IDENTIFICATION AND PHYSIOLOGICAL ANALYSIS OF MEDULLA BILATERAL LARGE NEURONS INVOLVED IN MUTUAL INTERACTION OF BILATERALLY PAIRED CIRCADIAN CLOCKS IN INSECTS

延髓双侧大神经元(MBN)是连接双侧昼夜节律时钟部位的视觉中间神经元，即视髓区。两侧各有26个神经节，根据其形态和感受野可分为4组。在这项研究中，我们研究了4组MBN中的哪一组传递时钟之间相互耦合所需的时钟信息，以及这些神经元如何编码时钟信息。利用高效液相色谱-电子捕获检测器，我们首先检测了MBN中可能涉及的生物胺。在包括MBN胞体在内的小组织中，检测到5-羟色胺、多巴胺、章鱼胺和一些未知的胺。由于MBN不被抗5-羟色胺和抗多帕明抗体标记，其神经递质可能是章鱼胺或未知胺。然而，5-羟色胺和多巴胺系统可能在MBN系统的信息传递中发挥重要作用，因为电刺激MBN会降低对侧视叶中这些胺的水平。对与MBN的感受野相对应的复眼的部分毁损表明，MBN-4最有可能是神经元的候选者，其感受野位于眼的背尾区，负责传递时钟耦合所需的时钟信息。它们对光的反应比其他MBN弱得多，但它们的昼夜差异清晰可见，这表明它们将时钟信息编码为其反应的大小。其他MBN的反应也表现出昼夜差异，尽管它们的反应模式和昼夜变化有所不同。这些结果表明，MBN-4将其一侧的光照信息传递给对侧时钟，其他MBN在板球昼夜节律系统中也具有与时钟相关的功能。

Medulla bilateral large neurons (MBNs) are visual interneurons connecting the bilateral circadian clock sites, i.e., optic medulla regions. There are 26 MBNs in each side and they could be classified into 4 groups according to their morpholoy and receptive fields. In this study, we examined which of the 4 group of MBNs transmitts the clock information necessary for mutual coupling between the clocks and how those neurons encode the clock information. With HPLC-ECD we first examined the biogenic amines which would be involved in the MBNs. In the small tissue including MBN somata, serotonin, dopamine, octopamine and some unknown amines were detected. Since MBNs were not labelled by anti-serotonin andanti-doapmine antibodies, their neurotransmitter may be either octopamine or the unknown amine. Howeer, serotonergic and dopaminergic system may play an important role in the information transmission in MBN system, since the electricl stimulation of MBNs reduces the level of these amines in the contralateral optic lobe.Partial destruction of the compound eye corresponding to the receptive fields of the MBNs revealed that MBN-4s, whose receptive field lies in the dorso-caudal area of the eye, are the most likely candidates for the neuron mediating the clock information necessary for the clock coupling. Their response to light was rather weaker than those other MBNs, but their day-night difference was clearly seen, suggesting that they encode the clock information as the magnitude of their response. Other MBNs also showed day night difference in their responsiveness, although the pattern of their responses and day night change were different with each other. These results suggest that MBN-4 conveys the lighting information on its side to the contralateral clock and that other MBNs also have clock related functions in the cricket circadian system.