Electron microscopic and experimental studies of the pineal organ in the white-crowned sparrow,Zonotrichia leucophrys gambelii

Summary The structure of the pineal organ of Zonotrichia leucophrys gambelii, as revealed by light- and electron-microscopy, resembles that of Passer domesticus (Oksche and Kirschstein, 1969; Ueck, 1970). The typical cellular element is the pinealocyte with certain basic structural features of the pineal photoreceptors of lower vertebrates (see Oksche, 1971). However, instead of the characteristic, cone-like outer segments, there are, as in other species of birds, only bulbous cilia with ectopic whorls of lamellae. This structure of the outer segment is, in a sense, contrary to the demonstration of synaptoid contacts, numerous unmyelinated, and occasional myelinated nerve fibers by electron microscopy. In Nissl preparations it was possible to demonstrate typical nerve cells. The pinealocytes of Z. l. gambelii are secretory; their Golgi complex forms granulated vesicles (800–1,400 Å in diameter) that belong to the group of granular inclusions characteristic of monoamines. Autonomie nerve fibers course within the connective tissue capsule of the pineal organ. In many pinealocytes of Z. l. gambelii, the granular endoplasmic reticulum contains extensively expanded cisternae that are filled with a flocculent material and closely associated with bundles of filaments. In a number of cases such loop-like structures are selectively stainable with aldehyde fuchsin. It was not possible to demonstrate specific secretory activity in the supporting cells. Extirpation of the pineal organ in Z. l. gambelii had no definitely detectable influence on the photoperiodic control of testicular growth.Aves, Passeriformes, Fringillidae.Supported by grants from the Deutsche Forschungsgemeinschaft to Professor Oksche and by the National Science Foundation (GB 11905) to Professor Farner. A part of this investigation was effected while Professor Kobayashi held a Visiting Professorship at the University of Giessen.