Gene transfer has proven to be an effective neurobiological tool in a number of neurodegenerative diseases and we have used it to correct a sleep disorder. We have focused on narcolepsy, a neurodegenerative sleep disorder linked to the loss of neurons containing the neuropeptide hypocretin, also known as orexin. To restore orexin levels we have inserted the gene for orexin into surrogate neurons and blocked narcoleptic behavior in two reliable and valid mice models of narcolepsy. The effects were site specific and depended on the connectivity of the surrogate neurons. We now propose to further narrow the site-specificity by confining expression of orexin only in MCH neurons and selectively activating them during waking. The MCH neurons are still viable in human narcolepsy and are connected to the same downstream targets as the orexin neurons. These neurons are normally silent during waking and we hypothesize that by selectively activating them during waking we will block cataplexy and lengthen waking bouts.
In aim 1 we will insert the genes for channelrhodopsin-2 (ChR2), a light sensitive cation channel, and orexin only in MCH neurons (MCH promoter driven). Optogenetic stimulation will drive the MCH-ChR2-Orexin containing neurons and its effects on cataplexy and wake duration will be determined during both the day and night cycles.
Aim 2 will utilize a new emerging methodology that relies on Designer Receptors Exclusively Activated by Designer Drugs to activate the MCH neurons. Experiments with appropriate controls, including orexin receptor antagonist are proposed to strengthen the conclusions. C-Fos will identify activation of the MCH neurons and an in vitro calcium imaging study will determine functionality of the genetically inserted ChR2 and hM3Dq receptors. These studies will for the first time identify neurons that can be selectively activated to block narcoleptic behavior.
Current pharmacological approaches for treating narcolepsy lack specificity since the drugs bathe the entire brain and body. The proposed studies will utilize optogenetics and DREADD to identify neurons that can be selectively activated to block narcoleptic behavior and lengthen wake bouts. We believe that the gene transfer approach can serve as a methodological tool to quickly and cost-effectively identify these neurons.
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