CHANGES IN THE PINEAL GLAND, LH-RH NEURON SYSTEM AND PITUITARY-GONADAL AXIS IN GOLDEN HAMSTERS UNDER ARTIFICIAL WINTER CONDITIONS

抄録

Male golden hamsters were exposed gradually to low temperatures and short photoperiods in a climatic chamber, and kept finally in an environment of 5°C and 3 h light/21 h darkness (3L/21D) for more than 5 weeks. Control animals were maintained at 20°C and 14L/10D or 12L/12D. The following changes were induced in animals kept under the artificial winter conditions. 1) Pinealocytes showed proliferation of the smooth- and rough-surfaced endoplasmic reticulum (sER and rER) and marked development of the Golgi apparatus, indicating an enhanced cellular function. Secretory granules were increased in cell processes, and lipid droplets and myeloid bodies were frequently observed. 2) LH-RH-positive neurons in the brain were immunostained more numerously than in controls, in agreement with a significant increase in hypothalamic LH-RH demonstrated by radioimmunoassay. 3) Pituitary gonadotrophs showed signs of suppressed secretory activity, such as accumulation of granules, whereas mammotrophs showed signs of activation including a marked development of the rER and Golgi apparatus. 4) Testes and accessory sex organs exhibited significant atrophy, whose weight was decreased to 13% and to 39% of that in the respective controls. It was assumed that pineal hormones secreted excessively under the experimental winter condition inhibited the discharge of hypothalamic LH-RH, resulting in a suppression of gonadotropin release and subsequent gonadal atrophy.