Modes of protein and peptide uptake in the pineal gland of the Mongolian gerbil: An ultrastructural study

Abstract

The possible existence of either a blood-brain barrier or a CSF-brain barrier was examined in the pineal gland of the Mongolian gerbil using the ultrastructural tracers, horseradish peroxidase (HRP) and microperoxidase (MP). The mechanism of protein and peptide transport within the pineal gland and its possible relationship to pineal concretions was also considered. Gerbils were injected with either MP or HRP intravenously (IV), or they received intraventricular (IVT) injections of HRP. The IV injections resulted in both MP and HRP movement through the endothelial cells of the gland by vesicular transport and by diffusion through the endothelial cells of the gland by vesicular transport and by diffusion through the endothelial intercellular junctions. Following the IVT injections, the tracer was demonstrated in the subarachnoid space as well as in the glial cells associated with the periphery of the gland. In addition, after the IVT injections, rounded enlargements of the intercellular space that resembled canaliculi were filled with reaction product. In both cases (IVT and IV), the reaction product was localized to the perivascular space, to the glial cells and pinealocytes, and to the intercellular spaces. More importantly, there was specific localization of the tracers in the vacuolated pinealocytes and in the pineal concretions. The results of this study demonstrate several significant findings: 1) neither a blood-brain barrier nor a CSF-brain barrier exists in the pineal gland of the gerbil, 2) localization of the tracers in pineal concretions indicates a relationship between these structures and protein and peptide storage within the gland, and 3) the presence of the tracers within canaliculi after the IVT injections suggests a possible mode of secretion of pineal substances into the CSF.

The anatomy and innervation of the mammalian pineal gland

“…After intravascular injection of hydrophilic tracers with low molecular weights, such as fluorescein or Lissamine green, the pineal glands displaying either continuous or fenestrated capillaries were stained by the tracers (Møller et al 1978b;Møller and van Veen 1981). Also high molecular weight tracers, for example horseradish peroxidase (MW 40,000) permeate both the continuous capillaries of the gerbil pineal (Welsh and Beitz 1981) and the fenestrated capillaries of the mouse pineal (Møller et al 1978b). Some studies have suggested that the capillaries of the deep pineal are less permeable to high molecular weight tracers (Chen et al 1994).…”

Cytochemical Analysis of Calcium Distribution in the Superficial Pineal Gland of the Mongolian Gerbil

“…Lukaszyk and Reiter [ 19751 have proposed that the concretions are a consequence of the-secretory process of the pineal. Welsh and Beitz [1981] have reported a possible protein or polypeptide storage function of the PC as peroxidase reaction product was localized around and within the concre- Transmission electron micrograph of the pineal gland of the gerbil. Note the incrrasing gradient of reaction product toward the intracellular pineal concretion (PC).…”

Third ventricular pineal gland grafts in the gerbil: An electron microscopical and immunohistochemical investigation

“…Donor age: 4 weeks; graft age: 6 weeks. in the in situ pineal complex in the gerbil (Welsh and Beitz, 1981). Although the source of graft blood vessels and their functional capabilities remain an area of continued debate, it has been shown that tissue that does not normally possess a blood-brain barrier will not have a barrier following grafting to a new site (Rosenstein and Brightman, 1986).…”