221 105 105 1 1 Akio Sato 81-3-3964-3241 81-3-3964-1415 Yuko Sato Robert F. Schmidt Department of the Autonomic Nervous System Tokyo Metropolitan Institute of Gerontology 35-2 Sakaecho, Itabashi-ku 173 Tokyo Japan Laboratory of Physiology, Tsukuba College of Technology 305 Tsukuba Japan Physiologisches Institut der Universität Würzburg Röntgenring 9 D-97070 Würzburg Germany Abstract Modulation of somatosympathetic reflexes at the spinal cord and the brainstem was studied by administering opioid receptor agonists into the intrathecal space of the lumbar spinal cord and into the subarachnoid space of the cisterna magna in rats anesthetized with α-chloralose and urethane. Somatocardiac sympathetic A-and C-reflexes were elicited by electrical stimulation of myelinated (A) and unmyelinated (C) afferent fibers of the tibial nerve, respectively. Intrathecal administration of the μ-opioid receptor agonist DAMGO selectively depressed the C-reflex in a dose-dependent manner (minimum effective dose 10 ng), whereas the intrathecal injection of the δ-opioid receptor agonist DPDPE and the κ-opioid receptor agonist U-50,488H only at doses of 10 μg and 100 μg, respectively, led to a significant depression of the C-reflex. Injection of DAMGO into the cisterna magna enhanced both A-and C-reflexes in a dose-dependent manner (minimum effective dose 1 ng). The administration of neither DPDPE nor U-50,488H into the cisterna magna affected A-or C-reflexes. It is concluded that the activation of μ-opioid receptors is mainly or exclusively responsible for suppressing somatosympathetic C-reflexes at the spinal cord and for enhancing them at the brainstem.
Experimental Brain Research – Springer Journals
Published: Jul 1, 1995
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