Differential effects of (R)- and (S)-8-hydroxy-2-(di-n-propylamino)tetralin on the monosynaptic spinal reflex in rats.
We examined the effects of (R)- and (S)-8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide (8-OH-DPAT) on the monosynaptic spinal reflex in rats. In intact rats, (R)-8-OH-DPAT (10 microg/kg, i.v.) enhanced the amplitude of the monosynaptic reflex, whereas at 100 microg/kg, it reduced the amplitude. (S)-8-OH-DPAT enhanced the monosynaptic reflex dose-dependently. In spinalized rats, (R)-8-OH-DPAT produced dose-dependent inhibition, but the (S)-enantiomer did not affect the monosynaptic reflex. Pretreatment with spiroxatrine or 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]-piperazine (NAN-190) inhibited (R)-8-OH-DPAT-induced monosynaptic reflex enhancement in intact rats, as did 5-hydroxytryptamine (5-HT) depletion. Ketanserin reduced the effect of (R)-8-OH-DPAT. These pretreatment regimens had no effect on the monosynaptic reflex depression produced by the (R)-enantiomer in intact and spinalized rats. Pretreatment with prazosin inhibited (S)-8-OH-DPAT-induced monosynaptic reflex enhancement in intact rats, as did noradrenaline and 5-HT depletion. These results suggest that supraspinal 5-HT1A receptors and the descending serotonergic system are involved in the stimulatory effect of (R)-8-OH-DPAT on the monosynaptic reflex, while both the descending serotonergic and noradrenergic systems, the latter acting via alpha1-adrenoceptors, are involved in the effect of the (S)-enantiomer on this reflex.
Department of Pharmacology, Faculty of Pharmaceutical Sciences, Science University of Tokyo, Japan.
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Honda
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Ono
D015115:5,6-Dihydroxytryptamine / Q000494:pharmacology; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000737:chemistry / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D003655:Decerebrate State; D004146:Dioxanes / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012023:Reflex, Monosynaptic / Q000187:drug effects*; D012701:Serotonin / Q000378:metabolism; D018490:Serotonin Agents / Q000494:pharmacology; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology*; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D013141:Spiro Compounds / Q000494:pharmacology; D013237:Stereoisomerism
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D010879:Piperazines; D018490:Serotonin Agents; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013141:Spiro Compounds; C058895:1-(2-methoxyphenyl)-4-(4-(2-phthalimido)butyl)piperazine; D012701:Serotonin; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin; C018387:spiroxatrine; D015115:5,6-Dihydroxytryptamine; D009638:Norepinephrine; D011224:Prazosin