British journal of pharmacology
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Comparative Study
Intrathecal CGRP8-37-induced bilateral increase in hindpaw withdrawal latency in rats with unilateral inflammation.
1. Recent work in our laboratory has demonstrated that intrathecal administration of a selective antagonist of calcitonin gene-related peptide (CGRP), CGRP8-37, increased the hindpaw withdrawal latency (HWL) to thermal stimulation and hindpaw withdrawal threshold (HWT) to pressure in normal rats, and that these effects were more pronounced than in rats with mononeuropathy. 2. The present study was performed to investigate the effects of intrathecal administration of CGRP8-37 on the HWL and HWT in rats with unilateral hindpaw inflammation induced by subcutaneous injection of carrageenin. ⋯ Intrathecal administration of CGRP8-37 increased the HWL to thermal stimulation and HWT to pressure bilaterally. 9. The results indicate that CGRP plays a role in the transmission of presumed nociceptive information in the spinal cord of rats with experimentally induced inflammation. Furthermore, our findings suggest that opioids can modulate CGRP-related effects in the spinal cord.
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Comparative Study
An isobolographic analysis of the effects of N-methyl-D-aspartate and NK1 tachykinin receptor antagonists on inflammatory hyperalgesia in the rat.
1. The interaction between N-methyl-D-aspartate (NMDA) and NK1 tachykinin receptors was analyzed isobolographically in rats with inflammatory hyperalgesia induced by intraplantar injection of complete Freund's adjuvant-saline emulsion (CFA, 100 micrograms Mycobacterium tuberculosis). 2. Thermal hyperalgesia of the inflamed paw, determined by paw withdrawal response to a heat stimulus, was dose-dependently attenuated by intrathecal administration of an NMDA receptor antagonist, dextrorphan (2.5-40 micrograms, ED50 = 7.2 micrograms), and two NK1 tachykinin receptor antagonists, WIN 51,708 (0.01-200 micrograms, ED50 = 10.4 micrograms) or CP-96,345 (5-200 micrograms, ED50 = 82.1 micrograms). ⋯ Isobolographic analysis revealed that the ED50s obtained from the three combination ratios were not significantly different from those that were expected from a simple additive effect. 4. Thus, an additive interaction was demonstrated between NMDA and NK1 tachykinin receptor systems at the spinal level. These results suggest that both NMDA and NK1 tachykinin receptors are activated in response to peripheral inflammation, but that they may contribute independently to development of hyperalgesia.
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Comparative Study
Differential desensitization of mu- and delta- opioid receptors in selected neural pathways following chronic morphine treatment.
1. Morphine produces a plethora of pharmacological effects and its chronic administration induces several side-effects. The cellular mechanisms by which opiates induce these side-effects are not fully understood. ⋯ In the nucleus accumbens and the caudate putamen, desensitization of delta-opioid receptor-mediated inhibition without modification of mu-opioid receptor-mediated inhibition was observed. An indirect mechanism probably involving dopaminergic systems is proposed to explain the desensitization of delta-mediated responses and the lack of mu-opioid receptor desensitization after chronic morphine treatment in caudate putamen and nucleus accumbens. 7. These results suggest that adaptive responses occurring during chronic morphine administration are not identical in all opiate-sensitive neural populations.
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Comparative Study
Evidence for the participation of glutamate in reflexes involving afferent, substance P-containing nerve fibres in the rat.
1. Responses mediated, either peripherally or centrally, by substance P-containing primary afferent C-fibres were investigated in the rat following impairment of axonal transport by colchicine (120 micrograms kg-1, i.p., daily for 3 days), and after treatment with the tachykinin antagonist SR-140333 (10-100 micrograms kg-1, i.v.) or the N-methyl-D-aspartate (NMDA) antagonist MK-801 (100 micrograms kg-1). 2. Peripheral effects mediated by afferent C-fibres were measured by plasma protein extravasation (Evans blue method), following antidromic stimulation of the sciatic nerve, topical application of mustard oil and, as control, i.v. injection of substance P. ⋯ SR-140333 was effective only on peripherally mediated responses. 7. The recent evidence for the concomitant release of glutamate and substance P from central terminals of afferent C-fibres, known to mediate reflexes abolished after capsaicin treatment allows the following conclusions: (a) the inhibition by MK-801 indicates an essential role for glutamate in the central transmission of these reflexes; (b) tachykinin antagonists such as SR-140333 do not affect these responses when administered systemically. Centrally released substance P could be involved in functions of the CNS other than those investigated here unless the access of neurokinin antagonists to their receptors in the CNS is insufficient.