Juan Herrero - Academia.edu (original) (raw)

Papers by Juan Herrero

Brit J Pharmacol, 2002

1 Non-steroidal anti-in¯ammatory drugs (NSAIDs) are eective anti-in¯ammatory and analgesic drugs ... more 1 Non-steroidal anti-in¯ammatory drugs (NSAIDs) are eective anti-in¯ammatory and analgesic drugs although they also induce unwanted side eects due to the inhibition of the physiological eects regulated by prostaglandins. This has led to the search for new compounds with fewer side eects, such as the nitro-NSAIDs (NO-NSAIDs). Paracetamol is an analgesic drug devoid of some of the side eect of the NSAIDs but without anti-in¯ammatory activity. NCX-701 is a nitric oxide releasing version of paracetamol with anti-in¯ammatory and analgesic properties.

European Journal of Pharmacology, 2004

The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspina... more The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspinal sites is not well known, we studied the systemic effects of its agonist N-cyclopentyl-adenosine (CPA) in single motor units from adult-spinalized, intact and sham-spinalized rats. CPA was not effective after spinalization, but it was very effective in intact animals (ID50: 92+/-1.3 microg/kg, noxious pinch) and over 10-fold more potent in sham-spinalized animals (ID50 of 8.3+/-1 microg/kg). Wind-up was also inhibited by CPA. We also studied the effect of CPA in the immature spinal cord preparation, where CPA dose-dependently inhibited responses to low (IC50s: 9+/-0.7 and 7.7+/-1.3 nM) and high intensity stimulation (IC50s: 4.9+/-0.5 and 12.1+/-2 nM). We conclude that the integrity of the spinal cord is crucial for the antinociceptive activity of systemic CPA in adult rats but not in immature rats, not yet influenced by a completely developed supraspinal control.

Survey of Anesthesiology, 1995

The observation that peripheral trauma causes enhanced spinal neuronal excitability has provided ... more The observation that peripheral trauma causes enhanced spinal neuronal excitability has provided the scientific rationale for the concept of "pre-emptive analgesia." The premise has been that only noxious stimuli cause sensitization in sensory pathways, but this premise has not been tested in the conscious state. Responses of single spinal neurons were recorded in instrumented sheep that were untrained and free from drugs or recent surgery, in either fully conscious or halothane-anesthetized states. Receptive field (RF) size was measured before and after non-noxious mechanical conditioning stimulation. Noxious conditioning stimuli in anesthetized sheep caused enlargement of RF areas, as expected. Conditioning with nonpainful scratching or other stimuli was without effect in anesthetized animals; in marked contrast, it caused enlargement of RF size in conscious animals, in which 29 of 33 wide dynamic range units but only 1 of 12 low-threshold mechanoreceptive neurons were affected. Sensitization of spinal sensory neurons evidently is a process that is not restricted to pathologic pain states but rather that occurs under normal physiologic conditions independent of painful stimuli. The significance of such sensitization processes therefore needs reevaluation. The sensitization triggered by non-nociceptive afferents is likely to be opioid-resistant and therefore may contribute to the rather disappointing results seen in several clinical trials of "pre-emptive analgesia."

Cns Drug Rev, 2006

New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their tra... more New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their traditional parent compounds. They are also safer than the classic non-steroidal anti-inflammatory drugs (NSAIDs) and are starting to be used not only for low to moderate intensity pain, but also for high intensity pain. Three different strategies have been followed to improve the pharmacological profile of COX inhibitors:

The peptide neurotransmitter substance P modulates sensitivity to pain by activating the neurokin... more The peptide neurotransmitter substance P modulates sensitivity to pain by activating the neurokinin-1 (NK-1) receptor, which is expressed by discrete populations of neurons throughout the central nervous system. Substance P is synthesized by small-diameter sensory 'pain' fibres, and release of the peptide into the dorsal horn of the spinal cord following intense peripheral stimulation promotes central hyperexcitability and increased sensitivity to pain. However, despite the availability of specific NK-1 antagonists, the function of substance P in the perception of pain remains unclear. Here we investigate the effect of disrupting the gene encoding the NK-1 receptor in mice. We found that the mutant mice were healthy and fertile, but the characteristic amplification ('wind up') and intensity coding of nociceptive reflexes was absent. Although substance P did not mediate the signalling of acute pain or hyperalgesia, it was essential for the full development of stress-induced analgesia and for an aggressive response to territorial challenge, demonstrating that the peptide plays an unexpected role in the adaptive response to stress.

Wind-up is a frequency-dependent increase in the excitability of spinal cord neurones, evoked by ... more Wind-up is a frequency-dependent increase in the excitability of spinal cord neurones, evoked by electrical stimulation of afferent C-fibres. Although it has been studied over the past thirty years, there are still uncertainties about its physiological meaning. Glutamate (NMDA) and tachykinin NK1 receptors are required to generate wind-up and therefore a positive modulation between these two receptor types has been suggested by some authors. However, most drugs capable of reducing the excitability of spinal cord neurones, including opioids and NSAIDs, can also reduce or even abolish wind-up. Thus, other theories involving synaptic efficacy, potassium channels, calcium channels, etc. have also been proposed for the generation of this phenomenon. Whatever the mechanisms involved in its generation, wind-up has been interpreted as a system for the amplification in the spinal cord of the nociceptive message that arrives from peripheral nociceptors connected to C-fibres. This probably reflects the physiological system activated in the spinal cord after an intense or persistent barrage of afferent nociceptive impulses. On the other hand, wind-up, central sensitisation and hyperalgesia are not the same phenomena, although they may share common properties. Wind-up can be an important tool to study the processing of nociceptive information in the spinal cord, and the central effects of drugs that modulate the nociceptive system. This paper reviews the physiological and pharmacological data on wind-up of spinal cord neurones, and the perceptual correlates of wind-up in human subjects, in the context of its possible relation to the triggering of hyperalgesic states, and also the multiple factors which contribute to the generation of wind-up.

Life Sciences, 2005

We have reported that subanalgesic doses of new generation non-steroidal anti-inflammatory drugs ... more We have reported that subanalgesic doses of new generation non-steroidal anti-inflammatory drugs (NSAIDs) enhance the antinociceptive activity of the mu-opiate fentanyl, and the duration of its effect, in acute nociception. Since this therapy is intended for situations of hyperalgesia, we have compared the antinociceptive activity of fentanyl in the absence and in the presence of subeffective doses of NCX-701 (nitroparacetamol) in normal animals and in animals with carrageenan-induced monoarthritis. Subanalgesic dose of NCX-701 did not modify any of the nociceptive responses on its own but reduced the ID50 of fentanyl more than two-fold in both the normal and sensitized states. When administered alone, full recovery from fentanyl was always observed within 15 to 20 minutes, however, full recovery was not observed in the presence of NCX-701. Naloxone was unable to reverse the effect, suggesting a possible reduction of other opiate-mediated secondary effects. We therefore studied the possibility that combining administration of fentanyl and nitroparacetamol (NCX-701) would reduce the development of acute tolerance to fentanyl in behavioral experiments. Acute tolerance to fentanyl in behavioral nociceptive reflexes was developed within 72 h after the constant infusion of the drug, whereas in animals treated with small doses of NCX-701 tolerance was not observed. In summary, our results, both in normal animals and in animals with hyperalgesia, show that fentanyl antinociception can be strongly potentiated with subanalgesic doses of the NSAID NCX-0024-3205/$ -see front matter D Life Sciences 77 www.elsevier.com/locate/lifescie 701 and that the development of acute tolerance to fentanyl in normal animals is prevented by this combination of drugs. D

Pharmacology Biochemistry and Behavior, 2005

Adenosine A1 receptor agonists are effective antinociceptive agents in neuropathic and inflammato... more Adenosine A1 receptor agonists are effective antinociceptive agents in neuropathic and inflammatory pain, though they appear to be weak analgesics in acute nociception. Important discrepancies are observed on the effectiveness and potency of adenosine analogues when comparing different studies, probably due to the use of different ligands, models of antinociception, routes of administration and types of sensitization. We studied the systemic antinociceptive effects of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) in spinal cord neuronal responses from adult male rats in acute nociception and in sensitization due to arthritis and neuropathy. The experiments showed that CPA was effective in the three experimental conditions, with a similar potency in reducing responses to noxious mechanical stimulation (ID50s: 20 +/- 1.2 microg/kg in acute nociception, 18 +/- 1.1 microg/kg in arthritis, 17.4 +/- 2 microg/kg in neuropathy). The phenomenon of wind-up was also dose-dependently reduced by CPA in the three experimental situations although the main action was seen in arthritis. Depression of blood pressure by CPA was not dose-dependent. We conclude that systemic CPA is a potent and effective analgesic in sensitization due to arthritis and neuropathy but also in acute nociception. The effect is independent of the cardiovascular activity and is centrally mediated since wind-up was inhibited.

Neuroscience Letters, 1996

The (RS)-a-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate receptor antagonist... more The (RS)-a-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate receptor antagonists 2,3-dihydroxy-6-nitro-7sulfamoylbenzo[]]quinoxaline (NBQX) and 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) were examined by microiontophoretic administration in electrophysiological tests on spinal neurones in a-chloralose anaesthetized rats. The antagonists significantly reduced extracellularly recorded nociceptive and non-nociceptive responses, as expected; concurrently they reduced background discharge. When the background discharge rate was held constant, the antagonists no longer significantly reduced the evoked responses. This indicates that in the absence of such control, the antagonists decreased cell excitability and only indirectly affected the test responses. Unless such indirect effects have been controlled for, the interpretation of the actions of AMPA/kainate antagonists on evoked synaptic responses is compromised and may be erroneous.

Neuroscience Letters, 1996

During hyperalgesia there is an enhancement of wind-up and the appearance of a novel wind-up of t... more During hyperalgesia there is an enhancement of wind-up and the appearance of a novel wind-up of the A-fibre-mediated responses. We have examined if these phenomena are influenced by supraspinal mechanisms by analysing single motor unit activity in control and arthritic rats, either intact or acutely spinalised. Enhancement of the C-fibre wind-up and the novel A-fibre wind-up were only observed in the intact arthritic animals. We conclude that C-fibre wind-up is a spinal phenomenon, whereas the enhancement of the C-fibre windup and the novel A-fibre wind-up during arthritis depend also on supraspinal influences.

Neuroscience, 1997

The importance of receptors for N-methyl-D-aspartate in synaptic plasticity and in triggering lon... more The importance of receptors for N-methyl-D-aspartate in synaptic plasticity and in triggering long-term pronociceptive changes is explained by their voltage-dependence. This suggests that their contribution to acute nociceptive responses would be determined both by the magnitude of synaptic input and by the level of background excitation. We have now examined the role of N-methyl-D-aspartate receptors in acute nociceptive transmission in the spinal cord. Drugs selectively affecting activity mediated by these receptors were tested on responses of dorsal horn neurons to noxious stimuli of different intensities and at different levels of ongoing spike discharge. The drugs used were the N-methyl-D-aspartate receptor channel blocker ketamine; the competitive antagonists, 3-((R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (D-CPP) and D-2-amino-5-phosphonopentanoic acid (D-AP5), and the positive modulator thyrotropin-releasing hormone. The activity of dorsal horn wide dynamic range neurons was recorded extracellularly in alpha-chloralose-anaesthetized spinalized rats. Their responses to noxious stimuli (pinch, heat and electrical) were monitored in parallel with responses to iontophoretic N-methyl-D-aspartate and (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA). Drugs were given i.v. or (D-AP5) iontophoretically. At doses that selectively inhibited responses to exogenous N-methyl-D-aspartate, ketamine (4 or 8, mean 5 mg/kg i.v.) reduced the nociceptive responses of the majority of the cells in deep dorsal horn. Ketamine also reduced wind-up of the responses to repetitive electrical stimulation. Ketamine (4 or 8 mg/kg). D-CPP (2 mg/kg), D-AP5 (iontophoretically) and thyrotrophin-releasing hormone (1 mg/kg) were tested on different magnitude nociceptive responses evoked by alternating intensities of noxious heat or pinch. In percentage terms, the less vigorous responses were affected by all four drugs as much as or more than the more vigorous responses. When background activity of neurones was enhanced by continuous activation of C-fibres with cutaneous application of mustard oil, ketamine was less effective against superimposed noxious pinch responses. Ongoing background activity was affected in parallel with evoked responses. When background discharge of the cells was maintained at a stable level with continuous ejection of kainate, neither the N-methyl-D-aspartate antagonists nor thyrotrophin-relasing hormone affected the responses to noxious pinch or heat, although responses to exogenous N-methyl-D-aspartate were still blocked. The wind-up of the electrical responses was, however, reduced by ketamine irrespective of the level of background activity. The results indicate that under these conditions in vivo, N-methyl-D-aspartate receptors mediate ongoing low-frequency background activity rather than phasic high-frequency nociceptive responses. The effects of N-methyl-D-aspartate antagonists and positive modulators on nociceptive responses are evidently indirect, being secondary to changes in background synaptic excitation. These results cannot be explained simply in relation to the voltage-dependence of N-methyl-D-aspartate receptor-mediated activity; other factors, such as modulation by neuropeptides, must be involved.

Neuropharmacology, 2001

Non-steroidal antiinflammatory drugs (NSAIDs) inhibit the cyclooxygenase (COX) enzyme and so they... more Non-steroidal antiinflammatory drugs (NSAIDs) inhibit the cyclooxygenase (COX) enzyme and so they are effective analgesic, antiinflammatory and antipyretic drugs. The discovery of COX-2 led to the search for new NSAIDs with a selective action over this isoenzyme. The experiments performed to date have shown either more, less or no different efficacy of new COX-2 selective NSAIDs when compared to the non-selective inhibitors, probably because the comparison has not been performed under similar conditions. We have therefore compared the analgesic activity of six NSAIDs with different selectivity for the COX isoenzymes. The experiments were performed using the recording of spinal cord nociceptive reflexes in anaesthetised rats and in awake mice. The non-selective COX inhibitors, such as dexketoprofen trometamol, were effective in reducing nociceptive responses both in normal and monoarthritic rats (ED50s: 0.31 and 3.97 µmol/kg, respectively), and in mice with paw inflammation (12.5 µmol/kg, pϽ0.01). The COX-1 selective inhibitor SC-58560 showed efficacy in normal rats (ED50: 0.8 µmol/kg) and in mice with paw inflammation (15 µmol/kg, pϽ0.05), but not in monoarthritic rats. The COX-2 selective inhibitors celecoxib (105 µmol/kg) and rofecoxib (128 µmol/kg) however, were not effective in any of the groups studied. We conclude that inhibition of both COX isoenzymes is needed to achieve an effective analgesia in inflammation. 

Neuropharmacology, 1997

Ketoprofen is a non-steroidal antiinflammatory drug (NSAID) which provides effective analgesia in... more Ketoprofen is a non-steroidal antiinflammatory drug (NSAID) which provides effective analgesia in situations of pain provoked by tissue inflammation. However, the location of its analgesic effects, (peripheral tissues versus central nervous system), have not been clearly identified and separated. In the present study the effectiveness of ketoprofen was examined in two different types of experiments: (i) Open field behavioural tests in conscious rats, and (ii) spinal cord nociceptive reflexes (single motor units) activated by electrical and thermal stimulation in chloralose anaesthetised rats. The experiments were performed in rats with carrageenaninduced inflammation of one hindpaw, or of one knee joint. The administration of ketoprofen significantly inhibited the reduction of exploratory movements caused by inflammation in open field experiments. Ketoprofen was also effective in depressing reflex activity evoked by electrical and noxious thermal stimulation of the skin, either in inflamed tissue or in normal tissue of monoarthritic animals. It was also effective in the reduction of reflex wind-up; a phenomenon in which the activity of spinal cord neurones increases progressively with high frequency electrical stimulation. We therefore conclude that ketoprofen has central as well as peripheral analgesic activity. 0 1997 Published by Elsevier Science Ltd.

Laboratory Animals, 2003

The technique of recording spinal cord withdrawal re exes as single motor units (SMUs) does not r... more The technique of recording spinal cord withdrawal re exes as single motor units (SMUs) does not require intense preparatory surgery and allows the study of the nociceptive system in physiological conditions. It has been used to show that the wind-up phenomenon depends on the level of excitability of spinal cord neurones, the integrity of the spinal cord and the parameters of the stimulation used. We have now used SMU recordings to assess whether wind-up is also an heterogeneous phenomenon depending on the muscle studied, and, if so, how the presence of hyperalgesia affects its generation. The experiments were performed in normal and carrageenan-induced in ammation in male Wistar rats anesthetized with achloralose. Wind-up was recorded in units from peroneus longus, tibialis anterior and extensor digitorum longus. The results showed that in normal animals, the curves of C-bre mediated wind-up reached saturation at different times and the shape of the curves was different depending on the muscle studied and on the intensity of stimulation used. In in ammation, however, C-bre mediated wind-up became very uniform in the muscles studied, with a similar shape and saturation point. A-bre mediated wind-up was only observed in animals with in ammation and no differences were observed between muscles. We conclude that in the absence of preparatory surgery and in ammation, C-bre wind-up is heterogeneous, and supports a modular organization of nociceptive spinal re exes. In hyperalgesia, however, wind-up curves are similar in units from different muscles, con rming a loss of modular organization that also affects the generation of wind-up.

Journal of Neuroscience Methods, 1997

Recordings of withdrawal reflexes have been used extensively to study sensory-motor integration a... more Recordings of withdrawal reflexes have been used extensively to study sensory-motor integration and processing of nociceptive information in the spinal cord. We describe here a new technique for the manufacture of improved EMG electrodes that permit the characterisation of the physiological properties of single motor units as well as the easy location of the muscles studied. Individual motor units from three rat hind-limb muscles: peroneus longus, tibialis cranialis and extensor digitorum longus, were activated by thermal and mechanical stimulation applied to their cutaneous receptive fields, which were located mainly on the 4th and 5th toes. Thresholds for thermal and mechanical (Von Frey hairs) stimulation were similar in the three muscles studied, with a value of 44 +/- 1 degrees C and 100 mN (median), respectively. However, when a mechanical pincher with a stimulus area of 14 mm2 was used, the values seen were similar for peroneus longus and tibialis cranialis (342 +/- 23 and 330 +/- 71 mN, respectively, mean +/- S.E.M.) but lower for extensor digitorum longus (220 +/- 37 mN, mean +/- S.E.M.). The firing rate of the single motor units was similar for all types of stimulation at threshold intensity, and showed a linear relationship with stimulus intensity, except for units of the tibialis cranialis, which showed a greater degree of adaptation.

Journal of Neuroinflammation, 2007

Background: Gabapentin is a structural analogue of gamma-aminobutyric acid with strong anticonvul... more Background: Gabapentin is a structural analogue of gamma-aminobutyric acid with strong anticonvulsant and analgesic activities. Important discrepancies are observed on the effectiveness and potency of gabapentin in acute nociception and sensitization due to inflammation and neuropathy. There is also some controversy in the literature on whether gabapentin is only active in central areas of the nervous system or is also effective in the periphery. This is probably due to the use of different experimental models, routes of administration and types of sensitization. The aim of the present study was to investigate the influence of the spinal cord sensitization on the antinociceptive activity of gabapentin in the absence and in the presence of monoarthritis and neuropathy, using the same experimental protocol of stimulation and the same technique of evaluation of antinociception.

Inflammation Research, 1997

Objective and Design: To study the characteristics and site of the analgesic action of meloxicam.... more Objective and Design: To study the characteristics and site of the analgesic action of meloxicam. Subjects: Adult female Wistar rats. Treatment: Monoarthritis was induced (for behavioural studies) by injection of complete Freund's adjuvant into the ankle. Meloxicam was given for 5 days (0.1-4 mg/kg/ day i.p.). Inflammation of the knee or paw (for electrophysiology) was induced with carrageenan. Meloxicam was given i.v. (4-64 mg/kg). Methods: Rats were tested daily for joint hyperalgesia, and hindlimb posture (behaviour). At post-mortem, joint stiffness, oedema and gastric lesions were assessed. In anaesthetised rats, nociceptive reflex responses to stimulation of the paw were compared (electrophysiology). Statistics were performed using one-way analysis of variance. Results: Meloxicam reduced swelling and stiffness of the inflamed joint, joint hyperalgesia (ID50 ¼ 0:4 Ϯ 0:4 mg/kg/ day) and spontaneous pain-related behaviour. It also inhibited peripherally mediated reflex responses to stimulation of inflamed tissue (ID50 ¼ 7:6 Ϯ 0:8 mg/kg i.v.) without affecting centrally mediated reflexes. Conclusions: Systemic meloxicam produces analgesia largely via peripheral mechanisms. The rapidity of its actions indicates a direct effect on sensitised nociceptors.

European Journal of Pharmacology, 2004

The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspina... more The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspinal sites is not well known, we studied the systemic effects of its agonist N-cyclopentyl-adenosine (CPA) in single motor units from adult-spinalized, intact and sham-spinalized rats. CPA was not effective after spinalization, but it was very effective in intact animals (ID50: 92+/-1.3 microg/kg, noxious pinch) and over 10-fold more potent in sham-spinalized animals (ID50 of 8.3+/-1 microg/kg). Wind-up was also inhibited by CPA. We also studied the effect of CPA in the immature spinal cord preparation, where CPA dose-dependently inhibited responses to low (IC50s: 9+/-0.7 and 7.7+/-1.3 nM) and high intensity stimulation (IC50s: 4.9+/-0.5 and 12.1+/-2 nM). We conclude that the integrity of the spinal cord is crucial for the antinociceptive activity of systemic CPA in adult rats but not in immature rats, not yet influenced by a completely developed supraspinal control.

European Journal of Pharmacology, 2003

We have reported that subeffective doses of the nonsteroidal anti-inflammatory drug (NSAID) dexke... more We have reported that subeffective doses of the nonsteroidal anti-inflammatory drug (NSAID) dexketoprofen trometamol enhances micro-opioid receptor agonist fentanyl antinociception. The aim of this study was to assess if this effect can also be observed with other new cyclooxygenase-inhibitors such as nitroparacetamol, and in responses to high intensity electrical stimulation (wind-up). Single motor units were recorded in male Wistar rats under alpha-chloralose anaesthesia. The antinociceptive effect of fentanyl was studied alone and in the presence of subeffective doses of dexketoprofen trometamol or nitroparacetamol. In responses to noxious mechanical stimulation, the potency of fentanyl was enhanced by more than threefold in the presence of the NSAIDs and no significant recovery was observed after 45 min. The opioid antagonist naloxone and the alpha(2)-adrenoceptor antagonist atipamezol did not reverse the effect. The enhancement of the effect of fentanyl in wind-up was lower though significant. We conclude that the co-administration of subeffective doses of new cyclooxygenase-inhibitors and the micro-opioid receptor agonist fentanyl should be considered as a potential pain therapy.

Brit J Pharmacol, 2002

1 Non-steroidal anti-in¯ammatory drugs (NSAIDs) are eective anti-in¯ammatory and analgesic drugs ... more 1 Non-steroidal anti-in¯ammatory drugs (NSAIDs) are eective anti-in¯ammatory and analgesic drugs although they also induce unwanted side eects due to the inhibition of the physiological eects regulated by prostaglandins. This has led to the search for new compounds with fewer side eects, such as the nitro-NSAIDs (NO-NSAIDs). Paracetamol is an analgesic drug devoid of some of the side eect of the NSAIDs but without anti-in¯ammatory activity. NCX-701 is a nitric oxide releasing version of paracetamol with anti-in¯ammatory and analgesic properties.

European Journal of Pharmacology, 2004

The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspina... more The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspinal sites is not well known, we studied the systemic effects of its agonist N-cyclopentyl-adenosine (CPA) in single motor units from adult-spinalized, intact and sham-spinalized rats. CPA was not effective after spinalization, but it was very effective in intact animals (ID50: 92+/-1.3 microg/kg, noxious pinch) and over 10-fold more potent in sham-spinalized animals (ID50 of 8.3+/-1 microg/kg). Wind-up was also inhibited by CPA. We also studied the effect of CPA in the immature spinal cord preparation, where CPA dose-dependently inhibited responses to low (IC50s: 9+/-0.7 and 7.7+/-1.3 nM) and high intensity stimulation (IC50s: 4.9+/-0.5 and 12.1+/-2 nM). We conclude that the integrity of the spinal cord is crucial for the antinociceptive activity of systemic CPA in adult rats but not in immature rats, not yet influenced by a completely developed supraspinal control.

Survey of Anesthesiology, 1995

The observation that peripheral trauma causes enhanced spinal neuronal excitability has provided ... more The observation that peripheral trauma causes enhanced spinal neuronal excitability has provided the scientific rationale for the concept of "pre-emptive analgesia." The premise has been that only noxious stimuli cause sensitization in sensory pathways, but this premise has not been tested in the conscious state. Responses of single spinal neurons were recorded in instrumented sheep that were untrained and free from drugs or recent surgery, in either fully conscious or halothane-anesthetized states. Receptive field (RF) size was measured before and after non-noxious mechanical conditioning stimulation. Noxious conditioning stimuli in anesthetized sheep caused enlargement of RF areas, as expected. Conditioning with nonpainful scratching or other stimuli was without effect in anesthetized animals; in marked contrast, it caused enlargement of RF size in conscious animals, in which 29 of 33 wide dynamic range units but only 1 of 12 low-threshold mechanoreceptive neurons were affected. Sensitization of spinal sensory neurons evidently is a process that is not restricted to pathologic pain states but rather that occurs under normal physiologic conditions independent of painful stimuli. The significance of such sensitization processes therefore needs reevaluation. The sensitization triggered by non-nociceptive afferents is likely to be opioid-resistant and therefore may contribute to the rather disappointing results seen in several clinical trials of "pre-emptive analgesia."

Cns Drug Rev, 2006

New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their tra... more New generations of cyclooxygenase (COX) inhibitors are more potent and efficacious than their traditional parent compounds. They are also safer than the classic non-steroidal anti-inflammatory drugs (NSAIDs) and are starting to be used not only for low to moderate intensity pain, but also for high intensity pain. Three different strategies have been followed to improve the pharmacological profile of COX inhibitors:

The peptide neurotransmitter substance P modulates sensitivity to pain by activating the neurokin... more The peptide neurotransmitter substance P modulates sensitivity to pain by activating the neurokinin-1 (NK-1) receptor, which is expressed by discrete populations of neurons throughout the central nervous system. Substance P is synthesized by small-diameter sensory 'pain' fibres, and release of the peptide into the dorsal horn of the spinal cord following intense peripheral stimulation promotes central hyperexcitability and increased sensitivity to pain. However, despite the availability of specific NK-1 antagonists, the function of substance P in the perception of pain remains unclear. Here we investigate the effect of disrupting the gene encoding the NK-1 receptor in mice. We found that the mutant mice were healthy and fertile, but the characteristic amplification ('wind up') and intensity coding of nociceptive reflexes was absent. Although substance P did not mediate the signalling of acute pain or hyperalgesia, it was essential for the full development of stress-induced analgesia and for an aggressive response to territorial challenge, demonstrating that the peptide plays an unexpected role in the adaptive response to stress.

Wind-up is a frequency-dependent increase in the excitability of spinal cord neurones, evoked by ... more Wind-up is a frequency-dependent increase in the excitability of spinal cord neurones, evoked by electrical stimulation of afferent C-fibres. Although it has been studied over the past thirty years, there are still uncertainties about its physiological meaning. Glutamate (NMDA) and tachykinin NK1 receptors are required to generate wind-up and therefore a positive modulation between these two receptor types has been suggested by some authors. However, most drugs capable of reducing the excitability of spinal cord neurones, including opioids and NSAIDs, can also reduce or even abolish wind-up. Thus, other theories involving synaptic efficacy, potassium channels, calcium channels, etc. have also been proposed for the generation of this phenomenon. Whatever the mechanisms involved in its generation, wind-up has been interpreted as a system for the amplification in the spinal cord of the nociceptive message that arrives from peripheral nociceptors connected to C-fibres. This probably reflects the physiological system activated in the spinal cord after an intense or persistent barrage of afferent nociceptive impulses. On the other hand, wind-up, central sensitisation and hyperalgesia are not the same phenomena, although they may share common properties. Wind-up can be an important tool to study the processing of nociceptive information in the spinal cord, and the central effects of drugs that modulate the nociceptive system. This paper reviews the physiological and pharmacological data on wind-up of spinal cord neurones, and the perceptual correlates of wind-up in human subjects, in the context of its possible relation to the triggering of hyperalgesic states, and also the multiple factors which contribute to the generation of wind-up.

Life Sciences, 2005

We have reported that subanalgesic doses of new generation non-steroidal anti-inflammatory drugs ... more We have reported that subanalgesic doses of new generation non-steroidal anti-inflammatory drugs (NSAIDs) enhance the antinociceptive activity of the mu-opiate fentanyl, and the duration of its effect, in acute nociception. Since this therapy is intended for situations of hyperalgesia, we have compared the antinociceptive activity of fentanyl in the absence and in the presence of subeffective doses of NCX-701 (nitroparacetamol) in normal animals and in animals with carrageenan-induced monoarthritis. Subanalgesic dose of NCX-701 did not modify any of the nociceptive responses on its own but reduced the ID50 of fentanyl more than two-fold in both the normal and sensitized states. When administered alone, full recovery from fentanyl was always observed within 15 to 20 minutes, however, full recovery was not observed in the presence of NCX-701. Naloxone was unable to reverse the effect, suggesting a possible reduction of other opiate-mediated secondary effects. We therefore studied the possibility that combining administration of fentanyl and nitroparacetamol (NCX-701) would reduce the development of acute tolerance to fentanyl in behavioral experiments. Acute tolerance to fentanyl in behavioral nociceptive reflexes was developed within 72 h after the constant infusion of the drug, whereas in animals treated with small doses of NCX-701 tolerance was not observed. In summary, our results, both in normal animals and in animals with hyperalgesia, show that fentanyl antinociception can be strongly potentiated with subanalgesic doses of the NSAID NCX-0024-3205/$ -see front matter D Life Sciences 77 www.elsevier.com/locate/lifescie 701 and that the development of acute tolerance to fentanyl in normal animals is prevented by this combination of drugs. D

Pharmacology Biochemistry and Behavior, 2005

Adenosine A1 receptor agonists are effective antinociceptive agents in neuropathic and inflammato... more Adenosine A1 receptor agonists are effective antinociceptive agents in neuropathic and inflammatory pain, though they appear to be weak analgesics in acute nociception. Important discrepancies are observed on the effectiveness and potency of adenosine analogues when comparing different studies, probably due to the use of different ligands, models of antinociception, routes of administration and types of sensitization. We studied the systemic antinociceptive effects of the adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) in spinal cord neuronal responses from adult male rats in acute nociception and in sensitization due to arthritis and neuropathy. The experiments showed that CPA was effective in the three experimental conditions, with a similar potency in reducing responses to noxious mechanical stimulation (ID50s: 20 +/- 1.2 microg/kg in acute nociception, 18 +/- 1.1 microg/kg in arthritis, 17.4 +/- 2 microg/kg in neuropathy). The phenomenon of wind-up was also dose-dependently reduced by CPA in the three experimental situations although the main action was seen in arthritis. Depression of blood pressure by CPA was not dose-dependent. We conclude that systemic CPA is a potent and effective analgesic in sensitization due to arthritis and neuropathy but also in acute nociception. The effect is independent of the cardiovascular activity and is centrally mediated since wind-up was inhibited.

Neuroscience Letters, 1996

The (RS)-a-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate receptor antagonist... more The (RS)-a-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA)/kainate receptor antagonists 2,3-dihydroxy-6-nitro-7sulfamoylbenzo[]]quinoxaline (NBQX) and 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) were examined by microiontophoretic administration in electrophysiological tests on spinal neurones in a-chloralose anaesthetized rats. The antagonists significantly reduced extracellularly recorded nociceptive and non-nociceptive responses, as expected; concurrently they reduced background discharge. When the background discharge rate was held constant, the antagonists no longer significantly reduced the evoked responses. This indicates that in the absence of such control, the antagonists decreased cell excitability and only indirectly affected the test responses. Unless such indirect effects have been controlled for, the interpretation of the actions of AMPA/kainate antagonists on evoked synaptic responses is compromised and may be erroneous.

Neuroscience Letters, 1996

During hyperalgesia there is an enhancement of wind-up and the appearance of a novel wind-up of t... more During hyperalgesia there is an enhancement of wind-up and the appearance of a novel wind-up of the A-fibre-mediated responses. We have examined if these phenomena are influenced by supraspinal mechanisms by analysing single motor unit activity in control and arthritic rats, either intact or acutely spinalised. Enhancement of the C-fibre wind-up and the novel A-fibre wind-up were only observed in the intact arthritic animals. We conclude that C-fibre wind-up is a spinal phenomenon, whereas the enhancement of the C-fibre windup and the novel A-fibre wind-up during arthritis depend also on supraspinal influences.

Neuroscience, 1997

The importance of receptors for N-methyl-D-aspartate in synaptic plasticity and in triggering lon... more The importance of receptors for N-methyl-D-aspartate in synaptic plasticity and in triggering long-term pronociceptive changes is explained by their voltage-dependence. This suggests that their contribution to acute nociceptive responses would be determined both by the magnitude of synaptic input and by the level of background excitation. We have now examined the role of N-methyl-D-aspartate receptors in acute nociceptive transmission in the spinal cord. Drugs selectively affecting activity mediated by these receptors were tested on responses of dorsal horn neurons to noxious stimuli of different intensities and at different levels of ongoing spike discharge. The drugs used were the N-methyl-D-aspartate receptor channel blocker ketamine; the competitive antagonists, 3-((R)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (D-CPP) and D-2-amino-5-phosphonopentanoic acid (D-AP5), and the positive modulator thyrotropin-releasing hormone. The activity of dorsal horn wide dynamic range neurons was recorded extracellularly in alpha-chloralose-anaesthetized spinalized rats. Their responses to noxious stimuli (pinch, heat and electrical) were monitored in parallel with responses to iontophoretic N-methyl-D-aspartate and (RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA). Drugs were given i.v. or (D-AP5) iontophoretically. At doses that selectively inhibited responses to exogenous N-methyl-D-aspartate, ketamine (4 or 8, mean 5 mg/kg i.v.) reduced the nociceptive responses of the majority of the cells in deep dorsal horn. Ketamine also reduced wind-up of the responses to repetitive electrical stimulation. Ketamine (4 or 8 mg/kg). D-CPP (2 mg/kg), D-AP5 (iontophoretically) and thyrotrophin-releasing hormone (1 mg/kg) were tested on different magnitude nociceptive responses evoked by alternating intensities of noxious heat or pinch. In percentage terms, the less vigorous responses were affected by all four drugs as much as or more than the more vigorous responses. When background activity of neurones was enhanced by continuous activation of C-fibres with cutaneous application of mustard oil, ketamine was less effective against superimposed noxious pinch responses. Ongoing background activity was affected in parallel with evoked responses. When background discharge of the cells was maintained at a stable level with continuous ejection of kainate, neither the N-methyl-D-aspartate antagonists nor thyrotrophin-relasing hormone affected the responses to noxious pinch or heat, although responses to exogenous N-methyl-D-aspartate were still blocked. The wind-up of the electrical responses was, however, reduced by ketamine irrespective of the level of background activity. The results indicate that under these conditions in vivo, N-methyl-D-aspartate receptors mediate ongoing low-frequency background activity rather than phasic high-frequency nociceptive responses. The effects of N-methyl-D-aspartate antagonists and positive modulators on nociceptive responses are evidently indirect, being secondary to changes in background synaptic excitation. These results cannot be explained simply in relation to the voltage-dependence of N-methyl-D-aspartate receptor-mediated activity; other factors, such as modulation by neuropeptides, must be involved.

Neuropharmacology, 2001

Non-steroidal antiinflammatory drugs (NSAIDs) inhibit the cyclooxygenase (COX) enzyme and so they... more Non-steroidal antiinflammatory drugs (NSAIDs) inhibit the cyclooxygenase (COX) enzyme and so they are effective analgesic, antiinflammatory and antipyretic drugs. The discovery of COX-2 led to the search for new NSAIDs with a selective action over this isoenzyme. The experiments performed to date have shown either more, less or no different efficacy of new COX-2 selective NSAIDs when compared to the non-selective inhibitors, probably because the comparison has not been performed under similar conditions. We have therefore compared the analgesic activity of six NSAIDs with different selectivity for the COX isoenzymes. The experiments were performed using the recording of spinal cord nociceptive reflexes in anaesthetised rats and in awake mice. The non-selective COX inhibitors, such as dexketoprofen trometamol, were effective in reducing nociceptive responses both in normal and monoarthritic rats (ED50s: 0.31 and 3.97 µmol/kg, respectively), and in mice with paw inflammation (12.5 µmol/kg, pϽ0.01). The COX-1 selective inhibitor SC-58560 showed efficacy in normal rats (ED50: 0.8 µmol/kg) and in mice with paw inflammation (15 µmol/kg, pϽ0.05), but not in monoarthritic rats. The COX-2 selective inhibitors celecoxib (105 µmol/kg) and rofecoxib (128 µmol/kg) however, were not effective in any of the groups studied. We conclude that inhibition of both COX isoenzymes is needed to achieve an effective analgesia in inflammation. 

Neuropharmacology, 1997

Ketoprofen is a non-steroidal antiinflammatory drug (NSAID) which provides effective analgesia in... more Ketoprofen is a non-steroidal antiinflammatory drug (NSAID) which provides effective analgesia in situations of pain provoked by tissue inflammation. However, the location of its analgesic effects, (peripheral tissues versus central nervous system), have not been clearly identified and separated. In the present study the effectiveness of ketoprofen was examined in two different types of experiments: (i) Open field behavioural tests in conscious rats, and (ii) spinal cord nociceptive reflexes (single motor units) activated by electrical and thermal stimulation in chloralose anaesthetised rats. The experiments were performed in rats with carrageenaninduced inflammation of one hindpaw, or of one knee joint. The administration of ketoprofen significantly inhibited the reduction of exploratory movements caused by inflammation in open field experiments. Ketoprofen was also effective in depressing reflex activity evoked by electrical and noxious thermal stimulation of the skin, either in inflamed tissue or in normal tissue of monoarthritic animals. It was also effective in the reduction of reflex wind-up; a phenomenon in which the activity of spinal cord neurones increases progressively with high frequency electrical stimulation. We therefore conclude that ketoprofen has central as well as peripheral analgesic activity. 0 1997 Published by Elsevier Science Ltd.

Laboratory Animals, 2003

The technique of recording spinal cord withdrawal re exes as single motor units (SMUs) does not r... more The technique of recording spinal cord withdrawal re exes as single motor units (SMUs) does not require intense preparatory surgery and allows the study of the nociceptive system in physiological conditions. It has been used to show that the wind-up phenomenon depends on the level of excitability of spinal cord neurones, the integrity of the spinal cord and the parameters of the stimulation used. We have now used SMU recordings to assess whether wind-up is also an heterogeneous phenomenon depending on the muscle studied, and, if so, how the presence of hyperalgesia affects its generation. The experiments were performed in normal and carrageenan-induced in ammation in male Wistar rats anesthetized with achloralose. Wind-up was recorded in units from peroneus longus, tibialis anterior and extensor digitorum longus. The results showed that in normal animals, the curves of C-bre mediated wind-up reached saturation at different times and the shape of the curves was different depending on the muscle studied and on the intensity of stimulation used. In in ammation, however, C-bre mediated wind-up became very uniform in the muscles studied, with a similar shape and saturation point. A-bre mediated wind-up was only observed in animals with in ammation and no differences were observed between muscles. We conclude that in the absence of preparatory surgery and in ammation, C-bre wind-up is heterogeneous, and supports a modular organization of nociceptive spinal re exes. In hyperalgesia, however, wind-up curves are similar in units from different muscles, con rming a loss of modular organization that also affects the generation of wind-up.

Journal of Neuroscience Methods, 1997

Recordings of withdrawal reflexes have been used extensively to study sensory-motor integration a... more Recordings of withdrawal reflexes have been used extensively to study sensory-motor integration and processing of nociceptive information in the spinal cord. We describe here a new technique for the manufacture of improved EMG electrodes that permit the characterisation of the physiological properties of single motor units as well as the easy location of the muscles studied. Individual motor units from three rat hind-limb muscles: peroneus longus, tibialis cranialis and extensor digitorum longus, were activated by thermal and mechanical stimulation applied to their cutaneous receptive fields, which were located mainly on the 4th and 5th toes. Thresholds for thermal and mechanical (Von Frey hairs) stimulation were similar in the three muscles studied, with a value of 44 +/- 1 degrees C and 100 mN (median), respectively. However, when a mechanical pincher with a stimulus area of 14 mm2 was used, the values seen were similar for peroneus longus and tibialis cranialis (342 +/- 23 and 330 +/- 71 mN, respectively, mean +/- S.E.M.) but lower for extensor digitorum longus (220 +/- 37 mN, mean +/- S.E.M.). The firing rate of the single motor units was similar for all types of stimulation at threshold intensity, and showed a linear relationship with stimulus intensity, except for units of the tibialis cranialis, which showed a greater degree of adaptation.

Journal of Neuroinflammation, 2007

Background: Gabapentin is a structural analogue of gamma-aminobutyric acid with strong anticonvul... more Background: Gabapentin is a structural analogue of gamma-aminobutyric acid with strong anticonvulsant and analgesic activities. Important discrepancies are observed on the effectiveness and potency of gabapentin in acute nociception and sensitization due to inflammation and neuropathy. There is also some controversy in the literature on whether gabapentin is only active in central areas of the nervous system or is also effective in the periphery. This is probably due to the use of different experimental models, routes of administration and types of sensitization. The aim of the present study was to investigate the influence of the spinal cord sensitization on the antinociceptive activity of gabapentin in the absence and in the presence of monoarthritis and neuropathy, using the same experimental protocol of stimulation and the same technique of evaluation of antinociception.

Inflammation Research, 1997

Objective and Design: To study the characteristics and site of the analgesic action of meloxicam.... more Objective and Design: To study the characteristics and site of the analgesic action of meloxicam. Subjects: Adult female Wistar rats. Treatment: Monoarthritis was induced (for behavioural studies) by injection of complete Freund's adjuvant into the ankle. Meloxicam was given for 5 days (0.1-4 mg/kg/ day i.p.). Inflammation of the knee or paw (for electrophysiology) was induced with carrageenan. Meloxicam was given i.v. (4-64 mg/kg). Methods: Rats were tested daily for joint hyperalgesia, and hindlimb posture (behaviour). At post-mortem, joint stiffness, oedema and gastric lesions were assessed. In anaesthetised rats, nociceptive reflex responses to stimulation of the paw were compared (electrophysiology). Statistics were performed using one-way analysis of variance. Results: Meloxicam reduced swelling and stiffness of the inflamed joint, joint hyperalgesia (ID50 ¼ 0:4 Ϯ 0:4 mg/kg/ day) and spontaneous pain-related behaviour. It also inhibited peripherally mediated reflex responses to stimulation of inflamed tissue (ID50 ¼ 7:6 Ϯ 0:8 mg/kg i.v.) without affecting centrally mediated reflexes. Conclusions: Systemic meloxicam produces analgesia largely via peripheral mechanisms. The rapidity of its actions indicates a direct effect on sensitised nociceptors.

European Journal of Pharmacology, 2004

The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspina... more The adenosine A(1) receptor is involved in spinal cord antinociception. As its role at supraspinal sites is not well known, we studied the systemic effects of its agonist N-cyclopentyl-adenosine (CPA) in single motor units from adult-spinalized, intact and sham-spinalized rats. CPA was not effective after spinalization, but it was very effective in intact animals (ID50: 92+/-1.3 microg/kg, noxious pinch) and over 10-fold more potent in sham-spinalized animals (ID50 of 8.3+/-1 microg/kg). Wind-up was also inhibited by CPA. We also studied the effect of CPA in the immature spinal cord preparation, where CPA dose-dependently inhibited responses to low (IC50s: 9+/-0.7 and 7.7+/-1.3 nM) and high intensity stimulation (IC50s: 4.9+/-0.5 and 12.1+/-2 nM). We conclude that the integrity of the spinal cord is crucial for the antinociceptive activity of systemic CPA in adult rats but not in immature rats, not yet influenced by a completely developed supraspinal control.

European Journal of Pharmacology, 2003

We have reported that subeffective doses of the nonsteroidal anti-inflammatory drug (NSAID) dexke... more We have reported that subeffective doses of the nonsteroidal anti-inflammatory drug (NSAID) dexketoprofen trometamol enhances micro-opioid receptor agonist fentanyl antinociception. The aim of this study was to assess if this effect can also be observed with other new cyclooxygenase-inhibitors such as nitroparacetamol, and in responses to high intensity electrical stimulation (wind-up). Single motor units were recorded in male Wistar rats under alpha-chloralose anaesthesia. The antinociceptive effect of fentanyl was studied alone and in the presence of subeffective doses of dexketoprofen trometamol or nitroparacetamol. In responses to noxious mechanical stimulation, the potency of fentanyl was enhanced by more than threefold in the presence of the NSAIDs and no significant recovery was observed after 45 min. The opioid antagonist naloxone and the alpha(2)-adrenoceptor antagonist atipamezol did not reverse the effect. The enhancement of the effect of fentanyl in wind-up was lower though significant. We conclude that the co-administration of subeffective doses of new cyclooxygenase-inhibitors and the micro-opioid receptor agonist fentanyl should be considered as a potential pain therapy.