Alan I. Leshner

Dominance status and adrenocortical reactivity to stress in squirrel monkeys (Saimiri sciureus)

Squirrel monkeys (Saimiri sciureus, Iquitos) were exposed to a sequence of three stresses: A live snake, ether anesthesia, and physical restraint. Plasma cortisol concentrations were determined both following each stress exposure and before and after the sequence of stresses. Dominant males demonstrated lower unstressed plasma cortisol levels than subordinates. Although the form of the relationship between adrenal activity and social dominance differs for the types of stress, dominant animals always show the greatest adrenal reactivity to stress.

A simple method for carcass analysis

Abstract A relatively simple and rapid carcass analysis technique is described. First, water content is determined by drying the whole carcass. The dried carcass is then ground to a powder and the fat content is determined using an ether extraction method. The protein content is determined on the fat extracted material using a modification of the Biuret method. In this way, three separate methods are combined to provide an accurate but simple and rapid method for carcass water, fat and protein determinations. The usefulness of this method for behavioral studies involving large numbers of animals is discussed.

The effects of gonadectomy on the sex differences in dietary self-selection patterns and carcass compositions of rats.

Abstract The relationship of dietary self-selection patterns and carcass composition was studied in intact and gonadectomized male and female rats. Males consumed a significantly greater proportion of their diets as protein and had a greater proportion of their carcasses as fat than females. Gonadectomy increased the percentage protein selected by females to the level of intact males and altered the proportions of the carcass tissues to the levels of these males. The results were discussed in terms of the regulatory consequences of varying nutritional intake patterns and the role of female sex hormones in the regulation of body weight and composition.

Hormonal control of submissiveness in mice: Irrelevance of the androgens and relevance of the pituitary-adrenal hormones ☆

Abstract Two experiments were conducted to begin to determine the role of endocrine factors in the control of submissiveness in mice. Experiment 1 examined the effects of castration and showed no effects of reducing androgen levels on the readiness to surrender following attack by an opponent. Experiment 2 examined the effects of manipulating the levels of the pituitary-adrenocortical hormones. This study showed, first, that increasing the level of these hormones increases submissiveness, and, second, that the critical pituitary-adrenal hormone in the control of this agonistic characteristic is corticosterone. These studies, in combination with earlier studies of hormones and aggression, suggest that different hormones are involved in the control of different classes of agonistic responses.

Pituitary adrenocortical activity and intermale aggressiveness in isolated mice

Abstract Three experiments were conducted to clarify the role of the hormones of the pituitary adrenocortical axis in the control of intermale aggressiveness in mice. The first experiment tested the possibility that adrenalectomy decreases aggressiveness through decreasing androgen levels by treating adrenalectomized mice with testosterone propionate. None of the dosages of testosterone used in this study were effective in restoring the aggressiveness of adrenalectomized mice. The second and third experiments examined whether manipulations of pituitary adrenocortical activity affect aggressiveness because of changes in ACTH levels or because of changes in circulating glucocorticoid levels. In the second experiment, dexamethasone treatment restored the aggressiveness of adrenalectomized mice; and in the third experiment, ACTH decreased the aggressiveness of both intact mice and mice with controlled levels of corticosterone and/or testosterone. These findings suggest that ACTH levels, rather than glucocorticoid levels, are the critical parameters in the control of aggressiveness by the hormones of the pituitary adrenocortical axis and that ACTH affects aggressiveness independently of its effects on either adrenocortical or gonadal activity.

Dietary self-selection by pregnant and lactating rats ☆

Abstract Protein-carbohydrate choice was studied in female rats through the course of the estrus cycle and during pregnancy and lactation. Both selecting and control diet fed animals grew at the same rates. Food intake was reduced during the estrus phase, but there were no changes in the dietary selection pattern. During both pregnancy and lactation protein intake was increased while carbohydrate intake was maintained at a level equal to nonimpregnated controls. These data were interpreted as supporting other studies showing that dietary self-selection follows the varying nutritional requirements of the organism.

Effects of corticosterone on submissiveness in mice: Some temporal and theoretical considerations☆

Abstract Two experiments were conducted to examine directly the effects of corticosterone on submissiveness in mice. A repeated testing paradigm was used in both of these studies, in order to begin to identify whether corticosterones effects on submissiveness are of the “baseline” or the “feedback” variety. Experiment 1 examined the dose-response relationship between levels of corticosterone administered over a three week period and levels of submissiveness. This study showed that only a very high dosage (350 μg/day) increased submissiveness during an initial test, but that lower dosages increased submissiveness during a second submission test. Thus, the combination of corticosterone treatment and a prior experience of defeat is a more powerful facilitator of submissiveness than is either a prior defeat alone or corticosterone treatment alone. Experiment 2 examined the effects on submissiveness of a single treatment with corticosterone either before an initial test, before a second submission test, before both tests, or before neither test. This study showed that corticosterone did not affect submissiveness during the test which followed its application, but corticosterone treatment before the first test did increase submissiveness as measured during the second test. Thus, again, coupling corticosterone treatment with an initial experience of defeat increased future submissiveness. The findings of these two experiments show, first, that the duration of corticosterone treatment is not important to its effects on submissiveness. Second, these findings suggest that corticosterone affects submissiveness in what has been called a feedback way and may not operate at all on submissiveness in a baseline way.

Menstrual cycle status and adrenocortical reactivity to pyschological stress

Women either using or not using oral contraceptives were exposed to the psychological stress of self-evaluation at the premenstrual or midcycle phase. Baseline cortisol levels were established for the midcycle phase prior to testing using the microfluorometric technique. A stress-inducing behavioral test was given after which the 60 subjects rated their affective state on a 7-point scale for depressed, confused, embarrassed, confident, cheerful, anxious, excitable, and apathetic. Following this task, a blood sample was collected. Subjects taking oral contraceptives had significantly higher baseline cortisol levels. Changes in cortisol levels as a function of the test were analyzed as a percent difference score. Analysis of variance showed a significant (p less than .05) interaction of the main variables. Subjects tested premenstrually and not taking oral contraceptives responded to the task with a significantly greater increase in cortisol levels than those subjects in other groups, which did not differ from each other. The subjects reports of their affective responses to the task did not differ as a function of either menstrual cycle status or oral contraceptive use.

Pituitary-adrenal effects on avoidance-of-attack in mice: separation of the effects of ACTH and corticosterone.

Abstract Two experiments were conducted to separate the effects of ACTH and corticosterone on avoidance-of-attack. In Experiment 1, treatment with corticosterone restored the avoidance performance of hypophysectomized mice to normal levels. In Experiment 2, ACTH treatment increased the avoidance retention of intact mice but did not affect the avoidance responding of mice which were adrenalectomized and treated with a replacement dosage of corticosterone (controlled-corticosterone condition). These two studies suggest that corticosterone is the critical hormone of the pituitary-adrenal axis in the control of avoidance responding in agonistic situations. In addition, these studies demonstrate that (1) ACTH and corticosterone affect avoidance-of-attack differently from the way they have been shown to affect avoidance responding in shock-mediated situations, and (2) different hormones of the pituitary-adrenal axis are involved in the control of aggressiveness and avoidance-of-attack.

Endocrine effects of grouping and dominance rank in squirrel monkeys

Abstract Urinary 17-hydroxycorticosteroids (17-OHCS), total catecholamines and 17-ketosteroids (17-KS) were determined for two groups of squirrel monkeys. One group had been colonized for four years and the other group had lived in isolation for three years. Compared to the isolated animals, the colonized monkeys showed elevated 17-OHCS but unchanged catecholamine and 17-KS levels. In the colonized group the dominant animals had the highest 17-OHCS levels and the lowest catecholamine levels, while the subordinate animals showed lower 17-OHCS levels and elevated catecholamine levels. 17-KS levels were related to dominance rank by a J-shaped function. The data are interpreted as showing that high levels of adrenocortical output are necessary for the maintenance of the group of behaviors that result in a high position in the dominance order. It is suggested that the results of this study on primates were contrary to the results of most studies on rodentia because these orders use different behavioral methods to determine dominance relationships.