Synchronized Bilateral Synaptic Inputs toDrosophila melanogasterNeuropeptidergic Rest/Arousal Neurons

Abstract

Neuropeptide Pigment-Dispersing Factor (PDF)-secreting large ventrolateral neurons (lLNvs) in the Drosophila brain regulate daily patterns of rest and arousal. These bilateral wake-promoting neurons are light-responsive and integrate information from the circadian system, sleep circuits, and light environment. In order to begin to dissect the synaptic circuitry of the circadian neural network, we performed simultaneous dual whole-cell patch clamp recordings of pairs of lLNvs. Both ipsilateral and contralateral pairs of lLNvs exhibit synchronous rhythmic membrane activity with a periodicity of about 5 to 10 seconds. This rhythmic lLNv activity is blocked by tetrodotoxin (TTX) voltage-gated sodium blocker, or α-bungarotoxin (α-BuTX) nicotinic acetylcholine receptor antagonist, indicating that action potential-dependent cholinergic synaptic connections are required for rhythmic lLNv activity. Since injecting current into one neuron of the pair had no effect on the membrane activity of the other neuron of the pair, this suggests that the synchrony is due to bilateral inputs and not coupling between the pairs of lLNvs. To further elucidate the nature of these synaptic inputs to lLNvs, we blocked or activated a variety of neurotransmitter receptors and measured effects on network activity and ionic conductances. These measurements indicate the lLNvs possess excitatory nicotinic ACh receptors, inhibitory ionotropic GABAA receptors, and inhibitory ionotropic glutamate-gated chloride (GluCl) receptors. We demonstrate that cholinergic input, but not GABAergic input, is required for synchronous membrane activity, while GABA can modulate firing patterns. We conclude that neuropeptidergic lLNvs that control rest and arousal receive synchronous synaptic inputs mediated by ACh.

Glutamate is an inhibitory neurotransmitter in the Drosophila olfactory system

“…Specifically, several studies have reported that bath-applied glutamate inhibits the large ventrolateral neurons of the Drosophila circadian clock circuit (28)(29)(30). Collectively, these studies suggest roles for both ionotropic and metabotropic glutamate receptors in glutamatergic inhibition.…”

Epigenetic Regulation of Axonal Growth ofDrosophilaPacemaker Cells by Histone Acetyltransferase Tip60 Controls Sleep

“…These observations suggest that the sLNvs can also integrate signals from GABAergic or other sleeppromoting neurons via their axon terminals. Indeed, the firing rate of sLNvs is thought to be dependent on a finely balanced interaction of cholinergic, GABAergic, and glutamate signaling (McCarthy et al 2011). Based on these studies, we propose a model by which the overelaborated sLNv synaptic arbors observed in flies co-expressing Tip60 WT and APP may provide additional input sites for signals from sleep-promoting neurons in the vicinity that counteract the arousing effect of PDF overexpression on nocturnal sleep (Figure 9).…”

Characterization of the target of ivermectin, the glutamate-gated chloride channel, fromAnopheles gambiae

“…This ganglion is responsible for integrating sensory signals from the antennae and eyes . GluCl is also expressed in the supraesophageal ganglion of D. melanogaster and has been shown to play a key role in circadian rhythms and olfactory processing (McCarthy et al, 2011;Liu and Wilson, 2013). Importantly, hemolymph has been shown to circulate to all of these structures, highlighting the fact that IVM in the hemolymph could affect physiological processes associated with these tissues found relatively far away from the midgut (Boppana and Hillyer, 2014).…”