A quantitative morphological study of the pineal organ in the goldfish, Carassius auratus

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Abstract
Stereological techniques applied to a light and electron microscopic study of the pineal organ of the goldfish indicated that photoreceptor and supportive cells were comparable in their number and cell volume and that approximately 500 nerve cells were present in the pineal end vesicle. There were approximately 310 nerve fibers descending the distal part of the pineal tract. Quantitative analysis of organelles in photoreceptor cells revealed that the endoplasmic reticulum and Golgi bodies, in the vicinity of which were situated both clear and dense-cored vesicles, formed a substantial part of the cytoplasmic volume. Other new observations reported for this species include a close association between mitochondria and parts of the smooth endoplasmic reticulum, a characteristic feature of photoreceptor cells, and the presence of subsurface cisternae formed from profiles of endoplasmic reticulum. Moreover, specialized contacts were found between both photoreceptor and supportive cells. Some of these ultrastructural features are similar to those reported in the secretory pinealocytes of mammals. These findings suggest that (1) the pineal organ in this species has a high degree of photosensitivity as evidenced by the large number of photoreceptor cells related to each nerve cell, and (2) photoreceptor cells are metabolically active possibly having functions other than photoreception.