Sleep-related epilepsy in a Long-Evans hooded rat model of depression

7,8-Dihydroxyflavone reduces sleep during dark phase and suppresses orexin A but not orexin B in mice

Brain-derived neurotrophic factor (BDNF) binds to Tropomyosin-receptor-kinase B (TrkB) receptors that regulate synaptic strength and plasticity in the mammalian nervous system. 7,8-Dihydroxyflavone (DHF) is a recently identified small molecule Trk B agonist that has been reported to ameliorate depression, attenuate the fear response, improve memory consolidation, and exert neuroprotective effects. Poor and disturbed sleep remains a symptom of major depressive disorder and most current antidepressants affect sleep. Therefore, we conducted sleep/wake recordings and concomitant measurement of brain orexins, endogenous peptides that suppress sleep, in mice for this study. Baseline polysomnograph recording was performed for 24 h followed by treatment with either 5 mg/kg of DHF or vehicle at the beginning of the dark phase. Animals were sacrificed the following day, one hour after the final treatment with DHF. Orexin A and B were quantified using ELISA and radioimmunoassay, respectively. Total sleep was significantly decreased in the DHF group, 4 h after drug administration in the dark phase, when compared with vehicle-treated animals. This difference was due to a significant decrease of non-rapid eye movement sleep, but not rapid eye movement sleep. DHF increased power of alpha and sigma bands but suppressed power of gamma band during sleep in dark phase. Interestingly, hypothalamic levels of orexin A were also significantly decreased in the DHF group (97 pg/mg) when compared with the vehicle-treated group (132 pg/mg). However, no significant differences of orexin B were observed between groups. Additionally, no change was found in immobility tests.

Chronic escitalopram treatment attenuated the accelerated rapid eye movement sleep transitions after selective rapid eye movement sleep deprivation: a model-based analysis using Markov chains

Background

Shortened rapid eye movement (REM) sleep latency and increased REM sleep amount are presumed biological markers of depression. These sleep alterations are also observable in several animal models of depression as well as during the rebound sleep after selective REM sleep deprivation (RD). Furthermore, REM sleep fragmentation is typically associated with stress procedures and anxiety. The selective serotonin reuptake inhibitor (SSRI) antidepressants reduce REM sleep time and increase REM latency after acute dosing in normal condition and even during REM rebound following RD. However, their therapeutic outcome evolves only after weeks of treatment, and the effects of chronic treatment in REM-deprived animals have not been studied yet.

Results

Chronic escitalopram- (10 mg/kg/day, osmotic minipump for 24 days) or vehicle-treated rats were subjected to a 3-day-long RD on day 21 using the flower pot procedure or kept in home cage. On day 24, fronto-parietal electroencephalogram, electromyogram and motility were recorded in the first 2 h of the passive phase. The observed sleep patterns were characterized applying standard sleep metrics, by modelling the transitions between sleep phases using Markov chains and by spectral analysis.

Based on Markov chain analysis, chronic escitalopram treatment attenuated the REM sleep fragmentation [accelerated transition rates between REM and non-REM (NREM) stages, decreased REM sleep residence time between two transitions] during the rebound sleep. Additionally, the antidepressant avoided the frequent awakenings during the first 30 min of recovery period. The spectral analysis showed that the SSRI prevented the RD-caused elevation in theta (5–9 Hz) power during slow-wave sleep. Conversely, based on the aggregate sleep metrics, escitalopram had only moderate effects and it did not significantly attenuate the REM rebound after RD.

Conclusion

In conclusion, chronic SSRI treatment is capable of reducing several effects on sleep which might be the consequence of the sub-chronic stress caused by the flower pot method. These data might support the antidepressant activity of SSRIs, and may allude that investigating the rebound period following the flower pot protocol could be useful to detect antidepressant drug response. Markov analysis is a suitable method to study the sleep pattern.