Two Distinct Serotonin Receptors Co-mediate Non-photic Signals to the Circadian Clock

Chronobiologic parameter changes in patients with major depressive disorder and sleep disturbance treated with adjunctive brexpiprazole: An open-label, flexible-dose, exploratory substudy

BACKGROUND

Circadian rhythm disturbances have been reported in patients with major depressive disorder (MDD). Among these is an increased phase angle between peak cortisol concentration and dim-light melatonin onset (DLMO). The aim of this study was to evaluate changes in chronobiologic parameters of sleep in patients with MDD receiving adjunctive brexpiprazole.

METHODS

This was an interventional, multicenter, open-label, flexible-dose, exploratory study in patients with MDD and inadequate response to antidepressant treatment who were experiencing sleep disturbances. Patients received adjunctive brexpiprazole 2-3 mg/day for 8 weeks. Outcome measures included cortisol and melatonin levels, used to calculate phase angle, and the Biological Rhythms Interview of Assessment in Neuropsychiatry (BRIAN).

RESULTS

The mean (standard error) phase angle between peak cortisol and DLMO increased by 108 (61) minutes from baseline to Week 8 (n = 9). BRIAN Total score changed (improved) by -14.6 (4.6) points from baseline to Week 8 (n = 9). Change in phase angle and BRIAN Total score showed a moderate-to-high correlation (Pearson coefficient: 0.68; 95% confidence limits: 0.04, 0.93; p = 0.040).

LIMITATIONS

This study is limited by its small sample size, and its single-arm, open-label design.

CONCLUSIONS

The findings provide a preliminary indication that the phase angle between peak cortisol and DLMO is of interest as a potential biomarker for depression and therapeutic response. Adjunctive brexpiprazole may represent a strategy for correcting circadian dysfunction in patients with MDD and inadequate response to antidepressant treatment. ClinicalTrials.gov identifier: NCT01942733.

Disruption of running activity rhythm following restricted feeding in female mice: Preventive effects of antidepressants

Biological rhythms are critical in the etiology of mood disorders; therefore, effective mood disorder treatments should address rhythm disturbances. Among the variables synchronized with the light-dark cycle, spontaneous activity in rodents is useful for investigating circadian rhythms. However, previous studies have focused only on the increase of wheel-running activity under restricted feeding conditions, while little information is available on circadian rhythm of running activity. In this study, chronometrical analysis was used to assess whether circadian rhythms during wheel-running are altered by restricted feeding and affected by antidepressant drugs. Wheel revolutions were automatically recorded and analyzed using cosinor-rhythmometry in 8-week old ICR albino mice. When feeding was restricted to 1 h per day (21:00-22:00), wheel-running rhythms were reliably disrupted. Female mice exhibited marked alterations in the pattern and extent of wheel-running beginning on day 1. Subchronic treatment with imipramine or paroxetine, as well as tandospirone and (-)-DOI, prevented wheel-running rhythm disruption. Thus, altering the circadian activity rhythms of female mice on a 1-h feeding schedule may be useful for investigating disturbances in biological rhythms.

Selective pharmacological blockade of the 5-HT7 receptor attenuates light and 8-OH-DPAT induced phase shifts of mouse circadian wheel running activity

Recent reports have illustrated a reciprocal relationship between circadian rhythm disruption and mood disorders. The 5-HT7 receptor may provide a crucial link between the two sides of this equation since the receptor plays a critical role in sleep, depression, and circadian rhythm regulation. To further define the role of the 5-HT7 receptor as a potential pharmacotherapy to correct circadian rhythm disruptions, the current study utilized the selective 5-HT7 antagonist JNJ-18038683 (10 mg/kg) in three different circadian paradigms. While JNJ-18038683 was ineffective at phase shifting the onset of wheel running activity in mice when administered at different circadian time (CT) points across the circadian cycle, pretreatment with JNJ-18038683 blocked non-photic phase advance (CT6) induced by the 5-HT1A/7 receptor agonist 8-OH-DPAT (3 mg/kg). Since light induced phase shifts in mammals are partially mediated via the modulation of the serotonergic system, we determined if JNJ-18038683 altered phase shifts induced by a light pulse at times known to phase delay (CT15) or advance (CT22) wheel running activity in free running mice. Light exposure resulted in a robust shift in the onset of activity in vehicle treated animals at both times tested. Administration of JNJ-18038683 significantly attenuated the light induced phase delay and completely blocked the phase advance. The current study demonstrates that pharmacological blockade of the 5-HT7 receptor by JNJ-18038683 blunts both non-photic and photic phase shifts of circadian wheel running activity in mice. These findings highlight the importance of the 5-HT7 receptor in modulating circadian rhythms. Due to the opposite modulating effects of light resetting between diurnal and nocturnal species, pharmacotherapy targeting the 5-HT7 receptor in conjunction with bright light therapy may prove therapeutically beneficial by correcting the desynchronization of internal rhythms observed in depressed individuals.

Serotonin 2C receptor as a superhero: diversities and talents in the RNA universe for editing, variant, small RNA and other expected functional RNAs

The serotonin 2C receptor subtype (5-HT2C) has a unique profession and continues to provide exciting and critical new information. The 5-HT2C is modulated at the RNA level by several mechanisms, including editing, short variant generation, and small RNAs. Recently, these phenomena, which had been demonstrated individually, were shown to be associated with each other. At present, many reports provide information about the influence of RNA regulation on receptor protein activities and expression, which was thought to be the final functional product. However, complicated behavior at the RNA stage allows us to imagine that the RNA itself has functional roles in the RNA universe. The 5-HT2C RNA may play several roles. This review will outline previous 5-HT2C studies and prospects for future studies.