PDF(Pubmed)
Abstract：
Neuronal circuits are hallmarks of complex decision-making processes in the animal world. How animals without neurons process information and respond to environmental cues promises a new window into studying precursors of neuronal control and origin of the nervous system as we know it today. Robust decision making in animals, such as in chemotaxis or thermotaxis, often requires internal symmetry breaking (such as anterior-posterior (AP) axis) provided naturally by a given body plan of an animal. Here we report the discovery of robust thermotaxis behaviour in Trichoplax adhaerens, an early-divergent, enigmatic animal with no anterior-posterior symmetry breaking (apolar) and no known neurons or muscles. We present a quantitative and robust behavioural response assay in Placozoa, which presents an apolar flat geometry. By exposing T. adhaerens to a thermal gradient under a long-term imaging set-up, we observe robust thermotaxis that occurs over timescale of hours, independent of any circadian rhythms. We quantify that T. adhaerens can detect thermal gradients of at least 0.1°C cm-1. Positive thermotaxis is observed for a range of baseline temperatures from 17°C to 22.5°C, and distributions of momentary speeds for both thermotaxis and control conditions are well described by single exponential fits. Interestingly, the organism does not maintain a fixed orientation while performing thermotaxis. Using natural diversity in size of adult organisms (100 µm to a few millimetres), we find no apparent size-dependence in thermotaxis behaviour across an order of magnitude of organism size. Several transient receptor potential (TRP) family homologues have been previously reported to be conserved in metazoans, including in T. adhaerens. We discover naringenin, a known TRPM3 antagonist, inhibits thermotaxis in T. adhaerens. The discovery of robust thermotaxis in T. adhaerens provides a tractable handle to interrogate information processing in a brainless animal. Understanding how divergent marine animals process thermal cues is also critical due to rapid temperature rise in our oceans.
摘要：
神经元回路是动物界复杂决策过程的标志。没有神经元的动物如何处理信息并对环境线索做出反应，这将为我们今天所知道的研究神经元控制和神经系统起源的前体提供新的窗口。动物强有力的决策，例如趋化性或热趋化，通常需要动物给定身体计划自然提供的内部对称性破坏（例如前后（AP）轴）。在这里，我们报告了在Trichoplaxadhaerens中发现的强大的热轴行为，一个早期的分歧，无前后对称破坏（非极性）且无已知神经元或肌肉的神秘动物。我们提出了一种定量和强大的行为反应测定法，它呈现了一个极地平坦的几何形状。通过在长期成像设置下将T.adhaerens暴露于热梯度，我们观察到在几个小时的时间尺度上发生的强劲的热运动，独立于任何昼夜节律。我们量化了T.adhaerens可以检测到至少0.1°Ccm-1的热梯度。在17°C至22.5°C的基线温度范围内观察到正的热轴，通过单指数拟合很好地描述了热轴和控制条件下的瞬时速度分布。有趣的是,生物体在进行热轴时不保持固定的方向。利用成年生物大小的自然多样性（100µm至几毫米），我们发现，在生物体大小的数量级上，热轴行为没有明显的大小依赖性。先前已报道几种瞬时受体电位（TRP）家族同源物在后生动物中保守，包括T.Adhaerens.我们发现柚皮素,一种已知的TRPM3拮抗剂，抑制T.adhaerens的热轴性。在T.adhaerens中发现了强大的热轴，为无脑动物的询问信息处理提供了一种易于处理的方法。由于我们海洋的温度迅速上升，了解不同的海洋动物如何处理热线索也至关重要。
