A testosterone metabolite is rewarding to ovariectomized female rats

Conditioned preferences: Gated by experience, context, and endocrine systems

Central to the navigation of an ever-changing environment is the ability to form positive associations with places and conspecifics. The functions of location and social conditioned preferences are often studied independently, limiting our understanding of their interplay. Furthermore, a de-emphasis on natural functions of conditioned preferences has led to neurobiological interpretations separated from ecological context. By adopting a naturalistic and ethological perspective, we uncover complexities underlying the expression of conditioned preferences. Development of conditioned preferences is a combination of motivation, reward, associative learning, and context, including for social and spatial environments. Both social- and location-dependent reward-responsive behaviors and their conditioning rely on internal state-gating mechanisms that include neuroendocrine and hormone systems such as opioids, dopamine, testosterone, estradiol, and oxytocin. Such reinforced behavior emerges from mechanisms integrating past experience and current social and environmental conditions. Moreover, social context, environmental stimuli, and internal state gate and modulate motivation and learning via associative reward, shaping the conditioning process. We highlight research incorporating these concepts, focusing on the integration of social neuroendocrine mechanisms and behavioral conditioning. We explore three paradigms: 1) conditioned place preference, 2) conditioned social preference, and 3) social conditioned place preference. We highlight nonclassical species to emphasize the naturalistic applications of these conditioned preferences. To fully appreciate the complex integration of spatial and social information, future research must identify neural networks where endocrine systems exert influence on such behaviors. Such research promises to provide valuable insights into conditioned preferences within a broader naturalistic context.

Neuroendocrine underpinning of social recognition in males and females

Social recognition is an essential skill for the expression of appropriate behaviors towards conspecifics in most social species. Several studies point to oxytocin (OT) and arginine vasopressin (AVP) as key mediators of social recognition in males and females. However, sex differences in social cognitive behaviors highlight an important interplay between OT, AVP and the sex steroids. Estrogens facilitate social recognition by regulating OT action in the hypothalamus and that of OT receptor in the medial amygdala. The role of OT in these brain regions appears to be essential for social recognition in both males and females. Conversely, social recognition in male rats and mice is more dependent on AVP release in the lateral septum than in females. The AVP system comprises a series of highly sexually dimorphic brain nuclei, including the bed nucleus of the stria terminalis, the amygdala and the lateral septum. Various studies suggest that testosterone and its metabolites, including estradiol, influence social recognition in males by modulating the activity of the AVP at V1a receptor. Intriguingly, both estrogens and androgens can affect social recognition very rapidly, through non-genomic mechanisms. In addition, the androgen metabolites, namely 3α-diol and 3β-diol, may also have an impact on social behaviors either by interacting with the estrogen receptors or through other mechanisms. Overall, the regulation of OT and AVP by sex steroids fine tunes social recognition and the behaviors that depend upon it (e.g., social bond, hierarchical organization, aggression) in a sex-dependent manner. Elucidating the sex-dependent interaction between sex steroids and neuroendocrine systems is essential for understanding sex differences in the normal and abnormal expression of social behaviors.

'Roid rage in rats? Testosterone effects on aggressive motivation, impulsivity and tyrosine hydroxylase

In humans and animals, anabolic-androgenic steroids (AAS) increase aggression, but the underlying behavioral mechanisms are unclear. AAS may increase the motivation to fight. Alternatively, AAS may increase impulsive behavior, consistent with the popular image of 'roid rage. To test this, adolescent male rats were treated chronically with testosterone (7.5mg/kg) or vehicle and tested for aggressive motivation and impulsivity. Rats were trained to respond on a nose-poke on a 10 min fixed-interval schedule for the opportunity to fight in their home cage with an unfamiliar rat. Although testosterone increased aggression (6.3±1.3 fights/5 min vs 2.4±0.8 for controls, p<0.05), there was no difference in operant responding (28.4±1.6 nose-pokes/10 min for testosterone, 32.4±7.0 for vehicle). This suggests that testosterone does not enhance motivation for aggression. To test for impulsivity, rats were trained to respond for food in a delay-discounting procedure. In an operant chamber, one lever delivered one food pellet immediately, the other lever gave 4 pellets after a delay (0, 15, 30 or 45 s). In testosterone- and vehicle-treated rats, body weights and food intake did not differ. However, testosterone-treated rats chose the larger, delayed reward more often (4.5±0.7 times in 10 trials with 45 s delay) than vehicle controls (2.5±0.5 times, p<0.05), consistent with a reduction in impulsive choice. Thus, although chronic high-dose testosterone enhances aggression, this does not include an increase in impulsive behavior or motivation to fight. This is further supported by measurement of tyrosine hydroxylase (TH) by Western immunoblot analysis in brain regions important for motivation (nucleus accumbens, Acb) and executive function (medial prefrontal cortex, PFC). There were no differences in TH between testosterone- and vehicle-treated rats in Acb or PFC. However, testosterone significantly reduced TH (to 76.9±3.1% of controls, p<0.05) in the caudate-putamen, a brain area important for behavioral inhibition, motor control and habit learning.

Sexy thoughts: effects of sexual cognitions on testosterone, cortisol, and arousal in women

Previous research suggests that sexual stimuli increase testosterone (T) in women and shows inconsistent effects of sexual arousal on cortisol (C), but effects of cognitive aspects of arousal, rather than behaviors or sensory stimuli, are unclear. The present study examined whether sexual thoughts affect T or C and whether hormonal contraceptive (HC) use moderated this effect, given mixed findings of HC use confounding hormone responses. Participants (79 women) provided a baseline saliva sample for radioimmunoassay. We created the Imagined Social Situation Exercise (ISSE) to test effects of imagining social interactions on hormones, and participants were assigned to the experimental (sexual) or one of three control (positive, neutral, stressful) conditions. Participants provided a second saliva sample 15 min post-activity. Results indicated that for women not using HCs, the sexual condition increased T compared to the stressful or positive conditions. In contrast, HC using women in the sexual condition had decreased T relative to the stressful condition and similar T to the positive condition. The effect was specific to T, as sexual thoughts did not change C. For participants in the sexual condition, higher baseline T predicted larger increases in sexual arousal but smaller increases in T, likely due to ceiling effects on T. Our results suggest that sexual thoughts change T but not C, baseline T levels and HC use may contribute to variation in the T response to sexual thoughts, and cognitive aspects of sexual arousal affect physiology.

The testosterone metabolite 3α-diol enhances female rat sexual motivation when infused in the nucleus accumbens shell

AIM

The purpose of this study was to provide a quantitative assessment of female rat sexual behaviors after acute exposure to the A-ring reduced testosterone metabolite, androstanediol (3α-Diol), through the nucleus accumbens (NA) shell.

MAIN OUTCOME MEASURES

Quantitative analyses of female rat sexual behaviors and assessment of protein levels for the enzyme glutamic acid decarboxylase isoform 67 (GAD67) and gephyrin, a protein that participates in the clustering of GABA-A receptors in postsynaptic cells, were accomplished.

METHODS

Female rats were ovariectomized and primed with estrogen and progesterone to induce sexual behaviors. Females received a 3α-Diol infusion via guided cannula that aimed to the NA shell five minutes prior to a sexual encounter with a stud male. The following parameters were videotaped and measured in a frame by frame analysis: lordosis quotient (LQ), Lordosis rating (LR), frequency and duration of proceptive behaviors (hopping/darting and ear wiggling). Levels of GAD67 and gephyrin were obtained by Western blot analysis two or twenty-four hours after the sexual encounter.

RESULTS

Acute exposure to 3α-Diol in the NA shell enhanced LR, ear wiggling, and hopping/darting but not LQ. Some of these behavioral effects were counteracted by co-infusion of 3α-Diol plus the GABAA-receptor antagonist GABAzine. A transient reduction of GAD67 levels in the NA shell was detected.

CONCLUSIONS

The testosterone metabolite 3α-Diol enhances sexual proceptivity, but not receptivity, when infused into the NA shell directly. The GABAergic system may participate in the androgen-mediated enhancement of female rat sexual motivation.

How good are current approaches to nonclinical evaluation of abuse and dependence?

Nonclinical assessment of drug abuse and dependence is the subject of several recent regulatory guidelines, which are generally aligned on the methods to be employed. The most direct approach to assessing reinforcing properties of a drug is the self-administration procedure whereby animals can initiate intravenous injections of the test substance, something they readily do with prototypic drugs of abuse. Complications arise because there is no standardized procedure for evaluating substances with differing potencies, reinforcement properties, or pharmacokinetics. Moreover, the choice of training substance, species, and procedural parameters can radically affect the outcome. Apart from the lower cost of rats, primates present several advantages for self-administration studies with similarity to human pharmacokinetics in particular. The most powerful method for assessing similarities between a test substance and a prototypic drug of abuse is the drug discrimination procedure. In contrast to self-administration, drug discrimination is pharmacologically very specific, often reflecting functional activity at receptor level. Dependence is assessed by the occurrence of withdrawal effects on drug discontinuation. Although conceptually simple, interpretation can be complicated by factors such as duration and frequency of administration and observations as well as the choice of end points. Telemetry allows continuous observation of multiple parameters during withdrawal, thereby increasing sensitivity. Presently available tools identify all substances known to cause abuse or dependence, with little risk of false-positives. It remains unclear, however, how predictive these models are with entirely novel substances. Nonetheless, drug abuse/dependence is an area of safety pharmacology where the predictive value of animal models is remarkably high.

The neurosteroid 3alphaDIOL modulates place preference when infused in the basolateral amygdala according to sex

Three different behavioral tasks were used to study the role of the neurosteroid 5alpha -androstane-3alpha, 17beta-diol (3alphaDIOL) in affective components of behavior when infused into the basolateral amygdala (BLA) of both sexes. Female rats were ovariectomized; half received implants containing estradiol benzoate (OVX-EB), whereas the other half received empty implants (OVX). Male rats were gonadally intact. No differences were noted in male behavior according to the conditioned place preference (CPP) test, the modified Vogel conflict test (VCT), or the elevated plus maze (EPM) upon infusion of 3alphaDIOL. In contrast, 3alphaDIOL modulated CPP and VCT performance among female rats. Therefore, the authors propose that 3alphaDIOL modulates affect through the BLA via a sex-specific mechanism.

The anabolic steroids testosterone propionate and nandrolone, but not 17alpha-methyltestosterone, induce conditioned place preference in adult mice

Anabolic androgenic steroids (AAS) are often misused by adolescents and athletes. Their effects vary according to chemical structure and metabolism, route of administration, and AAS regimen. In this study, adult C57Bl/6 male mice were systemically exposed to testosterone propionate (TP), nandrolone or 17alpha-methyltestosterone (17alpha-meT), type I, type II and type III AAS, respectively, in order to determine the hedonic or aversive properties of each drug. For this purpose, the conditioned place preference (CPP) test was employed at three different AAS doses (0.075, 0.75 and 7.5 mg/kg). Other behavioral domains monitored were light-dark transitions (side changes) and general activity. TP shifted place preference at all doses tested, and nandrolone shifted place preference at 0.75 and 7.5 mg/kg, but not at 0.075 mg/kg, the lower dose tested. Conversely, mice receiving 17alpha-meT did not show alteration in the preference score. The lower dose of nandrolone did modify exploratory-based anxiety showing a decrease in light-dark transitions if compared to vehicle-treated animals, while mice treated with TP or 17alpha-meT were not affected. Our data suggest that when studying hedonic and rewarding properties of synthetic androgens, distinction has to be made based on type of AAS and metabolism.

Anabolic-androgenic steroid dependence? Insights from animals and humans

Anabolic-androgenic steroids (AAS) are drugs of abuse. They are taken in large quantities by athletes and others to increase performance, with negative health consequences. As a result, in 1991 testosterone and related AAS were declared controlled substances. However, the relative abuse and dependence liability of AAS have not been fully characterized. In humans, it is difficult to separate the direct psychoactive effects of AAS from reinforcement due to their systemic anabolic effects. However, using conditioned place preference and self-administration, studies in animals have demonstrated that AAS are reinforcing in a context where athletic performance is irrelevant. Furthermore, AAS share brain sites of action and neurotransmitter systems in common with other drugs of abuse. In particular, recent evidence links AAS with opioids. In humans, AAS abuse is associated with prescription opioid use. In animals, AAS overdose produces symptoms resembling opioid overdose, and AAS modify the activity of the endogenous opioid system.

Non-genomic actions of androgens

Previous work in the endocrine and neuroendocrine fields has viewed the androgen receptor (AR) as a transcription factor activated by testosterone or one of its many metabolites. The bound AR acts as transcription regulatory element by binding to specific DNA response elements in target gene promoters, causing activation or repression of transcription and subsequently protein synthesis. Over the past two decades evidence at the cellular and organismal level has accumulated to implicate rapid responses to androgens, dependent or independent of the AR. Androgen's rapid time course of action; its effects in the absence or inhibition of the cellular machinery necessary for transcription/translation; and in the absence of translocation to the nucleus suggest a method of androgen action not initially dependent on genomic mechanisms (i.e. non-genomic in nature). In the present paper, the non-genomic effects of androgens are reviewed, along with a discussion of the possible role non-genomic androgen actions have on animal physiology and behavior.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Exposure to an anabolic steroid changes female mice's sexual responses according to sex partner

INTRODUCTION

Anabolic androgenic steroids (AAS) affect human female sexual behaviors. Animal models have been useful in uncovering the neural mechanisms governing changes in female sexual response upon AAS exposure.

AIM

We quantify the sexual response of AAS-exposed gonadally intact female mice when paired with gonadally intact female or male pairs.

METHODS

C57Bl/6 female mice were systemically exposed to the AAS 17alpha-methyltestosterone (7.5 mg/kg) for 17 days via a subcutaneous osmotic implant. On days 15-17, these females were allowed to mate with males or proestrus female partners in familiar and unfamiliar testing arenas for 10 minutes.

MAIN OUTCOME MEASURES

The following behavioral responses were registered: parameters related to mounting behavior such as the frequency of mounts, attempts to mount, and the latency to the first mount, anogenital investigation, fights and escapes, rejections, pelvic thrusts, and lordotic responses.

RESULTS

We found that males displayed a significant decrease in the frequency of mounts to AAS-exposed females, when compared with mating encounters with control females. We found no difference in the lordosis strength when control females were mounted by either a male or AAS-exposed females. However, females under androgen exposure attempted to mount control females, but not males, and their behavior was accompanied by significant increases in the number of fights, escapes, and rejections to the male. There were no differences between AAS-exposed females and males when the frequency of mounts and pelvic thrusts toward control females were compared. The lordotic quotient of control females was similar for either partner.

CONCLUSIONS

Aside from showing a male-like pattern, AAS-exposed females displayed a higher frequency of anogenital investigations toward control females than males, and their latency to the first mount was as fast as that of males. Taken together, we conclude that the sex partner greatly influences the sexual response of AAS-exposed female mice.

Central effects of the anabolic steroid 17alpha methyltestosterone in female anxiety

The androgen 17alpha-methyltestosterone (17alpha-meT) is one of the most commonly abused anabolic androgenic steroids (AAS). We assessed the impact of 17alpha-meT after bilateral infusion into the dorsomedial hypothalamus (DMH) in female anxiety. A paradoxical effect in Vogel conflict test (VCT) behavior was noted: while AAS infusion induced an increase in the latency to display the appetitive reaction of the task, it also increased the number of punished responses. No changes in elevated plus maze (EPM) behavior were noted. However, AAS infusion induced an increase in social interactions. Changes in social interactions were mimicked by muscimol infusion and counteracted by co-infusion of AAS plus the GABAA receptor (GABAA-R) antagonist GABAzine. A reduction of systolic blood pressure was registered after AAS infusion in the DMH. No changes in fluid intake or locomotor behaviors were noted. We conclude that the AAS 17alpha-meT modulates distinct anxiety domains in females through a fast-acting mechanism.