Loesel R, Homberg U
Fachbereich Biologie/Tierphysiologie, Universität Marburg, D-35032 Marburg, Germany.
J Comp Neurol. 2001 Oct 15;439(2):193-207. doi: 10.1002/cne.1342.
The accessory medulla (AMe), a small neuropil in the insect optic lobe, has been proposed to serve a circadian pacemaker function analogous to the role of the suprachiasmatic nucleus in mammals. Building upon considerable knowledge of the circadian system of the cockroach Leucophaea maderae, we investigated the properties of AMe neurons in this insect with intracellular recordings combined with dye injections. Responses of neurons with processes in the AMe to visual stimuli, including stationary white light, moving objects, and polarized light were compared with the responses of adjacent medulla tangential neurons. Neurons with processes in the AMe and additional ramifications in the medulla strongly responded to stationary light stimuli and might, therefore, be part of photic entrainment pathways to the clock. Accessory medulla neurons lacking significant processes in the medulla but with projections to the midbrain or to the contralateral optic lobe, in contrast, responded weakly or not at all to light and, thus, seem to be part of the clock's output pathway. Two types of commissural neurons with tangential arborizations in both medullae were sensitive to polarized light, suggesting a role of these neurons in celestial navigation. Sidebranches in the AMae of one of the two cell types are discussed with respect to a possible involvement of the AMe in polarization vision. Finally, neurons responding to movement stimuli did not arborize in the AMe. The results show that the AMe receives photic input and support a role of this neuropil in circadian timekeeping functions.
副髓质（AMe）是昆虫视叶中的一个小神经纤维网，有人提出它具有类似于哺乳动物视交叉上核的昼夜节律起搏器功能。基于对德国蜚蠊昼夜节律系统的大量了解，我们通过细胞内记录结合染料注射的方法研究了这种昆虫中AMe神经元的特性。将在AMe中有突起的神经元对视觉刺激（包括静止白光、移动物体和偏振光）的反应与相邻髓质切向神经元的反应进行了比较。在AMe中有突起且在髓质中有额外分支的神经元对静止光刺激有强烈反应，因此可能是通向生物钟的光诱导途径的一部分。相比之下，在髓质中没有明显突起但投射到中脑或对侧视叶的副髓质神经元对光的反应微弱或根本没有反应，因此似乎是生物钟输出途径的一部分。两种在两个髓质中都有切向分支的连合神经元对偏振光敏感，表明这些神经元在天体导航中起作用。针对AMe可能参与偏振视觉的情况，讨论了两种细胞类型之一在AMae中的侧支。最后，对运动刺激有反应的神经元在AMe中没有分支。结果表明，AMe接收光输入，并支持这个神经纤维网在昼夜节律计时功能中的作用。
