The Molecular Mechanism Of Olfactory Bulb Regulation Of Rapid Eye Movement Sleep

Working pressure, mental stress and, anxiety lead to sleep disorders, of which depression-caused sleep disorder is the majority. More than80%depressive patients suffer from sleep disorders, whose symptoms like rapid eye movement (REM) sleep disorder, with difficulties in falling into sleep, waking up early, less deep sleep, and hypersomnia during daytime. Olfactory dysfunction with increased olfactory threshold, impaired odour discrimination and decreased odour identification, is very common in patients with REM sleep behavior disorder (RBD). And the relationship between depression and sleep is still controversial. In1977, Cairncross et. al found that rats with olfactory bulbectomy (OBX) showed depressive-related behavior. Since then OBX becomes a model for antidepressant drug evaluation. Olfactory bulb plays a key role in olfactory sensation regulation, also involves in regulation of foraging, adapting to environment and other sensory function. Studies have shown that the olfactory bulb can also be involved in regulating biological rhythm. Thus, we assume that olfactory bulb may play an important role in sleep-wake regulation, especially REM sleep regulation.The first part of this study is aimed to clarify the effect of OBX in sleep-wake behavior and distinguish the causality of depression and REM sleep abnormality. It showed that OBX increased REM sleep significantly in rats, especially between15:00and18:00during the light period. Acute application of fluoxetine (10mg/kg, i.p.) a serotonin transporter inhibitor, immediately abolished the OBX-induced increase in REM sleep, but depressive behavior remained unchanged. These results indicate that there is no causality between REM sleep abnormalities and depressive behaviors in rats, and the increase in REM sleep may be mediated by olfactory bulb directly.Our group reported that adenosine A2A receptors (A2AR) are key receptors involved in regulation of sleep-wake cycles. The A2AR has been reported to be expressed in the OB, but the role of this receptor in the OB is unknown. Herein, we used microinjections of A2AR-specific agonists and antagonists into the OB and focal RNA interference to silence the expression of A2ARs in the OB by local infection with adeno-associated virus (AAV) carrying short-hairpin RNA for the A2AR (AAV-shA2AR) to clarify the role of A2ARs in REM sleep regulation in the OB. Furthermore, we used the conditipnal expression of humanized Renilla green fluorescent protein (hrGFP) for neuronal tract tracing to identify efferent pathways of A2AR-containing neurons in the OB. In this approach, the expression of hrGFP is transcriptionally silenced by a neo cassette flanked by loxH/loxP sites (AVV-lox-Stop-hrGFP) in wild-type mice, but hrGFP is activated in neurons of mice, which express Cre recombinase under the A2AR promoter (A2AR-cre mice).The second part showed that bilateral injections of CGS21680, an A2AR agonist, into the rat OB decreased REM sleep, but did not alter non-REM sleep, whereas microinjection of SCH58261, an A2AR antagonist, into the OB increased REM sleep. Similar to the A2AR antagonist, selective A2AR knockdown by AAV-shA2AR in the rat OB promoted REM sleep. When the AAV-lox-Stop-hrGFP vector was microinjected into the OB of A2AR-cre mice, terminals of axonal projections of A2AR-positive OB neurons were found in the amygdale. These findings indicated that A2ARs in the OB regulate REM sleep in rodents.