PDF Cells Are a GABA-Responsive Wake-Promoting Component of the Drosophila Sleep Circuit

Self Cite

277

278

The neural circuits that regulate sleep and arousal as well as their integration with circadian circuits remain unclear, especially in Drosophila. This issue intersects with that of photoreception, because light is both an arousal signal in diurnal animals and an entraining signal for the circadian clock. To identify neurons and circuits relevant to light-mediated arousal as well as circadian phase-shifting, we developed genetic techniques that link behavior to single cell-type resolution within the Drosophila central brain. We focused on the unknown function of the 10 PDFcontaining large ventral lateral neurons (l-LNvs) of the Drosophila circadian brain network and show here that these cells function in light-dependent arousal. They also are important for phase shifting in the late-night (dawn), indicating that the circadian photoresponse is a network property and therefore non-cell-autonomous. The data further indicate that the circuits underlying light-induced arousal and circadian photoentrainment intersect at the l-LNvs and then segregate.L ight promotes arousal in diurnal species. Drosophila arousalsleep circuits remain largely uncharacterized. Exceptions are the mushroom body with a role in sleep-arousal (1, 2) as well as neurons of the pars intercerebralis (PI) and the ellipsoid body (EB) of the central complex (CC) with roles in locomotion (3, 4). Importantly, there is no indication of how the poorly understood fly sleep-movement circuits are coordinated or communicate with the well-studied brain circadian network, or whether these Ϸ150 circadian neurons impact directly on sleep or arousal.

Section: Discussionsupporting

confidence: 88%

Section: L-lnvs Are a Major Subset Of Peptidergic Arousal Circuits Inmentioning

confidence: 92%

Light-arousal and circadian photoreception circuits intersect at the large PDF cells of the Drosophila brain

Shang

Griffith

Rosbash

2008

Self Cite

277

278

“…Subsequent work on the LNv indicates that these neurons also mediate light-driven arousal behavior (9)(10)(11). The CRY-dependent rapid electrophysiological response to blue light recorded in the LNv suggests that the loss of CRY attenuates acute behavioral arousal responses to blue light, but not to wavelengths beyond its absorbance cutoff above 530 nm (1).…”

Section: Resultsmentioning

confidence: 99%

“…CRY is expressed in a small subset of central brain circadian, arousal, and photoreceptor neurons in D. melanogaster and other insects, including the large lateral ventral neuron (LNv; l-LNv) subset (1,2,7,8). The l-LNvs are light-activated arousal neurons (1,2,(9)(10)(11), whereas the small lateral ventral neurons (s-LNvs) are critical for circadian function (5,12). Previous results suggest that light activated arousal is likely attenuated in cry-null mutants.…”

mentioning

confidence: 99%

CRYPTOCHROME-mediated phototransduction by modulation of the potassium ion channel β-subunit redox sensor

Fogle

Baik

Houl

et al. 2015

121

Blue light activation of the photoreceptor CRYPTOCHROME (CRY) evokes rapid depolarization and increased action potential firing in a subset of circadian and arousal neurons in Drosophila melanogaster. Here we show that acute arousal behavioral responses to blue light significantly differ in mutants lacking CRY, as well as mutants with disrupted opsin-based phototransduction. Lightactivated CRY couples to membrane depolarization via a well conserved redox sensor of the voltage-gated potassium (K + ) channel β-subunit (Kvβ) Hyperkinetic (Hk). The neuronal light response is almost completely absent in hk −/− mutants, but is functionally rescued by genetically targeted neuronal expression of WT Hk, but not by Hk point mutations that disable Hk redox sensor function. Multiple K + channel α-subunits that coassemble with Hk, including Shaker, Ether-a-go-go, and Ether-a-go-go-related gene, are ion conducting channels for CRY/Hk-coupled light response. Light activation of CRY is transduced to membrane depolarization, increased firing rate, and acute behavioral responses by the Kvβ subunit redox sensor.phototransduction | potassium channel | redox | cryptochrome

“…Also, suppressing GABA activity reduces sleep time in flies, and mutations in the GABA A receptor confer resistance to GABA antagonists that promote wakefulness (51). As for dopamine and octopamine, the sleep-promoting effect of GABA A receptors is mediated outside the MBs by the pigment-dispersing factor neurons (52). However, GABAergic inputs through the anterior paired lateral neurons modulate the odor-specific activation pattern in the MBs (53).…”

Section: Discussionmentioning

confidence: 99%

Sleep- and wake-dependent changes in neuronal activity and reactivity demonstrated in fly neurons using in vivo calcium imaging

Bushey

Tononi

Cirelli

2015

Sleep in Drosophila shares many features with mammalian sleep, but it remains unknown whether spontaneous and evoked activity of individual neurons change with the sleep/wake cycle in flies as they do in mammals. Here we used calcium imaging to assess how the Kenyon cells in the fly mushroom bodies change their activity and reactivity to stimuli during sleep, wake, and after short or long sleep deprivation. As before, sleep was defined as a period of immobility of >5 min associated with a reduced behavioral response to a stimulus. We found that calcium levels in Kenyon cells decline when flies fall asleep and increase when they wake up. Moreover, calcium transients in response to two different stimuli are larger in awake flies than in sleeping flies. The activity of Kenyon cells is also affected by sleep/wake history: in awake flies, more cells are spontaneously active and responding to stimuli if the last several hours (5-8 h) before imaging were spent awake rather than asleep. By contrast, long wake (≥29 h) reduces both baseline and evoked neural activity and decreases the ability of neurons to respond consistently to the same repeated stimulus. The latter finding may underlie some of the negative effects of sleep deprivation on cognitive performance and is consistent with the occurrence of local sleep during wake as described in behaving rats. Thus, calcium imaging uncovers new similarities between fly and mammalian sleep: fly neurons are more active and reactive in wake than in sleep, and their activity tracks sleep/wake history.T he fundamental features that characterize mammalian sleep also define Drosophila melanogaster sleep (1-3). Most crucially, in both flies and mammals, sleep is distinguished from simple rest (quiet wake) by an increased arousal threshold, i.e., a reduced ability to respond to external stimuli. Moreover, in flies and mammals sleep is controlled homeostatically by the duration as well by the intensity of prior wake, suggesting basic similarities in the mechanisms of sleep regulation across species. Thus, in flies both sleep deprivation and a rich learning experience lead to a sleep rebound characterized by overall increased sleep time, increased arousal threshold, and longer sleep episodes (4-6). As in mammals, overall neuronal activity in flies is also high during wake and low during sleep (6-8). Specifically, a seminal study using local field potential (LFP) recordings from the Drosophila medial protocerebrum found high spike-like potentials that disappeared after the block of synaptic transmission in the mushroom bodies (MBs) (7). This high spike activity was present when flies were moving or had been quiescent for only a few seconds, but disappeared with sleep (i.e., after periods of immobility >5 min), when the overall LFP power in all frequencies also decreased by ∼60% (7). The study concluded that neural activity in the sleeping fly brain, or at least in a central region spanning the MBs, resembles that seen in mammals in several brainstem cell groups including noradrenergic ne...