title: Inhibitory effects of dopamine on spinal synaptic transmission via dopamine D1-like receptors in neonatal rats.
abstract: OBJECTIVE
  Dopamine released from the endings of descending dopaminergic nerve fibres in the spinal cord may be involved in modulating functions such as locomotion and nociception. Here, we examined the effects of dopamine on spinal synaptic transmissions in rats.
  
  
  METHODS
  Spinal reflex potentials, monosynaptic reflex potential (MSR) and slow ventral root potential (sVRP), were measured in the isolated spinal cord of the neonatal rat. Dopamine release was measured by HPLC.
  
  
  RESULTS
  Dopamine at lower concentrations (<1 µM) depressed sVRP, which is a C fibre-evoked polysynaptic response and believed to reflect nociceptive transmission. At higher concentrations (>1 µM), in addition to a potent sVRP depression, dopamine depolarized baseline potential and slightly depressed MSR. Depression of sVRP by dopamine was partially reversed by dopamine D(1) -like but not by D(2) -like receptor antagonists. SKF83959 and SKF81297, D(1) -like receptor agonists, and methamphetamine, an endogenous dopamine releaser, also caused the inhibition of sVRP. Methamphetamine also depressed MSR, which was inhibited by ketanserin, a 5-HT(2A/2C) receptor antagonist. Methamphetamine induced the release of dopamine and 5-HT from spinal cords, indicating that the release of endogenous dopamine and 5-HT depresses sVRP and MSR respectively.
  
  
  CONCLUSIONS
  These results suggested that dopamine at lower concentrations preferentially inhibited sVRP, which is mediated via dopamine D(1) -like and other unidentified receptors. The dopamine-evoked depression is involved in modulating the spinal functions by the descending dopaminergic pathways.
authors.affiliation: Laboratories of Pharmacology             Toxicology, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Kawamoto
authors.forename: K
authors.initials: K
authors.lastname: Otsuguro
authors.forename: M
authors.initials: M
authors.lastname: Ishizuka
authors.forename: S
authors.initials: S
authors.lastname: Ito
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001552:Benzazepines / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology*; D015259:Dopamine Agents / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D005260:Female; D005727:Ganglia, Spinal / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D008297:Male; D008694:Methamphetamine / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000502:physiology*; D012018:Reflex / Q000187:drug effects / Q000502:physiology; D013116:Spinal Cord / Q000187:drug effects* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects* / Q000502:physiology
chemical_list: D001552:Benzazepines; D015259:Dopamine Agents; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D008694:Methamphetamine; C067113:SK&F 81297; D004298:Dopamine