Insufficient augmentation of ambient GABA responsible for age-related cognitive deficit.
Age-related degeneration of intracortical inhibition could underlie declines in cognitive function during senescence. Based on a hypothesis that a decrease in basal concentration of ambient (extrasynaptic) GABA with aging leads to depressing intracortical inhibition, we investigated how the basal concentration affects stimulus-evoked activity (as signal), ongoing-spontaneous activity (as noise) of neurons and their (signal-to-noise) ratio S/N. We simulated a neural network model equipped with a GABA transport system that regulates ambient GABA concentration in a neuronal activity-dependent manner. An increase in basal concentration augmented ambient GABA, increased GABA-mediated inhibitory current, and depressed ongoing-spontaneous activity while still keeping stimulus-evoked activity. This led to S/N improvement, for which it was necessary for the reversal potential of GABA transporter to be close to the resting potential of neurons. Above the resting potential, ongoing-spontaneous activity was predominantly enhanced due to excessive GABA-uptake from the extracellular space by transporters. Below the resting potential, stimulus-evoked activity was predominantly depressed, caused by excessive GABA-release. We suggest that the insufficient augmentation of ambient GABA due to a decrease in its basal concentration may be one of the possible causes of cognitive deficit with aging, increasing ongoing-spontaneous neuronal activity as noise. GABA transporter may contribute to improving S/N, provided that its reversal potential is close to the resting potential.
Department of Intelligent Systems Engineering, Ibaraki University, 4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan.
Hideyuki
H
Fujiwara
Meihong
M
Zheng
Ai
A
Miyamoto
Osamu
O
Hoshino
D000375:Aging / Q000502:physiology*; D003072:Cognition Disorders / Q000503:physiopathology*; D050485:GABA Plasma Membrane Transport Proteins; D006801:Humans; D008564:Membrane Potentials / Q000502:physiology; D008959:Models, Neurological; D009415:Nerve Net / Q000503:physiopathology*; D009433:Neural Inhibition / Q000502:physiology; D009474:Neurons / Q000502:physiology; D011963:Receptors, GABA-A / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
D050485:GABA Plasma Membrane Transport Proteins; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid