Multiphasic Morphine Modulation of Substance P Release from Capsaicin-Sensitive Primary Afferent Fibers |
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| Authors: | Cano Georgina Arcaya José Luís Gómez Gerber Maixner William Suarez-Roca Heberto |
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| Institution: | (1) Sec. of Pharmacology, Instituto de Investigaciones Clinicas, Univ. del Zulia, Venezuela;(2) INBIOMED, Maracaibo, Apartado 1151, Venezuela;(3) Dental Research Center, University of North Carolina, Chapel Hill, NC, 27599-7455;(4) Present address: Dept. of Neuroscience, Univ. of Pittsburgh, 446 Crawford Hall, Pittsburgh, PA, 15260;(5) University of Zulia, Instituto de Investigaciones Clinicas, Section of Pharmacology, Apartado Postal 1151, Maracaibo, 4001-A, Venezuela |
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| Abstract: | Morphine produces a multiphasic modulation of K+-evoked substance P release from trigeminal slices and dorsal root ganglion neurons in culture. We now found that the C-fiber stimulant, capsaicin (1  M), evoked release of substance P that was inhibited, enhanced and inhibited by 0.1 nM, 1 M, and 10 M morphine, respectively. This morphine's multiphasic effect was blocked by naloxone (100 nM). Neonatal treatment with capsaicin produced thermal hypoalgesia and abolished the multiphasic effect of morphine on substance P release evoked by 50 mM K+. These findings suggest that the multiphasic modulation of substance P release by morphine is dependent on C-type afferents and may be of relevance to nociception. |
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| Keywords: | Substance P capsaicin primary afferents release naloxone morphine trigeminal nucleus |
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