Cayre Myriam, Scotto-Lomassese Sophie, Malaterre Jordane, Strambi Colette, Strambi Alain
Institut de Biologie du Developpement de Marseille Luminy, CNRS Parc scientifique de Luminy, case 907, 13288 Marseille, cedex 09, France.
Chem Senses. 2007 May;32(4):385-95. doi: 10.1093/chemse/bjm010. Epub 2007 Apr 2.
Since the discovery of adult neurogenesis, a major issue is the role of newborn neurons and the function-dependent regulation of adult neurogenesis. We decided to use an animal model with a relatively simple brain to address these questions. In the adult cricket brain as in mammals, new neurons are produced throughout life. This neurogenesis occurs in the main integrative centers of the insect brain, the mushroom bodies (MBs), where the neuroblasts responsible for their formation persist after the imaginal molt. The rate of production of new neurons is controlled not only by internal cues such as morphogenetic hormones but also by external environmental cues. Adult crickets reared in an enriched sensory environment experienced an increase in neuroblast proliferation as compared with crickets reared in an impoverished environment. In addition, unilateral sensory deprivation led to reduced neurogenesis in the MB ipsilateral to the lesion. In search of a functional role for the new cells, we specifically ablated MB neuroblasts in young adults using brain-focused gamma ray irradiation. We developed a learning paradigm adapted to the cricket, which we call the "escape paradigm." Using this operant associative learning test, we showed that crickets lacking neurogenesis exhibited delayed learning and reduced memory retention of the task when olfactory cues were used. Our results suggest that environmental cues are able to influence adult neurogenesis and that, in turn, newly generated neurons participate in olfactory integration, optimizing learning abilities of the animal, and thus its adaptation to its environment. Nevertheless, odor learning in adult insects cannot always be attributed to newly born neurons because neurogenesis is completed earlier in development in many insect species. In addition, many of the irradiated crickets performed significantly better than chance on the operant learning task.
自发现成体神经发生以来，一个主要问题是新生神经元的作用以及成体神经发生的功能依赖性调节。我们决定使用一种大脑相对简单的动物模型来解决这些问题。在成年蟋蟀的大脑中，如同在哺乳动物中一样，终生都会产生新的神经元。这种神经发生发生在昆虫大脑的主要整合中心——蘑菇体（MBs）中，负责其形成的神经母细胞在成虫蜕皮后仍然存在。新神经元的产生速率不仅受形态发生激素等内部信号的控制，还受外部环境信号的控制。与饲养在贫瘠环境中的蟋蟀相比，饲养在丰富感觉环境中的成年蟋蟀神经母细胞增殖增加。此外，单侧感觉剥夺导致损伤同侧蘑菇体中的神经发生减少。为了寻找新细胞的功能作用，我们使用脑聚焦伽马射线照射特异性地消融了年轻成虫中的蘑菇体神经母细胞。我们开发了一种适用于蟋蟀的学习范式，我们称之为“逃避范式”。使用这种操作性联想学习测试，我们发现缺乏神经发生的蟋蟀在使用嗅觉线索时表现出学习延迟和任务记忆保持能力下降。我们的结果表明，环境信号能够影响成体神经发生，反过来，新生成的神经元参与嗅觉整合，优化动物的学习能力，从而使其适应环境。然而，成年昆虫的气味学习并不总是归因于新生成的神经元，因为在许多昆虫物种中神经发生在发育早期就已完成。此外，许多接受照射的蟋蟀在操作性学习任务上的表现明显优于随机水平。
