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Mechanical forces are known to be involved in various biological processes. However, it remains unclear whether brain functions are mechanically regulated under physiological conditions. Here, we demonstrate that treadmill running and passive head motion (PHM), both of which produce mechanical impact on the head, have similar effects on the hallucinogenic 5-hydroxytryptamine (5-HT) receptor subtype 2A (5-HT 2A) signaling in the prefrontal cortex (PFC) of rodents. PHM generates interstitial fluid movement that is estimated to exert shear stress of a few pascals on cells in the PFC. Fluid shear stress of a relevant magnitude on cultured neuronal cells induces ligand-independent internalization of 5-HT 2A receptor, which is observed in mouse PFC neurons after treadmill running or PHM. Furthermore, inhibition of interstitial fluid movement by introducing polyethylene glycol hydrogel eliminates the effect of PHM on 5-HT 2A receptor signaling in the PFC. Our findings indicate that neuronal cell function can be physiologically regulated by mechanical forces in the brain.

Light addressing is an emerging and sophisticated technique that can induce pinpoint and/or patterned neuronal activation in cultured neurons. We previously developed a light-addressable electrode using hydrogenated amorphous silicon (a-Si:H), which was sandwiched between a tin oxide (SnO(2)) substrate and a passivation layer of zinc antimonate (ZnOSb(2)O(5)) dispersed epoxy. This research developed an experimental system that simultaneously implemented light-addressed stimulation and Ca(2+) imaging of neuronal activities. The translucent and thin laminated structure of our electrode permitted optical accesses from two directions: Ca(2+) imaging from above and light addressing from beneath. The submillisecond bright/dark switching property of our electrode offered light-addressed stimulation without causing interference with Ca(2+) imaging. To provide patterned illumination for light addressing, a digital micromirror device was installed in the system as an active photomask. The system could induce pinpoint neuronal activation at a cellular level.

The authors propose a light-addressable planar electrode with a simple three-layer laminated structure that can induce pinpoint neuronal activation on the culture substrate. The structure consists of a tin oxide (SnO2), hydrogenated amorphous silicon (a-Si:H), and passivation layer. The passivation layer was a spin-coated low-conductive zinc antimonate (ZnOSb2O5)-dispersed epoxy, which was proved to be effective for preventing penetration of culture medium and thus avoiding deterioration of a-Si:H layer. Illumination to the electrode locally elevated the conductivity with 60-fold stimulus charge density. The fluo-4 calcium imaging of neurons cultured on the developed electrode showed that the neuronal activation was confined around the illuminated location, thus demonstrating the light-addressing capability of the proposed electrode.