GABA is the most important inhibitory neurotransmitter in the adult brain. But during early development, GABA acts mostly depolarizing/excitatory (see figure). Considering the hypothesis of an activity-dependent optimization of neuronal circuits we want to determine the biological relevance of GABA-mediated excitation during development for the maturation of neuronal circuits in the brain.

GABA-induced somatic [Ca²⁺]-transients in an acute brain slice of a 3 day old mouse. A, Confocal fluorescence image of a part of the upper cortical plate in the occipital cortex, stained with the high affinity Ca²⁺-indicator dye Oregon Green 488 BAPTA-1 (AM). B, Application of GABA (100 µM, 200 ms) induced a transient increase in intracellular (somatic) Ca²⁺-concentration. Latter is caused by the activation of voltage-gated Ca²⁺-channels and therefore an indication of GABAergic depolarization.

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