title: Extracellular GABA concentrations in area 17 of cat visual cortex during topographic map reorganization following binocular central retinal lesioning.
abstract: Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system of mammals, plays an important role in cortical reorganization following sensory deprivation, by regulating the level of cortical inhibition and gating changes in receptive field size and synaptic efficacy. In cats it has been shown that 2 weeks after the induction of binocular retinal lesions, GABAergic inhibition, as determined by immunocytochemistry, is decreased in the deafferented region of area 17, whereas 3 months post-lesion, normal GABAergic control is restored within the cortical scotoma. In this study we used in vivo microdialysis to investigate the extracellular GABA concentrations 1-2 months post-lesion, in the sensory-deprived and remote, non-deprived region of area 17. Data were collected at those sample times and sites for which the extracellular glutamate concentrations had been determined in a previous investigation to elucidate the role of this excitatory neurotransmitter in cortical reorganization. As for glutamate, we observed significantly increased extracellular GABA concentrations in non-deprived area 17, whereas in deafferented area 17, extracellular GABA concentrations were comparable to those observed in normal, control subjects. These data suggest that 1-2 months post-lesion the deafferented cortex behaves like normal visual cortex, in contrast to remote, non-deprived cortex. Notwithstanding the increase in extracellular GABA concentration of 134%, the parallel increase in glutamate concentration of 269% could give rise to a net increase in excitability in remote area 17. We therefore suggest that LTP-like mechanisms, and thereby cortical reorganization, might still be facilitated, while possible excessive hyperexcitability is balanced by the moderately increased GABAergic control.
authors.affiliation: Laboratory of Neuroendocrinology and Immunological Biotechnology, Katholieke Universiteit Leuven, B-3000 Leuven, Belgium.
authors.forename: Ann
authors.initials: A
authors.lastname: Massie
authors.forename: Lieselotte
authors.initials: L
authors.lastname: Cnops
authors.forename: Ilse
authors.initials: I
authors.lastname: Smolders
authors.forename: Katrien
authors.initials: K
authors.lastname: Van Damme
authors.forename: Erik
authors.initials: E
authors.lastname: Vandenbussche
authors.forename: Frans
authors.initials: F
authors.lastname: Vandesande
authors.forename: Ulf T
authors.initials: UT
authors.lastname: Eysel
authors.forename: Lutgarde
authors.initials: L
authors.lastname: Arckens
mesh_terms: D000818:Animals; D002415:Cats; D005110:Extracellular Space / Q000378:metabolism; D017403:In Situ Hybridization; D017551:Microdialysis; D012160:Retina / Q000293:injuries / Q000502:physiology*; D012683:Sensory Deprivation; D014793:Visual Cortex / Q000378:metabolism*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D005680:gamma-Aminobutyric Acid