PubMed Health⌕ Search

Biomedical subjects

A Dray

Publications and source records attributed to A Dray.

At least 55 records · Page 3Linked to original sources
PubMed1993

Contribution of NK1 and NK2 receptor activation to high threshold afferent fibre evoked ventral root responses in the rat spinal cord in vitro.

The contribution of neurokinin and NMDA receptor activation to the generation of the prolonged high threshold evoked ventral root potential (VRP) and its temporal summation has been assessed in the neonatal rat hemisected spinal cord maintained in vitro. High intensity single shock stimulation of the dorsal roots evoked a prolonged VRP (9.81 +/- 0.9 s, n = 11). A low frequency (1-10 Hz) repetitive stimulation (20 s duration) of high threshold afferent fibres evoked a summated VRP. This summated VRP reflected the temporal summation of EPSP's in spinal cord neurones which underlies the phenomenon of 'Windup'. The integrated area and duration of the high threshold evoked VRP were significantly reduced following superfusion of the spinal cord with the NK2 receptor antagonist MEN,10376 (100 nM). In the presence of D-AP5 (20 microM) the area of the C-fibre evoked VRP was also significantly reduced. The VRP duration was unaffected. Superfusion with either CP-96,345 (500 nM) or RP,67580 (100 nM), both non-peptide NK1 antagonist, did not have any significant effect upon the area or duration of the prolonged VRP following high threshold stimulation. The simultaneous application of D-AP5 (20 microM) with either MEN,10376 (100 nM) or CP-96,345 (500 nM) together produced a reduction in the area of the evoked VRP which was comparable to the value obtained by addition of their individual effects. The amplitude of the summated VRP was significantly reduced following application of D-AP5 (20 microM). No significant effect upon the amplitude was observed following separate application of either MEN,10376 (100 nM), CP-96,345 (500 nM) or RP,67580 (100 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1993

Analogues of capsaicin with agonist activity as novel analgesic agents; structure-activity studies. 1. The aromatic "A-region".

A series of analogues of capsaicin, the pungent principle of chilli peppers, was synthesized and tested in assays for capsaicin-like agonism in vitro. The results of these assays were compared with activities in an acute nociceptive model and a correlation was observed which established that the results of these in vitro assays were predictive of analgesia. Using a modular approach the structure-activity profile of specific regions of capsaicin congeners was established using an in vitro assay measuring 45Ca2+ uptake into neonatal rat dorsal root ganglia neurones. Substituted benzylnonanamides 2a-z and N-octyl-substituted phenylacetamides 4a-v were made to test the requirements for activity in the aromatic "A-region" of the molecule. Compounds with the natural substitution pattern (2b and 4c) and the corresponding catechols (2i and 4g) were the most potent, although the catechols were less potent in vivo. Other substitution patterns have reduced activity. These results have established stringent structural requirements for capsaicin-like activity in this part of the molecule.

Analgesics↗
PubMed1993

Analogues of capsaicin with agonist activity as novel analgesic agents; structure-activity studies. 2. The amide bond "B-region".

A series of compounds incorporating replacements for the amide bond "B-region" moiety of capsaicin have been synthesized, including vanillylamides and esters, homovanillic acid amides and esters, ureas, and thioureas. These have been tested in an in vitro assay for agonism (45Ca2+ influx into dorsal root ganglia neurones), which is predictive of analgesic activity, to investigate the requirements in this region of capsaicin for activity. N-(4-Hydroxy-3-methoxybenzyl)-N'-octylthiourea (14a) emerged as the most potent analogue (EC50 = 0.06 microM). An operational model based on multiple hydrogen-bonding interactions is proposed to explain the structure-activity profile observed. In combination with studies on the other regions of the capsaicin molecule these results describe a picture of the molecular interactions of capsaicin with its putative receptor.

Analgesics↗
PubMed1993

Analogues of capsaicin with agonist activity as novel analgesic agents; structure-activity studies. 3. The hydrophobic side-chain "C-region".

Structural variants of the hydrophobic side chain ("C region") of the capsaicin molecule have been incorporated into a series of vanillylamides and vanillylthioureas. These compounds have been tested in an in vitro assay for agonism (45Ca2+ influx into dorsal root ganglia neurones), previously shown to be predictive of analgesic activity. The results of this study have established the requirement for a hydrophobic substituent of limited size (molar refractivity, MR, < 55) in order to obtain high potency. Combination of the information gained here about the "C-region" of the capsaicin molecule with the studies described in the preceding two papers provides a rational basis for the design of compounds of increased potency.

Analgesics↗
PubMed1993

Actions of capsaicin on mouse dorsal root ganglion cells in vitro.

The effects of capsaicin were investigated on different populations of dorsal root ganglion cells in the in vitro mouse spinal cord-dorsal root ganglion preparation using intracellular electrodes. Dorsal root ganglion cells were characterised by the conduction velocity of their propagated action potential evoked by electrical stimulation of the dorsal root, and by the shape of their action potential. All cells with C-fiber characteristics (conduction velocity < 0.6 m/s; broad action potential with shoulder on the descending slope) were depolarised and generated action potentials when capsaicin (100-700 nM) was added to the bathing solution for 30 s. At these concentrations the membrane potential of DRG cells with myelinated fibers (conduction velocity > 2.0 m/s) was unaffected. Concentrations of capsaicin of 1.0-5.0 microM depolarised 50% of cells with conduction velocity > 10 m/s. During the depolarization of the membrane no action potentials were generated. In 50% of the capsaicin-sensitive neurons with conduction velocity faster than 10 m/s there was an initial hyperpolarization. Electrical stimulation of the dorsal root failed to evoke action potentials during the depolarization in 38% of the DRG cells with myelinated fibers and in all C-fibers tested within 10 min of the onset of the capsaicin effect. Passive depolarization of the membrane by intrasomal current injection mimicked the conduction block in neurons with large myelinated fibers. These observations confirm that capsaicin applied directly to the dorsal root ganglion affects, in a dose-dependent manner, both myelinated and unmyelinated primary afferents with a higher potency for C-neurons. Capsaicin evoked action potentials in C-neurons but not in neurons with myelinated fibers.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1993

Pharmacological characterization of the effects of 5-hydroxytryptamine and different prostaglandins on peripheral sensory neurons in vitro.

The excitatory and sensitizing properties of 5-HT and different prostaglandins (PGD2, PGE1, PGE2, PGF2 alpha, PGI2 and PGI2-analogue, cicaprost) were characterized on an in vitro preparation of the neonatal rat spinal cord with functionally attached tail. Prolonged (10 min) perfusion of the tail with 5-hydroxy-tryptamine (5-HT, 0.5-10 microM) or any of the tested prostaglandins (0.1-5 microM) did not evoke an excitatory response recorded from a lumbar ventral root, but significantly enhanced responses of peripheral nociceptors to thermal and chemical (bradykinin, capsaicin) stimuli. PGD2 did not induce such an enhancement. Following sensitization of peripheral nociceptors with low concentrations of bradykinin or capsaicin, 5-HT (1-10 microM) evoked a ventral root response. Using specific 5-HT-receptor agonists and antagonists, 5-HT-evoked excitation was determined to be mediated via a 5-HT1-like receptor while 5-HT-induced sensitization involved 5-HT2 receptors.

Animals↗
PubMed1993

Bradykinin and inflammatory pain.

There is compelling evidence linking bradykinin (BK) with the pathophysiological processes that accompany tissue damage and inflammation, especially the production of pain and hyperalgesia. Several mechanisms have been proposed to account for hyperalgesia including the direct activation of nociceptors as well as sensitization of nociceptors through the production of prostanoids or the release of other mediators. In keeping with this, antagonists of the BK B2 receptor are efficacious analgesic and anti-inflammatory agents in acute inflammatory pain. More recently it has been suggested that when inflammation is prolonged, BK B1 receptors, which are not expressed in healthy tissues to a significant degree, also play an important role in the maintenance of hyperalgesia. This may be one of a number of adaptive mechanisms that occur peripherally and centrally following the prolonged activation of nociceptors during inflammation or injury.

Animals↗
PubMed1993

Activity of deep dorsal horn neurons in the anaesthetized rat during hyperalgesia of the hindpaw induced by ultraviolet irradiation.

Thermal hyperalgesia was induced by UV irradiation of the glabrous skin of the hindpaw of adult female Sprague-Dawley rats. We have recorded single cell activity and studied excitability changes in wide dynamic range neurons in the lumbar spinal segments during the early phase (days 1-3) and late phase (days 5-7) of thermal hyperalgesia in animals under urethane anaesthesia. The proportion of spontaneously active wide dynamic range cells was increased following UV irradiation and the degree of spontaneous activity was enhanced during the course of hyperalgesia. In addition there was a significant increase in the total number of spikes evoked by standardized mechanical and noxious heat stimuli when tested at days 1-3 and days 5-7. The duration of the evoked responses was also significantly prolonged in both UV-treated groups. The noxious temperature threshold to radiant heat stimulation was significantly decreased on the UV-treated but not on the contralateral hindpaw. The average size of the receptive fields on the UV-treated paws was expanded in comparison to control. To differentiate between possible central and peripheral components of the hyperactivity of wide dynamic range cells we performed in situ dorsal rhizotomy during the recording. Cutting the dorsal roots (L2-5) evoked a significantly larger and more prolonged discharge in wide dynamic range cells in both UV-treated groups in comparison to control. Spontaneous activity in spinal wide dynamic range neurons was reduced after rhizotomy in each group. However, the decrease was only significant at days 1-3 (P < 0.05) but not at days 5-7.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1993

Sensitization of peripheral afferent fibres in the in vitro neonatal rat spinal cord-tail by bradykinin and prostaglandins.

The sensitization of peripheral nociceptors by different prostaglandins was studied in an in vitro preparation of the neonatal spinal cord with functionally attached tail. Nociceptors in the rat tail were activated by chemical (bradykinin, capsaicin) and thermal (heated saline) stimuli and responses were recorded as a depolarization of a ventral root in the lumbar region of the spinal cord (L3-L5). Responses evoked by bradykinin, capsaicin or submaximal thermal stimulation were enhanced in the presence of prostaglandin E1, prostaglandin E2, prostaglandin F2 alpha, prostaglandin I2 and the stable prostaglandin I2 analogue cicaprost, but not by prostaglandin D2. Cyclic AMP and threshold concentrations of bradykinin also induced an enhancement of responses to chemical and thermal stimuli. Responses evoked by small concentrations of bradykinin on unsensitized preparations were reduced by indomethacin or aspirin, whereas responses to maximal concentrations of bradykinin were not affected. Immunocytochemical localization of protein gene product 9.5 and growth associated protein 43 indicated that the neuronal innervation of subepidermal skin layers was preserved in the tail following removal of the most superficial skin layers which was performed in order to facilitate drug access to peripheral nerve endings. These results indicate that different prostaglandins and cyclic AMP sensitize peripheral nerve endings to noxious stimulation without directly activating nociceptors. The stimulation of nociceptors by bradykinin was only partially mediated via arachidonic acid metabolites whereas bradykinin-induced sensitization was independent of cyclo-oxygenase activity.

Afferent Pathways↗
PubMed1993

Capsaicin-induced activation of fine afferent fibres from rat skin in vitro.

A preparation of the hindpaw-skin together with the saphenous nerve from the adult rat was maintained in vitro. This was used to characterize the properties of sensory receptors with slowly conducting nerve fibres (C- and A delta) and to evaluate the effects of capsaicin and the capsaicin antagonist, capsazepine. Mechano-heat sensitive C-fibres were the most sensitive to capsaicin (threshold < 0.3 microM) applied to the receptive field. Other types of C-fibres were less sensitive (mechano-cold sensitive fibres threshold 1 microM) or insensitive (high- and low-threshold mechano-sensitive fibres). Mechano-heat and mechano-cold sensitive A delta-receptors were also activated by capsaicin but high- and low-threshold mechano-sensitive A delta-fibres were insensitive to capsaicin (maximum concentration 3 microM). The capsaicin-induced activation of mechano-heat sensitive C-fibres was concentration dependent with an EC50 = 350 nM. Responses to capsaicin, administered at submaximal concentrations were highly reproducible when administrations were separated by 30 min. Administrations at greater frequency reduced responsiveness to capsaicin. This was accompanied by a slowing of conduction velocity or production of a conduction blockade which was reversible after a few minutes. The activation of mechano-heat sensitive C-fibres by capsaicin could be prevented by capsazepine, indicating the involvement of specific capsaicin receptor-sites. These data show that fine afferents in the rat hindpaw-skin retain receptive properties when maintained in vitro. These fibres exhibit differential sensitivity to capsaicin; mechano-heat sensitive C-fibres being the most sensitive. The activation of this class of fibre was mediated via a specific capsaicin-receptor.

Afferent Pathways↗
PubMed1993

The role of neurokinin and N-methyl-D-aspartate receptors in synaptic transmission from capsaicin-sensitive primary afferents in the rat spinal cord in vitro.

The rat spinal cord with connected dorsal root ganglia was used to study neurokinin and N-methyl-D-aspartate receptors involved in the sensory synaptic transmission of dorsal horn cells. Selective C-fibre excitation was produced by capsaicin (200-500 nM) administered to the dorsal root ganglions. Sixty-nine per cent of dorsal horn cells responded with a postsynaptic depolarization and enhanced synaptic activity, recorded via intracellular electrodes, to capsaicin-activated primary afferent input. Dorsal horn neurons activated by the capsaicin-evoked input were also excited by a 1-min perfusion of the neurokinin-1 receptor agonists substance P methyl ester or GR73 632 and by the neurokinin-2 agonist neurokinin-A. These cells were also depolarized by N-methyl-D-aspartate. Responses to substance P methyl ester and GR73 632 were selectively reduced by the neurokinin-1 receptor antagonist CP96,345, and responses to neurokinin-A were completely blocked by the neurokinin-2 receptor antagonist MEN10 376. The depolarization evoked by N-methyl-D-aspartate was not altered by either of the antagonists, but was completely blocked by the selective N-methyl-D-aspartate receptor antagonist (-)-2-amino-5-phosphonovaleric acid. Capsaicin-evoked responses in the dorsal horn were inhibited by MEN10,376 (63 +/- 13% inhibition) but no significant change was observed with CP96,345. The N-methyl-D-aspartate receptor antagonist (-)-2-amino-5-phosphonovaleric acid consistently inhibited the capsaicin-induced response by 76 +/- 14%. Combination of (-)-2-amino-5-phosphonovaleric acid and MEN10,376 produced an almost complete abolition of the capsaicin-evoked depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1993

Cobalt uptake enables identification of capsaicin- and bradykinin-sensitive subpopulations of rat dorsal root ganglion cells in vitro.

A novel modification of the stimulated cobalt uptake technique has been used to identify rat dorsal root ganglion cells expressing capsaicin and bradykinin receptors. The technique involves incubating intact dorsal root ganglia in vitro in a modified Krebs solution in which cobalt chloride has been substituted for calcium. Activation of dorsal root ganglion cells by capsaicin or bradykinin in the presence of the cobalt ions results in cobalt influx into the excited cells. Histochemical methods were then used to visualize the intracellular accumulation of cobalt, and labelled cells were counted and characterized. Capsaicin (2 microM) or bradykinin (500 nM) applied for 20 min induced cobalt uptake in 13.8 +/- 0.6 and 9.6 +/- 0.5% of neuronal profiles in dorsal root ganglia (L4), respectively, a significantly larger number than stained in control ganglia (in the absence of agonists: 1.8 +/- 0.7%). The longest diameter of the soma of stained dorsal root ganglion cells following capsaicin and bradykinin perfusion were significantly different from each other and from the non-labelled population (17.5 +/- 0.7 and 24.5 +/- 0.2 microns for capsaicin; 23.2 +/- 0.9 and 25.5 +/- 0.4 microns for bradykinin; labelled and non-labelled cells, respectively). The distribution of cell diameters revealed that while capsaicin-sensitive cells were exclusively small-sized, bradykinin-sensitive cells were predominantly small and medium sized. The selective bradykinin-2 receptor antagonist HOE-140 (5.0 microM) blocked the bradykinin-induced staining (2.16 +/- 0.02%) but not that of capsaicin. The bradykinin-1 agonist [des-Arg9]-bradykinin did not induce any significant increase in stained cells over the control number (2.2 +/- 0.7%).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

An in vitro study of the properties of single vagal afferents innervating guinea-pig airways.

1. A novel preparation of the trachea and main bronchi with attached vagus nerve from the guinea-pig maintained in vitro was used to study the properties of single vagal afferent nerve fibres with identified receptive fields. 2. Recordings were made from twenty-eight C fibres with a mean conduction velocity of 0.9 +/- 0.1 m s-1 and twenty-four A delta fibres with a mean conduction velocity of 8.4 +/- 1.3 m s-1. Receptive fields for C and A delta fibres were of small diameter, distributed throughout the trachea and right bronchus and possessed very low mechanical thresholds of 2.2 +/- 0.4 and 1.1 +/- 0.3 mN respectively. 3. The chemosensitivity of isolated afferents was studied by applying drugs directly onto identified receptive fields. A delta fibres were insensitive to capsaicin (up to 3 microM), bradykinin (3 microM), histamine (10 microM) and 5-hydroxytryptamine (5-HT; 10 microM) applied for up to 1 min. Histamine (10 microM), 5-HT (10 microM) and m-chlorophenylbiguanide (10 microM) were also ineffective in exciting C fibres. 4. Capsaicin, at concentrations ranging from 30 nM to 3 microM, evoked a sustained firing of all C fibres tested when applied for a period of 30 s directly onto receptive fields. Bradykinin (0.1-1 microM) also potently excited C fibres in a concentration-related manner. The effect of bradykinin appeared to be mediated by a B2 receptor since it was not mimicked by the selective B1 receptor agonist [des-Arg9]-bradykinin (3 microM) and was abolished by prior application of the selective B2 receptor antagonist D-Arg-[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin (HOE 140; 0.1 microM). HOE 140 was without effect against capsaicin-evoked discharge of C fibres. 5. Capsaicin- and bradykinin-evoked discharge of C fibres was present to a similar degree in preparations pretreated with ibuprofen (1 microM), indicating that it was not dependent on, or influenced by, endogenous prostaglandin production. 6. These data demonstrate that single vagal afferents may be studied in vitro and provide the first examination of the properties of sensory fibres innervating guinea-pig airways. C and A delta fibres both exhibit low threshold mechanical sensitivity but show marked differences in terms of their chemosensitivity.

Amino Acid Sequence↗
PubMed1992

Neuropharmacological mechanisms of capsaicin and related substances.

Capsaicin activates poorly myelinated primary afferent neurons, many of which are polymodal nociceptors. Activation is accompanied by membrane depolarization and the opening of a unique, cation-selective, ion channel which can be blocked by the polyvalent dye ruthenium red. The capsaicin-induced activation is mimicked by resiniferatoxin, a potent analogue, and by low pH. Activation is mediated by a specific membrane receptor which can be selectively and competitively antagonized by capsazepine. Repetitive administration of capsaicin produces a desensitization and an inactivation of sensory neurons. Several mechanisms are involved including receptor inactivation, block of voltage activated calcium channels, intracellular accumulation of ions leading to osmotic changes, and activation of proteolytic enzyme processes. Systemic and topical capsaicin produces a reversible antinociceptive and anti-inflammatory action after an initial undesirable algesic effect. Capsaicin analogues, such as olvanil, have similar properties with minimal initial algesic activity. Antinociception produced by capsaicin does not involve neurotoxicity, sensory neuropeptide depletion or activity at peripheral receptors; rather, systemic capsaicin produces antinociception by activating capsaicin receptors on afferent nerve terminals in the spinal cord. Spinal neurotransmission is blocked by a prolonged inactivation of sensory neurotransmitter release. However, local or topical applications of capsaicin block C-fibre conduction and inactive neuropeptide release from peripheral nerve endings. These mechanisms account for localized antinociception and the reduction of neurogenic inflammation, respectively.

Animals↗
PubMed1992

Mechanism of action of capsaicin-like molecules on sensory neurons.

Capsaicin produces pain by selectively activating polymodal nociceptive neurons. This involves a membrane depolarization and the opening of a unique, cation-selective, ion channel which can be blocked by ruthenium red. The capsaicin-induced activation is mediated by a specific membrane receptor which can be selectively and competitively antagonised by capsazepine. Repetitive administrations of capsaicin produces a desensitization and an inactivation of sensory neurons. Several mechanisms are involved. These include receptor inactivation, block of voltage activated calcium channels, intracellular accumulation of ions leading to osmotic changes and activation of proteolytic enzyme processes. Systemic and topical capsaicin produces a reversible antinociceptive and antiinflammatory action after an initial undesirable algesic effect. Capsaicin analogues, such as olvanil, have similar properties with minimal initial pungency. Systemic capsaicin produces antinociception by activating capsaicin receptors on afferent nerve terminals in the spinal cord. Spinal neurotransmission is subsequently blocked by a prolonged inactivation of sensory neurotransmitter release. Local or topical application of capsaicin blocks C-fibre conduction and inactivates neuropeptide release from peripheral nerve endings. These mechanisms account for localized antinociception and the reduction of neurogenic inflammation respectively.

Animals↗
PubMed1992

Synaptic activation of dorsal horn neurons by selective C-fibre excitation with capsaicin in the mouse spinal cord in vitro.

Low doses (0.2-0.8 microM) of capsaicin were used to achieve selective excitation of C-fibres and the consequent synaptic activation of dorsal horn neurons (laminae I-VI) in the spinal cord of the 12-20-day-old mouse, maintained in vitro. Most dorsal horn cells were activated by application of capsaicin to dorsal root ganglia. The response consisted of a long-lasting membrane depolarization with increased regenerative (synaptic) activity in 79% of the cells, and in a further 7% only an increased synaptic activity was evoked. These effects of capsaicin were completely blocked by removing extracellular calcium ions from the superfusate to the spinal cord, or by the addition of 1 microM tetrodotoxin, suggesting a presynaptic origin of the capsaicin action. Only 67% of cells excited by capsaicin were sensitive to exogenous substance P. The excitatory amino acid antagonists, kynurenic acid (50-100 microM) or (-)-2-amino-5-phosphonovaleric acid (10-20 microM) completely blocked the capsaicin-evoked response in deep dorsal horn cells, indicating the involvement of excitatory amino acid receptors in the synaptic pathway. However, in superficial dorsal horn neurons these antagonists attenuated, but never completely abolished, the capsaicin-evoked depolarization. The kynurenic acid-resistant component of the capsaicin-evoked excitation in superficial dorsal horn cells suggests the involvement of non-amino acid excitatory transmitters--possibly neuropeptides--in the synaptic transmission. Activation of primary afferents by high-intensity electrical stimulation of the dorsal roots induced a prolonged (0.5-3 s) postsynaptic excitation in the majority of deep dorsal horn cells. The duration of the synaptic response was significantly reduced by (-)-2-amino-5-phosphonovaleric acid. Following repeated application of capsaicin, desensitization of the capsaicin-evoked synaptic activation of dorsal horn cells occurred. This effect was paralleled with the loss of the prolonged (-)-2-amino-5-phosphonovaleric acid-sensitive phase of the excitatory postsynaptic potential evoked by the high-intensity electrical stimulation of dorsal roots. This observation suggested that activation of the N-methyl-D-aspartate receptors in the dorsal horn can be activated by small-calibre capsaicin-sensitive fibres. In summary, our data suggest that the selective activation of C-fibre afferents with capsaicin produces synaptic activity in the dorsal horn which has a strong excitatory amino acid component as well as a non-excitatory amino acid, possibly peptidergic, component.

Animals↗