Seasonal Changes in Glycogen Level and Size of Pinealocytes of the White‐Footed Mouse, Peromyscus leucopus: A Semiquantitative Histochemical Study

Abstract

Glycogen level in and size of pinealocytes of the feral, white-footed mouse Peromyscus leucopus, were studied by a semiquantitative histochemical method to determine whether seasonal changes exist in them under natural conditions, what temporal pattern they exhibit, and whether 24-hour changes in these parameters exist in different seasons, as shown in the laboratory dd-mice. Marked seasonal changes were seen in both glycogen levels and nuclear densities (ANOVA p less than 0.005). The size of pinealocytes at 09:00 to 10:00 showed one peak (and nadir) seasonal change, with the smallest size in winter (December and February) and a larger size in warmer seasons, with the maximum value in July. Glycogen level in pinealocytes at 09:00 to 10:00 showed bimodal seasonal changes, with lower levels in fall and spring and higher levels in winter and summer. In fall, a circadian trend in glycogen level in pinealocytes was seen, with a higher level at the end of the light period. In winter, the glycogen levels were very high at 09:00, 13:00, 17:00, and 21:00 examined and showed dampening of time-of-day differences. On the other hand, the size of pinealocytes followed a time-of-day change (P less than 0.005), being largest at 13:00 and smallest at 21:00. Thus, marked changes in quantitative structure and chemical activities, suggesting changes in functional activity, in pinealocytes were noted especially in severe, cold winter.

Morphological Studies of the Pineal Gland in the Common Gull (Larus canus) Reveal Uncommon Features of Pinealocytes

“…Marked seasonal changes in glycogen levels with bimodal level—lower in fall and spring and higher in winter and summer were noted in the white‐footed mouse ( Peromyscus leucopus ). In winter, the glycogen level in pinealocytes was very high and did not show of time‐of‐day differences (Kachi and Quay, 1984). Glycogen metabolism and its diurnal rhythm in the pinealocytes are regulated by the sympathetic innervations.…”

Effect of photoperiod on pineal gland volume and pinealocyte size in the chinese hamster, Cricetulus griseus

“…By contrast, pinealocytes of the hare are larger in size from summer to fall (Lincoln, 1976), and maximal nuclear diameters in pinealocytes of the bat are obtained in the fall (beginning of hibernation) in males and in early spring (arousal and dispersal from hibernation) in females (Quay, 1976). Additionally, pinealocyte sizes in the white-footed mouse are increased in summer and decreased in winter (Kachi and Quay, 1984). In feral animals under field conditions, it is possible that seasonal changes in a variety of environmental factors other than photoperiod may cause changes in sizes of pinealocytes and pineal glands.…”

“…Sizes of pinealocytes or pineal glands in several seasonally breeding animals are reported to increase when the gonads are regressed (golden hamster, Mogler, 1958;dormouse, Legait et al, 1975;hare, Lincoln, 1976;13-lined ground squirrel, McNulty et al, 1980;elephant seal, Griffths and Bryden, 19811, whereas pinealocytes of the white-footed mouse are larger when the gonads are active (Kachi and Quay, 1984). Thus, interspecies differences may exist in the relationships between pinealocyte or pineal gland sizes and reproductive function.…”

“…Sizes of pinealocytes or pineal glands have been reported to undergo seasonal variations in many wild animals under natural conditions (golden hamster, Mogler, 1958;dormouse, Legait et al, 1975;hare, Lincoln, 1976;bat, Quay, 1976;13-lined ground squirrel, Mc-Nulty et al, 1980;elephant seal, Griffiths and Bryden, 1981; white-footed mouse, Kachi and Quay, 1984). In these studies, the relationships between sizes of pinealocytes or pineal glands and seasons are not always consistent.…”