Modulation of GABAA receptor desensitization uncouples sleep onset and maintenance in Drosophila

Abstract

Many lines of evidence indicate that GABA and GABA A receptors make important contributions to human sleep regulation. Pharmacological manipulation of these receptors has differential effects on sleep onset and sleep maintenance insomnia. Here we show that sleep is regulated by GABA in Drosophila and that a mutant GABA A receptor, Rdl A302S , specifically decreases sleep latency. The drug carbamazepine (CBZ) has the opposite effect on sleep; it increases sleep latency as well as decreasing sleep. Behavioral and physiological experiments indicated that Rdl A302S mutant flies are resistant to the effects of CBZ on sleep latency and that mutant RDL A302S channels are resistant to the effects of CBZ on desensitization, respectively. These results suggest that this biophysical property of the channel, specifically channel desensitization, underlies the regulation of sleep latency in flies. These experiments uncouple the regulation of sleep latency from that of sleep duration and suggest that the kinetics of GABA A receptor signaling dictate sleep latency.Insomnia is the most common sleep problem and affects approximately one third of the adult American population 1 . Patients with insomnia are generally subdivided into three categories: sleep onset insomnia, sleep maintenance insomnia and terminal insomnia (early-morning awakening coupled with an inability to return to sleep) 2 . The biological basis for these insomnia classifications remains unknown. Nonetheless, a single class of drugs, agonistic modulators of GABA A receptors, effectively ameliorates these diverse symptoms 2,3 . GABA A receptors are a family of pentameric ligand-gated Cl -channels 4 and are a major source of inhibitory currents throughout the CNS 5,6 . These receptors are also an important target for pharmacologic treatment of many other neurological disorders in addition to sleep 7 .The fruit fly Drosophila melanogaster is an ideal model for dissecting the relationships between molecules and behaviors, as well as between different sleep states 8,9 . As in mammals, it has been shown that the sleep-like state of Drosophila is associated with reduced sensory responsiveness and reduced brain activity 10,11 , and is subject to both circadian and homeostatic regulation 12,13 . Researchers have also identified a number of genes 14,15 , Notably, the mutation that causes the insecticide resistance phenotype (A302S) 20 specifically decreases the rate of RDL desensitization with little or no effect on other channel properties 23 . As a consequence, the mutant receptor has a longer single channel open duration and, therefore, increased channel current, at least under certain conditions (see below). Because of these characteristics, and because this mutation does not have obvious effects on health or viability, we decided to establish the importance of GABAergic transmission to sleep in flies and to examine the effects of the Rdl mutation.Interestingly, flies with this mutant GABA A receptor subunit slept more, primarily because of decreased sleep lat...

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

“…Moreover, both dopamine and octopamine modulate calcium and cAMP levels (46) in response to cholinergic inputs and play an important role in modulating MB neuronal activity during associative olfactory learning (47)(48)(49)(50), suggesting that they could affect the excitability of Kenyon cells. 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).…”

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

“…For sleep analysis, data from days 6 -8 were collected by using 1-min bin. The sleep-like resting state is defined as no movement for 5 min (32)(33)(34). Total sleep measures the amount of sleep per 24 h, whereas maximum sleep measures the duration of the longest sleep episode in each genotype.…”

Drosophila D1 dopamine receptor mediates caffeine-induced arousal

“…Although dDA1 is strongly expressed in MBs, where most genes affecting baseline sleep in Drosophila are expressed (26)(27)(28)(29)(30)(31), the average amount of sleep and activity during waking were indistinguishable between WT and dumb 1 flies (Fig. S4 A and B), in contrast to fmn flies, which have lowered baseline amounts of sleep and increased locomotor activity during waking (ref.…”