Male risk taking, female odors, and the role of estrogen receptors

Modulation of marble-burying behavior in adult versus adolescent C57BL/6J mice of both sexes by ethologically relevant chemosensory stimuli

The marble-burying test is a pharmacologically validated paradigm used to study anxiety-like behaviors in laboratory rodents. Our laboratory has employed this assay as part of a behavioral screen to examine drug-induced negative affective states. Historically, the majority of our prior binge alcohol-drinking studies employed male subjects exclusively and reliably detected adolescent-adult differences in both basal and alcohol withdrawal-induced negative affect. However, age-related differences in marble-burying behavior were either absent or opposite those observed in our prior work when female subjects were included in the experimental design. As chemosensory cues from females are reported to be anxiolytic in males, the present study examined how odors from adult members of the opposite and same sex (obtained from soiled bedding) influence marble-burying behavior in adult, as well as adolescent, mice. Control studies examined the responsiveness of mice in the presence of novel neutral (vanilla) and aversive (tea tree) odors. Adult males exhibited reduced signs of anxiety-like behavior in the presence of female-soiled bedding, while adult females and adolescent mice of both sexes increased marble-burying behavior in the presence of both male- and female-soiled bedding. All mice exhibited increased burying in the presence of an aversive odor, while only adolescents increased marble-burying in response to the novel neutral odor. These data indicate sex by age interactions in the effects of volatile and nonvolatile odors from sexually-naive adult conspecifics on indices of anxiety-like behavior in the marble-burying test of relevance to the experimental design and procedural timing of experiments including sex as a biological variable.

Sex differences in risk behavior parameters in adolescent mice: Relationship with brain-derived neurotrophic factor in the medial prefrontal cortex

Adolescence is as a period of development characterized by impulsive and risk-seeking behaviors. Risk behaviors (RB) involves exposure to dangerous or negative consequences to achieve goal-directed behaviors, such as reward-seeking. On the other hand, risk aversion/assessment behaviors allow the individual to gather information or avoid potentially threatening situations. Evidence has suggested that both behavioral processes, RB and risk assessment (RA), may have sex-differences. However, sex-specific behavioral patterns implicated in RB and RA are not fully understood. To address that, we investigated sex differences in risk-behavioral parameters in a decision-making task developed for rodents. In addition, we investigated the potential role of sex-dependent differences in gene expression of brain-derived neurotrophic factor (BDNF) exon IV in the medial prefrontal cortex (mPFC), which has been implicated to mediate PFC-related behavioral dysfunctions. Male and female C57BL/6J adolescent mice were evaluated in the elevated plus-maze (EPM) to assess anxiety-like behaviors and in the predator-odor risk taking (PORT) task. The PORT task is a decision-making paradigm in which a conflict between the motivation towards reward pursuit and the threat elicited by predatory olfactory cues (coyote urine) is explored. After behavioral testing, animals were euthanized and BDNF exon IV gene expression was measured by RT-qPCR. Comparative and correlational analyses for behavioral and molecular parameters were performed for both sexes. We observed that female mice spent more time exploring the middle chamber of the PORT apparatus in the aversive condition, which is an indicative of avoidance behavior. Female mice also had a higher latency to collect the reward than male mice and presented less time exploring the open arms of the EPM. BDNF exon IV gene expression was higher among females, and there was a positive correlation between the BDNF and PORT behavioral parameters. Our findings suggest sex-dependent effects in the PORT task. Females presented higher RA and avoidance behavior profile and expressed higher levels of BDNF exon IV in the mPFC. Moreover, higher BDNF expression was correlated with RA behaviors, which suggests that adolescent females tend to evaluate the risks more than adolescent males and that BDNF gene expression may be mediating decision-making processes.

Sexual cues influence cocaine-induced locomotion, anxiety and the immunoreactivity of oestrogen receptor alpha and tyrosine hydroxylase in both sexes

Dyadic physical social interaction influences cocaine-seeking behaviour, although whether limited sexual cues (LSC) from an opposite-sex partner influence the behavioural responses to cocaine is unclear. We investigated this issue using a cylindrical wire cage containing a stimulus mouse; the subject mouse (of the opposite sex) had access to this stimulus mouse during a "binge" injection pattern (injected with cocaine or saline vehicle twice a day at 6-hour intervals). Following the second injection, locomotion and anxiety-like behaviours were examined using the open-field and elevated plus maze test, at the same time as oestrogen receptor (ER)α and tyrosine hydroxylase (TH) immunoreactivities were also examined. The data indicate that LSC enhanced cocaine-stimulated locomotion in both sexes and inhibited the levels of anxiety caused by cocaine in males only. Accompanying these changes, the interaction between LSC and cocaine altered ERα immunoreactivity in the ventral medial nuclei of the hypothalamus (VMH) and medial amygdaloid nucleus (MeA) of males, whereas such interaction effects occurred in the VMH, MeA, arcuate nucleus (AR), bed nucleus of the stria terminalis (BNST) and lateral septum (LS) of females. LSC increased cocaine-induced ERα immunoreactivity in the VMH in males and reduced cocaine-induced ERα immunoreactivity in the AR and LS in females. LSC up-regulated cocaine-induced increases in ventral tegmental area (VTA) TH immunoreactivity in females only. Our present data suggest that interactions between LSC and cocaine led to changes in ERα and TH immunoreactivity in a brain region-specific manner, which showed subtle differences in both sexes. The effects of LSC-mediated cocaine-induced locomotion and anxiety may be associated with alterations in ERα and dopamine activation.

Familiarity modulates social approach toward stressed conspecifics in female rats

Familiarity between conspecifics may influence how social affective cues shape social behaviors. In a social affective preference test, experimental rats, when given the choice to explore an unfamiliar stressed or a naive adult, will avoid interaction with a stressed conspecific. To determine if familiarity would influence social interactions with stressed conspecifics, male and female test rats underwent 2 social affective preference tests in isosexual triads where an experimental rat was presented with a naïve and a stressed target conspecific who were either familiar (cagemate) or unfamiliar. Male and female experimental rats avoided stressed unfamiliar conspecifics. However, experimental female rats demonstrated a preference to interact with their stressed, familiar cagemates. Male and female rats exhibited more self-grooming and immobility behavior in the presence of stressed conspecifics, which may indicate emotion contagion. These findings suggest a sex-specific role of familiarity in social approach and avoidance, and warrant further mechanistic exploration.

Out-Group Threat Responses, In-Group Bias, and Nonapeptide Involvement Are Conserved across Vertebrates: (A Comment on Bruintjes et al., "Out-Group Threat Promotes Within-Group Affiliation in a Cooperative Fish")

The challenges and threats posed by out-groups have major effects on human social behavior and how individuals interact with one another. We briefly review evidence here that out-group threat similarly affects nonhuman animal behavior. Actual and potential threats posed by out-group individuals (unfamiliar and genetically nonrelated individuals of the same species) affect social behavior promoting "out-group" avoidance and "in-group" bias and enhancing in-group (familiar and/or genetically related individuals) affiliation and interactions. Individuals from out-groups present risks of pathogen exposure as well as being threats to resources, territory, and offspring. All of these threats function to promote in-group bias in humans and nonhumans. There are also striking similarities in the underlying neurobiological mechanisms mediating the responses to out-group threat and the expression of in-group bias. In particular, the evolutionarily conserved, hormone-regulated nonapeptide systems (oxytocin, arginine-vasopressin, and homologous neuropeptides and their receptors) are involved in the mediation of the detection and avoidance of out-groups and response to in-groups and facilitation of in-group responses across multiple vertebrate species. Consequently, comparative investigations of both the behavioral expression of and the mechanism underlying out-group avoidance and in-group bias are necessary for a full understanding of the evolution of social behavior and responses to in- and out-groups.

Toxoplasma gondii infection and testosterone congruently increase tolerance of male rats for risk of reward forfeiture

Decision making under risk involves balancing the potential of gaining rewards with the possibility of loss and/or punishment. Tolerance to risk varies between individuals. Understanding the biological basis of risk tolerance is pertinent because excessive tolerance contributes to adverse health and safety outcomes. Yet, not much is known about biological factors mediating inter-individual variability in this regard. We investigate if latent Toxoplasma gondii infection can cause risk tolerance. Using a rodent model of the balloon analogous risk task, we show that latent T. gondii infection leads to a greater tolerance of reward forfeiture. Furthermore, effects of the infection on risk can be recapitulated with testosterone supplementation alone, demonstrating that greater testosterone synthesis by the host post-infection is sufficient to change risk tolerance. T. gondii is a frequent parasite of humans and animals. Thus, the infection status can potentially explain some of the inter-individual variability in the risky decision making.

Host manipulation by cancer cells: Expectations, facts, and therapeutic implications

Similar to parasites, cancer cells depend on their hosts for sustenance, proliferation and reproduction, exploiting the hosts for energy and resources, and thereby impairing their health and fitness. Because of this lifestyle similarity, it is predicted that cancer cells could, like numerous parasitic organisms, evolve the capacity to manipulate the phenotype of their hosts to increase their own fitness. We claim that the extent of this phenomenon and its therapeutic implications are, however, underappreciated. Here, we review and discuss what can be regarded as cases of host manipulation in the context of cancer development and progression. We elaborate on how acknowledging the applicability of these principles can offer novel therapeutic and preventive strategies. The manipulation of host phenotype by cancer cells is one more reason to adopt a Darwinian approach in cancer research.

Estrogen involvement in social behavior in rodents: Rapid and long-term actions

This article is part of a Special Issue ("Estradiol and cognition"). Estrogens have repeatedly been shown to influence a wide array of social behaviors, which in rodents are predominantly olfactory-mediated. Estrogens are involved in social behavior at multiple levels of processing, from the detection and integration of socially relevant olfactory information to more complex social behaviors, including social preferences, aggression and dominance, and learning and memory for social stimuli (e.g. social recognition and social learning). Three estrogen receptors (ERs), ERα, ERβ, and the G protein-coupled ER 1 (GPER1), differently affect these behaviors. Social recognition, territorial aggression, and sexual preferences and mate choice, all requiring the integration of socially related olfactory information, seem to primarily involve ERα, with ERβ playing a lesser, modulatory role. In contrast, social learning consistently responds differently to estrogen manipulations than other social behaviors. This suggests differential ER involvement in brain regions important for specific social behaviors, such as the ventromedial and medial preoptic nuclei of the hypothalamus in social preferences and aggression, the medial amygdala and hippocampus in social recognition, and the prefrontal cortex and hippocampus in social learning. While the long-term effects of ERα and ERβ on social behavior have been extensively investigated, our knowledge of the rapid, non-genomic, effects of estrogens is more limited and suggests that they may mediate some social behaviors (e.g. social learning) differently from long-term effects. Further research is required to compare ER involvement in regulating social behavior in male and female animals, and to further elucidate the roles of the more recently described G protein-coupled ERs, both the GPER1 and the Gq-mER.

The role of oxytocin in male and female reproductive behavior

Oxytocin (OT) is a nonapeptide with an impressive variety of physiological functions. Among them, the 'prosocial' effects have been discussed in several recent reviews, but the direct effects on male and female sexual behavior did receive much less attention so far. As our contribution to honor the lifelong interest of Berend Olivier in the control mechanisms of sexual behavior, we decided to explore the role of OT in the present review. In the successive sections, some physiological mechanisms and the 'pair-bonding' effects of OT will be discussed, followed by sections about desire, female appetitive and copulatory behavior, including lordosis and orgasm. At the male side, the effects on erection and ejaculation are reviewed, followed by a section about 'premature ejaculation' and a possible role of OT in its treatment. In addition to OT, serotonin receives some attention as one of the main mechanisms controlling the effects of OT. In the succeeding sections, the importance of OT for 'the fruits of labor' is discussed, as it plays an important role in both maternal and paternal behavior. Finally, we pay attention to an intriguing brain area, the ventrolateral part of the ventromedial hypothalamic nucleus (VMHvl), apparently functioning in both sexual and aggressive behavior, which are at first view completely opposite behavioral systems.

Morphological aspects and expression of estrogen and progesterone receptors in the interdigital sinus in cyclic ewes

Many species that belong to Artiodactyls order show an interdigital sinus (IS), as it occurs in sheep, in all four extremities. These are considered to be scent glands responsible for sexual communication having strong attractiveness to mature males at the peak of the breeding season. The aim of this study was to evaluate, in IS in cyclic ewes, the microscopic and ultrastructure (scanning and transmission electron microscopy) anatomy, secretion composition, and mRNA and protein expression of estrogen receptors a and b and progesterone receptors. Glandular sebaceous structures occupy a superficial area of the pouch. The other glands present in the IS show a coiled tubular structure and tall and polyhedral secretory cells with irregular luminal surface resulting from the secretory process. Protein and mRNA gene transcription studies were performed to determine the presence of ER (a and b) and P4r in IS. At the follicular phase, IS cell populations analyzed using flow cytometry expressed higher levels of ERb compared with ERa (P<0.05), whereas no difference was observed between them in the luteal phase. The IS amount of secretion was the highest in the follicular phase compared with luteal phase (P<0.05) or pregnancy (P<0.001).To the best of our knowledge, for the first time, the presence of ER (a and b) within the IS was demonstrated. As estrogen action is mediated by specific receptors in target cells, the presence of these receptors in IS might be needed to trigger signaling pathways involved in conspecific chemical (sexual) communication attributed to this area.