Sociodemographic inequalities of suicide: a population-based cohort study of adults in England and Wales 2011-21

BACKGROUND

The risk of suicide is complex and often a result of multiple interacting factors. Understanding which groups of the population are most at risk of suicide is important to inform the development of targeted public health interventions.

METHODS

We used a novel linked dataset that combined the 2011 Census with the population-level mortality data in England and Wales. We fitted generalized linear models with a Poisson link function to estimate the rates of suicide across different sociodemographic groups and to identify which characteristics are independent predictors of suicide.

RESULTS

Overall, the highest rates of suicide were among men aged 40-50 years, individuals who reported having a disability or long-term health problem, those who were unemployed long term or never had worked, and those who were single or separated. After adjusting for other characteristics such as employment status, having a disability or long-term health problem, was still found to increase the incidence of suicide relative to those without impairment [incidence rate ratio minimally adjusted (women) = 3.5, 95% confidence interval (CI) = 3.3-3.6; fully adjusted (women) 3.1, 95% CI = 3.0-3.3]. Additionally, while the absolute rate of suicide was lower in women compared with men, the relative risk in people reporting impairments compared with those who do not was higher in women compared with men.

CONCLUSIONS

The findings of this work provide novel population-level insights into the risk of suicide by sociodemographic characteristics in England and Wales. Our results highlight several sociodemographic groups who may benefit from more targeted suicide prevention policies and practices.

Risk of COVID-19 death in adults who received booster COVID-19 vaccinations in England

The emergence of the COVID-19 vaccination has been critical in changing the course of the COVID-19 pandemic. To ensure protection remains high in vulnerable groups booster vaccinations in the UK have been targeted based on age and clinical vulnerabilities. We undertook a national retrospective cohort study using data from the 2021 Census linked to electronic health records. We fitted cause-specific Cox models to examine the association between health conditions and the risk of COVID-19 death and all-other-cause death for adults aged 50-100-years in England vaccinated with a booster in autumn 2022. Here we show, having learning disabilities or Down Syndrome (hazard ratio=5.07;95% confidence interval=3.69-6.98), pulmonary hypertension or fibrosis (2.88;2.43-3.40), motor neuron disease, multiple sclerosis, myasthenia or Huntington's disease (2.94, 1.82-4.74), cancer of blood and bone marrow (3.11;2.72-3.56), Parkinson's disease (2.74;2.34-3.20), lung or oral cancer (2.57;2.04 to 3.24), dementia (2.64;2.46 to 2.83) or liver cirrhosis (2.65;1.95 to 3.59) was associated with an increased risk of COVID-19 death. Individuals with cancer of the blood or bone marrow, chronic kidney disease, cystic fibrosis, pulmonary hypotension or fibrosis, or rheumatoid arthritis or systemic lupus erythematosus had a significantly higher risk of COVID-19 death relative to other causes of death compared with individuals who did not have diagnoses. Policy makers should continue to priorities vulnerable groups for subsequent COVID-19 booster doses to minimise the risk of COVID-19 death.

In vivo evidence of microstructural hypo-connectivity of brain white matter in 22q11.2 deletion syndrome

22q11.2 deletion syndrome, or 22q11.2DS, is a genetic syndrome associated with high rates of schizophrenia and autism spectrum disorders, in addition to widespread structural and functional abnormalities throughout the brain. Experimental animal models have identified neuronal connectivity deficits, e.g., decreased axonal length and complexity of axonal branching, as a primary mechanism underlying atypical brain development in 22q11.2DS. However, it is still unclear whether deficits in axonal morphology can also be observed in people with 22q11.2DS. Here, we provide an unparalleled in vivo characterization of white matter microstructure in participants with 22q11.2DS (12-15 years) and those undergoing typical development (8-18 years) using a customized magnetic resonance imaging scanner which is sensitive to axonal morphology. A rich array of diffusion MRI metrics are extracted to present microstructural profiles of typical and atypical white matter development, and provide new evidence of connectivity differences in individuals with 22q11.2DS. A recent, large-scale consortium study of 22q11.2DS identified higher diffusion anisotropy and reduced overall diffusion mobility of water as hallmark microstructural alterations of white matter in individuals across a wide age range (6-52 years). We observed similar findings across the white matter tracts included in this study, in addition to identifying deficits in axonal morphology. This, in combination with reduced tract volume measurements, supports the hypothesis that abnormal microstructural connectivity in 22q11.2DS may be mediated by densely packed axons with disproportionately small diameters. Our findings provide insight into the in vivo white matter phenotype of 22q11.2DS, and promote the continued investigation of shared features in neurodevelopmental and psychiatric disorders.

White matter microstructure in face and body networks predicts facial expression and body posture perception across development

Facial expression and body posture recognition have protracted developmental trajectories. Interactions between face and body perception, such as the influence of body posture on facial expression perception, also change with development. While the brain regions underpinning face and body processing are well-defined, little is known about how white-matter tracts linking these regions relate to perceptual development. Here, we obtained complementary diffusion magnetic resonance imaging (MRI) measures (fractional anisotropy [FA], spherical mean Ṧ_μ ), and a quantitative MRI myelin-proxy measure (R1), within white-matter tracts of face- and body-selective networks in children and adolescents and related these to perceptual development. In tracts linking occipital and fusiform face areas, facial expression perception was predicted by age-related maturation, as measured by Ṧ_μ and R1, as well as age-independent individual differences in microstructure, captured by FA and R1. Tract microstructure measures linking posterior superior temporal sulcus body region with anterior temporal lobe (ATL) were related to the influence of body on facial expression perception, supporting ATL as a site of face and body network convergence. Overall, our results highlight age-dependent and age-independent constraints that white-matter microstructure poses on perceptual abilities during development and the importance of complementary microstructural measures in linking brain structure and behaviour.

Risk of death following COVID-19 vaccination or positive SARS-CoV-2 test in young people in England

Several studies have reported associations between COVID-19 vaccination and risk of cardiac diseases, especially in young people; the impact on mortality, however, remains unclear. We use national, linked electronic health data in England to assess the impact of COVID-19 vaccination and positive SARS-CoV-2 tests on the risk of cardiac and all-cause mortality in young people (12 to 29 years) using a self-controlled case series design. Here, we show there is no significant increase in cardiac or all-cause mortality in the 12 weeks following COVID-19 vaccination compared to more than 12 weeks after any dose. However, we find an increase in cardiac death in women after a first dose of non mRNA vaccines. A positive SARS-CoV-2 test is associated with increased cardiac and all-cause mortality among people vaccinated or unvaccinated at time of testing.

Evaluation of Risk Factors for Postbooster Omicron COVID-19 Deaths in England

This cohort study of adults in England evaluates the association of sociodemographic and clinical risk factors with death from COVID-19 among individuals who completed primary vaccination and received a messenger RNA (mRNA) booster.

Risk of covid-19 related deaths for SARS-CoV-2 omicron (B.1.1.529) compared with delta (B.1.617.2): retrospective cohort study

OBJECTIVE

To assess the risk of covid-19 death after infection with omicron BA.1 compared with delta (B.1.617.2).

DESIGN

Retrospective cohort study.

SETTING

England, United Kingdom, from 1 December 2021 to 30 December 2021.

PARTICIPANTS

1 035 149 people aged 18-100 years who tested positive for SARS-CoV-2 under the national surveillance programme and had an infection identified as omicron BA.1 or delta compatible.

MAIN OUTCOME MEASURES

The main outcome measure was covid-19 death as identified from death certification records. The exposure of interest was the SARS-CoV-2 variant identified from NHS Test and Trace PCR positive tests taken in the community (pillar 2) and analysed by Lighthouse laboratories. Cause specific Cox proportional hazard regression models (censoring non-covid-19 deaths) were adjusted for sex, age, vaccination status, previous infection, calendar time, ethnicity, index of multiple deprivation rank, household deprivation, university degree, keyworker status, country of birth, main language, region, disability, and comorbidities. Interactions between variant and sex, age, vaccination status, and comorbidities were also investigated.

RESULTS

The risk of covid-19 death was 66% lower (95% confidence interval 54% to 75%) for omicron BA.1 compared with delta after adjusting for a wide range of potential confounders. The reduction in the risk of covid-19 death for omicron compared with delta was more pronounced in people aged 18-59 years (number of deaths: delta=46, omicron=11; hazard ratio 0.14, 95% confidence interval 0.07 to 0.27) than in those aged ≥70 years (number of deaths: delta=113, omicron=135; hazard ratio 0.44, 95% confidence interval 0.32 to 0.61, P<0.0001). No evidence of a difference in risk was found between variant and number of comorbidities.

CONCLUSIONS

The results support earlier studies showing a reduction in severity of infection with omicron BA.1 compared with delta in terms of hospital admission. This study extends the research to also show a reduction in the risk of covid-19 death for the omicron variant compared with the delta variant.

Androgen threshold to activate copulation differs in male rats prenatally exposed to alcohol, stress, or both factors

Few male rats prenatally exposed to a combination of alcohol and stress copulate spontaneously. This study determined adult sensitivity to testosterone (T) in males prenatally exposed to alcohol, to stress, or to both factors. Sexually naive males were tested with receptive females following castration and implantation of 20-, 30-, or 45-mm Silastic T-filled capsules. Serum T levels provided by these implants were measured. The behavior shown by males exposed only to prenatal alcohol did not differ from untreated control animals at any T dosage. Prenatal stress alone diminished the copulatory potential below control levels only when the intermediate T dosage was provided. Few males exposed to both alcohol and stress copulated under the lowest or the intermediate dose of adult T replacement, but most ejaculated normally when the largest capsule was implanted. The threshold to the sexual behavior-activating-properties of adult T exposure was moderately raised by prenatal stress but was severely affected when prenatal stress was combined with alcohol. We conclude that a diminished sensitivity to androgen in adulthood underlies some copulatory deficits resulting from treatments that alter fetal T levels. Such deficits may be concealed when behavior is evaluated in gonadally intact animals.

Fetal alcohol exposure blocks full masculinization of the dorsolateral nucleus in rat spinal cord

Male rats prenatally exposed to a combination of stress and ethanol show severely impaired ejaculatory patterns. This study examined two sexually dimorphic nuclei in the lumbar spinal cord implicated in the control of male copulatory reflexes in rats whose mothers were exposed to alcohol, to stress, or to both treatments during pregnancy. Alcohol exposure led to a marked decrease (22%) in the number of motor neurons in the dorsolateral nucleus (DLN) of the adult male offspring, but no significant change in cell count was detectable in the sexually dimorphic nucleus of the bulbocavernosus (SNB). The combination of alcohol and stress did not enhance the effect on the DLN above that produced by alcohol alone. Somal sizes in the DLN and SNB were not altered by any of the treatment conditions. Alcohol exposure probably leads to incomplete masculinization of the DLN in male rats by decreasing testicular steroidogenesis during the fetal stage(s) when sexual differentiation is ongoing in that CNS structure.

Prenatal alcohol and stress interact to attenuate ejaculatory behavior, but not serum testosterone or LH in adult male rats

Restraint stress reduced blood alcohol levels in pregnant rats given a liquid alcohol diet. The male offspring prenatally exposed to both stress and alcohol failed to ejaculate spontaneously, although they copulated normally following exogenous testosterone (T) administration. Males prenatally exposed only to alcohol or only to stress showed no behavioral deficits. Adult serum T and luteinizing hormone levels were normal in both of the fetal alcohol exposed male groups. It appears that the androgen threshold for ejaculatory behavior is elevated in males prenatally exposed to alcohol plus stress and cannot be realized with normal testosterone titers, but it can be attained with exogenous hormone administration. Presumably the alcohol and stress combination interfered with ontogenetic patterns of T needed to fully masculinize the fetal nervous system.

Prenatal alcohol and stress interact to attenuate ejaculatory behavior, but not serum testosterone or LH in adult male rats

Restraint stress reduced blood alcohol levels in pregnant rats given a liquid alcohol diet. The male offspring prenatally exposed to both stress and alcohol failed to ejaculate spontaneously, although they copulated normally following exogenous testosterone (T) administration. Males prenatally exposed only to alcohol or only to stress showed no behavioral deficits. Adult serum T and luteinizing hormone levels were normal in both of the fetal alcohol exposed male groups. It appears that the androgen threshold for ejaculatory behavior is elevated in males prenatally exposed to alcohol plus stress and cannot be realized with normal testosterone titers, but it can be attained with exogenous hormone administration. Presumably the alcohol and stress combination interfered with ontogenetic patterns of T needed to fully masculinize the fetal nervous system.

Critical periods of sensitivity of sexually dimorphic spinal nuclei to prenatal testosterone exposure in female rats

Male rats normally have more neurons than do females in two nuclei of the lumbar spinal cord, the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). Female rats exposed to testosterone propionate (TP) on the 2 days of gestation (Days 18 and 19) when males normally experience a surge in plasma testosterone showed a maximal increase in both SNB and DLN neuronal number. TP exposure just prior to, or following, Days 18 and 19 led to smaller increments. Administration of a small (5 microg) dose of TP after birth, while having no effect by itself, synergized with prenatal TP to enhance the number of SNB neurons. DLN neurons were less responsive to postnatal TP. The somal and nuclear size of SNB, but not DLN, neurons was increased by perinatal TP. Paradoxically, the number of DLN neurons with large somas (1358 microm2 or larger) was reduced by perinatal TP, a finding congruent with a previous report that females and feminized males have more of these large DLN neurons than control males. Our data suggest an exquisite sensitivity of the developing spinal nuclei to the timing of hormonal surges normally found in fetal males. Exposure to androgens during a brief prenatal period is needed to assure responsiveness to the low amounts of androgen circulating during neonatal ontogeny, when the process of sexual differentiation is completed.

Male and female sexual behavior potential of male rats prenatally exposed to the influence of alcohol, stress, or both factors

Adult sexual behaviors were characterized in male rats prenatally exposed to ethanol, stress, or ethanol combined with stress; 60% to 75% of each group exhibited female-typical lordosis. A substantial proportion of males subjected to alcohol (44%) or to alcohol with stress (54%) failed to ejaculate. The adult genitalia and testicular size appeared normal in all groups. Either alcohol or stress can suppress fetal plasma testosterone. Thus, exposing pregnant dams to alcohol, particularly in association with stress, may alter the hormonal milieu of their male fetuses sufficiently to block full masculinization and defeminization of sexually dimorphic copulatory behavior potentials, but not anatomy. It appears that certain pharmacological and stressful factors can interact during fetal ontogeny to influence the process of sexual behavior differentiation.

Sexually dimorphic areas in the rat medial amygdala: resistance to the demasculinizing effect of prenatal stress

Exposure to prenatal stress blocks full masculinization of several sexually dimorphic nuclei in the brain and spinal cord of male rats. We now compare the adult volume of the medical amygdala (MA) and two of its component cell groups, posterodorsal (MePD) and posteroventral (MePV), in prenatally stressed male rats and nonstressed males and females. Previous reports of sex differences (male > female) in the overall size of the MA and the MePD component were confirmed, and we identified a previously unreported sex difference (male > female) in MePV. Prenatal stress had no effect on the size of the total MA, or of the MePD or MePV in males. Maternal stress attenuates the surge in plasma testosterone (T) which normally occurs on days 18 and 19 of gestation in male rats. This brief suppression of T during prenatal development leads to incomplete masculinization of some sexually dimorphic features of the CNS (i.e. the SDN-MPOA of the hypothalamus, and SNB and DLN of the spinal cord) but not others (i.e. the MA, MePD, and MePV). The selective effects of prenatal stress on neural differentiation may be due to differences in the onset and duration of the periods when each of these structures in most sensitive to T and/or its metabolites.

Male and female sexual behavior potential of male rats prenatally exposed to the influence of alcohol, stress, or both factors

Adult sexual behaviors were characterized in male rats prenatally exposed to ethanol, stress, or ethanol combined with stress; 60% to 75% of each group exhibited female-typical lordosis. A substantial proportion of males subjected to alcohol (44%) or to alcohol with stress (54%) failed to ejaculate. The adult genitalia and testicular size appeared normal in all groups. Either alcohol or stress can suppress fetal plasma testosterone. Thus, exposing pregnant dams to alcohol, particularly in association with stress, may alter the hormonal milieu of their male fetuses sufficiently to block full masculinization and defeminization of sexually dimorphic copulatory behavior potentials, but not anatomy. It appears that certain pharmacological and stressful factors can interact during fetal ontogeny to influence the process of sexual behavior differentiation.

Patterns of ano-genital licking mother rats exhibit toward prenatally stressed neonates

The duration of ano-genital (AG) licking received by control and prenatally stressed male and female rat pups was compared under several testing conditions and ages. When tested with their own litters on day 2 postpartum. Sprague-Dawley dams stressed by exposure to intense light and restraint from days 14-21 of pregnancy spent as much time licking their pups as control dams. When tested with unfamiliar 8-9 day old pups both groups of mothers licked males more than females, but exhibited the same amount of licking toward males from control and prenatally stressed litters. When given simultaneous access to unfamiliar 11-12 day old control and prenatally stressed males, neither stressed nor control mothers displayed distinguishable patterns of licking. In adulthood a larger proportion of prenatally stressed than control males exhibited the female lordotic pattern, but a smaller percentage ejaculated. The data do not support previous suggestions that the abnormal sexual behavior patterns shown by prenatally stressed male rats are related to insufficient levels of AG stimulation received during neonatal ontogeny.

Prenatal beta-endorphin can modulate some aspects of sexual differentiation in rats

Sexually dimorphic traits were studied in offspring of rats injected with 33 micrograms rat beta-endorphin (beta-END) three times daily from Day 14 to Day 21 of pregnancy. beta-END males had shorter neonatal anogenital distances than did controls and were more likely to show the female lordosis pattern as adults, but they did not differ in male copulatory behavior. When given a choice between spending time with an estrous female or a male, beta-END males showed a lower preference for the female than did control males. The number and somal size of neurons in the bulbocavernosus and dorsolateral nucleus of the lumbar spinal cord were unaffected by drug exposure. Elevated beta-END during fetal ontogeny apparently alters the differentiation of some, but not all, sexually dimorphic traits. The data suggest that endogenous opioids may contribute to the etiology of the prenatal stress syndrome.

SDN-MPOA volume in male rats is decreased by prenatal stress, but is not related to ejaculatory behavior

A computer-assisted image analysis technique was used to measure the adult volume of the sexually dimorphic nucleus of the medial preoptic area (SDN-MPOA) in prenatally stressed male rats and in groups of non-stressed males and females. The SDN-MPOA of male offspring from dams stressed daily (i.e. three 45-min exposures to physical restraint and bright light) during the last week of pregnancy was significantly smaller than in males not exposed to stress, but was larger than in females. Maternal stress has been shown to attenuate the surge in fetal plasma testosterone (T) which normally occurs on days 18 and 19 of gestation in male rats. The present results suggest that suppression of T during prenatal development leads to an incomplete masculinization of the SDN-MPOA in male rats. There was no difference in SDN-MPOA volume between males that exhibited the ejaculatory pattern when tested with estrous females and males that failed to ejaculate in either the control or prenatal stress group. SDN-MPOA volume does not appear to be predictive of masculine ejaculatory performance.

Prenatal flutamide alters sexually dimorphic nuclei in the spinal cord of male rats

The effects of prenatal exposure to the antiandrogen flutamide on two sexually dimorphic nuclei of the lumbar spinal cord, the dorsolateral nucleus (DLN) and the spinal nucleus of the bulbocavernosus (SNB), were investigated. Rat dams were given daily injections of 5 mg flutamide or vehicle alone from day 11 through 21 of pregnancy. The spinal cords and perineal morphology of their male and female offspring were examined in adulthood. Flutamide reduced the number of SNB and DLN neurons, reduced the somal and nuclear area of SNB neurons, and reduced the weight of the perineal muscles in males. Flutamide produced no effect in females. No sexual dimorphism was found in the mean somal area of DLN neurons, but a sexual dimorphism was found in the distribution of somal areas in our samples; females had proportionately more large neurons than males. Flutamide-treated males also had proportionately more large neurons than control males but fewer than females. A sexual dimorphism was found in the nuclear areas of DLN neurons but flutamide did not influence this trait.

Prenatal !b-endorphin can modulate some aspects of sexual differentiation in rats

Sexually dimorphic traits were studied in offspring of rats injected with 33 micrograms rat beta-endorphin (beta-END) three times daily from Day 14 to Day 21 of pregnancy. beta-END males had shorter neonatal anogenital distances than did controls and were more likely to show the female lordosis pattern as adults, but they did not differ in male copulatory behavior. When given a choice between spending time with an estrous female or a male, beta-END males showed a lower preference for the female than did control males. The number and somal size of neurons in the bulbocavernosus and dorsolateral nucleus of the lumbar spinal cord were unaffected by drug exposure. Elevated beta-END during fetal ontogeny apparently alters the differentiation of some, but not all, sexually dimorphic traits. The data suggest that endogenous opioids may contribute to the etiology of the prenatal stress syndrome.

Prenatal stress feminizes juvenile play patterns in male rats

Sexually dimorphic rough-and-tumble play patterns were compared in male and female rats derived from control mothers and mothers stressed from days 14-21 of pregnancy. Animals were weaned into groups of 8 consisting of 2 males and 2 females from each treatment. Play in the home cage was recorded at 25, 28, 31, 34, 37 and 45 days of age and was most intense on day 31. The overall level of play was significantly higher in control males than in females or stressed males. Control males showed higher levels of the pinning component of rough-and-tumble play than females or stressed males. No play partner preferences were detected in any group. In adulthood, a higher percentage of stressed than control males displayed the female lordotic pattern. No deficits in ejaculatory behavior occurred in the stressed males. Since maternal stress alters patterns of plasma testosterone in male fetuses, the data suggest that the sexual differentiation of social play begins during prenatal ontogeny in the rat. The present results show that sexually dimorphic behaviors displayed before puberty are incompletely masculinized in prenatally stressed males, a finding similar to that reported for a number of adult behaviors.

Prenatal stress alters sexually dimorphic nuclei in the spinal cord of male rats

The spinal nucleus bulbocavernosus (SNB), the dorsolateral nucleus of the spinal cord (DLN), and the bulbocavernosus/levator ani (BC/LA) muscle complex were examined in prenatally stressed and control adult male rats, which had been screened for male copulatory behavior. There was a small but significant decrease in the number of DLN (5%) and SNB (3%) neurons in prenatally stressed males compared to controls. Prenatal stress had no effect on the somal or nuclear area of individual neurons within either nucleus, nor did it affect the weight of the BC/LA muscle complex. There were no differences in any of these measures between males that ejaculated and those did not in either the stressed or the control group. These data suggest that exposure of pregnant rats to transient environmental stressors may result in permanent alterations in androgen-sensitive CNS structures in their male offspring.

Naltrexone normalizes the suppression but not the surge of delta 5-3 beta-hydroxysteroid dehydrogenase activity in Leydig cells of stressed rat fetuses

Rat fetuses from mothers stressed chronically by immobilization and high intensity illumination beginning on day 14 of gestation have higher than normal levels of delta 5-3 beta-hydroxysteroid dehydrogenase (3 beta HSD) activity in Leydig cells on day 17 of gestation and lower than normal levels on days 18 and 19. Plasma testosterone titers in normal and stressed male fetuses closely parallel the activity of 3 beta HSD in fetal Leydig cells. In the present study quantitative cytochemistry was used to determine whether the stress-induced alterations in 3 beta HSD activity could be prevented by treating the mother with naltrexone, an opioid receptor blocker, before each stress session. Naltrexone normalized 3 beta HSD activity on days 18 and 19 of gestation, suggesting that the stress-induced suppression involves the endogenous opioid system. In contrast, naltrexone did not prevent the elevation in enzyme activity seen on day 17 in stressed fetuses. The persistence of a stress-induced surge on day 17, in spite of naltrexone therapy, suggests that some nonopioid mechanism is operational at that time.

Plasma luteinizing hormone levels in normal and prenatally stressed male and female rat fetuses and their mothers

Concentrations of luteinizing hormone (LH) were measured in plasma of fetal and neonatal rats obtained from control mothers and from mothers exposed to stress from Days 14 to 21 of gestation. The regimen of stress used is known to be associated with an abnormal ontogenetic pattern of testosterone secretion from the fetal testes. The overall ontogenetic pattern of immunoreactive LH levels in plasma was similar in male and female rats, and was unaffected by stress. In all groups, LH was low from Days 16 to 20 of gestation, and then rose progressively through birth, i.e. Day 23. However, stressing the mother significantly decreased the already low levels of LH between Days 16 and 20, as indicated by a larger percentage of samples from stressed fetuses of both sexes with LH levels below the limit of sensitivity of the assay. Sex differences in both the control and stressed group became evident only after Day 20 of gestation, with plasma concentrations of females exceeding those of males from Day 21 to 23 post-conception.

Prenatal and neonatal androgen exposure interact to affect sexual differentiation in female rats

Rats were injected with oil on Days 17.5 and 18.5 of pregnancy or with 2 mg of testosterone propionate (TP) on Days 15.5 and 16.5, or Days 17.5 and 18.5, or Days 19.5 and 20.5. The female offspring were given oil or 5 micrograms of TP on Day 25 postconception. Among females exposed to TP only during prenatal ontogeny, a lower proportion of those treated on Days 17.5-18.5 of gestation displayed lordotic behavior than did the control group. Postnatal TP alone did not affect lordosis. However, all groups receiving combined pre- and postnatal TP showed impaired estrous patterns. The development of several components of morphology also was differentially affected by the timing of the androgen exposure. The data suggest that the differentiation of sexual behavior and reproductive morphology in the rat are influenced by an interaction of androgen dependent processes operating at different stages of perinatal ontogeny. Further, there may be an optimal fetal period during which androgenization sensitizes animals to low levels of testosterone circulating during neonatal development.

Prenatal and neonatal androgen exposure interact to affect sexual differentiation in female rats

Rats were injected with oil on Days 17.5 and 18.5 of pregnancy or with 2 mg of testosterone propionate (TP) on Days 15.5 and 16.5, or Days 17.5 and 18.5, or Days 19.5 and 20.5. The female offspring were given oil or 5 micrograms of TP on Day 25 postconception. Among females exposed to TP only during prenatal ontogeny, a lower proportion of those treated on Days 17.5-18.5 of gestation displayed lordotic behavior than did the control group. Postnatal TP alone did not affect lordosis. However, all groups receiving combined pre- and postnatal TP showed impaired estrous patterns. The development of several components of morphology also was differentially affected by the timing of the androgen exposure. The data suggest that the differentiation of sexual behavior and reproductive morphology in the rat are influenced by an interaction of androgen dependent processes operating at different stages of perinatal ontogeny. Further, there may be an optimal fetal period during which androgenization sensitizes animals to low levels of testosterone circulating during neonatal development.

Naltrexone blocks the effects of prenatal stress on sexual behavior differentiation in male rats

The male offspring of rats stressed three times daily during days 14-21 of pregnancy were more likely to show lordotic behavior when tested in adulthood than were control males. This feminization of sexual behavior was not observed if the mothers were injected with the opioid antagonist naltrexone before being stressed. These data suggest that endogenous opioids released under conditions of stress can alter the normal process of sexual behavior differentiation in the fetal male rat.

Prepuberal social rearing conditions and sexual behavior in control and neonatally castrated male rats

Male and female sexual behaviors were assessed in control and neonatally castrated male rats that had been housed with a female, a control male, or a neonatally castrated male from day 16 until adulthood. Prepuberal housing conditions had no differential effect on lordosis or ejaculatory potentials of neonatally castrated males tested as adults. A smaller percentage of control males raised with a neonatal castrate ejaculated than did animals housed with a female or a control male. However, a greater proportion of control males caged with a female showed lordosis than did those living with another control male or with a neonatal castrate. The data demonstrate the modulating effects which specific types of social stimulation experienced during early life have on sexual behaviors displayed in adulthood.

Prenatal stress and prepuberal social rearing conditions interact to determine sexual behavior in male rats

The two major categories of factors known to influence adult sexual behavior potentials are the relative amounts of androgen present during specific stages of perinatal ontogeny and adequate social stimulation during prepuberal development. The possible interaction between these two was evaluated by characterizing the ejaculatory and lordotic behavior potentials of prenatally stressed and control male rats that had been weaned at 16 days of age and raised either in total social isolation or with a same-age female, a control male, or a prenatally stressed male. The decrement in male sexual behavior produced by prenatal stress was attenuated by raising the male with either a female or a control male. Social isolation alone or in combination with stress resulted in severely deficient male behavior. Peripheral skin shock promoted ejaculatory behavior in many previously noncopulating prenatally stressed males raised with other stressed males, but it was ineffective in most isolated animals. The high lordosis potential characteristic of prenatally stressed male rats was slightly lower in the group with a female cagemate and was markedly decreased by social isolation. These results support and extend the finding by Dunlap, Zadina, and Gougis (1978) that prenatal hormonal events and prepuberal rearing conditions can interact to attenuate or accentuate the effects that either treatment alone has on the development of adult sexual behavior potentials.

Prenatal stress and prepuberal social rearing conditions interact to determine sexual behavior in male rats

The two major categories of factors known to influence adult sexual behavior potentials are the relative amounts of androgen present during specific stages of perinatal ontogeny and adequate social stimulation during prepuberal development. The possible interaction between these two was evaluated by characterizing the ejaculatory and lordotic behavior potentials of prenatally stressed and control male rats that had been weaned at 16 days of age and raised either in total social isolation or with a same-age female, a control male, or a prenatally stressed male. The decrement in male sexual behavior produced by prenatal stress was attenuated by raising the male with either a female or a control male. Social isolation alone or in combination with stress resulted in severely deficient male behavior. Peripheral skin shock promoted ejaculatory behavior in many previously noncopulating prenatally stressed males raised with other stressed males, but it was ineffective in most isolated animals. The high lordosis potential characteristic of prenatally stressed male rats was slightly lower in the group with a female cagemate and was markedly decreased by social isolation. These results support and extend the finding by Dunlap, Zadina, and Gougis (1978) that prenatal hormonal events and prepuberal rearing conditions can interact to attenuate or accentuate the effects that either treatment alone has on the development of adult sexual behavior potentials.

Differential effects of maternal stress on circulating levels of corticosterone, progesterone, and testosterone in male and female rat fetuses and their mothers

Testosterone, progesterone, and corticosterone titers were measured by RIA in plasma of stressed and control pregnant rats and their male and female fetuses on days 17, 18, 19, and 21 of gestation and on the day of birth. The regimen of stress used (three 45-min periods of restraint under intense illumination daily from days 14-21 of pregnancy) causes failure of masculinization and defeminization of behavioral potentials in male offspring. In fetuses of both sexes, corticosterone titers increased sharply between days 17 and 18 postconception (pc) to a peak that was maintained through day 19 and then declined. This pattern resembled that obtained for testosterone in control male fetuses in which the levels of testosterone also rose sharply between days 17 and 18 pc. Corticosterone titers were elevated in samples obtained during the middle of the stress session from both the mothers (serum) and their male and female fetuses (plasma). Increased corticosterone levels were no longer evident in samples obtained from fetuses 75-165 min after the end of a stress session. Testosterone titers were altered by stress only in male fetuses. Their testosterone levels were elevated on day 17 pc, and the surge on days 18 and 19 pc, characteristic of control males, was absent in samples obtained 75-165 min after termination of stress. Progesterone titers were not affected by stress in either mothers or their fetuses. In both stressed and control groups, progesterone concentrations were identical in male and female fetuses, were higher in mothers than in fetuses, and declined in both fetuses and mothers between days 19 and 21 pc. Thus, a persistent effect of stress was observed only on testosterone and only in males.

The prenatal stress syndrome: current status

Exposure of female rats to stressors during the last week of pregnancy results in a selective feminization and demasculinization of adult sexual behaviors in the male offspring. No behavioral abnormalities are detectable in the female offspring, and reproductive morphological structures appear normal in both sexes. Existing data suggest that the mechanism mediating the so called Prenatal Stress Syndrome in male rats is an alteration in fetal testicular enzyme activity. This, in turn, leads to abnormal levels of testosterone, the hormone believed to masculinize sexual behavior potentials at critical stages of perinatal development. Specifically, the activity of the steroidogenic enzyme delta 5-3 beta-hydroxysteroid dehydrogenase in fetal Leydig cells and plasma titers of testosterone are low in prenatally stressed males on days 18 and 19 of gestation, a time when both of these substances reach maximal levels in control males. The implications of this model for sexual behavior differentiation in higher organisms is explored.

Environmental stress alters the developmental pattern of delta 5-3 beta-hydroxysteroid dehydrogenase activity in Leydig cells of fetal rats: a quantitative cytochemical study

Quantitative cytochemistry was used to determine the effect of subjecting pregnant rats to environmental stress on the activity of delta 5-3 beta hydroxysteroid dehydrogenase (3 beta-HSD) in Leydig cells of their fetuses. Enzyme activity was measured by microspectrophotometry in individual Leydig cells in cryostat sections of fetal testes on Days 16-21 postconception. Fetuses of stressed mothers lacked the peak of enzyme activity on Days 18 and 19 of gestation that is characteristic of Leydig cells of normal fetuses at this time. In addition, both before and after these 2 days, 3 beta-HSD activity in Leydig cells of stressed fetuses was significantly higher than normal. The altered developmental pattern of 3 beta-HSD activity in the stressed fetuses largely corresponds to the changes in plasma testosterone found previously in male fetuses of mothers exposed to the same regimen of stress. Thus, in the fetal Leydig cell, the activity of 3 beta-HSD, a key steroidogenic enzyme, can be modified by environmental stress, and provides an index of steroidogenic activity of the fetal testes and of the titers of circulating testosterone.

Reproductive functioning in the prenatally stressed female rat

The reproductive behavior and physiology of female offspring of rats stressed during pregnancy were assessed. Mothers were restrained and placed under bright, hot lights from Day 14 through 21 of gestation. This treatment, which is known to disrupt the sexual behavior of male offspring, did not alter reproductive functioning in the female offspring. The females showed evidence of normal cyclicity, sexual behavior, pregnancy, parturition, pup survival, and maternal behavior when tested beginning at 70 or at 140 days of age.

Fetal female rats are masculinized by male littermates located caudally in the uterus

Female rats are masculinized in utero by male littermates sharing the same uterine horn. Increased anogenital distances in neonatal females and mounting behavior in adult females are related to the presence of males on the caudal side of the females in the uterine horn. Contrary to current beliefs, interamniotic diffusion may not be responsible for the exchange of masculinizing agents among fetuses. Since uterine blood flow in the rat is from the direction of the cervix toward the ovary, masculinizing hormones secreted by fetal males may be carried via the uterine vasculature to female littermates located further downstream.

Intralimbic progesterone and methysergide facilitate lordotic behavior in estrogen-primed female rats

Intracranial administration of progesterone or a serotonergic receptor blocker into either the dorsal hippocampus or corticomedial amygdala, but not the septum, activate lordotic behavior in estrogen-primed female rats. The same intra-amygdaloid sites mediated the effects of both treatments, whereas in the hippocampus the regio superior was responsive to serotonergic receptor blockade and the dentate gyrus was responsive to progesterone. This is the first demonstration that the amygdala and hippocampus participate both in the facilitation of lordosis by progesterone and in a serotonergic system which inhibits female sexual behavior.

Sexual behavior in male rats following intracerebral estrogen application

The effects on sexual behavior and morphology of estradiol benzoate (EB) applied directly to the medial preoptic nucleus were assessed in three groups of male rats with varying sexual behavior potentials. High levels of lordotic behavior were observed in all EB-treated groups. Cholesterol was uniformly ineffective. Central EB failed to facilitate male copulatory behavior in any group. However, there was evidence that cannula implantation may have impaired the potential for male behavior. Significant reductions in testis and epididymis weights were evident in some but not all EB-treated males. It was concluded that EB can activate lordotic behavior consistently in male rats if applied in sufficient amounts to the medial preoptic region.

Maternal stress alters plasma testosterone in fetal males

Titers of testosterone in plasma were determined by radioimmunoassay in male rat fetuses of stressed and control mothers on days 17, 18, 19, 21, and 23 (the day of birth) after conception. In fetuses of stressed mothers, testosterone concentrations were highest on day 17, declined on days 18 and 19, and then remained unchanged. In the control fetuses, testosterone increased from relatively low concentrations on day 17 to the highest amounts on days 18 and 19, and then declined. Thus, the persistence of feminine and impaired masculine sexual behavior in male offspring of stressed mothers could be due to the absence of a surge of circulating testosterone during days 18 and 19 after conception, a period postulated to be critical in the development of the central nervous system in the rat.

Plasma testosterone and progesterone titers of pregnant rats, their male and female fetuses, and neonatal offspring

Testosterone and progesterone titers were determined by RIA in the plasma of pregnant rats and their male and female fetuses from day 17 of gestation through the day of birth and in male and female neonates on days 3 and 5 post partum. Males had significantly higher mean testosterone levels than females from day 18 of gestation through day 5 post partum. Sex differences in plasma testosterone concentrations were greatest in the fetuses on days 18 and 19 of gestation when testosterone levels peaked in the males. Instances in which female fetuses had testosterone titers equal to or greater than their male littermates were found on every day of gestation except day 18. Mean testosterone concentrations in plasma of female fetuses were high throughout gestation (greater than 1000 pcg/ml). Testosterone concentrations decreased in both sexes after birth. Differences between the sexes remained significant, and although there was an overlap in the values for males and females, testosterone concentrations in females exceeded those of their male littermates in only one out of nine pairs of samples on day 5 and in none of seven pairs on day 3 post partum. There were no significant differences in progesterone levels in plasma of males and females, either pre- or postnatally. Progesterone titers changed as a function of days post conception in both the fetuses and their mothers. In the fetuses, progesterone levels declined progressively from day 18 post conception through the day of birth, while in the mother they rose from days 18 to 19 then declined between days 20 and 21 of pregnancy. Fetuses had lower progesterone titers than their mothers. From these data, we conclude that day 18 and possibly day 19 post conception represent a critical period during which the central nervous system of the male is primed by high levels of testosterone. Thereafter, the process of masculinization is completed by exposure to testosterone levels that are relatively low and need not be consistently higher than those of female littermates.

Effects of perinatal androstenedione on sexual differentiation in female rats

Androstenedione was administered prenatally, postnatally, postnatally, or both pre-and postnatally to female rats. The extent to which reproductive morphology, ovarian functioning, and adult sexual behavior were masculinized and defeminized depended on the dosage, timing, and duration of the hormone treatment. The combined pre-plus postnatal treatment resulted in the greatest degree of modification in that such females were anatomically masculinized and did not ovulate. When tested in adulthood, they showed a high potential for the male copulatory pattern and little lordotic behavior. It is concluded that androstenedione, while not as potent an androgen as testosterone propionate, nevertheless has the potential to participate in the process of sexual differentiation.

Central progesterone induces female sexual behavior in estrogen-primed intact males rats

Progesterone induced high levels of female lordotic behavior in 10 of 17 intact, estrogen-primed male rats when it was applied directly to the medial preoptic-anterior hypothalamic area. All 17 males previously had shown lordosis when the serotonergic antagonist methysergide was applied to the same central sites. Few males responded to systemic progesterone and none to intracralial cholesterol. Intradiencephalic Metycaine, a local anesthetic, induced lordosis in eight male that previously had responded to central progesterone. These data indicate that estrogen and progesterone act synergistically to induce lordosis in male rats when progesterone is administered directly to sensitive brain sites.

Exogenous androgen activates female behavior in noncopulating, prenatally stressed male rats

Male copulatory behavior was severely impaired in the male offspring of female rats stressed during pregnancy. This deficiency persisted even after castration and prolonged treatment with testosterone propionate and after exposure to electric skin shock. However, androgen treatment effectively activated female lordotic behavior in a large percentage of prenatally stressed males but not in any control animals and in only a negligible number of postnatally stressed males. Although prenatal stress demasculinizes and feminizes behavior, no modifications of reproductive morphology were detectable. It is postulated that prenatal stress alters normal sexual behavior differentiation by attenuating testosterone secretion from the fetal testes.

Monoaminergic mediation of female sexual behavior

Lordotic behavior was facilitated in estrogen-primed female rats by direct application of progesterone or serotonergic or beta-adrenergic receptor blockers to specific telencephalic, anterior hypothalamic-medial preoptic, or posterior hypothalamic sites. Blockade of the alpha-adrenergic system was ineffective in facilitating lordosis, as was the application of the active drugs to control sites in the thalamus or basal ganglia. Female soliciting behavior was not evoked by any of the treatments. It is concluded that the lordotic behavior component of the female rat's estrous behavior pattern is inhibited by a specific central monoaminergic system that also responds to progesterone. Soliciting behavior appears to be mediated by systems that are anatomically, and possibly neurochemically, separable from those regulating lordosis.

Female lordotic behavior mediated by monoamines in male rats

Direct application of serotonergic of beta-adrenergic receptor blockers to anterior or posterior areas of the hypothalamus induced lordosis in intact estrogen-primed male rats. Such treatment with an alpha-adrenergic blocker or systemic administration of progesterone failed to increase lordosis. Centrally elicited lordosis did not occur without estrogen priming. Anatomical and neurochemical similarity may exist in the brain mechanism mediating lordotic behavior in male and female adult rats.