone are harder to interpret and are discussed in terms of the negative BOLD response. This study provides the first evidence that the effects of AMPA receptor-mediating compounds can be observed using phMRI.

The implications of HIV for the anaesthetist and the intensivist

The acquired immune deficiency syndrome has reached pandemic proportions. Anaesthetists should be aware of the implications of dealing with increasing numbers of both diagnosed and undiagnosed, symptomatic and asymptomatic, human immunodeficiency virus‐infected patients in the fields of intensive therapy, operating theatre anaesthesia, obstetrics and pain management. With recent advances, important insights have been gained into the pathogenesis of human immunodeficiency virus. Molecular techniques allow quantification of viral burden, and together with CD4 T‐lymphocyte count, prognosis and response to therapy can be evaluated. New drugs and therapeutic regimens have improved prognosis for those who are infected with the virus and vertical transmission of infection from mother to infant can be minimised. Should accidental occupational exposure to the virus occur, a prophylactic regimen of antiretroviral drugs can be administered in an attempt to prevent subsequent human immunodeficiency virus infection.

Future treatment strategies for neuropathic pain.

The prevalence of people suffering from chronic pain is extremely high and pain affects millions of people worldwide. As such, persistent pain represents a major health problem and an unmet clinical need. The reason for the high incidence of chronic pain patients is in a large part due to a paucity of effective pain control. An important reason for poor pain control is undoubtedly a deficit in our understanding of the underlying causes of chronic pain and as a consequence our arsenal of analgesic therapies is limited. However, there is considerable hope for the development of new classes of analgesic drugs by targeting novel processes contributing to clinically relevant pain. In this chapter we highlight a number of molecular species which are potential therapeutic targets for future neuropathic pain treatments. In particular, the roles of voltage-gated ion channels, neuroinflammation, protein kinases and neurotrophins are discussed in relation to the generation of neuropathic pain and how by targeting these molecules it may be possible to provide better pain control than is currently available.

AMPA receptor potentiation can prevent ethanol-induced intoxication

We present a substantial series of behavioral and imaging experiments, which demonstrate, for the first time, that increasing AMPA receptor-mediated neurotransmission via administration of potent and selective biarylsulfonamide AMPA potentiators LY404187 and LY451395 reverses the central effects of an acutely intoxicating dose of ethanol in the rat. Using pharmacological magnetic resonance imaging (phMRI), we observed that LY404187 attenuated ethanol-induced reductions in blood oxygenation level dependent (BOLD) in the anesthetized rat brain. A similar attenuation was apparent when measuring local cerebral glucose utilization (LCGU) via C14-2-deoxyglucose autoradiography in freely moving conscious rats. Both LY404187 and LY451395 significantly and dose-dependently reversed ethanol-induced deficits in both motor coordination and disruptions in an operant task where animals were trained to press a lever for food reward. Both prophylactic and acute intervention treatment with LY404187 reversed ethanol-induced deficits in motor coordination. Given that LY451395 and related AMPA receptor potentiators/ampakines are tolerated in both healthy volunteers and elderly patients, these data suggest that such compounds may form a potential management strategy for acute alcohol intoxication.

Promoting organizational well-being: a comprehensive review of Trauma Risk Management.

BACKGROUNDnTrauma Risk Management (TRiM) is a peer support system developed within the British Armed Forces. It aims to ensure that trauma-exposed personnel are properly supported and encouraged to seek timely help should they develop mental health problems that fail to resolve spontaneously.nnnAIMSnTo summarize current knowledge about TRiM and make recommendations for further research.nnnMETHODSnA search of PsychINFO, CINAHL and PubMed identified 13 published papers.nnnRESULTSnTRiM outcomes were represented in different ways within the relevant studies suggesting that TRiM may have effects additional to those that it seeks to achieve. For example, a randomized controlled trial demonstrated that TRiM had a specific positive occupational effect and did no harm; a qualitative study suggested that TRiM enhanced liaison between mental health workers and line managers and a service evaluation suggested that it reduced sickness absence. In general, the process appears to enhance trauma-exposed personnels reliance on peer support and TRiM was reportedly acceptable and sustainable.nnnCONCLUSIONSnEvidence suggests that TRiMs utility has moved beyond the military to other organizations where personnel risk occupational traumatic exposure. Further research would help to understand how TRiM is perceived by line managers and how it functions within the trauma-prone populations.