Application of cortical optogenetic stimulation of animal model for modulating motor plasticity

Cortical theta burst stimulation (TBS) can modulate motor plasticity via long-term potentiation/depression (LTP/LTD)-like mechanisms and enhance motor performance, which make TBS a potential non-invasive therapy for motor deficit diseases such as Parkinson’s disease (PD). In previous rodent study, we had demonstrated that cortical electrical stimulation (CES)-TBS protocols were capable to change motor-evoked potentials (MEPs), and enhance motor performance in chronic PD rats. However, the cellular mechanism of TBS is still unknown. CES excited all types of neurons surrounding the electrode in cortex, it is difficult to differentiate the effect of TBS on specific neural circuit that responses to MEP modulation. LTP/LTD occurred dominantly at glutamatergic synapse, therefore the cell type-specific stimulation will be applied using optogenetic approach to reveal the functional roles of glutamatergic neuron in motor plasticity. CaMKIIalpha promoter driven channelrhodopsin-2 (CaMKIIalpha-ChR2) was expressed in glutamatergic pyramidal neuron in primary motor cortex (M1). Optogenetic stimulation was achieved using blue laser guided by optical fiber. Local field potentials (LFPs) and MEPs were collected during and after optogenetic TBS treatment. The results showed that MEPs amplitude were increased after optogenetic TBS treatment, which indicated that motor plasticity could be modulated by applying TBS on glutamatergic neurons in M1. However, there was no significant change in cortical excitability revealed by LFPs. In summary, these results suggested that LTP/LTD- like effects induced by cortical TBS treatment might be located at glutamatergic projections downstream of M1. We had demonstrated the modulation of motor plasticity using cell type-specific TBS scheme in M1. This finding may contribute to develop high efficient therapies for neural disorders via targeting specific neural circuit.