Mammalian behavior and the adrenal cortex. A review

Adrenocortical Expression Profiling of Cattle with Distinct Juvenile Temperament Types

Temperament affects ease of handling, animal welfare, and economically important production traits in cattle. The use of gene expression profiles as molecular traits provides a novel means of gaining insight into behavioural genetics. In this study, differences in adrenocortical expression profiles between 60 F₂ cows (Charolais × German Holstein) of distinct temperament types were analysed. The cows were assessed in a novel-human test at an age of 90 days. Most of the adrenal cortex transcripts which were differentially expressed (FDR <0.05) were found between temperament types of 'fearful/neophobic-alert' and all other temperament types. These transcripts belong to several biological functions like NRF2-mediated oxidative stress response, Glucocorticoid Receptor Signalling and Complement System. Overall, the present study provides new insight into transcriptional differences in the adrenal cortex between cows of distinct temperament types. Genetic regulations of such molecular traits facilitate uncovering positional and functional gene candidates for temperament type in cattle.

NGF, brain and behavioral plasticity

Nerve Growth Factor (NGF) was initially studied for its role as a key player in the regulation of peripheral innervations. However, the successive finding of its release in the bloodstream of male mice following aggressive encounters and its presence in the central nervous system led to the hypothesis that variations in brain NGF levels, caused by psychosocial stressor, and the related alterations in emotionality, could be functional to the development of proper strategies to cope with the stressor itself and thus to survive. Years later this vision is still relevant, and the body of evidence on the role of NGF has been strengthened and expanded from trophic factor playing a role in brain growth and differentiation to a much more complex messenger, involved in psychoneuroendocrine plasticity.

A standardized protocol for repeated social defeat stress in mice

A major impediment to novel drug development has been the paucity of animal models that accurately reflect symptoms of affective disorders. In animal models, prolonged social stress has proven to be useful in understanding the molecular mechanisms underlying affective-like disorders. When considering experimental approaches for studying depression, social defeat stress, in particular, has been shown to have excellent etiological, predictive, discriminative and face validity. Described here is a protocol whereby C57BL/6J mice that are repeatedly subjected to bouts of social defeat by a larger and aggressive CD-1 mouse results in the development of a clear depressive-like syndrome, characterized by enduring deficits in social interactions. Specifically, the protocol consists of three important stages, beginning with the selection of aggressive CD-1 mice, followed by agonistic social confrontations between the CD-1 and C57BL/6J mice, and concluding with the confirmation of social avoidance in subordinate C57BL/6J mice. The automated detection of social avoidance allows a marked increase in throughput, reproducibility and quantitative analysis. This protocol is highly adaptable, but in its most common form it requires 3-4 weeks for completion.

Functional role of Calcium-stimulated adenylyl cyclase 8 in adaptations to psychological stressors in the mouse: implications for mood disorders

The Ca(2+)/calmodulin stimulated adenylyl cylcase 8 (AC8) is a pure Ca(2+) sensor, catalyzing the conversion of ATP to cAMP, with a critical role in neuronal plasticity. A role for AC8 in modulating complex behavioral outcomes has been demonstrated in AC8 knock out (KO) mouse models in which anxiety-like responses were differentially modulated following repeated stress experiences, suggesting an involvement of AC8 in stress adaptation and mood disorders. To further investigate the role of this enzyme in phenotypes relevant for psychiatric conditions, AC8 KO mice were assessed for baseline behavioral and hormonal parameters, responses to repeated restraint stress experience, and long-term effects of chronic social defeat stress. The lack of AC8 conferred a hyperactive-phenotype both in home-cage behaviors and the forced swim test response as well as lower leptin plasma levels and adrenal hypertrophy. AC8 KO mice showed baseline "anxiety" levels similar to wild type littermates in a variety of procedures, but displayed decreased anxiety-like responses following repeated restraint stress. This increased stress resilience was not seen during the chronic social defeat procedure. AC8 KO did not differ from wild type mice in response to social stress; similar alterations in body weight, food intake and increased social avoidance were found in all defeated subjects. Altogether these results support a complex role of cAMP signaling pathways confirming the involvement of AC8 in the modulation of stress responses. Furthermore, the hyperactivity and the increased risk taking behavior observed in AC8 KO mice could be related to a manic-like behavioral phenotype that warrants further investigation.

Social stress, therapeutics and drug abuse: preclinical models of escalated and depressed intake

The impact of ostensibly aversive social stresses on triggering, amplifying and prolonging intensely rewarding drug taking is an apparent contradiction in need of resolution. Social stress encompasses various types of significant life events ranging from maternal separation stress, brief episodes of social confrontations in adolescence and adulthood, to continuous subordination stress, each with its own behavioral and physiological profile. The neural circuit comprising the VTA-accumbens-PFC-amygdala is activated by brief episodes of social stress, which is critical for the DA-mediated behavioral sensitization and increased stimulant consumption. A second neural circuit comprising the raphe-PFC-hippocampus is activated by continuous subordination stress and other types of uncontrollable stress. In terms of the development of therapeutics, brief maternal separation stress has proven useful in characterizing compounds acting on subtypes of GABA, glutamate, serotonin and opioid receptors with anxiolytic potential. While large increases in alcohol and cocaine intake during adulthood have been seen after prolonged maternal separation experiences during the first two weeks of rodent life, these effects may be modulated by additional yet to be identified factors. Brief episodes of defeat stress can engender behavioral sensitization that is relevant to escalated and prolonged self-administration of stimulants and possibly opioids, whereas continuous subordination stress leads to anhedonia-like effects. Understanding the intracellular cascade of events for the transition from episodic to continuous social stress in infancy and adulthood may provide insight into the modulation of basic reward processes that are critical for addictive and affective disorders.

Environmental pollutant Aroclor 1242 (PCB) disrupts reproduction in adult male rhesus monkeys (Macaca mulatta)

Adult male rhesus monkeys (Macaca mulatta) were given oral treatment of either Aroclor 1242 or vehicle (corn oil and glycerol) at a dose of 200 microg/kg body wt/day for 6 months to investigate the effects of the pollutant on plasma testosterone and the morphology of testes and accessory glands. Aroclor 1242 treatment significantly decreased testicular size and testosterone levels in plasma and adversely affected spermatogenic activity by disrupting epithelial organization. All components of the germinal epithelium were greatly reduced. The spermatogonia were either hypertrophied or had shrunken vesiculated cytoplasm with distorted mitochondria and nuclear pyknosis. Changes were milder in the Sertoli cells, where nuclear infoldings were reduced. Characteristic features of treated Leydig cells were the presence of electron-dense and electron-opaque zones, appearing as plaques, cell membrane abnormalities, and high variability in nuclear shape and heterochromatin distribution. All the Aroclor 1242-treated accessory glands contained more connective tissue than their vehicle-treated counterparts. The epithelium contained many layers of irregularly shaped necrotic cells possessing stereocilia in the epididymides, either hypochromic and hypertrophied or hyperchromic and hypotrophied cells in the prostate and shrunken cuboidal cells with elongated nuclei in the seminal vesicles. In conclusion, Aroclor 1242 treatment causes severe structural alterations on gonads and accessory organs in adult male rhesus monkeys, and these effects could be mediated through both estrogen and Ah receptors.

Prenatal corticosterone treatment induces long-term changes in spontaneous and apomorphine-mediated motor activity in male and female rats

The potential influence of glucocorticoids on fetal brain development was investigated after corticosterone administration via pellets to pregnant rats during the last trimester of gestation. We examined both spontaneous motor activity and dopamine-mediated motor responses to apomorphine, a D1, D2 and D3 receptor agonist, given at a postsynaptic dose (1 mg/kg, s.c.) to both prepubertal and adult male and female offspring. Prenatal corticosterone was found to produce the following alterations in the offspring. (1) Prepubertal stage: Male offspring: a statistically significant (P < 0.05) increase was observed in spontaneous rearing, motility and locomotion (activity measured during the first 30 min) without changes in apomorphine-induced motor responses. Female offspring: a reduction (P < 0.05) only in spontaneous rearing activity was observed during the exploratory phase (activity measured during the first 10 min) without significant changes in apomorphine-induced motor responses. (2) Adult stage: Male offspring: the exploratory activity to the novel environment was increased (P < 0.05) without significant changes in apomorphine-induced motor activity. Female offspring: an increase (P < 0.05) in spontaneous locomotion was observed during the first 30 min of testing without significant changes in exploratory activity to the novel environment. However, the apomorphine-induced motility and locomotion were reduced (P < 0.05) during the first 30 min. These observations indicate that prenatal corticosterone induces both short-term and long-term changes in spontaneous motor activity as well as long-lasting alterations in dopamine receptor response in the motor network mechanisms controlled by DA receptors. These changes are in part age and sex-dependent. The possible relationship between prenatal programming of the mesolimbic and nigrostriatal dopaminergic pathways by corticosterone and the observed changes in motor function is discussed.

Prenatal corticosterone increases spontaneous and d-amphetamine induced locomotor activity and brain dopamine metabolism in prepubertal male and female rats

Recently, both glucocorticoid receptor immunoreactivity and glucocorticoid receptor messenger RNA levels were found in multiple brain areas, especially in the neuroepithelium during the late prenatal development of the rat brain. To better understand the potential influence of stress on fetal brain development by release of maternal adrenocortical steroids, we have investigated the effects of corticosterone administration to pregnant rats on the locomotor activity of their prepubertal offspring. On day 16 of pregnancy female rats were implanted with either placebo or corticosterone pellets (release of 2.4 mg/day for seven days). After birth their offspring were nursed by foster mothers to avoid any postnatal effects of the corticosterone pellets. At three weeks of age, the offspring were tested for spontaneous motor behaviours. Both male and female offspring from corticosterone treated mothers showed significantly increased spontaneous ambulation, motility and rearing compared to placebo treated groups. No significant sex differences were found in locomotor activity between male and female offspring from placebo groups. Following d-amphetamine (1.5 mg/kg) treatment, a preferential dopamine releasing agent, we observed a significant increase in ambulation, motility and rearing activity in the male offspring treated with corticosterone. In the female offspring, only the rearing activity was significantly higher after d-amphetamine treatment in the prenatal corticosterone group compared with the placebo treated group. Basal dopamine metabolism (dihydroxyphenylacetic acid/dopamine ratio) was increased in the dorsal striatum and ventral striatum of male and female offspring from corticosterone-treated dams. In the male offspring, corticosterone treatment was associated with a disappearance of the right side dominance of dopamine metabolism in the dorsal striatum.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of anxiety in subordinate male mice sexual behavior

Dominant and subordinate male mice behave differently when exposed to a female, with subordinates showing impairment of their sexual performance in the presence of the male antagonist. In the present study, we investigate whether these rank-related behavioral differences can be modified by an anxiolytic treatment. In a first experiment, diazepam (0.25 mg/kg) improves the performance of subordinate mice toward the female, as shown by the increase of proxemic behavior, anogenital sniffing, and social grooming of the female. Social grooming of the female is the only behavior modified by a higher dose of the anxiolytic drug (0.5 mg/kg). A second experiment, in which dominant and isolated mice are subjected to the same experimental procedure, demonstrates that social behavior of these two classes of males is not affected by the pharmacological treatment. The results are discussed in terms of the advantages of using subordinate males in such a sexual context as a model for the study of anxiolytic drugs.

Female-female interactions and social stress in prairie voles

Trios of prairie voles (Microtus ochrogaster) composed of either two estrous sibling or nonsibling females and one male were monitored via time-lapse videotaping over 72 hr. Social and sexual behaviors were analyzed as a function of trio type (sibling or nonsibling) and fate (survivor or nonsurvivor) across 12-h time blocks. Within nonsibling trios, females that were able to maintain prolonged physical contact with the male within the first 3 days of trio formation later survived and successfully produced litters; females that did not maintain male contact later died of undetermined causes, presumably related to social stress. Frequencies of sexual behavior were similar in both trio types and both surviving and nonsurviving females received equivalent amounts of copulatory stimulation from the male. Sibling groups exhibited higher levels of female-female side-by-side contact; nonsibling groups exhibited greater amounts of female-initiated anogenital sniffing, and female-initiated aggression. Female-female social interactions may be determined by prior familiarity and/or relatedness and may play a dominant role in determining the social organization and mating system of this species.

Corticosterone and prolactin responses to predictable and unpredictable novelty stress in rats

Prolactin along with corticosterone is a stress responsive hormone. The present study examined the effect of predictable and unpredictable psychological stress on corticosterone and prolactin secretion. Repeated unpredictable exposure to the novelty cage produced a more substantial increase in the level of corticosterone than predictable exposure to the same novelty apparatus. In contrast, predictable novelty stress induced a more substantial elevation in prolactin levels than unpredictable stress. Furthermore, it was observed that both corticosterone and prolactin returned to control levels 30 minutes after the fifth exposure to the novelty cage. It was concluded that the pattern of exposure to novelty is an important paradigm which effects the magnitude of hormonal responding. An important relationship between corticosterone release and prolactin secretion is also indicated.

[3H]corticosterone binding in the caudate-putamen

Autoradiographic data indicate little specific binding of corticosterone in the caudate-putamen. However, chronic glucocorticoid treatment has been reported to alter certain biochemical parameters within the caudate-putamen, including high-affinity choline uptake. We asked whether glucocorticoid receptors in the caudate-putamen of adrenalectomized rats could be detected by a biochemical approach. We determined the amount of specific [3H]corticosterone binding in cytosols from the caudate-putamen and the ability of nuclei in this brain region to retain [3H]corticosterone in vivo. Results indicated that 72 h post-adrenalectomy, the caudate-putamen has 56% of the maximal binding capacity of the hippocampus (205 +/- 11 vs 361 +/- 19 fmol/mg protein). The apparent Kd of [3H]corticosterone in the two tissues did not differ substantially. The cytosolic binding capacity of the caudate-putamen was similar to that of the cerebellum, a brain region which also fails to demonstrate marked retention of glucocorticoids in autoradiographic studies. When cytosol binding was measured at a shorter time period after adrenalectomy (12 h), no differences were observed between the binding capacities of the hippocampus and the caudate-putamen. In competition experiments using [3H]corticosterone as ligand, no differences between the caudate-putamen and the hippocampus were found in the relative affinities of any of 8 steroids; the order of relative affinities obtained was in good agreement with those reported for the classical glucocorticoid receptor in other tissues. Rats were injected via the tail vein with [3H]corticosterone, 36 nmol/kg, an amount calculated to saturate more than half the nuclear sites.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of the parental environment on sexual maturation in male mice

Experiments were designed to examine the influence of either one or both parents on the sexual maturation of male mice. A pregnant female and an adult vasectomized male were housed together and, at delivery, the litter was reduced to 6 pups, 3 of each sex. After weaning, mother, foster-father or both, stayed in cohabitation with their pups until sacrifice. The results showed that: (1) the permanent presence of one or both parents did not affect either testicular growth or the age at first fertile matings. (2) in maturing males (30-40 days), seminal vesicle growth was accelerated by the presence of the mother, inhibited by the presence of the foster-father. (3) in maturing males, the presence of one or both parents lowered plasma testosterone levels. On the opposite, in 90-day-old males, the same conditions increased testosterone levels. These results indicate that only the endocrine function of the testis is affected by the parental environment. The effects are age-dependent.

Acute influences of some ACTH-related peptides of fighting and adrenocortical activity in male laboratory mice

A number of corticotrophin preparations when given acutely enhanced fighting behavior, an event which may be consequent upon elevation of circulating corticosterone. A series of short ACTH analogues (ACTH 11-24, ACTH 4-10) had slight influences on circulating plasma corticosterone values and on fighting behavior. However, 20 microgram ACTH 1-10 given 12 hr before testing did increase fighting C.F. controls. As this compound only caused a slight stimulation of plasma corticosterone titers, the possibility exists of an extra-adrenal influence. One cannot, it appears, eliminate glucocorticoid influences using these preparations in the mouse. Acutely, ACTH 1-24 had virtually no influences on Animex-assessed motor activity but did enhance fighting in castrated mice maintained with either androgen or estrogen. It is tentatively concluded that the ACTH influences on aggression in the mouse are partially mediated via glucocorticoid influences on the CNS combined with an extra adrenal influence of part of the ACTH molecule. A possible reason for the differing acute and chronic influences of ACTH on fighting in mice is presented.

Theoretical review: a model of hormones and agonistic behavior

A model of the interaction between endocrine function and agonistic responding was developed that incorporates three specific hypotheses about the relationship between hormones and agonistic behavior: (1) The baseline hormonal state of the organism contributes to the determination of whether, in what way, and how intensely the animal will react when it is exposed to appropriate environmental stimuli. (2) One function of the hormonal responses to environmental stimulation and behavioral experiences is to modify the continuing and future behavior of the individual in the same or similar situations. (3) Another function of these hormonal responses is to modify the individual's stimulus qualities so that other individuals' agonistic reactions to it will be modified. The data on hormones and agonistic behavior were reviewed in the context of this model, and some directions for future research were proposed.

Effects of adrenalectomy on rhythmic and non-rhythmic aggressive behavior in the male golden hamster

Male golden hamsters, adrenalectomized and maintained by subcutaneous implants od deoxycorticosterone-acetate (adx-DOCA), show a loss of the nocturnal rhythm in aggression seen in sham operated (sham-op) animals. A similar loss of the nocturnal aggression rhythm is evident in hamsters adrenalectomized and implanted with separate pellets of DOCA and cortisol-acetate (adx-DOCA-cortisol). However, while Adx-DOCA animals do not differ from sham-op animals in the level of aggression summed over all tests (overall aggression), the overall aggression levels of the adx-DOCA-cortisol animals are significantly higher than the levels of either the adx-DOCA or sham-op animals. Nocturnal rhythms in locomotor activity persist in all three groups. It is suggested that circadian rhythms of the pituitary-adrenocoritcal axis are important for the expression of the aggression rhythm. A possible mechanism of action is discussed.

Adrenal response of male mice to variations in living space

CFW and CF 1 male mice were weaned, isolated for 7 days, then randomly assigned to one of three cage sizes for an additional 7 days. There was a significant increase in adrenal weights for males of both strains after exposure to the smallest living space. A significant decrease in final body weights occurred after housing CFW males in medium size cages and CFW and CF 1 males in small cages. The possible influence of spatial parameters on the endocrine stress response of populations of high density is discussed.