Pain and neurotransmitters.
1. To study physiological roles of substance P (SP), gamma-aminobutyric acid (GABA), enkephalins and other endogenous substances, we developed several kinds of isolated spinal cord preparations of newborn rats. 2. In these preparations, various slow responses of spinal neurons evoked by stimulation of primary afferent C fibers were depressed by a tachykinin antagonist, spantide. These results together with many other lines of evidence suggest that SP and neurokinin A serve as pain transmitters in a subpopulation of primary afferent C fibers. 3. Some C-fiber responses in various isolated spinal cord preparations were depressed by GABA, muscimol, and opioid peptides. In contrast, bicuculline (GABA antagonist) and naloxone (opioid antagonist) potentiated the "tail pinch potential," i.e., a nociceptive response of the ventral root evoked by pinch stimulation of the tail in isolated spinal cord-tail preparation of the newborn rat. The latter results support the hypothesis that some primary afferents activate inhibitory spinal interneurons which release GABA and enkephalins as transmitters to modulate pain inputs.
Department of Pharmacology, Faculty of Medicine, Tokyo Medical and Dental University, Japan.
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Otsuka
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Yanagisawa
D000200:Action Potentials / Q000187:drug effects; D000344:Afferent Pathways / Q000187:drug effects / Q000503:physiopathology; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D004745:Enkephalins / Q000494:pharmacology / Q000502:physiology; D018756:GABA Antagonists; D051379:Mice; D018377:Neurotransmitter Agents / Q000037:antagonists & inhibitors / Q000494:pharmacology / Q000502:physiology*; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D013116:Spinal Cord / Q000187:drug effects / Q000503:physiopathology*; D013373:Substance P / Q000031:analogs & derivatives / Q000494:pharmacology / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D000700:Analgesics; D004745:Enkephalins; D018756:GABA Antagonists; D018377:Neurotransmitter Agents; D013373:Substance P; D005680:gamma-Aminobutyric Acid; C042867:spantide