Primary spermatogonia have highly lobate nuclei and can be distinguished as pale and dark types on the basis of nuclear and cytoplasmic features. Nuclei of secondary spermatogonia are also lobate. Primary spermatocytes have spherical nuclei and display synaptinemal complexes in late zygotene-pachytene. Spermatocytes are connected by intercellular bridges, which persist through spermiogenesis. During spermiogenesis no acrosomal granule is formed. The acrosomal vesicle is large and forms in the apical part of the cell. A helical system of perinuclear microtubules accompanies the phase of nuclear elongation. Microtubules disappear in late spermatids and there forms a compact bundle of filaments which extends into the subacrosomal area. These filaments probably derive from the breakdown of the microtubules. A mitochondrial sleeve is formed around the proximal portion of the tail and much of it is cast off in the mature spermatid. The tail is composed of a spirally coiled contractile element and a stiff fibrous axial rod connected together by an undulating membrane. The axial rod and the axoneme-associated rodlet derive from a dense, juxtacentriolar fibrous mass. Sertoli cells surrounding the spermatogonial and spermatocyte cysts are slender and have oblong nuclei. In contrast, those associated with spermatids are columnar and have deeply indented nuclei. They possess many Golgi complexes, elongated mitochondria, cisternae of smooth endoplasmic reticulum, lysosome-like bodies, masses of glycogen particles, few lipid droplets, and an array of microtubules running longitudinally around the elongating spermatid nuclei. Desmosomes are formed between adjacent Sertoli cells.

Adult, Charles River CD-1, male mice were housed in an environmental control chamber under strict conditions of controlled light (12D/12L) and temperature. The mice were sacrificed at various times throughout the twenty-four hour clock and their pineals prepared routinely for electron microscopy. The number of dense-cored or granulated vesicles present in the polar terminals of pinealocytes were quantitated in thin cross sections through pericapillary areas. A distinct circadian rhythm was observed in the number of granulated vesicles with a three- to four-fold difference between late photoperiod maximum and late dark period minimum. The rhythm was abolished by bilateral superior cervical ganglionectomy. These results are consistent with the hypothesis that the granulated vesicles are synthesized and stored in the pinealocytic cytoplasm during the photoperiod under the tropic influence of norepinephrine, and are released during the dark period when melatonin synthesis is greatest. Melatonin, administered as daily intraperitoneal doses of 50 microgram over a period of five days, was observed to increase markedly the number of pinealocytic granulated vesicles during the light period, but led during the dark period to a decrease in their numbers to levels below that of diluent-treated controls. It may be that melatonin stimulates the synthesis and/or release of granulated vesicles which represent the packaged form of a major secretory product.

No abstract

Previous studies in rabbits and mice have revealed distinct circadian rhythms in the number of pinealocyte granulated vesicles (PGVs) and control of their synthesis and/or secretion by sympathetic nerves. The present study demonstrates the absence of a circadian rhythm in PGV content in hamsters "functionally pinealectomized" by maintenance under long photoperiod (L/D = 14/10 h). On the other hand, a highly significant rhythm of low amplitude was noted in PGVs of hamsters placed in photoperiods (less than 12.5 h) which are known to initiate pineal antigonadotropic activity. Bilateral optic enucleation, which also leads to pineal-mediated gonadal atrophy in the hamster, produced a significant decrease in the number of perivascular PGVs when compared to intact control animals. Daily late afternoon injections of melatonin produced no significant difference in the number of PGVs between treated and control animals at any sample time examined.