Synchronized Bilateral Synaptic Inputs to Drosophila melanogaster Neuropeptidergic Rest/Arousal Neurons

摘要

Neuropeptide PDF (pigment-dispersing factor)-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. 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 ∼5–10 s. This rhythmic lLNv activity is blocked by TTX, voltage-gated sodium blocker, or α-bungarotoxin, 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 attributable 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 GluCl (glutamate-gated chloride) receptors. We demonstrate that cholinergic input, but not GABAergic input, is required for synchronous membrane activity, whereas GABA can modulate firing patterns. We conclude that neuropeptidergic lLNvs that control rest and arousal receive synchronous synaptic inputs mediated by ACh.