Optogenetic inactivation of the subthalamic nucleus improves forelimb akinesia in a rat model of Parkinson disease.
BACKGROUND
The inhibition of neuronal activity by electrical deep brain stimulation is one of the mechanisms explaining the therapeutic effects in patients with Parkinson disease (PD) but cannot specifically activate or inactivate different types of neurons. Recently, a new technology based on optogenetics has been developed to modulate the activity of specific neurons. However, the therapeutic effects of optical inactivation in the subthalamic nucleus (STN) have not been fully investigated.


OBJECTIVE
To perform various behavioral tests to evaluate changes in motor functions in a PD rat model after optogene expression and, unlike previous studies, to assess the therapeutic effects of direct optogenetic inactivation in the STN.


METHODS
6-Hydroxydopamine-induced hemiparkinsonian rats received injections of hSynapsin1-NpHR-YFP adeno-associated virus or an equivalent volume of phosphate-buffered saline. Three weeks after injection of adeno-associated virus or phosphate-buffered saline, the optic fiber was implanted into the ipsilateral STN. A stepping test, a cylinder test, and an apomorphine-induced rotation test were performed in 3 sequential steps: during light-off state, during light stimulation, and again during light-off state.


RESULTS
Stepping tests revealed that optical inhibition of the STN significantly improved 6-hydroxydopamine-induced forelimb akinesia. PD motor signs, as assessed by cylinder and apomorphine tests, were not affected by optical inhibition. Immunofluorescence revealed that halorhodopsin was highly expressed and colocalized with vesicular glutamate transporter 2 in the STN.


CONCLUSIONS
Optogenetic inhibition in the STN may be effective in improving contralateral forelimb akinesia but not in changing forelimb preference or reducing dopaminergic receptor supersensitivity. These findings are useful as a basis for future studies on optogenetics in PD.
‡Department of Neurological Surgery and **Department of Biochemistry and Molecular Biology, University of Ulsan College of Medicine, Seoul, Republic of Korea; §Department of Neurological Surgery, Gangneung Asan Hospital, University of Ulsan College of Medicine, Gangneung, Republic of Korea; ¶Department of Computer Science and Engineering, Bioengineering Graduate Program, University of Notre Dame, Notre Dame, Indiana; ‖Center for Neural Science and WCI Center for Functional Connectomics, Korea Institute of Science and Technology, Seoul, Republic of Korea; #Center for Bionics of Korea Institute of Science and Technology, Seoul, Republic of Korea.
Hyung Ho
HH
Yoon
Jin Hoon
JH
Park
Yong Hwan
YH
Kim
Joongkee
J
Min
Eunmi
E
Hwang
C Justin
CJ
Lee
Jun-Kyo Francis
JK
Suh
Onyou
O
Hwang
Sang Ryong
SR
Jeon
D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D035841:Behavioral Research / Q000379:methods; D004195:Disease Models, Animal; D004409:Dyskinesia, Drug-Induced / Q000503:physiopathology / Q000517:prevention & control*; D005552:Forelimb / Q000503:physiopathology; D020868:Gene Silencing; D025602:Halorhodopsins / Q000008:administration & dosage / Q000032:analysis; D008297:Male; D009046:Motor Neurons / Q000378:metabolism; D062308:Optogenetics; D010300:Parkinson Disease / Q000150:complications / Q000503:physiopathology* / Q000628:therapy*; D051381:Rats; D017208:Rats, Wistar; D013378:Substantia Nigra / Q000166:cytology; D020531:Subthalamic Nucleus / Q000473:pathology / Q000503:physiopathology*; D050599:Vesicular Glutamate Transport Protein 2 / Q000737:chemistry
D025602:Halorhodopsins; D050599:Vesicular Glutamate Transport Protein 2