Endocrine patterns before and after examination stress in males and females.

Plasma levels of cortisol, adrenocorticotropin (ACTH), and growth hormone (GH), were determined by radioimmunoassay in medical students just before (Exp.1) plasma values of cortisol were higher than their control values in both sexes, statistically significantly, however, only in males. The difference of cortisol behavior between the sexes was not significant. The males' ACTH values were lower than their control levels, but there was no such difference in the females. Plasma levels and differences of growth hormone varied greatly in both sexes. After the examination (Exp.2) plasma values of cortisol were unaffected compared with their control values in both sexes. The ACTH values were lower than the control values in both sexes, significantly though only in the males. The GH values were higher than control values in the males but not in the females. The results are in line with previous observations suggesting that psychological stress is associated with slightly different hormonal effects in males and females.

Examination stress decreases plasma level of luteinizing hormone in male students.

Plasma levels of luteinizing hormone (LH) and testosterone were determined by radioimmunoassay in medical students just before (Exp. 1) and after (Exp. 2) an academic examination and corresponding control periods. Before the examination (Exp. 1), the males' LH values were lower than their control levels, but there was no such difference in the females. Testosterone levels were unaffected in both sexes. There was no correlation between the values of LH and testosterone. There was, however, a significant negative correlation in the males, and an almost significant negative correlation in the females, between the preexamination testosterone values and the examination scores achieved. After the examination (Exp. 2), again the LH values were lower than the control values in the males, but not in the females, and the testosterone values were unaffected in both sexes. There was a weak positive correlation between the postexamination LH and testosterone values in the males, but not in the females. The results are in line with earlier observations suggesting that psychological stress is associated with different hormonal effects in males and females.

Lighting conditions affect the levels of plasma gonadotropins differently in old and young castrated male rats.

It has been suggested that the decreased plasma levels of FSH and LH, often found in old male rats, are due to a diminished adenohypophyseal capacity to secrete the hormones and/or by changes in the hypothalamic regulatory system. We studied the effect of varying lighting conditions (12/12 h LD, continuous light and continuous darkness) on the plasma levels of the gonadotropins in castrated young adult and old male rats. We expected the sensitivity of the regulatory system to light to decrease or disappear with aging. The results for FSH supported this hypothesis: the plasma levels of FSH were more stable to changes of lighting conditions in the old rats. In disagreement with our hypothesis, the levels of LH were more sensitive to light changes in old than in young rats. It was concluded that the regulatory systems of the two hormones vary differently with age.

Effects of partial food restriction on nocturnal meal size and feeding speed are counteracted by concurrent REM sleep deprivation in the rat.

Effects of rapid eye movement (REM) sleep deprivation on meal size and feeding speed were investigated by means of the cuff pedestal technique in 9 male rats exposed to partial food restriction. Reduction of available food by 50% alone, when accomplished by providing the pellets at the beginning of each dark period, during 7 consecutive days, induced a quite linear increase both in the meal size and feeding speed. When the same feeding schedule was repeated in combination with REM sleep deprivation, the meal size remained smaller and the feeding time was prolonged (during the first 3-4 days) when compared to those during food restriction alone, although losses of body weight were almost doubled. These findings are in agreement with the effects of REM sleep deprivation on the meal pattern in rats on ad libitum diet and provide further support for the suggestion of the importance of REM sleep in the generation of the light/dark rhythm of feeding in the rat.

Decision-making to initiate voluntary movements in the rat is altered during deprivation of rapid eye movement sleep.

Eight male rats were deprived of rapid eye movement (REM) sleep for 6 days by means of a cuff pedestal which makes it possible to use the animal as its own control. In order to obtain access to food, the rat had to jump from its pedestal to a strip of wire mesh suspended from the ceiling of the deprivation chamber. The number as well as duration of hangings on the wire mesh was continuously recorded. An initial increase in jumping frequency was associated with decreased duration of hangings. This initial effect was totally reversed from the fourth day of deprivation onwards. It is suggested that the threshold in decision making to initiate voluntary movement is altered during the course of REM sleep deprivation.

Food consumption and mouse-killing in Sprague-Dawley rats.

The effects of daily 10-min mouse exposure tests on food consumption were studied in killer and non-killer Sprague-Dawley rats. The results showed both mouse-killers and non-killers significantly to decrease their food consumption when tested daily for mouse-killing. The effect was more pronounced in mouse-killers than in non-killers and the day-to-day individual fluctuation of food consumption was greater in mouse-killers during the mouse confrontation period.

Mouse-killing in Sprague-Dawley rats: effects of lighting conditions.

Sixteen male Sprague-Dawley rats were studied in artificial daylight and in red light for mouse-killing. Fifty percent of the rats killed mice. Killing varied, however, considerably: only seldom did it occur on consecutive days. More killing occurred during tests in red light than in artificial daylight. In red light, the mean latency between confrontation of the rat with the mouse and the killing was gradually shortened but not in daylight.