Menstrual cycle and social behavior in vervet monkeys

Characterization of pathogenic factors for premenstrual dysphoric disorder using machine learning algorithms in rats

We established a methodology using machine learning algorithms for determining the pathogenic factors for premenstrual dysphoric disorder (PMDD). PMDD is a disease characterized by emotional and physical symptoms that occurs before menstruation in women of childbearing age. Owing to the diverse manifestations and various pathogenic factors associated with this disease, the diagnosis of PMDD is time-consuming and challenging. In the present study, we aimed to establish a methodology for diagnosing PMDD. Using an unsupervised machine-learning algorithm, we divided pseudopregnant rats into three clusters (C1 to C3), depending on the level of anxiety- and depression-like behaviors. From the results of RNA-seq and subsequent qPCR of the hippocampus in each cluster, we identified 17 key genes for building a PMDD diagnostic model using our original two-step feature selection with supervised machine learning. By inputting the expression levels of these 17 genes into the machine learning classifier, the PMDD symptoms of another group of rats were successfully classified as C1-C3 with an accuracy of 96%, corresponding to the classification by behavior. The present methodology would be applicable for the clinical diagnosis of PMDD using blood samples instead of samples from the hippocampus in the future.

Altered exploratory behaviour and increased food intake in the spiny mouse before menstruation: a unique pre-clinical model for examining premenstrual syndrome

STUDY QUESTION

Does the newly discovered menstruating spiny mouse exhibit behavioural and metabolic changes in correlation with premenstrual phases of the menstrual cycle?

SUMMARY ANSWER

This is the first report of cycle variability in the exploratory and interactive behaviour, and food consumption in menstruating spiny mice, and demonstrates that physiological changes are also dependent on within-subject variation.

WHAT IS KNOWN ALREADY

Premenstrual syndrome (PMS) is a prominent cyclic disorder that affects millions of women worldwide. More than 70% of women endure symptoms of impending menstruation, such as bloating, abdominal cramping and nausea to some degree. Consequently, ~8% of women experience recurrent physical and emotional symptoms which are extreme enough to disrupt daily life and seek intervention. Due to a lack of an appropriate animal model, the mechanisms underlying PMS are poorly understood, and subsequently, effective treatments are limited.

STUDY DESIGN, SIZE, DURATION

This study analyses the changes in behavioural responses to the investigator during vaginal lavage (n = 14), exploratory behaviour (n = 11) and metabolism (n = 20) across the menstrual cycle in the spiny mouse (Acomys cahirinus).

PARTICIPANTS/MATERIALS, SETTING, METHODS

We performed vaginal lavages on virgin spiny mice (6-8 months of age) and subjected each cohort of females to repeated measures for vaginal lavage, exploratory behaviour and metabolism. Stages of the menstrual cycle were designated as early follicular, late follicular, early luteal, late luteal, early menstrual and late menstrual, with the late luteal and early menstrual phases considered as premenstrual phases and analysed using generalized estimating equations. For vaginal lavage, the behavioural responses to researcher handling were scored on an increasing scale of severity during the lavage process (e.g. restraint, frequency of vocalizations, total handling time). For exploratory behaviour, exploration, memory and sociability were assessed through subjection to Open Field (OF), Novel Object Recognition (NORT), Social Novelty (SN) and Elevated Plus Maze (EPM) tests. For metabolism, physiological changes were measured over a 24-h period in metabolic cages. Results are mean ± SD with statistical significance set to P < 0.05.

MAIN RESULTS AND THE ROLE OF CHANCE

Qualitative behavioural assessment showed that compared to early follicular controls, during premenstrual phases, cycling females had significantly increased probability of: manifesting difficulties during restraint (4×, P < 0.01), vocalizing (8×, P < 0.01) and exhibiting isolation in the cage (40×, P = 0.041). We saw significant increases in handling time during the premenstrual phase in cycling females (76 ± 16 s) compared to controls (55 ± 7 s, P < 0.001). For exploratory behaviour, cycling females in their early menstrual phase travelled significantly less distance in the outer zone of the OF arena (13.3 ± 9.0 m) than females in their early luteal phase (22.3 ± 9.9 m, P = 0.038) and at significantly reduced velocities (40.2 ± 10.5 mm/s and 78.8 ± 31.0 mm/s, respectively, P = 0.006). These females also had fewer entries into the EPM open arms during the same phases (9.6 ± 6.1 and versus 20.0 ± 7.2, respectively, P = 0.030) and travelled less distance (3.2 ± 2.8 m versus 7.0 ± 5.5 m, respectively, P = 0.026). No differences were observed in NORT or SN across the cycle. In the metabolism studies, spiny mice demonstrated a significant increase in food consumption (percentage of body weight) during the early follicular and late luteal phases (3.9 ± 2.4% and 3.8 ± 2.1%, respectively) compared to the late follicular phase (2.3 ± 2.6%, P = 0.015).

LARGE SCALE DATA

N/A.

LIMITATIONS, REASONS FOR CAUTION

This is an observational study to determine fundamental changes in behaviour and metabolism in a novel species, and as such, lacks commercially available laboratory reagents and protocols specific to the spiny mouse.

WIDER IMPLICATIONS OF THE FINDINGS

The timing of these behavioural and physiological changes suggests that spiny mice exhibit symptoms analogous to PMS in higher order primates, thus providing a pre-clinical model for testing novel interventions to alleviate premenstrual symptoms and overcoming many limitations associated with this research area.

STUDY FUNDING/COMPETING INTEREST(S)

N.B. is supported by a Research Training Program stipend through Monash University. J.E. is supported by a Fellowship awarded by the Peter Fielding Foundation. The Hudson Institute of Medical Research is supported by the Victorian Government Operational Research Infrastructure Support. The authors declare no conflicts of interest.

Fight or flight? Effects of vaginal oestrus on cortisol, testosterone, and behaviour in guinea pig female-female interaction

It is accepted that social stress in relation to confrontation and competition can elicit behavioural and hormonal changes in social mammals. These effects have, however, been less frequently studied among female-female interactions. In the present study female-female confrontation experiments were carried out to monitor socio-positive and agonistic behaviour by controlling for the oestrus cycles of 12 individuals. Additionally, plasma cortisol (CORT) and testosterone (T) levels were determined before and after the experiments. During non-oestrus conditions a significant increase in CORT levels from pre- to post confrontation was registered and females spent more time to sit side by side. During vaginal oestrus the confrontation experiments revealed avoiding of a conspecific female by showing increased flight behaviour. However, during that period no changes in CORT levels were found. But, a non-significant increase in T was measured from pre- to post confrontation in both cycle phases, while no differences in the display of aggressive behaviours were found. These findings indicate considerable influences of different oestrus cycle phases on social stress-induced CORT secretion and the modulation of socio-positive and agonistic behaviour in female guinea pigs.

Acute and sub-chronic effects of purified cathinone from khat (Catha edulis) on behavioural profiles in vervet monkeys (Chlorocebus aethiops)

We investigated the cumulative effects of cathinone on behavioural alterations in single-caged vervet monkeys. Fourteen adult vervets were divided into tests (12 animals) and controls (2 animals), and exposed to escalating doses of cathinone at alternate days of each week for 4 months in presence and absence of cage enrichment. One month of pre-treatment phase served to establish baseline values. Composite behavioural scores of aggression, anxiety, abnormal responses, withdrawal and appetite loss were done. A series of repeated measures analysis of variances were conducted to examine the extent to which cathinone administration was associated with patterns of changes in behavioural data. Results indicate a dose-dependent effect of cathinone on increases of aggression, anxiety, abnormal responses, withdrawal, and appetite loss. The findings demonstrate that at high doses and long-term exposure, cathinone causes behavioural alterations probably via changes in presynaptic striatal dopamine system.

The impact of anxiety on social decision-making: behavioral and electrodermal findings

Anxiety plays an important role in social behavior. For instance, high-anxious individuals are more likely to avoid such social interactions as communicating with strangers. In this study, we investigate the impact of anxiety on social decision-making. The classic ultimatum game (UG) paradigm was utilized in concert with skin conductance recording. Behavioral results reveal that when playing as responders, high-trait anxiety (HTA) participants with lower levels of self-esteem, as well as low-trait anxiety (LTA) participants with higher levels of impulsivity, were more likely to accept human-proposed inequitable offers. In addition, the HTA participants rejected more computer-proposed inequitable offers than did LTA participants. Moreover, the skin conductance response to inequitable offers was correlated with levels of anxiety in the HTA group, but not in the LTA group. In conclusion, people differing in levels of anxiety showed distinct behavior patterns and autonomic neural responses during social decision-making, whereas the levels of self-esteem, impulsivity, and depression might be additional moderating factors. These findings contextualize high-anxious people's avoidance tendency in social interaction.

Premenstrual enhancement of snake detection in visual search in healthy women

It is well known that adult humans detect images of snakes as targets more quickly than images of flowers as targets whether the images are in color or gray-scale. When such visual searches were performed by a total of 60 adult premenopausal healthy women in the present study to examine whether their performance would fluctuate across the phases of the menstrual cycle, snake detection was found to become temporarily enhanced during the luteal phase as compared to early or late follicular phases. This is the first demonstration of the existence of within-individual variation of the activity of the fear module, as a predictable change in cognitive strength, which appears likely to be due to the hormonal changes that occur in the menstrual cycle of healthy women.

Update on research and treatment of premenstrual dysphoric disorder

Many women in their reproductive years experience some mood, behavioral. or physical symptoms in the week prior to menses. Variability exists in the level of symptom burden in that some women experience mild symptoms, whereas a small minority experience severe and debilitating symptoms. For an estimated 5%-8% of premenopausal women, work or social functioning are affected by severe premenstrual syndrome. Many women in this group meet diagnostic criteria for premenstrual dysphoric disorder (PMDD). Among women who suffer from PMDD, mood and behavioral symptoms such as irritability, depressed mood, tension, and labile mood dominate. Somatic complaints, including breast tenderness and bloating, also can prove disruptive to women's overall functioning and quality of life. Recent evidence suggests that individual sensitivity to cyclical variations in levels of gonadal hormones may predispose certain women to experience these mood, behavioral, and somatic symptoms. Treatments include: antidepressants of the serotonin reuptake inhibitor class, taken intermittently or throughout the menstrual cycle; medications that suppress ovarian cyclicity; and newer oral contraceptives with novel progestins.

Premenstrual syndrome

Most women of reproductive age have some physical discomfort or dysphoria in the weeks before menstruation. Symptoms are often mild, but can be severe enough to substantially affect daily activities. About 5-8% of women thus suffer from severe premenstrual syndrome (PMS); most of these women also meet criteria for premenstrual dysphoric disorder (PMDD). Mood and behavioural symptoms, including irritability, tension, depressed mood, tearfulness, and mood swings, are the most distressing, but somatic complaints, such as breast tenderness and bloating, can also be problematic. We outline theories for the underlying causes of severe PMS, and describe two main methods of treating it: one targeting the hypothalamus-pituitary-ovary axis, and the other targeting brain serotonergic synapses. Fluctuations in gonadal hormone levels trigger the symptoms, and thus interventions that abolish ovarian cyclicity, including long-acting analogues of gonadotropin-releasing hormone (GnRH) or oestradiol (administered as patches or implants), effectively reduce the symptoms, as can some oral contraceptives. The effectiveness of serotonin reuptake inhibitors, taken throughout the cycle or during luteal phases only, is also well established.

Characteristics and regulation of the ovarian cycle in vervet monkeys (Chlorocebus aethiops)

This study was designed to evaluate the timecourse of ovarian and pituitary endocrine events throughout the menstrual cycle in the vervet monkey, and whether circulating luteinizing hormone (LH) or the uterus regulates the functional lifespan of the vervet corpus luteum. Daily saphenous blood samples were collected from adult females (1) during spontaneous menstrual cycles (n = 7), and (2) during cycles in which a gonadotropin-releasing hormone antagonist (acyline) was administered for 3 days at midluteal phase (n = 3), and (3) for 30 days following recovery from hysterectomy (n = 4). Estradiol (E) and progesterone (P) levels were assayed using electrochemoluminescent assays. Gonadotropin levels were measured by radioimmunoassay using reagents developed for the assay of follicle-stimulating hormone and LH in macaques. Spontaneous cycles exhibited a midcycle E rise (476+/-49 pg/ml), engendering an LH surge, 12+/-1 days after onset of menses, followed by a luteal phase with peak P levels of 4.7+/-0.9 ng/ml. Histologic evaluation of the ovaries at late follicular phase or early luteal phase revealed the presence of a single, large Graafian follicle or developing corpus luteum, respectively. Acyline treatment caused a significant (P<0.05) decline in P levels (2.9+/-0.5 vs 0.5+/-0.3 ng/ml, 0 vs 48 h post-treatment) and premature menstruation compared with untreated controls (P<0.05). Hysterectomy had no apparent effect on the monthly pattern or levels of circulating E or P. Thus, the characteristics and regulation of the ovarian cycle in vervets appear similar to those in women and macaques, with cyclicity dependent on pituitary gonadotropin hormones and independent of a uterine luteolytic factor.

Plasticity of GABAA receptor subunit expression during the oestrous cycle of the rat: implications for premenstrual syndrome in women

Many women experience psychological changes during the luteal phase of their menstrual cycle. The late luteal (premenstrual) phase, when symptoms become most severe, is characterized by declining levels of ovarian progesterone. In female rats, withdrawal from prolonged dosing with progesterone leads to upregulation of alpha4 and delta subunits of the GABAA receptor in several brain regions. During the oestrous cycle of the rat, the natural fall in progesterone that occurs in late dioestrus is associated with a parallel increase in expression of alpha4, beta1 and delta GABAA receptor subunits in neurones in the periaqueductal grey matter (PAG), suggesting that new receptors of the alpha4beta1delta composition have been formed. Recombinant alpha4beta1delta receptors display a low EC50 for GABA, which is consistent with activation by extracellular levels of GABA. They are also likely to be located extrasynaptically and to carry tonic currents. In the PAG, a region involved in mediating panic-like anxiety, alpha4, beta1 and delta GABAA receptor subunits are located principally on GABAergic interneurones. On-going GABAergic neuronal activity normally limits and controls the excitability of the panic circuitry. During late dioestrus, when expression of alpha4, beta1 and delta subunits on GABAergic interneurones is upregulated, the increase in tonic current would be expected to lead to a reduction in the activity of the GABAergic population. Thus the panic circuitry would become intrinsically more excitable. It is suggested that during the menstrual cycle in women, plasticity of GABAA receptor subunit expression in brain regions such as the PAG, which are involved in mediating anxiety behaviour, may underlie some of the changes in mood that occur during the premenstrual period.

Female testosterone, dominance rank, and aggression in an Ethiopian population of hybrid baboons

Studies on the relationship between female testosterone (T) measures and behavior, particularly in free-ranging primate populations, remain scant. In this study we used fecal steroid analysis to examine the effects of seasonal, reproductive, and social factors on female T in a group of free-ranging hybrid baboons (Papio sp.) in the Awash National Park of Ethiopia. We collected behavioral and hormonal data from 25 adult females across an 11-month period. Solid phase extraction and radioimmunoassay (RIA) techniques were used to quantify T in 776 fecal samples collected weekly from each female. The results indicate that 1) the females had elevated T during pregnancy and during the wet season relative to other periods, 2) female dominance rank was positively related to T measures, and 3) female T and aggression were positively related within subjects but not across subjects. Higher T concentrations during pregnancy are consistent with other published profiles of pregnancy in primates. In combination with data on foraging, wet season increases in T may indicate contest competition for females. The rank-T relationship may be mediated by supplants or aggression. Finally, we discuss the different interpretations of the hormone-behavior relationship based on within- and across-subject analyses.

How does premenstrual dysphoric disorder relate to depression and anxiety disorders?

Premenstrual dysphoric disorder (PMDD) is a severe variant of premenstrual syndrome that afflicts approximately 5% of all women of fertile age. The hallmark of this condition is the surfacing of symptoms during the luteal phase of the menstrual cycle, and the disappearance of symptoms shortly after the onset of menstruation. Whereas many researchers have emphasized the similarities between PMDD and anxiety disorders, and in particular panic disorder, others have suggested that PMDD should be regarded as a variant of depression. Supporting both these notions, the treatment of choice for PMDD, the serotonin reuptake inhibitors (SRIs), is also first line of treatment for depression and for most anxiety disorders. In this review, the relationship between PMDD on the one hand, and anxiety and depression on the other, is being discussed. Our conclusion is that PMDD is neither a variant of depression nor an anxiety disorder, but a distinct diagnostic entity, with irritability and affect lability rather than depressed mood or anxiety as most characteristic features. The clinical profile of SRIs when used for PMDD, including a short onset of action, suggests that this effect is mediated by other serotonergic synapses than the antidepressant and anti-anxiety effects of these drugs. Although we hence suggest that PMDD should be regarded as a distinct entity, it should be emphasized that this disorder does display intriguing similarities with other conditions, and in particular with panic disorder, which should be the subject of further studies. Also, the possibility that there are subtypes of PMDD more closely related to depression, or anxiety disorders, than the most common form of the syndrome, should not be excluded.

Association between estrus cycle-related changes in respiration and estrus cycle-related aggression in outbred female Wistar rats

Premenstrual dysphoric disorder is characterized by irritability surfacing during the luteal phase of the menstrual cycle, and disappearing shortly after the onset of menstruation. Although the cardinal symptoms of premenstrual dysphoria are different from those of panic disorder, the two conditions share a number of traits indicating that they both may be associated with abnormalities in the regulation of respiration. Both subjects with panic disorder and subjects with premenstrual dysphoria are hence reported to display enhanced respiratory variability, and to experience anxiety when exposed to CO(2). In the present study, the possible influence of the estrus cycle on respiratory parameters in outbred female rats of the Wistar strain was investigated. Before being tested with respect to respiration, the rats were subdivided into two groups: those displaying estrus cycle-related variation in aggression, as evaluated using the resident intruder paradigm, and those not showing aggression throughout the cycle. Whereas the former group was found to display higher respiratory rate during the diestrus phase than during the proestrus/estrus phase, no cycle-related variation in respiration was observed in animals not showing cycle-related variation in aggression. The results support previous studies indicating that the estrus cycle exerts an influence on respiration, and suggest that rats prone to cycle-related aggression are more sensitive also to the influence of hormonal cyclicity on respiration. The possible bearing of these findings for the aberration in respiration displayed by subjects with premenstrual dysphoria is discussed.

Animal models of social stress: effects on behavior and brain neurochemical systems

Social interactions serve as an evolutionarily important source of stress, and one that is virtually ubiquitous among mammalian species. Animal models of social stress are varied, ranging from a focus on acute, intermittent, or chronic exposure involving agonistic behavior, to social isolation. The relative stressfulness of these experiences may depend on the species, sex, and age of the subjects, and subject sex also appears to influence the value of hypothalamic--pituitary--adrenal (HPA) axis activity as a general criterion for stress response: higher glucocorticoid levels are typically found in dominant females in some species. Social stress models often produce victorious and defeated, or dominant and subordinate, animals that may be compared to each other or to controls, but the appropriateness of specific types of comparisons and the interpretations of their differences may vary for the different models. Social stress strongly impacts behavior, generally reducing aggression and enhancing defensiveness, both inside and outside the stress situation. Social and sexual behaviors may be reduced in subordinate animals, as is activity and responsivity to normally rewarding events. However, some components of these changes may be dependent on the presence of a dominant, rather than representing a longer-term and general alteration in behavior. Social stress effects on brain neurotransmitter systems have been most extensively investigated, and most often found in serotonin and noradrenergic systems, with changes also reported for other monoamine and for peptidergic systems. Morphological changes and alterations of neogenesis and of cell survival particularly involving the hippocampus and dentate gyrus have been reported with severe social stress, as have longer-term changes in HPA axis functioning. These findings indicate that social stress models can provide high magnitude and appropriate stressors for research, but additionally suggest a need for caution in interpretation of the findings of these models and care in analysis of their underlying mechanisms.

Behavioral responses to ovariectomy and chronic anabolic steroid treatment in female cynomolgus macaques

A pilot study was conducted to investigate the effects of ovariectomy on rates of aggressive and affiliative behavior, as well as body size, in 38 young adult female cynomolgus monkeys (Macaca fascicularis) living in isosexual social groups of four to five animals. In addition, we assessed the effects of nandrolone decanoate (an anabolic steroid used for postmenopausal hormone replacement therapy) on indices of aggression, submission, and body size. Animals were randomized into three experimental conditions: 1) sham ovariectomized, untreated (SHAM); 2) ovariectomized, untreated (OVX); and, 3) ovariectomized, treated with nandrolone decanoate for 24 months (NAN). Each individual was observed for 10 min, one to two times per month, and all instances of agonistic and affiliative behavior were recorded by means of focal animal sampling. Ovariectomized, untreated animals exhibited a two- to threefold increase in aggression compared to SHAM or NAN animals; F(2, 32) = 4.09, p = 0.026; however, the expression of prosocial or affiliative behaviors as measured by rates of grooming and initiating friendly behavior was unaffected. At an i.m. dose of 25 mg every 2 weeks, nandrolone decanoate caused a 60% increase in body weight of the animals compared to untreated intact and ovariectomized animals, F(2, 31) = 161.57, p < 0.0001.

Serotonin and gender-specific psychiatric disorders

The serotonergic system has been linked to the etiology of several, albeit disparate, psychiatric disorders. The accumulation of many lines of evidence support the view that there are gender differences in the serotonergic system in humans. It is further proposed that a gender differentiated serotonergic system acts as the nidus for the development of gender-specific psychiatric disorders. Depression, anxiety and eating disorders are largely seen in females, whereas alcoholism, aggressivity and suicide predominate in males. Evidence from both animal and human studies suggesting that the serotonergic system mediates between social-environmental experience and biological states is presented and reviewed. A reconceptualization of the serotonergic system as a gender-specific psychobiological interface is proposed. (Int J Psych Clin Prac 1997; 1: 3-13).