Quantitative morphology and environmental responses of the pineal gland in the collared lemming (Dicrostonyx groenlandicus)

Abstract

Collared lemmings from Churchill, Manitoba, and their descendants were studied in captivity to define neuroendocrine and related histophsiological characteristics and responses, particularly in relation to photic and temperature conditions. Relatively great pineal size (0.1755 +/- 0.0167 mm3, or 3.08 +/- 0.30 = pineal volume in mm3 X 10(3)/body weight in gm; N = 16) shown in this arctic rodent is consistent with the suggestion that pineal size and significance may tend to be greater in more northern (higher latitude) species. Total number of nucleated cells per pineal averaged 137,000 +/- 10,500. Pinealocytes (105,000 +/- 8,700/pineal) and other cell types were present in relative numbers typical of mammalian pineal glands, and were not numerically correlated with age, sex, or location or circumstances of birth and early postnatal life. Chronic exposure to warmer (21-27 degrees C) in comparison with colder (-9 to -6 degrees C) environments, whatever the illumination, led to greater pinealocyte activity, as shown especially by nucleolar diameter, throughout most of the nine regions of the organ analyzed cytologically (all regions combined: P less than 0.001). Increased pinealocyte activity in chronic darkness was suggested by similar evidence (P less than 0.01), but in comparison with the thermal effects, was less marked and more variable in different regions of the organ. These and other findings of this study indicate that the Dicrostonyx pineal organ is morphologically unique, relatively large in size, and cytologically responsive to environmental conditions.

Estradiol Modulation of Pineal Gland Activity in the Wild Bandicoot Rat, <i>Bandicota bengalensis</i>

“…For nuclear diameter, about 5(X) parenchymal nuclei were considered at random from five mid-sections for each individual gland. The cell size of the pinealocytes was estimated through the population density determined by counting the nuclei present per microscopic field [9,19,26[ and this count was corrected following Abercrombie's |1] correlation method. At least 100 microscopic fields were considered from random sections of each pineal gland.…”

Pineal atrophy and other neuroendocrine and circumventricular features of the naked mole-rat,heterocephalusglaber (R�ppell), a fossorial, equatorial rodent

“…Camera lucida outline tracings of the pineal remnant were made from histological sections spaced at intervals. Planimetry of the pineal area represented in these was used as a basis for calculating total pineal volume, as explained and evaluated in more detail elsewhere (Quay, 1956(Quay, , 1978.…”

Comparative Gross and Fine Morphology of the Mammalian Pineal Gland

“…Probably, pineal lipids are primarily involved in the general cell metabolism and in membrane structure and function of pinealocytes, not playing any role as hormones or hormone precursors. It is, however, of some interest that pineal lipid content in the rat demonstrates a circadian rhythmicity showing a peak at midday and being lowest at midnight (Quay, 1965(Quay, , 1974. Moreover, pineal lipid content is in some way correlated with the activity of the gonadal axis.…”

“…Variations in pineal volume have been studied in three species of rodents (Quay, 1956(Quay, , 1978Legait et al, 1975). Although pineal weight is known to show, inter alia~ circadian and seasonal variations, interspecies variations are much greater.…”

“…MUch has been speculated about their possible functional significance. The chemistry and histochemistry of pineal lipids has been thoroughly reviewed by Quay (1974). No lipid compounds have been identified which are characteristic of pinealocytes only.…”