Effects of orexin gene transfer in the dorsolateral pons in orexin knockout mice.

STUDY OBJECTIVES: Narcolepsy is a sleep disorder characterized by loss of orexin neurons. Previously, our group demonstrated that transfer of the orexin gene into surrogate neurons in the lateral hypothalamus and the zona incerta significantly reduced cataplexy bouts in the orexin-ataxin-3 mice model of narcolepsy. The current study determined the effects of orexin gene transfer into the dorsolateral pontine neurons in the orexin knockout (KO) mice model of narcolepsy. The dorsolateral pons was chosen because it plays a critical role in regulating muscle tone and thus it is conceivable to be involved in cataplexy as well. Cataplexy is the pathognomonic symptom in narcolepsy. DESIGN: Independent groups of orexin KO mice were given bilateral microinjections (0.75 µL each side) of either recombinant adenoassociated virus-orexin (rAAV-orexin; n = 7), or rAAV-green fluorescent protein (rAAV-GFP; n = 7) into the dorsolateral pons. A group of orexin KO mice that did not receive rAAV (n = 7) and a group of wild-type mice (C57BL/J6; n = 5) were used as controls. Three weeks after rAAV-mediated gene transfer narcolepsy symptoms were examined using sleep and behavioral recordings. Number, location of the orexin-immunoreactive neurons, and relative density of orexin immunoreactive fibers were determined. MEASUREMENTS AND RESULTS: Orexin gene transfer into the dorsolateral pons significantly decreased cataplexy and modestly improved wake maintenance compared to the orexin KO mice that did not receive rAAV. In contrast, GFP gene transfer worsened narcoleptic symptoms compared to the no-rAAV orexin KO group. CONCLUSION: Orexin gene transfer into the dorsolateral pontine neurons can control cataplexy attacks and modestly improve wake maintenance.

Orexin gene transfer into zona incerta neurons suppresses muscle paralysis in narcoleptic mice.

Cataplexy, a sudden unexpected muscle paralysis, is a debilitating symptom of the neurodegenerative sleep disorder, narcolepsy. During these attacks, the person is paralyzed, but fully conscious and aware of their surroundings. To identify potential neurons that might serve as surrogate orexin neurons to suppress such attacks, the gene for orexin (hypocretin), a peptide lost in most human narcoleptics, was delivered into the brains of the orexin-ataxin-3 transgenic mouse model of human narcolepsy. Three weeks after the recombinant adenoassociated virus (rAAV)-mediated orexin gene transfer, sleep-wake behavior was assessed. rAAV-orexin gene delivery into neurons of the zona incerta (ZI), or the lateral hypothalamus (LH) blocked cataplexy. Orexin gene transfer into the striatum or in the melanin-concentrating hormone neurons in the ZI or LH had no such effect, indicating site specificity. In transgenic mice lacking orexin neurons but given rAAV-orexin, detectable levels of orexin-A were evident in the CSF, indicating release of the peptide from the surrogate neurons. Retrograde tracer studies showed that the amygdala innervates the ZI consistent with evidence that strong emotions trigger cataplexy. In turn, the ZI projects to the locus ceruleus, indicating that the ZI is part of a circuit that stabilizes motor tone. Our results indicate that these neurons might also be recruited to block the muscle paralysis in narcolepsy.