Role of the Catecholamine and Limbic Systems in Narcolepsy/Cataplexy

In this thesis I investigated the neural circuits that trigger cataplexy in mice. Specifically, I first addressed the theory that cataplexy is a REM sleep disorder. I then investigated a role for the noradrenergic and dopaminergic systems in murine cataplexy. Finally, I addressed the role of the amygdala in triggering cataplexy. From this work several specific conclusions can be drawn: 1. Cataplexy does not share a common executive mechanism with REM sleep, although the two may share a common mechanism that generates muscle atonia. Muscle tone during REM sleep and cataplexy is similar, however increasing REM sleep pressure does not increase cataplexy and positive affective stimuli that can increase cataplexy tend to decrease REM sleep. 2. Systemic manipulation of dopamine receptors can modulate cataplexy without affecting behavioral state. Specifically, manipulation of D2-like dopamine receptors at specific doses can modulate cataplexy while having no affect on sleep-wake state or sleep attacks, and manipulation of D1-like receptors potently affects sleep-wake state and sleep attacks without affecting cataplexy. 3. Systemic modulation of noradrenergic activity in orexin KO mice is sufficient to modulate cataplexy. Specifically, activation of excitatory α1 receptors reduces the occurrence of cataplexy while blockade of these receptors exacerbates it. 4. Withdrawal of an endogenous α1-mediated noradrenergic drive from motor neurons during wakefulness contributed to the loss of muscle tone during cataplexy. Re-establishing this excitatory drive exogenously alleviated cataplexy-dependant muscle atonia. 5. The amygdala is a critical part of the neural mechanism that triggers cataplexy in orexin KO mice. Ablation of the amygdala resulted in significant decreases in both baseline cataplexy and emotionally-induced cataplexy. The amygdala may trigger cataplexy through direct projections to brainstem areas that regulate muscle atonia.Ph