Mice: Six D1 dopamine receptor (D1DR)-Cre mice (Drd1a-cre+; derived from Gensat strain EY262; aged 3 months; 25–32 g) were used in this study. Mice genetics were verified by genotyping, using primers for the D1-Cre recombinase transgene (D1-Cre-F: 5′-AGG GGC TGG GTG GTG AGT GAT TG; D1-Cre-R: CGC CGC ATA ACC AGT GAA ACA GC-3′). All procedures were approved by the Institutional Animal Care and Use Committee (#0062039) at the University of Iowa, in accordance with the National Institutes of Health Guide for the Care and Use of Laboratory Animals and the ARRIVE guidelines.
Dopamine-depletion and ChR2 expression
As in our previous work, we used an adeno-associated vector (AAV) construct with floxed inverted channelrhodopsin (AAV-ChR2), along with mCherry (University of North Carolina at Chapel Hill (UNC) Vector Core; AAV5-EF1a-DIO-hChR2(H134R)-mCherry) to stimulate neurons expressing D1DRs 24,25. We injected mice with AAV-ChR2 (0.5 µL of approximately ≥ 1x1013 vg/ml) into the dorsal striatum (AP + 0.5/ML -1.5/DV -3.0) and immediately placed an optical fiber cannula (200 µm core, 0.22 NA, Doric Lenses) at the same coordinates as the injection site. We also unilaterally injected the neurotoxin, 6-hydroxydopamine (6-OHDA; 2.5 µl with 2 ug/ul), into the dorsal striatum in two injection locations (AP + 0.4/ML -1.8/DV -3.5 and AP + 1.1/ML -2.0/DV -3.5) to deplete dopamine; of note, this manipulation reliably kills nigrostriatal dopamine terminals and produces reliable impairments in striatal field potentials 10,26.
Phase-adaptive brain stimulation (PABST)
For PABST, we implanted 16-channel microwire optrodes (Microprobes) in the dorsal striatum at AP + 0.5/ML -1.5/DV -3.0 (Fig. 1). We recorded LFPs across 16 channels using an Open Ephys system. The raw signal was amplified with a total gain of 198X, high-pass filtered at 0.1 Hz, and recorded with 16-bit resolution at a 30k-Hz sampling rate.
To estimate phase, LFPs were streamed from the Open Ephys system to a notebook computer (Dell) via a zeroMQ data messaging system. Real-time analysis was performed in MATLAB; data were buffered over ~ 10 milliseconds. Wavelet-based frequency and phase estimation were performed using a complex Morelet. Instantaneous frequency and phase were calculated using wavelets and predicted for 50 milliseconds in the future using linear estimation.
During closed-loop experiments, D1DR + mice with optical cannula were connected to the optical patch cable through a zirconia ferrule (Doric Lenses) without anesthesia. Light was generated using a 473-nm diode-pumped solid-state (DPSS) laser source (OEM Laser Systems), and an optical rotary joint (Doric Lenses) was used to facilitate animal rotation. Before each experiment, the power output of the laser was adjusted to 8 mW at the fiber tip. Power measurements verified that the laser reached 90% power within 0.74 milliseconds of TTL triggers and maintained 8 mW with < 5% error.
Motion tracking
We captured motion using a 3-D motion-tracking system (OptiTrack); we have previously used this system to track mouse movement in detail 10,26. Briefly, we implanted two 4-mm infrared-reflective spheres attached to the recording headstage in the anterior-posterior dimension. Four infrared cameras recorded the X (right-left), Y (forward-back), and Z (up-down) coordinates of the mouse’s head at 120 frames/per second (frames/s) to track head position 10. Automated computer tracking data were synchronized with a video camera at 30 frames/s and neurophysiological recording hardware.
Histology: ChR2 expression and electrode localization were confirmed by immunohistochemistry. Briefly, mice were deeply anesthetized with ketamine (100 mg/kg) and xylazine (10 mg/kg) and intracardially perfused with ice-cold 4% paraformaldehyde. Brains were post-fixed in 4% paraformaldehyde overnight and immersed in 30% sucrose until the brains sank. Brains were sectioned (50 µm) with a cryostat (Leica) and stored in PBS. Immunostaining procedures were performed with free-floating brain sections. Primary antibodies to Cre (mouse anti-Cre; Millipore-MAB 3120; 1:500), D1 receptor (rat anti-D1DR; Sigma-D2944; 1:200), and tyrosine hydroxylase (rabbit anti-TH; Millipore -MAB152; 1:500) were incubated overnight at 4° C. Sections were visualized with Alexa Fluor fluorescent secondary antibodies (goat anti-mouse IgG Alexa 633, goat anti-rat IgG Alexa 568, goat anti-rabbit IgG Alexa 488, and goat anti-mouse IgG Alexa 350; Thermo Fisher Scientific; 1:1,000) and matched with the host primary by incubating 2 hours at room temperature. Images were captured on an Olympus VS120 microscope.
Statistics
All procedures were reviewed by the Biostatistics, Epidemiology, and Research Design Core within the University of Iowa Institute for Clinical and Translational Science. To avoid making any distributional assumptions about the data, continuous measures were reported as medians and inter-quartile ranges. Testing for significant differences followed the non-parametric Wilcoxon rank sum test.