Impaired plasticity at specific subset of striatal synapses in the Ts65Dn mouse model of Down syndrome

Trisomy 21 or Down syndrome (DS) is the most frequent genetic cause of mental retardation. There is limited insight into the biological basis for the cognitive and motor deficits in DS. Because the striatum plays a key role in the regulation and learning of voluntary movements and in cognitive processes, our study was aimed at investigating striatal synaptic transmission and plasticity in a well-accepted genetic model of DS.

Electrophysiological recordings were performed in a corticostriatal slice preparation from trisomic (Ts65Dn) and wild-type mice. Synaptic properties and plasticity, long-term potentiation (LTP) and long-term depression (LTD), were investigated.

The basal electrophysiological properties of striatal principal spiny neurons and cholinergic interneurons were spared in the Ts65Dn mouse model of DS. Striatal principal spiny neurons from Ts65Dn mice maintained their ability to undergo LTP and LTD. Conversely, LTP was lost in striatal cholinergic interneurons of Ts65Dn mice. The loss of LTP in striatal cholinergic interneurons of Ts65Dn mice was accompanied by a severe impairment of endogenous cholinergic signaling within the striatum.

The intrastriatal cholinergic system that was thought to be spared in DS is functionally altered in the Ts65Dn genetic model of DS. Altered cholinergic transmission might play a critical role in the pathophysiology of motor and cognitive deficits in DS, leading to an abnormal processing of neuronal inputs within the basal ganglia. Targeting striatal cholinergic transmission might represent a new therapeutic strategy in DS.