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The GABAergic parafacial zone is a medullary slow wave sleep-promoting center.

Anaclet C, Ferrari L, Arrigoni E, Bass CE, Saper CB, Lu J, Fuller PM - Nat. Neurosci. (2014)

Bottom Line: Work in animals and humans has suggested the existence of a slow wave sleep (SWS)-promoting/electroencephalogram (EEG)-synchronizing center in the mammalian lower brainstem.We used genetically targeted activation and optogenetically based mapping to examine the downstream circuitry engaged by SWS-promoting PZ neurons, and we found that this circuit uniquely and potently initiated SWS and EEG SWA, regardless of the time of day.PZ neurons monosynaptically innervated and released synaptic GABA onto parabrachial neurons, which in turn projected to and released synaptic glutamate onto cortically projecting neurons of the magnocellular basal forebrain; thus, there is a circuit substrate through which GABAergic PZ neurons can potently trigger SWS and modulate the cortical EEG.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Division of Sleep Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.

ABSTRACT
Work in animals and humans has suggested the existence of a slow wave sleep (SWS)-promoting/electroencephalogram (EEG)-synchronizing center in the mammalian lower brainstem. Although sleep-active GABAergic neurons in the medullary parafacial zone (PZ) are needed for normal SWS, it remains unclear whether these neurons can initiate and maintain SWS or EEG slow-wave activity (SWA) in behaving mice. We used genetically targeted activation and optogenetically based mapping to examine the downstream circuitry engaged by SWS-promoting PZ neurons, and we found that this circuit uniquely and potently initiated SWS and EEG SWA, regardless of the time of day. PZ neurons monosynaptically innervated and released synaptic GABA onto parabrachial neurons, which in turn projected to and released synaptic glutamate onto cortically projecting neurons of the magnocellular basal forebrain; thus, there is a circuit substrate through which GABAergic PZ neurons can potently trigger SWS and modulate the cortical EEG.

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Administration of CNO induces all polygraphic manifestations of slow–wave–sleep (SWS) in mice expressing the hM3Dq receptor in GABAergic PZ neuronsExample hypnogram, fast Fourier transform (FFT)–derived delta (0.5–4 Hz) power and EMG activity over 12 hrs following (a) vehicle (b) or CNO (0.3 mg/kg, IP; ZT12) administration in a mouse with bilateral hM3Dq receptor expression in PZ GABAergic neurons. Panel c shows the hypnogram, FFT–derived delta (0.5–4 Hz) power and EMG activity during 12 hr light period following panel b. The raw EEG and EMG traces following vehicle or CNO injection (arrow on the hypnogram) in 2a and b respectively provide unambiguous evidence of CNO–induced SWS/SWA in mice expressing hM3Dq in GABAergic PZ neurons. Note that, as compared to vehicle injection, CNO injection rapidly induced SWS, itself characterized by increased SWA density and amount. Color code: red = wakefulness (W), green = SWS and blue = REM sleep (RS). CNO: clozapine– N–oxide
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Figure 2: Administration of CNO induces all polygraphic manifestations of slow–wave–sleep (SWS) in mice expressing the hM3Dq receptor in GABAergic PZ neuronsExample hypnogram, fast Fourier transform (FFT)–derived delta (0.5–4 Hz) power and EMG activity over 12 hrs following (a) vehicle (b) or CNO (0.3 mg/kg, IP; ZT12) administration in a mouse with bilateral hM3Dq receptor expression in PZ GABAergic neurons. Panel c shows the hypnogram, FFT–derived delta (0.5–4 Hz) power and EMG activity during 12 hr light period following panel b. The raw EEG and EMG traces following vehicle or CNO injection (arrow on the hypnogram) in 2a and b respectively provide unambiguous evidence of CNO–induced SWS/SWA in mice expressing hM3Dq in GABAergic PZ neurons. Note that, as compared to vehicle injection, CNO injection rapidly induced SWS, itself characterized by increased SWA density and amount. Color code: red = wakefulness (W), green = SWS and blue = REM sleep (RS). CNO: clozapine– N–oxide

Mentions: Following IP vehicle injections at 7PM [lights–off], mice expressing the hM3Dq receptor in GABAergic PZ neurons displayed a typical night hypnogram with long bouts of wakefulness marked by high EMG activity and low EEG SWA (Fig. 2a). Following IP CNO injections however mice fell asleep with a short latency (Fig. 3b and Supplementary Table 2) and SWS, marked by low electromyogram (EMG) activity and high EEG SWA (Fig. 2b–c), was significantly increased during the 3 hr post–injection period as compared with vehicle (Fig. 3b and Supplementary Table 2). SWS bout length was also significantly increased during the 3 hr post–CNO injection period (Supplementary Table 2), indicating a consolidate CNO–induced SWS. More specifically, when SWS bout duration was analyzed as a function of bout length for baseline or vehicle injection conditions, the preponderance of SWS occurred in 1–10 min bouts, with no bouts exceeding 20 min. (Fig. 3e). Following administration of CNO however the preponderance of SWS occurred in bouts longer than 5 min and ca. 35% of the SWS amount occurred in bouts longer than 20 min. The SWS EEG was also enriched with SWA during the first hour of CNO–induced SWS as compared with SWS following vehicle injection (Fig. 2b, Fig. 3c and Supplementary Fig. 4). By contrast, higher frequencies such as beta and gamma were decreased. Because SWA is a widely accepted marker of SWS quality and intensity9, 15, 16 and high EEG frequencies are indicative of cortical activation and wakefulness17, our findings suggest that GABAergic PZ neurons can influence both the quantitative and qualitative aspects of SWS. SWS delta power is typically maximal during the dark period, following long, consolidated bouts of wakefulness. Interestingly, activation of PZ GABAergic neurons by CNO resulted in higher SWS delta power than the maximum observed during time–of–day equivalent spontaneous sleep in these mice. The same was true when CNO injections were performed during the light period (Fig. 4c), which is a time of high “sleep drive” in mice. Even more significantly, activation of PZ GABAergic neurons by CNO during the normal sleeping period increased SWS amount and bout lengths beyond the maximum observed during time–of–day equivalent spontaneous sleep (Fig. 4b,e and Supplementary Table 2). The consolidated SWS and elevated SWA observed after activation of PZ GABAergic neurons is similar to the sleep rebound following sleep deprivation. Furthermore, the deep SWS induced by CNO administration appeared to satisfy the homeostatic need for sleep for the remainder of the dark period (Fig. 2b). In general agreement with the behavioral and EEG findings, CNO administration produced a marked reduction in cortical c–Fos (Supplementary Fig. 5), indicative of a quiescent cellular cortex. Finally, acute and selective silencing of PZ GABAergic neurons at 10AM (a time of high sleep pressure in the mouse), which we achieved using a cre-enabled inhibitory modified muscarinic G protein-coupled receptor (DIO-hM4Di-mCherry-AAV10), strongly decreased the percentage time spent in SWS over a 2 hour post-CNO injection period as compared with vehicle injections (Supplementary Fig. 6). Hence, and in agreement with our previous findings, PZ GABAergic neurons also appear to be necessary for the initiation of normal SWS, even during times of high sleep drive.


The GABAergic parafacial zone is a medullary slow wave sleep-promoting center.

Anaclet C, Ferrari L, Arrigoni E, Bass CE, Saper CB, Lu J, Fuller PM - Nat. Neurosci. (2014)

Administration of CNO induces all polygraphic manifestations of slow–wave–sleep (SWS) in mice expressing the hM3Dq receptor in GABAergic PZ neuronsExample hypnogram, fast Fourier transform (FFT)–derived delta (0.5–4 Hz) power and EMG activity over 12 hrs following (a) vehicle (b) or CNO (0.3 mg/kg, IP; ZT12) administration in a mouse with bilateral hM3Dq receptor expression in PZ GABAergic neurons. Panel c shows the hypnogram, FFT–derived delta (0.5–4 Hz) power and EMG activity during 12 hr light period following panel b. The raw EEG and EMG traces following vehicle or CNO injection (arrow on the hypnogram) in 2a and b respectively provide unambiguous evidence of CNO–induced SWS/SWA in mice expressing hM3Dq in GABAergic PZ neurons. Note that, as compared to vehicle injection, CNO injection rapidly induced SWS, itself characterized by increased SWA density and amount. Color code: red = wakefulness (W), green = SWS and blue = REM sleep (RS). CNO: clozapine– N–oxide
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Related In: Results  -  Collection

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Figure 2: Administration of CNO induces all polygraphic manifestations of slow–wave–sleep (SWS) in mice expressing the hM3Dq receptor in GABAergic PZ neuronsExample hypnogram, fast Fourier transform (FFT)–derived delta (0.5–4 Hz) power and EMG activity over 12 hrs following (a) vehicle (b) or CNO (0.3 mg/kg, IP; ZT12) administration in a mouse with bilateral hM3Dq receptor expression in PZ GABAergic neurons. Panel c shows the hypnogram, FFT–derived delta (0.5–4 Hz) power and EMG activity during 12 hr light period following panel b. The raw EEG and EMG traces following vehicle or CNO injection (arrow on the hypnogram) in 2a and b respectively provide unambiguous evidence of CNO–induced SWS/SWA in mice expressing hM3Dq in GABAergic PZ neurons. Note that, as compared to vehicle injection, CNO injection rapidly induced SWS, itself characterized by increased SWA density and amount. Color code: red = wakefulness (W), green = SWS and blue = REM sleep (RS). CNO: clozapine– N–oxide
Mentions: Following IP vehicle injections at 7PM [lights–off], mice expressing the hM3Dq receptor in GABAergic PZ neurons displayed a typical night hypnogram with long bouts of wakefulness marked by high EMG activity and low EEG SWA (Fig. 2a). Following IP CNO injections however mice fell asleep with a short latency (Fig. 3b and Supplementary Table 2) and SWS, marked by low electromyogram (EMG) activity and high EEG SWA (Fig. 2b–c), was significantly increased during the 3 hr post–injection period as compared with vehicle (Fig. 3b and Supplementary Table 2). SWS bout length was also significantly increased during the 3 hr post–CNO injection period (Supplementary Table 2), indicating a consolidate CNO–induced SWS. More specifically, when SWS bout duration was analyzed as a function of bout length for baseline or vehicle injection conditions, the preponderance of SWS occurred in 1–10 min bouts, with no bouts exceeding 20 min. (Fig. 3e). Following administration of CNO however the preponderance of SWS occurred in bouts longer than 5 min and ca. 35% of the SWS amount occurred in bouts longer than 20 min. The SWS EEG was also enriched with SWA during the first hour of CNO–induced SWS as compared with SWS following vehicle injection (Fig. 2b, Fig. 3c and Supplementary Fig. 4). By contrast, higher frequencies such as beta and gamma were decreased. Because SWA is a widely accepted marker of SWS quality and intensity9, 15, 16 and high EEG frequencies are indicative of cortical activation and wakefulness17, our findings suggest that GABAergic PZ neurons can influence both the quantitative and qualitative aspects of SWS. SWS delta power is typically maximal during the dark period, following long, consolidated bouts of wakefulness. Interestingly, activation of PZ GABAergic neurons by CNO resulted in higher SWS delta power than the maximum observed during time–of–day equivalent spontaneous sleep in these mice. The same was true when CNO injections were performed during the light period (Fig. 4c), which is a time of high “sleep drive” in mice. Even more significantly, activation of PZ GABAergic neurons by CNO during the normal sleeping period increased SWS amount and bout lengths beyond the maximum observed during time–of–day equivalent spontaneous sleep (Fig. 4b,e and Supplementary Table 2). The consolidated SWS and elevated SWA observed after activation of PZ GABAergic neurons is similar to the sleep rebound following sleep deprivation. Furthermore, the deep SWS induced by CNO administration appeared to satisfy the homeostatic need for sleep for the remainder of the dark period (Fig. 2b). In general agreement with the behavioral and EEG findings, CNO administration produced a marked reduction in cortical c–Fos (Supplementary Fig. 5), indicative of a quiescent cellular cortex. Finally, acute and selective silencing of PZ GABAergic neurons at 10AM (a time of high sleep pressure in the mouse), which we achieved using a cre-enabled inhibitory modified muscarinic G protein-coupled receptor (DIO-hM4Di-mCherry-AAV10), strongly decreased the percentage time spent in SWS over a 2 hour post-CNO injection period as compared with vehicle injections (Supplementary Fig. 6). Hence, and in agreement with our previous findings, PZ GABAergic neurons also appear to be necessary for the initiation of normal SWS, even during times of high sleep drive.

Bottom Line: Work in animals and humans has suggested the existence of a slow wave sleep (SWS)-promoting/electroencephalogram (EEG)-synchronizing center in the mammalian lower brainstem.We used genetically targeted activation and optogenetically based mapping to examine the downstream circuitry engaged by SWS-promoting PZ neurons, and we found that this circuit uniquely and potently initiated SWS and EEG SWA, regardless of the time of day.PZ neurons monosynaptically innervated and released synaptic GABA onto parabrachial neurons, which in turn projected to and released synaptic glutamate onto cortically projecting neurons of the magnocellular basal forebrain; thus, there is a circuit substrate through which GABAergic PZ neurons can potently trigger SWS and modulate the cortical EEG.

View Article: PubMed Central - PubMed

Affiliation: Department of Neurology, Division of Sleep Medicine, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.

ABSTRACT
Work in animals and humans has suggested the existence of a slow wave sleep (SWS)-promoting/electroencephalogram (EEG)-synchronizing center in the mammalian lower brainstem. Although sleep-active GABAergic neurons in the medullary parafacial zone (PZ) are needed for normal SWS, it remains unclear whether these neurons can initiate and maintain SWS or EEG slow-wave activity (SWA) in behaving mice. We used genetically targeted activation and optogenetically based mapping to examine the downstream circuitry engaged by SWS-promoting PZ neurons, and we found that this circuit uniquely and potently initiated SWS and EEG SWA, regardless of the time of day. PZ neurons monosynaptically innervated and released synaptic GABA onto parabrachial neurons, which in turn projected to and released synaptic glutamate onto cortically projecting neurons of the magnocellular basal forebrain; thus, there is a circuit substrate through which GABAergic PZ neurons can potently trigger SWS and modulate the cortical EEG.

Show MeSH
Related in: MedlinePlus