Long-term effects of pubertal stressors on female sexual receptivity and estrogen receptor-α expression in CD-1 female mice

Exposure to stress during puberty can lead to long-term behavioral alterations. Female mice, of the inbred C57BL/6 strain, have been shown to display lower levels of sexual receptivity in adulthood when exposed to shipping stress or to an immune challenge during puberty. The present study investigated whether this effect can be extended to CD1 outbred mice and examined a possible mechanism through which exposure to stressors could suppress sexual receptivity. The results revealed that CD1 mice injected with lipopolysaccharide (LPS) or exposed to shipping stress at 6 weeks old display lower levels of sexual receptivity in response to estradiol and progesterone in adulthood than control mice. Moreover, mice exposed to shipping stress at 8 weeks old also displayed reduced sexual receptivity, but those injected with LPS at that time showed slightly reduced effects, suggesting that the sensitive pubertal period extends to 8 weeks of age in this strain of mice. The examination of estrogen receptor-α (ER-α) expression revealed that mice exposed to shipping stress during the sensitive period (6 weeks) display lower levels of ER-α expression in the medial preoptic area and the ventromedial nucleus and the arcuate nucleus of the hypothalamus than mice shipped at a younger age. These findings support the prediction that exposure to shipping stress or LPS during puberty decreases behavioral responsiveness to estradiol and progesterone in adulthood in an outbred strain of mice through enduring suppression of ER-α expression in some brain areas involved in the regulation of female sexual behavior.     

Impact of pubertal and adult estradiol treatments on cocaine self-administration

Estradiol is thought to play a critical role in the increased vulnerability to psychostimulant abuse in women. Sex differences in the ability of estradiol to influence cocaine self-administration in adult rats have been hypothesized to depend upon pubertal estradiol exposure. The current study investigated whether the presence of gonadal hormones during puberty affected cocaine self-administration behavior and its sensitivity to adult estradiol treatment in male and female Sprague–Dawley rats. Subjects were gonadectomized or SHAM-operated at postnatal day (PD) 22, and received either OIL or estradiol benzoate (EB) during the approximate time of puberty (PD27 to PD37). Adult rats were subsequently treated with either EB or OIL 30 min before cocaine self-administration (0.3 mg/kg/inf) in order to examine the effects of pubertal manipulations on the estradiol sensitivity of acquisition on a fixed ratio (FR) 1 schedule, total intake on a FR5 schedule and motivation on a progressive ratio schedule. Adult EB treatment only affected cocaine self-administration in females, which is consistent with previous research. Adult EB treatment enhanced acquisition in all females irrespective of puberty manipulations. All females, except those treated with EB during puberty, displayed increased cocaine intake following adult EB treatment. Adult EB treatment only enhanced motivation in females that were intact during puberty, whereas those treated with EB during puberty showed reduced motivation. Therefore, the sensitivities of different self-administration behaviors to adult estradiol treatment are organized independently in females, with pubertal estradiol exerting a greater influence over motivational processes, and negligible effects on learning/acquisition.     

Effects of gonadal steroids during pubertal development on androgen and estrogen receptor-alpha immunoreactivity in the hypothalamus and amygdala

Perinatal development is often viewed as the major window of time for organization of steroid-sensitive neural circuits by steroid hormones. Behavioral and neuroendocrine responses to steroids are dramatically different before and after puberty, suggesting that puberty is another window of time during which gonadal steroids affect neural development. In the present study, we investigated whether the presence of gonadal hormones during pubertal development affects the number of androgen receptor and estrogen receptor alpha-immunoreactive (AR-ir and ER alpha-ir, respectively) cells in limbic regions. Male Syrian hamsters were castrated either before or after pubertal development, and 4 weeks later they received a single injection of testosterone or oil vehicle 4 h prior to tissue collection. Immunocytochemistry for AR and ER alpha was performed on brain sections from testosterone-treated and oil-treated males, respectively. Adult males that had been castrated before puberty had a greater number of AR-ir cells in the medial preoptic nucleus than adult males that had been castrated after puberty. There were no significant differences in ER alpha-ir cell number in any of the brain regions examined. The demonstration that exposure to gonadal hormones during pubertal development is associated with reduced AR-ir in the medial preoptic nucleus indicates that puberty is a period of neural development during which hormones shape steroid-sensitive neural circuits.     

Long-term alteration of anxiolytic effects of ovarian hormones in female mice by a peripubertal immune challenge

Recent reports indicate that exposure to some stressors, such as shipping or immune challenge with the bacterial endotoxin, lipopolysaccharide (LPS), during the peripubertal period reduces sexual receptivity in response to ovarian hormones in adulthood. We hypothesized that a peripubertal immune challenge would also disrupt the response of a non-reproductive behavior, anxiety-like behavior, to ovarian hormones in adulthood. Female C57Bl/6 mice were injected with LPS during the peripubertal period and tested for anxiety-like behavior in adulthood, following ovariectomy and ovarian hormone treatment. Treatment with estradiol followed by progesterone reduced anxiety-like behavior in control, but not LPS-treated females. We next determined if the disruptive effect of LPS on adult behavior were limited to the peripubertal period by treating mice with LPS either during this period or in adulthood. LPS treatment during the peripubertal period disrupted the anxiolytic effect of ovarian hormones, whereas treatment in adulthood did not. We further tested if this model of peripubertal immune challenge was applicable to an outbred strain of mice (CD-1). Similar to C57Bl/6 mice, LPS treatment during the peripubertal period, but not later, disrupted the anxiolytic effect of estradiol and progesterone. These data suggest that a peripubertal immune challenge disrupts the regulation of anxiety-like behavior by ovarian hormones in a manner that persists at least for weeks after the termination of the immune challenge.     

Peripubertal exposure to male odors influences female puberty and adult expression of male-directed odor preference in mice

Testosterone-dependent olfactory signals emitted by male are well known to accelerate female puberty in mice (Vandenbergh effect). However, it remains unclear whether these chemosignals also influence adult expression of male-directed odor preference. Therefore, we exposed female mice to intact or castrated male bedding (vs clean bedding as control) during the peripubertal period (postnatal day (PD) 21–38) and measured male-directed odor preference in adulthood. At PD45 or PD60, females exposed to intact male odors, and thus showing puberty acceleration, preferred to investigate odors from intact males over females or castrated males. Females exposed to castrated male odors did not show puberty acceleration but preferred male (intact or castrated) over female odors. Finally, control females did not show any odor preference when tested at PD45, although a preference for male odors emerged later (PD60). In a second experiment, females that were exposed to intact male odors after pubertal transition (PD36–53) also preferred intact male over castrated male odors. In conclusion, our results indicate that peripubertal exposure to male odors induced early expression of male-directed odor preference regardless of puberty-accelerating effect and that induction of male-directed odor preference is not specific to the peripubertal period.     

Cognitive effects of variations in pubertal timing: Is puberty a period of brain organization for human sex-typed cognition?

There is considerable interest in the organizational effects of pubertal sex hormones on human sex-related characteristics. Recent evidence from rodents suggests that there is a decreasing window of sensitivity to sex hormones throughout adolescence. If adolescence also represents a period of brain organization in human beings, then the timing of exposure to sex-typical hormones at puberty should have long-term effects on sex-typed characteristics: individuals with early timing should be more sex-typed than individuals with late timing. We tested this hypothesis in 320 young adults by relating their pubertal timing (retrospective comparison to peers) to cognitive abilities that show sex differences. Results provide partial support for the hypothesis. For men, pubertal timing was inversely related to scores on a test of three-dimensional mental rotations. Effects do not appear to be due to duration of hormone exposure (time since puberty), but other potential influences need further study.     

Neonatal infection produces significant changes in immune function with no associated learning deficits in juvenile rats

The current experiments examined the impact of early‐life immune activation and a subsequent mild immune challenge with lipopolysaccharide (LPS; 25µg/kg) on hippocampal‐dependent learning, proinflammatory cytokine expression in the brain, and peripheral immune function in juvenile male and female rats at P24, an age when hippocampal‐dependent learning and memory first emerges. Our results indicate that neonatal infection did not produce learning deficits in the hippocampal‐dependent context pre‐exposure facilitation effect paradigm in juvenile males and females, contrary to what has been observed in adults. Neonatal infection produced an increase in baseline IL‐1β expression in the hippocampus (HP) and medial prefrontal cortex (mPFC) of juvenile rats. Furthermore, neonatally infected rats showed exaggerated IL‐1β expression in the HP following LPS treatment as juveniles; and juvenile females, but not males, showed exaggerated IL‐1β expression in the mPFC following LPS treatment. Neonatal infection attenuated the production of IL‐6 expression following LPS treatment in both the brain and the spleen, and neonatal infection decreased the numbers of circulating white blood cells in juvenile males and females, an effect that was further exacerbated by subsequent LPS treatment. Together, our data indicate that the consequences of neonatal infection are detectable even early in juvenile development, though we found no concomitant hippocampal‐dependent learning deficits at this young age. These findings underscore the need to consider age and associated on‐going neurodevelopmental processes as important factors contributing to the emergence of cognitive and behavioral disorders linked to early‐life immune activation. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1221–1236, 2017     

Adolescents and androgens, receptors and rewards

Adolescence is associated with increases in pleasure-seeking behaviors, which, in turn, are shaped by the pubertal activation of the hypothalamo-pituitary-gonadal axis. In animal models of naturally rewarding behaviors, such as sex, testicular androgens contribute to the development and expression of the behavior in males. To effect behavioral maturation, the brain undergoes significant remodeling during adolescence, and many of the changes are likewise sensitive to androgens, presumably acting through androgen receptors (AR). Given the delicate interaction of gonadal hormones and brain development, it is no surprise that disruption of hormone levels during this sensitive period significantly alters adolescent and adult behaviors. In male hamsters, exposure to testosterone during adolescence is required for normal expression of adult sexual behavior. Males deprived of androgens during puberty display sustained deficits in mating. Conversely, androgens alone are not sufficient to induce mating in prepubertal males, even though brain AR are present before puberty. In this context, wide-spread use of anabolic-androgenic steroids (AAS) during adolescence is a significant concern. AAS abuse has the potential to alter both the timing and the levels of androgens in adolescent males. In hamsters, adolescent AAS exposure increases aggression, and causes lasting changes in neurotransmitter systems. In addition, AAS are themselves reinforcing, as demonstrated by self-administration of testosterone and other AAS. However, recent evidence suggests that the reinforcing effects of androgens may not require classical AR. Therefore, further examination of interactions between androgens and rewarding behaviors in the adolescent brain is required for a better understanding of AAS abuse.     

Effects of gonadal steroids during pubertal development on androgen and estrogen receptor‐α immunoreactivity in the hypothalamus and amygdala

Perinatal development is often viewed as the major window of time for organization of steroid‐sensitive neural circuits by steroid hormones. Behavioral and neuroendocrine responses to steroids are dramatically different before and after puberty, suggesting that puberty is another window of time during which gonadal steroids affect neural development. In the present study, we investigated whether the presence of gonadal hormones during pubertal development affects the number of androgen receptor and estrogen receptor α‐immunoreactive (AR‐ir and ERα‐ir, respectively) cells in limbic regions. Male Syrian hamsters were castrated either before or after pubertal development, and 4 weeks later they received a single injection of testosterone or oil vehicle 4 h prior to tissue collection. Immunocytochemistry for AR and ERα was performed on brain sections from testosterone‐treated and oil‐treated males, respectively. Adult males that had been castrated before puberty had a greater number of AR‐ir cells in the medial preoptic nucleus than adult males that had been castrated after puberty. There were no significant differences in ERα‐ir cell number in any of the brain regions examined. The demonstration that exposure to gonadal hormones during pubertal development is associated with reduced AR‐ir in the medial preoptic nucleus indicates that puberty is a period of neural development during which hormones shape steroid‐sensitive neural circuits. © 2000 John Wiley & Sons, Inc. J Neurobiol 44: 361–368, 2000     

Neonatal immune challenge alters reproductive development in the female rat

This article is part of a Special Issue "Neuroendocrine-Immune Axis in Health and Disease." Neonatal lipopolysaccharide (LPS) exposure alters neuroendocrine, immune and behavioural responses in adult rats. Recent findings indicate that neonatal LPS treatment may have a more pronounced effect on the mating behaviours of females compared to males. The current study further explored the impact of neonatal inflammation on reproductive development in the female rat. Wistar rats were administered LPS (0.05mg/kg, i.p.) or saline (equivolume) on postnatal days (PNDs) 3 and 5. The immediate effect of treatment was assessed on plasma corticosterone and tyrosine hydroxylase (TH) phosphorylation in the adrenal medulla. Weight gain and vaginal opening were recorded, and oestrous cyclicity was monitored post-puberty and in late adulthood. Blood and ovaries were collected throughout development to assess HPA and HPG hormones and to examine ovarian morphology. Reproductive success in the first (F1) generation and reproductive development in the second (F2) generation were also assessed. Neonatal LPS exposure resulted in increased TH phosphorylation in the neonatal adrenals. LPS treatment increased the corticosterone concentrations of females as juveniles, adolescents and adults, and reduced FSH in adolescence. Increased catch-up growth was evident in LPS-treated females, prompting earlier onset of puberty. Diminished follicular reserve was observed in neonatally LPS-treated females along with the advanced reproductive senescence. While fertility rates were not compromised, higher mortality and morbidity were observed in litters born to LPS-treated mothers. Female offspring of LPS-treated mothers displayed increased corticosterone on PND 14, increased catch-up growth and delayed emergence of the first oestrous cycle. No differences in any of the parameters assessed were observed in F2 males. These data suggest that neonatal immunological challenge has a profound impact on the female reproductive development, via the alteration of metabolic and neuroendocrine factors which regulate sexual maturation. Evidence of altered development in the female, but not male offspring of LPS-treated dams suggests increased susceptibility of females to the deleterious effects of neonatal immunological stress and its possible transferability to a subsequent generation.     

Long-lasting consequences of neonatal maternal separation on social behaviors in ovariectomized female mice

Maternal separation (MS) stress is known to induce long-lasting alterations in emotional and anxiety-related behaviors, but effects on social behaviors are not well defined. The present study examined MS effects on female social behaviors in the social investigation (SIT) and social preference (SPT) tests, in addition to non-social behaviors in the open-field (OFT) and light-dark transition (LDT) tests in C57BL/6J mice. All females were tested as ovariectomized to eliminate confounding effects of endogenous estrogen during behavioral testing. Daily MS (3 hr) from postnatal day 1 to 14 did not affect anxiety levels in LDT, but were elevated in OFT with modified behavioral responses to the novel environment. Furthermore, MS altered social investigative behaviors and preference patterns toward unfamiliar stimulus mice in SIT and short- and long-term SPT paradigms. In SIT, MS reduced social investigation duration and increased number of stretched approaches towards both female and male unfamiliar stimulus mice, suggesting increased social anxiety levels in MS females. Similarly, MS heightened levels of social anxiety during short-term SPT but no MS effect on social preference was found. On the other hand, MS females displayed a distinctive preference for female stimuli, unlike control females, when tested for long-term SPT over a prolonged period of 5 days. Evaluation of FosB expression in the paraventricular nucleus, medial and central amygdala following stimulus exposure demonstrated greater number of FosB immunopositive cells in all three brain regions in MS females compared to control females. These results suggest that MS females might differ in neuroendocrine responses toward unfamiliar female and male opponents, which may be associated with modifications in social behaviors found in the present study. Taken together, this study provides new evidence that early life stress modifies female social behaviors by highlighting alterations in behavioral responses to situations involving social as well as non-social novelty.     

Peri-Pubertal Emergence of UNC-5 Homologue Expression by Dopamine Neurons in Rodents

Puberty is a critical period in mesocorticolimbic dopamine (DA) system development, particularly for the medial prefrontal cortex (mPFC) projection which achieves maturity in early adulthood. The guidance cue netrin-1 organizes neuronal networks by attracting or repelling cellular processes through DCC (deleted in colorectal cancer) and UNC-5 homologue (UNC5H) receptors, respectively. We have shown that variations in netrin-1 receptor levels lead to selective reorganization of mPFC DA circuitry, and changes in DA-related behaviors, in transgenic mice and in rats. Significantly, these effects are only observed after puberty, suggesting that netrin-1 mediated effects on DA systems vary across development. Here we report on the normal expression of DCC and UNC5H in the ventral tegmental area (VTA) by DA neurons from embryonic life to adulthood, in both mice and rats. We show a dramatic and enduring pubertal change in the ratio of DCC:UNC5H receptors, reflecting a shift toward predominant UNC5H function. This shift in DCC:UNC5H ratio coincides with the pubertal emergence of UNC5H expression by VTA DA neurons. Although the distribution of DCC and UNC5H by VTA DA neurons changes during puberty, the pattern of netrin-1 immunoreactivity in these cells does not. Together, our findings suggest that DCC:UNC5H ratios in DA neurons at critical periods may have important consequences for the organization and function of mesocorticolimbic DA systems.     

Effects of early pubertal exposure to di-(2-ethylhexyl) phthalate on social behavior of mice

Di-(2-ethylhexyl) phthalate (DEHP), a main member of phthalates used as plasticizer in PVC plastics, is an environmental endocrine disrupter. The present study investigated the effect of DEHP on social behavior of mice following pubertal exposure (1, 10, 50, and 200 mg/kg/d) from postnatal day 28 through postnatal day 42. The results showed that, in pubertal females, DEHP reduced the time spent in social play and social investigation and inhibited sociability, but a contrary effect was found in pubertal males, suggesting that the effect of DEHP on pubertal social behavior displays sex differences. In adults, DEHP reduced sociability in females and inhibited social play and social investigation in males, suggesting that early pubertal exposure to DEHP not only plays a significant role in puberty but also alters social behavior in adults. In addition, the present study showed that the higher dose of DEHP (50, 200 mg/kg/d) reduced the relative weight of bilateral testis and anogenital distance of pubertal or adult males, suggesting an anti-androgenic activity of DEHP. These results suggest that early pubertal exposure to DEHP sex- and age- specifically affected the social behaviors of pubertal and even adult mice.     

Long-Term Behavioral Programming Induced by Peripuberty Stress in Rats Is Accompanied by GABAergic-Related Alterations in the Amygdala

Stress during childhood and adolescence is a risk factor for psychopathology. Alterations in γ-aminobutyric acid (GABA), the main inhibitory neurotransmitter in the brain, have been found following stress exposure and fear experiences and are often implicated in anxiety and mood disorders. Abnormal amygdala functioning has also been detected following stress exposure and is also implicated in anxiety and social disorders. However, the amygdala is not a unitary structure; it includes several nuclei with different functions and little is known on the potential differences the impact of early life stress may have on this system within different amygdaloid nuclei. We aimed here to evaluate potential regional differences in the expression of GABAergic-related markers across several amygdaloid nuclei in adult rats subjected to a peripuberty stress protocol that leads to enhanced basal amygdala activity and psychopathological behaviors. More specifically, we investigated the protein expression levels of glutamic acid decarboxylase (GAD; the principal synthesizing enzyme of GABA) and of GABA-A receptor subunits α2 and α3. We found reduced GAD and GABA-A α3, but not α2, subunit protein levels throughout all the amygdala nuclei examined (lateral, basolateral, basomedial, medial and central) and increased anxiety-like behaviors and reduced sociability in peripubertally stressed animals. Our results identify an enduring inhibition of the GABAergic system across the amygdala following exposure to early adversity. They also highlight the suitability of the peripuberty stress model to investigate the link between treatments targeting the dysfunctional GABAergic system in specific amygdala nuclei and recovery of specific stress-induced behavioral dysfunctions.     

Functional Programming of the Autonomic Nervous System by Early Life Immune Exposure: Implications for Anxiety

Neonatal exposure of rodents to an immune challenge alters a variety of behavioural and physiological parameters in adulthood. In particular, neonatal lipopolysaccharide (LPS; 0.05 mg/kg, i.p.) exposure produces robust increases in anxiety-like behaviour, accompanied by persistent changes in hypothalamic-pituitary-adrenal (HPA) axis functioning. Altered autonomic nervous system (ANS) activity is an important physiological contributor to the generation of anxiety. Here we examined the long term effects of neonatal LPS exposure on ANS function and the associated changes in neuroendocrine and behavioural indices. ANS function in Wistar rats, neonatally treated with LPS, was assessed via analysis of tyrosine hydroxylase (TH) in the adrenal glands on postnatal days (PNDs) 50 and 85, and via plethysmographic assessment of adult respiratory rate in response to mild stress (acoustic and light stimuli). Expression of genes implicated in regulation of autonomic and endocrine activity in the relevant brain areas was also examined. Neonatal LPS exposure produced an increase in TH phosphorylation and activity at both PNDs 50 and 85. In adulthood, LPS-treated rats responded with increased respiratory rates to the lower intensities of stimuli, indicative of increased autonomic arousal. These changes were associated with increases in anxiety-like behaviours and HPA axis activity, alongside altered expression of the GABA-A receptor α2 subunit, CRH receptor type 1, CRH binding protein, and glucocorticoid receptor mRNA levels in the prefrontal cortex, hippocampus and hypothalamus. The current findings suggest that in addition to the commonly reported alterations in HPA axis functioning, neonatal LPS challenge is associated with a persistent change in ANS activity, associated with, and potentially contributing to, the anxiety-like phenotype. The findings of this study reflect the importance of changes in the perinatal microbial environment on the ontogeny of physiological processes.     

Vagotomy Affects Lipopolysaccharide-Induced Changes of Urocortin 2 Gene Expression in the Brain and on the Periphery

The corticotropin-releasing hormone family of peptides is involved in regulating the neuroendocrine stress response. Also, the vagus nerve plays an important role in the transmission of immune system-related signals to brain structures, thereby orchestrating the neuroendocrine stress response. Therefore, we investigated gene expression of urocortin 2 (Ucn2) and c-fos, a markers of neuronal activity, within the hypothalamic paraventricular nucleus (PVN), a brain structure involved in neuroendocrine and neuroimmune responses, as well as in the adrenal medulla and spleen in vagotomized rats exposed to immune challenge. In addition, markers of neuroendocrine stress response activity were investigated in the adrenal medulla, spleen, and plasma. Intraperitoneal administration of lipopolysaccharide (LPS) induced a significant increase of c-fos and Ucn2 gene expression in the PVN, and adrenal medulla as well as increases of plasma corticosterone levels. In addition, LPS administration induced a significant increase in the gene expression of tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) in the adrenal medulla. In the spleen, LPS administration increased gene expression of c-fos, while gene expression of TH and PNMT was significantly reduced, and gene expression of Ucn2 was not affected. Subdiaphragmatic vagotomy significantly attenuated the LPS-induced increases of gene expression of c-fos and Ucn2 in the PVN and Ucn2 in the adrenal medulla. Our data has shown that Ucn2 may be involved in regulation of the HPA axis in response to immune challenge. In addition, our findings indicate that the effect of immune challenge on gene expression of Ucn2 is mediated by vagal pathways.

     

Binge-pattern alcohol exposure during puberty induces long-term changes in HPA axis reactivity

Adolescence is a dynamic and important period of brain development however, little is known about the long-term neurobiological consequences of alcohol consumption during puberty. Our previous studies showed that binge-pattern ethanol (EtOH) treatment during pubertal development negatively dysregulated the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis, as manifested by alterations in corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP), and corticosterone (CORT) during this time period. Thus, the primary goal of this study was to determine whether these observed changes in important central regulators of the stress response were permanent or transient. In this study, juvenile male Wistar rats were treated with a binge-pattern EtOH treatment paradigm or saline alone for 8 days. The animals were left undisturbed until adulthood when they received a second round of treatments consisting of saline alone, a single dose of EtOH, or a second binge-pattern treatment paradigm. The results showed that pubertal binge-pattern EtOH exposure induced striking long-lasting alterations of many HPA axis parameters. Overall, our data provide strong evidence that binge-pattern EtOH exposure during pubertal maturation has long-term detrimental effects for the healthy development of the HPA axis.     

Dendritic pruning of the medial amygdala during pubertal development of the male Syrian hamster

The medial amygdala (Me), a brain region essential for mating behavior, changes in size during puberty. In pre-, mid-, and late pubertal (21, 35, and 49 days of age) male Syrian hamsters, we examined neuronal structure in Me and protein levels of spinophilin and synaptophysin in the amygdaloid complex for evidence of synaptic plasticity coincident with behavioral and physiological development. Body weight, testes weight, and testosterone levels increased during puberty. Mounting behavior, including ectopic, nonintromittive, and intromittive mounts, also increased. Neuronal structure in the posterodorsal medial amygdala (MePD) was assessed in Golgi-impregnated neurons. Pruning occurred during puberty in the number of dendrites emanating from the cell body and in terminal dendritic spine densities. Approximately half of all MePD neurons analyzed had an axon emanating from a dendrite rather than the cell body. However, prepubertal males were more likely to have the axon emanating from a higher order dendritic segment (secondary or tertiary) than were mid- and late pubertal males. Finally, protein levels in the amygdaloid complex varied with pubertal age. Spinophilin decreased, while synaptophysin and GAPDH protein levels increased. These results suggest that puberty is a period of dramatic synaptic plasticity in Me. Specifically, pruning of dendrites and spines, in combination with axonal changes, is likely to modify the afferent influences and electrophysiological properties of Me neurons. Because the Me is an integral component of a social behavior neural network, these changes may be related not only to sexual behavior, but also to other behaviors that mature during puberty, including aggressive, risk-taking, fear-related, and parental behaviors.     

Gender-Dependent Effects of Maternal Immune Activation on the Behavior of Mouse Offspring

Autism spectrum disorders are neurodevelopmental disorders characterized by two core symptoms; impaired social interactions and communication, and ritualistic or repetitive behaviors. Both epidemiological and biochemical evidence suggests that a subpopulation of autistics may be linked to immune perturbations that occurred during fetal development. These findings have given rise to an animal model, called the “maternal immune activation” model, whereby the offspring from female rodents who were subjected to an immune stimulus during early or mid-pregnancy are studied. Here, C57BL/6 mouse dams were treated mid-gestation with saline, lipopolysaccharide (LPS) to mimic a bacterial infection, or polyinosinic:polycytidylic acid (Poly IC) to mimic a viral infection. Autism-associated behaviors were examined in the adult offspring of the treated dams. Behavioral tests were conducted to assess motor activity, exploration in a novel environment, sociability, and repetitive behaviors, and data analyses were carried independently on male and female mice. We observed a main treatment effect whereby male offspring from Poly IC-treated dams showed reduced motor activity. In the marble burying test of repetitive behavior, male offspring but not female offspring from both LPS and Poly IC-treated mothers showed increased marble burying. Our findings indicate that offspring from mothers subjected to immune stimulation during gestation show a gender-specific increase in stereotyped repetitive behavior.     

Regulation of neural oxytocin gene expression by gonadal steroids in pubertal rats

We have previously demonstrated that neuronal oxytocin mRNA increases during the pubertal development of female rats. In this paper we have examined the factors that regulate this developmental increase in both male and female rats. Northern blot analysis demonstrated that neural oxytocin mRNA increased 5- to 10-fold from postnatal day 20 (P20) to P60 in animals of both sexes, coincident with puberty. Mature male rats and females at all stages of the estrous cycle expressed similar levels of neural oxytocin mRNA. Pubertal up-regulation of oxytocin mRNA was largely, but not completely, inhibited by prepubescent gonadectomy, indicating a requirement for intact gonads as well as some other as yet undefined factor(s). Pubertal treatment of gonadectomized animals with estradiol or testosterone abolished the effects of gonadectomy; treated animals expressed levels of neural oxytocin mRNA similar to those in controls. However, treatment of prepubertal animals with estradiol or testosterone from P10 to P20 had no effect on oxytocin mRNA levels, suggesting that neural maturation or other factors are necessary requisites for steroid sensitivity. To determine whether neural activin played any role in regulating oxytocin mRNA during puberty, we examined levels of inhibin/activin beta A-chain mRNA. This mRNA was expressed at similar levels in all brain regions and did not vary as a function of gonadectomy or steroid treatment, making it unlikely that activin mediates the observed changes. Together, these data indicate that neural oxytocin mRNA is induced by gonadal steroids during puberty, and suggest a mechanism for coordinating development of reproductive functions with other pubertal changes.