The Ultrastructure of the Nerve Fibers and Pinealocytes in the Rat Pineal Stalk

Abstract

In view of the increasing interest in the central innervation of the mammalian pineal gland, this aspect was studied in depth in the rat. This species is especially suited since the nerve fibers in question form a distinct bundle running from the deep to the superficial pineal gland through the pineal stalk. The axons were counted and analysed ultrastructurally in the pineal stalks cut transversely at three levels (proximal, intermediate, and distal) relative to the neural axis and in longitudinal sections. The number of nerve fibers was highly variable, ranging from 551 to 1,132 proximally and from 110 to 448 distally, indicating that many fibers terminate in the stalk or leave the stalk after forming a loop. Large myelinated axons, which are abundant proximally, appear to lose their sheaths along their course through the stalk. Most of the axons were small and unmyelinated. A few of these had the appearance of sympathetic fibers and disappeared after sympathectomy. Others contained abundant neurosecretory granules, and, according to the literature, may originate in the hypothalamic paraventricular nuclei. The majority of the small axons which are apparently devoid of granules and dense-cored vesicles may come from the habenular nuclei and the stria medullaris. In addition to axons, the stalk contains astrocytes, a few oligodendrocytes and Schwann cells, as well as pinealocytes identical to those of the superficial pineal gland.

Components and connections of the circadian timing system in mammals

“…A direct connection between the habenular nuclei and pineal gland has been suggested by short latencies in electrophysiological studies (Rønnekleiv et al 1980;Semm et al 1981;Reuss et al 1984), by HRP tracing (Dafny 1983;Møller andKorf 1983, 1987), and by electron-microscopic studies in the guinea pig . These connections, which may be interpreted as being part of a functional central innervation of the pineal gland, seem to involve the pineal stalk, which contains myelinated and unmyelinated fibres that decrease in number from proximal to distal (Luo et al 1984). However, combined neuronal tracing and immunocytochemistry of the habenular-pineal connection have not been conducted as yet.…”

The anatomy and innervation of the mammalian pineal gland

“…Thus, at the ultrastructural level many myelinated nerve fibers are observed in the deep pineal gland and these fibers continue into the rostral part of the pineal stalk. However, in the stalk the number of myelinated fibers decreases and only a few are present in its rostral part (Møller and Korf 1983a;Luo et al 1984). Immunohistochemistry has indicated that central nerve fibers from the paraventricular nucleus contain vasopressin and oxytocin (Buijs and Pévet 1980;Nürnberger and Korf 1981).…”

Low-grade oligodendroglioma of the pineal gland: a case report and review of the literature

“…The principal cell is the pineal parenchymal cell or pineocyte, which is surrounded by a stroma of fibrillary astrocytes admixed with sympathetic neurons [16-18]. The presence of glial cells in the pineal gland was first demonstrated by impregnation techniques with gold chloride-sublimate [15,19].…”

“…Moreover, according to Burger et al [5], definite proof of the incospicious existence of pineal astrocytes comes from the occurrence of gliotic tissue in lesions such as craniopharyngiomas and hemangioblastomas. In addition to fibrillar astrocytes, there are some oligodendrocytes which are restricted to the proximal part of the stalk, near the deep pineal tissue where myelinated axons are abundant [18,20]. Adjacent to the gland there are ependymal cells and cells forming the choroid plexus of the third ventricle, as well as glial cells from the brainstem [21].…”