Dopamine is a wake-promoting neuromodulator in mammals and fruit flies. In Drosophila melanogaster , the network of clock neurons that drives sleep/activity cycles comprises both wake- and sleep-promoting cell types. The large and small ventrolateral neurons (l-LNvs and s-LNvs) have been identified as wake-promoting neurons within the clock neuron network. The l-LNvs are innervated by dopaminergic neurons, and earlier work proposed that dopamine signaling raises cAMP levels in the l-LNvs and thus induces excitatory electrical activity (action potential firing), which results in wakefulness and inhibits sleep. Here, we test this hypothesis by combining cAMP imaging and patch-clamp recordings in isolated brains. We find that dopamine application indeed increases cAMP levels and depolarizes the l-LNvs, but surprisingly, it does not result in increased firing rates. Down-regulation of the excitatory dopamine receptor, Dop1R1 in the l- and s-LNvs, but not of Dop1R2, abolished the depolarization of l-LNvs in res...