Korf H W, Liesner R, Meissl H, Kirk A
Cell Tissue Res. 1981;216(1):113-30. doi: 10.1007/BF00234548.
The morphological and physiological properties of the pineal complex of Xenopus laevis were investigated in larval, juvenile and adult animals. In a representative majority of adult X. laevis, the frontal organ does not display signs of degeneration. Fully differentiated frontal organs contain photoreceptors typical of the pineal complex of lower vertebrates. By means of the acetylcholinesterase (AChE)-reaction approximately 30 neurons of two different types were demonstrated in the frontal organ. The frontal-organ nerve is composed of approximately 10 myelinated and 40 unmyelinated nerve fibers. The neuropil areas of the frontal organ are generally similar to the corresponding structures of the intracranial epiphysis. The neuronal apparatus of the epiphysis cerebri of X. laevis consists of (i) photoreceptor cells, (ii) approximately 100 AChE-positive neurons, (iii) complex neuropil areas, and (iv) a pineal tract formed by approximately 10 myelinated and approximately 100 unmyelinated nerve fibers. Some of them exhibit granular inclusions indicating that pinealopetal elements may enter the pineal complex of X. laevis via this pathway. The topography of the pineal tract of X. laevis differs considerably from that in ranid species. The most conspicuous element of the plexiform zones is the ribbon synapse. The basal processes of the photoreceptor cells may be presynaptic elements of simple, tangential, dyad or triad synaptic contacts. Conventional synapses were observed only occasionally. Electrophysiological recordings revealed that the pineal complex of Xenopus laevis is directly sensitive to light. In response to light stimuli, two types of responses, achromatic and chromatic, were recorded from the nerve of the frontal organ. In contrast, the epiphysis exhibited only achromatic units. The opposed color mechanism of the chromatic response showed a maximum sensitivity at approximately 360 nm for the inhibitory and at 520 nm for the excitatory event. The action spectrum of the achromatic response of the epiphysis and the frontal organ peaked between 500 and 520 nm and showed no Purkinje-shift during dark adaptation. The functional significance of these phenomena is discussed.
在非洲爪蟾的幼体、幼年期和成体动物中，对松果体复合体的形态学和生理学特性进行了研究。在大多数具有代表性的成年非洲爪蟾中，额器官未显示出退化迹象。完全分化的额器官含有低等脊椎动物松果体复合体特有的光感受器。通过乙酰胆碱酯酶（AChE）反应，在额器官中证实了大约30个两种不同类型的神经元。额器官神经由大约10条有髓神经纤维和40条无髓神经纤维组成。额器官的神经毡区域通常与颅内松果体的相应结构相似。非洲爪蟾松果体的神经元装置由（i）光感受器细胞，（ii）大约100个AChE阳性神经元，（iii）复杂的神经毡区域，以及（iv）由大约10条有髓神经纤维和大约100条无髓神经纤维形成的松果体束组成。其中一些显示出颗粒状内含物，表明松果体向心性成分可能通过这条途径进入非洲爪蟾的松果体复合体。非洲爪蟾松果体束的拓扑结构与蛙科动物有很大不同。丛状区最显著的成分是带状突触。光感受器细胞的基部突起可能是简单、切向、二元或三元突触接触的突触前成分。仅偶尔观察到传统突触。电生理记录显示，非洲爪蟾的松果体复合体对光直接敏感。对光刺激的反应中，从额器官神经记录到了两种类型的反应，即消色差反应和彩色反应。相比之下，松果体仅表现出消色差单位。彩色反应的对立颜色机制在抑制性事件中约360nm处显示出最大敏感性，在兴奋性事件中约520nm处显示出最大敏感性。松果体和额器官的消色差反应的作用光谱在500至520nm之间达到峰值，并且在暗适应期间没有浦肯野位移。讨论了这些现象的功能意义。
