The Role And Mechanism Of Neuropeptide S And Cognate Receptor System In Anti-anxiety Behavior And Sleep

Disturbed sleep is a common subjective complaint among individuals with anxiety disorders,and insomnia is the most commonly reported sleep disturbance.Sleep deprivation increases general and specific anxiety symptoms among healthy individuals,meanwhile most of people suffering from anxiety disorders are also sleep deprived.Anxiety and sleep are related to each other in a bidirectional way,generally,sleep disorder and anxiety disorder are comorbid condition.Neuropeptide S(NPS)and NPS receptors(NPSR)are proposed as a novel endogenous arousal and anxiolytic system.A higher level of NPSR m RNA in the amygdala,which is well-known to play a key role in control of anxiety and mood-induced sleep,has been found in previous studies,suggesting that NPS-NPSR system should be involved in the amygdaloid regulation of anxiety-like behavior and sleep.The purpose of the present study is to reveal the role and mechanism of NPS-NPSR system in anti-anxiety behavior and sleep.The first part of the present study,paradoxical sleep deprivation(PSD)(also known as rapid eye movement(REM)sleep deprivation,REMSD)was conducted with modified multiple platform method(MMPM)in rats for 24 h(8:00-8:00 h).The behavioral tests of open field test(OFT)and light-dark box(LDB),and the polysomnographic recording(8:00-8:00 h)including electroencephalogram(EEG)and electromyogram(EMG)for cortical EEG power spectrum and sleep-wake states analysis were employed to evaluate,respectively,the anxiety-like behavior and sleep-wake cycle pattern following 24-h PSD,and the effect of central action of NPS on PSD-induced anxiety-like behavior and sleep.Real-time quantitative polymerase chain reaction(RT-qPCR)was used for detecting PSD-induced NPSR mRNA expression in the amygdala.Furthermore,immunohistochemistry of c-Fos and dual-immunofluorescence of c-Fos and NPSR were respectively performed to reveal the activated neurons induced by NPS and these neurons bearing NPSR in the amygdala.The second part study,according to the result of first part,[D-Val5] NPS,a selective NPSR antagonist,was administered into the bilateral basolateral amygdala(BLA).The behavioral tests including elevated plus maze(EPM),OFT and LDB,and the polysomnographic recording were employed to evaluate whether inactivation of the BLA by NPSR antagonist induced anxiety-like behavior and sleep,and local NPS action attenuated NPSR antagonist-induced anxiety-like behavior and sleep.Results: 24-h PSD in rats induced anxiety-like behavior,which was characterized by diminishing the time spent in central area,decreasing the rearing number and increasing the time spent in grooming in OFT;and decreasing the time spent in light box and transition number in LDB.The 24-h sleep-wake pattern in PSD rats had a long latency of SWS and a subsequent PS rebound accompanied with an increase in EEG theta(4.5-8.5 Hz)activities across light and dark phase.The increase in PS time was due to increase in episode number instead of mean duration.Central action of NPS(1 nmol)counteracted PSD-induced anxiety-like behavior,and altered PSD-induced sleep-wake pattern through increasing wakefulness,and suppressing PS and EEG theta activities.PSD significantly enhanced NPSR mRNA expression level in the amygdala.NPS remarkably increased the number of Fos immunoreactive(-ir)neurons in the BLA,the central amygdala(CeA)and medial amygdala(MeA).Dual-immunofluorescence for Fos and NPSR showed that the percentage of Fos-ir neurons bearing NPSR was 77.9 % in the BLA,65.1% in the CeA and 64.8% in the MeA,respectively.Microinjection of [D-Val5] NPS(10 nmol/side)into the bilateral BLA caused anxiety-like behavior,which displayed a decrease in the time spent in the open arms and the entries into the open arms in EPM;and in the time spent in central area and rearing number and an increase in the time spent in grooming in OFT;a decrease in the time spent in light box and transition number in LDB.[D-Val5] NPS administration of the bilateral BLA increased SWS time with a short sleep latency and decreased W time in the first hour without alteration of PS.However,the PS episode number was significantly increased and PS mean duration was decreased.Co-injection of NPS(0.25 nmol/side)and [D-Val5] NPS(10 nmol/side)into the bilateral BLA attenuated [D-Val5] NPS-induced anxiety-like behavior and sleep.The amount of SWS and W was returned to control level.Conclusion: PSD-induced anxiety-like behavior and sleep are closely related to the upregulation of NPSR mRNA level in the amygdala.NPS counteracts PSD-induced anxiety-like behavior and sleep-wake pattern through activating the neurons bearing NPSR in the amygdala.The evidence that inactivation of the BLA by NPSR antagonist causes anxiety-like behavior and sleep alteration,suggests that the BLA is a key center of NPS-NPSR system for regulating anxiety-like behavior and sleep.