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Optogenetic Manipulations
Recent advanced optogenetic techniques enable reversible manipulations (activation or silencing) of neuronal activities using light-induced light-sensitive channels or pumps (Fig. 1A). These manipulations are precise (cell-type specific), transient (millisecond), and chemical delivery free.
We have integrated optogenetic techniques with LSCI imaging system to control and image neuronal behavior simultaneously in rodent cortex. We demonstrated for the first time the feasibility of LSCI to detect modulations in neuronal activities induced by optogenetic manipulation. Results in Fig. 1B show that light-induced activation of eNpHR during forepaw stimulation, decreased the amplitude and the extent of CBF responses as detected by LSCI. These results introduce an exciting and novel minimally invasive approach to studying neuronal behavior in vivo.
(A) (B)
Fig. 1 (A) Top: Cartoon illustration of the mechanism of light induced activation of channel ChR2 to increase neural firing rates, and light induced activation of pump eNpHR to decrease neural firing rates. Bottom: Immunostaining results to confirm protein (Lenti-CaMKIIa-eNpHR-EYFP-WPRE) expression in the excitatory neurons. Fig. 1 (B) Light induced activation of eNpHR: both the extent and the amplitude of CBF in response to the contra-lateral forepaw stimulation decreased, as revealed in LSCI images. Top left: CBF response Z-map without light. Top right: CBF response Z-map with light. Bottom: CBF responses amplitude (%) with and without stimulation light. The red line in the bottom plot represents stimulation duration.
In our collaboration with Dr. Galit Pelled's group, we focused on developing strategy to manipulate and control the transcallosal activity to facilitate appropriate plasticity by guiding the cortical reorganization in a rat model of sensory deprivation in the right forepaw. The excitatory neurons in rat S1 were engineered to express eNpHR. Results from electrophysiology, LSCI imaging, and BOLD fMRI measurements are concordant with those within the deprived S1, and activity in response to intact forepaw electrical stimulation was significantly increased by concurrent illumination of halorhodopsin over the healthy S1. Optogenetic manipulations effectively decreased the adverse inhibition of deprived cortex and revealed the major contribution of the transcallosal projections, showing interhemispheric neuroplasticity and thus, setting a foundation to develop improved rehabilitation strategies to restore cortical functions.
Nan Li, MSE
John E. Downey
Galit Pelled, PhD - F. M. Kirby Research Center for Functional Brain Imaging at Kennedy Krieger Institute. Assistant Professor of Radiology, Johns Hopkins School of Medicine
Piotr Walczak, MD - Assistant Professor of Radiology, Johns Hopkins School of Medicine
Assaf Gilad, PhD - Assistant Professor of Radiology, Johns Hopkins School of Medicine
NIH 1R01NS072171-01
NIH 1R21EB012829-01
Li N, Downey JE, Bar-Shir A, Gilad AA, Walczak P, Kim H, Joel SE, Pekar JJ, Thakor NV, Pelled G, Optogenetic-guided cortical plasticity after nerve injury, PNAS, 108(21):8838-43, 2011

Li N, Pelled G, Gilad AA, Walczak P, Thakor NV, An in vivo optical system: control and monitor cortical activity with improved laser speckle contrast imaging and optogenetics, Conf Proc IEEE Eng Med Biol Soc on Neural Eng, April 27 2011-May 1 2011
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