Ultrastructural evidence for seasonal changes in pinealocytes of the 13‐lined ground squirrel, spermophilus tridecemlineatus: A qualitative and quantitative study

Abstract

The fine structure of pinealocytes in the hibernating ground squirrel, Spermophilus tridecemlineatus, was found to vary both qualitatively and quantitatively according to the season in which the animals were sacrificed. Ultrastructural features of pinealocytes from fall (prehibernation) and winter (hibernation) periods, when the animals were sexually quiescent, included: 1) arrangement of the endoplasmic reticulum into flattened stacks or concentric rings (formations which have been implicated in antigonadotropic activity of the pineal); 2) condensations of a fine granular material; and 3) dilation of the cisternae of the endoplasmic reticulum and Golgi bodies with an increased number of Golgi associated vesicles. Moreover, there was an apparent increase in the number of dense-cored vesicles and microtubules in pinealocytes of winter animals. These findings indicate that a circannual rhythm in pinealocyte ultrastructure occurs in this species and further suggest that cellular activity is seasonal.

The Photoperiod-Driven Cyclical Secretion of Pineal Melatonin Regulates Seasonal Reproduction in Geese (Anser cygnoides)

“…Moreover, we observed through electron microscopy that the number of Golgi apparatus complexes increased slightly, gradually accumulating numerous vesicles at the AE. These characteristic morphological changes in the cell were suggestive of active secretory functions of the pineal gland, and the phenomena described here were consistent with the results reported by Frink et al (1978) and McNulty et al (1980) [50,51]. In addition, the current study confirmed that 5-HT is a fundamental component of melatonin biosynthesis [47].…”

Morphofunctional aspects of the mammalian pineal gland

“…17, 18) may also be associated with pineal secretion. McNulty and Dombrowski (1980) and Karasek (1981) believe that an increase in the number of microtubules in activated pinealocytes may indicate their role in organelle movement, perhaps associated with the secretory processes. Theron et al (1979) suggested that synaptic ribbons may be involved in the synthesis andl or storage of melatonin.…”

Ultrastructure of the mammalian pinealocyte under natural and experimental conditions: Quantitative aspects

“…In addition to previously mentioned study of the annual rhythm of pinealocyte SR and SS (Karasek et al, 1988a), ultrastructural investigation utilizing sterology has been used to study seasonal changes in the pinealocytes of the ground squirrel (McNulty and Dombrowski, 1980). The volume densities of mitochondria and lipid droplets exhibited peaks in winter and nadirs in the fall, whereas surface density of granular endoplasmic reticulum showed an inverse behaviour (McNulty and Dombrowski, 1980).…”