Testosterone prevents synaptic loss in the perineal motoneuron pool in the spinal cord in male rats exposed to chronic stress

Chronic stress is known to induce disorders of reproductive neuroendocrine functions. Motoneurons of the spinal nucleus of the bulbocavernosus (SNB) in male rats play an important role in copulatory behavior. In the present study, it was examined whether chronic stress would alter synaptic organization of the SNB motoneurons and whether androgen would modify the changes under chronic stress. Five male rats were under restraint stress for 5 days per week for 3 weeks, and five males implanted subcutaneously with Silastic capsules containing testosterone were also exposed to stress. Five males served as unstressed controls. After 3 weeks of restraint stress, cholera toxin-horseradish peroxidase (CT-HRP) was injected into the bulbocavernosus muscles and animals were killed 2 days later. The spinal cords containing the SNB were dissected, processed with a modified tetramethylbenzidine (TMB) method for visualization of retrogradely transported CT-HRP, and examined ultrastructurally. Neuronal structures apposing the membranes of 150 SNB motoneurons (total for three groups) were analyzed by measuring the percentage of somatic membranes covered by synaptic contacts. The mean percentage of somatic membranes covered by synapses in males exposed to chronic stress was significantly less than that in controls or stressed males treated with testosterone. Size and number of synaptic contacts per unit length of somatic membranes in males exposed to stress were also significantly less than those in controls or stressed males treated with testosterone. There was no significant difference in any of the parameters between controls and stressed males treated with testosterone. Changes in plasma levels of testosterone showed the same profile as changes in the synaptic contacts. These results suggest that the SNB motoneurons of male rats exposed to chronic stress retain a considerable synaptic plasticity in response to androgen, and that androgen treatment can rescue the SNB system in male rats when under chronic restraint stress.     

Genotype modulates prenatal stress effects on aggression in male and female mice

Prenatal stress (heat and restraint) significantly increased postpartum aggression (proportion of animals fighting and/or the intensity of the behavior) in C57BL/6J female mice and reduced the behavior in DBA/2J females. For intermale aggression, prenatal stress increased the behavior (intensity of aggression) in C57BL/6J males but did not affect aggressive behavior in DBA/2J animals. Infanticidal behavior (the killing of young) exhibited by male mice was not influenced by prenatal stress in either strain. Relative anogenital distance measurements in neonates at birth did not serve as a reliable predictor of strain variation in prenatal stress effects. Prenatal stress did not influence this measure of prenatal androgen exposure in DBA/2J or C57BL/6J females. For males, prenatal stress elevated relative anogenital distance in C57BL/6J mice and decreased this measure in DBA/2J animals. Prenatal stress effects on aggressive behavior in male and female mice therefore depend upon genotype. Strain-dependent differences may be modulated by differences in endocrine reactivity to prenatal stress/and or differential central neural tissue sensitivity to hormones.     

Lex talionis: Testosterone and the law of retaliation

Research examining both the organizing and activating effects of testosterone in one-shot bargaining contexts has been vexed by inconsistencies. Some research finds that high-testosterone men are more likely to reject unfair offers in an ultimatum game and exogenous administration of testosterone to men leads to less generous offers. In contrast, other research finds that higher prenatal exposure to testosterone predicts more generous dictator game offers and administering testosterone to women leads to more generous ultimatum game offers. The current research seeks to resolve these inconsistencies by examining how the organizing effects of testosterone affect bargaining behavior. Because testosterone is associated with status seeking and concerns with social reputation, we hypothesized that testosterone would predict aggressive bargaining but only after provocation. Two studies found that prenatal testosterone exposure, as measured by 2D:4D ratio, led to aggressive responses for both males and females, but only after they received unfair offers. Furthermore, perceptions of fairness violations moderated but did not mediate the effect of testosterone on retributional responding. These results suggest that the organizing effects of testosterone have consistent effects on bargaining behavior for both males and females but its predictive ability requires some form of provocation to emerge.     

Altered grooming responses to stress in rats exposed prenatally to ethanol

The effects of prenatal alcohol exposure on grooming, locomotion, and rearing in response to stress were examined in adult rats whose mothers consumed a liquid diet containing 35% ethanol-derived calories (EDC). Offspring of both pair-fed 0% EDC mothers and ad libitum chow-fed mothers were included as controls. In Experiment 1, females groomed more than males following placement into a novel test chamber, but no differences due to prenatal treatment were observed. Ethanol-exposed animals groomed more than controls following the stress of a forced 1-min swim (Experiment 2), but when rats tested in Experiment 1 were observed again after forced swim stress (Experiment 3), no differences due to prenatal treatment or sex were observed. Experiment 4 examined the effects of pretreatment with 1 mg/kg naloxone on novelty-induced grooming and as in Experiment 1 prenatal treatment did not affect grooming responses. Females again groomed significantly more than males and naloxone reduced grooming equally for all groups. The results suggest that novelty-induced grooming is a sex-influenced behavior, with females grooming more than males, and that animals exposed prenatally to alcohol and tested as adults may have altered responses to certain stressors (i.e., forced swim) under specific conditions. The altered grooming response of alcohol-exposed rats to swim stress can be eliminated by preexposing them to novelty stress.     

Gender differences in acute and chronic stress in Wistar Kyoto (WKY) rats

While females are considered more susceptible to depressive behavior, this assertion is not strongly supported by the experimental literature. Since stress contributes to depressive behavior, male and female Wistar Kyoto (WKY) rats were exposed to either one session (acute stress) or 5 sessions (chronic stress) of restraint plus cold in order to study depressive behavior in male and female rats. After their respective treatment exposure, rats were tested in the open field test (OFT) and for retention of a passive-avoidance (P-A) task. One stress session resulted in significant immobility in the OFT for males, whereas 5 sessions were required to produce similar immobility in female rats. Acute stress interfered with the retention of the P-A response for males, while both acute and chronic stress produced poor P-A responses in female rats. Food consumption decresed, progressively, as a function of stress sessions, in female rats, whereas feeding in males returned to control levels after five stress days. Both acute and chronic stress exacerbated the stress ulcer response in male rats, but not in female rats. Chronic, but not acute, stress resulted in an increase in serotonin transporter mRNA levels in the dorsal raphe nucleus of both male and, female rats. The general consensus from these data suggested that female rats were more vulnerable to chronic stress and consequently supported the notion that females may be more susceptible to stress induced behavioral depression.     

Prenatal stress alters early neurobehavior, stress reactivity and learning in non-human primates: a brief review

In this paper we review three prospective longitudinal studies from our laboratory examining the effects of prenatal stress on early neuro behavior, stress reactivity and learning performance in rhesus monkeys. Either a noise stressor or ACTH treatment was administered to pregnant monkeys during specific periods of pregnancy and offspring were examined repeatedly across development. In all three studies, the prenatally stressed monkeys showed reduced attention and impaired neuromotor functioning during the first month of life compared to controls from undisturbed pregnancies. When the monkeys were separated from their mothers or peers at 6-8 months of age, prenatally stressed monkeys exhibited more disturbance behavior and showed hypothalamic-pituitary-adrenal axis dysregulation. During adolescence, they exhibited impairments in learning, compared to controls.     

Gender differences in acute and chronic stress in Wistar Kyoto (WKY) rats.

While females are considered more susceptible to depressive behavior, this assertion is not strongly supported by the experimental literature. Since stress contributes to depressive behavior, male and female Wistar Kyoto (WKY) rats were exposed to either one session (acute stress) or 5 sessions (chronic stress) of restraint plus cold in order to study depressive behavior in male and female rats. After their respective treatment exposure, rats were tested in the open field test (OFT) and for retention of a passive-avoidance (P-A) task. One stress session resulted in significant immobility in the OFT for males, whereas 5 sessions were required to produce similar immobility in female rats. Acute stress interfered with the retention of the P-A response for males, while both acute and chronic stress produced poor P-A responses in female rats. Food consumption decreased progressively, as a function of stress sessions, in female rats, whereas feeding in males returned to control levels after five stress days. Both acute and chronic stress exacerbated the stress ulcer response in male rats, but not in female rats. Chronic, but not acute, stress resulted in an increase in serotonin transporter mRNA levels in the dorsal raphe nucleus of both male and female rats. The general consensus from these data suggested that female rats were more vulnerable to chronic stress and consequently supported the notion that females may be more susceptible to stress-induced behavioral depression. Key Words: WKY rats, acute and chronic stress, gender, passive avoidance, open field behavior, stress-ulcer, adrenal weight, serotonin, dorsal raphe nucleus     

Maternal gestational stress alters adaptive and social behavior in adolescent rhesus monkey offspring

Data from rodent studies have indicated that stress experienced by pregnant mothers may result in behavioral and biological abnormalities in their offspring. However, few studies have examined the effects of prenatal stress on the offspring beyond the childhood period. In this study, 7 prenatally stressed (PNS) monkeys and 7 monkeys from undisturbed pregnancies were tested under mildly challenging conditions at 4 years of age. Following separation from cagemates and group formation, PNS monkeys showed more locomotion, abnormal and disturbance behavior than controls. Controls showed approximately six times more play than PNS animals. The PNS males showed the most clinging to others and the largest increase in contact with other animals over the period. Group differences were also found when the monkeys were observed as groups or alone in a playroom. Controls showed more explanatory behavior in the playroom, whereas PNS monkeys showed more inactivity. Control animals showed a decrease in distress vocalizations over time in the playroom, whereas PNS animals showed the opposite pattern. Control animals spent more time in proximity to and contact with cagemates than PNS animals. These results indicate that prenatal stress can have effects on adaptive and social behavior that persist into adolescence.     

Sex differences in spatial and non-spatial Y-maze performance after chronic stress

Chronic restraint is known to alter hippocampal CA3 dendritic morphology and spatial memory in male rats. The present study examined whether female rats, which exhibit different anatomical adaptations to chronic stress than those of males, would also show spatial memory impairments. Male and female Sprague-Dawley rats were restrained for 6 h/day for 21 days, a time frame previously demonstrated to cause hippocampal CA3 dendritic atrophy. The day after the last restraint session, rats were tested on a Y-maze, a habituation task that can be used to assess spatial memory. Chronic stress impaired Y-maze performance in both sexes without affecting levels of locomotion as measured by total arm entries in the first minute. However, Y-maze performance of stressed females improved in 2-5 min when chronically stressed males continued to show poor Y-maze performance. The enhanced Y-maze performance of chronically stressed females occurred when total arm entries were higher compared to the entries made by males. Therefore, correlations were performed between total arm entries and spatial memory in 1 and 2-5 min. In the first minute when control females demonstrated functional spatial memory, female controls with the lowest locomotor levels exhibited the best performance. The correlations for stressed females were not significant, and neither were the correlations for any group in 2-5 min. Overall, these results show important sex differences in response to chronic stress with females exhibiting an ability to recover quickly from deficits in Y-maze performance.     

Prenatal maternal stress: Differential effects upon male and female offspring responses to restraint stress as adults

Pregnant primiparous rats were subjected to four days of light restraint stress on postconception days 7 through 10, inclusive, coincident with the development of the fetal gastrointestinal system. Twenty male and twenty female offspring from prenatally stressed and nonstressed rats were then subjected to two hours of supine cold-restraint as adults. Eighty percent of nonprenatally stressed offspring developed gastric lesions, while 47.5% of offspring of prenatally stressed mothers displayed lesions. A significant sex-stress interaction was detected, indicating that male offspring from prenatally stressed mothers display less severe gastric lesions in response to restraint stress as adults than do male offspring from nonprenatally stressed mothers. Female offspring from both prenatal stress conditions showed similar levels of stress-induced lesions.     

Variation in aggressive behavior and anatomo-physiological correlates generated by crowding without physical contact in the house mouse

Behavioral, physiological (i.e., endocrine), and anatomical consequences of crowding in mice were studied in a situation where animals were in auditory, visual, olfactory, and tactile contact but restrained from full physical interactions, to prevent overt aggression. Males that cohabited with females undisturbed by neighboring conspecifics showed greater propensity to attack same-sex intruders and had higher plasma testosterone levels than did their “crowded” counterparts, that is, males cohabiting with females and housed adjacent to other male/female pairs. In this respect, the latter animals resembled submissive males. However, a significant increase in weight of androgen-dependent target organs (i.e., seminal vesicles and preputial glands) was found in crowded males. These data indicate that despite the observed inhibition of social aggression these males are not physiologically comparable (homologous) to male mice that experienced defeat and the stress of submission during fighting. The intriguing possibility that different conversion pathway of testosterone are accelerated, as a result of social communication, in males living in these two environments and the behavioral implications of these possibilities are discussed. Finally, the parental behavior of crowded animals, although not freely interacting with each other, was disrupted, causing a marked decrease in reproductive success. In this situation a high incidence of infanticide of their offspring by both parents was observed, whereas this behavior was virtually absent in non-crowded male/female pairs.     

Effects of stress on nonassociative learning processes in male and female rats

In this study we assessed habituation and sensitization of the acoustic startle response (ASR) to discern whether intense, inescapable stress affects nonassociative learning differently in male and female rats. Rats were inescapably stressed 2 hours per day over 3 consecutive days. ASR magnitudes were measured at several times post-stress (1, 4, 8, and 15 days after cessation). Females generally showed greater ASR magnitudes (compared to males), but both sexes exhibited short and long-term habituation across the testing days. ASR magnitudes were only affected by stress in male subjects. The effect in males was an increase in short-term sensitization of the ASR on post-stress day-4. The results suggest that stressed males and females react differently to ASR testing, in that stress males appear to develop an exaggerated ASR response over repeated test sessions due to short-term sensitization. The source of the short-term sensitization is discussed with regards to possible stress-induced enhanced contextual learning during ASR testing on post-stress day-1.     

Prenatal testosterone and preschool Disruptive Behavior Disorders

Disruptive Behavior Disorders (DBD), including Oppositional-Defiant Disorder (ODD) and Attention-Deficit/Hyperactivity Disorder (ADHD), are fairly common and highly impairing childhood behavior disorders that can be diagnosed as early as preschool. Prenatal exposure to testosterone may be particularly relevant to these early-emerging DBDs that exhibit a sex-biased prevalence rate favoring males. The current study examined associations between preschool DBD symptom domains and prenatal exposure to testosterone measured indirectly via right 2D:4D finger-length ratios. The study sample consisted of 109 preschool-age children between ages 3 and 6 (64% males; 72% with DBD) and their primary caregivers. Primary caregivers completed a semi-structured interview (i.e., Kiddie Disruptive Behavior Disorder Schedule), as well as symptom questionnaires (i.e., Disruptive Behavior Rating Scale, Peer Conflict Scale); teachers and/or daycare providers completed symptom questionnaires and children provided measures of prenatal testosterone exposure, measured indirectly via finger-length ratios (i.e., right 2D:4D). Study results indicated a significant association of high prenatal testosterone (i.e., smaller right 2D:4D) with high hyperactive–impulsive ADHD symptoms in girls but not boys, suggesting that the effect may be driven by, or might only exist in, girls. The present study suggests that prenatal exposure to testosterone may increase risk for early ADHD, particularly hyperactivity–impulsivity, in preschool girls.     

Effects of Stress on Nonassociative Learning Processes in Male and Female Rats

In this study we assessed habituation and sensitization of the acoustic startle response (ASR) to discern whether intense, inescapable stress affects nonassociative learning differently in male and female rats. Rats were inescapably stressed 2 hours per day over 3 consecutive days. ASR magnitudes were measured at several times post-stress (1, 4, 8, and 15 days after cessation). Females generally showed greater ASR magnitudes (compared to males), but both sexes exhibited short and long-term habituation across the testing days. ASR magnitudes were only affected by stress in male subjects. The effect in males was an increase in short-term sensitization of the ASR on post-stress day-4. The results suggest that stressed males and females react differently to ASR testing, in that stress males appear to develop an exaggerated ASR response over repeated test sessions due to short-term sensitization. The source of the short-term sensitization is discussed with regards to possible stress-induced enhanced contextual learning during ASR testing on post-stress day-1.     

Sex reversal in female Betta splendens as a function of testosterone manipulation and social influence

In Experiment 1, female Betta given daily injections of testosterone (T) for 9 weeks acquired anatomical features characteristic of males as indicated by changes in fin length, body coloration, and gonadal morphology. These findings suggested that a potential for sex reversal exists in females of this species. In Experiment 2 we measured changes in aggressive behavior during testosterone-induced anatomical changes. Aggression decreased toward females and increased toward males as treatment with T progressed. The final displays of aggressive behavior and anatomical characteristics of fish injected with T resembled those of typical males. In Experiment 3, female Betta primed with T injections for 3 or 6 weeks and permitted to interact socially with females continued to display characteristics of sex reversal after T supplementation ceased. Sex reversal in isolated fish injected with T for 3 or 6 weeks was not sustained, and fish receiving only the control vehicle showed negligible change in both the isolated and community conditions. We discuss the results in terms of similarities with the sex change process found in isolated communities of coral reef fish.     

Perinatal exposure to diethylstilbestrol improves olfactory discrimination learning in male and female Swiss-Webster mice

During late prenatal and early postnatal brain development, estrogen induces structural sex differences that correspond to behavioral differences in certain domains such as learning and memory. The typically superior performance of males is attributed to the action of elevated concentrations of estrogen, derived inside neurons from the aromatization of testosterone. In contrast, female performance appears dependent on minimal estrogenic activity. Rat models of the relationship between hormones and cognitive behavior predominate the field, but the advent of genetically modified mice as research tools necessitates development of analogous mouse models. This study examined how early postnatal exposure to the synthetic estrogen diethylstilbestrol (DES) affected the ability of male and female Swiss-Webster mice to learn a two-choice olfactory discrimination and three repeated reversals. Mice treated with subcutaneous injections of DES from postnatal days 1-10 learned reversals more readily than oil-treated controls, a difference that became evident after repeated testing. DES-exposed males and females learned reversals at a comparable rate, suggesting that early postnatal estrogen exposure does not influence this mode of learning through a sexually differentiated mechanism in mice. An analysis of response patterns during qualitatively different phases of reversal learning revealed that DES-induced improvements probably were not due to greater inhibitory control. Instead, DES appeared to enhance associative ability. Early postnatal estrogen exposure may have the potential to preserve certain cognitive skills in adulthood.     

Male-female differences and the influence of neonatal and adult testosterone on intraspecies aggression in rats.

Male and female albino rats were tested for intraspecies aggression without the use of shock. In the first experiment, male pairs showed more biting attacks, offensive sideways movements, and self-grooming than did female pairs; male pairs also showed more stereotyped defensive/submissive behaviors and were wounded more frequently. The second experiment examined the effects of neonatal castration and testosterone propionate (TP) administration on fighting. Males castrated at birth attacked other males less frequently than did controls when tested with TP treatment as adults. The TP given at birth to neonatally castrated males restored attacks to control levels. Females given TP as neonates did not differ from either male or female controls. Other aggressive/defensive behaviors, however, did not show this pattern. The results suggest that while the presence of testosterone during a brief postnatal period and during adulthood is necessary for attack behavior to occur, other related behaviors may not be affected in a similar manner.     

The expression of the genes of aggressiveness in mice: The effect of androgen on aggression and sexual behavior in females

Female mice of strains selectively bred for aggressiveness or nonaggressiveness were injected with testosterone propionate (TF′) at the age of 2 days and as adults, or they were injected as adults only. Aggressive and sexual behavior was then tested with female, receptive female, and male partners before, during, and after the latter TP treatment. The females that had received both TP treatments displayed as much or as little aggression as males of the same strain, leading to the conclusion that aggressiveness genes are not linked with the male sex chromosome, even though they depend on it for their expression. The sexual behavior of the females of both strains that had received both TP treatments was altered to the male type. In the females of the aggressive strain even adult treatment alone was sufficient for this change. Aggressiveness and male sexual behavior would seem to be determined separately, although aggressiveness facilitates the display of male sexual behavior.     

Hypothalamo-pituitary-adrenocortical axis function and hedonic behavior in adult male and female rats prenatally stressed by maternal food restriction

Neuroendocrine activation during stress is affected by many factors contributing to the variability of the stress response. The present study was aimed at evaluating long-term changes in hypothalamo-pituitary-adrenocortical (HPA) axis function and in hedonic behavior in adult offspring prenatally stressed by maternal food restriction, with attention on possible gender differences. Adult offspring were blood sampled via a tail artery cannula. Prenatally stressed females had significantly higher adrenal weights compared to males. Plasma ACTH levels, which rose in response to acute stress induced by handling, were significantly higher in females compared to those in males. A similar pattern was found in plasma corticosterone. The rise in ACTH levels was more pronounced in prenatally stressed rats though the rise in corticosterone failed to be modified. Corticotropin releasing hormone (CRH) and proopiomelanocortin mRNA levels in the hypothalamic paraventricular nucleus and anterior pituitary, respectively, were found to be unchanged. The present experiments failed to reveal a decrease in hedonic behavior in prenatally stressed rats. In contrast, in male offspring a tendency to a higher sucrose preference was observed. These data together with observed changes in hormone and CRH mRNA levels indicate that the gestational stress used did not result in a depression-like state in adult offspring.     

Role of neonatal androgens in sexual differentiation of brain structure, scent marking, and gonadotropin secretion in gerbils

Gerbils display a sexually dimorphic scent marking behavior that responds to testosterone (T) in adulthood and develops under the influence of testosterone perinatally. A complex of cell groups between the preoptic area and anterior hypothalamus of the gerbil brain is also sexually dimorphic and responsive to testosterone. One of these cell groups, the sexually dimorphic area pars compacta (SDApc), usually exists only in males. Even when given testosterone, adult female gerbils rarely have an SDApc. To determine if the SDApc develops under the influence of testosterone, male gerbils were castrated or given sham operations on the day they were born or 1 day later, or were not manipulated. Female gerbils were injected subcutaneously with 0, 50, or 100 micrograms testosterone propionate (TP) on the day after birth. When given ovarian transplants as adults, neonatally castrated males scent marked at low levels typical of females. Neonatally androgenized females given testosterone as adults scent marked at high levels typical of males. Neonatal castration did not affect the probability that the SDApc would develop, but neonatal androgenization did. Half the females given either dose of TP as neonates had SDApcs bilaterally. The sizes of the SDApcs present in females depended on the dose of testosterone given neonatally. The larger dose produced larger SDApcs. The 100-micrograms dose of TP also defeminized gonadotropin secretion, but the 50-micrograms dose did not. The castration of males neonatally prevented the defeminization normally caused by endogenous testosterone. Both groups of neonatally castrated males formed corpora lutea in their ovarian transplants, but control males did not.