Three-dimensional analysis for neural network of photosensory pineal organ

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In the pineal organ of river lamprey, Lampetra japonica, there are two types pineal photoreccptors, typical and modified, which are regarded as the pure photoreceptor cell like visual cells in retina and the photoneuroendocrine cell secreting the melatonin, respectively. We investigate for the structure and the subtype of pineal photoreceptors and ganglion cells and their neural network three-dimensionally by use of a fluorescent labeling technique and a confocal laser-scanning microscope. The results are summarized below.1. The photoneuroendocrine cell, which shows serotonin immunoreactivity, possesses a basal process, and it appears that the process does not branch out. These processes contact each other at the basal region of the end vesicle, .2. Most of serotonin-immunoreactive cells showed iodopsin immunoreactivity, but not all. The results suggest that the iodopsin (red-cone visual pigment)-immunoreactive cells are predominant in the end-vesicle of lamprey pineal organ as neuroendocrine cells.3. Some visinin (cone-specific Ca2+binding protein)-immunoreactive cells show no iodopsin immunoreactivity. Many visinin-immunoreactive cells showed rhodopsin immunoreactivity. The results suggest that another cone-type photoreceptor exits in the pineal complex besides iodopsin immunoreactive cells.4. Globular and large ganglion cells were mainly located at peripheral region of the end vesicle. The ganglion cells connecting with the visinin-immunoreactive cells were globular in shape and large in size.