No abstract

Electron microscopy was employed in a study of the pineal gland of the Mongolian gerbil (Meiones unguiculatus). It was determined that the gerbil pineal gland contains pinealocytes and glial cells with the pinealocytes being the predominant cell type. The pinealocytes contain numerous organelles traditionally considered as being either synthetic or secretory in function such as an extensive Golgi region, smooth (SER) and rough (RER) endoplasmic reticulum, secretory vesicles and microtubules. Other cytoplasmic components are also present in the pinealocytes (synaptic ribbons, subsurface cisternae) for which no function has been assigned. Dense-cored vesicles are rare. Vacuolated pinealocytes are present and appear to be intimately associated with the formation of the pineal concertions. Evidence presented supports the proposal that the concretions form within the vacuoles. Once the concretions reach an enlarged state, the vacuolated pinealocytes break down and the concretions are thus extruded into the extracellular space where they apparently continue to increase in size. The morphology of the glial cells was interpreted as indicative of a high synthetic activity. The glial cells contain predominantly the rough variety of endoplasmic reticulum and form an expansion around the wide perivascular area.

Much of the parenchyma of the normal pronephros of the adult Fundulus hereroclitus. a euryhaline teleost, is haematopoietic tissue which was examined in cytocentrifuge preparations and plastic embedded thick sections. As we have not characterized many of the blood cells functionally, the terminology used is based on their morphological resemblance to similarly named cells in higher vertebrates. Approximately 80% of the nonerythroid elements observed in the pronephros are mature eosinophilic granulocytes (48%). immature eosinophilic granulocytes (25%), or cells likely to be their precursors [e.g. small blast cells (6O/o) and large blast cells (2%)]. Although there are macrophages in the pronephros that are capable of endocytotic activity, the mature and immature granulocytes are not. The granulocytes are non-specific esterase positive, PAS positive, acid phosphatase negative, and are capable of being mobilized by a RES activating agent, Ecteinuscidiu turbinutu.

The pineal gland of four-month-old gerbils contains numerous calcareous deposits (corpora arenacea or concretions). Also, the tissue appears vacuolated due to the presence of a number of large rounded spaces. The deposits are usually associated with or lying within these "vacuoles". By eight months of age, the number of both the corpora arenacea and the "vacuoles" are increased over those present in the pineals of four-month-old gerbils. Bilateral superior cervical ganglionectomy at one month of age prevents the formation of both the concretions and "vacuoles". The cells in the sympathetically denervated pineal glands are smaller than those in pineal glands of animals that possess intact superior cervical ganglia.

Postnatal development of S-Ag and GFAP immunoreactivity in the in situ pineal glands of golden hamsters and gerbils was examined using the avidin-biotin-peroxidase immunohistochemical technique. S-Ag was present in the gerbil pineal gland on the first postnatal day (P1), whereas it did not appear in the hamster pineal until P6. GFAP-immunoreactive astrocytes were first observed in the hamster pineal gland on P7 and in the gerbil pineal gland on P10. The number of S-Ag-immunoreactive pinealocytes and GFAP-immunoreactive astrocytes in the pineal glands of hamsters and gerbils increased with increasing age from P7 to 3 weeks. By 4 weeks, strong S-Ag and GFAP immunoreactivity was observed in both hamster and gerbil pineal glands. GFAP-immunoreactive stellate astrocytes were distributed evenly throughout the gerbil superficial pineal gland, but they were more often located in the peripheral region of the hamster superficial pineal. For the pineal grafts, pineal glands from neonatal (3-5 day old) hamsters were transplanted into the third cerebral ventricle (infundibular recess or posterior third ventricle) or beneath the renal capsule of adult male hamsters. S-Ag immunoreactivity appeared in the pineal grafts within 1 week following transplantation. By 4 weeks the pineal grafts showed strong S-Ag immunoreactivity which was maintained until at least 12 weeks after transplantation. The time course of glial cell maturation in the cerebroventricular pineal grafts is generally parallel to the hamster pineal gland in situ before 4 weeks. By 12 weeks, however, more astrocytes differentiated and developed GFAP-immunoreactivity in the pineal grafts than in the in situ pineals. These studies have described the postnatal development of S-Ag and GFAP immunoreactivity in in situ pineal glands and in neonatal pineal grafts.