Dissociation between the output of the circadian clock and external environmental cues is a major cause of human cognitive dysfunction. While the effects of ablation of the molecular clock on memory have been studied in many systems, little has been done to test the role of specific clock circuit output signals. To address this gap, we examined the effects of mutations of Pigment-dispersing factor (Pdf) and its receptor, Pdfr, on associative memory in male and female Drosophila. Loss of PDF signaling significantly decreases the ability to form associative memory. Appetitive short-term memory (STM), which in wild-type (WT) is time-of-day (TOD) independent, is decreased across the day by mutation of Pdf or Pdfr, but more substantially in the morning than in the evening. This defect is because of PDFR expression in adult neurons outside the core clock circuit and the mushroom body (MB) Kenyon cells (KCs). The acquisition of a TOD difference in mutants implies the existence of multiple oscillators that act to normalize memory formation across the day for appetitive processes. Interestingly, aversive STM requires PDF but not PDFR, suggesting that there are valence-specific pathways downstream of PDF that regulate memory formation. These data argue that the circadian clock uses circuit-specific and molecularly diverse output pathways to enhance the ability of animals to optimize responses to changing conditions.

SIGNIFICANCE STATEMENT From humans to invertebrates, cognitive processes are influenced by organisms' internal circadian clocks, the pace of which is linked to the solar cycle. Disruption of this link is increasingly common (e.g., jetlag, social jetlag disorders) and causes cognitive impairments that are costly and long lasting. A detailed understanding of how the internal clock regulates cognition is critical for the development of therapeutic methods. Here, we show for the first time that olfactory associative memory in Drosophila requires signaling by Pigment-dispersing factor (PDF), a neuromodulatory signaling peptide produced only by circadian clock circuit neurons. We also find a novel role for the clock circuit in stabilizing appetitive sucrose/odor memory across the day.

昼夜节律时钟的输出与外部环境提示之间的分离是人类认知功能障碍的主要原因。尽管在许多系统中已经研究了消融分子时钟对存储器的影响，但是很少测试特定时钟电路输出信号的作用。为了解决这个空白，我们研究了色素分散因子（Pdf）及其受体Pdfr突变对果蝇雄性和雌性联想记忆的影响。PDF信号的丢失会大大降低形成联想记忆的能力。竞争性短期记忆（STM）在野生型（WT）中不依赖于一天中的时间（TOD），但由于Pdf或Pdfr，但早上比晚上更重要。该缺陷是由于PDFR在核心时钟回路和蘑菇体（MB）的Kenyon细胞（KC）之外的成年神经元中表达。突变体中TOD差异的获得意味着存在多个振荡子，这些振荡子可以正常化一天中对于记忆过程的记忆形成。有趣的是，厌恶性STM需要PDF而不是PDFR，这表明PDF下游存在价态特异性通路，可调节记忆形成。这些数据表明，昼夜节律时钟使用特定于电路的分子多样性输出路径来增强动物优化对不断变化的条件做出反应的能力。

意义声明从人类到无脊椎动物，认知过程受生物体内部生物钟的影响，生物钟的节奏与太阳周期有关。这种联系的中断越来越普遍（例如，时差，社会时差疾病），并导致代价高昂且持久的认知障碍。对内部时钟如何调节认知的详细了解对于开发治疗方法至关重要。在这里，我们首次显示果蝇中的嗅觉联想记忆需要通过色素分散因子（PDF）进行信号传递，色素分散因子（PDF）仅由昼夜节律电路神经元产生。我们还发现时钟电路在稳定全天食用蔗糖/气味的记忆中具有新颖的作用。