Light-evoked CIN action potentials evoke glutamatergic responses in MSNs.

<p>(A) <i>inset,</i> Schematic diagram of the recording conditions: whole-cell recordings were made from MSNs that neighbored ChR2-expressing CINs (red). The blue circle indicates the region stimulated by blue light. <i>main panel,</i> Example EPSP recorded in an MSN in response to a 4 ms light pulse (blue bar). (B) Amplitudes of light-evoked EPSPs in the presence of antagonists of GABA_A (Picrotoxin, Ptx), muscarinic (Scopolamine, Scop), and nicotinic (Mecamylamine, Mec) receptors and following application of the AMPA/kainate glutamate receptor antagonist NBQX. (C) Example of light evoked (blue bar) CIN-mediated EPSCs in a voltage-clamped MSN at holding potentials of −70 and +40 mV demonstrating the large current that is visible more than 100 ms after the light pulse at +40 mV. The amplitudes of the rapid −70 and prolonged +40 mV EPSC components were measured in the periods indicated by the gray bars. (D) Confocal image of mCherry-positive ChR2-expressing fibers in the motor cortex, white matter (WM) and underlying striatum (Str). Large bundles of corticofugal fibers (white arrowheads) and diffuse small axonal collaterals are visible throughout the dorsolateral striatum. Scale bar 200 µm. (E) <i>inset,</i> Schematic diagram of the recording conditions: whole-cell recordings were made from MSNs neighboring ChR2-expressing corticostriatal fibers (red), and blue light was delivered to the region indicated by the blue circle. <i>main panel,</i> Example EPSCs recorded in an MSN in response to a blue light pulse at the indicated holding potentials. (F) <i>left</i>, Average amplitudes of light-evoked EPSCs measured in MSNs held at either −70 or +40 mV in response to ChR2-mediated activation of either CINs or corticostriatal fibers (Cx). <i>right</i>, Average ratio of +40/−70 mV current amplitudes measured following ChR2-mediated activation of either CINs or corticostriatal fibers.