Figure 5.
A model of the neural pathways through which positive emotions may trigger cataplexy. During wakefulness, neurons in the LC, DR, vlPAG, and adjacent LPT inhibit neurons in the SLD that generate atonia. With strong, positive emotions, neurons in the CeA may receive excitatory signals from PFC or VTA dopamine neurons and inhibit these brainstem regions. Normally, this CeA inhibition is offset by excitatory signals from the orexin neurons. Loss of orexin signaling in narcolepsy upsets this balance, so that the CeA can inhibit the vlPAG/LPT and monoaminergic neurons, resulting in cataplexy. Direct excitatory signals from monoaminergic nuclei and orexin neurons to motor neurons, not depicted here, could also increase muscle tone.