Implication of dopaminergic mechanisms in the wake-promoting effects of amphetamine: a study of D- and L-derivatives in canine narcolepsy

Abstract

Using a canine model of narcolepsy and selective DA and NE uptake inhibitors, we have recently shown that DA uptake inhibition promotes wakefulness, while NE uptake inhibition inhibits rapid eye movement sleep and cataplexy. In order to further delineate the respective roles of the dopaminergic and noradrenergic systems in the pharmacological control of symptoms of narcolepsy, we compared the potency of amphetamine isomers (D- and L-amphetamines) and a derivative (L-methamphetamine) on wakefulness and cataplexy. Their respective effects on these narcolepsy symptoms were then compared with their in vivo effects on extracellular DA levels in the caudate and NE levels in the frontal cortex during local drug perfusion in narcoleptic dogs. Polygraphic recordings demonstrated that D-amphetamine was about twice as potent as L-amphetamine, and was six times more potent than L-methamphetamine in increasing wakefulness and reducing slow-wave sleep. D-Amphetamine and L-amphetamine were equipotent in reducing rapid eye movement sleep and cataplexy, and L-methamphetamine was about half as potent as L- and D-amphetamines. D-Amphetamine was found to be more potent in increasing DA efflux than L-amphetamine, and L-methamphetamine was found to have little effect on DA efflux; there was no significant difference in the potencies of the three derivatives on NE efflux. The potencies of these amphetamines on wakefulness correlated well with DA, but not NE, efflux in the brain of narcoleptic dogs during local drug perfusion. Our current results further exemplify the importance of the DA system for the pharmacological control of electroencephalogram arousal and suggest that increased DA transmission mediates the wake-promoting effects of amphetamine-like stimulants.