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Dopamine D2 mechanisms in canine narcolepsy
S Nishino1, J Arrigoni, D Valtier
1Stanford Sleep Disorders Research Center, Palo Alto, California 94304.
Summary
Central D2 receptors critically control cataplexy and REM sleep. D2 antagonists suppress cataplexy, while D2 agonists worsen it, suggesting a secondary effect via noradrenergic systems.
Area of Science:
- Neuroscience
- Sleep Medicine
- Pharmacology
Background:
- Narcolepsy is a sleep disorder featuring abnormal rapid-eye-movement (REM) sleep and excessive daytime sleepiness.
- Cataplexy, a symptom of narcolepsy, involves REM-sleep atonia.
Purpose of the Study:
- To investigate the role of central dopamine D2 receptors in controlling cataplexy and REM sleep using a canine model.
- To determine the pharmacological effects of D2 antagonists and agonists on cataplexy.
Main Methods:
- Utilized a canine model of narcolepsy.
- Administered central D2 antagonists and agonists, including stereospecific enantiomers.
- Correlated in vivo pharmacological potency with in vitro drug affinity for D2, D1, and alpha 2 receptors.
- Tested selective D1 compounds.
- Examined the effects of selective dopamine reuptake inhibitors.
Main Results:
- Central D2 antagonists suppressed cataplexy, while D2 agonists aggravated it.
- The effects were stereospecific for D2 antagonists (S(-) sulpiride) and D2 agonists (R(+) 3-PPP).
- A significant correlation existed between in vivo potency and in vitro affinity for D2 receptors among tested D2 antagonists.
- Selective D1 compounds yielded inconsistent results.
- Dopamine reuptake inhibitors did not alter cataplexy.
Conclusions:
- Central D2-type receptors are critically involved in the regulation of cataplexy and REM sleep.
- The observed effects of D2 compounds on cataplexy are likely mediated secondarily via noradrenergic systems, not directly by dopamine reuptake inhibition.
- These findings highlight the complex interplay between neurotransmitter systems in sleep-wake disorders.