PubMed Health⌕ Search

Biomedical subjects

A Dray

Publications and source records attributed to A Dray.

At least 37 records · Page 2Linked to original sources
PubMed1996

New pharmacological strategies for pain relief.

The recent advances made in elucidating the processes of nociception have altered the way that chronic pain therapy and analgesic drug development are approached. Recent studies have highlighted new targets for drug discovery, including inhibition of inflammatory mediators (kinins, growth factors), newly expressed proteins (B1 receptors, COX-2), and blockers of afferent fiber activity (capsaicin analogues, ion channel blockers). In the CNS, a further multiplicity of strategies can be pursued, including the development of antagonists of specific neuropeptide and glutamate receptors or agonists for purine and amine receptors. Such drugs will inevitably supplement or replace conventional NSAID and opioid analgesics. Further characterization of gene regulation will allow the development of drugs that genetically modify cellular activity altered by chronic pain conditions.

Analgesics↗
PubMed1995

Possible branching of myelinated primary afferent fibres in the dorsal root of the rat.

A combined physiological and morphological examination of rat dorsal root ganglion cells revealed branching of the central process of neurones with myelinated fibres (conduction velocity > 2 m/s; n = 24). Single shock electrical stimulation of spinal dorsal roots triggered double action potentials (early and late spike) in two dorsal root ganglion cells recorded by intracellular electrodes in the in vitro spinal cord-dorsal root ganglion preparation from 12-20 day-old rats. The action potentials had different stimulus thresholds (lower for the late spike). In one dorsal root ganglion cell the differences in delay between the two spikes inhibited the soma invasion of the second spike, when both action potentials were evoked at resting membrane potential. Depolarization of the soma membrane by DC current, injected through the electrode, recovered the blocked action potential. Membrane depolarization by GABA reduced the threshold for the early spike and changed the pattern of activation. After electrophysiological characterisation, intracellular biotin/avidin staining of the neurone revealed branching of the central axon in the dorsal root. None of the other cells, which responded with single action potentials after dorsal root stimulation showed secondary branching (n = 5). This rare observation shows that differences between the conduction velocities and activation thresholds in branches of individual dorsal root ganglion cell axons may produce block of spike invasion into the soma and perhaps the spinal terminal field of large primary afferents.

Action Potentials↗
PubMed1995

Bradykinin depolarises the rat isolated superior cervical ganglion via B2 receptor activation.

Experiments were undertaken to characterise the action of kinins on sympathetic neurones of the rat superior cervical ganglion (SCG) by use of in vitro grease-gap, extracellular recording techniques in conjunction with selective agonists and antagonists for B1 and B2 bradykinin (BK) receptors. Superfusion of BK (10 nM to 10 microM) to the ganglion produced a concentration-related depolarisation (pD2 = 7.02 +/- 0.04, n = 7) which was inhibited by the selective B2 antagonist HOE 140 (10-100 nM), but not by the B1 antagonist Leu8desArg9 BK (1 microM), indomethacin (7 microM) or the nitric oxide synthase inhibitor L-NG-nitroarginine methyl ester (300 microM). DesArg9BK (10 nM to 10 microM) had no effect on membrane potential. Pre-treatment of animals with intravenous bacterial lipopolysaccharide (LPS, 3 mg kg-1) failed to induce B1 receptor-mediated depolarisations of SCG neurones, or change responses to BK (P > 0.05, n = 4). These experiments highlight and characterise the action of BK as a neuromodulator of sympathetic neurones via B2 receptor activation.

Adrenergic Fibers↗
PubMed1995

No evidence for contribution of nitric oxide to spinal reflex activity in the rat spinal cord in vitro.

The effects of nitric oxide (NO) synthase inhibition, NO generation and an N-methyl-D-aspartic acid (NMDA) receptor antagonist upon spinal reflex responses evoked by electrical activation of high threshold afferent fibres and brief application of NMDA have been compared in an in vitro preparation of the neonatal rat spinal cord. Reflex responses of spinal cords prepared from naive animals and those exhibiting a behavioural hyperreflexia following UV irradiation of the left hindpaw have been compared. C-fibre evoked and NMDA induced ventral root potential responses were significantly reduced by the selective NMDA receptor antagonist D-AP5 (40 microM) but completely unaffected by application of 7-nitroindazole (30 microM), NG-nitro-L-arginine methyl ester (L-NAME; 100 microM) or sodium nitroprusside (50 microM) either in hyperalgesic or naive animals. In vivo behavioural experiments performed upon age-matched rat pups showed that reflex sensitivity was significantly reduced following administration of L-NAME (30 mg kg-1). The present study has failed to provide evidence that NO is involved in nociceptive spinal reflex activity measured in vitro. In contrast, an NO synthase inhibitor was shown to influence nociceptive reflex responses observed in vivo. We suggest it is possible that NO participates in post-injury induced hyperreflexia at sites other than directly upon spinal neurones.

2-Amino-5-phosphonovalerate↗
PubMed1995

Stimulation of guinea-pig tracheal afferent fibres by non-isosmotic and low-chloride stimuli and the effect of frusemide.

1. Inhalation of low-chloride or non-isosmotic solutions evokes cough or reflex bronchoconstriction in humans that is inhibited by frusemide (furosemide), whilst capsaicin-evoked cough is unaffected. Here we have examined the responses of single vagal afferent fibres innervating the isolated guinea-pig trachea to these stimuli, and tested the effect of frusemide on fibre responses. 2. Both distilled water and hypertonic saline applied for 30 s onto identified receptive fields produced marked excitation of all A delta and C fibres tested. Isotonic glucose, a low-chloride solution, was a less potent stimulant and caused excitation in 37% of A delta fibres and 69% of C fibres. There was no difference in the distribution of low-chloride sensitive and insensitive receptive fields. 3. In the presence of frusemide, responses of A delta fibres to isotonic glucose were significantly inhibited to 34.2 +/- 6.2% of the pre-drug control level. However, frusemide was without effect either on responses of A delta fibres to distilled water or hypertonic saline, or on responses of C fibres to capsaicin. 4. These data support a role for tracheo-bronchial A delta and C fibres in airway reflexes evoked by hypotonic, hypertonic and low-chloride stimuli. The protective effect of frusemide against airway responses to low-chloride but not to non-isosmotic solutions may reflect an action on sensory nerve endings.

Animals↗
PubMed1995

Kinins and kinin receptors in the nervous system.

Kinins, including bradykinin and kallidin, are peptides that are produced and act at the site of tissue injury or inflammation. They induce a variety of effects via the activation of specific B1 or B2 receptors that are coupled to a number of biochemical transduction mechanisms. In the periphery the actions of kinins include vasodilatation, increased vascular permeability and the stimulation of immune cells and peptide-containing sensory neurones to induce pain and a number of neuropeptide-induced reflexes. Mechanisms for kinin synthesis are also present in the CNS where kinins are likely to initiate a similar cascade of events, including an increase in blood flow and plasma leakage. Kinins are potent stimulators of neural and neuroglial tissues to induce the synthesis and release of other pro-inflammatory mediators such as prostanoids and cytotoxins (cytokines, free radicals, nitric oxide). These events lead to neural tissue damage as well as long lasting disturbances in blood-brain barrier function. Animal models for CNS trauma and ischaemia show that increases in kinin activity can be reversed either by kinin receptor antagonists or by the inhibition of kinin production. A number of other central actions have been attributed to kinins including an effect on pain signalling, both within the brain (which may be related to vascular headache) and within the spinal dorsal horn where primary afferent nociceptors can be stimulated. Kinins also appear to play a role in cardiovascular regulation especially during chronic spontaneous hypertension. Presently, however, direct evidence is lacking for the release of kinins in pathophysiological conditions of the CNS and it is not known whether spinal or central neurones, other than afferent nerve terminals, are sensitive to kinins. A more detailed examination of the effects of kinins and their central pharmacology is necessary. It is also important to determine whether the inhibition of kinin activity will alleviate CNS inflammation and whether kinin receptor antagonists are useful in pathological conditions of the CNS.

Amino Acid Sequence↗
PubMed1995

Nerve growth factor induces mechanical allodynia associated with novel A fibre-evoked spinal reflex activity and enhanced neurokinin-1 receptor activation in the rat.

A single dose of nerve growth factor (NGF, 1 microgram/g, i.p.) administered to rats aged between postnatal days (PND) 12 and 14 resulted in a behavioural hypersensitivity of the hindlimb flexion withdrawal reflex to mechanical stimuli which developed 2 h after NGF and remained significant for 24 h. Heat hyperalgesia occurred some 4 h following NGF injection and lasted for 24 h. Isolated spinal cords were prepared from animals treated with NGF and were maintained in vitro for physiological and pharmacological analysis of lumbar spinal reflex activity. Repetitive, low-frequency group I/II A beta-fibre stimulation evoked a novel wind-up response after NGF injection similar to that produced by C-fiber group III/IV stimulation in normal animals. The neurokinin-1 (NK1) receptor antagonist RP67580 reduced the C fiber-evoked responses following NGF treatment but not in naive preparations. The novel A beta fiber-evoked wind-up response was also reduced by RP67580. The NGF-induced changes in NK1 receptor responses occurred in the absence of any detectable changes in either spinal cord NK1 receptor dose-response relationships or NK1 receptor mRNA levels. These findings are likely to be related to the behavioural allodynia observed in the present study and to central excitability changes observed after chronic inflammation where NGF levels are increased.

Analgesics↗
PubMed1995

Effects of capsazepine against capsaicin- and proton-evoked excitation of single airway C-fibres and vagus nerve from the guinea-pig.

We have examined the effects of low pH and the selectivity of the capsaicin antagonist capsazepine on single sensory fibres innervating the guinea-pig trachea in vitro, and on the whole isolated vagus nerve. Application of a pH 5 solution for 1 min to the exposed receptive fields of single fibres caused excitation of all C-fibres tested but had no effect on A delta-fibres. Capsazepine (1 microM) perfused onto the receptive field for 5 min produced a reversible inhibition of both low pH- and capsaicin (60 nM)-evoked firing of C-fibres. In contrast, capsazepine had no effect on responses of C-fibres to bradykinin (0.1 microM) or of A delta-fibres to hypertonic saline. Perfusion of tissues with zero-calcium Krebs' solution containing trypsin produced denudation of the epithelium. In these tissues responses to low pH and capsaicin were unchanged and, moreover, the inhibitory effect of capsazepine against low pH and capsaicin was maintained. C- and A delta-fibre responses to bradykinin and hypertonic saline were similarly unaffected by epithelium removal. Perfusion of the whole guinea-pig vagus nerve with capsaicin (0.3 microM) or pH 5 buffer caused depolarization. However, in this preparation prior perfusion with capsazepine (1 microM) abolished responses to capsaicin whilst low pH-evoked depolarization was unchanged. These data show that capsazepine is a specific antagonist of proton- and capsaicin-evoked activation of the peripheral endings of sensory nerves in the guinea-pig airways, and suggest the release by protons of an endogenous ligand for the capsaicin receptor that does not originate from the epithelium.

Afferent Pathways↗
PubMed1995

Comparison of the sensory threshold in healthy human volunteers with the sensory nerve response of the rat in vitro hindlimb skin and saphenous nerve preparation on cutaneous electrical stimulation.

We report a comparative study of stimulation thresholds of cutaneous fibres of the rat in vitro skin and saphenous nerve preparation with psychophysical measurements of sensibility to cutaneous electrical stimulation in human volunteers. The same clinical diagnostic stimulator and modified skin electrodes were used in both animal and human experiments. Axons were recruited by increasing the stimulus strength, and correlation was made between the stimulus intensity required for unit activation and their conduction velocities. The findings suggest that an initial "tingling" sensation is due to recruitment of A beta fibres and that later sharp "pricking" occurs with recruitment of A delta fibres.

Adult↗
PubMed1995

Inflammatory mediators of pain.

While sensory fibres normally respond to a range of physical and chemical stimuli their activity and metabolism are profoundly altered by a variety of mediators generated by tissue injury and inflammation. These include substances produced by damaged tissue, substances of vascular origin as well as substances released by afferent fibres themselves, sympathetic fibres and various immune cells. The effects of inflammatory mediators, to activate or sensitize afferent fibres, are produced by changing membrane ion channels which are coupled directly via receptors or more commonly are regulated through receptor-coupled second messenger cascades. These latter processes also have the potential to alter gene transcription and thereby induce long-term alterations in the biochemistry of sensory neurones. This can have far-reaching consequences as the expression of novel proteins for ion channels (Na channels) and receptors (capsaicin, NPY) as well as the induction of novel enzymes (i-NOS) can profoundly affect the properties of nociceptors and their ability to transmit pain signals. However, such changes may be targeted successfully for the development of new analgesic and anti-inflammatory agents.

Adenosine Triphosphate↗
PubMed1994

Cobalt accumulation in neurons expressing ionotropic excitatory amino acid receptors in young rat spinal cord: morphology and distribution.

Excitatory amino acids (EAA) acting on N-methyl-D-aspartate (NMDA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and kainate receptors play an important role in synaptic transmission in the spinal cord. Quantitative autoradiography and physiological experiments suggest that NMDA receptors are localized mainly in lamina II while kainate and AMPA receptors are found on both dorsal and ventral horn neurons. However the cell types expressing EAA receptors and their laminar distribution is not known. We have used a cobalt uptake method to study the morphology and distribution of spinal cord neurons expressing AMPA, kainate, or NMDA excitatory amino acid receptors in the lumbar enlargement of the rat spinal cord. The technique involved superfusion of hemisected spinal cords of 14 day-old rat pups in vitro with excitatory amino acid receptor ligands in the presence of CoCl2. Cobalt has been shown to enter cells through ligand-gated ion channels in place of Ca2+. Cells which accumulated cobalt ions following activation by ionotropic excitatory amino acid receptors were visualized histochemically. The cobalt uptake generated receptor-specific labeling of cells, as the NMDA receptor antagonist D-(-)-2-amino-(5)-phosphonovaleric acid (D-AP-5) (20 microM) blocked the NMDA, but not kainate-induced cobalt uptake. The kainate-induced cobalt labeling was reduced by the non-selective excitatory amino acid receptor antagonist kynurenic acid (4 mM). Passive opening of the voltage-gated Ca(2+)-channels by KCl (50 mM) did not result in cobalt uptake, indicating that cobalt enters the cells through ligand-gated Ca(2+)-channels. AMPA (500 microM), kainate (500 microM), or NMDA (500 microM) each induced cobalt uptake with characteristic patterns and distributions of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal staining. Overall, kainate induced cobalt uptake in the greatest number of neuronal perikarya while NMDA-induced uptake was the lowest. AMPA and kainate, but not NMDA superfusion, resulted in cobalt labeling of glial cells. Our results show that the cobalt uptake technique is a useful way to study the morphology and distribution of cells expressing receptors with ligand-gated Ca2+ channels.

Animals↗
PubMed1994

Tachykinin induced regulation of excitatory amino acid responses in the rat spinal cord in vitro.

The interaction between neurokinin and excitatory amino acid receptors in the spinal cord have been characterised using the neonatal rat spinal cord in vitro preparation. Ventral root (VR) depolarization evoked by N-methyl-D-aspartate (NMDA) and quisqualate was reversibly enhanced in the presence of subthreshold concentrations of neurokinin A (NKA; 1.0-10 nM), but not by substance P (1.0-5.0 nM). When substance P (SP) was replaced by the metabolically stable substance P methyl ester (SPOMe), both NMDA and quisqualate responses were significantly enhanced. VR depolarization evoked by kainate was not altered by any of the neurokinin (NK) receptor agonists. In the presence of the endopeptidase inhibitors, bestatin, captopril and thiorphan (each 1.0 microM), SP significantly enhanced NMDA-evoked responses. The selective NK1 receptor antagonist (+/-) CP96 345 (100 nM) reversibly blocked the enhancement of NMDA-evoked depolarization by SPOMe. Furthermore, MEN10 376 (50 nM), a selective NK2 receptor antagonist blocked the enhancement of NMDA- and quisqualate-evoked depolarization by NKA. The protein kinase C and protein kinase A inhibitor staurosporine (1.0 microM) blocked the enhancement of excitatory amino acid-induced responses by NK-receptor activation. However, whilst NKA-evoked ventral root depolarization was completely abolished in the presence of staurosporine, SPOMe- and SP-induced depolarizations were unaffected. These data show that activation of NK1 or NK2 receptors enhances NMDA- and quisqualate-evoked ventral root depolarization in the neonatal rat spinal cord. The interaction between neurokinin and excitatory amino acid receptors involves protein kinase C activation.

Alkaloids↗
PubMed1994

Pharmacology of chronic pain.

Chronic pain, which is associated with prolonged tissue damage or injuries to the peripheral or central nervous system, results from a number of complex changes in nociceptive pathways. These include alterations of cell phenotype and changes in the expression of proteins such as receptors, transmitters and ion channels, as well as modifications of neural structure, for example, cell loss, nerve regeneration and synaptic reorganizations. The resultant increase in neural excitability can be reduced with receptor-selective drugs that block peripheral or central chemical mediators or that control ectopic activity or cellular phenotype changes. In this article, Andy Dray, Laszlo Urban and Anthony Dickenson focus on some current mechanistic aspects of chronic pain imposed by inflammation and peripheral neuropathy, and review in particular the molecular changes involving the pharmacology of nociceptive pathways since these have important implications for the management of pain.

Analgesics↗
PubMed1994

Modulation of spinal excitability: co-operation between neurokinin and excitatory amino acid neurotransmitters.

Activation of C fibres with strong 'potentially tissue damaging' chemical, mechanical or thermal stimuli produces painful sensations that are significantly enhanced during pathological conditions, such as neuropathy and inflammation. The pronounced painful symptoms of hyperalgesia and allodynia are induced, in part, by the development of spinal hyperexcitability. This involves plastic changes in synaptic transmission between primary afferents and dorsal horn neurones induced by sustained activity of peripheral nociceptors. L. Urban, S. W. N. Thompson and A. Dray describe some of the central mechanisms that account for central hyperexcitability occurring in hyperalgesia and allodynia based on evidence from experiments both in vivo and in vitro with neurokinin and N-methyl-D-aspartate receptor antagonists.

Animals↗
PubMed1994

Opioids suppress spontaneous activity of polymodal nociceptors in rat paw skin induced by ultraviolet irradiation.

Changes in chemical sensitivity of peripheral nociceptors following injury or inflammation have been studied in in vitro preparation of the saphenous nerve-hind paw skin from adult rats. Heat hyperalgesia in the hind paw was induced by a prior ultraviolet irradiation and the skin from these animals was investigated five days later. Polymodal nociceptors were quiescent in normal skin but were spontaneously active in the majority of fibres after ultraviolet exposure. Capsaicin-induced activation of fine fibres was enhanced after ultraviolet pretreatment. Direct administration of morphine, DAGOL (mu-receptor agonist) and U-69593 (kappa-receptor agonist), but not DPDPE (delta-receptor agonist) to the receptive field produced a concentration-related and naloxone-reversible suppression of spontaneous firing in polymodal nociceptors of ultraviolet-treated skin. Morphine did not reduce the activity of fibres in normal skin when these were driven by KCl depolarization. These data show that polymodal nociceptors change their activity and sensitivity to exogenous chemicals following the induction of peripheral hyperalgesia by ultraviolet irradiation. Specifically, evidence is provided for the expression of opioid sensitivity and inhibition of polymodal nociceptor activity through mu- and kappa-opioid receptors. These observations may account for peripheral antinociceptive actions of opioids during specific states of peripheral hyperalgesia.

Amino Acid Sequence↗
PubMed1994

Regulation of bradykinin sensitivity in peripheral sensory fibres of the neonatal rat by nitric oxide and cyclic GMP.

Bradykinin-induced activation of peripheral sensory fibres was studied using an in vitro preparation of the neonatal rat spinal cord with attached tail. Noxious heat stimulation, as well as the applications of bradykinin and capsaicin, to the tail evoked reproducible responses recorded as a depolarization of a lumbar ventral root. Prolonged administration of a supramaximal concentration of bradykinin invariably induced a complete but selective desensitization to a subsequent bradykinin challenge. Bradykinin-induced desensitization was significantly attenuated by concanavalin-A and the effect of concanavalin-A was prevented by alpha-methyl mannoside. Both cyclic GMP and sodium nitroprusside induced a long lasting reduction of bradykinin responsiveness in peripheral fibres. The effect of nitroprusside was prevented by concanavalin-A, and by methylene blue, an inhibitor of guanylyl cyclase. Methylene blue also reduced bradykinin-induced desensitization. L-arginine, but not D-arginine, induced a desensitization to bradykinin. On the other hand, 7-nitroindazole (7-NI, 200-500 nM), an inhibitor of NOS, reduced the desensitization of bradykinin responses but higher concentrations of 7-NI (IC50 = 6.7 +/- 0.9 microM) selectively attenuated responses to bradykinin. The effects of 7-NI were attenuated by L-arginine pretreatment. These data suggest that bradykinin-induced desensitization of peripheral sensory fibres is mediated in part via NO and cyclic GMP dependent mechanisms: possibly NO production is required for guanylate cyclase activation.

Animals↗
PubMed1994

Injury-induced plasticity of spinal reflex activity: NK1 neurokinin receptor activation and enhanced A- and C-fiber mediated responses in the rat spinal cord in vitro.

A- and C-fiber evoked ventral root potential (VRP) responses have been examined in isolated spinal cord preparations maintained in vitro that were taken from young rats in which behavioral hyperalgesia (thermal and mechanical) was induced following UV irradiation of one hindpaw. Evoked VRPs were compared with those in naive untreated animals. The duration of both the A- and C-fiber evoked VRP was significantly increased in UV-treated animals. The amplitude of the summated VRP evoked by repeated low-frequency (1.0-5.0 Hz) C-fiber stimulation, a measure of windup, was significantly greater in UV-treated animals. In UV-treated animals, repeated low-frequency (1.0-5.0 Hz) stimulation of A-fiber inputs to the spinal cord also evoked a significant summated VRP, which was not observed in spinal cords from untreated animals. In naive animals the prolonged VRP evoked following single shock C-fiber stimulation was significantly antagonized by the NMDA receptor antagonist D-AP5 and the NK2 receptor antagonist MEN, 10376 but not by the NK1 receptor antagonists CP-96,345 or RP,67580. Summated VRPs evoked by repeated C-fiber stimulation in naive animals were significantly antagonized only by D-AP5. In hyperalgesic animals the prolonged VRP evoked by C-fiber stimulation was significantly reduced by NK1, NK2, and NMDA antagonists. The summated VRP was also significantly reduced by these antagonists. In both untreated and UV-irradiated animals the single shock evoked A-fiber ventral root response was significantly antagonized only by D-AP5. However, the summated VRP evoked by repeated A-fiber stimulation in UV-treated animals was also significantly reduced by NMDA, NK1, and NK2 receptor antagonists. The present study has demonstrated enhanced A- and C-fiber evoked responses in the rat spinal cord in vitro following induction of a peripheral injury by UV irradiation and which was associated with behavioral hyperalgesia to thermal and mechanical stimuli. Under this condition, repetitive stimulation of A-fiber primary afferents was capable of producing an enhancement of spinal excitability similar to that evoked by C-fibers in normal animals. Furthermore, we have observed the expression of an NK1 receptor component to the C-fiber evoked response following the establishment of the peripheral injury. The enhanced ventral root responses and changes in receptor sensitivity may contribute to the phenomenon of central sensitization and may be directly related to the behavioral hyperalgesia observed. Moreover, these findings may be relevant to the mechanisms of enhanced central excitability that occur in clinical conditions of inflammatory hyperalgesia and neuropathic pain.

Animals↗