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CerebraLux: A Low-Cost, Open-Source, Wireless Probe for Optogenetic Stimulation

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CerebraLux: A Low-Cost, Open-Source, Wireless Probe for Optogenetic Stimulation

Robel Dagnew et al. Neurophotonics.

Abstract

The use of optogenetics to activate or inhibit neurons is an important toolbox for neuroscientists. Several optogenetic devices are in use. These range from wired systems where the optoprobe is physically connected to the light source by a tether, to wireless systems that are remotely controlled. There are advantages and disadvantages of both; the wired systems are lightweight but limit movement due to the tether, and wireless systems allow unrestricted movement but may be heavier than wired systems. Both systems can be expensive to install and use. We have developed a low cost, wireless optogenetic probe, CerebraLux, built from off-the-shelf components. CerebraLux consists of two separable units; an optical component consisting of the baseplate holding the fiber-optic in place and an electronic component consisting of a light-emitting diode, custom-printed circuit board, an infrared receiver, microcontroller, and a rechargeable, lightweight lithium polymer battery. The optical component (0.5 g) is mounted on the head permanently, whereas the electronic component (2.3 g) is removable and is applied for each experiment. We describe the device, provide all designs and specifications, the methods to manufacture and use the device in vivo, and demonstrate feasibility in a mouse behavioral paradigm.

Keywords: infrared; low cost; open source; optogenetics; wireless optogenetic probe.

Figures

Fig. 1
Fig. 1
Overview of the CerebraLux optogenetic probe. This schematic shows the two components of the probe: (1) the electronic components consist of the battery, female header, infrared receiver, microcontroller, PCB, and LED. (2) The optic components consist of a baseplate, ferrule, and fiber-optic. The optic component is the only part to be permanently implanted and weighs only 0.5 g, whereas the electronic component weighs 2.3 g and is attached when experiments are run. The electronic and optic components both have magnets that allow for easy attachment and correct alignment between the fiber-optic and LED.
Fig. 2
Fig. 2
Overview of the optics component on the CerebraLux probe. This schematic shows greater detail of the optic component. The milled baseplate has slots for the magnets, LED, and fiber-optic. The alignment magnets are glued into their respective slots, and the fiber-optic and ferrule are inserted in the central channel of the baseplate. The LED is on the underneath of the PCB and aligns magnetically into the upper slot in the baseplate. This component is inserted into the correct region of the skull using a milled stereotaxic adapter that also has two aligning magnets (Appendix, CerebraLux manual; Sec. A1.5).
Fig. 3
Fig. 3
The Python-based GUI. The LED on the PCB is controlled through this Python-based GUI, which can be run on any computer interface. Once installed and the IR controller connected to the computer, the LED is turned on by clicking “activate LED” and turned off by clicking “STOP.” The ON time, OFF time, and intensity can be altered to implement pulse width modulation and light intensity. The GUI also calculates and outputs the period and frequency of the on–off times entered into the GUI.
Fig. 4
Fig. 4
The flowchart demonstrating CerebraLux activation. The computer GUI is connected to an Arduino Uno-controlled IR LED. After pressing “activate LED” on the GUI, the transmitter sends IR pulses to the head-mounted module, where it is received by the photodiode and sent to the ATMega328p microcontroller for processing. The microcontroller then outputs the desired on-time, off-time, and light intensity to the LEDs for stimulating the region of interest in the mouse brain.
Fig. 5
Fig. 5
The electronic component of CerebraLux. A fully assembled PCB is shown here. The battery, female headers, MCU, and IR receiver are on the upper side of the PCB and are shown in the left panels with the schematic in the top panel and the device in the lower panel. The magnets and LED are on bottom portion of the PCB. This view is shown in the right panels with the schematic view in the top panel and the device in the lower panel. The module has a footprint of 15×15  mm and, along with female headers and battery, has a weight of 2.3 g. This includes magnets that align with and attach to those on the baseplate of the optic component.
Fig. 6
Fig. 6
Power output as a function of forward voltage. The effect of varying the forward voltage or intensity (%) on light power output was assessed in the same device connected to three fully charged batteries of different recharge cycles. The data are shown as the total power output (a) and irradiance (b) and show that power output was reduced by 3% if the forward voltage is reduced by 40%. Across all voltages, the battery with fewer recharge cycles (1) had a higher power output compared to batteries with more recharge cycles (2, 3) but all batteries showed the same % reduction with a decrease in forward voltage.
Fig. 7
Fig. 7
Battery runtime. The lifetime and performance of three batteries was assessed by recording light power output at experimental conditions (10 Hz, 100% forward voltage or intensity) until a threshold of 200  μW was passed. The battery with fewer recharge cycles (1) had a highest initial power output compared to a battery that had recharged 3 (2) or 10+ times (3). During the first 30 min, the power output of all three batteries showed a steady decrease of 10% for each 10’ of stimulation that was independent of the initial power output. Thereafter, power output declined but remained above 50% of the initial output for 35 min (3) or 50 min (1, 2).
Fig. 8
Fig. 8
Validation of CerebraLux in vivo. (A) White HDPE. Mice (Ai27 x D1-cre, n=3) were implanted with the baseplate, made from white HDPE, containing the fiber-optic (the optic component) and allowed to recover. Shortly before the experiment, the PCB (the electronic component) was attached and mouse placed in the open field for 5 min, the probe was turned on for 5 min (a) and then off for the last 5 min. The behavior was video-tracked and the data exported and analyzed. We found that ChR2 activation in the right striatum (b) increased the number of counter-clockwise rotations, (c) did not alter the number of clockwise rotations, and increased distance traveled (% baseline, d), velocity (% baseline, e), and time spent mobile or % mobility (% baseline, f). *p<0.05 versus the first “OFF” period. (B) Black HDPE. Mice (Ai27 x D1-cre, n=2) were implanted with the baseplate, made from black HDPE, and the same experiment was conducted as in A (experiment). There was a marked reduction in light seen when the probe was turned on (g) but the same relative increase in counter-clockwise, but not clockwise, rotations was observed as in mice implanted with a white HDPE baseplate. A sham mouse (Ai27 × D1 cre), implanted with an optoprobe without the intracerebral fiber-optic, showed no counter-clockwise rotations and a decrease in clockwise rotations when the probe was turned on (h) and (f).
Fig. 9
Fig. 9
Increased turning when Cerebralux is turned on. This video shows turning behavior in a mouse implanted with a CerebraLux probe. The mouse, with a white HDPE-CerebraLux probe, placed in the right striatum, was placed in an open-field chamber on an elevated, semitransparent, and glass plate. The video, was taken by a camera mounted below the subject and shows turning behavior for 10 s before the optoprobe was turned on, for 5 min when the probe was on and for 10  s after stimulation has finished. Note that the view of subject is from below this reversing the direction of rotation and that the speed of the video is increased to a 2× speed throughout (Video 1, MP4, 10.3 MB [URL: http://dx.doi.org/10.1117/1.NPh.4.4.045001.1]).
Fig. 10
Fig. 10
Tools needed for milling.
Fig. 11
Fig. 11
Spoilholder design.
Fig. 12
Fig. 12
Baseplate dimensions.
Fig. 13
Fig. 13
The stereotaxic adapter.
Fig. 14
Fig. 14
Orientation of SMD components.
Fig. 15
Fig. 15
Orientation of LED.
Fig. 16
Fig. 16
Soldering of female header.
Fig. 17
Fig. 17
CerebraLux with a connected battery.
Fig. 18
Fig. 18
Batter charging circuit.
Fig. 19
Fig. 19
Max IR LED schematic.

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