Different responsiveness of spleen lymphocytes from two lines of psychogenetically selected rats (Roman high and low avoidance)

Individual differences in inflammatory and oxidative mechanisms of stress-related mood disorders

Emotional stress leads to the development of peripheral disorders and is recognized as a modifiable risk factor for psychiatric disorders, particularly depression and anxiety. However, not all individuals develop the negative consequences of emotional stress due to different stress coping strategies and resilience to stressful stimuli. In this review, we discuss individual differences in coping styles and the potential mechanisms that contribute to individual vulnerability to stress, such as parameters of the immune system and oxidative state. Initial differences in inflammatory and oxidative processes determine resistance to stress and stress-related disorders via the alteration of neurotransmitter content in the brain and biological fluids. Differences in coping styles may serve as possible predictors of resistance to stress and stress-related disorders, even before stressful conditions. The investigation of natural variabilities in stress resilience may allow the development of new methods for preventive medicine and the personalized treatment of stress-related conditions.

Coping style and immunity in animals: making sense of individual variation

Predicting the individual vulnerability to immune mediated disease is one of the main challenges of modern biomedical research. However, the question of individual behavioral and physiological characteristics that might predict this vulnerability has been subject of research and debate for a long time. This paper will argue that animal models aimed at individual vulnerability should consider the biological function of variation in nature. An increasing number of studies show the ecological significance of variation within a species. Based on behavioral studies in several vertebrate species two coping style can be distinguished. Variation in coping style appears to play a role in the population dynamics and the evolutionary fitness of the species. Coping styles are reflected in a stable differentiation in the behavioral and physiological stress responsiveness over time and across situations. Based on the observations that the individual level of offensive aggressive behavior (i.e., the tendency to defend the home territory) is strongly related to the way animals react to various other environmental challenges, it is argued that the individual's level of offensiveness is an important indicator and component of a more trait-like behavioral and physiological response pattern (coping style) to environmental demands. The coping style of aggressive animals is principally aimed at a (pro)active prevention or manipulation of a stressor whereas the non-aggressive individuals tend to passively accept or react to it. Proactive coping is associated with high sympathetic reactivity to stressors whereas the more passive or reactive coping style generally has a higher HPA axis reactivity. In view of the immune modulating nature of these major neuroendocrine stress systems, one might expect that coping styles will be reflected in a differential vulnerability to immune mediated disease as well. Indeed, several studies have demonstrated such a relationship, indicating that the functional variation in coping style and related neuroendocrine stress reactivity, as it occurs in nature, might be a good standard for studies aimed at understanding individual vulnerability. This is in agreement with more recent views that also in humans stress reactivity may be the best predictor for the individual vulnerability to immune mediated diseases. This asks for a more fundamental and translational approach of individual disease vulnerability based on a common biological basis of individual differentiation in behavior and physiology in humans and animals.

Immunological characteristics of Hatano high-and low-avoidance rats

Hatano high- and low-avoidance (HAA and LAA) rats have been genetically selected on the basis of their two-way active avoidance behavior, and have been shown to differ in other behavioral and hormonal parameters. Since close interconnections among the nervous, endocrine and immune systems have been well documented, these two strains might possess differences in aspects of immunological action. In Experiment 1, plasma levels of IgG, IgM, complement 3 (C3), classical pathway hemolytic complement (CH50) and beta(2)-microglobulin were compared between males of the two strains at 5 and 24 weeks of age. Plasma levels of IgG and CH50 were lower in LAA than HAA rats at 5 weeks of age, whereas those differences disappeared at 24 weeks of age. There were no differences between the two strains in plasma levels of IgM, C3 and beta(2)-microglobulin. In Experiment 2, antibody production to sheep red blood cells (SRBC) and mitogen-induced lymphocyte proliferation were compared between 12-week-old males of the two strains. Antibody responses in the PFC assay, plasma anti-SRBC-IgM levels and spleen weights were higher in LAA than HAA rats. LPS-induced lymphocyte proliferation was greater in LAA than HAA rats. It was concluded that HAA rats show earlier development of immunological development, but that antibody production and mitotic response of B lymphocytes may be more pronounced in adult LAA than HAA rats. The strain differences observed in the immunological response may indicate the usefulness of using Hatano rats in studies of behavioral-immunological relationships.

Reduced splenic natural killer cell activity in rats with a hyperreactive dopaminergic system

Interactions between the nervous system and the immune system have been recognized as important regulatory processes in determining the activity of the immune response. We have previously shown that rats, which differ in the reactivity of the dopaminergic system (APO-SUS and APO-UNSUS rats), also differ in experimental metastasis formation and in susceptibility to autoimmunity. APO-SUS rats have a high response to administration of apomorphine and can be characterized as hyperdopaminergic, whereas their APO-UNSUS counterparts show low susceptibility to apomorphine and have a hypodopaminergic phenotype. In this study we investigated whether the decreased experimental metastasis formation of APO-SUS rats compared to APO-UNSUS rats is associated with higher natural killer cell activity in APO-SUS rats. Surprisingly, splenic NK cell activity of hyperdopaminergic APO-SUS female as well as male rats is significantly lower than NK cell activity of their hypodopaminergic APO-UNSUS counterparts. The reduced splenic NK activity of female APO-SUS rats is associated with lower percentages of NK cells in the spleen cell population. In contrast, male APO-SUS and APO-UNSUS rats show similar numbers of NK cells in the spleen. There was no difference in plasma dopamine levels between APO-SUS and APO-UNSUS rats and i.p. treatment of rats with the dopaminergic agonist quinpirole did not alter NK cell activity. In conclusion, our data demonstrate that differences in the reactivity of the dopaminergic system are associated with differences in splenic NK cell activity. Moreover, our data demonstrate that in this model lower splenic NK cell activity is not related to increased experimental lung metastasis formation.

The decade 1989-1998 in Spanish psychology: an analysis of research in psychobiology

In this paper, we present an analysis of the research published during the 1989-1998 decade by tenured Spanish faculty members from the area of psychobiology. Database search and direct correspondence with the 110 faculty members rendered a list of 904 psychobiological papers. Classification and analysis of these papers led to the definition of at least 70 different research trends. Topics are grouped into several specific research areas: Learning and Memory; Development and Neural Plasticity; Emotion and Stress; Ethology; Neuropsychology; Sensory Processing; and Psychopharmacology. The international dissemination of this research, published in journals of high impact index, and the increasing number of papers are two noteworthy features.

Coping styles in animals: current status in behavior and stress-physiology

This paper summarizes the current views on coping styles as a useful concept in understanding individual adaptive capacity and vulnerability to stress-related disease. Studies in feral populations indicate the existence of a proactive and a reactive coping style. These coping styles seem to play a role in the population ecology of the species. Despite domestication, genetic selection and inbreeding, the same coping styles can, to some extent, also be observed in laboratory and farm animals. Coping styles are characterized by consistent behavioral and neuroendocrine characteristics, some of which seem to be causally linked to each other. Evidence is accumulating that the two coping styles might explain a differential vulnerability to stress mediated disease due to the differential adaptive value of the two coping styles and the accompanying neuroendocrine differentiation.

Differences in NK cell function in mice bred for high and low aggression: genetic linkage between complex behavioral and immunological traits?

In previous studies, we found differences in cellular immune responsiveness in Institute for Cancer Research (ICR) mice selectively bred for high and low levels of aggression. Compared to the high aggressive line, the low aggressive line had low levels of natural killer (NK) and T cell activity and increased susceptibility to tumor development. To dissect further this novel association, experiments were designed to test two competing hypotheses. The first hypothesis was that the phenotypic expression of the line differences in NK cell activity are dependent on and regulated by the expression of high and low levels aggressive behavior in the lines. The alternative hypothesis was that the differences in immune status are independent of the expression of aggression by the lines, suggesting linkage between a subset of genes involved in determining these complex behavioral and immunological traits or pleiotropic gene effects on both traits. In Experiment 1, three conditions of postweaning social experience (mice singly housed, group housed within line, or group housed between lines) were tested in males to determine whether experiential conditions which modify the expression of aggression would in turn modify the line differences in NK cell activity. This experiment revealed that the difference in NK cell activity between high aggressive and low aggressive male mice was attributable to line only. The different postweaning social conditions examined had no effect on modifying the differences in NK activity, and social dominance hierarchy did not correlate with levels of NK cell activity. Whereas males of the high and low lines exhibit differences in aggressive behaviors across most contexts, females do not exhibit such differences except in response to an intruder during the postpartum period. Therefore, in Experiment 2 we compared the NK cell activity of nulliparous females of the high and low aggressive lines. Under these conditions, females of the low aggressive line had low levels of NK activity compared to high aggressive females (differences comparable to those seen between males of the high and low lines). Taken together, these experiments lend support to the hypothesis that this association may be due to a genetic linkage between subsets of genes involved in determining these complex behavioral and immunological traits, or may possibly represent a fortuitous association which occurred during the selective breeding.

A genetic basis for neuroendocrine-immune interactions

Psychoneuroimmunology is an exciting, complex field that elucidates interactions among the nervous, endocrine, and immune systems. The contribution of psychosocial factors and behavioral processes to these interactions has been the focus of numerous studies designed to investigate the intricate pathways that are involved in the "mind-body connection." In addition, the effects of this connection on the development and progression of various disease conditions are of considerable interest. Although efforts have been made to identify the cellular and molecular mechanisms underlying these relationships, the impact of genetic makeup on the communication among these systems has yet to be fully realized. The development of sophisticated genetic analytical methods and gene mapping techniques now provide the "tools" to determine the influence of genetics on behavior-neuroendocrine-immune interactions--an area of study that may represent the next frontier in psychoneuroimmunology.

Differences of nu/+ and nu/nu mice in some behaviors reflecting temperament traits

The goal of this paper is to discover a pattern of consistent behavioral differences between athymic CD1 nu/nu mice and euthymic CD1 nu/+ ones. The following behaviors, thought to be correlates of temperament traits, were measured along 3 trials: ambulation, rear, and defecation in two open fields of varying light intensity, interaction time with a conspecific, and variables in the light-darkness test (time in the lit compartment, latency to leave the dark compartment, and number of crossings between compartments). Besides, weight and (IgM and IgG) antibodies to rat erythrocytes were measured. Relative to nu/nu mice, nu/+ mice were heavier, yielded much higher antibody responses, interacted more with a conspecific (the males, but not the females), and ambulated slightly more in the open fields, although the proportion of variance in the behaviors accounted for by the nude mutation was small (< 20%). Therefore, the nude mutation participated in the expression of the activity or extraversion traits.

Genetic analysis of the relationships between behavioral and neuroendocrine traits in Roman High and Low Avoidance rat lines

In order to determine whether the coselection observed between the selection trait (active avoidance behavior) of the Roman High Avoidance (RHA) and Roman Low Avoidance (RLA) rat lines and their neuroendocrine characteristics were genetically determined, we analyzed, in nonsegregating (RHA, RLA, and F1) and segregating (F2 and the two backcrosses) crosses, the inheritance pattern and the phenotypic correlations among behavioral (shuttle-box behavior), physiological (body, adrenal, and thymus weights), and neuroendocrine (corticosterone and prolactin reactivity, catecholamine enzyme activities) variables. Physiological characteristics and enzyme activities have a crucial role in sex dissociation. Avoidance behavior and prolactin reactivity to novel environment remained associated in segregating crosses despite gene rearrangement. They represented the most important variables to differentiate the Roman lines, perhaps sharing a common regulatory mechanism under genetic control.

Maturation of the behavioral and neuroendocrine differences between the Roman rat lines

The behavioral and/or neuroendocrine reactivity to psychological (open-field exposure) and physiological (CRF challenge) stimulations, as well as adrenal tyrosine hydroxylase (TH) and phenylethanolamine N-methyl transferase (PNMT) activities were measured, at different ages, in the Roman high avoidance (RHA) and Roman low avoidance (RLA) rat lines that have been genetically selected on the basis of their divergent active avoidance behavior. The highest locomotor activity in the open field, associated to blunted prolactin and renin reactivity to an emotional stress and lower specific TH and PNMT activities, characterized the RHA rats of all ages. HPA axis reactivity to psychological and/or physiological stimulations was identical in young animals (14 weeks old) of the two lines. Nevertheless, it displayed with age maturation processes, since the amplitude of postopen-field secretion peak for ACTH was larger in RLA rats from 20 weeks on, the response to CRF being not increased until 42 weeks. These maturation processes could result from genetically influenced changes related to environmental stimulations. Therefore, the Roman lines may be an excellent model to study the interactions between the genetic and developmental factors controlling the coupling between both behavioral and neuroendocrine functions.

Antibody response and some behaviors as differential traits between two inbred strains of mice (C57BL/6 and BALB/c)

The goals of this research were to find out if the antibody response and some behaviors are differential traits for murine strains C57BL/6 and BALB/c and to study the influence of strain and isolation on both behavior and the antibody response. 21 C57BL/6 male mice and 28 BALB/c male mice were used; of those, 11 C57BL/6 and 16 BALB/c were kept isolated, and the remaining mice were housed 2 per cage. The tests were Open-fields 1, 2, and 3 (of varying light and sound stimulation), holeboard, light-darkness test, immunization with rat erythrocytes; in addition, the mice were weighed. The traits that best differentiated both strains (according to discriminant analysis) were weight, IgM primary response, and emotional behavior (ambulation, rearing, and defecation in stimulating open-fields). Social isolation (of adult mice) influenced emotional behavior, but not the antibody response.

Prolactin as a link between behavioral and immune differences between the Roman rat lines

Roman high (RHA)- and low (RLA)-avoidance rats are two lines of Wistar rats genetically selected on the basis of their active avoidance behavior in a shuttle-box. They also differ in several other behavioral responses, such as their locomotor activity in novel environments (open-field, circular corridor), with the RHA rats being more active than the RLA animals, as well as in endocrine reactivity and immune functions. These experiments were designed to investigate further the neuroendocrine characteristics of these animals as a possible link between the brain and immune functions. Despite the marked behavioral and immune differences observed, no between-lines variation could be found in basal hypothalamo-pituitary-adrenocortical axis activity or in its responses to different protocols of novel environment stress, or after corticotropin-releasing factor (CRF) challenge. On the other hand, stimulated prolactin levels were higher in the low avoidance line. These results exclude the pituitary-adrenocortical axis and suggest prolactin as a link between behavioral and immune differences between the Roman lines. Moreover, these results indicate that these rats may be an excellent model for the study of the relationships between the brain and the immune system.

Behavioral factors in stress-induced immunomodulation

Individual differences in the exploratory response to novelty were found to be related with the vulnerability to develop stress-induced immunological alterations. We studied the effect of exposure to inescapable shock on antibody formation against sheep red blood cells (SRBC) in rats selected according to their locomotor activity in a novel situation. Interestingly, antibody titers were only enhanced in shocked animals with the highest locomotor activity. These results emphasize the importance of taking into account individual differences for the study of the mechanisms involved in stress-induced immunomodulation, suggesting a behavioral procedure (novelty reactions) to deal with individual variability in the effects of stress on the immune system.

Behavioral, neuroendocrine, and immunological outcomes of escapable or inescapable shocks

The present study was designed to evaluate the effects of repeated exposure to escapable or inescapable shocks on subsequent behavior in an activity cage, and on the reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis and the immune system. We also studied the possible influence of behavioral factors on the behavioral and physiological impact of stress. Although exposure to different stressful situations pointed out marked differential effects in subsequent behavior, it failed to elicit differences in the neuroendocrine and immunological parameters studied. However, interesting results were found in analyzing the influence of behavioral factors. The degree of control exerted over the shock was inversely related to ACTH and corticosterone levels. In addition, individual differences in the exploratory activity to novelty were correlated with poststress lymphoproliferation and antibody formation. These data indicate that the behavioral and physiological outcomes of stress depend on the interrelations between environmental and individual factors (including both preexisting individual differences and the coping responses during stress).

Prolonged increase of corticosterone secretion by chronic social stress does not necessarily impair immune functions

The influence of a chronic social stress upon immunity was investigated in Wistar rats, submitted for four weeks to two different behavioral situations, balanced in a factorial design: housing with three females and membership rotation. The combination of these two factor led to adrenal enlargement (43.3%), thymus involution (39.5%) and increased basal corticosterone levels, all indices of activation of the hypothalamic-hypophysis-adrenal axis. However, neither natural killer cell activity, splenocyte reactivity to mitogen nor the rate of spontaneous development of antibodies against Mycoplasma pulmonis, a common pathogen of the respiratory tract, were changed in the endocrine activated animals. Analysis of the data on kinetics of stress at 1, 7 and 28 days after the initial mixing of the animals gave the same results. These data question the immunosuppressant activity usually conferred to corticosteroids, at least when adrenal hyperactivity is induced by chronic environmental stressors.