Development of the HPA axis: where and when do sex differences manifest?

Sex differences in the synergistic effect of prior binge drinking and traumatic stress on subsequent ethanol intake and neurochemical responses in adult C57BL/6J mice

Alcohol-use disorders (AUDs) are characterized by repeated episodes of binge drinking. Based on reports that exposure to predator odor stress (PS) consistently increases ethanol intake, the present studies examined whether prior binge drinking differentially altered responsivity to PS and subsequent ethanol intake in male and female mice, when compared to mice without prior binge exposure. Initial studies in naïve male and female C57BL/6J mice confirmed that 30-min exposure to dirty rat bedding significantly increased plasma corticosterone (CORT) levels and anxiety-related behavior, justifying the use of dirty rat bedding as PS in the subsequent drinking studies. Next, separate groups of male and female C57BL/6J mice received seven binge ethanol sessions (binge) or drank water (controls), followed by a 1-month period of abstinence. Then, 2-bottle choice ethanol intake (10% or 10E vs. water, 23 h/day) was measured in lickometer chambers for 4 weeks. After baseline intake stabilized, exposure to intermittent PS (2×/week × 2 weeks) significantly enhanced ethanol intake after the 2nd PS in male, but not female, binge mice vs. baseline and vs. the increase in controls. However, in a subgroup of females (with low baselines), PS produced a similar increase in 10E intake in control and binge mice vs. baseline. Analysis of lick behavior determined that the enhanced 10E intake in binge male mice and in the female low baseline subgroup was associated with a significant increase in 10E bout frequency and 10E licks throughout the circadian dark phase. Thus, PS significantly increased 10E intake and had a synergistic interaction with prior binge drinking in males, whereas PS produced a similar significant increase in 10E intake in the low baseline subgroup of binge and control females. Plasma CORT levels were increased significantly in both binge and control animals after PS. CORT levels at 24-h withdrawal from daily 10E intake were highest in the groups with elevated 10E licks (i.e., binge males and control females). At 24-h withdrawal, protein levels of GABAA receptor α1 subunit, corticotropin releasing factor receptor 1, and glucocorticoid receptor in prefrontal cortex (PFC) and hippocampus (HC) were differentially altered in the male and female mice vs. levels in separate groups of age-matched naïve mice, with more changes in HC than in PFC and in females than in males. Importantly, the sexually divergent changes in protein levels in PFC and HC add to evidence for sex differences in the neurochemical systems influenced by stress and binge drinking, and argue for sex-specific pharmacological strategies to treat AUD.

Chronic Stress in Children and Adolescents: A Review of Biomarkers for Use in Pediatric Research

PROBLEM

Incorporating biomarkers of chronic stress into pediatric research studies may help to explicate the links between exposure to adversity and lifelong health, but there are currently very few parameters to guide nurse researchers in choosing appropriate biomarkers of chronic stress for use in research with children and adolescents.

METHODS

Biomarkers of chronic stress are described, including primary mediators (glucocorticoids, catecholamines, and cytokines) and secondary outcomes (neurologic, immune, metabolic, cardiovascular, respiratory, and anthropometric) of the chronic stress response.

RESULTS

Evidence of the use of each biomarker in pediatric research studies is reviewed. Recommendations for pediatric researchers, including selection of appropriate biomarkers, measurement considerations, potential moderators, and future directions for research, are presented.

DISCUSSION

A wide range of biomarkers is available for use in research studies with children. While primary mediators of chronic stress have been frequently measured in studies of children, measurement of secondary outcomes, particularly immune and metabolic biomarkers, has been limited. With thoughtful and theoretically based approaches to selection and measurement, these biomarkers present an important opportunity to further explore the physiologic pathways linking exposure to chronic stress with later health and disease.

CONCLUSION

The incorporation of chronic stress biomarkers into pediatric research studies may provide valuable insight into the mechanisms through which stressful environments "get under the skin" and ultimately inform efforts to promote health and reduce inequities among children exposed to adversity.

Chronic stress from adolescence to aging in the prefrontal cortex: A neuroimmune perspective

The development of the organism is a critical variable which influences the magnitude, duration, and reversibility of the effects of chronic stress. Such factors are relevant to the prefrontal cortex (PFC), as this brain region is the last to mature, the first to decline, and is highly stress-sensitive. Therefore, this review will examine the intersection between the nervous system and immune system at glutamatergic synapses in the PFC across three developmental periods: adolescence, adulthood, and aging. Glutamatergic synapses are tightly juxtaposed with microglia and astrocytes, and each of these cell types exhibits their own developmental trajectory. Not only does chronic stress differentially impact each of these cell types across development, but chronic stress also alters intercellular communication within this quad-partite synapse. These observations suggest that developmental shifts in both neural and immune function across neurons, microglia, and astrocytes mediate shifting effects of chronic stress on glutamatergic transmission.

Seasonal changes in plasma testosterone and cortisol suggest an androgen mediated regulation of the pituitary adrenal axis in the Tarabul's gerbil Gerbillus tarabuli (Thomas, 1902)

In the desert gerbil Gerbillus tarabuli (Thomas, 1902), cortisol is the main glucocorticosteroid produced by the adrenal glands. Plasma cortisol concentrations show highest values when testosterone is reduced and lowest values during the breeding season which occurs from early winter to late spring. In order to specify the implication of testicular androgens in these corticosteroid seasonal variations we investigated the effects induced by gonadectomy performed during the breeding season on the pituitary adrenal axis. The animals collected in winter were assessed into three groups: sham-operated (Controls; n=13), gonadectomised (GDX; n=13) and testosterone replaced gonadectomised (GDX+T; n=13). Physiological replacement of testosterone enanthate (75µg/100gb.w./twice daily) was applied during one week, while GDX group received the vehicle (40µL sesame oil) alone. The right adrenal glands removed from euthanized animals were fixed for histomorphometry and androgen receptors (ARs) immunohistochemistry and the left ones were frozen with plasma samples until hormonal assays. Gonadectomy induces the enlargement of the adrenal cortex essentially due to that of zonae fasciculata (ZF) and reticularis (ZR) and perimedullary connective tissue which is abundant in the gerbil adrenals. The ARs immunostaining present at both cytoplasmic and nucleus level, is enhanced intensely in the ZR and moderately in the ZF and zona glomerulosa (ZG) cells. GDX group shows reduced plasma ACTH concentration (p=0.0126) by 61% despite the increase in cortisol concentration occurring both in plasma (+216%; p=0.0436) and adrenal tissue (+117%; p=0.0348). Plasma aldosterone is also enhanced significantly (p=0.0147) by 189% but androstenedione synthesis increased in adrenal tissue (p=0.0459) by 65% instead a decrease at circulatory level (p=0.0355) by 58% due to lack of testicular origin. So, testosterone deprivation activates corticosteroidogenesis also evidenced by the adrenal structure changes and the gonadectomy-induced increase in the plasma cholesterol. All of the gonadectomy-induced responses are reversible after physiological testosterone replacement. We conclude that the assessment of circulating adrenocorticotropic hormone (ACTH) concentrations together with cortisol levels essentially, reflecting the hypothalamic-pituitary adrenal (HPA) axis feedback loop control during the annual endogenous changes of testosterone secretion, represents a well-adapted response of this desert species living in an extreme environment.

Developmental plasticity of the stress response in female but not in male guppies

To survive, animals must respond appropriately to stress. Stress responses are costly, so early-life experiences with potential stressors could adaptively tailor adult stress responses to local conditions. However, how multiple stressors influence the development of the stress response remains unclear, as is the role of sex. Trinidadian guppies (Poecilia reticulata) are small fish with extensive life-history differences between the sexes and population variation in predation pressure and social density. We investigated how sex and early-life experience influence hormonal stress responses by manipulating conspecific density and perceived predation risk during development. In adults, we sampled cortisol twice to measure initial release and change over time in response to a recurring stressor. The sexes differed considerably in their physiological stress response. Males released more cortisol for their body mass than females and did not reduce cortisol release over time. By contrast, all females, except those reared at high density together with predation cues, reduced cortisol release over time. Cortisol responses of males were thus less dynamic in response to current circumstances and early-life experiences than females, consistent with life-history differences between the sexes. Our study underscores the importance of early-life experiences, interacting ecological factors and sex differences in the organization of the stress response.

Neonatal Handling Produces Sex Hormone-Dependent Resilience to Stress-Induced Muscle Hyperalgesia in Rats

Neonatal handling (NH) of male rat pups strongly attenuates stress response and stress-induced persistent muscle hyperalgesia in adults. Because female sex is a well established risk factor for stress-induced chronic muscle pain, we explored whether NH provides resilience to stress-induced hyperalgesia in adult female rats. Rat pups underwent NH, or standard (control) care. Muscle mechanical nociceptive threshold was assessed before and after water avoidance (WA) stress, when they were adults. In contrast to male rats, NH produced only a modest protection against WA stress-induced muscle hyperalgesia in female rats. Gonadectomy completely abolished NH-induced resilience in male rats but produced only a small increase in this protective effect in female rats. The administration of the antiestrogen drug fulvestrant, in addition to gonadectomy, did not enhance the protective effect of NH in female rats. Finally, knockdown of the androgen receptor by intrathecal antisense treatment attenuated the protective effect of NH in intact male rats. Together, these data indicate that androgens play a key role in NH-induced resilience to WA stress-induced muscle hyperalgesia.

PERSPECTIVE

NH induces androgen-dependent resilience to stress-induced muscle pain. Therefore, androgens may contribute to sex differences observed in chronic musculoskeletal pain and its enhancement by stress.

Sickness-induced changes in physiology do not affect fecundity or same-sex behavior

Previous work in our lab has shown that early-life infection affects female reproductive physiology and function (i.e., smaller ovaries, abnormal estrous cycles) and alters investigation and aggression towards male conspecifics in a reproductive context. Although many studies have investigated the effects of postnatal immune challenge on physiological and behavioral development, fewer studies have examined whether these changes have ultimate effects on reproduction. In the current study, we paired Siberian hamsters (Phodopus sungorus) and simulated a bacterial infection in early life by administering lipopolysaccharide (LPS) to male and female pups on pnd3 and pnd5. In adulthood, hamsters were paired with novel individuals of the same sex, and we scored an array of social behaviors (e.g., investigation, aggression). We then paired animals with individuals of the opposite sex for 5 consecutive nights, providing them with the opportunity to mate. We found that females exhibited impaired reproductive physiology and function in adulthood (i.e., smaller ovaries and abnormal estrous cycles), similar to our previous work. However, both LPS-treated males and females exhibited similar same-sex social behavior when compared with saline-treated controls, they successfully mated, and there were no significant changes in fecundity. These data suggest that the physiological changes in response to neonatal immune challenge may not have long-term effects on reproductive success in a controlled environment. Collectively, the results of this study are particularly important when investigating the relationships between physiology and behavior within an ultimate context. Animals exposed to early-life stress may in fact be capable of compensating for changes in physiology in order to survive and reproduce in some contexts.

Prenatal fluoxetine modifies the behavioral and hormonal responses to stress in male mice: role for glucocorticoid insensitivity

Women with major depressive disorder during pregnancy often use selective serotonin reuptake inhibitors (SSRIs) antidepressants. These drugs readily cross the placental barrier and impact the developing fetal brain. Recently, we reported that prenatal fluoxetine (FLX), an SSRI antidepressant drug, altered corticosterone and behavioral responses to stress in female mouse offspring. The present study assessed the effects of prenatal FLX on these responses in males. The results showed that prenatal FLX significantly augmented the corticosterone response to acute stress in young prepubescent mice. The corticosterone response to continuous stress was not affected by prenatal FLX irrespective of age. In addition, continuous stress reduced general activity, and anxiety-like and depressive-like behaviors in adult animals prenatally exposed to FLX, but not in controls. The dexamethasone suppression test showed that prenatal FLX induced a state of glucocorticoid insensitivity in adult males, indicating that the negative feedback control of the hypothalamic-pituitary-adrenal axis response to stress was disrupted. Together, these findings indicate that prenatal FLX altered hormonal and behavioral responses to stress and suggest a role for the development of glucocorticoid insensitivity in these effects. These findings may aid understanding of the limitations and precautions that should be taken in the use of SSRIs by pregnant women.

Sex differences in the neuro-immune consequences of stress: Focus on depression and anxiety

Women appear to be more vulnerable to the depressogenic effects of inflammation than men. Chronic stress, one of the most pertinent risk factors of depression and anxiety, is known to induce behavioral and affective-like deficits via neuroimmune alterations including activation of the brain's immune cells, pro-inflammatory cytokine expression, and subsequent changes in neurotransmission and synaptic plasticity within stress-related neural circuitry. Despite well-established sexual dimorphisms in the stress response, immunity, and prevalence of stress-linked psychiatric illnesses, much of current research investigating the neuroimmune impact of stress remains exclusively focused on male subjects. We summarize and evaluate here the available data regarding sex differences in the neuro-immune consequences of stress, and some of the physiological factors contributing to these differences. Furthermore, we discuss the extent to which sex differences in stress-related neuroinflammation can account for the overall female bias in stress-linked psychiatric disorders including major depressive disorder and anxiety disorders. The currently available evidence from rodent studies does not unequivocally support the peripheral inflammatory changes seen in women following stress. Replication of many recent findings in stress-related neuroinflammation in female subjects is necessary in order to build a framework in which we can assess the extent to which sex differences in stress-related inflammation contribute to the overall female bias in stress-related affective disorders.

The effects of six-day SSRI administration on diurnal cortisol secretion in healthy volunteers

RATIONALE

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis has been widely reported in depression, and evidence suggests that selective serotonin reuptake inhibitors (SSRIs) might exert their therapeutic effects through altering cortisol secretion.

OBJECTIVE

This study assessed the effects of SSRI administration on diurnal cortisol secretion in healthy volunteers.

METHODS

Sixty-four healthy men and women were randomised to receive either 10 mg escitalopram or placebo for six days in a double-blind fashion. On day six of medication, saliva samples were obtained at home for measurement of diurnal cortisol parameters (cortisol slope, cortisol awakening response, total daily cortisol output).

RESULTS

Women receiving escitalopram had significantly steeper cortisol slopes across the day compared with those receiving placebo (F(1, 36) = 7.54, p = 0.009). This alteration in cortisol slope was driven by increases in waking cortisol levels (F(1, 35) = 9.21, p = 0.005). Escitalopram did not have any significant effect on the cortisol awakening response or the total daily cortisol output.

CONCLUSIONS

Flattened cortisol slopes have been seen in depression. The results of this study suggest that escitalopram might exert its therapeutic effect in women in part through correction of a flattened diurnal cortisol rhythm.

An examination of sex differences on neurocognitive functioning and behavior problems in maltreated youth

OBJECTIVE

In the developmental traumatology model, the biological construct of sex is considered a moderator that may negatively influence child maltreatment sequelae including those pertaining to neurocognitive function.

METHOD

This study examined sex-differences in neurocognitive function and behavior problems in maltreated boys (n = 42), maltreated girls (n = 56) versus nonmaltreated boys (n = 45) and girls (n = 59). Maltreated boys were hypothesized to have poorer neurocognitive functioning than maltreated girls, and nonmaltreated boys and girls, in all neurocognitive domains, particularly pertaining to executive function and attention. We also examined correlations between cognitive function and parent report of child behavior problems for maltreated and nonmaltreated children.

RESULTS

Maltreated boys performed more poorly on measures of intelligence, attention, language, memory, executive function, and academic achievement in both reading and math than nonmaltreated boys. Maltreated boys did not perform more poorly on these cognitive measures or behavioral measures than maltreated girls, except for one memory measure. Maltreated girls performed more poorly on measures of intelligence, language, memory, executive function, and academic achievement than nonmaltreated girls. Maltreated girls with better visual-spatial skills had more internalizing and externalizing problems. Effect sizes for these sex differences ranged from small to large.

CONCLUSIONS

Both maltreated boys and girls showed poorer cognitive function than their nonmaltreated sex-matched controls. Maltreated girls had subtle sparing of attention and short-term memory (STM). Understanding sex differences in neurocognitive functioning may have implications for designing large population studies of maltreated youth. (PsycINFO Database Record

Sex differences in early-life programming of the hypothalamic-pituitary-adrenal axis in humans

Increasing evidence supports fetal glucocorticoid exposure with associated altered offspring hypothalamic-pituitary-adrenal (HPA) axis activity as a key mechanism linking early life events with later life disease. Alterations in HPA axis activity are linked to a range of cardiometabolic and psychiatric diseases. As many of these diseases manifest sex differences in presentation we review the evidence for programmed sex-differences in the HPA axis. Available literature suggests vulnerability of the female HPA axis to prenatal stressors with female offspring demonstrating increased HPA axis reactivity. This may be due to changes in placental glucocorticoid metabolism leading to increased fetal glucocorticoid exposure. We discuss the potential consequences of increased vulnerability of the female HPA axis for later life health and consider the underlying mechanisms. Further studies are needed to determine whether sex-differences in early-life programming of the HPA axis represent a pathway underpinning the sex-differences in common cardiometabolic and psychiatric diseases.

Glucocorticoid treatment earlier in childhood and adolescence show dose-response associations with diurnal cortisol levels

Heightened levels of glucocorticoids in children and adolescents have previously been linked to prolonged changes in the diurnal regulation of the stress-hormone cortisol, a glucocorticoid regulated by the hypothalamic-pituitary-adrenal-axis (HPA-axis). To address this question, we examined the salivary cortisol awakening response (CAR) and daily cortisol output in 36 children and adolescents (25 girls/11 boys) aged 7-16 years previously treated with glucocorticoids for nephrotic syndrome or rheumatic disorder and 36 healthy controls. Patients and controls did not significantly differ in the CAR or diurnal cortisol output; however, sex-dependent group differences were observed. Specifically, female patients had a higher CAR relative to female controls, while male patients had higher daily cortisol levels compared to male controls. Notably, CAR in female patients and daily cortisol levels in male patients showed a positive linear relationship with the mean daily glucocorticoid doses administered during treatment. The observed dose-response associations suggest that glucocorticoid therapy during childhood and adolescence might trigger long-term changes in HPA-axis regulation, which may differ for males and females.

Evening salivary cortisol and alpha-amylase at 14months and neurodevelopment at 4years: Sex differences

Stress system activity in early life can have long-term effects on neurodevelopment. The main aim of this study was to assess the association of child evening salivary cortisol and alpha-amylase basal levels at 14months of age with longer-term neuropsychological development at 4years in a low-risk population-based birth cohort derived from the INMA (Environment and Childhood) project in Spain. We included 186 parent-children pairs with information on both stress system activity and neurodevelopment. Both stress markers at 14months of age showed an association with neuropsychological development at 4years. Salivary cortisol showed a sex-specific pattern of association. In girls, cortisol levels at 14months were negatively associated with cognitive development [long-term declarative memory (β=-17.8, p=0.028; 95% CI=-33.2 to -2.5); executive function (β=-9.8, p=0.08; 95% CI=-21 to 1)] and gross motor development (β=-13; p=0.022; 95% CI=-24 to -2), whereas in boys cortisol levels were negatively associated with socioemotional development [autistic-like behaviours: Incidence Rate Ratio (IRR)=1.6, p=0.039; 95% CI=1.01 to 2.41]. Salivary alpha-amylase was positively associated with socioemotional development in boys only [social competence (β=2.11, p=0.013; 95% CI=0.47 to 3.72), autistic-like behaviours (IRR=0.93, p=0.042; 95% CI=0.87 to 0.99) and hyperactivity symptoms (IRR=0.81, p=0.021; 95% CI=0.69 to 0.97)]. These results suggest that stress system activity in early life is associated with longer-term neurodevelopment and that sex is an important factor in this relationship.

Is HPA axis reactivity in childhood gender-specific? A systematic review

BACKGROUND

In adults, hypothalamus-pituitary-adrenal (HPA) axis activity shows sexual dimorphism, and this is thought to be a mechanism underlying sex-specific disease incidence. Evidence is scarce on whether these sex differences are also present in childhood. In a meta-analysis, we recently found that basal (non-stimulated) cortisol in saliva and free cortisol in 24-h urine follow sex-specific patterns. We explored whether these findings could be extended with sex differences in HPA axis reactivity.

METHODS

From inception to January 2016, PubMed and EMBASE.com were searched for studies that assessed HPA axis reactivity in healthy girls and boys aged ≤18 years. Articles were systematically assessed and reported in the categories: (1) diurnal rhythm, (2) cortisol awakening response (CAR), (3) protocolled social stress tests similar or equal to the Trier Social Stress Test for children (TSST-C), (4) pharmacological (ACTH and CRH) stress tests, and (5) miscellaneous stress tests.

RESULTS

Two independent assessors selected 109 out of 6158 records for full-text screening, of which 81 studies (with a total of 14,591 subjects) were included. Studies showed that girls had a tendency towards a more variable diurnal rhythm (12 out of 29 studies), a higher CAR (8 out of 18 studies), and a stronger cortisol response to social stress tests (9 out of 21 studies). We found no evidence for sex differences in cortisol response after a pharmacological challenge or to miscellaneous stress tests.

DISCUSSION

Sex differences in HPA axis reactivity appear to be present in childhood, although evidence is not unequivocal. For a better evaluation of sex differences in HPA axis reactivity, standardization of protocols and reports of stress tests is warranted.

Effects of developmental conditions on glucocorticoid concentrations in adulthood depend on sex and foraging conditions

Developmental conditions in early life frequently have long-term consequences on the adult phenotype, but the adult environment can modulate such long-term effects. Glucocorticoid hormones may be instrumental in mediating developmental effects, but the permanency of such endocrine changes is still debated. Here, we manipulated environmental conditions during development (small vs. large brood size, and hence sibling competition) and in adulthood (easy vs. hard foraging conditions) in a full factorial design in zebra finches, and studied effects on baseline (Bas-CORT) and stress-induced (SI-CORT) corticosterone in adulthood. Treatments affected Bas-CORT in females, but not in males. Females reared in small broods had intermediate Bas-CORT levels as adults, regardless of foraging conditions in adulthood, while females reared in large broods showed higher Bas-CORT levels in hard foraging conditions and lower levels in easy foraging conditions. Female Bas-CORT was also more susceptible than male Bas-CORT to non-biological variables, such as ambient temperature. In line with these results, repeatability of Bas-CORT was higher in males (up to 51%) than in females (25%). SI-CORT was not responsive to the experimental manipulations in either sex and its repeatability was high in both sexes. We conclude that Bas-CORT responsiveness to intrinsic and extrinsic conditions is higher in females than in males, and that the expression of developmental conditions may depend on the adult environment. The latter finding illustrates the critical importance of studying of causes and consequences of long-term developmental effects in other environments in addition to standard laboratory conditions.

Checks and balances: The glucocorticoid receptor and NFĸB in good times and bad

Mutual regulation and balance between the endocrine and immune systems facilitate an organism's stress response and are impaired following chronic stress or prolonged immune activation. Concurrent alterations in stress physiology and immunity are increasingly recognized as contributing factors to several stress-linked neuropsychiatric disorders including depression, anxiety, and post-traumatic stress disorder. Accumulating evidence suggests that impaired balance and crosstalk between the glucocorticoid receptor (GR) and nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) - effectors of the stress and immune axes, respectively - may play a key role in mediating the harmful effects of chronic stress on mood and behavior. Here, we first review the molecular mechanisms of GR and NFκB interactions in health, then describe potential shifts in the GR-NFκB dynamics in chronic stress conditions within the context of brain circuitry relevant to neuropsychiatric diseases. Furthermore, we discuss developmental influences and sex differences in the regulation of these two transcription factors.

Neuroendocrine Networks and Functionality

Women undergo developmental and cyclic changes in hormonal exposures that affect brain function and mental health. Some women are more vulnerable to the effects of these hormonal exposures, for reasons that remain to be determined. Evidence to date indicates that anxiety and mood disorders are the most sensitive to hormonal fluctuations in women but there is also growing evidence for a protective effect of female reproductive hormones on schizophrenia. The hormonal exposures of the menstrual cycle, pregnancy, the postpartum period, lactation, and menopause are quite different and may be associated with at least partially distinct symptom profiles.

A systematic review of sex and age factors in neuroleptic malignant syndrome diagnosis frequency

OBJECTIVE

To examine sex and age distributions in neuroleptic malignant syndrome (NMS) patients based on a systematic literature review.

METHOD

EMBASE and PubMed databases were searched to identify any observation of NMS published from January 1, 1998 through November 1, 2014 that was accessible and interpretable (using language translation software). Redundant and equivocal reports were excluded. Sex ratio and age distributions were examined using standard graphical techniques and measures of association.

RESULTS

Twenty-eight independent sex ratio estimates were included. Males predominated in most (75%) estimates with an overall median sex ratio of 1.47 (95% CI, 1.20-1.80). NMS incidence peaked at age 20-25 years and declined steadily thereafter, with males consistently outnumbering females at all but the oldest age intervals.

CONCLUSION

NMS patients are 50% more likely to be males, and NMS is most likely to occur in young adulthood.

Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism interacts with gender to influence cortisol responses to mental stress

Brain-derived neurotrophic factor (BDNF) Val66Met polymorphism has been associated with cortisol responses to stress with gender differences reported, although the findings are not entirely consistent. To evaluate the role of Val66Met genotype and gender on cortisol responses to stress, we conducted a 45-min mental stress protocol including four tasks and four rest periods. Blood cortisol was collected for assay immediately before and after each task and rest period. A significant two-way interaction of Val66Met genotype×gender (P=0.022) was observed on the total area under the curve (AUC), a total cortisol response over time, such that the Val/Val genotype was associated with a larger cortisol response to stress as compared to the Met group in women but not in men. Further contrast analyses between the Val/Val and Met group for each stress task showed a similar increased cortisol pattern among women Val/Val genotype but not among men. The present findings indicate the gender differences in the effect of Val66Met genotype on the cortisol responses to stress protocol, and extend the evidence for the importance of gender and the role of Val66Met in the modulation of stress reactivity and subsequent depression prevalence. Further studies and the underlying mechanism need to be investigated, which may provide an insight for prevention, intervention, and treatment strategies that target those at high risk.

Neurobehavioral assessment of maternal odor in developing rat pups: implications for social buffering

Social support can attenuate the behavioral and stress hormone response to threat, a phenomenon called social buffering. The mother's social buffering of the infant is one of the more robust examples; yet we understand little about the neurobiology. Using a rodent model, we explore the neurobiology of social buffering by assessing neural processing of the maternal odor, a major cue controlling social buffering in rat pups. We used pups before (postnatal day (PN) 7) and after (PN14, PN23) the functional emergence of social buffering. Pups were injected with 14C 2-deoxyglucose (2-DG) and presented with the maternal odor, a control preferred odor incapable of social buffering (acetophenone), or no odor. Brains were removed, processed for autoradiography and brain areas identified as important in adult social buffering were assessed, including the amygdala basolateral complex (Basolateral Amygdala [BLA]), medial prefrontal cortex (mPFC), and anterior cingulate cortex (ACC). Results suggest dramatic changes in the processing of maternal odor. PN7 pups show mPFC and ACC activation, although PN14 pups showed no activation of the mPFC, ACC, or BLA. All brain areas assessed were recruited by PN23. Additional analysis suggests substantial changes in functional connectivity across development. Together, these results imply complex nonlinear transitions in the neurobiology of social buffering in early life that may provide insight into the changing role of the mother in supporting social buffering.

Gender-specific differences in hypothalamus-pituitary-adrenal axis activity during childhood: a systematic review and meta-analysis

BACKGROUND

Gender-specific differences in hypothalamus-pituitary-adrenal (HPA) axis activity have been postulated to emerge during puberty. We conducted a systematic review and meta-analysis to test the hypothesis that gender-specific differences in HPA axis activity are already present in childhood.

METHODS

From inception to January 2016, PubMed and EMBASE.com were searched for studies that assessed non-stimulated cortisol in serum or saliva or cortisol in 24-h urine in healthy males and females aged ≤18 years. Studies that conform with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement were reported. Standardized mean differences (95% CIs) were calculated and analyzed using fixed-effect meta-analysis stratified for age: <8 years (prepubertal) and 8-18 years (peri-/postpubertal). For comparison, we ran the same analyses using random-effects models.

RESULTS

Two independent assessors selected 413 out of 6158 records (7%) for full-text screening, of which 79 articles were included. Of these, 58 (with data on 16,551 subjects) were included in the meta-analysis. Gender differences in cortisol metabolism differed per age group. Boys aged <8 years had 0.18 (0.06; 0.30) nmol/L higher serum and 0.21 (0.05; 0.37) nmol/L higher salivary cortisol levels, while between 8 and 18 years, boys had 0.34 (0.28; 0.40) nmol/L lower serum and 0.42 (0.38; 0.47) nmol/L lower salivary cortisol levels. In 24-h urine, cortisol was consistently higher in boys, being 0.34 (0.05; 0.64) and 0.32 (0.17; 0.47) μg/24 h higher in the <8- and 8-18-year groups, respectively. However, gender-differences in serum cortisol <8 years and between 8 and 18 years were absent when using random-effects models.

CONCLUSIONS

Gender differences in cortisol metabolism are already present in childhood, with higher salivary cortisol in boys aged <8 years compared to girls. This pattern was reversed after the age of 8 years. In contrast, the gender-specific difference in cortisol production as assessed through 24-h urine did not change with age. Although differences were small, and analyses of gender differences in serum cortisol were inconclusive, they might contribute to gender-specific origins of health and disease.

Corticotropin-releasing factor overexpression in mice abrogates sex differences in body weight, visceral fat, and food intake response to a fast and alters levels of feeding regulatory hormones

BACKGROUND

Corticotropin-releasing factor overexpressing (CRF-OE) male mice showed an inhibited feeding response to a fast, and lower plasma acyl ghrelin and Fos expression in the arcuate nucleus compared to wild-type (WT) mice. We investigated whether hormones and hypothalamic feeding signals are impaired in CRF-OE mice and the influence of sex.

METHODS

Male and female CRF-OE mice and WT littermates (4-6 months old) fed ad libitum or overnight fasted were assessed for body, adrenal glands and perigonadal fat weights, food intake, plasma hormones, blood glucose, and mRNA hypothalamic signals.

RESULTS

Under fed conditions, compared to WT, CRF-OE mice have increased adrenal glands and perigonadal fat weight, plasma corticosterone, leptin and insulin, and hypothalamic leptin receptor and decreased plasma acyl ghrelin. Compared to male, female WT mice have lower body and perigonadal fat and plasma leptin but higher adrenal glands weights. CRF-OE mice lost these sex differences except for the adrenals. Male CRF-OE and WT mice did not differ in hypothalamic expression of neuropeptide Y (NPY) and proopiomelanocortin (POMC), while female CRF-OE compared to female WT and male CRF-OE had higher NPY mRNA levels. After fasting, female WT mice lost more body weight and ate more food than male WT, while CRF-OE mice had reduced body weight loss and inhibited food intake without sex difference. In male WT mice, fasting reduced plasma insulin and leptin and increased acyl ghrelin and corticosterone while female WT showed only a rise in corticosterone. In CRF-OE mice, fasting reduced insulin while leptin, acyl ghrelin and corticosterone were unchanged with no sex difference. Fasting blood glucose was higher in CRF-OE with female > male. In WT mice, fasting increased hypothalamic NPY expression in both sexes and decreased POMC only in males, while in CRF-OE mice, NPY did not change, and POMC decreased in males and increased in females.

CONCLUSIONS

These data indicate that CRF-OE mice have abnormal basal and fasting circulating hormones and hypothalamic feeding-related signals. CRF-OE also abolishes the sex difference in body weight, abdominal fat, and fasting-induced feeding and changes in plasma levels of leptin and acyl ghrelin.

Intrinsic factors, adrenal gland morphology, and disease burden in captive cheetahs (Acinonyx jubatus) in South Africa

Adrenal gland weight (AW) and corticomedullary ratio (ACMR) are used as indicators of stress in animals. Captive cheetahs (Acinonyx jubatus) have higher ACMRs than free-ranging ones and stress has been linked to gastritis, amyloidosis, glomerulosclerosis, and myocardial fibrosis. We reviewed age, sex, body weight (BW), kidney weight (KW), and left AW and ACMR with necropsy findings in 51 South African captive cheetahs. Eleven common histopathologic lesions were counted for each animal as measure of its disease burden. Adrenal corticomedullary hyperplasia was significantly correlated with left AW and ACMR. Males had significantly higher AWs than females; other parameters showed no difference between the sexes. Disease burden, gastritis, and myocardial fibrosis were moderately correlated with adrenal morphology supporting prior evidence that gastritis and myocardial fibrosis are linked to stress. Glomerulosclerosis was not correlated with adrenal morphology and neither kidney nor liver amyloidosis contributed significantly to variation in AW or ACMR on multivariate analyses. Interstitial nephritis showed much stronger correlations with kidney and liver amyloidosis than gastritis. All three adrenal parameters were correlated with age; age was the only significant variable affecting ACMR on the multivariate analyses; and disease burden as well as systemic amyloidosis and kidney disease (except for fibrosis) showed moderate correlations with age. Age may, therefore, be important in the pathogenesis of disease in captive cheetahs, particularly of amyloidosis and kidney disease. None of the intrinsic measurements or adrenal parameters were sufficiently closely linked to disease to be used as ante-mortem proxies for disease burden or specific diseases. Zoo Biol. 36:40-49, 2017. © 2016 Wiley Periodicals, Inc.

Advances in TRH signaling

The activity of the hypothalamus-pituitary-thyroid axis (HPT) is coordinated by hypophysiotropic thyrotropin releasing hormone (TRH) neurons present in the paraventricular nucleus of the hypothalamus. Hypophysiotropic TRH neurons act as energy sensors. TRH controls the synthesis and release of thyrotropin, which activates the synthesis and secretion of thyroid hormones; in target tissues, transporters and deiodinases control their local availability. Thyroid hormones regulate many functions, including energy homeostasis. This review discusses recent evidence that covers several aspects of TRH role in HPT axis regulation. Knowledge about the mechanisms of TRH signaling has steadily increased. New transcription factors engaged in TRH gene expression have been identified, and advances made on how they interact with signaling pathways and define the dynamics of TRH neurons response to acute and/or long-term influences. Albeit yet incomplete, the relationship of TRH neurons activity with positive energy balance has emerged. The importance of tanycytes as a central relay for the feedback control of the axis, as well as for HPT responses to alterations in energy balance, and other stimuli has been reinforced. Finally, some studies have started to shed light on the interference of prenatal and postnatal stress and nutrition on HPT axis programing, which have confirmed the axis susceptibility to early insults.

Energetic stress: The reciprocal relationship between energy availability and the stress response

The worldwide epidemic of metabolic syndromes and the recognized burden of mental health disorders have driven increased research into the relationship between the two. A maladaptive stress response is implicated in both mental health disorders and metabolic disorders, implicating the hypothalamic-pituitary-adrenal (HPA) axis as a key mediator of this relationship. This review explores how an altered energetic state, such as hyper- or hypoglycemia, as may be manifested in obesity or diabetes, affects the stress response and the HPA axis in particular. We propose that changes in energetic state or energetic demands can result in "energetic stress" that can, if prolonged, lead to a dysfunctional stress response. In this review, we summarize the role of the hypothalamus in modulating energy homeostasis and then briefly discuss the relationship between metabolism and stress-induced activation of the HPA axis. Next, we examine seven mechanisms whereby energetic stress interacts with neuroendocrine stress response systems, including by glucocorticoid signaling both within and beyond the HPA axis; by nutrient-induced changes in glucocorticoid signaling; by impacting the sympathetic nervous system; through changes in other neuroendocrine factors; by inducing inflammatory changes; and by altering the gut-brain axis. Recognizing these effects of energetic stress can drive novel therapies and prevention strategies for mental health disorders, including dietary intervention, probiotics, and even fecal transplant.

Prenatal SSRI alters the hormonal and behavioral responses to stress in female mice: Possible role for glucocorticoid resistance

Life time prevalence of major depression disorder (MDD) is higher in women compared to men especially during the period surrounding childbirth. Women suffering from MDD during pregnancy use antidepressant medications, particularly Selective Serotonin Reuptake Inhibitors (SSRI). These drugs readily cross the placental barrier and impact the developing fetal brain. The present study assessed the effects of prenatal exposure to fluoxetine (FLX), an SSRI antidepressant drug, on corticosterone and behavioral responses to stress in female mice. In young females, prenatal FLX significantly elevated corticosterone response to continuous stress. In adults, prenatal FLX augmented corticosterone response to acute stress and suppressed the response to continuous stress. Additionally, prenatal FLX significantly augmented stress-induced increase in locomotion and reduced anxiety- and depressive-like behaviors in adult, but not young mice. The dexamethasone suppression test revealed that prenatal FLX induced a state of glucocorticoid resistance in adult females, indicating that the negative feedback control of the hypothalamic-pituitary-adrenal axis response to stress was disrupted. These findings provide the first indication of altered hormonal and behavioral responses to continuous stress and suggest a role for the development of glucocorticoid resistance in these effects. According to these findings, prenatal environment may have implications for stress sensitivity and responsiveness to life challenges. Furthermore, this study may assist in understanding the limitations and precautions that should be taken in the use of SSRIs during pregnancy.

Sex and stress steroids in adolescence: Gonadal regulation of the hypothalamic-pituitary-adrenal axis in the rat

This review provides an overview of the current understanding of the role of the hypothalamic-pituitary-gonadal (HPG) axis in regulating the hypothalamic-pituitary-adrenal (HPA) axis response to stressors. HPA function is influenced by both organizational (programming) and activational effects of gonadal hormones. Typically, in adult rats, estradiol increases and androgens decrease the HPA response to stressors, thereby contributing to sex differences in HPA function, and sensitivity of the HPA axis to gonadal steroids is in part determined by exposure to these hormones in early development. Although developmental differences in HPA function are well characterized, the extent to which gonadal steroids contribute to age differences in HPA function is not well understood. Deficits in the understanding of the relationships between the HPA and HPG axes are greatest for the adolescent period of development. The critical outstanding questions are, when do gonadal hormones begin to regulate HPA function in adolescence, and what mechanisms precipitate change in sensitivity of the HPA axis to the HPG axis at this stage of life.

The effect of sex and irritable bowel syndrome on HPA axis response and peripheral glucocorticoid receptor expression

BACKGROUND AND AIMS

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has been reported in irritable bowel syndrome (IBS). Enhanced HPA axis response has been associated with reduced glucocorticoid receptor (GR) mediated negative feedback inhibition. We aimed to study the effects of IBS status, sex, or presence of early adverse life events (EAL) on the cortisol response to corticotropin-releasing factor (CRF) and adrenocorticotropic hormone (ACTH), and on GR mRNA expression in peripheral blood mononuclear cells (PBMCs).

METHODS

Rome III+ IBS patients and healthy controls underwent CRF (1μg/kg ovine) and ACTH (250μg) stimulation tests with serial plasma ACTH and cortisol levels measured (n=116). GR mRNA levels were measured using quantitative PCR (n=143). Area under the curve (AUC) and linear mixed effects models were used to compare ACTH and cortisol response measured across time between groups.

RESULTS

There were divergent effects of IBS on the cortisol response to ACTH by sex. In men, IBS was associated with an increased AUC (p=0.009), but in women AUC was blunted in IBS (p=0.006). Men also had reduced GR mRNA expression (p=0.007). Cumulative exposure to EALs was associated with an increased HPA response. Lower GR mRNA was associated with increased pituitary HPA response and increased severity of overall symptoms and abdominal pain in IBS.

CONCLUSION

This study highlights the importance of considering sex in studies of IBS and the stress response in general. Our findings also provide support for PBMC GR mRNA expression as a peripheral marker of central HPA response.

Circadian and ultradian glucocorticoid rhythmicity: Implications for the effects of glucocorticoids on neural stem cells and adult hippocampal neurogenesis

Psychosocial stress, and within the neuroendocrine reaction to stress specifically the glucocorticoid hormones, are well-characterized inhibitors of neural stem/progenitor cell proliferation in the adult hippocampus, resulting in a marked reduction in the production of new neurons in this brain area relevant for learning and memory. However, the mechanisms by which stress, and particularly glucocorticoids, inhibit neural stem/progenitor cell proliferation remain unclear and under debate. Here we review the literature on the topic and discuss the evidence for direct and indirect effects of glucocorticoids on neural stem/progenitor cell proliferation and adult neurogenesis. Further, we discuss the hypothesis that glucocorticoid rhythmicity and oscillations originating from the activity of the hypothalamus-pituitary-adrenal axis, may be crucial for the regulation of neural stem/progenitor cells in the hippocampus, as well as the implications of this hypothesis for pathophysiological conditions in which glucocorticoid oscillations are affected.

Prenatal and postnatal stress and asthma in children: Temporal- and sex-specific associations

BACKGROUND

Temporal- and sex-specific effects of perinatal stress have not been examined for childhood asthma.

OBJECTIVES

We examined associations between prenatal and/or postnatal stress and children's asthma (n = 765) and effect modification by sex in a prospective cohort study.

METHODS

Maternal negative life events were ascertained prenatally and postpartum. Negative life event scores were categorized as 0, 1 to 2, 3 to 4, or 5 or greater to assess exposure-response relationships. We examined effects of prenatal and postnatal stress on children's asthma by age 6 years, modeling each as independent predictors, mutually adjusting for prenatal and postnatal stress, and finally considering interactions between prenatal and postnatal stress. Effect modification by sex was examined in stratified analyses and by fitting interaction terms.

RESULTS

When considering stress in each period independently, among boys, a dose-response relationship was evident for each level increase on the ordinal scale prenatally (odds ratio [OR], 1.38; 95% CI, 1.06-1.79; P value for trend = .03) and postnatally (OR, 1.53; 95% CI, 1.16-2.01; P value for trend = .001); among girls, only the postnatal trend was significant (OR, 1.60; 95% CI, 1.14-2.22; P value for trend = .005). Higher stress in both the prenatal and postnatal periods was associated with increased odds of receiving a diagnosis of asthma in girls (OR, 1.37; 95% CI, 0.98-1.91; Pinteraction = .07) but not boys (OR, 1.08; 95% CI, 0.82-1.42; Pinteraction = .61).

CONCLUSIONS

Although boys were more vulnerable to stress during the prenatal period, girls were more affected by postnatal stress and cumulative stress across both periods in relation to asthma. Understanding sex and temporal differences in response to early-life stress might provide unique insight into the cause and natural history of asthma.

Immunohistochemical analysis of the hypothalamic-pituitary-adrenal axis in dogs: Sex-linked and seasonal variation

This study evaluated sexual dimorphism and seasonal variations in corticotrophs and adrenal zona fasciculata in dogs, as well as the expression of oestrogen receptor alpha (ERα). An immunohistochemical analysis was conducted in pituitaries for ACTH and in adrenal glands for ERα and for the melanocortin-2-receptor (MC2R) in winter and summer. Double immunofluorescence was performed to identify ERα in corticotrophs. Females had a greater proportion of corticotrophs per field (p<0.01), with a greater cellular area and optical density (p<0.001) than males. Optical density of corticotrophs was greater in winter for both sexes (p<0.001). In zona fasciculata, ERα and MC2R expression was greater in females (p<0.001) and was greater in winter (p<0.001). ERα was identified in corticotrophs. This study is the first to demonstrate ERα expression in corticotrophs and the adrenal cortex in dogs, providing evidence for sexual dimorphism and seasonal variations.

Stress is a principal factor that promotes tobacco use in females

Tobacco use is a major economic and health problem. It is particularly concerning that women consume more tobacco products, have a more difficult time quitting smoking, and are less likely to benefit from smoking cessation therapy than men. As a result, women are at higher risk of developing tobacco-related diseases. Clinical evidence suggests that women are more susceptible to anxiety disorders, and are more likely to smoke in order to cope with stress than men. During smoking abstinence, women experience more intense anxiety than men and report that the anxiety-reducing effects of smoking are the main reason for their continued tobacco use and relapse. Consistent with this, pre-clinical studies using rodent models suggest that females display more intense stress during nicotine withdrawal than males. This review posits that in women, stress is a principal factor that promotes the initiation of tobacco use and relapse behavior during abstinence. Studies are reviewed at both the clinical and pre-clinical levels to provide support for our hypothesis that stress plays a central role in promoting tobacco use vulnerability in females. The clinical implications of this work are also considered with regard to treatment approaches and the need for more research to help reduce health disparities produced by tobacco use in women.

Endocrine and Cognitive Adaptations to Cope with Stress in Immature Common Marmosets (Callithrix jacchus): Sex and Age Matter

Phenotypic sex differences in primates are associated with body differentiation during the early stages of life, expressed in both physiological and behavioral features. Hormones seem to play a pivotal role in creating a range of responses to meet environmental and social demands, resulting in better reactions to cope with challenges to survival and reproduction. Steroid hormones actively participate in neuroplasticity and steroids from both gonads and neurons seem to be involved in behavioral modulation in primates. Indirect evidence suggests the participation of sexual steroids in dimorphism of the stress response in common marmosets. This species is an important experimental model in psychiatry, and we found a dual profile for cortisol in the transition from juvenile to subadult, with females showing higher levels. Immature males and females at 6 and 9 months of age moved alone from the family group to a new cage, over a 21-day period, expressed distinct patterns of cortisol variation with respect to range and duration of response. Additional evidence showed that at 12 months of age, males and females buffered the hypothalamic-pituitary-adrenal axis during chronic stress. Moreover, chronic stressed juvenile marmoset males showed better cognitive performance in working memory tests and motivation when compared to those submitted to short-term stress living in family groups. Thus, as cortisol profile seems to be sexually dimorphic before adulthood, age and sex are critical variables to consider in approaches that require immature marmosets in their experimental protocols. Moreover, available cognitive tests should be scrutinized to allow better investigation of cognitive traits in this species.

HIV-1 proteins accelerate HPA axis habituation in female rats

Congenital infection by the Human Immunodeficiency Virus (HIV) has been shown to lead to multiple co-morbidities, and people living with HIV have a higher incidence of affective and anxiety disorders. A marked increase in mood disorders is evident during the sensitive phase of adolescence and this is further pronounced in females. Depression has been linked to dysfunction of the intracellular response system to corticosteroids at the level of the hippocampus (HC) and prefrontal cortex (PFC) with a notable role of the glucocorticoid receptor (GR) and its co-chaperones (FKBP5 and FKBP4). The current study examined the extent to which HIV protein expression in adolescent female rats altered the stress response at both the level of corticosterone output and molecular regulation of the glucocorticoid receptor in the brain. WT and HIV-1 genotype female rats were randomly allocated in control, acute stress and repeat stress groups. Corticosterone plasma levels and expression of GR, FKBP4, and FKBP5 in the HC and PFC were measured. The presence of HIV-1 proteins facilitates habituation of the corticosterone response to repeated stressors, such that HIV-1 TG rats habituated to repeated restraint and WT rats did not. This was reflected by interactions between stress exposure and HIV-1 protein expression at the level of GR co-chaperones. Although expression of the GR was similarly reduced after acute and repeat stress in both genotypes, expression of FKBP5 and FKBP4 was altered in a brain-region specific manner depending on the duration of the stress exposure and the presence or absence of HIV-1 proteins. Collectively, the data presented demonstrate that HIV-1 proteins accelerate habituation to repeated stressors and modify the influence of acute and repeat stressors on GR co-chaperones in a brain region-specific manner.

RasGRF1 regulates the hypothalamic-pituitary-adrenal axis specifically in early-adolescent female mice

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis has been implicated in the induction and prolongation of a variety of psychiatric disorders. As such, much effort has been made to understand the molecular mechanisms involved in its control. However, the vast majority of the studies on the HPA axis have used adult animals, and among these the majority has used males. Here we show that in knockout mice lacking the guanine nucleotide exchange factor, RasGRF1, habituation to 30 min/day of restraint stress is markedly accelerated, such that these mice do not display elevated corticosterone levels or enhanced locomotion after 7 days of stress exposure, like WT mice do. Strikingly, this phenotype is present in early-adolescent female RasGRF1 knockout mice, but not in their early-adolescent male, mid-adolescent female, adult female or adult male counterparts. Moreover, not only is there a clear response to restraint stress in early-adolescent female RasGRF1 knockout mice, their response after one, three and five exposures is magnified approximately threefold compared to WT mice. These findings imply that distinct mechanisms exist to regulate the HPA axis in early-adolescent females that involves RasGRF1. A full understanding of how RasGRF1 controls the HPA axis response to stress may be required to design effective strategies to combat stress-associated psychiatric disorders initiated in young females.

Strain and sex differences in puberty onset and the effects of THC administration on weight gain and brain volumes

The use of recreational marijuana is widespread and frequently begins and persists through adolescence. Some research has shown negative consequences of adolescent marijuana use, but this is not seen across studies, and certain factors, like genetic background and sex, may influence the results. It is critical to identify which characteristics predispose an individual to be susceptible to the negative consequences of chronic exposure to marijuana in adolescence on brain health and behavior. To this end, using males and females of two strains of rats, Long-Evans hooded (LER) and Wistar (WR) rats, we explored whether these anatomically and behaviorally dimorphic strains demonstrated differences in puberty onset and strain-specific effects of adolescent exposure to Δ9-tetrahydrocannabinol (THC), the main psychoactive component of marijuana. Daily 5 mg/kg treatment began on the day of puberty onset and continued for 14 days. Of particular interest were metrics of growth and volumetric estimates of brain areas involved in cognition that contain high densities of cannabinoid receptors, including the hippocampus and its subregions, the amygdala, and the frontal cortex. Brain volumetrics were analyzed immediately following the treatment period. LER and WR females started puberty at different ages, but no strain differences were observed in brain volumes. THC decreased weight gain throughout the treatment period for all groups. Only the hippocampus and some of its subregions were affected by THC, and increased volumes with THC administration was observed exclusively in females, regardless of strain. Long-term treatment of THC did not affect all individuals equally, and females displayed evidence of increased sensitivity to the effects of THC, and by extension, marijuana. Identifying differences in adolescent physiology of WR and LER rats could help determine the cause for strain and sex differences in brain and behavior of adults and help to refine the use of animal models in marijuana research.

The CYP11B subfamily

The biosynthesis of steroid hormones is dependent on P450-catalyzed reactions. In mammals, cholesterol is the common precursor of all steroid hormones, and its conversion to pregnenolone is the initial and rate-limiting step in hormone biosynthesis in steroidogenic tissues such as gonads and adrenal glands. The production of glucocorticoids and mineralocorticoids takes place in the adrenal gland and the final steps are catalyzed by 2 mitochondrial cytochromes P450, CYP11B1 (11β-hydroxylase or P45011β) and CYP11B2 (aldosterone synthase or P450aldo). The occurrence and development of these 2 enzymes in different species, their contribution to the biosynthesis of steroid hormones as well as their regulation at different levels (gene expression, cellular regulation, regulation on the level of proteins) is the topic of this chapter.

Peri-pubertal exposure to testicular hormones organizes response to novel environments and social behaviour in adult male rats

Previous research has shown that exposure to testicular hormones during the peri-pubertal period of life has long-term, organizational effects on adult sexual behaviour and underlying neural mechanisms in laboratory rodents. However, the organizational effects of peri-pubertal testicular hormones on other aspects of behaviour and brain function are less well understood. Here, we investigated the effects of manipulating peri-pubertal testicular hormone exposure on later behavioural responses to novel environments and on hormone receptors in various brain regions that are involved in response to novelty. Male rodents generally spend less time in the exposed areas of novel environments than females, and this sex difference emerges during the peri-pubertal period. Male Lister-hooded rats (Rattus norvegicus) were castrated either before puberty or after puberty, then tested in three novel environments (elevated plus-maze, light-dark box, open field) and in an object/social novelty task in adulthood. Androgen receptor (AR), oestrogen receptor (ER1) and corticotropin-releasing factor receptor (CRF-R2) mRNA expression were quantified in the hypothalamus, hippocampus and medial amygdala. The results showed that pre-pubertally castrated males spent more time in the exposed areas of the elevated-plus maze and light-dark box than post-pubertally castrated males, and also confirmed that peri-pubertal hormone exposure influences later response to an opposite-sex conspecific. Hormone receptor gene expression levels did not differ between pre-pubertally and post-pubertally castrated males in any of the brain regions examined. This study therefore demonstrates that testicular hormone exposure during the peri-pubertal period masculinizes later response to novel environments, although the neural mechanisms remain to be fully elucidated.

To stress or not to stress: a question of models

Stress research is a rapidly evolving field that encompasses numerous disciplines ranging from neuroscience to metabolism. With many new researchers migrating into the field, navigating the hows and whys of specific research questions can sometimes be enigmatic given the availability of so many models in the stress field. Additionally, as with every field, there are many seemingly minor experimental details that can have dramatic influences on data interpretation, although many of these are unknown to those not familiar with the field. The aim of this overview is to provide some suggestions and points to guide researchers moving into the stress field and highlight relevant methodological points that they should consider when choosing a model for stress and deciding how to structure a study. We briefly provide a primer on the basics of endpoint measurements in the stress field, factors to consider when choosing a model for acute stress, the difference between repeated and chronic stress, and importantly, influencing variables that modulate endpoints of analysis in stress work.

Sex differences in anxiety and depression clinical perspectives

Sex differences are prominent in mood and anxiety disorders and may provide a window into mechanisms of onset and maintenance of affective disturbances in both men and women. With the plethora of sex differences in brain structure, function, and stress responsivity, as well as differences in exposure to reproductive hormones, social expectations and experiences, the challenge is to understand which sex differences are relevant to affective illness. This review will focus on clinical aspects of sex differences in affective disorders including the emergence of sex differences across developmental stages and the impact of reproductive events. Biological, cultural, and experiential factors that may underlie sex differences in the phenomenology of mood and anxiety disorders are discussed.

Baleen hormones: a novel tool for retrospective assessment of stress and reproduction in bowhead whales (Balaena mysticetus)

Arctic marine mammals are facing increasing levels of many anthropogenic stressors. Novel tools are needed for assessment of stress physiology and potential impacts of these stressors on health, reproduction and survival. We have investigated baleen as a possible novel tissue type for retrospective assessment of stress and reproductive hormones. We found that pulverized baleen powder from bowhead whales (Balaena mysticetus) contained immunoreactive cortisol and progesterone that were detectable with commercially available enzyme immunoassay kits. Both assays passed parallelism and accuracy validations using baleen extracts. We analysed cortisol and progesterone at the base of the baleen plate (most recently grown baleen) from 16 bowhead whales of both sexes. For a subset of 11 whales, we also analysed older baleen from 10, 20 and 30 cm distal to the base of the baleen plate. Immunoreactive cortisol and progesterone were detectable in all baleen samples tested. In base samples, females had significantly higher concentrations of cortisol and progesterone compared with males. Cortisol concentrations in older baleen (10, 20 and 30 cm locations) were significantly lower than at the base and did not exhibit correlations with age-class or sex. Progesterone concentrations were significantly higher in females than in males at all baleen locations tested and were significantly higher in pregnant females than in non-pregnant females. Four of five mature females showed dramatic variation in progesterone concentrations at different locations along the baleen plate that may be indicative of previous pregnancies or luteal phases. In contrast, all males and all immature females had uniformly low progesterone. Baleen hormone analysis is a novel approach that, with further methodological development, may be useful for determining individual longitudinal profiles of reproductive cycles and stress responses.