Orexin released from the orexin nerve terminal exerts different functions in various regions of the brain. Orexin producing neurons (orexin neurons) extend nerve projections throughout the brain. They consist of about 30 amino acid residues and function as neurotransmitters to convey information between neurons. Orexin A and orexin B are neuropeptides produced from a single gene in certain neurons of the hypothalamus. It is also highly expected that new therapy would be developed for cataplexy. By identifying neuronal pathway, orexin neuron - serotonin neuron in the dorsal raphe nucleus - the amygdala, the team believes that the current study has made a big step forward to understanding of the whole picture of the narcolepsy mechanism. In fact, it is known that the amygdala of narcolepsy patients without orexin neurons responds excessively when the patients see, for example, interesting photos. This study has revealed that serotonin neurons do not directly suppress muscle tone weakening but inhibit cataplexy by reducing and controlling activities of the amygdala, which is involved in communicating emotional excitement. Furthermore, the effect of orexin neurons inhibiting cataplexy was found to be abolished when serotonin release was inhibited selectively in the amygdala.Ĭataplexy takes place, triggered by a sudden emotional excitement of positive valence such as a big laughter. When the amygdala activity was artificially reduced in a direct manner, cataplexy was inhibited, while artificially augmented, frequency of cataplexy attack increased. In addition, the team found that serotonin release reduced the amygdala activity. The same experimental operation in the other brain region that controls REM sleep did not inhibit cataplexy. In this study, with an optogenetic*6 tool, the team has discovered that catalepsy was almost completely inhibited by artificial augmentation of serotonin release induced by selectively stimulating serotonin nerve terminals in the amygdala in the narcolepsy model mice*7. Serotonin neurons in the dorsal raphe nucleus extend projections throughout the brain and send information. In this study, the international research team led by the researchers of Kanazawa University has discovered that serotonin neurons in the dorsal raphe nucleus inhibits catalepsy by reducing activities of the amygdala*5 that controls emotion. The one is noradrenaline neurons in the locus coeruleus of the brain, suppressing strong sleepiness, and the other is serotonin*4 neurons in the dorsal raphe nucleus of the brain, inhibiting cataplexy. The research team previously found two types of neurons preventing narcolepsy by receiving orexin from orexin neurons. Cataplexy attack is thought that atonia, a characteristics of REM sleep, takes place while one is awoken. doi:10.Dreams are dreamt usually during REM sleep, where most of the muscles are controlled to be relaxed (called atonia) in order to prevent the dreamer to make real actions. The mammalian target of rapamycin (mTOR) kinase mediates haloperidol-induced cataleptic behavior. Ramírez-Jarquín, U.N., Shahani, N., Pryor, W. Haloperidol–induced catalepsy is ameliorated by deep brain stimulation of the inferior colliculus. Adenosine antagonists reverse the cataleptic effects of haloperidol: implications for the treatment of Parkinson's disease. Trevitt J, Vallance C, Harris A, Goode T. Dopaminergic mechanisms underlying catalepsy, fear and anxiety: do they interact? Behav Brain Res. doi:10.5498/wjp.v6.i4.391Ĭolombo AC, de Oliveira AR, Reimer AE, Brandão ML. Catatonia: Our current understanding of its diagnosis, treatment and pathophysiology.
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