title: Electrophysiological identification of horizontal synaptic connections in rat visual cortex in vitro.
abstract: The presence of intrinsic horizontal synaptic connections in rat visual cortex was explored electrophysiologically using in vitro slice preparations. Intracellular recordings were made from pyramidal neurons located in the superficial and deep layers. Electrical stimulation at the gray matter in the same or different layers but 0.8-2.7 mm apart from the recording site evoked compound synaptic potentials composed of excitatory and inhibitory postsynaptic potentials of fast and slow time courses. Glutamate blockers, DNQX (5 microM) and kynurenate (2 mM) reduced the excitatory postsynaptic potential (EPSP), and GABAB receptor antagonist, phaclofen (0.5 mM), abolished the inhibitory postsynaptic potential of the slow time course. EPSP of the fast time course followed 20 Hz repetitive stimulation in the medium of high Ca2+ (6.0 mM) and Mg2+ (4.0 mM) concentration, suggesting that this fast EPSP was monosynaptic. Conduction velocity of the fibers mediating the monosynaptic EPSP was estimated to be 0.15-0.55 m/s. These results provide physiological evidence for the horizontal synaptic connections in the rat visual cortex, which had been previously suggested by morphology.
authors.affiliation: Department of Pharmacology, Faculty of Medicine, Tokyo Medical and Dental University, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Murakoshi
authors.forename: J Z
authors.initials: JZ
authors.lastname: Guo
authors.forename: T
authors.initials: T
authors.lastname: Ichinose
mesh_terms: D000818:Animals; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000187:drug effects; D018691:Excitatory Amino Acid Antagonists; D066298:In Vitro Techniques; D007736:Kynurenic Acid / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D018080:Receptors, GABA-B / Q000187:drug effects / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*
chemical_list: D018691:Excitatory Amino Acid Antagonists; D011810:Quinoxalines; D018080:Receptors, GABA-B; C052329:phaclofen; C056723:FG 9041; D007736:Kynurenic Acid; D001418:Baclofen; D008274:Magnesium; D002118:Calcium