Estimation of ambient GABA levels in layer I of the mouse neonatal cortex in brain slices.
GABAergic synapses on Cajal-Retzius neurons in layer I of the murine neocortex experience GABA(B) receptor (GABA(B)R)-mediated tonic inhibition. Extracellular GABA concentration ([GABA](o)) that determines the strength of GABA(B)R-mediated inhibition is controlled by GABA transporters (GATs). In this study, we hypothesized that the strength of presynaptic GABA(B)R activation reflects [GABA](o) in the vicinity of synaptic contacts. Slices obtained from two age groups were used, namely postnatal days (P)2-3 and P5-7. GABAergic postsynaptic currents (IPSCs) were recorded using the whole-cell patch-clamp technique. Minimal electrical stimulation in layer I was applied to elicit evoked IPSCs (eIPSCs) using a paired-pulse protocol. Three parameters were selected for comparison: the mean eIPSC amplitude, paired-pulse ratio, and failure rate. When GAT-1 and GAT-2/3 were blocked by NO-711 (10 microM) and SNAP-5114 (40 microM), respectively, no tonic GABA(B)R-mediated inhibition was observed. In order to restore the control levels of GABA(B)R-mediated inhibition, 250 and 125 nm exogenous GABA was required at P2-3 and P5-7, respectively. Addition of 3-mercaptopropionic acid, a glutamate decarboxylase inhibitor, did not significantly change the obtained values arguing against the suggestion that a mechanism different from GATs contributes to [GABA](o) control. We conclude that juxtasynaptic [GABA](o) is higher (about 250 nM) at P2-3 than at P5-7 (about 125 nM). As both radial cell migration and corticogenesis in general are strongly dependent on [GABA](o) and the formation of the last layer 2/3 is finished by P4 in rodents, the observed [GABA](o) reduction in layer I might reflect this crucial event in the cortical development.
Dvorzhak
Anton
A
Institute of Physiology and Pathophysiology, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, Mainz, Germany.
Myakhar
Olga
O
Unichenko
Petr
P
Kirmse
Knut
K
Kirischuk
Sergei
S
D015097:3-Mercaptopropionic Acid / Q000494:pharmacology; D000818:Animals; D000840:Anisoles / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019706:Excitatory Postsynaptic Potentials; D018756:GABA Antagonists / Q000494:pharmacology; D050485:GABA Plasma Membrane Transport Proteins / Q000378:metabolism; D058805:GABA Uptake Inhibitors; D058788:GABA-B Receptor Antagonists; D005968:Glutamate Decarboxylase / Q000037:antagonists & inhibitors / Q000378:metabolism; D066298:In Vitro Techniques; D051379:Mice; D008810:Mice, Inbred C57BL; D019579:Neocortex / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D009557:Nipecotic Acids / Q000494:pharmacology; D010091:Oximes / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011810:Quinoxalines / Q000494:pharmacology; D018080:Receptors, GABA-B / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000096:biosynthesis / Q000378:metabolism*
C092337:1-(2-(tris(4-methoxyphenyl)methoxy)ethyl)-3-piperidinecarboxylic acid; D000840:Anisoles; D004791:Enzyme Inhibitors; D018691:Excitatory Amino Acid Antagonists; D018756:GABA Antagonists; D050485:GABA Plasma Membrane Transport Proteins; D058805:GABA Uptake Inhibitors; D058788:GABA-B Receptor Antagonists; D009557:Nipecotic Acids; D010091:Oximes; D011810:Quinoxalines; D018080:Receptors, GABA-B; C078793:NNC 711; D005680:gamma-Aminobutyric Acid; C056723:FG 9041; D015097:3-Mercaptopropionic Acid; D005968:Glutamate Decarboxylase