Search PubMed⌕ Search

Biomedical subjects

L Urban

Publications and source records attributed to L Urban.

At least 55 records · Page 3Linked to original sources
PubMed1996

Metabotropic glutamate receptor activation contributes to nociceptive reflex activity in the rat spinal cord in vitro.

The contribution of metabotropic glutamate receptor activation to the spinal segmental reflex response evoked at high-intensity electrical stimulation suggesting a role in nociception, has been examined in an in vitro preparation of neonatal rat spinal cord. Segmental reflex responses were recorded as a ventral root depolarization evoked following drug perfusion to the spinal cord or by electrical activation of high-threshold nociceptive afferent fibres. Superfusion of the selective metabotropic glutamate receptor agonist, (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid [(1S,3R)-ACPD], to the spinal cord produced a dose-dependent, reversible ventral root depolarization (EC50 = 58 +/- 7 microM; n = 4), which was antagonized by the selective metabotropic glutamate receptor antagonist, (+)-alpha-methyl-4-carboxyphenylglycine (MCPG; IC50 = 243 +/- 61 microM; n = 4). MCPG, over the same concentration range (10 microM-5.0 mM) did not affect N-methyl-D-aspartate-induced ventral root depolarizations. In contrast, the specific N-methyl-D-aspartate receptor antagonist D(-)-2-amino-5-phosphonopentanoic acid (D-AP5) reduced N-methyl-D-aspartate-evoked ventral root depolarization but did not affect the depolarization evoked by (1S,3R)-ACPD, thus indicating the specificity of the antagonists for these aggregate responses. MCPG significantly reduced the prolonged phase of the single shock C-fibre-evoked ventral root depolarization (IC50 = 2.9 +/- 0.2 mM; n = 3-5). Low frequency high intensity stimulation of the dorsal root evoked a wind-up response, the amplitude of which was attenuated by both D-AP5 and MCPG in a dose-dependent manner. The ventral root depolarization evoked by capsaicin application (1.0 microM, 30 s) was blocked by both MCPG (IC50 = 809 +/- 35 microM; n = 4) and D-AP5 (IC50 = 143 +/- 43 microM; n = 4). These data suggest that both D-AP5 and MCPG reduced C-fibre-induced ventral root responses. In addition to N-methyl-D-aspartate receptor, metabotropic glutamate receptor activation appears to be involved in the generation of the segmental spinal reflex evoked by high-intensity stimulation in the neonatal rat spinal cord in vitro.

Animals↗
PubMed1996

B1 bradykinin receptors and sensory neurones.

1. The location of the B1 bradykinin receptors involved in inflammatory hyperalgesia was investigated. 2. No specific binding of the B1 bradykinin receptor ligand [3H]-des-Arg10-kallidin was detected in primary cultures of rat dorsal root ganglion neurones, even after treatment with interleukin-1 beta (100 iu ml-1). 3. In dorsal root ganglion neurones, activation of B2 bradykinin receptors stimulated polyphosphoinositidase C. In contrast, B1 bradykinin receptor agonists (des-Arg9-bradykinin up to 10 microM and des-Arg10-kallidin up to 1 microM) failed to activate polyphosphoinositidase C, even in neurones that had been treated with interleukin-1 beta (100 iu ml-1), prostaglandin E2 (1 microM) or prostaglandin I2 (1 microM). 4. Dorsal root ganglion neurones removed from rats (both neonatal and 14 days old) that had been pretreated with inflammatory mediators (Freund's complete adjuvant, or carrageenan) failed to respond to B1 bradykinin receptor selective agonists (des-Arg9-bradykinin up to 10 microM and des-Arg10-kallidin up to 1 microM). 5. Bradykinin (25 nM to 300 nM) evoked ventral root responses when applied to peripheral receptive fields or central terminals of primary afferents in the neonatal rat spinal cord and tail preparation. In contrast, des-Arg9-bradykinin (50 nM to 500 nM) failed to evoke ventral root depolarizations in either control rats or in animals that developed inflammation following ultraviolet irradiation of the tail skin. 6. The results of the present study imply that the B1 bradykinin receptors that contribute to hypersensitivity in models of persistent inflammatory hyperalgesia are located on cells other than sensory neurones where they may be responsible for releasing mediators that sensitize or activate the nociceptors.

Animals↗
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↗
PubMed1996

In vitro characterization of a peripheral afferent pathway of the rat after chronic sciatic nerve section.

1. We have studied the characteristics of the abnormal properties of damaged myelinated fibers (conduction velocity > 2.0 m/ s) after peripheral nerve injury in a novel in vitro model of the rat sciatic nerve/dorsal root ganglion/dorsal root (L4-5) preparation removed from control naíve or sham-operated rats and animals that had received sciatic neurectomy 12-24 days before the in vitro study. A total of 122-245 filaments were recorded in each dorsal root. The proportion of A alpha, beta and A delta fibers were not significantly different between control, sham-operated, and axotomized nerves. Spontaneous activity was recorded in 3.4% (A alpha, beta) and 4.6% (A delta) of fibers in comparison with 0.4% (A alpha, beta) and 0.3% (A delta) in naíve controls. 2. A sporadic, irregular, low-frequency (< 1 Hz) firing was seen in 26% of the fibers with spontaneous activity. Periodical (irregular) bursting pattern was observed in 43% of spontaneously active fibers, whereas a relatively stable, ongoing firing pattern (median frequency: 7.1 Hz) was displayed by 31% of active fibers. 3. Mechanosensitivity of the neuroma/peripheral nerve was displayed in preparations from lesioned [axotomized: 18.2% (A alpha, beta) and 14.1% (A delta), sham operated: 2% (A alpha, beta) and 0% (A delta)], but not control naíve animals. There was no correlation between the presence of spontaneous activity and mechanosensitivity in single fibers. 4. The principal site of spontaneous activity generation was the dorsal root ganglion. Transection of the peripheral nerve (or removal of the neuroma), while recording from dorsal root filaments, produced a cessation of firing in 21% of fibers firing with ongoing discharge. The remaining active fibers continued firing until the DRG was removed. A sustained injury discharge was observed in damaged fibers but not control, undamaged fibers from naíve animals after acute peripheral nerve transection. 5. We present an in vitro model for the study of abnormal primary sensory activity in peripheral neuropathy. Although our data are consistent with in vivo electrophysiological findings in published reports, the proportion of damaged afferent fibers displaying spontaneous activity was significantly lower under in vitro conditions. This model may serve as a valuable tool for further physiological and pharmacological studies of peripheral neuropathy.

Afferent Pathways↗
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

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↗
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

Repetitive stimulation induced potentiation of excitatory transmission in the rat dorsal horn: an in vitro study.

1. The effects of repetitive stimulation of primary afferents in lumbar dorsal roots on synaptic transmission in the dorsal horn (DH) were studied in a rat spinal cord slice-dorsal root ganglion (DRG)-peripheral nerve trunk preparation by the use of intracellular recording from neurons (n = 115) of the spinal dorsal horn (depth 147 +/- 139, mean +/- SD). All DH neurons were excited synaptically by electrical stimulation of the dorsal root or the peripheral nerve trunk. The electrical shocks were calibrated to produce activation either of large fibers (10-20 V, 0.02 ms) or the whole fiber population including unmyelinated afferents (supramaximal stimulus: > 35 V, 0.5 ms). Postsynaptic potentials induced by low intensity repetitive stimulation of primary afferents at frequencies below 5 Hz failed to produce a prolonged change in the resting membrane potential. In 97/115 DH neurons, slow excitatory postsynaptic potentials (EPSP)--evoked by high intensity low-frequency repetitive stimulation (0.1-2 Hz) of primary afferents--summated, producing a prolonged cumulative depolarization. In the remaining 18/115 DH neurons, high intensity low-frequency stimulation produced a cumulative hyperpolarizing response. 2. In 22 of 97 neurons that responded to high intensity repetitive stimulation with a cumulative depolarization, wind-up in the firing of action potentials was recorded. In all but two experiments, neurons that responded with wind-up to stimulation of one root responded with wind-up to stimulation of the adjacent dorsal root. In 14/22 wind-up neurons, the synaptic response to high intensity stimulation of primary afferents was composed of a short latency EPSP, followed by an inhibitory postsynaptic potential (IPSP), followed by a slow EPSP. The decrease of the amplitude and duration of the IPSP obtained during train stimulation did not seem to contribute to facilitation of transmission induced by repetitive stimulation. 3. The wind-up in firing of action potentials was followed by a prolonged potentiation of synaptic transmission in tetanized synapses. A test of other, adjacent primary afferents revealed that these synapses in the neurons in the superficial laminae had not undergone potentiation. This "synaptic specificity" of post-wind-up potentiation suggested that the mechanism for the induction of stimulation-dependent changes in the excitability of the DH neuron is presynaptic to the recorded-from neuron. 4. In a concentration of 0.5 microM and higher, tetrodotoxin (TTX) applied to sensory neurons selectively blocked action potentials in large myelinated primary afferents.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗