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Bernal L, Lopez-Garcia JA, Roza C. Spontaneous activity in C-fibres after partial damage to the saphenous nerve in mice: Effects of retigabine. Eur J Pain 2016; 20:1335-45. [PMID: 27061852 DOI: 10.1002/ejp.858] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/17/2015] [Indexed: 12/13/2022]
Abstract
BACKGROUND Spontaneous pain is the most devastating positive symptom in neuropathic pain patients. Recent data show a direct relationship between spontaneous discharges in C-fibres and spontaneous pain in neuropathic patients. Unfortunately, to date there is a lack of experimental animal models for drug testing. METHODS We recorded afferent fibres from a new experimental model in vitro. The preparation contains a neuroma formed in a peripheral branch of the saphenous nerve together with the undamaged branches, which maintain intact terminals in a skin flap. RESULTS Fibres with stable rates of ectopic spontaneous discharges were found among axotomized (5 A- and 18 C-fibres, mean discharge 0.48 ± 0.08 Hz) and 'putative intact' fibres (12 C-fibres, mean discharge 0.28 ± 0.08 Hz). A proportion (~9%) of axotomized fibres had mechanical receptive fields in the skin far beyond the site of injury. Collision experiments demonstrated that action potentials evoked from neuroma and skin travelled by the same fibre, indicating functional cross-talk between neuromatose and putative intact fibres. Retigabine, the specific Kv7 channel opener, depressed spontaneous discharges by 70% in 15/18 units tested. In contrast, responses to mechanical stimulation of the skin were unaltered by retigabine. CONCLUSIONS Partial damage to a peripheral nerve may increase the incidence of spontaneous activity in C-fibres. Retigabine reduced spontaneous activity but not stimulus-evoked activity, suggesting an important role for ion channels in the control of spontaneous pain and demonstrating the utility of the model for the testing of compounds in clinically relevant variables. WHAT DOES THIS STUDY ADD?: Our in vitro experimental model of peripheral neuropathy allows for pharmacological characterization of spontaneously active fibres. Using this model, we show that retigabine inhibits aberrant spontaneous discharges without altering physiological responses in primary afferents.
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Affiliation(s)
- L Bernal
- Dpto. Biología de Sistemas, Edificio de Medicina Universidad de Alcalá, Alcalá de Henares, Madrid, Spain
| | - J A Lopez-Garcia
- Dpto. Biología de Sistemas, Edificio de Medicina Universidad de Alcalá, Alcalá de Henares, Madrid, Spain
| | - C Roza
- Dpto. Biología de Sistemas, Edificio de Medicina Universidad de Alcalá, Alcalá de Henares, Madrid, Spain
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Mazo I, Roza C, Zamanillo D, Merlos M, Vela JM, Lopez-Garcia JA. Effects of centrally acting analgesics on spinal segmental reflexes and wind-up. Eur J Pain 2015; 19:1012-20. [PMID: 25469831 DOI: 10.1002/ejp.629] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/15/2014] [Indexed: 12/30/2022]
Abstract
BACKGROUND The spinal cord is a prime site of action for analgesia. Here we characterize the effects of established analgesics on segmental spinal reflexes. The aim of the study was to look for the pattern of action or signature of analgesic effects on these reflexes. METHODS We used a spinal cord in vitro preparation of neonate mice to record ventral root responses to dorsal root stimulation. Pregabalin, clonidine, morphine and duloxetine and an experimental sigma-1 receptor antagonist (S1RA) were applied to the preparation in a cumulative concentration protocol. Drug effects on the wind-up produced by repetitive stimulation of C-fibres and on responses to single A- and C-fibre intensity stimuli were analysed. RESULTS All compounds produced a concentration-dependent inhibition of total spikes elicited by repetitive stimulation. Concentrations producing ∼50% reduction in this parameter were (in μM) clonidine (0.01), morphine (0.1), pregabalin (1), duloxetine (10) and S1RA (30). At these concentrations clonidine, pregabalin and S1RA had significant effects on the wind-up index and little depressant effects on responses to single stimuli. Morphine and duloxetine did not depress wind-up index and showed large effects on responses to single stimuli. None of the compounds had strong effects on the amplitude of the non-nociceptive monosynaptic reflex. CONCLUSIONS morphine and duloxetine had general depressant effects on spinal reflexes, whereas the effects of clonidine, pregabalin and S1RA appeared to be restricted to signals originated by strong repetitive activation of C-fibres. Results are discussed in the context of reported behavioural effects of the compounds studied.
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Affiliation(s)
- I Mazo
- Department of Systems Biology (Division Physiology), Edificio Medicina, Universidad de Alcala, Madrid, Spain
| | - C Roza
- Department of Systems Biology (Division Physiology), Edificio Medicina, Universidad de Alcala, Madrid, Spain
| | - D Zamanillo
- Esteve, Drug Discovery and Preclinical Development, Parc Científic de Barcelona, Spain
| | - M Merlos
- Esteve, Drug Discovery and Preclinical Development, Parc Científic de Barcelona, Spain
| | - J M Vela
- Esteve, Drug Discovery and Preclinical Development, Parc Científic de Barcelona, Spain
| | - J A Lopez-Garcia
- Department of Systems Biology (Division Physiology), Edificio Medicina, Universidad de Alcala, Madrid, Spain
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Munro G, Lopez-Garcia JA, Rivera-Arconada I, Erichsen HK, Nielsen EØ, Larsen JS, Ahring PK, Mirza NR. Comparison of the novel subtype-selective GABAA receptor-positive allosteric modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile] with diazepam, zolpidem, bretazenil, and gaboxadol in rat models of inflammatory and neuropathic pain. J Pharmacol Exp Ther 2008; 327:969-81. [PMID: 18791060 DOI: 10.1124/jpet.108.144568] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Spinal administration of GABA(A) receptor modulators, such as the benzodiazepine drug diazepam, partially alleviates neuropathic hypersensitivity that manifests as spontaneous pain, allodynia, and hyperalgesia. However, benzodiazepines are hindered by sedative impairments and other side effect issues occurring mainly as a consequence of binding to GABA(A) receptors containing the alpha(1) subunit. Here, we report on the novel subtype-selective GABA(A) receptor-positive modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile], which possesses a functional efficacy selectivity profile of alpha(5) > alpha(3) > alpha(2) > alpha(1) at GABA(A) alpha subunit-containing receptors. Oral administration of NS11394 (1-30 mg/kg) to rats attenuated spontaneous nociceptive behaviors in response to hindpaw injection of formalin and capsaicin, effects that were blocked by the benzodiazepine site antagonist flumazenil. Ongoing inflammatory nociception, observed as hindpaw weight-bearing deficits after Freund's adjuvant injection, was also completely reversed by NS11394. Likewise, hindpaw mechanical allodynia was fully reversed by NS11394 in two rat models of peripheral neuropathic pain. Importantly, NS11394-mediated antinociception occurred at doses 20 to 40-fold lower than those inducing minor sedative or ataxic impairments. In contrast, putative antinociception associated with administration of either diazepam, zolpidem, or gaboxadol only occurred at doses producing intolerable side effects, whereas bretazenil was completely inactive despite minor influences on motoric function. In electrophysiological studies, NS11394 selectively attenuated spinal nociceptive reflexes and C-fiber-mediated wind-up in vitro pointing to involvement of a spinal site of action. The robust therapeutic window seen with NS11394 in animals suggests that compounds with this in vitro selectivity profile could have potential benefit in clinical treatment of pain in humans.
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Affiliation(s)
- G Munro
- NeuroSearch A/S, Ballerup, Denmark
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Martinez-Gomez J, Lopez-Garcia JA. Simultaneous assessment of the effects of L-type current modulators on sensory and motor pathways of the mouse spinal cord in vitro. Neuropharmacology 2007; 53:464-71. [PMID: 17669442 DOI: 10.1016/j.neuropharm.2007.06.007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2006] [Revised: 06/05/2007] [Accepted: 06/05/2007] [Indexed: 11/21/2022]
Abstract
The effects of modulators of L-type currents in the processing of nociceptive stimuli across sensory and motor circuits were studied using an in vitro preparation of the young mouse spinal cord. Responses to repetitive C-fibre intensity stimuli delivered to a lumbar dorsal root were simultaneously recorded from motor axons in the corresponding ventral root and from putative sensory axons in the anterolateral pathway. L-current antagonists verapamil, diltiazem and nimodipine as well as the agonist Bay K8644 were superfused at a range of concentrations and their effects on responses to afferent stimulation were assessed. All antagonists produced a concentration-dependent depression of transmission across sensory and motor pathways by inhibiting sustained firing and wind-up. All antagonists showed concentration-dependent depression of evoked firing in anterolateral fibres with LogIC50 of -4.2 for verapamil, -4.1 for diltiazem and -4.9 for nimodipine. Applied at high concentrations (>or=100 microM) verapamil and diltiazem produced almost complete blockade of the ascending signals whereas nimodipine produced only partial depression. The effects of the antagonists on motor pathways were significantly greater and the LogIC50 decreased to -5 for verapamil, to -4.9 for diltiazem and to -5.3 for nimodipine. Bay K8644 applied at 2 microM produced only a slight potentiation of responses in anterolateral axons and a very large and long-lasting potentiation of responses from motor neurons. We conclude that mice motor pathways are more sensitive to L-type current modulators than the anterolateral pathway and that analgesic effects reported for some L-type antagonists may be due to a mixture of selective and non-selective effects of these agents on sensory neurones.
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Affiliation(s)
- J Martinez-Gomez
- Departamento de Fisiologia, Facultad de Medicina, Campus Universitario, Universidad de Alcala, Alcala de Henares, 28871 Madrid, Spain
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Rivera-Arconada I, Lopez-Garcia JA. Retigabine-induced population primary afferent hyperpolarisation in vitro. Neuropharmacology 2006; 51:756-63. [PMID: 16844148 DOI: 10.1016/j.neuropharm.2006.05.015] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2006] [Revised: 05/03/2006] [Accepted: 05/16/2006] [Indexed: 11/28/2022]
Abstract
Retigabine is a compound of potential interest in analgesia which acts as an M-channel opener to depress neuronal excitability. Here we study the effects of retigabine and its antagonist XE-991 on populations of primary afferents. Experiments were performed using a hemisected spinal cord preparation from rat pups maintained under in vitro conditions. Recording from dorsal roots were performed using tight fitting suction electrodes coupled to AC and DC amplifiers. The adjacent dorsal root was electrically stimulated at regular intervals. The effects of the modulators on basal potential, spontaneous potentials and dorsal root-dorsal root responses were studied. Superfusion of retigabine (10 microM) produced long lasting and robust hyperpolarisation of primary afferents which persisted during superfusion of picrotoxin (20 microM) and tetrodotoxin (0.5 microM). Other effects of retigabine were (1) increase in stimulation threshold; (2) increase in size of responses to suprathreshold stimuli; and (3) increase in amplitude and decrease in frequency of spontaneous dorsal root potentials. Superfusion of XE-991 had little effect on its own but blocked all the effects of retigabine. These results indicate the presence of functional M-currents in central terminals of primary afferents and in the interneurones that mediate dorsal root potentials. The depressant effects of retigabine on the excitability of these structures may contribute to its analgesic effects after pain-inducing treatments.
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Affiliation(s)
- I Rivera-Arconada
- Department of Physiology, Edificio de Medicina, Campus Universitario, University of Alcala, Alcala de Henares, 28871 Madrid, Spain
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Abstract
M-currents have been shown to control neuronal excitability in a variety of central and peripheral neurones. Here we studied the effects of specific M-current modulators on the excitability of spinal neurones and their response to synaptic activation. Experiments were performed in vitro using the hemisected spinal cord from 7- to 11-day-old rats. Intracellular recordings were obtained from lumbar deep dorsal horn and motor neurones. Neuronal excitability was assessed by applying outward current pulses and synaptic responses were elicited by activation of a lumbar dorsal root. The M-current antagonist 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone (XE-991) and the agonist retigabine were superfused at 10 microM. Retigabine produced hyperpolarization and a large decrease in the excitability of motor (7/7) and dorsal horn neurones (11/12). The effects of retigabine were fully reversed by XE-991. XE-991 induced depolarization of most neurones tested and a large increase in the excitability of motor neurones (7/7) but only a weak increase in the excitability of a proportion of dorsal horn neurones (4/10). The effects of XE-991 were partly reversed by retigabine. Consistent with their effects on neuronal excitability, retigabine showed a general depressant effect on synaptic transmission, whereas XE-991 showed the opposite tendency to potentiate responses to dorsal root stimulation, particularly in motor neurones. The results show that retigabine can depress spinal excitability and the transmission of nociceptive information. Results also indicate a post-synaptic expression of functional M-currents in most motor neurones and a considerable proportion of deep dorsal horn neurones.
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Affiliation(s)
- I Rivera-Arconada
- Departamento de Fisiologia, Edificio de Medicina, Campus Universitario, Universidad de Alcala, Alcala de Henares, 28871 Madrid, Spain
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Martinez-Gomez J, Lopez-Garcia JA. Electrophysiological and pharmacological characterisation of ascending anterolateral axons in the in vitro mouse spinal cord. J Neurosci Methods 2005; 146:84-90. [PMID: 15935224 DOI: 10.1016/j.jneumeth.2005.01.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2004] [Revised: 01/17/2005] [Accepted: 01/24/2005] [Indexed: 10/25/2022]
Abstract
Here we describe a procedure to obtain electrophysiological recordings from cut ends of ascending axons of the spinal cord white matter. This procedure involves the use of an in vitro preparation of the neonate mouse spinal cord and suction microelectrodes of about 10 microm tip diameter. Using this procedure, we have recorded from axons of the anterolateral quadrant at the thoracic level which responded to electrical stimulation of a lumbar dorsal root. Using adequate stimulation parameters, we have identified axons responding exclusively to activation of C-fibres and axons responding to activation of A- and C-fibres. These axons are likely to originate at dorsal horn second order sensory neurons of different functional types. Simultaneous recordings from a lumbar ventral root and from ascending axons were used to assess the effects of noradrenaline and sevoflurane on motor and sensory pathways. The results obtained show that noradrenaline can potentiate responses of motor neurons to dorsal root stimulation while depressing responses of ascending axons to the same stimulus. In contrast both motor and sensory pathways were inhibited by sevoflurane. We believe that the procedures developed here may be of great interest to assess spinal nociceptive and antinociceptive mechanisms in vitro.
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Affiliation(s)
- J Martinez-Gomez
- Departamento de Fisiologia, Edificio de Medicina, Campus Universitario, Universidad de Alcala, 28871 Madrid, Spain
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Rivera-Arconada I, Martinez-Gomez J, Lopez-Garcia JA. M-current modulators alter rat spinal nociceptive transmission: an electrophysiological study in vitro. Neuropharmacology 2004; 46:598-606. [PMID: 14975684 DOI: 10.1016/j.neuropharm.2003.10.016] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2003] [Revised: 09/15/2003] [Accepted: 10/14/2003] [Indexed: 01/11/2023]
Abstract
M-currents constitute a unique effector system to control neuronal excitability due to their voltage and ligand sensitivities. Here we have used retigabine, an M-current agonist, and XE-991, an M-current antagonist, to study the possible involvement of these currents in the processing of spinal sensory and motor processing of nociceptive information in normal, untreated rats. Experiments were performed in a hemisected spinal cord preparation from rat pups using extracellular recordings. Responses to activation of nociceptive and non-nociceptive afferent fibres were recorded. M-current modulators were bath applied to the entire cord or applied locally by pressure ejection. Retigabine and XE-991 produced long-lasting and concentration-dependent effects on nociceptive reflexes showing only minor effects on non-nociceptive reflexes. Retigabine depressed responses to repetitive stimulation of the dorsal root recorded from motor neurones and dorsal horn neurones, whereas XE-991 showed the opposite potentiatory effect and reversed effects of retigabine. Local application of the modulators close by motor nuclei produced changes in reflex responses similar to those caused by bath application. These results constitute a clear indication of the existence of functional M-currents in dorsal and ventral horn elements of the mammalian spinal cord where they may serve to regulate early sensory and motor processing of nociceptive information. The weak effect of modulators on non-nociceptive reflexes suggest that M-currents constitute a promising novel target for analgesics.
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Affiliation(s)
- I Rivera-Arconada
- Departamento de Fisiologia, Facultad de Medicina, Campus Universitario, Universidad de Alcala, Alcala de Henares, 28871 Madrid, Spain
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Matute E, Lopez-Garcia JA. Characterisation of sevoflurane effects on spinal somato-motor nociceptive and non-nociceptive transmission in neonatal rat spinal cord: an electrophysiological study in vitro. Neuropharmacology 2003; 44:811-6. [PMID: 12681379 DOI: 10.1016/s0028-3908(03)00055-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Sevoflurane is the latest halogenated ether introduced in clinical anaesthesia, and its effects at the spinal level are not fully characterised. The rat hemisected spinal cord preparation was used to test the effects of sevoflurane on spinal nociceptive and non-nociceptive synaptic transmission as well as on excitations produced by application of glutamate-receptor agonists. Sevoflurane was dissolved in artificial cerebrospinal fluid (ACSF) with a specific vaporiser, and its final concentration was assessed with gas chromatography. Sevoflurane reduced the mono-synaptic reflex (EC(50) approximately 219 microM) and the slow components of the dorsal root-ventral root potentials (EC(50) approximately 72 microM) elicited by single dorsal root stimulation as well as the cumulative depolarisation (CD) elicited by repetitive stimulation (EC(50) approximately 98 microM). AMPA- and NMDA-induced depolarisations were also reduced by sevoflurane (respective EC(50)s were 206 and 127 microM). Inhibition of NMDA-induced depolarisation was TTX resistant. However, complete blockade of NMDA receptors with d-AP5 did not prevent further reduction of the CD by sevoflurane. All the effects reported were concentration-dependent and reversible. We conclude that sevoflurane applied at clinically relevant concentrations induces a strong depression of nociceptive and non-nociceptive spinal systems, which may be partly mediated by interfering with excitatory amino acid transmission.
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Affiliation(s)
- E Matute
- Departamento de Fisiología, Universidad de Alcalá, Alcalá de Henares, Madrid 28871, Spain
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Abstract
1. The identity of the serotonin (5-HT) receptors modulating the transmission of segmental C-fibre mediated signals was studied using an in vitro preparation of the hemisected spinal cord from rat pups. 2. Responses to trains of stimuli delivered to a lumbar dorsal root were recorded from the corresponding ventral root. The resulting cumulative depolarization (CD) mediated by unmyelinated fibres was quantified in terms of integrated area. The amplitude of the mono-synaptic reflex was also measured. Serotonergic agents were superfused at known concentrations and their effects on the reflexes evaluated. 3. 5-HT had depressant effects on the CD (EC(50) 34 microM). The rank order of potency of agonists for the depression of the CD was 5-carboxamidotryptamine (5-CT)>alpha-methylserotonin (alpha-met-5-HT) approximately 5-HT>42-methylserotonin (2-met-5-HT)approximately 8-OH-DPAT. 4. All the agonists including 2-met-5-HT and 8-OH-DPAT had strong depressant effects on the mono-synaptic reflex with the following order of potency: 5-CT>48-OH-DPAT>4alpha-met-5-HT approximate5-HTapproximate2-met-5-HT. 5. The inhibitory effects of 5-HT, alpha-met-5-HT and 5-CT were attenuated by the non-specific 5-HT antagonist methiothepin (1 microM) and by the 5-HT(1A/1B) antagonist SDZ 21009 (100 nM) but not by the selective 5-HT(1A) antagonist WAY 100135 (1 microM). 6. Other antagonists known to block 5-HT(2), 5-HT(6) and/or 5-HT(7) receptors (ketanserin, RO 04-6790, ritanserin and clozapine) did not change the effect of the agonists. 7. The data suggest an important contribution of 5-HT(1B) receptors to the inhibition of spinal C-fibre mediated nociceptive reflexes but no experimental support was found for the intervention of 5-HT(2), 5-HT(6) or 5-HT(7) receptors in this in vitro model.
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Affiliation(s)
- G Hedo
- Departamento de Fisiologia, Edificio de Medicina, Universidad de Alcala, Madrid 28871, Spain
| | - J A Lopez-Garcia
- Departamento de Fisiologia, Edificio de Medicina, Universidad de Alcala, Madrid 28871, Spain
- Author for correspondence:
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Abstract
The rat hemisected spinal cord preparation was used to assess the role of different adrenoceptor subtypes on the modulation of nociceptive reflexes. These were elicited by trains of high intensity electrical stimuli delivered to a lumbar dorsal root. Responses were recorded from the corresponding ventral root in AC- and DC-amplification modes simultaneously. Superfusion of noradrenaline produced a potentiation of action potential firing (AC channel) as well as a depression of the cumulative depolarisation (DC channel) in responses to repetitive afferent stimulation.Noradrenaline-induced potentiation of firing was mimicked by the alpha1A-adrenoceptor agonist A 61603 and the alpha1-adrenoceptor agonist methoxamine in a reversible and concentration-dependent manner. The order of potency of these agonists was A61603>>noradrenaline>methoxamine. The alpha(1A)-adrenoceptor antagonist 5-methyl-urapidil and the alpha1-adrenoceptor antagonist corynanthyne blocked the excitatory effects of noradrenaline. In contrast, the alpha(1B/D)-adrenoceptor antagonists chloroethylclonidine and BMY 7378 failed to block this effect.Noradrenaline-induced depression of cumulative depolarisation was mimicked by the alpha2-adrenoceptor agonist UK 14,304. In addition, this compound produced inhibition of firing in responses to afferent stimulation. These results show that noradrenaline has bi-directional modulatory effects on nociceptive reflexes and indicate that selective activation of alpha1A- but not alpha1B/D-adrenoceptors mediate potentiation of spinal nociceptive reflexes.
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Affiliation(s)
- G Hedo
- Departamento Fisiologia, Edificio de Medicina, Universidad de Alcala, Alcala de Henares, 28871, Madrid, Spain
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Laird JM, Olivar T, Lopez-Garcia JA, Maggi CA, Cervero F. Responses of rat spinal neurons to distension of inflamed colon: role of tachykinin NK2 receptors. Neuropharmacology 2001; 40:696-701. [PMID: 11311897 DOI: 10.1016/s0028-3908(00)00205-7] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Tachykinin NK2 receptors are implicated in nociception and the control of intestinal motility. Here we examined their involvement in responses of spinal lumbosacral neurons with colon input to distension of normal or inflamed colon in anesthetized rats. The responses of single neurons to colorectal distension (5-80 mmHg), to electrical stimulation of the pelvic nerve (bypassing sensory receptors) and to somatic stimulation were characterized. The effect of cumulative doses of an NK2 receptor antagonist, MEN 11420 (10-1000 microg kg(-1) IV), on responses to these stimuli was tested in control conditions (n=6), or 45 min after intracolonic instillation of acetic acid (n=6). After colonic inflammation, neuronal responses to colorectal distension and pelvic nerve stimulation were significantly greater. MEN 11420 dose-dependently inhibited the enhanced responses to colorectal distension after inflammation (ID50=402+/-14 microg kg(-1)), but had no significant effect on responses to pelvic nerve stimulation or distension of the normal colon, suggesting a peripheral action selective for the inflamed colon. We conclude that MEN 11420 possesses peripheral anti-hyperalgesic effects on neuronal responses to colorectal distension. These results provide a neurophysiological basis for a possible use of tachykinin NK2 receptor antagonists in treating abdominal pain in irritable bowel syndrome patients.
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Affiliation(s)
- J M Laird
- Department of Physiology, University of Alcalá, Alcalá de Henares, E-28871, Madrid, Spain.
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Hedo G, Laird JM, Lopez-Garcia JA. Time-course of spinal sensitization following carrageenan-induced inflammation in the young rat: a comparative electrophysiological and behavioural study in vitro and in vivo. Neuroscience 1999; 92:309-18. [PMID: 10392852 DOI: 10.1016/s0306-4522(98)00734-9] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Inflammation of peripheral tissues evokes spontaneous pain and an increased responsiveness to external stimuli known as hyperalgesia, produced by both peripheral and central changes. The central component is initiated by a sustained afferent barrage produced by sensitized peripheral nociceptors, but it is unclear to which extent ongoing nociceptive input is required to maintain these central changes. Here, we have used an isolated preparation of the spinal cord in vitro obtained from eight- to 12-day-old rats to examine spinal plasticity in the absence of naturally occurring afferent inputs. Spinal reflex responses in preparations obtained from naive rats were compared with those from animals with carrageenan-induced inflammation of one hindpaw of 3 h, 6 h and 20 h duration prior to the extraction of the cord. Measurements of thermal (heat) and mechanical hyperalgesia in awake animals were also made at the same time-points. At 6 h post-carrageenan, there was a significant increase in the wind-up evoked by trains of high-intensity (C-fibre) stimuli, and at 20 h increased responses to both trains and single high-intensity stimuli, and a novel wind-up to low-intensity (Abeta-fibre) trains were observed. In contrast, maximal behavioural hyperalgesia was observed by 3 h post-carrageenan, and thermal hyperalgesia had resolved by 20 h, although mechanical hyperalgesia remained. These results show that the induction of spinal plasticity independent of peripheral input is a progressive process with a slow time-course, since significant hyperreflexia in the isolated spinal preparation appears 6 h after inflammation and develops further within 20 h. We conclude that during the first 3 h following inflammation, hyperalgesia is the result of peripheral sensitization and of central mechanisms that depend on an ongoing peripheral input and thus changes were not observed in the isolated spinal cord.
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Affiliation(s)
- G Hedo
- Department of Physiology, University of Alcalá, Madrid, Spain
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Khasabov SG, Lopez-Garcia JA, Asghar AUR, King AE. Modulation of afferent-evoked neurotransmission by 5-HT3 receptors in young rat dorsal horn neurones in vitro: a putative mechanism of 5-HT3 induced anti-nociception. Br J Pharmacol 1999; 127:843-52. [PMID: 10433490 PMCID: PMC1566080 DOI: 10.1038/sj.bjp.0702592] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
1. The in vitro hemisected spinal cord from young rat was used to investigate the mechanism of serotoninergic modulation of primary afferent-mediated synaptic transmission in the dorsal horn through activation of the 5-HT3 receptor. 2. Dorsal root-evoked excitatory post-synaptic potentials (DR-EPSPs) were recorded intracellularly from dorsal horn neurones. Extracellular recordings of the population primary afferent depolarization (PAD) and the dorsal root-evoked dorsal root reflex (DR-DRR) were made from segmental dorsal roots. 3. 5-Hydroxytryptamine (5-HT) and the selective 5-HT3 receptor agonist 1-(m-chloro-phenyl)-biguanide hydrochloride (m-ChPB) (10 and 50 microM) induced statistically significant reductions of the DR-EPSP amplitude (P<0.001) and duration (P<0.001) in the majority of dorsal horn neurones. The 5-HT3 receptor selective antagonists 3-Tropanyl-indole-3-carboxylate hydrochloride (Tropisetron, 10 microM) and N-(1-Azabicyclo[2.2.2]oct-3-yl)-6-chloro-4-methyl-3-oxo-3,4-dihydro-2H-1 ,4-benzoxazine-8-carboxamide (Y-25130, 10 microM) abolished m-ChPB-induced DR-EPSP attenuation and partially blocked the 5-HT effect. 4. m-ChPB (50 microM)-induced DR-EPSP amplitude and duration attenuation was retained in the presence of the GABA(A) receptor antagonist bicuculline (30 microM), the GABA(B) receptor antagonist saclofen (50 microM) and the opioid receptor antagonist naloxone (50 microM). 5. Both 5-HT and m-ChPB (10 and 50 microM) induced a PAD but the mean peak amplitude of 5-HT-induced PAD was significantly greater than PAD to m-ChPB (98.6+/-12 microV compared to 51.8+/-10 V for 50 microM of agonist, respectively). Tropisetron partially reduced 5-HT-induced PAD and abolished m-ChPB-induced PAD. 5-HT, but not m-ChPB, significantly (P<0.001) reduced the peak amplitude of the DR-DRR and this action of 5-HT was unaffected by Tropisetron or Y-25130. 6. These data provide experimental evidence for a putative cellular mechanism at the level of the dorsal horn for anti-nociceptive effects of 5-HT3 receptor activation. This 5-HT3-mediated modulation of sensory afferent transmission was evidently independent of inhibitory GABA- or opioid-dependent interneuronal pathways. The extent to which the 5-HT3 receptor could be involved in the operation of endogenous analgesia and sensory modulation by descending monoamine bulbo-spinal pathways is discussed.
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Affiliation(s)
- S G Khasabov
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9NQ, U.K
| | - J A Lopez-Garcia
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9NQ, U.K
- 1-Depto. Fisiologia, Facultad de Medicina, Universidad de Alcala, Madrid 2871, Spain
| | - A U R Asghar
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9NQ, U.K
| | - A E King
- School of Biomedical Sciences, University of Leeds, Leeds, LS2 9NQ, U.K
- Author for correspondence:
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Abstract
The effect of 5-hydroxytryptamine (5-HT) on population primary afferent depolarisation (PAD) has been studied using in vitro spinal cord preparations from normal and capsaicin pre-treated (neonatal subcutaneous injection; 75 mg kg-1) rats aged 10-14 days. In preparations from untreated rats, the concentration-response curve for PAD in response to 0.1-100 microM 5-HT was bell-shaped but in the capsaicin pre-treated group, a non-saturating 5-HT-induced PAD concentration-response curve was generated. Quantitatively, the mean PAD responses to 0.1-10 microM 5-HT were of a greater amplitude in the control group compared to the capsaicin pre-treated group (p</=0. 05). For the highest 5-HT concentration of 100 microM, PAD values were significantly greater in the capsaicin pre-treated group (p</=0. 05). These data indicate that control of sensory afferent polarity may involve two 5-HT receptor types and that nociceptive and non-nociceptive afferents may be targets for released 5-HT.
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Affiliation(s)
- S G Khasabov
- Dept. of Physiology, University of Leeds, Leeds LS2 9NQ, UK
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16
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Lopez-Garcia JA. Serotonergic modulation of the responses to excitatory amino acids of rat dorsal horn neurons in vitro: implications for somatosensory transmission. Eur J Neurosci 1998; 10:1341-9. [PMID: 9749788 DOI: 10.1046/j.1460-9568.1998.00153.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Serotonin (5-HT) is one of the major transmitters involved in supraspinal control of somatic sensation and nociception. The aim of the present study was to investigate if the 5-HT-induced modulation of sensory transmission in the dorsal horn could be due to regulation of neuronal responses to excitatory amino acids. Experiments were performed in an in vitro preparation of the young rat spinal cord. Responses to dorsal root stimulation (DR-EPSP) and to droplet application of N-methyl-D-aspartic acid (NMDA) and alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic acid (AMPA) were obtained by means of intracellular recordings of dorsal horn neurons. Bath applications of 5-HT (50 microM) generally caused reductions in amplitude and integrated area of DR-EPSPs and of responses to NMDA but the responses to AMPA were unaltered. A linear correlation was found between the effects of 5-HT on the DR-EPSP and on the NMDA response measured as percentage change in amplitude (r2 = 0.45; P < or = 0.01) and integrated area (r2 = 0.77; P < or = 0.001). The NMDA receptor antagonist d-AP5 (50 microM) completely abolished NMDA responses and caused a depression of the DR-EPSP similar to that of 5-HT. The 5-HT1 receptor agonist 5-carboxamidotryptamine (5-CT; 1 microM) mimicked the depressant effects of 5-HT but had a stronger depressant action on the DR-EPSP than 5-HT. The depression of NMDA responses induced by 5-HT and 5-CT was tetrodotoxin (1 microM) resistant. It is concluded that 5-HT-induced depression of NMDA responses explains partially the depressant action of 5-HT on dorsal horn synaptic transmission activating a postsynaptic site sensitive to 5-CT. The possible activation of coadjuvant mechanisms is discussed.
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Affiliation(s)
- J A Lopez-Garcia
- Departamento de Fisiología, Facultad de Medicina, Universidad de Alcalá, Madrid, Spain.
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17
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Abstract
Non-steroidal anti-inflammatory drugs inhibit constitutive (COX-1) and induced cyclooxygenase (COX-2), blocking prostaglandin production. We have compared the effects on nociceptive reflexes of meloxicam, which is COX-2 selective, with indomethacin, which is non-selective, using an in vitro spinal cord preparation. Cords were taken from naive rats, and from rats with carrageenan-induced hyperalgesia of one hindpaw. Reflex thresholds were lower in carrageenan preparations. Superfusion with meloxicam (10-100 microM) dose-dependently inhibited baseline reflexes and wind-up in normal and carrageenan preparations, whereas indomethacin (100-300 microM) had no effect. Thus meloxicam inhibits spinal reflexes, whereas indomethacin does not, despite its high affinity for both COX isoforms. We conclude that meloxicam has spinal antinociceptive actions which cannot be explained by the current concept of COX inhibition.
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Affiliation(s)
- J A Lopez-Garcia
- Department of Physiology, School of Medicine, University of Alcalá, Alcalá de Henares, Madrid, Spain
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King AE, Slack JR, Lopez-Garcia JA, Ackley MA. Tachykinin actions on deep dorsal horn neurons in vitro: an electrophysiological and morphological study in the immature rat. Eur J Neurosci 1997; 9:1037-46. [PMID: 9182956 DOI: 10.1111/j.1460-9568.1997.tb01454.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
To assess whether functional neurokinin receptors exist in the deep dorsal horn of the rat, the actions of the selective neurokinin-1 receptor (NK1R) agonist [Sar9,Met(O2)11]substance P ([Sar9,Met(O2)11]SP), the neurokinin-2 receptor (NK2R) agonists [beta-Ala8]NKA(4-10) and GR64349 and the neurokinin-3 receptor (NK3R) agonist senktide were examined intracellularly in vitro. [Sar9,Met(O2)11]SP (1-4 microM) and senktide (1-2 microM) elicited slow depolarizations (<10 mV) associated with increased synaptic activity and cell firing. [beta-Ala8]NKA(4-10) (10-20 microM) and GR64349 (0.25-10 microM) caused small depolarizations (<2.0 mV) and no firing. Neurons were categorized as either 'tonic' or 'phasic' depending on their firing response to direct current step depolarizations. Tonic neurons, which, unlike phasic neurons, display no spike firing accommodation, generated a significantly larger depolarization to the NK1R and NK3R agonists. The putative contribution of these receptors to primary afferent-mediated synaptic transmission was assessed by testing the NK1R antagonist GR82334 (1 microM), the NK2R antagonist MEN10,376 (1 microM) and the NK3R antagonist [Trp7,beta-Ala8]NKA(4-10) (1 microM) against the dorsal root-evoked excitatory postsynaptic potential (DR-EPSP). GR82334 and [Trp7,beta-Ala8]NKA(4-10) significantly reduced (P < or = 0.05) the duration but not the amplitude of the DR-EPSP. MEN10,376 (1 microM) had no effect on DR-EPSP amplitude or duration. Morphological detail was obtained for seven biocytin-filled deep dorsal horn neurons tested with [Sar9,Met(O2)11]SP. Five neurons responded to the NK1R agonist, and two of these had dorsally directed dendrites into the substantia gelatinosa. The other three [Sar9,Met(O2)11]SP-sensitive neurons had dendrites within deeper laminae. These data support the existence of functional NK1Rs and NK3Rs in the deep dorsal horn which may be involved in mediating sensory afferent inputs from nociceptors.
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Affiliation(s)
- A E King
- Department of Physiology, University of Leeds, UK
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Lopez-Garcia JA, King AE. Pre- and post-synaptic actions of 5-hydroxytryptamine in the rat lumbar dorsal horn in vitro: implications for somatosensory transmission. Eur J Neurosci 1996; 8:2188-97. [PMID: 8921310 DOI: 10.1111/j.1460-9568.1996.tb00740.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Since the relative contribution of pre- versus post-synaptic actions of 5-hydroxytryptamine (5-HT) to modulation of somatosensory processing in the dorsal hom is not known, recordings from primary afferents and dorsal hom neurons from in vitro rat spinal cord were used to address this issue. 5-HT produced a depression of spontaneous dorsal root potentials and a slow primary afferent depolarization (PAD): the PAD versus 5-HT concentration-response curve was bell shaped (maximum at 5 microM; 250 +/- 41.5 microV). In 28/40 dorsal horn neurons, 5-HT elicited a slow depolarization not clearly associated with a specific input resistance change. Excitatory synaptic transmission from primary afferents to dorsal horn neurons was depressed by 5-HT in 40/45 neurons. 5-HT > or = 5 microM significantly (P < or = 0.05) decreased the amplitude, shortened the total duration and half-decay time of the excitatory post-synaptic potential (EPSP). A dominant effect of 5-HT on longer latency EPSP components was evident. There was not direct relationship between the magnitude of PAD and the reduction of the EPSP by 5-HT. 5-Carboxamidotryptamine, an agonist for 5-HT1 receptors, mimicked the depression of neurotransmission in the dorsal horn without producing PAD. A sample of dorsal horn neurons (n = 8) was injected with biocytin and their morphology described. All had somata within laminae III-VI. In five of these neurons 5-HT depressed the EPSP but in one interneuron-like and one unclassed neuron the EPSP was potentiated. These data suggest that whilst depression of synaptic transmission is the predominant effect of 5-HT in the deep dorsal horn, this is not easily related to PAD or cellular actions of 5-HT on dorsal horn neurons.
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Lopez-Garcia JA, King AE. A novel methodology for simultaneous assessment of the effects of 5-hydroxytryptamine on primary afferent polarisation and synaptic transmission in rat dorsal horn neurones in vitro. J Neurosci Methods 1996; 68:1-6. [PMID: 8884606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The rat hemisected spinal cord in vitro preparation was used to test simultaneously the effects of 5-hydroxytryptamine (5-HT) on primary afferent polarisation and synaptic transmission onto dorsal horn (DH) neurons. Primary afferent polarisation was measured from the cut end of a transected lumbar dorsal root (DR; L3-L6) using tight suction electrodes coupled to a D.C. amplifier. Conventional sharp microelectrodes were used to record intracellularly the excitatory postsynaptic potential (EPSP) evoked by high intensity electrical stimulation (100 microA, 100 microseconds) of another DR contiguous to that used for the suction electrode recording. Superfusion of 5-HT (5-10 microM) caused primary afferent depolarisations (PAD) of 227.5 +/- 26.5 microV (mean +/- SEM) and 221 +/- 32 microV, respectively, values comparable to the PAD caused by 10-100 microM gamma-aminobutyric acid (GABA) superfusion. 5-HT-induced PAD was tetrodotoxin (TTX) resistant and non-additive to capsaicin-induced PAD suggesting a direct depolarising action of 5-HT on a population of primary afferents which may include a high proportion of unmyelinated fibres. Simultaneous intracellular recordings showed that 5-HT, in addition to generating PAD, depressed primary afferent-evoked synaptic transmission to DH neurons reflected by a significant reduction (p < 0.05) in the amplitude and duration of the EPSP. In contrast, GABA, despite producing a PAD of similar amplitude, failed to depress synaptic transmission. These data suggest that PAD alone may be insufficient to account for the 5-HT-induced depression of synaptic transmission. This novel experimental approach offers a means to explore further the possible causal relationship between pre- and post-synaptic effects of 5-HT in the DH and its ability to modulate somatosensory processing and nociception.
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Lopez-Garcia JA, King AE. Membrane properties of physiologically classified rat dorsal horn neurons in vitro: correlation with cutaneous sensory afferent input. Eur J Neurosci 1994; 6:998-1007. [PMID: 7952286 DOI: 10.1111/j.1460-9568.1994.tb00594.x] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Dorsal horn neurons in the young rat spinal cord-hindlimb preparation were physiologically classified as wide dynamic range (WDR), nociceptive specific (NS) or low threshold (LT) according to their excitatory responses to low and high intensity mechanical stimuli applied to the hindlimb skin. Two additional types were classified: neurons displaying only sub-threshold excitations (SUB) and neurons displaying inhibitory events (INH), such as inhibitory post-synaptic potentials or interruption of spontaneous spiking following cutaneous stimulation. Direct intracellular current injection revealed four different patterns of spiking behaviour: group A neurons were characterized by tonic firing in response to depolarizing current pulses; group B neurons were strongly phasic, producing only one spike at the beginning of the pulse; group A-B neurons generated an early unsustained (< 300 ms) burst of spikes; and group C neurons exhibited anomalous rectification in response to hyperpolarizing current which was followed by a voltage-dependent rebound excitation. A statistically significant (P < or = 0.01) association existed between a neuron's physiological classification and its electrophysiological profile. The majority of WDR neurons responded with tonic firing and were assigned to group A, while NS neurons were strongly represented in group A-B. All INH neurons were assigned to group C. LT neurons were distributed between groups A and A-B, and SUB neurons were distributed between groups A and B. These data indicate, firstly, that dorsal horn neurons possess heterogeneous membrane properties and, secondly, that a relationship exists between a neuron's biophysical profile and its excitatory or inhibitory response to peripheral cutaneous afferent stimulation. The implications for dorsal horn somatosensory processing are discussed.
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22
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Abstract
The mechanoreceptive fields of 54 dorsal horn neurones were mapped intracellularly in the rat spinal cord-hindlimb preparation. A quantitative analysis of the parameters of excitation and inhibition was undertaken and a comparison was made between data obtained for innocuous versus noxious cutaneous stimulation. Neurones were classified as wide dynamic range (WDR), nociceptive specific (NS) or low threshold (LT) on the basis of their response to cutaneous stimuli. In WDR neurones, which responded differentially to both types of cutaneous stimuli, the EPSP produced by noxious pinch had a significantly larger amplitude and a longer duration (P < 0.01) compared to the excitatory postsynaptic potentials (EPSPs) produced by touch. A higher total number of spikes was also associated with the postsynaptic response to pinch in WDR neurones. A population of neurones which responded to mechanical stimuli with non-spiking excitation only were identified; their possible relevance to mechanisms of altered central sensitivity is discussed. Inhibitory components to the mechanoreceptive fields were identified; these were complex in form and co-incidental generation of EPSPs and inhibitory postsynaptic potentials (IPSPs) was common. Inhibition of spontaneous firing by cutaneous stimulation was also observed. This technique allows a quantitative intracellular analysis of naturally evoked postsynaptic excitation in physiologically classified dorsal horn neurones in vitro.
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Affiliation(s)
- A E King
- Department of Physiology, University of Leeds, UK
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23
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Abstract
1. The cutaneous mechanoreceptive fields (RFs) of forty-two lumbar dorsal horn neurones have been examined intracellularly using the hemisected spinal cord-hindlimb preparation of 10 to 14-day-old rats. The neurones were classified into three groups on the basis of their excitatory responses to innocuous and noxious mechanical stimulation; the majority (25/42) were activated by noxious and innocuous stimuli and were classed as 'wide-dynamic' type (WDR). 'Nociceptive-specific' neurones (NS) which were excited by noxious stimuli made up the next largest group (12/42) followed by 'low-threshold' neurones (LT, 5/42) which responded only weakly to noxious stimuli. Another fourteen neurones which did not respond to peripheral stimuli were used to test antagonist selectivity against excitatory amino acid agonists. 2. The response to light touch or pinch consisted of an initial EPSP and cell firing followed by subthreshold EPSPs. The mean +/- S.E.M. values for the amplitude (mV) and the duration (s) of the EPSP produced by noxious pinch were significantly greater than those to touch; in WDR neurones the respective values were 14.3 +/- 0.9 vs. 11.5 +/- 0.7 mV (P < 0.01) and 11.9 +/- 1.8 vs. 4.8 +/- 0.6 s (P < 0.01). 3. The non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 3-5 microM) antagonized DL-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA)-induced depolarizations. The amplitude and duration of the EPSPs produced in response to low- and high-threshold mechanical stimulation were potently attenuated and cell firing was abolished in WDR, NS, LT neurones. A similar profile of antagonism was produced in five WDR neurones superfused with ACSF containing 1 mM D-serine. 4. The NMDA-receptor antagonist D-aminophosphonovalerate (D-AP5, 50 microM) attenuated the EPSP amplitude and duration but never abolished cell firing produced by low- and high-intensity cutaneous mechanical stimulation. A preferential effect of D-AP5 against the EPSP duration resulted in failure of longer latency spikes. 5. The data indicate that non-NMDA receptors contribute substantially to dorsal horn neurotransmission and somatosensory processing of noxious and innocuous cutaneous stimuli, while the role of NMDA receptors is restricted to longer latency synaptic components.
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Affiliation(s)
- A E King
- Department of Physiology, University of Leeds
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Abstract
1. The aim of this paper is to present a new hypothesis to explain the evolution of the sleeping and waking states. 2. We propose that the reptilian waking state and the mammalian slow wave sleep are homologous states. 3. We also propose that instead of looking at the polygraphic sleep as a new evolutive acquisition of mammals and birds, it seems more convenient to look at the full waking state; the "advanced wakefulness" as the true new evolutionary acquisition of these animals. 4. These conclusions are reached after examining some available reports of slow wave electroencephalogram in waking reptiles, some other reports showing signs of rapid eye movement sleep in this same group and the coevolution between sleep states and thermoregulation. Finally, a clear parallelism between sleep ontogeny and phylogeny is shown under the light of the proposed hypothesis.
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Affiliation(s)
- R Rial
- Departmento de Biologia Fonamental i Ciències de la Salut, Universitat de les Illes Balears, Palma de Mallorca, Spain
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King AE, Lopez-Garcia JA, Cumberbatch M. Antagonism of synaptic potentials in ventral horn neurones by 6-cyano-7-nitroquinoxaline-2,3-dione: a study in the rat spinal cord in vitro. Br J Pharmacol 1992; 107:375-81. [PMID: 1358390 PMCID: PMC1907849 DOI: 10.1111/j.1476-5381.1992.tb12754.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. The rat spinal cord in vitro has been used to assess the effect of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) on the dorsal root evoked extracellular ventral root reflex (DR-VRR) and the intracellular excitatory postsynaptic potential (e.p.s.p.) in ventral horn neurones and motoneurones. 2. CNQX (1-5 microM) produces a selective and dose-dependent reduction in the amplitude of the monosynaptic component of the DR-VRR recorded from lumbar spinal segments. 3. With low intensity dorsal root stimulation CNQX selectively attenuates the amplitude of the short latency intracellular e.p.s.p. (70% reduction, P < 0.005) and its rise-time (75%, P < 0.01) without affecting the half-time to decay. 4. When high intensity stimulation is used CNQX significantly attenuates the amplitude of the e.p.s.p. (56%, P < 0.005), rise-time (76%, P < 0.01) and abolishes the short latency spike. In addition longer latency synaptic components are attenuated and the half-time to decay significantly reduced (47%, P < 0.005). 5. The results with CNQX are compared to D-aminophosphonovalerate and discussed in relation to the recruitment of low versus high threshold afferents. The data supports an involvement of non-NMDA receptors in transmission through both mono- and polysynaptic pathways in the ventral horn.
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Affiliation(s)
- A E King
- Department of Physiology, University of Leeds
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Brandão ML, Lopez-Garcia JA, Graeff FG, Roberts MH. Electrophysiological evidence for excitatory 5-HT2 and depressant 5-HT1A receptors on neurones of the rat midbrain tectum. Brain Res 1991; 556:259-66. [PMID: 1682008 DOI: 10.1016/0006-8993(91)90313-k] [Citation(s) in RCA: 71] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
It has been claimed that the aversive behaviour induced by electrical stimulation of the midbrain tectum (MT) has validity as an animal model of panic attack. A great deal of evidence obtained from behavioural studies suggests that 5-HT2 mechanisms phasically inhibit the substrates of aversion in the MT. In order to test this hypothesis we employed the technique of microiontophoresis of drugs onto neurons of the MT to assess the identity of the receptors mediating the effects of 5-hydroxytryptamine (5-HT). The results obtained show that the majority of 5-HT responsive cells in MT are cells excited by 5-HT (72%). These cells were silent or showed very low spontaneous firing activity, whereas cells depressed by 5-HT showed high spontaneous firing activity at baseline. The 5-HT1A receptor agonists, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), buspirone and gepirone caused consistent reduction in the firing rate of cells depressed by 5-HT while they did not change the firing activity of cells excited by 5-HT. The excitatory effects induced by 5-HT on MT neurones were clearly attenuated by concomitant application of ketanserin, a highly specific 5-HT2 antagonist. Excitatory responses to DL-homocysteic acid were not affected by ketanserin. Previous administration of zimelidine, a selective 5-HT uptake inhibitor, caused a significant enhancement of the excitatory effects of 5-HT while similar application of gepirone did not affect the size of the excitatory responses to 5-HT.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- M L Brandão
- Department of Physiology, University of Wales, College of Cardiff, U.K
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