Dopamine D2 Receptors Maintain Arousal And Mediate The Neurobiological Mechanism Of Psychotropic Drugs

Dopamine (DA) modulates diverse wake-related behaviors including movement, reward, and cognition. Recently, studies by pharmacological and gene knock-out animals revealed that dopamine D2R is an essential receptor in maintaining wakefulness. However, pharmacological tools used to determine the role of D2R in sleep-wake regulation show limited selectivity and/or incomplete blockade, and the D2R KO mice used for evaluating the maintenance of wakefulness are global KO mice. The target fields of D2R involved in the dopaminergic modulation of behavioral states remain unknown. To clarify the neuro anatomic location of D2R in maintaining wakefulness, we designed shRNA of D2R carried by adeno-associated virus (AAV), microinjected into the different nuclei to focal knock down (fKD) D2R, and performed the locomotor activity and sleep-wake behavior recording. On the other hand, we also designed the AAV carried-human D2R gene to focal rescue the D2R in different nuclei of D2R KO mice, to confirm the location of D2R in maintaining wakefulness. We tried to demonstrate the mechanism of D2R in sleep-wake regulation.Psychostimulants, such as methamphetamine and cocaine, can induce temporary improvements in either mental or physical function or both. Examples of these kinds of effects may include enhanced wakefulness, alertness, and locomotion, among others. The psycho simulants is at high risk of abuse. For the addiction patients, they usually have the serious sleep problems. To illustrate the role of D1R and D2R in methamphetamine and cocaine-induced wakefulness is helpful for withdrawal of addiction and treatment of addiction-related sleep-wake dysfunction.The AAV-shD2R-mCherry and AAV-hD2R, which we designed to focal knock down and rescue D2R, respectively, can express in the target nuclei efficiently and stably. In addition, the AAV is very safe for the experimenter, low toxicity and allergy.After fKD the D2R in the core of Nucleus accumbens (NAc core), the mice showed decreased locomotor activity during both day and night under the basal conditions, especially during the dark period, compared to the control mice. For the sleep-wake profile, compared with control mice, NAc core D2R fKD mice exhibited a significant decrease in wakefulness, with a concomitant increase in NREM and REM sleep, sleep fracment, and a drastic decrease in the low-frequency (1-2.5Hz) electroencephalogram delta power of NREM sleep during dark period. While the D2R were rescued, mice showed an increment of locomotor activity during the light period, especially during the first hour after lights on. But the locomotion during the night was unstable. Also, mice exhibited a significant increase in NREM sleep, with a concomitant decrease in wakefulness.Under the basal conditions, fKD D2R in the NAc shell, there were no significant differences of locomotion and sleep-wake profile between the fKD and control mice. When rescued the D2R in the NAc shell, mice exhibited the similar value of locomotion, wakefulness, NREM and REM sleep, compred with control mice.After fKD the D2R in the (Caudate-putamen, CPU), the mice exhibited decreased locomotor activity during both day and night under the basal conditions, especially during the dark period, compared to the control mice. However, there were no significant differences in wakefulness, NREM and REM sleep during the light and dark period between the CPU D2R fKD mice and control mice. While the D2R were rescued in CPU, mice showed an increment of locomotor activity during the light period, especially during the first hour after light on. Unfortunately, mice exhibited the same sleep-wake profile of D2R rescued mice and the control mice with the similar values. In D2R wild-type (WT) mice, intraperitoneal administration of methamphetamine induced wakefulness in a dose-dependent manner. Compared with the vehicle control, methamphetamine at doses of1,2, and4mg/kg significantly increased wakefulness for2,3, and4h, respectively, while the arousal effect lasted for1.5,2, and2.5h in D2R KO mice, respectively. Intraperitoneal administration of cocaine at doses of10,20, and40mg/kg significantly increased wakefulness for33,55, and106min, respectively, while the arousal effect lasted for20,32, and56min in D2R KO mice, respectively. Pretreatment with D1R antagonist SCH23390at30μg/kg decreased the arousal effects of methamphetamine and cocaine.Under the basal (physiologic) condtions, D2R highly expressed in the NAc core, plays an essential role in the maintenance of wakefulness.However, D2R located in NAc shell doesn’t meadiated the arousal effect and locomotion. D2R expressed in the CPU is important for controlling movement, but not meadiating wakefulness. D1R and D2R are essential for the arousal effects of methamphetamine and cocaine, with D2R being the receptor of primary importance.