Figure 7.

A model for the triggering of cataplexy by positive emotions. A, In wild-type mice, a positive stimulus such as chocolate activates the ACC and PLC that excite orexin, MCH, and amygdala neurons. The MCH and amygdala neurons inhibit the vlPAG/LPT neurons, but this inhibition is normally offset by excitation from the orexin neurons, resulting in sustained inhibition of the SLD by the vlPAG/LPT and no substantial loss of muscle tone. B, In orexin KO mice, the MCH and amygdala neurons are activated by the ACC and PLC, but in the absence of orexins, these systems can reduce activity in the vlPAG/LPT, leading to activation of the SLD and cataplexy. For simplicity, additional systems that regulate cataplexy and motor tone, including neurons producing norepinephrine, serotonin, and dopamine, are not shown in this model.