A wirelessly controlled implantable LED system for deep brain optogenetic stimulation

Abstract

In recent years optogenetics has rapidly become an essential technique in neuroscience. Its temporal and spatial specificity, combined with efficacy in manipulating neuronal activity, are especially useful in studying the behavior of awake behaving animals. Conventional optogenetics, however, requires the use of lasers and optic fibers, which can place considerable restrictions on behavior. Here we combined a wirelessly controlled interface and small implantable light-emitting diode (LED) that allows flexible and precise placement of light source to illuminate any brain area. We tested this wireless LED system in vivo, in transgenic mice expressing channelrhodopsin-2 in striatonigral neurons expressing D1-like dopamine receptors. In all mice tested, we were able to elicit movements reliably. The frequency of twitches induced by high power stimulation is proportional to the frequency of stimulation. At lower power, contraversive turning was observed. Moreover, the implanted LED remains effective over 50 days after surgery, demonstrating the long-term stability of the light source. Our results show that the wireless LED system can be used to manipulate neural activity chronically in behaving mice without impeding natural movements.

Keywords: channelrhodopsin; direct pathway; freely-behaving; optogenetics; striatonigral; wireless.

Figure 1

Block diagram of wireless optogenetic stimulator. A microcontroller containing two digital to analog converters (DAC) allows independent control of two blue LEDs.

Figure 2

Wireless optogenetic stimulation system with implantable LED. (A) Illustration of LED shank (all measurements in mm). (B) LED implants with connectors. (C) Digital radio PCB. (D) Assembled opto-stimulator PCB.

Figure 3

Characterization of LED stimulation. (A) Optical power increases linearly as a function of the input current. (B) Temperature change was measured in vivo. The temperature increases as a function of the duty cycle and the percent of input current.

Figure 4

In vivo wireless stimulation of striatonigral neurons drives behavior. (A) Photograph of a mouse with wireless headstage. (B) Schematic illustration of LED placement within the dorsal striatum of D1-ChR2 mice. (C) Representative serial coronal sections through the shank track. LED placement is indicated by arrowhead. Scale bars are 1 mm. (D) High power (32 mW) LED stimulation of striatonigral neurons induces twitching in freely behaving mice in a frequency dependent manner. (E) Behavioral response to LED stimulation is stable 41 days after the initial tests. (F) Control mice that lack opsin expression show no response to stimulation. The dotted lines are linear regression lines. (G) Proportion of time D1-ChR2 mice spent turning during low power (16 mW) stimulation. Values are mean ± s.e.m.