J. Balasch

Response of anterior pituitary hormones to chronic stress. The specificity of adaptation.

The effect of chronic noise stress on the response of anterior pituitary hormones to the same or to another stressor (forced swimming) was studied in adult male Wistar rats. Both acute stressors increased corticosterone, prolactin, LH and TSH secretion and inhibited GH secretion. Previous chronic exposure to noise reduced corticosterone response to the same stimulus without modifying corticosterone response to a novel acute stress. Neither prolactin nor TSH responses to acute noise were reduced by previous chronic exposure to noise. Since chronic noise increased basal levels of LH and decreased those of GH, the response of these hormones to acute stress was expressed as percent changes of their respective basal values. It was found that chronically stressed rats showed diminished LH response to noise but not to forced swimming. GH showed the same pattern without reaching statistical significance. These data indicate that the response of some anterior pituitary hormones can adapt after repeated exposure to the same stressor. When adaptation occurred, this was specific for the stressor which the animals were repeatedly exposed to. The pituitary-adrenal axis appears to be the most reliable index of adaptation to chronic stress among all the anterior pituitary endocrine axes.

Dissociation between adrenocorticotropin and corticosterone responses to restraint after previous chronic exposure to stress

The effect on emotional reactivity produced by a model for chronic stress in which different types of acute stresses were randomly combined for 29 days was studied in adult male rats. Chronically stressed rats showed a slight decrease in body weight gain and an increase in relative adrenal weight. Chronic stress did not modify defecation rate but reduced exploratory activity in the holeboard. Neither basal nor acute-stress induced levels of adrenocorticotropin (ACTH) were modified by previous chronic stress. Likewise, basal corticosterone levels were similar in both groups. However, corticosterone response to acute restraint stress was higher in chronically stressed than in control rats. The mechanisms underlying the dissociation between ACTH and corticosterone as well as its possible implications are discussed.

Sensitivity of corticosterone and some metabolic variables to graded levels of low intensity stresses in adult male rats

Adult male rats were subjected to different acute stressors, whose intensity was gradually increased, and their corticosterone, glucose, and serum lipid levels were studied. Serum corticosterone was sensitive to graded levels of stress intensities. Glucose followed the same trend. However, serum lipid responses were not related to the intensity of stress. Our results indicate that these latter variables were not sensitive indices of the emotional arousal elicited by brief stress stimuli.

Influence of various acute stressors on the activity of adult male rats in a holeboard and in the forced swim test

The effects of various acute stressors on the activity of adult male rats in a holeboard and in the forced swim test were studied. When tested immediately or 24 h after 1 h exposure to noise, restraint in tubes or tail shock, no changes in either defecation rate or activity in the holeboard were observed. In contrast, immediately after 1 h immobilization in wood-boards, a reduction of the number of areas crossed and the number of head-dips was found. The inhibitory effect of immobilization on head-dips persisted 24 h later. The behavior of the rats in the forced swim test was classified into three categories: struggling, mild swim and immobility. The changes in behavior were critically dependent on the type of stressor, and more specifically on its intensity, that was evaluated with three different physiological parameters (serum prolactin, corticosterone and glucose levels). Thus, if tested immediately after stress, noise did not alter the response of the rats, restraint in tubes and tail shock-reduced immobility, and the latter stressor increased mild swim. In the second experiment, immobilization in wood-boards reduced struggling. Twenty-four hours after stress, noise, restraint in tubes or tail shock were without effect, but immobilized rats showed increased immobility and reduced mild swim activity. The present data clearly indicate that behavior of rats in a holeboard and in a forced swim situation are not related, and that acute stress could have a differential effect on the various categories of behavior in a forced swim situation.

Adaptation of anterior pituitary hormones to chronic noise stress in male rats.

We have studied the effects of acute and chronic noise on serum levels of pituitary hormones in male Wistar rats. Acute noise increased serum levels of corticosterone, prolactin, and luteinizing hormone and decreased serum GH. FSH was unaffected by this stressor. Chronic noise did not modify basal levels of any hormone studied, however responsiveness of some hormones to the same stimuli was altered. Reduced corticosterone, prolactin, and GH responses to noise was observed after previous chronic exposure to this stimuli. LH response followed the same pattern although it did not reach statistical significance. It might be concluded that adaptation to a repeated stress stimulus is not confined to the pituitary-adrenal axis, however, the degree of adaptation could vary between different hormones.

Effect of Crowding on Emotional Reactivity in Male Rats

The effect of two different population densities (3 and 9 animals/cage) on emotional reactivity, measured by their performance in an exploratory box, and pituitary-adrenal response to acute noise stress are compared. The crowded rats showed a higher defecation rate and lower exploratory activity than the control rats. Adrenocorticotropin (ACTH) response to noise was higher in the crowded than in the control rats. The results clearly indicate that crowding increased emotional reactivity in adult male rats.

Effect of crowding on some physiological and behavioral variables in adult male rats

The effect of two population densities on body weight gain, food and water intake and the weight of some organs and glands was studied in adult male rats. Behavioral reactivity to open field was also assessed. Crowded rats (10 animals per cage) showed lower body weight gain than control rats (3 per cage) throughout all the experimental period. Crowding decreased food intake and increased water intake. Any effect of crowding on the weight of thymus, liver and endocrine glands (except testes) was found. Open field defecation and activity were the same in control and crowded rats. Discrepancies from earlier works could likely be due to methodological differences and these are discussed in the text.

Effect of Acute and Chronic Psychogenic Stress on Corticoadrenal and Pituitary-Thyroid Hormones in Male Rats

The effects of acute and chronic stress on serum corticosterone and pituitary-thyroid hormones were studied in male Wistar rats. Acute noise activated both the pituitary-adrenal and pituitary-thyroid axes. Chronic noise did not modify the basal serum levels of either corticosterone or pituitary-thyroid hormones. A decreased corticosterone response to noise was observed in chronically stressed rats, but the pituitary-thyroid response was the same in control and chronically stressed rats, suggesting that the mechanisms which control the responsiveness of both axes to a repeated stimulus are dissociated.

Chronic noise stress and insulin secretion in male rats

The effect of chronic noise, followed by acute noise and forced swimming, on basal glucose and insulin levels was studied in adult male rats. Chronic noise did not modify basal levels of either measured variable before or after the exposure of rats to acute stress. Acute noise decreased serum glucose and insulin levels, although hypoglycemia was transient. Forced swimming decreased insulin and increased glucose levels. Our results indicate that: serum insulin levels were sensitive to both physiological and psychological stresses, forced swimming caused more marked glucose and insulin responses than noise exposure, chronic intermittent noise did not alter pancreatic function, and no sign of adaptation was apparent after repeated exposure to noise.

The effect of conspecifics on corticoadrenal response of rats to a novel environment

The effect of housing conditions and the presence of a conspecific on corticoadrenal response to a novel environment was studied in male Sprague-Dawley rats. The response to a novel environment was the same in rats housed in groups and rats housed alone for 20 days before testing, suggesting that isolation during adulthood did not affect corticoadrenal response to a novel environment. The presence of a nonfamiliar rat (proceeding from another home cage) did not modify corticoadrenal response to the novel environment but the presence of a rat proceeding from the same home cage induced a higher corticoadrenal response to this stressful stimuli. These results can be explained considering that rats exhibit greater emotional reactivity, as measured by adrenal function, in situations which combine familiar (the other rat) and novel (the box) elements than those completely unfamiliar.