Denis Ardid

Lactobacillus acidophilus modulates intestinal pain and induces opioid and cannabinoid receptors

Abdominal pain is common in the general population and, in patients with irritable bowel syndrome, is attributed to visceral hypersensitivity. We found that oral administration of specific Lactobacillus strains induced the expression of μ-opioid and cannabinoid receptors in intestinal epithelial cells, and mediated analgesic functions in the gut—similar to the effects of morphine. These results suggest that the microbiology of the intestinal tract influences our visceral perception, and suggest new approaches for the treament of abdominal pain and irritable bowel syndrome.

Functional dysbiosis within the gut microbiota of patients with constipated-irritable bowel syndrome.

The role of the gut microbiota in patho‐physiology of irritable bowel syndrome (IBS) is suggested by several studies. However, standard cultural and molecular methods used to date have not revealed specific and consistent IBS‐related groups of microbes.

Antinociceptive effects of acute and ‘chronic’ injections of tricyclic antidepressant drugs in a new model of mononeuropathy in rats

&NA; The tricyclic antidepressant drugs (TCAs) are commonly used in the treatment of chronic, especially neuropathic, pain. We evaluated their possible effect on a new model of neuropathic pain‐related behaviour induced by ligatures tied loosely around the common sciatic nerve. The effects of 3 TCAs with different monoaminergic spectra (clomipramine, amitriptyline and desipramine) were assessed 2 weeks after surgery, the time of the maximum hyperalgesia, on a ‘phasic’ test (vocalization threshold to paw pressure) and on a ‘tonic’ test (score of the spontaneous pain‐related behaviour). TCAs were acutely (0.5 and 2 mg/kg i.v.) and ‘chronically’ injected (7 injections, once every half‐life of the drug: 0.75 and 1.5 mg/kg s.c., for clomipramine and 1.5 and 3 mg/kg s.c., for amitriptyline and desipramine). Acutely injected clomipramine and amitriptyline (0.5 mg/kg i.v.) and desipramine (2 mg/kg i.v.) showed an antinociceptive naloxone‐reversible effect, assessed by an increase in the vocalization threshold to the paw pressure test and, for amitriptyline, by a decrease in tonic pain scores. Chronically injected TCAs induced a significant and progressive increase in the vocalization threshold with a time course parallel to that of their suspected plasma or nerve tissue levels: (i) a regular increase of scores for the first 3–4 injections, (ii) then a plateau until the last injection, and (iii) a progressive decrease with a dose‐dependent duration of the effect, longer than that obtained with a corresponding acute dose. This study showed that in this new model of mononeuropathy, acutely and chronically injected TCAs induce an antinociceptive effect and suggested that their analgesic action could be related to the monoaminergic spectrum of the drug in relation to the opiate systems.

T-type calcium channels contribute to colonic hypersensitivity in a rat model of irritable bowel syndrome.

The symptoms of irritable bowel syndrome (IBS) include significant abdominal pain and bloating. Current treatments are empirical and often poorly efficacious, and there is a need for the development of new and efficient analgesics aimed at IBS patients. T-type calcium channels have previously been validated as a potential target to treat certain neuropathic pain pathologies. Here we report that T-type calcium channels encoded by the CaV3.2 isoform are expressed in colonic nociceptive primary afferent neurons and that they contribute to the exaggerated pain perception in a butyrate-mediated rodent model of IBS. Both the selective genetic inhibition of CaV3.2 channels and pharmacological blockade with calcium channel antagonists attenuates IBS-like painful symptoms. Mechanistically, butyrate acts to promote the increased insertion of CaV3.2 channels into primary sensory neuron membranes, likely via a posttranslational effect. The butyrate-mediated regulation can be recapitulated with recombinant CaV3.2 channels expressed in HEK cells and may provide a convenient in vitro screening system for the identification of T-type channel blockers relevant to visceral pain. These results implicate T-type calcium channels in the pathophysiology of chronic visceral pain and suggest CaV3.2 as a promising target for the development of efficient analgesics for the visceral discomfort and pain associated with IBS.

Interactive involvement of brain derived neurotrophic factor, nerve growth factor, and calcitonin gene related peptide in colonic hypersensitivity in the rat

Background and aims: Neutrophins are involved in somatic and visceral hypersensitivity. The action of nerve growth factor (NGF) on sensory neurones contributes to the development of referred colonic hypersensitivity induced by trinitrobenzene sulfonic acid (TNBS). Based on data on brain derived neurotrophic factor (BDNF) and calcitonin gene related peptide (CGRP) in pain, the aims of the present study were: (1) to investigate the involvement of BDNF and CGRP in this model of referred colonic hypersensitivity, (2) to test the effect of exogenous BDNF and CGRP on the colonic pain threshold, and (3) to investigate the relationship between BDNF, NGF, and CGRP by testing antineurotrophin antibodies or h-CGRP 8–37 (a CGRP antagonist) on bowel hypersensitivity induced by these peptides. Methods: Colonic sensitivity was assessed using a colonic distension procedure. Results: Anti-BDNF antibody and h-CGRP 8–37 reversed the induced decrease in colonic threshold (33.4 (2.1) and 40.3 (4.1) mm Hg, respectively, compared with a vehicle score of approximately 18 mm Hg; p<0.001). BDNF (1–100 ng/rat intraperitoneally) induced a significant dose dependent decrease in colonic reaction threshold in healthy rats. This effect was reversed by an anti-BDNF antibody and an anti-NGF antibody (33.4 (0.6) v 18.7 (0.7) mm Hg (p<0.001), anti-NGF v vehicle). NGF induced colonic hypersensitivity was reversed by h-CGRP 8–37 but not by the anti-BDNF antibody. Finally, antineurotrophin antibody could not reverse CGRP induced colonic hypersensitivity (at a dose of 1 µg/kg intraperitoneally). Conclusion: Systemic BDNF, NGF, and CGRP can induce visceral hypersensitivity alone and interactively. This cascade might be involved in TNBS induced referred colonic hypersensitivity in which each of these peptides is involved.

Audible and ultrasonic vocalization elicited by single electrical nociceptive stimuli to the tail in the rat

&NA; We describe audible and ultrasonic vocalization elicited in rats by a short electrical pulse applied to the tail. Three types of vocal emissions were recorded: (1) ‘peep’, characterized by a repartition of energy Over a wide range (0–50 kHz) of frequencies without any clear structure; (2) ‘chatters’, characterized by an audible (frequencies in hearing range of humans) fundamental frequency (2.47 ± 0.03 kHz) and harmonics; and (3) ‘ultrasonic emissions’, characterized by a succession of slightly modulated pulses with frequencies in the 20–35 kHz range. Peeps and chatters were never recorded before the application of the stimuli. Several different vocalization patterns were described in terms of these types of responses. Just after the stimulation, all the animals emitted a 1st peep, which was generally (61%) followed by a 2nd one. They appeared with reproducible latencies, durations and envelopes. The envelopes of the audible (peeps and chatters) responses were intensity‐dependent. Experimental data (moving the stimulation site, lidocaine injection) indicated that the 1st and 2nd peeps were triggered by two different groups of peripheral fibres with mean conduction velocities of 7.3 ± 0.8 and 0.7 ± 0.1 m/ sec, respectively. This suggested an involvement of A&dgr; and C fibres. Morphine showed a naloxone‐reversible and dose‐dependent antinociceptive effect by decreasing the 1st and 2nd peep envelopes. It is concluded that a short stimulus applied to the tail triggers a complex behavioural repertoire. It is proposed that this model will be a useful tool for physiological and pharmacological studies Of nociception.

State-dependent properties of a new T-type calcium channel blocker enhance CaV3.2 selectivity and support analgesic effects

Summary This study deciphers the mechanism of inhibition of T‐type calcium channels by TTA‐A2, demonstrating that TTA‐A2 affinity for CaV3.2‐inactivated state confers a preferential analgesic efficacy toward pathological pain. ABSTRACT T‐type calcium channels encoded by the CaV3.2 isoform are expressed in nociceptive primary afferent neurons where they contribute to hyperalgesia and thus are considered as a potential therapeutic target to treat pathological pain. Here we report that the small organic state‐dependent T‐type channel antagonist TTA‐A2 efficiently inhibits recombinant and native CaV3.2 currents. Although TTA‐A2 is a pan CaV3 blocker, it demonstrates a higher potency for CaV3.2 compared to CaV3.1. TTA‐A2 selectivity for T‐type currents was demonstrated in sensory neurons where it lowered cell excitability uniquely on neurons expressing T‐type channels. In vivo pharmacology in CaV3.2 knockout and wild type mice reveal that TTA‐A2‐mediated antinociception critically depends on CaV3.2 expression. The pathophysiology of irritable bowel syndrome (IBS) was recently demonstrated to involve CaV3.2 in a rat model of this disease. Oral administration of TTA‐A2 produced a dose‐dependent reduction of hypersensitivity in an IBS model, demonstrating its therapeutic potential for the treatment of pathological pain. Overall, our results suggest that the high potency of TTA‐A2 in the depolarized state strengthen its analgesic efficacy and selectivity toward pathological pain syndromes. This characteristic would be beneficial for the development of analgesics targeting T‐type channels, in particular for the treatment of pain associated with IBS.

Paracetamol exerts a spinal, tropisetron-reversible, antinociceptive effect in an inflammatory pain model in rats

Experiments were performed in carrageenin-treated rats to study, the antinociceptive and anti-inflammatory effects of paracetamol intravenously (i.v.) or intrathecally (i.t.) injected on rats submitted to a mechanical noxious stimulus. The influence of intrathecal tropisetron, a 5 hydroxytryptamine(3) (5-HT(3)) receptor antagonist, on the antinociceptive effects of paracetamol, was also studied. Paracetamol induced a significant antinociceptive effect after (100, 200 and 300 mg/kg) i.v. and (50, 100 and 200 microg/rat) i.t. injection, but no change occurred on edema volume. The effect of paracetamol was totally inhibited by tropisetron (10 microg/rat, i.t.). The foregoing results demonstrate that, in conditions of inflammatory pain, paracetamol exerts a central antinociceptive effect involving spinal 5-HT(3) receptors, without inducing any anti-inflammatory action. These data, give further arguments to consider paracetamol as a central analgesic drug which must be distinguished from non-steroidal anti-inflammatory drugs (NSAIDs), which justifies the usual combination of paracetamol in post-operative pain.

A new automated method of pain scoring in the formalin test in rats

Abstract The formalin test is a valuable tool widely used in animal pain studies. We offer a new automated technique based on continuous recording of movements of animals injected in a hindpaw with formalin (5%). This method, based on image processing, allows the discrimination of specific pain‐induced behaviors and general motor activity. The comparison of the pain scores evaluated by manual and automated methods showed the same biphasic response. This new process was validated by using compounds known to alter pain responses to formalin: morphine and a non‐steroidal anti‐inflammatory drug (ketoprofen). Morphine dose‐dependently usually affects the two phases of formalin response with ED50 of 2.0±0.5 and 1.5±0.5 mg/kg s.c. for the first and the second phase, respectively. The injection of ketoprofen significantly decreased pain scores of the second phase but not those of the first phase. The specificity of the method was studied by determining the effect of diazepam. This sedative compound induced a decrease in pain scores as well as a decrease in motor activity parameters. These data show that this automated technique can be considered as a relevant, sensitive and specific tool which allows the easier use of the formalin test especially for the screening of analgesic drugs.

Antihyperalgesic effect of levetiracetam in neuropathic pain models in rats.

The purpose of this study was to assess, in rats, the antinociceptive effects of levetiracetam (i.p.), a novel antiepileptic drug, in acute pain tests and in two models of human neuropathic pain. Levetiracetam and carbamazepine contrasted morphine by an absence of effect in the tail flick and hot plate tests. In normal rats, carbamazepine failed to modify the vocalisation thresholds to paw pressure whereas levetiracetam slightly increased this threshold only at the highest dose (540 mg/kg) for 30 min. In the sciatic nerve with chronic constriction injury model, the highest dose of levetiracetam (540 mg/kg) and carbamazepine (30 mg/kg) reversed the hyperalgesia. In streptozocin-induced diabetic rats, levetiracetam dose-dependently increased the vocalization threshold from 17 to 120 mg/kg reaching a similar effect as 10 mg/kg of carbamazepine. These results indicate that levetiracetam induces an antihyperalgesic effect in two models of human neuropathic pain, suggesting a therapeutic potential in neuropathic pain patients.