Pineal Ultrastructure and Indole Profiles Spanning the Summer Rise in Arginine Vasotocin Immunoactivity*

Abstract

A correlative radioimmunological-biochemical-ultrastructural study of the rat pineal gland was undertaken during the summer months when pineal arginine vasotocin (AVT) immunoactivity increases up to 200-fold. RIA confirmed a rapid rise in AVT activity during mid-August regardless of the time of day sampled. Pineal indoles were separated by HPLC and measured using electrochemical detection. Serotonin (5-HT) and 5-hydroxyindoleacetic acid levels were consistently elevated in daytime samples, and there was a significant trend for increased day and nighttime levels of 5-HT from July to September. Mid-dark levels of melatonin also exhibited a significant increase over the sample period. Nighttime levels of N-acetylserotonin mirrored fluctuations in 5-HT in the preceding photoperiod. Ultrastructural components implicated in peptide/protein and/or indole biosynthesis were quantified by stereological morphometry. The greatest amounts of rough endoplasmic reticulum stacks, lipid droplets, and annulate lamellae-like bodies coincided with peak AVT activity. Dense-cored vesicles and synaptic ribbons were consistently more frequent during the dark period. The number of dense-cored vesicles and nucleolar size tended to be greatest before and after the peak in AVT immunoactivity. These observations are consistent with the hypotheses that endoplasmic reticulum and lipid are functionally related to the synthesis and/or storage of peptide/protein factors and that numerical changes in synaptic ribbons and dense-cored vesicles are more closely related to day/night differences in indole metabolism.

Circannual Analysis of Pineal Gland Indoles and Vasotocin-Like Immunoreactivity in Male Rats Kept on Constant Photoschedules and Temperature

“…1,3) may be related to peptidergic modu lation of indole metabolism in the gland. A similar decline in nighttime melatonin levels preceding the August surge in pineal peptides was also found in an earlier investigation [13].…”

“…We specifically sought to determine if sea sonal differences occurred in pineal mela tonin metabolism independent of seasonal photoperiodic control and whether circadian rhythms in pineal melatonin synthesis were influenced by cyclical changes in pineal pep tides. An earlier investigation detected day versus night differences in indole constituents between July and September spanning the August rise in iVT [ 13],…”

Expression of tranferrin receptors in the pineal gland of postnatal and adult rats and its alteration in hypoxia and melatonin treatment

“…Earlier studies have shown that deprivation of sympathetic innervation led to a reduction in the volume of mitochondria in pinealocytes suggesting a lower metabolic and secretory activity of pinealocytes (Karasek et al, 2002). It has also been hypothesized that mitochondria and rough endoplasmic reticulum are functionally related to synthesis and storage of peptide/protein factors and indole biosynthesis (McNulty et al, 1985;Swietoslawski and Karasek, 1993). In this connection, it was also reported that the pineal gland begins to produce significant levels of melatonin around postnatal day 16 Fig.…”

Analysis of synaptic bodies in the Sprague–Dawley rat pineal gland under extreme photoperiods

“…In rat pinealocytes SBs undergo changes in number and size during a 24 h period Mori, 1977, 1980;McNulty et al, 1985McNulty et al, , 1987Riemann et al, 1990;Jastrow et al, 1997a) and further show changes in different photoluminous ''seasons'' (Karasek et al, 1988a;Martínez-Soriano et al, 1992). Light mediates functional and ultrastructural changes in pinealocytes (Karasek, 1981;Martínez-Soriano et al, 2002) via the retina-hypothalamic-reticulo-superior cervical ganglia pathway, providing adrenergic innervation of the pineal gland (Wurtman et al, 1967).…”