Wakefulness Induced by TAAR1 Partial Agonism in Mice Is Mediated Through Dopaminergic Neurotransmission

Abstract

Trace amine-associated receptor 1 (TAAR1) is a negative regulator of dopamine (DA) release. The partial TAAR1 agonist RO5263397 promotes wakefulness and suppresses NREM and REM sleep in rodents and non-human primates. We tested the hypothesis that the TAAR1-mediated effects on sleep/wake regulation were due, in part, to DA release. Male C57BL6/J mice (n = 8) were intraperitoneally administered the D1R antagonist SCH23390, the D2R antagonist eticlopride, a combination of D1R + D2R antagonists, or saline at ZT5.5, followed 30 min later by RO5263397 or vehicle per os. EEG, EMG, subcutaneous temperature, and activity were recorded across the 8 treatments and sleep architecture was analyzed for 6 h post-dosing. As described previously, RO5263397 increased wakefulness and delayed NREM and REM sleep onset. D1, D2, and D1 + D2 pretreatment reduced RO5263397-induced wakefulness for 1-2 h after dosing but only the D1 antagonist significantly reduced the TAAR1-mediated increase in NREM latency. Neither the D1 nor the D2 antagonist affected the TAAR1-mediated suppression of REM sleep. These results suggest that, whereas the TAAR1 effects on wakefulness are mediated, in part, through the D2R, D1R activation plays a role in reversing the TAAR1-mediated increase in NREM sleep latency. In contrast, the TAAR1-mediated suppression of REM sleep appears not to involve D1R or D2R mechanisms.

Keywords: agonists; dopaminergic antagonists; sleep; trace amine-associated receptor 1 (TAAR1).

Figure 1

Schematic illustrating the experimental design and Wake Time for 6 h after the second dosing. (A). Male C57BL/6 mice received a dopaminergic antagonist i.p. at ZT5.5 followed 30 min later by either p.o. RO3397 or saline at ZT6. (B–G). For ease of visualization, data are split into three subgroups in which the results from the negative (Sal + Veh) and positive (Sal + RO3397) control treatments are repeated in each graph. Hourly Wake Time (mean + SEM) for the first 6 h after the second dosing with (B) D1 antagonist SCH23390 +Veh or +RO3397, (C) D2 antagonist eticlopride +Veh or +RO3397, and (D) D1 + D2 antagonist + Veh or +RO3397. Colored symbols indicate statistical significance for that hour compared to Sal + Veh (*) or Sal + RO3397 (#) based on RM-ANOVA. Panels (E–G) present Wake Time (mean + SEM) summed in 3 h bins (ZT6-8 and ZT9-11) for each treatment. *, # p < 0.05; **, p < 0.01; ***, p < 0.005; ****, p < 0.001.

Figure 2

Latency to NREM sleep and NREM time for the first 6 h after the second dosing. For ease of visualization, data are split into three subgroups in which the results from the negative (Sal + Veh) and positive (Sal + RO3397) control treatments are repeated in each graph. (A–C). Latency to NREM sleep (mean + SEM). (D–F). Hourly NREM time (mean + SEM) for the first 6 h after the second dosing with (D) D1 antagonist + Veh or +RO3397, (E) D2 antagonist + Veh or +RO3397, and (F) D1 + D2 antagonist + Veh or +RO3397. Colored symbols indicate statistical significance for that hour compared to Sal + Veh (*) or Sal + RO3397 (#) based on RM-ANOVA. (G–I). NREM Time (mean + SEM) summed in 3 h bins (ZT6-8, ZT9-11) for each treatment. *, p < 0.05; **, p < 0.01; ***, p < 0.005; ****, p < 0.001.

Figure 3

Latency to REM sleep and REM time for the first 6 h after the second dosing. For ease of visualization, data are split into three subgroups in which the results from the negative (Sal + Veh) and positive (Sal + RO3397) control treatments are repeated in each graph. (A–C). Latency to REM sleep (mean + SEM). (D–F). Hourly REM time (mean + SEM) for the first 6 h after the second dosing with (D) D1 antagonist + Veh or +RO3397, (E) D2 antagonist + Veh or +RO3397, and (F) D1 + D2 antagonist + Veh or +RO3397. Colored symbols indicate statistical significance for that hour compared to Sal + Veh (*) or Sal + RO3397 (#) based on RM-ANOVA. (G–I). REM time (mean + SEM) summed in 3 h bins (ZT6-8, ZT9-11) for each treatment. *, # p < 0.05; **, p < 0.01.

Figure 4

Subcutaneous body temperature and activity for the first 6 h after the second dosing of male C57BL/6 mice that received a dopaminergic antagonist (D1, D2, or D1+D2) i.p. at ZT5.5 followed 30 min later by either p.o. RO3397 or saline at ZT6. (A–C). Body temperature in mice treated with a D1 antagonist (A), D2 antagonist (B), or D1+D2 antagonists (C) followed by RO3397 or saline. (D–F). Activity levels in mice treated with a D1 antagonist (D), D2 antagonist (E), or D1+D2 antagonists (F) followed by RO3397 or saline. Colored symbols indicate statistical significance (p < 0.05) for that hour compared to Sal + Veh (*) or Sal + RO3397 (#) based on RM-ANOVA. *, # p < 0.05.