Herman K G, Strumwasser F
J Comp Neurol. 1984 Dec 20;230(4):593-613. doi: 10.1002/cne.902300408.
The eye of the opisthobranch mollusc, Aplysia californica, contains a neuronal circadian oscillator system as well as a photoreceptor system. The retina contains five classes of receptors, several of which are described for the first time in this paper, and two types of neurons. The most conspicuous photoreceptor has long microvilli and is densely packed with small vesicles. The other four receptor types bear both microvilli and cilia and lack densely packed vesicles. Because of their small size, these four receptors occupy only a small fraction of the retinal area, but numerically they account for about half of the receptors. There are marked differences between the dorsal and ventral portions of the eye of Aplysia. The optic nerve head and associated bundles of axons within the retina form a boundary between two anatomically distinct regions of the eye. The microvillous photoreceptor and one of the receptors bearing both microvilli and cilia are found throughout the eye. The other three receptor types are restricted to the region ventral to the optic nerve head. One type of neuron, which has been shown in other studies to produce compound action potentials whose frequency varies with a circadian rhythm, is also found only ventral to the optic nerve head and associated axon bundles. There are also marked regional variations in cellular dimensions. The rhabdom originating from the microvillous photoreceptors is thickest in the dorsal and central retina, and the cross-sectional areas of these photoreceptors are largest dorsally. The pigmented layer is also much thicker in the dorsal retina. No other molluscan eye has been reported to have as many receptor types as Aplysia, nor has restriction of a receptor or neuronal type to a limited area been described. Regional variations in cellular dimensions have been reported previously primarily in the advanced cephalopod eyes. The significance of these unusual features is discussed in relation to both the visual properties of the eye and the circadian oscillator it contains.
后鳃亚纲软体动物加州海兔的眼睛包含一个神经元昼夜节律振荡器系统以及一个光感受器系统。视网膜包含五类感受器，其中有几类是本文首次描述的，还有两种神经元。最显著的光感受器有长微绒毛，并且密集地布满小囊泡。其他四种感受器类型既有微绒毛又有纤毛，且没有密集排列的囊泡。由于它们体积小，这四种感受器仅占据视网膜区域的一小部分，但在数量上它们约占感受器总数的一半。加州海兔眼睛的背侧和腹侧部分存在明显差异。视神经乳头以及视网膜内相关的轴突束在眼睛的两个解剖学上不同的区域之间形成了一个边界。微绒毛光感受器以及一种既有微绒毛又有纤毛的感受器在整个眼睛中都有发现。其他三种感受器类型则局限于视神经乳头腹侧的区域。一种神经元，在其他研究中已表明其能产生复合动作电位，其频率随昼夜节律变化，也仅在视神经乳头和相关轴突束的腹侧被发现。细胞尺寸也存在明显的区域差异。源自微绒毛光感受器的视杆在背侧和中央视网膜最厚，并且这些光感受器的横截面积在背侧最大。色素层在背侧视网膜也厚得多。据报道，没有其他软体动物的眼睛具有像加州海兔这么多的感受器类型，也没有描述过感受器或神经元类型局限于有限区域的情况。细胞尺寸的区域差异此前主要在高等头足类动物的眼睛中被报道过。本文结合眼睛的视觉特性及其所含的昼夜节律振荡器对这些不寻常特征的意义进行了讨论。
