Instituto de Investigación en Biomedicina de Buenos Aires (IBioBA), CONICET-Partner Institute of the Max Planck Society, C1425FQD Buenos Aires, Argentina.
Neurobiology and Genetics, Biocenter, University of Würzburg, 97074 Würzburg, Germany.
J Neurosci. 2020 Dec 9;40(50):9617-9633. doi: 10.1523/JNEUROSCI.1488-20.2020. Epub 2020 Nov 10.
Dopamine is a wake-promoting neuromodulator in mammals and fruit flies. In , the network of clock neurons that drives sleep/activity cycles comprises both wake-promoting and sleep-promoting cell types. The large ventrolateral neurons (l-LNs) and small ventrolateral neurons (s-LNs) have been identified as wake-promoting neurons within the clock neuron network. The l-LNs are innervated by dopaminergic neurons, and earlier work proposed that dopamine signaling raises cAMP levels in the l-LNs 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-LNs, but, surprisingly, it does not result in increased firing rates. Downregulation of the excitatory D-like dopamine receptor (Dop1R1) in the l-LNs and s-LNs, but not of Dop1R2, abolished the depolarization of l-LNs in response to dopamine. This indicates that dopamine signals via Dop1R1 to the l-LNs. Downregulation of Dop1R1 or Dop1R2 in the l-LNs and s-LNs does not affect sleep in males. Unexpectedly, we find a moderate decrease of daytime sleep with downregulation of Dop1R1 and of nighttime sleep with downregulation of Dop1R2. Since the l-LNs do not use Dop1R2 receptors and the s-LNs also respond to dopamine, we conclude that the s-LNs are responsible for the observed decrease in nighttime sleep. In summary, dopamine signaling in the wake-promoting LNs is not required for daytime arousal, but likely promotes nighttime sleep via the s-LNs. In insect and mammalian brains, sleep-promoting networks are intimately linked to the circadian clock, and the mechanisms underlying sleep and circadian timekeeping are evolutionarily ancient and highly conserved. Here we show that dopamine, one important sleep modulator in flies and mammals, plays surprisingly complex roles in the regulation of sleep by clock-containing neurons. Dopamine inhibits neurons in a central brain sleep center to promote sleep and excites wake-promoting circadian clock neurons. It is therefore predicted to promote wakefulness through both of these networks. Nevertheless, our results reveal that dopamine acting on wake-promoting clock neurons promotes sleep, revealing a previously unappreciated complexity in the dopaminergic control of sleep.
多巴胺是哺乳动物和果蝇中的一种促醒神经递质。在 中，驱动睡眠/活动周期的时钟神经元网络既包括促醒细胞类型，也包括促眠细胞类型。大型腹外侧神经元 (l-LNs) 和小型腹外侧神经元 (s-LNs) 已被确定为时钟神经元网络中的促醒神经元。l-LNs 被多巴胺能神经元支配，早期的工作提出，多巴胺信号会提高 l-LNs 中的 cAMP 水平，从而诱导兴奋性电活动（动作电位放电），导致觉醒并抑制睡眠。在这里，我们通过在分离的大脑中结合 cAMP 成像和膜片钳记录来测试这一假设。我们发现，多巴胺的应用确实会增加 cAMP 水平并使 l-LNs 去极化，但令人惊讶的是，它不会导致放电率增加。下调 l-LNs 和 s-LNs 中的兴奋性 D 样多巴胺受体 (Dop1R1)，而不是 Dop1R2，可消除多巴胺对 l-LNs 的去极化反应。这表明多巴胺信号通过 Dop1R1 传递到 l-LNs。下调 l-LNs 和 s-LNs 中的 Dop1R1 或 Dop1R2 不会影响雄性的睡眠。出乎意料的是，我们发现下调 Dop1R1 会导致日间睡眠适度减少，下调 Dop1R2 会导致夜间睡眠减少。由于 l-LNs 不使用 Dop1R2 受体，并且 s-LNs 也对多巴胺有反应，因此我们得出结论，观察到的夜间睡眠减少是由 s-LNs 引起的。总之，促醒 LNs 中的多巴胺信号对于白天的觉醒不是必需的，但可能通过 s-LNs 促进夜间睡眠。在昆虫和哺乳动物的大脑中，促眠网络与生物钟密切相关，睡眠和生物钟计时的机制在进化上是古老的，并且高度保守。在这里，我们表明，多巴胺作为果蝇和哺乳动物中一种重要的睡眠调节剂，在含时钟神经元对睡眠的调节中发挥着惊人复杂的作用。多巴胺抑制中枢脑睡眠中心的神经元以促进睡眠，并兴奋促醒的生物钟神经元。因此，它预计会通过这两个网络促进觉醒。然而，我们的结果表明，多巴胺作用于促醒时钟神经元会促进睡眠，揭示了多巴胺对睡眠的控制以前未被认识到的复杂性。
