Effect of morphine on the release of excitatory amino acids in the rat hind instep: Pain is modulated by the interaction between the peripheral opioid and glutamate systems.
Behavioral evidence supports a role for peripheral glutamate receptors in normal nociceptive transmission. In this study, we examined the release of the excitatory amino acids, glutamate and aspartate, in the s.c. perfusate of the rat hind instep by in vivo microdialysis. Antidromic stimulation of the sciatic nerve and noxious stimuli in the form of heat stimulation and local application of capsaicin cream (1%) to the instep caused an increase in excitatory amino acid release. This capsaicin-induced excitatory amino acid release was suppressed by pretreatment with capsaicin. Both systemic (10 mg/kg, i.v.) and local injections (10(-5) M in the perfusate) of morphine inhibited the increase in excitatory amino acid release evoked by local application of capsaicin cream to the instep. This inhibitory effect of morphine was antagonized by naloxone either given systemically (5 mg/kg, i.v.) or locally (10(-5) M). These results suggest that excitatory amino acids are released from small diameter afferent fibers by heat stimulation in the periphery or local application of capsaicin cream, and that activation of opioid receptors, present on the peripheral endings of small-diameter afferent fibers, can regulate noxious stimulus-induced excitatory amino acid release.
Department of Pharmacology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 565-0871, Japan.
Y H
YH
Jin
H
H
Nishioka
K
K
Wakabayashi
T
T
Fujita
N
N
Yonehara
D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology; D004195:Disease Models, Animal; D004347:Drug Interactions / Q000502:physiology; D004558:Electric Stimulation / Q000009:adverse effects; D018698:Glutamic Acid / Q000378:metabolism*; D006358:Hot Temperature / Q000009:adverse effects; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects / Q000378:metabolism; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects / Q000378:metabolism*; D018847:Opioid Peptides / Q000378:metabolism*; D010146:Pain / Q000139:chemically induced / Q000378:metabolism* / Q000503:physiopathology; D017288:Pain Threshold / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017470:Receptors, Glutamate / Q000187:drug effects / Q000378:metabolism; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D000701:Analgesics, Opioid; D009292:Narcotic Antagonists; D018847:Opioid Peptides; D017470:Receptors, Glutamate; D011957:Receptors, Opioid; D001224:Aspartic Acid; D018698:Glutamic Acid; D009020:Morphine; D002211:Capsaicin