Narcolepsy Flashcards
Two main symptoms of narcolepsy: -Daytime sleepiness -Cataplexy
Extreme day-time sleepiness and cataplexy are the main symptoms. Cataplexy is the sudden unexpected loss of muscle tone while awake which can lead to immediate collapse. It can be triggered by various forms of emotional arousal such as fear, anger, amusement or stress. Other symptoms include hallucinations and sleep paralysis.
Hypocretin explanation
Research has uncovered a link between Neurotransmitters hypocretin (or orexin) and narcolepsy. Hypocretin play an important role in maintaining wakefulness, effecting neural communication particularly messages relating to when the body should be awake and asleep. The levels of hypocretin decrease by up to 95% in the narcoleptic brain. Furthermore low hypocretin results in reduced norepinephrine which normally promotes wakefulness. Scar tissue has also been found in the hypothalamus of narcoleptics where hypocretin containing cells are present. This indicates the cells were present at birth but died later on, although it is not yet clear how.
Mishima et al: Narcoleptic dobermans
Early research demonstrated it is possible to breed strands of mice and dogs (Dobermans) that were narcoleptic, caused by either an absence of hypocretin or an absence of the hypocretin receptors. These findings were replicated in human narcoleptics demonstrating they had lower levels of hypocretin in their cerebrospinal fluid. Believed to be due to hypocretin producing cells in the hypothalamus of the brain drastically reduced. //The validity of this research questionable as this study was conducted via post mortem on the brains of only 5 narcoleptics. fairly small sample TF conclusions must be made carefully. FM, the exact way these genes are involved in REM sleep remains unclear. more research must be conducted to establish the reliability of Mishimas findings.
Psychology as science: evolution and ethics
Such R shows how very advanced psychology is becoming with a shift towards the biological paradigm. Explaining narcolepsy as a result of imbalanced hypocretin appeases the criteria for a science as it is valid, objective and falsified. However it could be argued that the use of animals in such research is unethical, particularly breeding dogs with narcolepsy. Although these dogs are often well treated, the treatment implications of such research for human narcoleptics outweighs the suffering of a small sample of dogs.
Siegel: 70,000 - 10,000
Furthermore Siegel found that neurologically normal individuals have about 70,000 hypocretin containing cells, whereas the narcoleptics had around 10,000 which is a significant decrease suggesting that hypocretin does play a central role in controlling REM sleep and causing narcolepsy.
Picchiono et al: nature v nurture
Realistically narcolepsy in humans is caused by a combination of genetic or neural susceptibility and one or more environmental triggers such as hormonal changes, infection, trauma or immune system dysfunction. Pichionno et al found several stressors including a major change of sleeping habit, flu and unexplained fevers carried a significant risk for narcolepsy. This demonstrates that narcolepsy is a nature-nurture phenomenon in humans as it has environmental as well as a biological cause.
Thannickel et al: autoimmune attacks
An alternative theory for the loss of hypocretin is proposed by Thannickel et al. They suggest that the hypocretin cells are killed by the immune system, which confuses these cells for an infectious agent such as a virus. Other cells, near where the hypocretin cells should be, appear to be normal; this indicates that whatever the cause of the cell loss, the hypocretin cells are targeted very specifically. Currently this is the leading hypothesis, however as yet numerous researchers have been unsuccessful in identifying people with narcolepsy who have suffered an autoimmune attack. Therefore there is no solid evidence for this hypothesis meaning it should be used in Holism with other explanations for narcolepsy.
Invasion of REM explanation
The symptoms of narcolepsy indicate an invasion of REM sleep phenomena into waking life. As exemplified by cataplexy, during REM the bodily muscles lose tone which may occur during waking hours. Furthermore dreams occur primarily in REM sleep and hallucinations are explained as dreams during waking hours. Finally when people with narcolepsy fall asleep they move directly into REM sleep, ignoring the other stages, so when they fall asleep in the day they immediately show signs of cataplexy as they are in REM sleep.
Vogel: narcolepsy case study
The REM hypothesis was first proposed after Vogel observed REM sleep at the onset of sleep in a narcoleptic patient. The explanation was further supported by recordings of neural activity in the brain stem of narcoleptic dogs that showed cataplexy is linked to the activations of cells that in normal animals are active only during REM sleep. However, in general research has not been convincing which suggests this explanation is better used in conjunction with others.
Use of Animals
In order to study narcolepsy in humans and produce treatments scientists have bred narcoleptic dogs and mice. However it is questionable to generalise non-human research of this type as it is shown that the inherited nature of narcolepsy is qualitatively different in humans compared to dogs and mice. Furthermore the breeding of dogs solely to study narcolepsy is ethically questionable, although as long as they are well looked after the treatment implications for humans would outweigh any disadvantages.
