Joanne Weinberg

Iron deficiency during early development in the rat: behavioral and physiological consequences.

Abstract An iron deficient diet regimen from birth through 28 to 30 days of age produced animals with decreases levels of brain non-heme iron as well as decreased brain weight and hematocrit. Weight gain was also somewhat slower. In contrast, brain levels of cytochrome c were not reduced. During subsequent testing iron deficient animals were less responsive than controls in a mildly aversive novel situation (the open field), and ambulated less in an exploratory task (the hole-board). Iron deficient males also exhibited longer response latencies when first exposed to the passive avoidance platform, but following shock, iron deficient animals of both sexes exhibited longer reentry latencies. Measurement of plasma levels of corticosterone indicated that although iron deficient animals had elevated basal levels of corticoids, they exhibited a smaller stress increment than controls when exposed to the combined stress of ether and cardiac puncture. Data from the three behavioral tasks taken together with the pituitary-adrenal response to ether and cardiac puncture suggest that iron deficiency may reduce an animals general responsiveness to environmental stimuli.

Psychobiology of Coping in Animals: The Effects of Predictability

The term stress had a common usage in everyday life as well as in biology and medicine long before Hans Selye’s initial report in 1936. However, the development of the stress field as a popular and important area of research can generally be traced to Selye’s concept of the “general adaptation syndrome” (Selye, 1936). Selye was surprised to find that a variety of very different agents such as cold, heat, x-rays, hormones, bacteria, toxins or muscular exercise produced essentially the same triad of symptoms. This was true despite the fact that a highly specific adaptive response existed for any one of these agents by itself. The triad of symptoms included (1) adrenal cortical hypertrophy (indicative of increased adrenocortical activity); (2) involution or shrinkage of the thymus, spleen, lymph nodes and all other lymphatic structures; (3) gastrointestinal ulceration. These symptoms were named the “alarm reaction” and were thought to represent a nonspecific adaptive response of the body. This nonspecific demand upon the body, according to Selye, was the essence of stress (Selye, 1973).

Long-term consequences of early iron deficiency in the rat.

A period of severe early iron deficiency (birth to 28 days of age) produced a persistent deficit (22%) in brain non-heme iron in adult rehabilitated animals. Long-term effects on behavior and physiological responsiveness were also observed. Although rehabilitated and control animals did not differ either in basal levels of plasma corticosterone or in the time course of the stress response following ether and cardiac puncture, possible differences in pituitary-adrenal responsiveness appeared to emerge following testing in an exploratory task. In addition, significant differences between rehabilitated and control animals were observed in both active and passive avoidance learning. Rehabilitated males made more intertrial responses than control males during active avoidance learning, and rehabilitated animals of both sexes performed better (i.e. showed longer reentry latencies) in a passive avoidance situation. It was suggested that shock may differentially affect motivation or arousal in rehabilitated and control animals.

Early handling effects on neophobia and conditioned taste aversion

Abstract The purpose of this study was to determine whether early handling, a manipulation which affects both behavioral and pituitary-adrenal responsiveness to novel and aversive situations, will affect responses in adult rats confronted with novel substances (neophobia) or with substances associated with illness (conditioned taste aversion). We found that (1) early handling reduces the neophobia shown by adult animals and that handled animals appear better able to distinguish between a preferred and a nonpreferred substance. (2) Handling reduces the magnitude of the initial taste aversion and also increases the rate of recovery of drinking to pretoxicosis levels. (3) These behavioral differences between handled and nonhandled animals are not due to differential pituitary-adrenal responses to LiCl. (4) Early handling does affect the conditioned elevation of plasma corticoids upon reexposure to milk under a Forced Extinction procedure. In this situation nonhandled animals show greater corticoid elevations than handled animals. (5) Manipulation of the number of exposures to a substance prior to pairing that substance with LiCl affects the magnitude of both the aversion and the elevation of plasma corticoids which are produced upon reexposure. As number of preexposures increase, both the magnitude of the aversion and the elevation of corticoids decrease.

Inhibition of pituitary-adrenal activity as a consequence of consummatory behavior

Abstract (1) We have demonstrated that if food and water are restricted to the morning hours, the circadian rhythms of the pituitary-adrenal system are re-entrained and the levels of plasma corticosteroids are elevated in the morning, whereas they are usually low during that period in the rodent. Following drinking, however, there is, within 5 min, a sharp decline in plasma corticoids accompanied by an equivalent drop in ACTH. Thus, in addition to the regulation of ACTH by the usual feedback of circulating corticosteroids, there appears to be an independent central nervous system inhibitory mechanism which can cause ACTH and corticosteroids to drop concomitantly. (2) We demonstrated that the availability of a consummatory response can reduce an organisms pituitary-adrenal response to a normally stressful situation. (a) When exposed to novelty, animals usually show a striking elevation of plasma corticosterone. However, if a consummatory response-drinking-is available in the novel environment, the response to this novel environment is markedly reduced. (b) The availability of an adjunct behavior-drinking-in a situation where animals are placed on an intermittent food reinforcement schedule also causes a significant reduction in plasma corticosterone levels. (c) Shock-induced fighting results in a reduced ACTH response to shock. Fighting behavior can also be viewed as a consummatory response. (3) We believe these experiments demonstrate the bidirectionality of the pituitary-adrenal system. Since the pituitary-adrenal system appears to provide a sensitive measure of arousal state, and since consummatory responses suppress the activity of this system, it therefore appears that consummatory behavior has arousal-reducing properties.

Shock-induced fighting attenuates the effects of prior shock experience in rats.

Abstract We compared the responses of animals exposed singly to inescapable shock with those of animals exposed to the same shock in pairs and thus able to fight in response to shock. During the shock sessions animals shocked in pairs showed a reduced ACTH response when compared with animals shocked individually, and the reduction in ACTH was not dependent on the amount of fighting which occurred. In addition, if animals had previous opportunities to fight, the response to shock was still attenuated even when the partner was no longer present. When subsequently tested in a novel task it was observed that fighters, like controls, showed a reduced pituitary-adrenal response to novelty when a consummatory response was available. Singly shocked animals, however, exhibited elevated levels of plasma corticosterone whether or not they could drink in the novel chamber. We hypothesized that fighting is a consummatory response, and that the reinforcement provided by performance of this consummatory response reduced the ACTH response to shock and permanently altered subsequent responsiveness.

Sex differences in biobehavioral responses to conflict in a taste aversion paradigm

A conditioned aversion to a novel milk solution was produced, and animals were then reexposed to milk while nondeprived (low conflict) or following a 72-hr food and water deprivation regimen (high conflict). No sex differences occurred if animals were nondeprived throughout testing. However, if deprived during the interval between conditioning and reexposure, sex differences in both behavior and adrenocortical responses occurred: (1) Presession corticoid levels of females were higher than those of males. (2) On the first reexposure day, females showed a suppression of plasma corticosterone below presession levels, while males maintained elevated or increased corticosterone levels. (3) On the second reexposure day, when no longer deprived, males showed a marked suppression of intake compared to females, and females subsequently recovered to pretoxicosis intake levels faster than males. (4) Gonadectomy eliminated these sex differences. While ovariectomized females continued to resemble intact females in both behavioral and hormonal responses, castrated males exhibited a corticoid suppression on the first reexposure day, and subsequently recovered to pretoxicosis intake levels at the same rate as females.

Long-term effects of early iron deficiency on consummatory behavior in the rat.

Two experiments were designed to investigate the effects of early iron deficiency on consummatory behavior in the adult rat. In experiment 1, animals were placed in a novel chamber, either with or without water available. Although there were no effects of iron deficiency per se, the data suggested that decreased caloric intake experienced early in life may have different long-term consequences for males and females. While ad lib control males, and females in all diet conditions, exhibited less elevation of plasma corticosterone when water was available in the novel chamber, calorically restricted males appeared unable to use the cues or reinforcement provided by consummatory behavior to reduce arousal. In Experiment 2, a conditioned taste aversion situation involving conflict, we were able to separate effects due to early iron deficiency from those due to early caloric restriction. When reexposed to milk, calorically restricted (weight control) males exhibited an attenuated plasma corticoid response, compared to that of ad lib control males, while weight control females resembled ad lib control females in their response. Thus, as in Experiment 1, early caloric restriction affected males more than females. Early iron deficiency, however, markedly altered pituitary-adrenal responsiveness in both males and females. Not only was the response to reexposure completely reversed in rehabilitated males and females, but also, the corticoid response to deprivation was increased in rehabilitated males and decreased in rehabilitated females. Taken together with previous data, these results suggest that early iron deficiency alters both behavioral and physiological arousal or responsiveness, and may do so differentially in males than females.

Early handling effects on the intake of novel substances: differential behavioral and adrenocortical responses.

Behavioral and pituitary-adrenal responses were examined in handled and nonhandled female rats after consumption of two novel solutions. Half the animals received a sucrose solution first and a saline solution second, while for the other half the order of presentation was reversed. Behavioral differences were observed during consumption of the sucrose solution. That is, while handled and nonhandled animals drank similar amounts of saline, handled animals drank significantly more of the sucrose solution than nonhandled animals. In contrast, differences in pituitary-adrenal activity were observed following consumption of the saline solution, and the pattern of response depended upon the animals early handling treatment, the solution presented, and the order of presentation. It was concluded that simultaneous measures of behavioral and physiological indices are necessary to indicate subtleties in responsiveness which would not be evident from measurement on one index alone.