The excitation and depression of spinal neurones by ibotenic acid.
1. The firing of spinal interneurones and Renshaw cells by microelectrophoretic (+/-)-ibotenate, which was approximately eight times more active as an excitant than L-glutamate, was followed by prolonged depression of the sensitivity of the neurones to excitant amino acids and acetylcholine. 2. The depression, which lasted for 15--30 min when ibotenate was ejected for 3--6 min, was blocked by the GABA-antagonist bicuculline methochloride, and was independent of prior firing since it occurred with subthreshold concentrations of ibotenate and when ibotenate firing had been blocked by DL-alpha-aminoadipate. 3. When administered electrophoretically for 5 min, muscimol, a potent GABA  agonist, reduced neuronal excitability for prolonged periods and this effect was also prevented by bicuculline methochloride. 4. The depression of neuronal excitability produced by GABA, taurine, isoguvacine or 3-aminopropane sulphonate, ejected for periods of 5--6 min, recovered rapidly. 5. It is suggested that ibotenate is converted in vivo to muscimol or a related compound which has a prolonged, bicuculline-sensitive depressant action on the excitability of neurones.
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001640:Bicuculline / Q000494:pharmacology; D002415:Cats; D007051:Ibotenic Acid / Q000494:pharmacology*; D007395:Interneurons / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D010080:Oxazoles / Q000494:pharmacology*; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology*
D010080:Oxazoles; D007051:Ibotenic Acid; D001640:Bicuculline