Another obstacle in examinations of the role of 5-HT signaling on sleep is its fundamental role in circadian timing, click here particularly on the entrainment of circadian rhythms by light (Ehlen et al., 2001). The mammalian circadian timing system is a primary sleep regulator and observations of 5-HT sleep regulatory properties have rarely ruled out the involvement of the central circadian pacemaker. Nakamaru-Ogiso and colleagues report that TSOI treatment temporarily eliminates the sleep–wake rhythm in rats by reducing total sleep amount during the rest phase and increasing it during the active phase. Consequently, it has no cumulative effect
on 24-h total sleep amount. TSOI injection also increased sleep/wake fragmentation, which is commonly reported in manipulations that disrupt central circadian timing. This observation suggests that the disruption of the sleep/wake rhythm is a secondary effect
of TSOI treatment on the central circadian pacemaker. However, the authors also report that the pacemaker-driven brain temperature rhythm remains intact, providing evidence that TSOI is acting downstream of the central circadian pacemaker. These findings are consistent with an earlier study by Kawai et al. (1994) who reported that tryptophan depletion disrupts the circadian wheel-running rhythm in rats. Taken together, these studies suggest that 5-HT may play an important role in coupling the Methamphetamine central circadian selleck chemicals pacemaker to behavioral rhythms. This report fills an important gap in our understanding of the regulatory role of 5-HT on sleep, but several important questions remain. For instance, total elimination of brain 5-HT by neurotoxins and TPH2 knockout leaves sleep and behavioral rhythms intact (Morin & Blanchard, 1991; Alenina et al., 2009). The rapid reduction of 5-HT by TSOI may preclude compensatory mechanisms
potentially present in non-reversible models of 5-HT depletion. The presence of sleep/wake rhythms in these non-reversible models is nonetheless paradoxical. Future studies investigating the potential role of the indoleamine melatonin, which also has sleep regulatory properties and is also tryptophan-dependent, may help to clarify these inconsistencies. “
“Postpartum depression (PPD) is a common complication following childbirth experienced by one in every five new mothers. Pregnancy stress enhances vulnerability to PPD and has also been shown to increase depressive-like behavior in postpartum rats. Thus, gestational stress may be an important translational risk factor that can be used to investigate the neurobiological mechanisms underlying PPD.