The GABAA Receptor RDL Acts in Peptidergic PDF Neurons to Promote Sleep in Drosophila

Abstract

SUMMARY Sleep is regulated by a circadian clock that largely times sleep and wake to occur at specific times of day and a sleep homeostat that drives sleep as a function of duration of prior wakefulness[1]. To better understand the role of the circadian clock in sleep regulation, we have been using the fruit fly Drosophila melanogaster[2]. Fruit flies display all of the core behavioral features of sleep including relative immobility, elevated arousal thresholds and homeostatic regulation[2, 3]. We assessed sleep-wake modulation by a core set of 20 circadian pacemaker neurons that express the neuropeptide PDF. We find that PDF neuron ablation, loss of pdf or its receptor pdfr results in increased sleep during the late night in light:dark (LD) conditions and more prominent increases on the first subjective day of constant darkness (DD). Flies deploy similar genetic and neurotransmitter pathways to regulate sleep as their mammalian counterparts, including GABA[4]. We find that RNAi-mediated knockdown of the GABAA receptor gene, Resistant to dieldrin (Rdl), in PDF neurons, reduced sleep consistent with a role for GABA in inhibiting PDF neuron function. Patch clamp electrophysiology reveals GABA-activated picrotoxin-sensitive chloride currents on PDF+ neurons. In addition, RDL is detectable most strongly on the large subset of PDF+ pacemaker neurons. These results suggest that GABAergic inhibition of arousal promoting PDF neurons is an important mode of sleep-wake regulation in vivo.

The Steroid Molting Hormone Ecdysone Regulates Sleep in Adult Drosophila melanogaster

“…In Drosophila, monoamines (i.e., dopamine and serotonin) have arousal and sleeppromoting effects that are similar to those observed in mammals (Andretic et al 2005;Kume et al 2005;Yuan et al 2006). It is also known that signaling pathways mediated by neurosecretory protein factors, such as pigment-dispersing factor (PDF) (Parisky et al 2008;Chung et al 2009) and epidermal growth factor (EGF) (Foltenyi et al 2007), play a role in sleep regulation in Drosophila. The effects of steroid hormones on Drosophila sleep, however, have not been investigated to date.…”

Independent Effects of γ-Aminobutyric Acid Transaminase (GABAT) on Metabolic and Sleep Homeostasis

“…Although the excess sleep is likely due to the high GABA levels in these mutants, it may also be attributable to altered glutamate levels. Glutamate is a wake-promoting neurotransmitter in eukaryotes and is directly metabolized by the enzyme glutamate decarboxylase into GABA, the main sleep-promoting molecule in mammals and flies (5)(6)(7)(8).…”

Calcineurin and Its Regulator Sra/DSCR1 Are Essential for Sleep inDrosophila

“…In Drosophila, mutations that decrease activity of the shaker voltage-gated K ϩ channel increase neuronal activity and decrease sleep (Cirelli et al, 2005). In addition, activity of various neurotransmitters and neuropeptides, including octopamine (Crocker and Sehgal, 2008), dopamine (Kume et al, 2005), and pigment-dispersing factor (pdf) Chung et al, 2009), are associated with decreased sleep in flies, while activity of others, including GABA Parisky et al, 2008) and serotonin (Yuan et al, 2006), are associated with increased sleep. However, intracellular molecular components mediating the effects of these molecules on sleep have not readily been identified.…”