LSD but not methysergide reduces the inhibitory effect of the medullary raphe stimulation on the spinal reflex in rats.
Conditioning stimulation of the nucleus raphe in the rat medulla enhanced the monosynaptic reflex (MSR) and depressed the polysynaptic reflex (PSR) in separate time courses. The PSR decreasing effect was reduced in preparations pretreated with reserpine, PCPA, or 5,6-DHT. The MSR increasing effect was not altered by these three pretreatments. Intravenously administered LSD but not methysergide reduced the PSR decreasing effect with no influence on the MSR increasing effect. These two drugs had similar effects on the unconditioned responses; the MSR was decreased and the PSR was increased. Thus, the PSR decreasing effect seems to be mediated via a serotonergic pathway probably descending from the nucleus raphe.
D000818:Animals; D001933:Brain Stem / Q000187:drug effects*; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology*; D008297:Male; D008784:Methysergide / Q000494:pharmacology*; D009433:Neural Inhibition / Q000187:drug effects*; D011903:Raphe Nuclei / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012018:Reflex / Q000187:drug effects*; D012023:Reflex, Monosynaptic / Q000187:drug effects; D012701:Serotonin / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects*; D013126:Spinal Nerve Roots / Q000187:drug effects
D012701:Serotonin; D008238:Lysergic Acid Diethylamide; D008784:Methysergide