Mutational Analyses of Learning and Memory

我们的目标是利用现代突变分子遗传学的力量和特异性来揭示学习和记忆的组成部分过程。我们的研究使用了最被理解的多细胞生物体(线虫)--第一个拥有完全测序的基因组和完全绘制的神经连接体。我们过去的工作以线虫的联想学习和记忆为特征，使用味觉和气味作为条件刺激，使用食物的存在或不存在作为非条件刺激。对突变蠕虫的筛选揭示了与蠕虫学习和记忆有关的新基因。例如，发现的一种新的学习突变(lrn-2)被克隆，并被证明是一种受体酪氨酸激酶SCD-2的特定突变。最令人惊讶的是，野生型SCD-2需要在一个中间神经元(AIA)中整合两个感觉刺激来控制行为，但在一个单独的神经元(NSM)中需要更长时间的联想记忆。此外，我们已经证明了蠕虫的高阶联想学习过程(卡明阻断和场合设置)，一些人可能认为只有在更复杂的动物中才存在这种过程。事实上，我们对蠕虫突变体的研究表明，卡明阻断联想学习可能是由于对记忆回忆的干扰，而不是记忆存储。在我们最强大的学习和记忆测试中，苯甲醛的气味和没有细菌的食物的单一组合会产生一种习惯性的避免通常首选的苯甲醛；一种持续几个小时的记忆。我们建议将重点放在这一实验上，以揭示特定的神经元和分子介导条件刺激(目标1)、非条件刺激(目标2)的影响，以及它们对所产生的记忆的联系和随后的存储(目标3)。

Our goal is to use the power and specificity of modern mutational molecular genetics to reveal the component processes of learning and memory. Our research employs the best-understood multicellular organism (the worm C. elegans) - the first to have a completely sequenced genome and a fully mapped neural connectome. Our past work has characterized associative learning and memory in C. elegans, using tastes and smells as conditioned stimuli and the presence or absence of food as unconditioned stimuli. Screens of mutant worms have revealed novel genes involved in worm learning and memory. For example, one novel learning mutation discovered (lrn-2) was cloned and shown to be a mutation specifically in scd-2, a receptor tyrosine kinase. Most surprising, wild type scd-2 is required in one interneuron (AIA) for the integration of two sensory stimuli to control behaviour but in a separate neuron (NSM) for longer-term associative memory. Moreover, we have demonstrated higher order associative learning processes in worms (Kamin blocking and occasion setting) that some might have imagined were present only in more complex animals. Indeed, our studies of worm mutants have revealed that Kamin blocking of associative learning may be due to interference with memory recall rather than memory storage. In our most robust assay for learning and memory, a single pairing of the smell of benzaldehyde and the absence of bacterial food produces a learned avoidance of the normally preferred benzaldehyde; a memory which then lasts for a few hours. We propose to focus on this assay in order to reveal the specific neurons and molecules mediating the effects of the conditioned stimulus (Objective 1), the unconditioned stimulus (Objective 2), and their association and subsequent storage of the memory produced (Objective 3).