Trypanosoma cruzi: effects of social stress in Calomys callosus a natural reservoir of infection

Social environment can represent a major source of stress affecting cortisol and/or corticosterone levels, thereby altering the immune response. We have investigated the effects of social isolation on the development of Trypanosoma cruzi infection in female Calomys callosus, a natural reservoir of this protozoan parasite. Animals were divided in groups of five animals each. The animals of one group were kept together in a single cage. In a second group, four females were kept together in a cage with one male. In the final group, five individuals were kept isolated in private cages. The isolated animals showed body weight reduction, decreased numbers of peritoneal macrophages, lower global leucocytes counts, smaller lytic antibody percentage and a significantly higher level of blood parasites compared to the other animals. Their behavior was also altered. They were more aggressive than grouped females, or females exposed to the presence of a male. These results suggest that isolation creates a distinct social behavior in which immunity is impaired and pathogenesis is enhanced.     

Effect of food type on the acute and chronic toxicity of copper to Daphnia magna

SUMMARY. Daphnia magna was maintained on two diets and exposed to acute and chronic copper stresses. Animals fed vitamin-enriched algae were less sensitive to a chronic copper stress than animals fed a trout-granule diet. This conclusion is based on the responses of cohorts as measured by survival, mean brood size and r , the instantaneous rate of population growth. Application factors were also significantly different for animals reared on the two foods (0.47 for algal-fed animals, 0.12 for animals reared on trout-granules). In contrast to chronic toxicity, 72 h LC₅₀ values were not significantly different for animals maintained on the two foods. This suggests that the mechanism of toxic action is different for acute and chronic toxicity and that, if so, the ratio between chronic and acute toxicity would not be a constant under different environmental conditions.     

Effect of group and isolated rearing of white rats on their resistance to exposure to emotional stress]

The influence of isolated vs. group breeding on the sensitivity of higher nervous and vegetative functions to chronic stress effects was studied in 50 albino random-bred male rats. It has been found that group breeding of the animals (ten specimens in each cage) from the 12th to the 30th week of their life enhances their resistance to external stress factors which begin to take effect from the 17th week on. The effect is linked to the positive emotions produced by mutual contacts among the animals and their intensified motor activity. Isolated breeding of the rats (beginning with the 17th week of their life) makes them vulnerable to the action of stress situations. By the end of the investigation they exhibit clear symptoms of an early stage of neurogenic hypertension. The isolation evidently sets up a negative emotional background, reduces drastically the motor activity and lowers the animals resistance to extreme environmental influences.     

Lymphoma development in mice chronically exposed to UMTS-modulated radiofrequency electromagnetic fields

There are public concerns regarding possible carcinogenic or cancer-promoting effects of electromagnetic fields (EMFs) from mobile phones and base stations. The objective of the present study was to investigate whether chronic exposure to EMFs of the UMTS (Universal Mobile Telecommunication System) influences the development of lymphoma in a lymphoma animal model, the AKR/J mouse. Unrestrained mice were chronically sham-exposed (n = 160) or exposed (n = 160) in identical exposure systems (radial waveguides) to a generic UMTS test signal (24 h per day, 7 days per week, 0.4 W/kg SAR). Additionally, 30 animals were kept as cage controls. Animals were checked visually each day and were weighed and palpated weekly to detect swollen lymph nodes. Starting at the age of 6 months, blood samples were taken from the tail every 2 weeks to perform differential leukocyte counts and to measure the hematocrit. Visibly diseased animals or those older than 43 weeks were killed humanely, and tissue slices were examined for metastatic infiltrations and lymphoma type. The study was performed in a blinded way. Cage control animals had a significantly lower growth rate than those kept in the radial waveguides. The number of ill animals, the mean survival time, and the severity code of the disease did not differ between the experimental groups. Therefore, the data show no negative effects from exposure and corroborate earlier findings in AKR/J mice exposed to GSM EMF (Sommer et al., BMC Cancer 4, 77-90, 2004).     

Sources of stress in captivity

Animals housed in artificial habitats are confronted by a wide range of potentially provocative environmental challenges. In this article, we review many of the potential stressors that may adversely affect animals living in captivity. These include abiotic, environmental sources of stress such as artificial lighting, exposure to loud or aversive sound, arousing odors, and uncomfortable temperatures or substrates. In addition, confinement-specific stressors such as restricted movement, reduced retreat space, forced proximity to humans, reduced feeding opportunities, maintenance in abnormal social groups, and other restrictions of behavioral opportunity are considered. Research in support of the claims for these environmental elements as stressors for captive animals reveals no unique suite of behavioral or physiological responses that will clearly indicate the cause of those responses; rather, it is up to us as managers and caretakers of animals in captivity to evaluate enclosures and husbandry practices to ensure the optimal well-being of animals in our care.     

Long-lasting effects of social stress on peritoneal inflammation in some strains of mice

Adult male mice were kept for one week either one or four animals per cage. Some were maintained under the same social conditions for an additional 9 days (controls); their counterparts were either grouped (4 per cage) or isolated (1 per cage). Changes in housing conditions caused a significant increase of plasma corticosterone measured 30 minutes after separation or grouping of SWISS, C57C3H, and BALB/c but not of C57BL/6 mice. Peritoneal inflammation was induced by i.p. zymosan injection on day 9 after changes in housing conditions when corticosterone was again at its initial level in each group. Peritonitis-connected pain symptoms, exudatory PMN numbers, and cytokine (IL-1beta and MPC-1) and corticosterone levels were compared between animals living in stable social conditions with those shifted 9 days earlier from separation to the group or vice versa. These factors were unaffected by social stress in C57BL/6 mice and in SWISS animals transferred from the group to isolation. In all other instances at least two parameters were significantly different in the post-stressed and control animals, being either enhanced or inhibited. In conclusion, social stress had long-term consequences on the course of inflammation in three out of four investigated strains of mice.     

Rehabilitation of research chimpanzees: stress and coping after long-term isolation

We report on the permanent retirement of chimpanzees from biomedical research and on resocialization after long-term social isolation. Our aim was to investigate to what extent behavioral and endocrine measures of stress in deprived laboratory chimpanzees can be improved by a more species-typical social life style. Personality in terms of novelty responses, social dominance after resocialization and hormonal stress susceptibility were affected by the onset of maternal separation of infant chimpanzees and duration of deprivation. Chimpanzees, who were separated from their mothers at a younger age and kept in isolation for more years appeared to be more timid personalities, less socially active, less dominant and more susceptible to stress, as compared to chimpanzees with a less severe deprivation history. However, permanent retirement from biomedical research in combination with therapeutic resocialization maximizing chimpanzees' situation control resulted in reduced fecal cortisol metabolite levels. Our results indicate that chimpanzees can recover from severe social deprivation, and may experience resocialization as less stressful than solitary housing.     

Sublethal stress: Impact of solar UV radiation on protein synthesis in the copepod Acartia tonsa

Aquatic organisms respond to environmental challenges such as thermal stress with the rapid induction of highly conserved polypeptides known as stress proteins or heat shock proteins (Hsps). Solar ultraviolet radiation (UVR, 280-400 nm) is an important environmental stressor in marine ecosystems. Here, we present results of experiments conducted with the marine copepod Acartia tonsa to follow the de novo protein synthesis and measure the level of constitutive and inducible isoforms of the Hsp70 gene family of stress proteins after UV exposure. Animals were collected from Tampa Bay, Florida (USA), and exposed to solar radiation (full spectrum), UV-A (320-400 nm) and PAR (400-700 nm), or PAR only, for periods of 0.5-4 h. Controls were kept in the dark. Protein synthesis was robust under all treatments when the copepods were exposed to low solar radiation intensities. Conversely, high solar radiation intensities (both UV-B and UV-A) caused an overall suppression in the protein synthesis of the copepods with no detectable induction of stress-inducible isoforms of Hsps. Immunochemical assays (western blotting) showed that UVR increased levels (3.5-4-fold increase compared to the dark control) of the constitutively expressed 70 kDa heat-shock (Hsc70) protein in A. tonsa, without indication of inducible isoform upregulation.     

Effects of Isolation on Stress Responses to Novel Stimuli in Subadult Chickens (Gallus gallus)

Extensive research has examined the effects of social isolation in neonatal and adult animal populations, but few studies have examined the effect of social isolation in early adulthood. Animals reaching reproductive age often experience extensive social changes as they leave their natal site, and a social stressor like isolation may uniquely affect this age group. Furthermore, adolescence is a time when sex differences in behavior become more pronounced. As such, the effects of social stressors are likely to vary by sex. In this study, we used noninvasive methods to evaluate stress responses to social change in male and female subadult chickens (Gallus gallus). Half of the birds experienced regular sessions of social isolation over the course of 2 wk, while the other half were never isolated. Subsequently, all of the animals were exposed to a suite of three novel probes, including an open‐field test. We monitored the birds’ behavioral (head movements) and physiological (fecal glucocorticoid metabolites, FGM) response to the tests. Our results indicate that, for subadult chickens, the effect of social isolation is sex dependent: Male FGM and behavioral responses did not change with subsequent experiences, in contrast to females. Females also exhibited more social reinstatement behavior compared to males. Our results are consistent with the expectations of differences between the sexes based on changes in the social environment due to sex‐biased dispersal patterns. For both sexes, the FGM and behavioral responses varied independently, which highlights the necessity for multiple measures of stress in animal populations.     

Social isolation-induced decreases in both the abundance of neuroactive steroids and GABA(A) receptor function in rat brain

The effects of social isolation on behavior, neuroactive steroid concentrations, and GABA(A) receptor function were investigated in rats. Animals isolated for 30 days immediately after weaning exhibited an anxiety-like behavioral profile in the elevated plus-maze and Vogel conflict tests. This behavior was associated with marked decreases in the cerebrocortical, hippocampal, and plasma concentrations of pregnenolone, progesterone, allopregnanolone, and allotetrahydrodeoxycorticosterone compared with those apparent for group-housed rats; in contrast, the plasma concentration of corticosterone was increased in the isolated animals. Acute footshock stress induced greater percentage increases in the cortical concentrations of neuroactive steroids in isolated rats than in group-housed rats. Social isolation also reduced brain GABA(A) receptor function, as evaluated by measuring both GABA-evoked Cl(-) currents in XENOPUS: oocytes expressing the rat receptors and tert-[(35)S]butylbicyclophosphorothionate ([(35)S]TBPS) binding to rat brain membranes. Whereas the amplitude of GABA-induced Cl(-) currents did not differ significantly between group-housed and isolated animals, the potentiation of these currents by diazepam was reduced at cortical or hippocampal GABA(A) receptors from isolated rats compared with that apparent at receptors from group-housed animals. Moreover, the inhibitory effect of ethyl-beta-carboline-3-carboxylate, a negative allosteric modulator of GABA(A) receptors, on these currents was greater at cortical GABA(A) receptors from socially isolated animals than at those from group-housed rats. Finally, social isolation increased the extent of [(35)S]TBPS binding to both cortical and hippocampal membranes. The results further suggest a psychological role for neurosteroids and GABA(A) receptors in the modulation of emotional behavior and mood.     

Survival after pathogen exposure in group‐living insects: don't forget the stress of social isolation!

A major cost of group‐living is its inherent risk of pathogen infection. To limit this risk, many group‐living animals have developed the capability to prophylactically boost their immune system in the presence of group members and/or to mount collective defences against pathogens. These two phenomena, called density‐dependent prophylaxis and social immunity, respectively, are often used to explain why, in group‐living species, individuals survive better in groups than in isolation. However, this survival difference may also reflect an alternative and often overlooked process: a cost of social isolation on individuals’ capability to fight against infections. Here, we disentangled the effects of density‐dependent prophylaxis, social immunity and stress of social isolation on the survival after pathogen exposure in group‐living adults of the European earwig Forficula auricularia. By manipulating the presence of group members both before and after pathogen exposure, we demonstrated that the cost of being isolated after infection, but not the benefits of social immunity or density‐dependent prophylaxis, explained the survival of females. Specifically, females kept constantly in groups or constantly isolated had higher survival rates than females that were first in groups and then isolated after infection. Our results also showed that this cost of social isolation was absent in males and that social isolation did not reduce the survival of noninfected individuals. Overall, this study gives a new perspective on the role of pathogens in social evolution, as it suggests that an apparently nonadaptive, personal immune process may promote the maintenance of group‐living under pathogenic environments.     

Effects of exposure to a 60-kV/m, 60-Hz electric field on the social behavior of baboons.

We found in a previously reported study that exposure to a 30-kV/m, 60-Hz electric field had significant effects on the social behavior of baboons. However, it was not established whether or not the effects were related specifically to the 30-kV/m intensity of the field. A new experiment was conducted to determine whether or not exposure to a 60-Hz electric field at 60 kV/m would produce like changes in the baboons' social behavior. We exposed one group of eight male baboons to an electric field 12 hours a day, 7 days a week, for 6 weeks. A second group of eight animals was maintained under sham-exposure (control) conditions. Rates of performing on each of six categories of social behavior and on four categories of nonsocial behavior were used as criteria for comparing exposed with unexposed subjects and for within-group comparisons during three six-week experimental periods: Pre-Exposure, Exposure, and Post-Exposure. The results indicate that (1) during the exposure period, exposed animals exhibited statistically significant differences from controls in means of performance rates based on several behavioral categories; (2) across all three periods, within-group comparisons revealed that behaviors of exposed baboons were significantly affected by exposure to the electric field; (3) changes in performance levels probably reflect a stress response to the electric field; and (4) the means of response rates of animals exposed at 60 kV/m were higher, but not double, those of animals exposed at 30 kV/m. As in the 30-kV/m experiment, animals exposed at 60 kV/m exhibited significant differences in performances of Passive Affinity, Tension, and Stereotypy. Mean rates of performing these categories were 122% (Passive Affinity), 48% (Tension), and 40% (Stereotypy) higher in the exposed group than in the control group during exposure to the 60-kV/m field.     

Tolerance to morphine induced by chronic mild environmental stressors

Pain-sensitivity as well as the analgesic and thermoregulatory effects of morphine were studied after two different types of chronic environmental stresses in rats (extra stimulation of newborns for 21 days, or social isolation for a month in adult age). The basal pain sensitivity and the base-line body temperature were similarly affected after the two interventions: an increased tail-flick latency, a decreased hot-plate latency and a decreased body temperature were noted. The analgesic and thermoregulatory effects of morphine were uniformly reduced in rats exposed to either stress. These findings suggest a common effect of various non painful mild environmental stresses on the activity of the endogenous opioid system.     

Effect of social isolation on 24-h pattern of stress hormones and leptin in rats

This work analyzes the effect of social isolation of growing male rats on 24-h changes of plasma prolactin, growth hormone, ACTH and leptin, and on plasma and adrenal corticosterone concentrations. At 35 days of life, rats were either individually caged or kept in groups (6-8 animals per cage) under a 12:12 h light/dark schedule (lights on at 08:00 h). A significant arrest of body weight gain regardless of unchanged daily food intake was found in isolated rats after 2 weeks of isolation. On the 4th week, rats were killed at 6 time intervals during a 24-h cycle, beginning at 09:00 h. In isolated rats the 24-h pattern of all parameters tested became distorted, as assessed by Cosinor analysis. When analyzed as a main factor in a factorial analysis of variance, isolation decreased plasma prolactin and growth hormone, increased plasma leptin and corticosterone while decreased adrenal corticosterone. Plasma corticosterone levels correlated significantly with plasma ACTH and with adrenal corticosterone levels in group-caged rats only. These changes can be attributed to an effect of mild stress on the endogenous clock that modulates the circadian hormone release.     

Genetics of behavioural adaptation of livestock to farming conditions

Behavioural adaptation of farm animals to environmental changes contributes to high levels of production under a wide range of farming conditions, from highly controlled indoor systems to harsh outdoor systems. The genetic variation in livestock behaviour is considerable. Animals and genotypes with a larger behavioural capacity for adaptation may cope more readily with varying farming conditions than those with a lower capacity for adaptation. This capacity should be exploited when the aim is to use a limited number of species extensively across the world. The genetics of behavioural traits is understood to some extent, but it is seldom accounted for in breeding programmes. This review summarizes the estimates of genetic parameters for behavioural traits in cattle, pigs, poultry and fish. On the basis of the major studies performed in the last two decades, we focus the review on traits of common interest in the four species. These concern the behavioural responses to both acute and chronic stressors in the physical environment (feed, temperature, etc.) and those in the social environment (other group members, progeny, humans). The genetic strategies used to improve the behavioural capacity for adaptation of animals differ between species. There is a greater emphasis on responses to acute environmental stress in fish and birds, and on responses to chronic social stress in mammals.     

Adolescent vulnerability to cardiovascular consequences of chronic social stress: Immediate and long‐term effects of social isolation during adolescence

It has been demonstrated that disruption of social bonds and perceived isolation (loneliness) are associated with an increased risk of cardiovascular morbidity and mortality. Adolescence is proposed as a period of vulnerability to stress. Nevertheless, the impact of chronic social stress during this ontogenic period in cardiovascular function is poorly understood. Therefore, the purpose of this study was to compare the impact in cardiovascular function of social isolation for 3 weeks in adolescent and adult male rats. Also, the long‐term effects of social isolation during adolescence were investigated longitudinally. Social isolation reduced body weight in adolescent, but not in adult animals. Disruption of social bonds during adolescence increased arterial pressure without affecting heart rate and pulse pressure (PP). Nevertheless, social isolation in adulthood reduced systolic arterial pressure and increased diastolic arterial pressure, which in turn decreased PP without affecting mean arterial pressure. Cardiovascular changes in adolescents, but not adults, were followed by facilitation of both baroreflex sensitivity and vascular reactivity to the vasodilator agent acetylcholine. Vascular responsiveness to either the vasodilator agent sodium nitroprusside or the vasoconstrictor agent phenylephrine was not affected by social isolation. Except for the changes in body weight and baroreflex sensitivity, all alterations evoked by social isolation during adolescence were reversed in adulthood after moving animals from isolated to collective housing. These findings suggest a vulnerability of adolescents to the effects of chronic social isolation in cardiovascular function. However, results indicate minimal cardiovascular consequences in adulthood of disruption of social bonds during adolescence. © 2015 Wiley Periodicals, Inc. Develop Neurobiol 76: 34–46, 2016     

Repeated (isolation) stress increases tribulin-like activity in the rat

1. The effect of repeated isolation stress on MAO inhibitory activity (tribulin) in rat tissues as well as on plasma catecholamine levels was investigated. 2. Animals were subjected to a daily period of isolation (9 min) and sacrificed on days 1, 2, 4, and 5. 3. In brain and cerebellum the levels of both inhibitory activities were found to be significantly higher in animals sacrificed on days 1-2 than in either controls or animals sacrificed on days 4-5. 4. In heart and kidney the highest levels of both activities were found in animals sacrificed on days 4-5. 5. Plasma levels of dopamine on day 4 were significantly higher than those in controls or in any of the experimental groups. Plasma levels of epinephrine showed step-by-step increments from day 1 up to day 5, reaching statistical significance only on day 5. Plasma levels of norepinephrine were significantly increased on days 2, 4, and 5. 6. Under the experimental conditions of this study, we have shown a rapid and short-lasting increment of tribulin in the central nervous system. Its disappearance on days 4-5 could be related to adaptation to the novel situation. Changes in the peripheral tissues appeared later, and a similar adaptation was absent during the period of observation. 7. Tribulin would be related to the stressful situation not only as an anxiety-promoting agent but also in contributing to the maintenance of high levels of circulating catecholamines.     

Effects of alprazolam on the free-choice ethanol consumption induced by isolation stress in aged rats.

Late-onset drinking is a common problem in elderly people related to stress induced by social isolation. Experiments were performed in order to evaluate the effects of alprazolam, a benzodiazepine agonist anxiolytic, on the free-choice ethanol consumption in aged rats subjected to isolation stress. The animals we offered a two-bottle choice consumption (one of 0.2% saccharin and the other with 10% ethanol/0.2% saccharin) and then exposed to 4 days of isolation stress on an irregular, unpredictable schedule. Stress resulted in significant increase in ethanol consumption. Treatment with alprazolam (1 mg/Kg) partially reversed this adverse effect of stress.     

Effect of 50 Hz, 0.2 mT magnetic fields on RBC properties and heart functions of albino rats

In this work the effect of sinusoidal 50 Hz, 0.2 mT magnetic fields on the red blood cells (RBCs) and heart functions of Albino rats were investigated. Twenty-four male Albino rats were equally divided into four groups, A, B, C, and D. Animals from groups B were continuously exposed to the magnetic field for 15 days; and groups C and D, for 30 days. Group A was used as control. Animals from group D were kept after exposure to the magnetic field for a period of 45 days for delayed effect studies. The osmotic fragility and shape of RBCs' membrane and hemoglobin (Hb) structure tests were carried out for all groups. The dielectric relaxation of Hb molecules was measured in the frequency range of 0.1-10 MHz and the dielectric increment (Deltaepsilon), relaxation time (tau), molecular radius (r), and Cole-Cole parameter (alpha) were calculated for all groups. The ECG was measured for all animals before and after exposure to the magnetic field. The results indicated that exposure of the animals to 50 Hz, 0.2 mT magnetic fields resulted in the decrease of RBCs membrane elasticity and permeability and changes in the molecular structure of Hb. The ECG of the exposed animals was considerably altered. The data also indicated that there was no sign of repair in the newly generated RBCs structure and the ECG after removing the animals from the magnetic field, which indicates that the blood generating system was severely injured. The injuries in the heart of the animals were attributed to the loss of some physiological functions of the RBCs as a result of exposures of the rats to the magnetic field.     

Stress-induced adrenal changes and their relation to reproductive failure in captive nine-banded armadillos (Dasypus novemcinctus)

Histological features of adrenal glands from captive and unstressed free-ranging nine-banded armadillos were compared to determine if undefined stress factors associated with captivity were capable of causing changes in adrenal morphology. Animals in captivity less than 3 mo showed histological features identical to unstressed free-ranging animals. Animals in captivity 6 mo or longer, however, showed adrenal changes like those previously described in other mammals exposed to various types of stress, except that there was no accompanying increase in adrenal weight. Similar adrenal changes were found in free-ranging animals exposed to extremely harsh winter weather. Females from both the chronic captive population and this stressed free-ranging population were seen to suffer reproductive failure. Reproductive function in males was not affected. There was no detectable sex difference in gross or histological adrenal changes; however, previous reports indicate there is a sex difference in the secretory product from the adrenals of captive nine-banded armadillos. A possible relationship between reproductive failure in the female and the sex difference in adrenal secretory products is discussed.