Gonadal hormones, but not sex, affect the acquisition and maintenance of a Go/No-Go odor discrimination task in mice

Vasopressin receptor 1a, oxytocin receptor, and oxytocin knockout male and female mice display normal perceptual abilities towards non-social odorants

Genetic knockouts of the vasopressin receptor 1a (Avpr1a), oxytocin receptor (Oxtr), or oxytocin (Oxt) gene in mice have helped cement the causal relationship between these neuropeptide systems and various social behaviors (e.g., social investigation, recognition, and communication, as well as territoriality and aggression). In mice, these social behaviors depend upon the olfactory system. Thus, it is critical to assess the olfactory capabilities of these knockout models to accurately interpret the observed differences in social behavior. Prior studies utilizing these transgenic mice have sought to test for baseline deficits in olfactory processing; predominantly through use of odor habituation/dishabituation tasks, buried food tests, or investigation assays using non-social odorants. While informative, these assays rely on the animal's intrinsic motivation and locomotor behavior to measure olfactory capabilities and thus, often yield mixed results. Instead, psychophysical analyses using operant conditioning procedures and flow-dilution olfactometry are ideally suited to precisely quantify olfactory perception. In the present study, we used these methods to assess the main olfactory capabilities of adult male and female Avpr1a, Oxtr, and Oxt transgenic mice to volatile non-social odorants. Our results indicate that homozygous and heterozygous knockout mice of all three strains have the same sensitivity and discrimination ability as their wild-type littermates. These data strongly support the hypothesis that the observed social deficits of these global knockout mice are not due to baseline deficits of their main olfactory system.

Neural and behavioral plasticity across the female reproductive cycle

Sex is fundamental for the evolution and survival of most species. However, sex can also pose danger, because it increases the risk of predation and disease transmission, among others. Thus, in many species, cyclic fluctuations in the concentration of sex hormones coordinate sexual receptivity and attractiveness with female reproductive capacity, promoting copulation when fertilization is possible and preventing it otherwise. In recent decades, numerous studies have reported a wide variety of sex hormone-dependent plastic rearrangements across the entire brain, including areas relevant for female sexual behavior. By contrast, how sex hormone-induced plasticity alters the computations performed by such circuits, such that collectively they produce the appropriate periodic switches in female behavior, is mostly unknown. In this review, we highlight the myriad sex hormone-induced neuronal changes known so far, the full repertoire of behavioral changes across the reproductive cycle, and the few examples where the relationship between sex hormone-dependent plasticity, neural activity, and behavior has been established. We also discuss current challenges to causally link the actions of sex hormones to the modification of specific cellular pathways and behavior, focusing on rodents as a model system while drawing a comparison between rodents and humans wherever possible.

Reducing local synthesis of estrogen in the tubular striatum promotes attraction to same-sex odors in female mice

Brain-derived 17β-estradiol (E2) confers rapid effects on neural activity. The tubular striatum (TuS, also called the olfactory tubercle) is both capable of local E2 synthesis due to its abundant expression of aromatase and is a critical locus for odor-guided motivated behavior and odor hedonics. TuS neurons also contain mRNA for estrogen receptors α, β, and the G protein-coupled estrogen receptor. We demonstrate here that mRNA for estrogen receptors appears to be expressed upon TuS dopamine 1 receptor-expressing neurons, suggesting that E2 may play a neuromodulatory role in circuits which are important for motivated behavior. Therefore, we reasoned that E2 in the TuS may influence attraction to urinary odors which are highly attractive. Using whole-body plethysmography, we examined odor-evoked high-frequency sniffing as a measure of odor attaction. Bilateral infusion of the aromatase inhibitor letrozole into the TuS of gonadectomized female adult mice induced a resistance to habituation over successive trials in their investigatory sniffing for female mouse urinary odors, indicative of an enhanced attraction. All males displayed resistance to habituation for female urinary odors, indicative of enhanced attraction that is independent from E2 manipulation. Letrozole's effects were not due to group differences in basal respiration, nor changes in the ability to detect or discriminate between odors (both monomolecular odorants and urinary odors). Therefore, de novo E2 synthesis in the TuS impacts females' but not males' attraction to female urinary odors, suggesting a sex-specific influence of E2 in odor hedonics.

Olfactory detection of trace amounts of plant volatiles is correlated with testosterone in a passerine bird

In response to damage by insects, plants release herbivore-induced plant volatiles (HIPVs) into the air. Insectivorous birds exploit these cues and, consequently, reduce the damages inflicted to the plants. However, little is known about whether they solely use HIPVs as foraging cues, or if they also use them to modulate traits linked to reproduction. As caterpillars are the primary food source required for insectivorous birds to raise offspring, their ability to locate and predict future peaks in caterpillar biomass using olfaction is likely to be advantageous. Therefore, we tested whether an insectivorous songbird that naturally inhabits oak dominated forests can be trained to detect early spring infestation by hatchling caterpillars, at a time when oaks begin bursting, and birds prepare to breed. Tree buds were either infested with caterpillars or left as a control and visually obscured in a Y-Maze choice test. Additionally, we measured testosterone and 17β-estradiol as they influence olfactory perception in mammals and are linked to reproduction in vertebrates. After being trained to associate the presence of HIPVs with that of food, blue tits spent more time with, were more active around, and more frequently chose to first visit the infested trees, showing that blue tits can smell caterpillar activity. Males with higher testosterone spent more time around infested trees, suggesting that foraging behavior during the pre-breeding season is linked with a major reproductive signal. There was no relationship between foraging and estradiol in females. These results are an important foundation for further investigation of the role of hormones in avian olfaction and how smell may be useful for making breeding decisions that could improve reproductive success.

The association between olfactory dysfunction and cardiovascular disease and its risk factors in middle-aged and older adults

While previous studies have reported olfactory dysfunction (OD) in relation to cardiovascular disease (CVD), few population-based studies have investigated whether such associations differ by sex. The purpose of this study was to identify the association between CVD and its risk factors with OD, and the sex-associated differences within the general population. We examined 20,016 adults aged 40 and older from the Korean National Health and Nutrition Examination Survey. All subjects reported on their history of OD. CVD and its risk factors included coronary artery disease (CAD), stroke, hypertension, diabetes, obesity, abdominal obesity, and hypertriglyceridemia; logistic regression was used to analyse their associations with OD, and additive interaction was used to analyse the interaction between risk factors and sex. In males, CAD was more likely to be associated with OD (odds ratio [OR] 1.81, 95% confidence interval [CI] 1.05–3.14), whereas abdominal obesity was associated with OD in females (OR 1.39, 95% CI 1.06–1.84).Additive interaction were observed between abdominal obesity and female sex with a relative excess risk of interaction of 0.45 (95% CI 0.26–0.63). Our findings suggest the relationship between OD and CVD and its risk factors and sex-associated differences among middle-aged and older adults.

Possible effects of low testosterone levels on olfactory function in males

Introduction

Functions attributed to androgens have increased, ranging from the role in hypothalamic–pituitary–gonadal axis and reproductive behaviors to modulation of cognition, mood and some other functions. Sex differences and changes in circulating sex hormones affect human sensory function. In the literature, authors reported this kind of influence for olfaction predominantly in females.

Objective

To investigate the effects of low testosterone levels on olfactory functions in males, in this prospective clinical study.

Methods

Male patients diagnosed with prostate cancer were included. Thirty-nine patients with prostate cancer whose testosterone levels were lower than 50 ng/dL due to castration, were the study group. Thirty-one patients with prostate cancer who were not castrated with testosterone levels higher than 50 ng/dL were selected as the control group. Acoustic rhinometry and peak nasal inspiratory flow tests were performed for all participants; and for evaluation of olfactory function, both groups completed the Connecticut chemosensory clinical research center olfactory test.

Results

The mean ages of the patients and controls were 69.6 ± 7.2 (57–89) and 66.3 ± 5.8 (50–78) years, respectively (p = 0.039). There was a significant difference between groups in terms of testosterone levels (p < 0.0001). The multivariate logistic regression revealed testosterone level as the only predictive factor determining the difference between the groups. In terms of olfactory parameters, all scores were lower in the emasculated group (butanol threshold test p = 0.019, identification p = 0.059, and Connecticut center score p = 0.029) There was a significant correlation between testosterone levels and olfactory parameters (p = 0.023; p = 0.025 for identification and Connecticut center scores, respectively).

Conclusion

Low testosterone levels in males have negative effects on olfactory functions. Further molecular research is required to understand the connection between testosterone and olfaction.

Pharmacotherapeutic strategies for the treatment of anorexia nervosa - too much for one drug?

INTRODUCTION

Anorexia nervosa is a severe psychiatric illness and no medication has been approved for its treatment. This lack of biological treatments requires the development of new directions for pharmacological research.

AREAS COVERED

There is modest but emerging evidence that dopamine D2 and serotonin 1A and 2A receptor agonistic and antagonist medication might be beneficial for weight gain, although the underlying mechanisms are uncertain. Improving quality of life including treating comorbid conditions is an additional important outcome measure, but this has not been well researched. Biological and psychological risk factors together with neurobiological alterations during the illness maintain the disorder 's pathophysiology. Neuroscience research can be used to understand those interactions and advance the research agenda. The authors discuss the above as well as give perspectives on future research.

EXPERT OPINION

If a multidisciplinary approach that includes evidence-based psychotherapy shows unsatisfactory success in weight normalization and cognitive-emotional recovery, then more experimental treatments that are safe and have indicated treatment effectiveness should be tried to augment treatment. Identification and treatment of comorbid conditions to improve quality of life of the patient should also be part of the treatment regimen, even if the effect on weight gain is uncertain.

The relationship between neuroticism and appetitive conditioning

Appetitive conditioning is considered a central mechanism for the vulnerability to psychiatric disorders. However, the investigation of individual differences that are related to altered appetitive learning has been almost neglected so far. The aim of this study was to investigate the link between neuroticism and appetitive conditioning processes. 79 subjects participated in a differential conditioning procedure in which a conditioned stimulus (CS+) was paired with a reward (money) after a fast behavioral response, while a second conditioned stimulus (CS-) was never followed by a reward, irrespective of the behavioral response. As a main result, neuroticism correlated negatively with the underlying neural processes of appetitive conditioning in females, but not in males. In detail, higher levels of neuroticism were associated with decreased neural responses in the left (p = .001) and right amygdala (p = .011), left (p = .063) and right (p = .019) nucleus accumbens, and left (p = .002) and right (p = .021) orbitofrontal cortex (all results are family-wise-error-corrected). The present results support previous findings, which also showed an inverse sex-specific effect in the context of neuroticism and emotional processing in females. In addition, the findings suggest that neuroticism is not solely linked to increased amygdala sensitivity during the processing of negative stimuli but also to decreased neural responses when processing rewarding stimuli. Possible explanations for the sex differences and implications are discussed.

Motivation to eat and not to eat - The psycho-biological conflict in anorexia nervosa

Anorexia nervosa is a severe psychiatric illness with high mortality. Brain imaging research has indicated altered reward circuits in the disorder. Here we propose a disease model for anorexia nervosa, supported by recent studies, that integrates psychological and biological factors. In that model, we propose that there is a conflict between the conscious motivation to restrict food, and a body-homeostasis driven motivation to approach food in response to weight loss. These opposing motivations trigger anxiety, which maintains the vicious cycle of ongoing energy restriction and weight loss.

The autism/neuroprotection-linked ADNP/NAP regulate the excitatory glutamatergic synapse

Activity-dependent neuroprotective protein (ADNP), essential for brain formation, was discovered as a leading de novo mutated gene causing the autism-like ADNP syndrome. This syndrome is phenotypically characterized by global developmental delays, intellectual disabilities, speech impediments, and motor dysfunctions. The Adnp haploinsufficient mouse mimics the human ADNP syndrome in terms of synapse density and gene expression patterns, as well as in developmental, motor, and cognitive abilities. Peripheral ADNP was also discovered as a biomarker for Alzheimer's disease and schizophrenia, with nasal administration of the ADNP snippet peptide NAP (enhancing endogenous ADNP activity) leading to partial cognitive and functional protection at the cellular, animal and clinical settings. Here, a novel formulation for effective delivery of NAP is provided with superior brain penetration capabilities. Also provided are methods for treating pertinent clinical implications such as autism, cognitive impairments, olfactory deficits, and muscle strength using the formulation in the Adnp haploinsufficient mouse. Results showed a dramatically specific increase in brain/body bioavailability with the new formulation, without breaching the blood brain barrier. Additional findings included improvements using daily intranasal treatments with NAP, at the behavioral and brain structural levels, diffusion tensor imaging (DTI), translatable to clinical practice. Significant effects on hippocampal and cerebral cortical expression of the presynaptic Slc17a7 gene encoding vesicular excitatory glutamate transporter 1 (VGLUT1) were observed at the RNA and immunohistochemical levels, explaining the DTI results. These findings tie for the first time a reduction in presynaptic glutamatergic synapses with the autism/Alzheimer's/schizophrenia-linked ADNP deficiency coupled with amelioration by NAP (CP201).

Hormonal regulation of social ascent and temporal patterns of behavior in an African cichlid

For many species, social rank determines which individuals perform certain social behaviors and when. Higher ranking or dominant (DOM) individuals maintain status through aggressive interactions and perform courtship behaviors while non-dominant (ND) individuals do not. In some species ND individuals ascend (ASC) in social rank when the opportunity arises. Many important questions related to the mechanistic basis of social ascent remain to be answered. We probed whether androgen signaling regulates social ascent in male Astatotilapia burtoni, an African cichlid whose social hierarchy can be readily controlled in the laboratory. As expected, androgen receptor (AR) antagonism abolished reproductive behavior during social ascent. However, we discovered multiple AR- and status-dependent temporal behavioral patterns that typify social ascent and dominance. AR antagonism in ASC males increased the time between successive behaviors compared to DOM males. Socially ascending males, independent of AR activation, were more likely than DOM males to follow aggressive displays with another aggressive display. Further analyses revealed differences in the sequencing of aggressive and courtship behaviors, wherein DOM males were more likely than ASC males to follow male-directed aggression with courtship displays. Strikingly, this difference was driven mostly by ASC males taking longer to transition from aggression to courtship, suggesting ASC males can perform certain DOM-typical temporal behavioral patterns. Our results indicate androgen signaling is necessary for social ascent and hormonal signaling and social experience may shape the full suite of DOM-typical behavioral patterns.

The discriminative stimulus effects of nicotine & ethanol with two distinct olfactory contexts in male and female rats

Odor cues and interoceptive cues can combine in promoting drug seeking behavior. Drug discrimination methodology was combined with odor-context conditioning in 8 male and 8 female rats. One drug (nicotine or EtOH) plus odorant (peppermint or anise) compound functioned as setting the occasion for sessions of food-reinforced nose poke responses (i.e., the S^D) that were maintained on a variable interval 30 s schedule (VI-30), whereas the opposite drug (EtOH or nicotine) plus odorant (anise or peppermint) compound predicted intermixed sessions of non-reinforcement of nose poking (i.e., the S^Δ). During brief non-reinforcement tests conducted with each condition there was significantly greater responding under the S^D drug plus odor compound compared to the S^Δ drug plus odor compound. Discriminative control was evident and there was a sex by stimulus role interaction with greater S^Δ responding in females. The odor contexts and drug contexts alone also sustained strong stimulus control but to a lesser extent compared to the full drug-odor compounds. These data suggest configural learning among drug and odor cues.