The GABAergic Hypothesis for Cognitive Disabilities in Down Syndrome

Abstract

Down syndrome (DS) is a genetic disorder caused by the presence of a third copy of chromosome 21. DS affects multiple organs, but it invariably results in altered brain development and diverse degrees of intellectual disability. A large body of evidence has shown that synaptic deficits and memory impairment are largely determined by altered GABAergic signaling in trisomic mouse models of DS. These alterations arise during brain development while extending into adulthood, and include genesis of GABAergic neurons, variation of the inhibitory drive and modifications in the control of neural-network excitability. Accordingly, different pharmacological interventions targeting GABAergic signaling have proven promising preclinical approaches to rescue cognitive impairment in DS mouse models. In this review, we will discuss recent data regarding the complex scenario of GABAergic dysfunctions in the trisomic brain of DS mice and patients, and we will evaluate the state of current clinical research targeting GABAergic signaling in individuals with DS.

Keywords: GABA; chloride homeostasis; cognitive impairment; down syndrome; gaba receptors.

Figure 1

Subregion-specific GABA-related dysfunctions in the hippocampus of the Ts65Dn mouse model. IPSC, inhibitory postsynaptic currents; sIPSC, spontaneous IPSC; mIPSC, miniature IPSC; eIPSC, evoked IPSC; freq, frequency; ampl, amplitude; mEPSC, miniature excitatory postsynaptic currents; [Cl]_I, intracellular chloride concentration; E_Cl, reversal potential of GABA_AR-mediated Cl currents; V_REST, resting membrane potential. Arrows indicate increases or decreases of the reported measures.