Buprenorphine was Antinociceptive
depicts % MPE for paw withdrawal latency as a function of time after intravenous administration of saline and buprenorphine. ANOVA revealed that buprenorphine caused significant (P = 0.0072) antinociception. Bonferroni post-hoc comparisons indicated that buprenorphine significantly (P < 0.05) increased % MPE at 20, 30, 60, and 120 min after injection. This antinociceptive dose of buprenorphine was used for subsequent studies of sleep and wakefulness.
Figure 1 Buprenorphine increased latency of paw withdrawal (PWL) away from a thermal stimulus. Ordinate shows PWL expressed as percent maximum possible effect (% MPE). Abscissa shows time-course of % MPE relative to injection at time zero. Asterisks (*) indicate (more ...)
Buprenorphine Altered the Temporal Organization of Sleep and Wakefulness
illustrates the temporal distribution of wakefulness, NREM sleep, and REM sleep for 24 h following intravenous administration of saline (control) and buprenorphine. summarizes group data for the light phase (1st 12 h after injection) showing buprenorphine-induced changes in the temporal organization of sleep and wakefulness. ANOVA indicated a significant (P < 0.01) effect of buprenorphine on percent of time spent in states of wakefulness, NREM sleep, and REM sleep, as well as a significant (P < 0.0001) drug-by-state interaction (). Paired t-tests with Bonferonni correction showed that buprenorphine significantly (P < 0.05) increased the percent of time spent in waking (25.2%) and significantly decreased the amount of time spent in NREM sleep (−22.1%) and REM sleep (−3.1%). Buprenorphine significantly delayed the onset of NREM sleep and REM sleep ().
Figure 2 Representative 24-h plots from one rat illustrating the buprenorphine-induced disruption of sleep architecture. Ordinate plots the temporal distribution of wakefulness (wake), nonrapid eye movement sleep (NREM), and rapid eye movement sleep (REM) for (more ...)
Figure 3 Buprenorphine altered the temporal organization of sleep and wakefulness and eszopiclone countered buprenorphine-induced sleep disruption. The left column summarizes the effect of buprenorphine relative to saline (control) on five dependent measures averaged (more ...)
There was a significant (P < 0.0001) drug main-effect and state-by-drug interaction (p < 0.0001) for the number of sleep/wake episodes (). Buprenorphine decreased the number of episodes of wakefulness (−88.2%), NREM sleep (−89.5%), and REM sleep (−90.8%). shows that buprenorphine significantly (P < 0.0001) altered the duration of sleep/wake episodes. Average duration of wakefulness was significantly increased (529.6%) and the duration of sleep epochs was decreased for both NREM sleep (−30.8%) and REM sleep (−87.5%). shows that buprenorphine also significantly (P < 0.0001) decreased the number of transitions (−89.8%) between states.
plots the percent state for each drug condition during the 12-h dark phase (rat subjective day) of the light/dark cycle that followed the 12-h light phase depicted by . Within the dark phase, when rats are normally awake and active, the time spent awake was significantly (P = 0.012) decreased by buprenorphine. The buprenorphine condition within the dark phase revealed significantly (P = 0.0019) more NREM sleep and a nonsignificant decrease in REM sleep compared to the saline condition.
Figure 4 The percent of time during the 12-h dark phase that rats (n = 7) spent in states of wakefulness (Wake), nonrapid eye movement sleep (NREM), and rapid eye movement sleep (REM). These recordings were obtained during hours 12 through 24 after administration (more ...)
The effect of buprenorphine on states of sleep and wakefulness can also be visualized by comparing the light phase () and dark phase () results. NREM sleep after buprenorphine increased significantly (P = 0.0003) from an average of 5.5% in the light phase () to 27.4% in the dark phase (). There was also a significant (P = 0.003) rebound increase in REM sleep from an average of 0.33% after buprenorphine during the light phase () to about 4% after buprenorphine during the dark phase ().
Eszopiclone Decreased the Sleep Disruption Caused by Buprenorphine
The five illustrations in the right column of summarize the results of experiments designed to determine whether the sedative/hypnotic eszopiclone countered the buprenorphine-induced inhibition of sleep. Eszopiclone when coadministered with buprenorphine prevented the significant increase in wakefulness () caused by buprenorphine alone (). Similarly, the significant buprenorphine-induced decrease in NREM sleep and REM sleep () was prevented by coadministration of eszopiclone (). Eszopiclone blocked the significant increase in latency to sleep onset (). Eszopiclone partially reversed the buprenorphine-induced decrease in both the number of wakefulness and NREM sleep episodes (). The 530% increase in average duration of waking episodes caused by buprenorphine () was reduced to a 171% increase by coadministration of eszopiclone (). Eszopiclone blocked the significant decrease in number of state transitions caused by buprenorphine ().
Buprenorphine Increased Electroencephalogram Delta Power during NREM Sleep
illustrate electroencephalogram power recorded across states of sleep and wakefulness after intravenous administration of buprenorphine to awake, freely moving rats. Buprenorphine did not alter electroencephalogram power during wakefulness or REM sleep (), but did increase electroencephalogram power in the delta frequency range during NREM sleep (). ANOVA revealed a significant (P = 0.007) buprenorphine main-effect on electroencephalogram frequency bands ranging from 0.5 to 5.0 Hz in 0.5 Hz increments (). The fast Fourier transform analyses were conducted for electroencephalogram measures obtained during the 12-h light period (i.e., rat's subjective night) that immediately followed buprenorphine administration. As and show, buprenorphine depressed NREM sleep for 6 to 8 h. Measurement of the increase in electroencephalogram delta power was conducted for up to 12-h after buprenorphine administration. A future study will be needed to determine whether, and for how long beyond 12-h, electroencephalogram delta power is increased by buprenorphine.
Figure 5 Electroencephalographic power (ordinate) plotted as a function of frequency (abscissa) averaged for 5 rats across states of sleep and wakefulness. During wakefulness (A) and rapid eye movement (REM) sleep (C) buprenorphine did not change electroencephalographic (more ...)
Buprenorphine Decreased Adenosine Levels in PnO and SI
Histological analyses confirmed that all microdialysis sites were localized to the PnO or to the SI (). shows the results of one representative experiment. Adenosine levels in the SI are plotted as a function of time during dialysis with Ringer's (121-180 min after probe placement) followed by dialysis delivery of buprenorphine (181-240 min after probe placement). confirm chromatographic identification of adenosine illustrates chromatograms produced by five known concentrations of adenosine. shows chromatograms reflecting brain adenosine (dialyzed Ringer's), a negative control (nondialyzed Ringer's), a positive control (brain adenosine sampled during dialysis delivery of the adenosine deaminase inhibitor EHNA), and an adenosine standard.
Figure 6 Microdialysis delivery of buprenorphine decreased adenosine levels in the basal forebrain and pontine reticular formation. Cresyl-violet stained coronal sections show representative dialysis sites in (A) the pontine reticular formation, oral part (PnO) (more ...)
summarizes a final set of experiments that quantified adenosine levels in SI and PnO as a function of route of buprenorphine administration. Microdialysis delivery of buprenorphine significantly (P = 0.03) decreased adenosine levels in PnO (−14.8%) and significantly (P = 0.0004) decreased adenosine levels in the SI region of the basal forebrain (−36.7%). plots adenosine levels in the SI before and after intravenous administration of buprenorphine to isoflurane-anesthetized rat. Buprenorphine significantly (P < 0.0001) decreased (−20.3%) adenosine levels in the SI.
Figure 7 Central and systemic delivery of buprenorphine decreased brain adenosine levels. (A) Microdialysis delivery of buprenorphine to the pontine reticular formation, oral part (PnO) (n=5 rats) or to the substantia innominata (SI) (n=5 rats) decreased adenosine (more ...)