Modulation of top-down influence affects trafficking of glutamatergic receptors in the primary visual cortex.

Numerous studies indicate that top-down influence plays critical roles in visual perception by enhancing neuronal excitability in the primary visual cortex (V1). The underlying mechanisms are poorly understood. This study examined changes of excitatory glutamatergic markers in the V1 cortex of cat after top-down influence of cortical area 7 (A7) was modulated by transcranial direct current stimulation (tDCS). Our results showed that the content of glutamate as well as the total cellular protein of glutamatergic receptors, including the key subunit GluA1 of AMPA receptors and subunit NR1 of NMDA receptors, in the V1 cortex had no significant change after anode- and cathode-tDCS relative to sham-tDCS in A7. However, the plasma membrane protein content of GluA1 and NR1 in the V1 was significantly increased after anode-tDCS, but decreased after cathode-tDCS when compared with that after sham-tDCS in A7. Further, the abundance of phosphorylated GluA1 and NR1 in the V1 also elevated significantly after anode-tDCS, but lowered after cathode-tDCS compared with that after sham-tDCS. Additionally, the content of phosphorylated CaMKII (p-CaMKII), a protein kinase preferentially boosting phosphorylation of glutamatergic receptors, in the V1 improved after anode-tDCS although no significant alteration occurred after c-tDCS in A7. Taken together, our results indicate that feedback influence of A7 may facilitate the trafficking of glutamatergic receptors to postsynaptic membrane in the V1 cortex through receptors' phosphorylation process, which could be an important mechanism of high-level cortex in modulating visual information processing in the V1 cortex.