Postnatal development of “Synaptic” ribbons and spherules in the guinea pig pineal gland

Abstract

Previous studies have shown that the functionally enigmatic pineal "synaptic" ribbons are structurally a heterogeneous group of organelles consisting of rodlike ribbons sensu stricto, spherules, and intermediate forms. As ribbons and spherules react differently under various experimental conditions, these organelles were studied qualitatively and quantitatively during the postnatal period in guinea pigs. It was found that the pinealocytes were highly differentiated at birth and contained all three forms of "synaptic" structures. Ribbons and intermediate forms were more abundant than spherules and exhibited a striking increase in number on postnatal days 1 and 2; this increase was followed by a distinct trough and by a second peak at days 12 and 13, after which their numbers declined to reach adult levels by day 20. The spherules were small in number at birth and did not show the large immediate postnatal increase observed for the ribbons and intermediate forms. Instead there was a steady numerical increase up to day 12 (absolute number) or day 15 (relative numbers), followed by a decrease to adult level by day 20. Whereas during the early postnatal period (days 1 to 3) the majority of pinealocytes were characterized by ribbons and intermediate forms, with increasing age spherule-bearing pinealocytes increased in number. As ribbons and spherules were usually not found in the same pinealocyte, the present findings are interpreted to mean that ribbons and spherules characterize different types of pinealocytes showing an inverse numerical development postnatally. Developmentally intermediate forms behave like ribbons.

Prenatal development of “synaptic” ribbons in the guinea pig pineal gland

“…True ribbon synapses were also seen in this study. Since they were not found in postnatal and adult guinea pig pineal glands (Banks et al, 1985; this study), but only in the embryonic stage, they may represent transitory structures. The synaptic nature of the "synaptic" ribbons in mammalian pineal glands may be lost during their development.…”

“…It was reported that the pineal "synaptic" ribbons appeared on day 4 postpartum in golden hamsters (Hewing, 1979) and on day 1 after delivery in rats (King and Doughtery, 1980). Recently, a n investigation of the postnatal development of "synaptic" ribbons in pineal glands of the Hartley strain of guinea pig revealed that SR, SS, and IMF were found in relatively high numbers in the pinealocytes of 1-hr newborn guinea pigs (Banks et al, 1985). That report indicates that "synaptic" ribbons may be present in prenatal pineal glands.…”

“…Recent studies have shown that "synaptic" ribbons are a heterogeneous population. In addition to "synap-0 1990 WILEY-LISS, INC. tic" ribbons (SR) sensu stricto, "synaptic" spherules (SS) and intermediate forms (IMF) are present (Vollrath et al, 1983;Banks et al, 1985).…”

“…In order to gain an insight into the origin and nature of the pineal "synaptic" ribbons in mammals, this study was designed to determine the time when the earliest "synaptic" ribbons appear, to quantitate the number of "synaptic" ribbons during the prenatal development period, and to explore the possible origin and formation of the "synaptic" ribbons. Because of previous work done on newborn guinea pigs (Banks et al, 1985), the same strain of animals was used for this study. Also, guinea pigs are noted for their long gestation period (59-72 days) and their precocious young (Harkness and Wagner, 1986).…”

Pinealocyte synaptic ribbons and neuroendocrine function

“…Note the diameter of SR,, is greater than the thickness of the SR, rod. 1984; Khaledpour and Vollrath, 1987;Diaz et al, ing ring-shaped and irregular-shaped SR (Matsushima 1990), which is seasonally dependent in some species et al, 1983a,b;Banks et al, 1985;Khaledpour and (Riemann et al, 1990), and respond differently to en- Vollrath, 1987). It is our opinion that many of these vironmental lighting (Vollrath, 1986) as well as to ex-intermediate forms represent SR, or SRFP cut in various ogenously applied indoles .…”