title: Excitatory and inhibitory action of GABA on synaptic transmission in slices of guinea pig superior colliculus.
abstract: The laminar distribution of gamma-aminobutyric acid (GABA) in the superior colliculus of the guinea pig was analyzed. The superficial gray layer, especially the upper half, was found to contain the highest amount, 37.4 +/- 1.1 mmol/kg dry. To investigate the role of GABA in the superficial gray layer, the effect of GABA on neurotransmission in the superficial gray layer was studied in superior colliculus slices in a perfusion system. Bath-applied GABA, 100 microM-1 mM, enhanced the amplitude of the postsynaptic field potential (PSP) in the superficial gray layer dose dependently and at concentrations above 1 mM it depressed the PSP dose dependently. A similar response pattern was obtained with muscimol (0.1-10 microM, enhancement; greater than 10 microM, depression). However, (-)-baclofen only inhibited the PSP dose dependently (0.1-1 microM). The excitatory effect of GABA was enhanced at concentrations of nipecotic acid less than 0.5 mM. Bicuculline 1 microM shifted the dose-response curve of GABA to the right and the excitatory effect was also enhanced. These results indicate that GABA has a dual action on neurotransmission in the superficial gray layer: an excitatory effect, possibly mediated by GABAA receptors and an inhibitory effect mediated by both GABAA and GABAB receptors.
authors.affiliation: Department of Physiology, Kobe University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Arakawa
authors.forename: Y
authors.initials: Y
authors.lastname: Okada
mesh_terms: D000818:Animals; D001418:Baclofen / Q000494:pharmacology; D001640:Bicuculline / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects; D018756:GABA Antagonists; D006168:Guinea Pigs; D066298:In Vitro Techniques; D009118:Muscimol / Q000494:pharmacology; D009557:Nipecotic Acids / Q000494:pharmacology; D010477:Perfusion; D011392:Proline / Q000031:analogs & derivatives*; D011963:Receptors, GABA-A / Q000187:drug effects; D013477:Superior Colliculi / Q000187:drug effects* / Q000378:metabolism; D013570:Synaptic Membranes / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology / Q000502:physiology*
chemical_list: D018756:GABA Antagonists; D009557:Nipecotic Acids; D011963:Receptors, GABA-A; C030278:nipecotic acid; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; D011392:Proline; C010983:homoproline; D001418:Baclofen; C006749:bicuculline methochloride; D001640:Bicuculline