Optogenetics is a new technology that allows control of brain cells with light- in a way that allows targeting of control to well-defined subsets of cells in vivo, even if those targeted cells are mixed in with other cell types. This provides substantial advantages for research into Parkinson’s disease (PD) pathophysiology and treatment, since excitation or inhibition may be targeted to defined subsets of cells, conferring the ability to test gain or loss of function only of those targeted cells in circuit performance or behavior while retaining the millisecond precision of electrodes. Moreover, simultaneous recording is possible with optogenetic stimulation since stimulation artifacts may be eliminated, allowing insight into how altered behavior may be linked to altered circuit dynamics and physiology.
The full promise of optogenetic technology can only be realized as specific classes of genetically-targeted cells are controlled by combinations of opsins over a range of temporal frequencies in behaving pre-clinical models; to date, the cell-type specificity of opsin expression has been achieved with the use of cell-type specific promoters or transgenic pre-clinical models. But it is rare to find promoter fragments that are sufficiently small, strong, and specific to be packaged in viral vectors, pre-clinical model promoters typically do not translate well to more relevant pre-clinical models in terms of specificity. Therefore non-promoter-based strategies will be particularly important for pre-clinical PD optogenetics research.
Here we propose to capitalize on a unique alignment of opportunities to take the first crucial and focused step in this direction, developing the optogenetic targeting strategies in the pre-clinical model that set the stage for a completely new perspective on PD pathophysiology and treatment in the pre-clinical model.
A promoter-independent circuit-targeting strategy for opsin expression may provide the required power in the pre-clinical model, in which the investigator target neurons that synapse onto or receive synapses from a specific cell-type within the same brain region or from another, distinct brain region. We propose to capitalize on emerging circuit targeting tools to develop this strategy in the pre-clinical model. The pre-clinical-model-suitable circuit-targeting strategies that we wish to explore fall into two categories: axonal trafficking and axonal transduction. It will require a systematic exploration of multiple opsins and multiple targeting strategies to achieve this goal.
Relevance to Diagnosis/Treatment of Parkinson’s Disease:
In this proposed research, we take the necessary first steps toward applying optogenetics to PD in pre-clinical models, by determining which optogenetic tools are best suited for the pre-clinical model in terms of efficacy and targetability. The proposed research is the first of its kind, and will lay the groundwork for understanding how to modulate and repair motor behavior in PD.
We expect to emerge from this exploratory work (pilot-experiment in magnitude, but still systematic and highly informative and necessary first step) with a clear idea of which excitatory opsins and which inhibitory or modulatory neurons are best suited for expression and axonal trafficking in the pre-clinical model, and which (alone or in combination with various projection-targeting strategies) will enable the most robust and precise circuit targeting.
We have completed the initial design and implementation of the research infrastructure. We have been able to show neurons that express the opsins in multiple areas of the pre-clinical brain. In addition, we have been able to alter the activity of these cells in pre-clinical motor cortex. Work is continuing on achieving precise circuit targeting for optogenetic modulation within the pre-clinical motor system.