High-yielding 18F radiosynthesis of a novel oxytocin receptor tracer, a probe for nose-to-brain oxytocin uptake in vivo

Intranasal delivery of imaging agents to the brain

The potential of intranasal administered imaging agents to altogether bypass the blood-brain barrier offers a promising non-invasive approach for delivery directly to the brain. This review provides a comprehensive analysis of the advancements and challenges of delivering neuroimaging agents to the brain by way of the intranasal route, focusing on the various imaging modalities and their applications in central nervous system diagnostics and therapeutics. The various imaging modalities provide distinct insights into the pharmacokinetics, biodistribution, and specific interactions of imaging agents within the brain, facilitated by the use of tailored tracers and contrast agents. Methods: A comprehensive literature search spanned PubMed, Scopus, Embase, and Web of Science, covering publications from 1989 to 2024 inclusive. Starting with advancements in tracer development, we going to explore the rationale for integration of imaging techniques, and the critical role novel formulations such as nanoparticles, nano- and micro-emulsions in enhancing imaging agent delivery and visualisation. Results: The review highlights the use of innovative formulations in improving intranasal administration of neuroimaging agents, showcasing their ability to navigate the complex anatomical and physiological barriers of the nose-to-brain pathway. Various imaging techniques, MRI, PET, SPECT, CT, FUS and OI, were evaluated for their effectiveness in tracking these agents. The findings indicate significant improvements in brain targeting efficiency, rapid uptake, and sustained brain presence using innovative formulations. Conclusion: Future directions involve the development of optimised tracers tailored for intranasal administration, the potential of multimodal imaging approaches, and the implications of these advancements for diagnosing and treating neurological disorders.

Intranasal oxytocin as a treatment for anxiety and autism: From subclinical to clinical applications

Animal and human studies have demonstrated that intranasal oxytocin (OT) can penetrate the brain and induce cognitive, emotional, and behavioral changes, particularly in social functioning. Consequently, numerous investigations have explored the potential of OT as a treatment for anxiety and autism, conditions characterized by social deficits. Although both subclinical and clinical studies provide converging evidence of the therapeutic effects of OT in reducing anxiety levels and improving social symptoms in autism, results are not always consistent. Additionally, the pharmacological mechanism of OT requires further elucidation for its effective clinical application. Therefore, this review aims to examine the contentious findings concerning the effects of OT on anxiety and autism, offer interpretations of the inconsistent results from the perspectives of individual differences and varying approaches to OT administration, and shed light on the underlying mechanisms of OT. Ultimately, standardization of dosage, frequency of administration, formulation characteristics, and nasal spray devices is proposed as essential for future human studies and clinical applications of OT treatment.

Targeting the Oxytocin Receptor for Breast Cancer Management: A Niche for Peptide Tracers

Breast cancer is a leading cause of death in women, and its management highly depends on early disease diagnosis and monitoring. This remains challenging due to breast cancer's heterogeneity and a scarcity of specific biomarkers that could predict responses to therapy and enable personalized treatment. This Perspective describes the diagnostic landscape for breast cancer management, molecular strategies targeting receptors overexpressed in tumors, the theranostic potential of the oxytocin receptor (OTR) as an emerging breast cancer target, and the development of OTR-specific optical and nuclear tracers to study, visualize, and treat tumors. A special focus is on the chemistry and pharmacology underpinning OTR tracer development, preclinical in vitro and in vivo studies, challenges, and future directions. The use of peptide-based tracers targeting upregulated receptors in cancer is a highly promising strategy complementing current diagnostics and therapies and providing new opportunities to improve cancer management and patient survival.

The effect of intranasal oxytocin on social reward processing in humans: a systematic review

Understanding the neurobiology of social reward processing is fundamental, holding promises for reducing maladaptive/dysfunctional social behaviors and boosting the benefits associated with a healthy social life. Current research shows that processing of social (vs. non-social) rewards may be driven by oxytocinergic signaling. However, studies in humans often led to mixed results. This review aimed to systematically summarize available experimental results that assessed the modulation of social reward processing by intranasal oxytocin (IN-OXY) administration in humans. The literature search yielded 385 results, of which 19 studies were included in the qualitative synthesis. The effects of IN-OXY on subjective, behavioral, and (neuro)physiological output variables are discussed in relation to moderating variables-reward phase, reward type, onset and dosage, participants' sex/gender, and clinical condition. Results indicate that IN-OXY is mostly effective during the consumption ("liking") of social rewards. These effects are likely exerted by modulating the activity of the prefrontal cortex, insula, precuneus, anterior cingulate cortex, amygdala, and striatum. Finally, we provide suggestions for designing future oxytocin studies.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021278945, identifier CRD42021278945.

Sniffing oxytocin: Nose to brain or nose to blood?

In recent years ample studies have reported that intranasal administration of the neuropeptide oxytocin can facilitate social motivation and cognition in healthy and clinical populations. However, it is still unclear how effects are mediated since intranasally administered oxytocin can both directly enter the brain (nose to brain) and increase peripheral vascular concentrations (nose to blood). The relative functional contributions of these routes are not established and have received insufficient attention in the field. The current study used vasoconstrictor pretreatment to prevent intranasal oxytocin (24 IU) from increasing peripheral concentrations and measured effects on both resting-state neural (electroencephalography) and physiological responses (electrocardiogram, electrogastrogram and skin conductance). Results demonstrated that intranasal oxytocin alone produced robust and widespread increases of delta-beta cross-frequency coupling (CFC) from 30 min post-treatment but did not influence peripheral physiological measures. As predicted, vasoconstrictor pretreatment greatly reduced the normal increase in peripheral oxytocin concentrations and, importantly, abolished the majority of intranasal oxytocin effects on delta-beta CFC. Furthermore, time-dependent positive correlations were found between increases in plasma oxytocin concentrations and corresponding increases in delta-beta CFC following oxytocin treatment alone. Our findings suggest a critical role of peripheral vasculature-mediated routes on neural effects of exogenous oxytocin administration with important translational implications for its use as an intervention in psychiatric disorders.

Towards better hypothesis tests in oxytocin research: Evaluating the validity of auxiliary assumptions

Various factors have been attributed to the inconsistent reproducibility of human oxytocin research in the cognitive and behavioral sciences. These factors include small sample sizes, a lack of pre-registered studies, and the absence of overarching theoretical frameworks that can account for oxytocin's effects over a broad range of contexts. While there have been efforts to remedy these issues, there has been very little systematic scrutiny of the role of auxiliary assumptions, which are claims that are not central for testing a hypothesis but nonetheless critical for testing theories. For instance, the hypothesis that oxytocin increases the salience of social cues is predicated on the assumption that intranasally administered oxytocin increases oxytocin levels in the brain. Without robust auxiliary assumptions, it is unclear whether a hypothesis testing failure is due to an incorrect hypothesis or poorly supported auxiliary assumptions. Consequently, poorly supported auxiliary assumptions can be blamed for hypothesis failure, thereby safeguarding theories from falsification. In this article, I will evaluate the body of evidence for key auxiliary assumptions in human behavioral oxytocin research in terms of theory, experimental design, and statistical inference, and highlight assumptions that require stronger evidence. Strong auxiliary assumptions will leave hypotheses vulnerable for falsification, which will improve hypothesis testing and consequently advance our understanding of oxytocin's role in cognition and behavior.

Effects of Intranasal Administration of Oxytocin and Vasopressin on Social Cognition and Potential Routes and Mechanisms of Action

Acute and chronic administration of intranasal oxytocin and vasopressin have been extensively utilized in both animal models and human preclinical and clinical studies over the last few decades to modulate various aspects of social cognition and their underlying neural mechanisms, although effects are not always consistent. The use of an intranasal route of administration is largely driven by evidence that it permits neuropeptides to penetrate directly into the brain by circumventing the blood-brain barrier, which has been considered relatively impermeable to them. However, this interpretation has been the subject of considerable debate. In this review, we will focus on research in both animal models and humans, which investigates the different potential routes via which these intranasally administered neuropeptides may be producing their various effects on social cognition. We will also consider the contribution of different methods of intranasal application and additionally the importance of dose magnitude and frequency for influencing G protein-coupled receptor signaling and subsequent functional outcomes. Overall, we conclude that while some functional effects of intranasal oxytocin and vasopressin in the domain of social cognition may result from direct penetration into the brain following intranasal administration, others may be contributed by the neuropeptides either entering the peripheral circulation and crossing the blood-brain barrier and/or producing vagal stimulation via peripheral receptors. Furthermore, to complicate matters, functional effects via these routes may differ, and both dose magnitude and frequency can produce very different functional outcomes and therefore need to be optimized to produce desired effects.

Oxytocin and the Neurobiology of Prosocial Behavior

Humans are an unusually prosocial species, who engage in social behaviors that include altruism-whereby an individual engages in costly or risky acts to improve the welfare of another person-care, and cooperation. Current perspectives on the neurobiology of human prosociality suggest that it is deeply rooted in the neuroendocrine architecture of the social brain and emphasize the modulatory role of the neuropeptide hormone oxytocin. In this review, we provide a conceptual overview of the neurobiology of prosocial behavior with a focus on oxytocin's modulatory role in human prosociality. Specifically, we aim to encourage a better understanding of the peptide's susceptibility to diverse factors that produce heterogeneity in outcomes and the resulting methodological implications for measuring the behavioral effects of oxytocin in humans. After providing an overview of the state-of-the-art research on oxytocin's exogenous use, we elaborate on the peptide's modulatory role in the context of care-based altruism, cooperation, and conflict and discuss its potential for therapeutic interventions in psychiatric disorders characterized by social dysfunction.

In the nose or on the tongue? Contrasting motivational effects of oral and intranasal oxytocin on arousal and reward during social processing

Intranasal oxytocin exerts wide-ranging effects on socioemotional behavior and is proposed as a potential therapeutic intervention in psychiatric disorders. However, following intranasal administration, oxytocin could penetrate directly into the brain or influence its activity via increased peripheral concentrations crossing the blood-brain barrier or influencing vagal projections. In the current randomized, placebo-controlled, pharmaco-imaging clinical trial we investigated effects of 24IU oral (lingual) oxytocin spray, restricting it to peripherally mediated blood-borne and vagal effects, on responses to face emotions in 80 male subjects and compared them with 138 subjects treated intranasally with 24IU. Oral, but not intranasal oxytocin administration increased both arousal ratings for faces and associated brain reward responses, the latter being partially mediated by blood concentration changes. Furthermore, while oral oxytocin increased amygdala and arousal responses to face emotions, after intranasal administration they were decreased. Thus, oxytocin can produce markedly contrasting motivational effects in relation to socioemotional cues when it influences brain function via different routes. These findings have important implications for future therapeutic use since administering oxytocin orally may be both easier and have potentially stronger beneficial effects by enhancing responses to emotional cues and increasing their associated reward.

Advances in the field of intranasal oxytocin research: lessons learned and future directions for clinical research

Reports on the modulatory role of the neuropeptide oxytocin on social cognition and behavior have steadily increased over the last two decades, stimulating considerable interest in its psychiatric application. Basic and clinical research in humans primarily employs intranasal application protocols. This approach assumes that intranasal administration increases oxytocin levels in the central nervous system via a direct nose-to-brain route, which in turn acts upon centrally-located oxytocin receptors to exert its behavioral effects. However, debates have emerged on whether intranasally administered oxytocin enters the brain via the nose-to-brain route and whether this route leads to functionally relevant increases in central oxytocin levels. In this review we outline recent advances from human and animal research that provide converging evidence for functionally relevant effects of the intranasal oxytocin administration route, suggesting that direct nose-to-brain delivery underlies the behavioral effects of oxytocin on social cognition and behavior. Moreover, advances in previously debated methodological issues, such as pre-registration, reproducibility, statistical power, interpretation of non-significant results, dosage, and sex differences are discussed and integrated with suggestions for the next steps in translating intranasal oxytocin into psychiatric applications.

Intranasal oxytocin affects the stress response to social isolation in sheep

Oxytocin (OT) is a neuropeptide hormone that modulates several social behaviors and can affect the anxiety and stress response. The aim of this study was to determine if administration of intranasal OT affects the stress response to social isolation in sheep. Twenty adult Merino ewes were assigned to two groups; 1) Control group (CG, n = 10), which received an intranasal administration of isotonic saline and 2) Oxytocin-treated group (OTG, n = 10), which received an intranasal administration of OT (24 IU) 40 min before the animals were placed in the social isolation test. During the social isolation test (10 min), the behavior of the sheep was recorded, and blood samples were obtained before and after the test for the determination of cortisol, glucose and serum proteins, and heart rate and surface temperature were recorded. The OTG ewes had a higher cortisol concentration (P = 0.04) after social isolation, tended to vocalize more (P = 0.06) during isolation, and tended to have lower globulin concentrations (P = 0.10) than the CG ewes. Contrary to what we expected, the administration of intranasal OT increased the stress response to social isolation in ewes, which was evidenced by endocrine (greater increase in cortisol concentration), physiological (a tendency to present lower concentration of globulins in blood) and behavioral (a tendency to vocalize more) indicators. This study suggests that the administration of intranasal OT increased the stress response to isolation possibly by strengthening the social bond among ewes.

Improving the precision of intranasal oxytocin research

The neuropeptide oxytocin has been popularized for its role in social behaviour and nominated as a candidate treatment for several psychiatric illnesses due to promising preclinical results. However, these results so far have failed to reliably translate from animal models to human research. In response, there have been justified calls to improve intranasal oxytocin delivery methodology in terms of verifying that intranasal administration increases central levels of oxytocin. Nonetheless, improved methodology needs to be coupled with a robust theory of the role of oxytocin in behaviour and physiology to ask meaningful research questions. Moreover, stringent methodology based on robust theory may yield interesting results, but such findings will have limited utility if they are not reproducible. We outline how the precision of intranasal oxytocin research can be improved by the complementary consideration of methodology, theory and reproducibility.

Effects of route of administration on oxytocin-induced changes in regional cerebral blood flow in humans

Could nose-to-brain pathways mediate the effects of peptides such as oxytocin (OT) on brain physiology when delivered intranasally? We address this question by contrasting two methods of intranasal administration (a standard nasal spray, and a nebulizer expected to improve OT deposition in nasal areas putatively involved in direct nose-to-brain transport) to intravenous administration in terms of effects on regional cerebral blood flow during two hours post-dosing. We demonstrate that OT-induced decreases in amygdala perfusion, a key hub of the OT central circuitry, are explained entirely by OT increases in systemic circulation following both intranasal and intravenous OT administration. Yet we also provide robust evidence confirming the validity of the intranasal route to target specific brain regions. Our work has important translational implications and demonstrates the need to carefully consider the method of administration in our efforts to engage specific central oxytocinergic targets for the treatment of neuropsychiatric disorders.

Automated radiosynthesis and preclinical evaluation of Al[18F]F-NOTA-P-GnRH for PET imaging of GnRH receptor-positive tumors

INTRODUCTION

Gonadotropin releasing hormone (GnRH) receptor is overexpressed in many human tumors. Previously we developed a ¹⁸F-labelled GnRH peptide. Although the GnRH-targeted PET probe can be clearly visualized by microPET imaging in a PC-3 xenograft model, clinical applications of the probe have been limited by complex labeling procedures, poor radiochemical yield, and unwanted accumulation in GnRH receptor negative tissues. In this study, we have designed a new ¹⁸F-labelled GnRH peptide that is more amenable to clinical development.

METHODS

GnRH peptide analogues NOTA-P-GnRH was synthesized and automated radiolabeled with ¹⁸F using a Al[¹⁸F]F complex on a modified PET-MF-2V-IT-I synthesis module. The GnRH receptor affinities of AlF-NOTA-P-GnRH and NOTA-P-GnRH were determined by in vitro competitive binding assay. For in vitro characterization determination of stability and partition coefficients were carried out, respectively. Dynamic microPET and biodistribution studies of Al[¹⁸F]F-NOTA-P-GnRH were evaluated in xenograft tumor mouse models.

RESULTS

The total radiochemical synthesis and purification of Al[¹⁸F]F-NOTA-P-GnRH was completed within 35 min with a decay-corrected yield of 35 ± 10%. The logP value of Al[¹⁸F]F-NOTA-P-GnRH was -2.74 ± 0.04 and the tracer was stable in phosphate-buffered saline, and bovine and human serum. The IC₅₀ values of AlF-NOTA-P-GnRH and NOTA-P-GnRH were 116 nM and 56.2 nM, respectively. Dynamic PET imaging together with ex vivo biodistribution analyses revealed that Al[¹⁸F]F-NOTA-P-GnRH was clearly delineated in both PC-3 and MDA-MB-231 xenografted tumors.

CONCLUSION

Al[¹⁸F]F-NOTA-P-GnRH can be efficiently produced on a commercially available automated synthesis module and has potential for use in clinical diagnosis of GnRH receptor-positive tumors.

ADVANCES IN KNOWLEDGE

Our studies developed the automated radiosynthesis of a new ¹⁸F-labelled GnRH tracer and preclinical evaluation for future clinical application.

IMPLICATIONS FOR PATIENT CARE

Quantitative and noninvasive imaging of GnRH expression would provide information for diagnosis and treatment of cancer patients.

In the eye of the beholder? Oxytocin effects on eye movements in schizophrenia

BACKGROUND

Individuals with schizophrenia have difficulty in extracting salient information from faces. Eye-tracking studies have reported that these individuals demonstrate reduced exploratory viewing behaviour (i.e. reduced number of fixations and shorter scan paths) compared to healthy controls. Oxytocin has previously been demonstrated to exert pro-social effects and modulate eye gaze during face exploration. In this study, we tested whether oxytocin has an effect on visual attention in patients with schizophrenia.

METHODS

Nineteen male participants with schizophrenia received intranasal oxytocin 40UI or placebo in a double-blind, placebo-controlled, crossover fashion during two visits separated by seven days. They engaged in a free-viewing eye-tracking task, exploring images of Caucasian men displaying angry, happy, and neutral emotional expressions; and control images of animate and inanimate stimuli. Eye-tracking parameters included: total number of fixations, mean duration of fixations, dispersion, and saccade amplitudes.

RESULTS

We found a main effect of treatment, whereby oxytocin increased the total number of fixations, dispersion, and saccade amplitudes, while decreasing the duration of fixations compared to placebo. This effect, however, was non-specific to facial stimuli. When restricting the analysis to facial images only, we found the same effect. In addition, oxytocin modulated fixation rates in the eye and nasion regions.

DISCUSSION

This is the first study to explore the effects of oxytocin on eye gaze in schizophrenia. Oxytocin had enhanced exploratory viewing behaviour in response to both facial and inanimate control stimuli. We suggest that the acute administration of intranasal oxytocin may have the potential to enhance visual attention in schizophrenia.

Circuits for social learning: A unified model and application to Autism Spectrum Disorder

Early life social experiences shape neural pathways in infants to develop lifelong social skills. This review presents the first unified circuit-based model of social learning that can be applied to early life social development, drawing together unique human developmental milestones, sensitive learning periods, and behavioral and neural scaffolds. Circuit domains for social learning are identified governing Activation, Integration, Discrimination, Response and Reward (AIDRR) to sculpt and drive human social learning. This unified model can be used to identify social delays earlier in development. We propose social impairments observed in Autism Spectrum Disorder are underpinned by early mistimed sensitive periods in brain development and alterations in amygdala development to disrupt the AIDRR circuits. This model directs how interventions can target neural circuits for social development and be applied early in life. To illustrate, the role of oxytocin and its use as an intervention is explored. The AIDRR model shifts focus away from delivering broad treatments based only on diagnostic classifications, to specifying and targeting the relevant circuits, at the right time of development, to optimize social learning.

A Comprehensive Review of Non-Covalent Radiofluorination Approaches Using Aluminum [18F]fluoride: Will [18F]AlF Replace 68Ga for Metal Chelate Labeling?

Due to its ideal physical properties, fluorine-18 turns out to be a key radionuclide for positron emission tomography (PET) imaging, for both preclinical and clinical applications. However, usual biomolecules radiofluorination procedures require the formation of covalent bonds with fluorinated prosthetic groups. This drawback makes radiofluorination impractical for routine radiolabeling, gallium-68 appearing to be much more convenient for the labeling of chelator-bearing PET probes. In response to this limitation, a recent expansion of the 18F chemical toolbox gave aluminum [18F]fluoride chemistry a real prominence since the late 2000s. This approach is based on the formation of an [18F][AlF]2+ cation, complexed with a 9-membered cyclic chelator such as NOTA, NODA or their analogs. Allowing a one-step radiofluorination in an aqueous medium, this technique combines fluorine-18 and non-covalent radiolabeling with the advantage of being very easy to implement. Since its first reports, [18F]AlF radiolabeling approach has been applied to a wide variety of potential PET imaging vectors, whether of peptidic, proteic, or small molecule structure. Most of these [18F]AlF-labeled tracers showed promising preclinical results and have reached the clinical evaluation stage for some of them. The aim of this report is to provide a comprehensive overview of [18F]AlF labeling applications through a description of the various [18F]AlF-labeled conjugates, from their radiosynthesis to their evaluation as PET imaging agents.

Oxytocin modulates hippocampal perfusion in people at clinical high risk for psychosis

Preclinical and human studies suggest that hippocampal dysfunction is a key factor in the onset of psychosis. People at Clinical High Risk for psychosis (CHR-P) present with a clinical syndrome that can include social withdrawal and have a 20-35% risk of developing psychosis in the next 2 years. Recent research shows that resting hippocampal blood flow is altered in CHR-P individuals and predicts adverse clinical outcomes, such as non-remission/transition to frank psychosis. Previous work in healthy males indicates that a single dose of intranasal oxytocin has positive effects on social function and marked effects on resting hippocampal blood flow. The present study examined the effects of intranasal oxytocin on hippocampal blood flow in CHR-P individuals. In a double-blind, placebo-controlled, crossover design, 30 CHR-P males were studied using pseudo-continuous Arterial Spin Labelling on 2 occasions, once after 40IU intranasal oxytocin and once after placebo. The effects of oxytocin on left hippocampal blood flow were examined in a region-of-interest analysis of data acquired at 22-28 and at 30-36 minutes post-intranasal administration. Relative to placebo, administration of oxytocin was associated with increased hippocampal blood flow at both time points (p = .0056; p = .034), although the effect at the second did not survive adjustment for the effect of global blood flow. These data indicate that oxytocin can modulate hippocampal function in CHR-P individuals and therefore merits further investigation as a candidate novel treatment for this group.

Mixed support for a causal link between single dose intranasal oxytocin and spiritual experiences: opposing effects depending on individual proclivities for absorption

Intranasal oxytocin (OT) has previously been found to increase spirituality, an effect moderated by OT-related genotypes. This pre-registered study sought to conceptually replicate and extend those findings. Using a single dose of intranasal OT vs placebo (PL), we investigated experimental treatment effects, and moderation by OT-related genotypes on spirituality, mystical experiences, and the sensed presence of a sentient being. A more exploratory aim was to test for interactions between treatment and the personality disposition absorption on these spirituality-related outcomes. A priming plus sensory deprivation procedure that has facilitated spiritual experiences in previous studies was used. The sample (N = 116) contained both sexes and was drawn from a relatively secular context. Results failed to conceptually replicate both the main effects of treatment and the treatment by genotype interactions on spirituality. Similarly, there were no such effects on mystical experiences or sensed presence. However, the data suggested an interaction between treatment and absorption. Relative to PL, OT seemed to enhance spiritual experiences in participants scoring low in absorption and dampen spirituality in participants scoring high in absorption.

Oxytocin Enhances the Neural Efficiency of Social Perception

Face perception is a highly conserved process that directs our attention from infancy and is supported by specialized neural circuitry. Oxytocin (OT) can increase accuracy and detection of emotional faces, but these effects are mediated by valence, individual differences, and context. We investigated the temporal dynamics of OT’s influence on the neural substrates of face perception using event related potentials (ERPs). In a double blind, placebo controlled within-subject design, 21 healthy male adults inhaled OT or placebo and underwent ERP imaging during two face processing tasks. Experiment 1 investigated effects of OT on neural correlates of fearful vs. neutral facial expressions, and Experiment 2 manipulated point-of-gaze to neutral faces. In Experiment 1, we found that OT reduced N170 latency to fearful faces. In Experiment 2, N170 latency was decreased when participant gaze was directed to the eyes of neutral faces; however, there were no OT-associated effects in response to different facial features. Findings suggest OT modulates early stages of social perception for socially complex information such as emotional faces relative to neutral. These results are consistent with models suggesting OT impacts the salience of socially informative cues during processing, which leads to downstream effects in behavior. Future work should examine how OT affects neural processes underlying basic components of social behavior (such as, face perception) while varying emotional expression of stimuli or comparing different characteristics of participants (e.g., gender, personality traits).

Oxytocin as Treatment for Social Cognition, Not There Yet

In a short time, oxytocin has progressed from being a regular hormone involved in parturition and breastfeeding to be possibly the neuromodulator that has gathered the most attention. Attributed many positive roles in the modulation of different aspects of social behavior, such as bonding, empathy, cooperation, trust, and generosity, as well as roles as a natural anxiolytic and antidepressant, the expectations on oxytocin becoming a treatment for a number of disorders with associated social deficits have dramatically raised over the last years. However, despite the field has been investigating oxytocin's role in social behavior for over twenty years, there are still many unknowns on oxytocin's mechanisms of action and efficiency and the increasing number of clinical trials administering oxytocin to different clinical groups seem to disagree in its properties and report in most cases conflicting results. This has led to some disappointment among researchers and clinicians as oxytocin might not be the miraculous molecule that works in a "one size fits all" fashion initially considered. Conversely, this down-side of oxytocin might merely reflect the complexity of its neurotransmission system. The current reality is that, although oxytocin seems to have potential therapeutic value, there are key questions that remain unanswered as to decide the optimal target groups and treatment course. Here, we present an overview on critical points regarding the oxytocin system in health and disease that need to be better understood to establish its therapeutic properties and to decide who could benefit the most from its treatment.

Penetration of the blood-brain barrier by peripheral neuropeptides: new approaches to enhancing transport and endogenous expression

The blood-brain barrier (BBB) is a structural and functional barrier between the interstitial fluid of the brain and the blood; the barrier maintains the precisely controlled biochemical environment that is necessary for neural function. This constellation of endothelial cells, macrophages, pericytes, and astrocytes forms the neurovascular unit which is the structural and functional unit of the blood-brain barrier. Peptides enter and exit the CNS by transport systems expressed by the capillary endothelial cells of the neurovascular unit. Limiting the transport of peptides and proteins into the brain are efflux transporters like P-gp are transmembrane proteins present on the luminal side of the cerebral capillary endothelium and their function is to promote transit and excretion of drugs from the brain to the blood. Nanocarrier systems have been developed to exploit transport systems for enhanced BBB transport. Recent approaches for enhancing endogenous peptide expression are discussed.