GABAB receptor-mediated inhibitory postsynaptic potentials evoked by electrical stimulation and by glutamate stimulation of interneurons in stratum lacunosum-moleculare in hippocampal CA1 pyramidal cells in vitro.
Following micropressure application of glutamate (500 microM) in stratum lacunosum-moleculare (L-M), inhibitory postsynaptic potentials (glut-IPSPs) were recorded in CA1 pyramidal cells. These glut-IPSPs were blocked by tetrodotoxin (1 microM) and, thus, were probably generated by the activation of local interneurons. The effects of pharmacological antagonists on glut-IPSPs and on electrically-evoked early and late IPSPs were assessed in the same cells during the same application of the antagonist. Local application of the GABAB antagonist 2-OH saclofen (1-4 mM) reduced both glut-IPSPs and late IPSPs but not early IPSPs. In contrast, the GABAB antagonist phaclofen (20 mM) reduced late IPSPs but not early IPSPs but not early IPSPs or glut-IPSPs. Early IPSPs were blocked by the GABAA antagonists bicuculline and picrotoxin but late IPSPs and glut-IPSPs were not. Repetitive electrical stimulation depressed early and late IPSPs as well as glut-IPSPs, suggesting that interneurons activated with glutamate were also stimulated electrically. Thus, interneurons in str. lacunosum-moleculare appear to inhibit pyramidal cells via a GABAB receptor-mediated IPSP. The discrepancy in the pharmacological profile of the GABAB glut-IPSPs and of the GABAB late IPSPs may suggest the presence of two GABAB mechanisms in CA1 pyramidal cells.
Centre de Recherche en Sciences Neurologiques, Université de Montréal, Québec, Canada.
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Williams
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Lacaille
D000818:Animals; D001464:Barium / Q000494:pharmacology; D001640:Bicuculline / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D018756:GABA Antagonists; D005971:Glutamates / Q000494:pharmacology; D018698:Glutamic Acid; D006624:Hippocampus / Q000166:cytology* / Q000187:drug effects; D007395:Interneurons / Q000187:drug effects*; D008297:Male; D011712:Pyramidal Tracts / Q000166:cytology* / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology
D018756:GABA Antagonists; D005971:Glutamates; D011963:Receptors, GABA-A; D001464:Barium; D018698:Glutamic Acid; D013779:Tetrodotoxin; D001640:Bicuculline