“Synaptic” ribbons and spherules of the guinea pig pineal gland: Inverse day/night differences in number

Abstract

The present study deals with the functionally enigmatic "synaptic" ribbons and spherules of guinea pig pinealocytes. Whereas the ribbons have been shown to exhibit a 24-hr rhythmicity with low numbers during the day and high numbers at night, very little of a definitive nature is known about the spherules. Sixteen male guinea pigs of the Hartley strain were perfusion fixed, 8 between 0900-1100 hr, and 8 between 2100-2300 hr. The ribbons and spherules were counted in the pineal parenchyma of the proximal, intermediate, and distal regions. In confirmation of earlier studies, it was found that "synaptic" ribbons are equally abundant in the proximal, intermediate, and distal regions of the gland, during both the day and the night, and that they increase significantly in number at night when compared with daytime values. The spherules, by contrast, are more abundant proximally and are present in greater numbers during the day than at night. As ribbons and spherules are usually not found in one and the same pinealocytic profile, and based on previous electrophysiological studies, it is proposed that the ribbons are morphological markers of nocturnally active pinealocytes, whereas spherules characterize diurnally active pinealocytes.

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

“…Quantitative assessment of the "synaptic" structures obtained from average values for the ages newborn to day 20 revealed that SR and IMF were present in equal numbers in the proximal (24.47; 7.191, intermediate (27.28; 7.091, and distal (23.51, 7.51) region of the gland. As noted previously (Vollrath et al, 1983), SP were significantly (p < 0.01) more abundant proximally (16.59) than in the other regions (region fi, 9.46; region C, 9.10). During development, the mean numbers of both the individual structures and the fields change, as demonstrated in Figure 9.…”

“…Moreover, IMF' also seem to increase at the expense of SR on day 2. The concomitant increase of absolute SR and SP numbers speaks against an assumption that SR differentiate to form SP, as does the observation that in most instances SR and SP are not seen within the same pinealocyte profile (Vollrath et al, 1983; this study). Apparently, there are major differences between pineal and inner ear ribbons and spherules inasmuch as in cochlear hair cells (Sobkowicz et al, 1982) and vestibular type I cells (Favre and Sans, 1979) the spheroid forms are replaced by platelike ribbons during ontogenesis.…”

“…In addition to SR and SP, intermediate forms (IMF) are present, appearing as irregularly thickened bars or irregular electron densities surrounded by electron-lucent vesicles (King and Dougherty, 1982a;Karsek and Vollrath, 1982;Vollrath et al, 1983). These IMF appear to be functionally more closely related to SR than to SP.…”

“…In the guinea pig where SR are equally numerous in the proximal, intermediate, and distal parts of the dumbbell-shaped pineal gland, SP are more abundant proximally than in other regions. At night, SR numbers increase while SP numbers decrease (Vollrath et al, 1983). As SR and SP are usually not found in the same pinealocyte profile in the guinea pig, and electrophysiological findings (Semm and Vollrath, 1980) show that darkness-activated cells exhibit a close parallelism to the nocturnal increase of melatonin synthesis, it has been suggested that SR characterize nocturnally active pinealocytes whereas SP may be typical of diurnally active pinealocytes (Vollrath et al, 1983).…”

“…Recently it has been emphasized that in addition to the SR the so-called synaptic spherules (SP, vesicle-crowned balls, Lues, 1971) may be of importance (Vollrath, 1981;Karasek and Vollrath, 1982;Vollrath et al, 1983). Whereas SR consist of an electrondense rod 30-40 nm in width, surrounded by electron-lucent vesicles 30-50 nm in diameter, the SP has a ball-like electron-dense core 4-6 times larger than that of the SR and the vesicles surrounding the SR (Vollrath, 1981).…”