Microinjection of morphine in rat rostromedial tegmental nucleus (RMTg) decreased non-rapid eye movement (NREM) sleep in a dose-dependent manner.

<p>(A) Nissl staining showed the implantation sites of the guide cannulas. (B, C) Morphine inhibited RMTg neurons in vitro. A typical trace showed that morphine induced hyperpolarization and inhibited spontaneous firing of a neuron in the RMTg (B) and changes of membrane potentials of RMTg neurons under whole-cell current-clamp with application of morphine. <i>n</i> = 4 cells, *<i>p</i> < 0.05 versus baseline using 1-way ANOVA followed by least significant difference (LSD) (C). (D) Time course of NREM and REM sleep and wakefulness during the light period (07:00–19:00 hours) in rats treated with artificial cerebrospinal fluid (ACSF) or morphine at 09:00 hour. (E) Sleep–wake quantities following ACSF or morphine microinjection in rats during post-injection period (10:00–13:00 hours). *<i>p</i> < 0.05, **<i>p</i> < 0.01 versus ACSF and #<i>p</i> < 0.05 versus 0.5 nmol/side morphine using 1-way ANOVA followed by LSD. (F–K) During the post-injection period (10:00–13:00 hours) after ACSF or morphine microinjection in rats, episode numbers of each stage (F); number of NREM (G) and REM (H) sleep bouts with different duration; mean duration of each stage (I); stage transitions between S (NREM sleep), W (wakefulness), and R (REM sleep) stages (J); and slow-wave activity (SWA) of NREM sleep (K). *<i>p</i> < 0.05, **<i>p</i> < 0.01 versus ACSF using unpaired <i>t</i> tests. MI, microinjection; Mor, morphine. ACSF (<i>n</i> = 6); morphine 0.5 nmol/side (<i>n</i> = 5); morphine 2 nmol/side (<i>n</i> = 5). The horizontal open bars on the <i>x</i>-axes indicate the 12-hour light period. Underlying data can be found in <a href="http://www.plosbiology.org/article/info:doi/10.1371/journal.pbio.2002909#pbio.2002909.s001" target="_blank">S1 Data</a>.</p>