Dopamine-beta-hydroxylase activity is necessary for hypothalamo-pituitary-adrenal (HPA) responses to ether, and stress-induced facilitation of subsequent HPA responses to acute ether emerges as HPA responses are inhibited by increasing corticosterone (B)

Sex-biased transcriptomic response of the reproductive axis to stress

Stress is a well-known cause of reproductive dysfunction in many species, including birds, rodents, and humans, though males and females may respond differently. A powerful way to investigate how stress affects reproduction is by examining its effects on a biological system essential for regulating reproduction, the hypothalamic-pituitary-gonadal (HPG) axis. Often this is done by observing how a stressor affects the amount of glucocorticoids, such as cortisol or corticosterone, circulating in the blood and their relationship with a handful of known HPG-producing reproductive hormones, like testosterone and estradiol. Until now, we have lacked a full understanding of how stress affects all genomic activity of the HPG axis and how this might differ between the sexes. We leveraged a highly replicated and sex-balanced experimental approach to test how male and female rock doves (Columba livia) respond to restraint stress at the level of their transcriptome. Females exhibit increased genomic responsiveness to stress at all levels of their HPG axis as compared to males, and these responsive genes are mostly unique to females. Reasons for this may be due to fluctuations in the female endocrine environment over the reproductive cycle and/or their evolutionary history, including parental investment and the potential for maternal effects. Direct links between genome to phenome cause and effect cannot be ascertained at this stage; however, the data we report provide a vital genomic foundation on which sex-specific reproductive dysfunction and adaptation in the face of stress can be further experimentally studied, as well as novel gene targets for genetic intervention and therapy investigations.

The dopamine β-hydroxylase gene in Chinese goose (Anas cygnoides): cloning, characterization, and expression during the reproductive cycle

BACKGROUND

Dopamine β-hydroxylase (DBH) is a critical enzyme in the biosynthesis of catecholamines. This enzyme's role in neuroendocrine regulation is well known, but there are some indications that it may also modulate reproduction and endocrine in mammals and birds. We selected goose (Anas cygnoides) as an ideal model species for investigating the role of DBH in avian reproduction.

RESULTS

Full-length cDNA encoding DBH was cloned from Zhedong goose using reverse transcription PCR and rapid amplification of cDNA ends. The cDNA consisted of a 126-base pair (bp) 5'-untranslated region (UTR), a 379-bp 3'-UTR, and an 1896-bp open reading frame encoding a polypeptide of 631 amino acids. The deduced amino acid sequence of gDBH shared high homology with an analogue from other birds and contained three conserved domains from a mono-oxygenase family including a DOMON domain and two Cu2_mono-oxygen domains. Real-time quantitative PCR analysis showed that gDBH mRNA was expressed in both reproductive and endocrine tissues of Zhedong goose, specifically in the hypothalamus, pituitary, ovary, and oviduct. More DBH mRNA of reproductive and endocrine tissues was detected at ovulation than at oviposition in Zhedong goose. Evidence of opposite trend of gDBH expression was found between the hypothalamus-pituitary and oviduct during the ovulation phase and the broody phase. In addition, we assessed DBH mRNA expression during ovulation in two breeds of geese that differ in egg production. The reproductive and endocrine tissues of Yangzhou geese with higher egg production had more gDBH expression than Zhedong geese. Finally, the five non-synonymous SNP(c.1739 C > T, c.1760G > T, c.1765A > G, c.1792 T > C and c.1861G > C) were identified in the coding region of DBH gene between Zhedong goose and Yangzhou goose.

CONCLUSIONS

We conclude that goose DBH mRNA show obvious periodically variation in reproductive and endocrine tissues during the reproductive cycle in geese.

Differential effects of glucocorticoids on energy homeostasis in Syrian hamsters

Syrian hamsters, like many humans, increase food intake and body adiposity in response to stress. We hypothesized that glucocorticoids (cortisol and corticosterone) mediate these stress-induced effects on energy homeostasis. Because Syrian hamsters are dual secretors of cortisol and corticosterone, differential effects of each glucocorticoid on energy homeostasis were investigated. First, adrenal intact hamsters were injected with varying physiological concentrations of cortisol, corticosterone, or vehicle to emulate our previously published defeat regimens (i.e., 1 injection/day for 5 days). Neither food intake nor body weight was altered following glucocorticoid injections. Therefore, we investigated the effect of sustained glucocorticoid exposure on energy homeostasis. This was accomplished by implanting hamsters with supraphysiological steady-state pellets of cortisol, corticosterone, or cholesterol as a control. Cortisol, but not corticosterone, significantly decreased food intake, body mass, and lean and fat tissue compared with controls. Despite decreases in body mass and adiposity, cortisol significantly increased circulating free fatty acids, triglyceride, cholesterol, and hepatic triglyceride concentrations. Although corticosterone did not induce alterations in any of the aforementioned metabolic end points, Syrian hamsters were responsive to the effects of corticosterone since glucocorticoids both induced thymic involution and decreased adrenal mass. These findings indicate that cortisol is the more potent glucocorticoid in energy homeostasis in Syrian hamsters. However, the data suggest that cortisol alone does not mediate stress-induced increases in food intake or body mass in this species.

Hormonal and psychological factors linked to the increased thermic effect of food in malnourished fasting anorexia nervosa

OBJECTIVES

In patients with anorexia nervosa (AN), weight gain is lower than that expected from the energy content of the meals. Thus we investigated the thermic effect of food (TEF) in relation to subjective feelings and plasma hormone levels in a group of AN patients.

METHODS

TEF, feelings (14 items), and plasma release of beta-endorphin, ACTH, cortisol, dopamine, and catecholamines were evaluated in 15 AN patients (body mass index, 13.6 +/- 1.2 kg.m(-2)) and in 15 healthy women after three gastric loads (0, 300, 700 kcal) infused by a nasogastric tube in a blind design.

RESULTS

In AN, the blind loads induced an energy-dependent increase in TEF (P < 0.001), which was higher than that observed in healthy women (P < 0.001). Only in AN, a load-dependent decline in the high basal plasma level of beta-endorphin (P < 0.01), an increase in plasma ACTH (P < 0.02) after the two caloric loads, and an increase in cortisol, norepinephrine, and dopamine levels after the 700-kcal load only (P < 0.05) were noted. A calorie-dependent (P < 0.001) increase in nausea, abdominal discomfort, and fear of being fat ratings and a decrease in liking to eat (P < 0.001) and body image were observed in AN patients (P < 0.05). TEF correlated with ratings on satiation, nausea, uncomfortable abdominal swelling, body image, and fear of being fat (for all, P < 0.01).

CONCLUSION

In AN women, blindly infused loads induced a dose-dependent increase in TEF, which correlated with the increase in plasma cortisol, ACTH, and catecholamines as in unpleasant sensations, fear of being fat, and anxiety as well as a decline in elevated basal beta-endorphin. These results could explain the difficulty for AN patients in gaining weight.

Stress sensitivity and the development of affective disorders

Depressive disorders are the most common form of mental illness in America, affecting females twice as often as males. The great variability of symptoms and responses to therapeutic treatment emphasize the complex underlying neurobiology of disease onset and progression. Evidence from human and animal studies reveals a vital link between individual stress sensitivity and the predisposition toward mood disorders. While the stress response is essential for maintenance of homeostasis and survival, chronic stress and maladaptive responses to stress insults can lead to depression or other affective disorders. A key factor in the mediation of stress responsivity is the neuropeptide corticotropin-releasing factor (CRF). Studies in animal models of heightened stress sensitivity have illustrated the involvement of CRF downstream neurotransmitter targets, including serotonin and norepinephrine, in the profound neurocircuitry failure that may underlie maladaptive coping strategies. Stress sensitivity may also be a risk factor in affective disorder development susceptibility. As females show an increased stress response and recovery time compared to males, they may be at an increased vulnerability for disease. Therefore, examination of sex differences in CRF and downstream targets may aid in the elucidation of the underlying causes of the increased disease presentation in females. While we continue to make progress in our understanding of mood disorder etiology, we still have miles to go before we sleep. As an encouraging number of new animal models of altered stress sensitivity and negative stress coping strategies have been developed, the future looks extremely promising for the possibility of a new generation of drug targets to be developed.

Effect of adrenalectomy on mating-induced prolactin surges and pseudopregnancy in the female rat

In the estrous female rat, mating stimulation induces an acute surge of prolactin (PRL) within 20 min after mating followed by the onset of twice-daily PRL surges which persist for an 8- to 13-day period of acyclicity called pseudopregnancy. In Experiment 1, we examined whether the release of adrenal hormones after mating modulates mating-induced PRL secretion during the first 38 h after mating. Ovariectomized females were adrenalectomized (Adx) or sham-operated (Sham) and were implanted with jugular vein catheters 2 days later. They were given estrogen and progesterone and mated 6 days after the last surgery until they received 15 intromissions or 15 mounts-without-intromission from a male. Blood samples were collected beginning 20 min before mating at 23:00 h and continuing for 38 h. Plasma PRL concentrations were measured using radioimmunoassay. Mating that included intromissions induced an acute (20-min) PRL response which was higher in Adx than in Sham animals, and advanced in the Adx animals in the onset of the first daily PRL surge to 10:00 h, some 18 h before the surge was observed at 04:00 h in the Sham-mated animals. A small but measurable nocturnal surge was observed in Adx and Sham groups 18-24 h later at 04:00-10:00 h. In Experiment 2, Adx- and Sham-cycling animals received 5 (5I) or 7 (7I) intromissions from a male 12-16 days after surgery. Adx animals receiving 5I showed a significantly higher incidence of pregnancy or pseudopregnancy (%P/PSP) than did Sham 5I animals, while there was no difference in %P/PSP in the 7I groups. We conclude that adrenal gland secretions normally suppress plasma PRL concentrations immediately post-mating and before the onset of the nocturnal mating-induced PRL surge and also inhibit pseudopregnancy when females receive a subthreshold number of intromissions normally required for its induction.

Toluene depresses plasma corticosterone in pregnant rats

Combined exposure to stressors and chemicals may result in synergistic effects. The effects of prenatal exposure to the organic solvent toluene resemble those observed in offspring of gestationally stressed dams, a possible common mechanism being transfer of stress-/toluene-induced increments of corticosteroids from the maternal to the foetal compartment. Pregnant rats were subjected to either 1500 ppm toluene 6 hr/day and/or a schedule of "Chronic mild stress" during the last two weeks of gestation. Exposure to toluene was associated with reduced birth weight and lower maternal weight gain, the latter being enhanced by maternal stress. A depressant effect of toluene on maternal corticosterone was observed, hence the study does not provide immediate evidence that transfer of elevated levels of corticosterone from the maternal to the foetal compartment mediates the effects of prenatal exposure to toluene.

Corticosterone can facilitate as well as inhibit corticotropin-releasing hormone gene expression in the rat hypothalamic paraventricular nucleus

We have used in situ hybridization to investigate how basal levels of circulating corticosterone modulate CRH gene transcription in the neuroendocrine parvicellular part of the hypothalamic paraventricular nucleus (PVHmpd) during sustained hypovolemia. In the absence of the stressor, the accumulation rate of the CRH primary transcript exhibited a dose dependency on low maintained levels of plasma corticosterone similar to that previously reported for the mature messenger RNA (mRNA); levels declined as plasma corticosterone increased. In response to hypovolemia, the absence of corticosterone compromised CRH gene transcription mechanisms to mount the activated response seen in intact animals. However, adrenalectomized rats with low doses of corticosterone (insufficient to normalize thymus weights) showed an augmented mRNA response compared with that in intact animals. When replaced corticosterone normalized thymus weights, the magnitude of the mRNA response was reduced to that seen in intact animals. In contrast to CRH gene regulation, PVHmpd proenkephalin mRNA levels were unaffected by corticosterone concentrations. These results suggest that corticosterone affects CRH gene transcription in the PVHmpd using two mechanisms: first, inhibition, which probably uses type II glucocorticoid receptor-dependent mechanisms and contributes to classic negative feedback; and second, facilitation, which is seen at low plasma concentrations and maintains gene transcription in the presence of sustained stress, possibly using type I mechanisms. This suggests that one reason why adrenal insufficiency severely compromises survival of sustained stress is that CRH gene transcription cannot be maintained without previous exposure to low levels of plasma corticosterone.

Neuroanatomical basis for facilitation of hypothalamic-pituitary-adrenal responses to a novel stressor after chronic stress

Animals exposed to chronic stress exhibit normal or enhanced hypothalamic-pituitary adrenal responses to novel, acute stimuli despite the inhibitory endogenous corticosteroid response to the chronic stressor. Prior stress is thought to induce a central facilitatory trace that, upon exposure to a novel stimulus, balances or overcomes the inhibitory effects of corticosterone. The neuroanatomical basis for this facilitation of hypothalamic pituitary adrenal responses is unknown. In this study, we first show increased adrenocorticotropin and corticosterone responses to the novel stressor of restraint in rats exposed to intermittent cold for seven days. We then compared numbers of Fos-immunoreactive cells in 26 sites in control and chronically stressed rats at various times after onset of a 30 min restraint. At 60 min, density of Fos-stained cells was significantly higher in chronically stressed than in control rats in the parabrachial/Kölliker-Fuse area, posterior paraventricular thalamus, central, basolateral and basomedial nuclei of the amygdala and parvocellular paraventricular hypothalamus. The posterior paraventricular nucleus of the thalamus receives projections from the parabrachial nucleus and projects heavily to the differentially stained subnuclei of the amygdala, which in turn project to the parvocellular paraventricular nucleus of the hypothalamus. We propose that increased activity in the parabrachial-posterior paraventricular thalamus-amygdala-parvocellular paraventricular hypothalamus underlies facilitation of the hypothalamic pituitary-adrenal axis to novel stress in chronically stressed rats. We confirmed part of this proposal by showing that lesions of the posterior paraventricular nucleus of the thalamus increase adrenocorticotropin responses to restraint only in previously chronically stressed animals. This potential circuit provides a basis for further examination of the functional roles of these regions in stress-induced facilitation of hypothalamic pituitary-adrenal activity.