Effect of the Cannabinoid Agonist WIN 55,212-2 on Neuropathic and Visceral Pain Induced by a Non-Diarrheagenic Dose of the Antitumoral Drug 5-Fluorouracil in the Rat.

5-fluorouracil (5-FU) is an antineoplastic drug used to treat colorectal cancer, but it causes, among other adverse effects, diarrhea and mucositis, as well as enteric neuropathy, as shown in experimental animals. It might also cause neuropathic pain and alterations in visceral sensitivity, but this has not been studied in either patients or experimental animals. Cannabinoids have antimotility and analgesic effects and may alleviate 5-FU-induced adverse effects. Our aim was to evaluate the effects of the cannabinoid agonist WIN 55,212-2 on neuropathic and visceral pain induced by a non-diarrheagenic dose of 5-FU. Male Wistar rats received a dose of 5-FU (150 mg/kg, ip) and gastrointestinal motility, colonic sensitivity, gut wall structure and tactile sensitivity were evaluated. WIN 55,212-2 (WIN) was administered to evaluate its effect on somatic (50-100 µg ipl; 1 mg/kg, ip) and visceral (1 mg/kg, ip) sensitivity. The cannabinoid tetrad was used to assess the central effects of WIN (1 mg/kg, ip). 5-FU decreased food intake and body weight gain, produced mucositis and thermal hyperalgesia, but these effects were reduced afterwards, and were not accompanied by diarrhea. Tactile mechanical allodynia was also evident and persisted for 15 days. Interestingly, it was alleviated by WIN. 5-FU tended to increase colonic sensitivity whereas WIN reduced the abdominal contractions induced by increasing intracolonic pressure in both control and 5-FU-treated animals. Importantly, the alleviating effects of WIN against those induced by 5-FU were not accompanied by any effect in the cannabinoid tetrad. The activation of the peripheral cannabinoid system may be useful to alleviate neuropathic and visceral pain associated with antitumoral treatment.

Radiographic and histopathological study of gastrointestinal dysmotility in lipopolysaccharide-induced sepsis in the rat.

BACKGROUND: Sepsis is a highly incident condition in which a cascade of proinflammatory cytokines is involved. One of its most frequent consequences is ileus, which can increase mortality. Animal models such as that induced by systemic administration of lipopolysaccharide (LPS) are useful to deeply evaluate this condition. The effects of sepsis on the gastrointestinal (GI) tract have been explored but, to our knowledge, in vivo studies showing the motor and histopathological consequences of endotoxemia in an integrated way are lacking. Our aim was to study in rats the effects of sepsis on GI motility, using radiographic methods, and to assess histological damage in several organs. METHODS: Male rats were intraperitoneally injected with saline or E. coli LPS at 0.1, 1, or 5 mg kg-1 . Barium sulfate was intragastrically administered, and X-rays were performed 0-24 h afterwards. Several organs were collected for organography, histopathology, and immunohistochemistry studies. KEY RESULTS: All LPS doses caused gastroparesia, whereas changes in intestinal motility were dose-and time-dependent, with an initial phase of hypermotility followed by paralytic ileus. Lung, liver, stomach, ileum, and colon (but not spleen or kidneys) were damaged, and density of neutrophils and activated M2 macrophages and expression of cyclooxygenase 2 were increased in the colon 24 h after LPS 5 mg kg-1 . CONCLUSIONS AND INFERENCES: Using radiographic, noninvasive methods for the first time, we show that systemic LPS causes dose-, time-, and organ-dependent GI motor effects. Sepsis-induced GI dysmotility is a complex condition whose management needs to take its time-dependent changes into account.

Short-term stress significantly decreases morphine analgesia in trigeminal but not in spinal innervated areas in rats.

Plenty information exists regarding the effects of chronic stress, although few data exist on the effects of short-lasting stressors, which would mimic daily challenges. Differences in craniofacial and spinal nociception have been observed, thus those observations obtained in spinally innervated areas cannot be directly applied to the orofacial region. Although, opioids are considered amongst the most effective analgesics, their use is sometimes hampered by the constipation they induce. Thus, our aims were to study if a short-lasting stressor, forced swim stress (FSS), modifies nociception, morphine antinociception and constipation in rats. Animals were submitted to 10-20 min of FSS for three days, nociception and gastrointestinal transit were studied 24 h after the last swimming session. Nociception and morphine (0.6-5 mg/kg) antinociception were evaluated in the formalin and hypertonic saline tests in the orofacial area and limbs. Morphine-induced modifications in the GI transit were studied through radiographic techniques. Naloxone was administered, before each swimming session, to analyse the involvement of the endogenous opioid system on the effect of stress. Overall, stress did not alter nociception, although interestingly it reduced the effect of morphine in the orofacial tests and in the inflammatory phase of the formalin tests. Naloxone antagonized the effect of stress and normalized the effect of morphine. Stress did not modify the constipation induced by morphine. Opioid treatment may be less effective under a stressful situation, whilst adverse effects, such as constipation, are maintained. The prevention of stress may improve the level of opioid analgesia.

Radiographic dose-dependency study of loperamide effects on gastrointestinal motor function in the rat. Temporal relationship with nausea-like behavior.

BACKGROUND: Loperamide is a potent mu opioid receptor agonist available over the counter to treat diarrhea. Although at therapeutic doses loperamide is devoid of central effects, it may exert them if used at high doses or combined with drugs that increase its systemic and/or central bioavailability. Recently, public health and scientific interest on loperamide has increased due to a growing trend of misuse and abuse, and consequent reports on its toxicity. Our aim was to evaluate in the rat the effects of increasing loperamide doses, with increasing likelihood to induce central effects, on gastrointestinal motor function (including gastric dysmotility and nausea-like behavior). METHODS: Male Wistar rats received an intraperitoneal injection of vehicle or loperamide (0.1, 1, or 10 mg kg-1 ). Three sets of experiments were performed to evaluate: (a) central effects (somatic nociceptive thresholds, immobility time, core temperature, spontaneous locomotor activity); (b) general gastrointestinal motility (serial X-rays were taken 0-8 hours after intragastric barium administration and analyzed semiquantitatively, morphometrically, and densitometrically); and (c) bedding intake (a rodent indirect marker of nausea). Animals from sets 1 and 3 were used to evaluate gastric dysmotility ex vivo at 2 and 4 hours after administration, respectively. KEY RESULTS: Loperamide significantly induced antinociception, hypothermia, and hypolocomotion (but not catalepsy) at high doses and dose-dependently reduced gastrointestinal motor function, with the intestine exhibiting higher sensitivity than the stomach. Whereas bedding intake occurred early and transiently, gastric dysmotility was much more persistent. CONCLUSIONS AND INFERENCES: Our results suggest that loperamide-induced nausea and gastric dysmotility might be temporally dissociated.

Indazolylketones as new multitarget cannabinoid drugs.

Multitarget cannabinoids could be a promising therapeutic strategic to fight against Alzheimer's disease. In this sense, our group has developed a new family of indazolylketones with multitarget profile including cannabinoids, cholinesterase and BACE-1 activity. A medicinal chemistry program that includes computational design, synthesis and in vitro and cellular evaluation has allowed to us to achieve lead compounds. In this work, the synthesis and evaluation of a new class of indazolylketones have been performed. Pharmacological evaluation includes functional activity for cannabinoid receptors on isolated tissue. In addition, in vitro inhibitory assays in AChE/BuChE enzymes and BACE-1 have been carried out. Furthermore, studies of neuroprotective effects in human neuroblastoma SH-SY5Y cells and studies of the mechanisms of survival/death in lymphoblasts of patients with Alzheimer's disease have been achieved. The results of pharmacological tests have revealed that some of these derivatives (5, 6) behave as CB2 cannabinoid agonists and simultaneously show BuChE and/or BACE-1 inhibition.

May a sigma-1 antagonist improve neuropathic signs induced by cisplatin and vincristine in rats?

BACKGROUND: The antineoplastic drugs cisplatin and vincristine induce peripheral neuropathies. The sigma-1 receptor (σ1R) is expressed in areas of pain control, and its blockade with the novel selective antagonist MR-309 has shown efficacy in nociceptive and neuropathic pain models. Our goal was to test whether this compound reduces neuropathic signs provoked by these antitumoural drugs. METHODS: Rats were treated with cisplatin or vincristine to induce neuropathies. The effects of acute or repeated administration of MR-309 were tested on mechanical and thermal sensitivity, electrophysiological activity of Aδ-primary afferents in the rat skin-saphenous nerve preparation, and gastrointestinal or cardiovascular functions. RESULTS: Rats treated with antitumourals developed tactile allodynia, while those treated with vincristine also developed mechanical hyperalgesia. These in vivo modifications correlated with electrophysiological hyperactivity (increased spontaneous activity and hyperresponsiveness to innocuous and noxious mechanical stimulation). Animals treated with cisplatin showed gastrointestinal impairment and those receiving vincristine showed cardiovascular toxicity. A single dose of MR-309 strongly reduced both nociceptive behaviour and electrophysiological changes. Moreover, its concomitant administration with the antitumourals blocked the development of neuropathic symptoms, thus restoring mechanical sensitivity, improving the impairment of feeding behaviour and gastrointestinal transit in the cisplatin-treated group along with ameliorating the altered vascular reactivity recorded in rats treated with vincristine. CONCLUSION: σ1R antagonist, MR-309, reduces sensorial and electrophysiological neuropathic signs in rats treated with cisplatin or vincristine and, in addition, reduces gastrointestinal and cardiovascular side effects. SIGNIFICANCE: σ1R antagonism could be an interesting and new option to palliate antitumoural neuropathies.

The gastrointestinal pharmacology of cannabinoids: focus on motility.

The marijuana plant Cannabis sp. and its derivatives and analogues, known as cannabinoids (CBs), induce many effects throughout the whole body. Herein we briefly review the gastrointestinal (GI) pharmacology of CBs, with special focus on motor function. Some drugs are available to treat nausea and emesis, and evidences in humans and animal models suggest that other GI motility alterations (gastro-oesophageal reflux, inflammatory bowel conditions or paralytic ileus) might benefit from modifications of the CB tone throughout the gut. However, central and peripheral (including GI) side effects may occur upon acute and chronic CB administration. Hopefully, the ongoing worldwide intense research on CBs will soon provide new, safer CB-based medicines.

Postnatal maturation of the gastrointestinal tract: a functional and immunohistochemical study in the guinea-pig ileum at weaning.

Gastrointestinal motility is mainly controlled by the myenteric plexus. The longitudinal muscle-myenteric plexus (LMMP) preparation from the guinea-pig ileum is the best characterised adult gastrointestinal preparation; it has also been studied in old and neonatal animals, but not at weaning, when milk is substituted with the food typical of adult animals. We used LMMP preparations from weanling and adult guinea-pigs to study different functional parameters and immunohistochemically identified subpopulations of myenteric neurones, including the excitatory motor neurones to the longitudinal muscle (LM-EMN). Excitatory stimuli (low-frequency electrical stimulation, acetylcholine, substance P, and naloxone in morphine-tolerant preparations) produced similar responses in weanling and adult guinea-pigs. The endogenous cannabinoid anandamide, but not the synthetic cannabinoid agonist WIN 55,212-2 or the opioid morphine, inhibited the electrically stimulated twitches less efficaciously, and in vitro tolerance to morphine was also lower in weanling compared to adult animals. The packing densities of the calbindin-immunoreactive neurones (sensory neurones) and of neurones immunoreactive to both calretinin (CR) and neurofilament triplet protein (NFT; ascending interneurones) were slightly but significantly lower in weanling animals, whereas those of the neurones immunoreactive to CR but not NFT (LM-EMN) or immunoreactive to nitric oxide synthase (mainly inhibitory motor neurones) were comparable to the adult. Although guinea-pigs are relatively mature and can even ingest solid food at birth, their myenteric plexus is still not fully mature at the standard time of weaning. The nutritional, behavioural and environmental changes associated with weaning may be essential to attain full maturation of the myenteric plexus and gastrointestinal motility.

[Cannabinoid and opioid system in the mechanisms and control of pain]. / Sistemas cannabinoide y opioide en los mecanismos y el control del dolor.

Opium and Hashish have been classically employed for the control of pain. The pharmacologic rationale for the use of these substances lies in the fact that they are able to modulate the endogenous opioid and cannabinoid systems respectively. Both systems, which depress the central nervous system (CNS), are capable of producing analgesia both in experimental animals and in humans by interfering with the transmission of pain signals (nociceptive) from the periphery to the superior centers of the CNS. We will review the main theories that explain the peripheral effects on both systems and its possible interest from the treatment of musculoskeletal pain standpoint.