Kinetics of oxytocin response to repeated restraint stress and/or chronic cold exposure

Endogenous oxytocin exerts anti-nociceptive and anti-inflammatory effects in rats

Oxytocin is involved in pain transmission, although the detailed mechanism is not fully understood. Here, we generate a transgenic rat line that expresses human muscarinic acetylcholine receptors (hM3Dq) and mCherry in oxytocin neurons. We report that clozapine-N-oxide (CNO) treatment of our oxytocin-hM3Dq-mCherry rats exclusively activates oxytocin neurons within the supraoptic and paraventricular nuclei, leading to activation of neurons in the locus coeruleus (LC) and dorsal raphe nucleus (DR), and differential gene expression in GABA-ergic neurons in the L5 spinal dorsal horn. Hyperalgesia, which is robustly exacerbated in experimental pain models, is significantly attenuated after CNO injection. The analgesic effects of CNO are ablated by co-treatment with oxytocin receptor antagonist. Endogenous oxytocin also exerts anti-inflammatory effects via activation of the hypothalamus-pituitary-adrenal axis. Moreover, inhibition of mast cell degranulation is found to be involved in the response. Taken together, our results suggest that oxytocin may exert anti-nociceptive and anti-inflammatory effects via both neuronal and humoral pathways.

Oxytocin involves in chronic stress-evoked melanoma metastasis via β-arrestin 2-mediated ERK signaling pathway

Stress is associated with an increased risk of lung metastasis in melanoma. However, the underlying mechanism is elusive. Oxytocin (OXT), a neurohormone produced by the hypothalamus, plays a vital role in laboring induction and lactation. Emerging evidence suggests that OXT also regulates human emotions, social cognition, social behaviors and stress-related disorders. Here, we reported that a significant up-regulation of oxytocin receptors (OXTRs) was observed in malignant melanoma. The activation of OXTRs dramatically promoted migration, invasion and angiogenesis but not the proliferation of melanoma cells in vitro and in vivo via β-arrestin 2-dependent ERK-VEGF/MMP-2 pathway. Next, chronic restraint stress significantly elevated the plasma level of OXT. Notably, 21 days chronic restraint stress facilitated lung metastasis of melanoma and reduced overall survival in mice, which were largely abrogated by knocking down either OXTR or β-arrestin 2. These findings provide evidence that chronic stress hormone-OXT promotes lung metastasis of melanoma via a β-arrestin 2-dependent mechanism and suggest that OXT, a novel pro-metastasis factor, is a potential therapeutic target for melanoma.

Associations Between Nurse-Guided Variables and Plasma Oxytocin Trajectories in Premature Infants During Initial Hospitalization

BACKGROUND

Oxytocin (OT) is a social hormone that may help researchers understand how nurse-guided interventions during initial infant hospitalization, such as supporting human milk expression, promoting comforting touch, and reducing exposure to stressors, affect preterm brain development.

PURPOSE

To determine whether factors related to human milk, touch, or stressor exposure are related to plasma OT trajectories in premature infants.

METHODS

Plasma from 33 premature infants, born gestational ages 25 to (Equation is included in full-text article.)weeks, was collected at 14 days of life and then weekly until 34 weeks' corrected gestational age (CGA). Variables related to feeding volumes of human milk and formula; touch, as indexed by skin-to-skin contact (SSC) and swaddled holding; and clinical stressors were extracted from the electronic medical record. Linear mixed-models tested associations between nurse-guided variables and plasma OT trajectories.

RESULTS

In the final model, same-day SSC was positively related not only to plasma OT levels at 27 weeks' CGA (β= .938, P = .002) but also to a decline in plasma OT levels over time (β=-.177, P = .001). Volume of enteral feeds (mL/kg/d), its interaction with CGA, and number of stressful procedures were not statistically significant (β= .011, P = .077; β=-.002, P = .066; and β= .007, P = .062, respectively).

IMPLICATIONS FOR PRACTICE

Nurse-guided interventions are associated with infant plasma OT levels, suggesting nurses may impact the neurobiology of the developing premature infant.

IMPLICATIONS FOR RESEARCH

Replication with larger sample sizes and randomized controlled trial designs is needed to test effects of specific nursing interventions on infant OT.

Evaluation of Short and Long Term Cold Stress Challenge of Nerve Grow Factor, Brain-Derived Neurotrophic Factor, Osteocalcin and Oxytocin mRNA Expression in BAT, Brain, Bone and Reproductive Tissue of Male Mice Using Real-Time PCR and Linear Correlation Analysis

The correlation between the Ngf/p75ntr-Ntrk1 and Bdnf, Osteocalcin-Ost/Gprc6a and Oxytocin-Oxt/Oxtr genes, was challenged investigating their mRNA levels in 3 months-old mice after cold-stress (CS). Uncoupling protein-1 (Ucp-1) was used as positive control. Control mice were maintained at room temperature T = 25°C, CS mice were maintained at T = 4°C for 6 h and 5-days (N = 15 mice). RT-PCR experiments showed that Ucp-1 and Ngf genes were up-regulated after 6 h CS in brown adipose tissues (BAT), respectively, by 2 and 1.5-folds; Ucp-1 was upregulated also after 5-days, while Ngfr (p75ntr) and Ntrk1 genes were downregulated after 6 h and 5-days CS in BAT. NGF and P75NTR were upregulated in bone and testis following 5-days, and P75NTR in testis after 6 h CS. Bdnf was instead up-regulated in bone following 5-days CS and down-regulated in testis. OST was upregulated by 16 and 3-fold in bone and BAT, respectively, following 5-days CS. Gprc6a was upregulated after 6 h in brain, while Bglap (Ost) gene was downregulated. Oxt gene was upregulated by 5-fold following 5-days CS in bone. Oxtr was upregulated by 0.5 and 0.3-fold, respectively, following 6 h and 5-days CS in brain. Oxtr and Oxt were downregulated in testis and in BAT. The changes in the expression levels of control genes vs. genes following 6 h and 5-days CS were correlated in all tissues, but not in BAT. Correlation in BAT was improved eliminating Ngfr (p75ntr) data. The correlation in brain was lost eliminating Oxtr data. In sum, Ucp-1 potentiation in BAT after cold stress is associated with early Ngf-response in the same tissue and trophic action in bone and testis. In contrast, BDNF exerts bone and neuroprotective effects. Similarly to Ucp-1, Bglap (Ost) signaling is enhanced in bone and BAT while it may exert local neuroprotective effects thought its receptor. Ngfr (p75ntr) regulates the adaptation to CS through a feed-back loop in BAT. Oxtr regulates the gene-response to CS through a feed-forward loop in brain. Overall these results expand the understanding of the physiology of these molecules under metabolic thermogenesis.

Blood pressure regulation in stress: focus on nitric oxide-dependent mechanisms

Stress is considered a risk factor associated with the development of various civilization diseases including cardiovascular diseases, malignant tumors and mental disorders. Research investigating mechanisms involved in stress-induced hypertension have attracted much attention of physicians and researchers, however, there are still ambiguous results concerning a causal relationship between stress and long-term elevation of blood pressure (BP). Several studies have observed that mechanisms involved in the development of stress-induced hypertension include increased activity of sympathetic nervous system (SNS), glucocorticoid (GC) overload and altered endothelial function including decreased nitric oxide (NO) bioavailability. Nitric oxide is well known neurotransmitter, neuromodulator and vasodilator involved in regulation of neuroendocrine mechanisms and cardiovascular responses to stressors. Thus NO plays a crucial role in the regulation of the stress systems and thereby in the BP regulation in stress. Elevated NO synthesis, especially in the initial phase of stress, may be considered a stress-limiting mechanism, facilitating the recovery from stress to the resting levels via attenuation of both GC release and SNS activity as well as by increased NO-dependent vasorelaxation. On the other hand, reduced levels of NO were observed in the later phases of stress and in subjects with genetic predisposition to hypertension, irrespectively, in which reduced NO bioavailability may account for disruption of NO-mediated BP regulatory mechanisms and accentuated SNS and GC effects. This review summarizes current knowledge on the role of stress in development of hypertension with a special focus on the interactions among NO and other biological systems affecting blood pressure and vascular function.

Relations between plasma oxytocin and cortisol: The stress buffering role of social support

Stress responses in humans can be attenuated by exogenous oxytocin administration, and these stress-buffering properties may be moderated by social factors. Yet, the influence of acute stressors on circulating endogenous oxytocin levels have been inconsistent, and limited information is available concerning the influence of social support in moderating this relationship. In the current investigation, undergraduate women (N = 67) were assessed in the Trier Social Stress Test (TSST) with either social support available from a close female friend or no social support being available. An additional set of women served as controls. The TSST elicited marked elevations of state anxiety and negative emotions, which were largely attenuated among women who received social support. Furthermore, baseline oxytocin levels were inversely related to women's general feelings of distrust, as well as basal plasma cortisol levels. Despite these associations, oxytocin levels were unaffected by the TSST, and this was the case irrespective of oral contraceptive use or estrogen levels. In contrast, plasma cortisol elevations were elicited by the psychosocial stressor, but only in women using oral contraceptives, an effect that was prevented when social support was available. Taken together, these data provisionally suggest that changes in plasma oxytocin might not accompany the stress attenuating effects of social support on cortisol levels. Moreover, as plasma oxytocin might not reliably reflect brain oxytocin levels, the linkage between oxytocin and prosocial behaviors remains tenuous.

Molecular changes induced by repeated restraint stress in the heart: the effect of oxytocin receptor antagonist atosiban

Even though stress belongs to the most common lifestyle risk factors of cardiovascular diseases, there are only limited data on direct influence of stressors on the heart. The aim of the present study was to explore selected protein signaling pathways in response to repeated immobilization stress in the heart tissue. Effects of simultaneous treatment with atosiban, an oxytocin receptor antagonist, on stress-induced changes in the heart were also investigated. Male Wistar rats were exposed to repeated immobilization (2 h daily, lasting 2 weeks). The results showed increased phosphorylation of Akt kinase, enhanced levels of Bcl-2, and decreased levels of cleaved caspase-3 in the left ventricle in response to chronic stress independently of the treatment. Exposure to restraint led to the rise of HSP-90 and p53 in vehicle-treated rats only. Stress failed to modify MMP-2 activity and ultrastructure of the heart tissue. Treatment with the oxytocin/vasopressin receptor antagonist atosiban reversed stress-induced rise in HSP-90 and p53 proteins. In conclusion, our data demonstrate that repeated restraint stress induces Akt kinase activation and this is associated with elevation of anti-apoptotic proteins (Bcl-2) and down-regulation of pro-apoptotic proteins (cleaved caspase-3). These findings suggest that activation of pro-survival anti-apoptotic Akt kinase pathway plays an important role in molecular mechanisms underlying responses and adaptation of the rat heart to repeated stress exposure. The results further indicate a regulatory role of oxytocin/vasopressin in the control of stress-induced activation in HSP-90 and related proteins.

Effects of atosiban on stress-related neuroendocrine factors

Atosiban, an oxytocin/vasopressin receptor antagonist, is used to decrease preterm uterine activity. The risk of preterm delivery is undoubtedly associated with stress, but potential side effects of atosiban on neuroendocrine functions and stress-related pathways are mostly unknown. These studies were designed to test the hypothesis that the chronic treatment of rats with atosiban modulates neuroendocrine functions under stress conditions. Male rats were treated (osmotic minipumps) with atosiban (600 μg/kg per day) or vehicle and were restrained for 120 min/day for 14 days. All animals were treated with a marker of cell proliferation 5-bromo-2-deoxyuridine. Anxiety-like behavior was measured using an elevated plus-maze. Treatment with atosiban failed to modify plasma concentrations of the stress hormones ACTH and corticosterone, but led to a rise in circulating copeptin. Atosiban increased prolactin levels in the non-stressed group. Oxytocin receptor mRNA levels were increased in rats exposed to stress. Treatment with atosiban, in both control and stressed animals, resulted in a decrease in oxytocin receptor gene expression in the hypothalamus. No changes were observed in vasopressin receptor 1A and 1B gene expression. The decrease in hippocampal cell proliferation induced by stress exposure was not modified by atosiban treatment. This study provides the first data, to our knowledge, revealing the effect of atosiban on gene expression of oxytocin receptors in the brain. Atosiban-induced enhancement of plasma copeptin indicates an elevation in vasopressinergic tone with potential influence on water-electrolyte balance.

An oxytocin-induced facilitation of neural and emotional responses to social touch correlates inversely with autism traits

Social communication through touch and mutual grooming can convey highly salient socio-emotional signals and has been shown to involve the neuropeptide oxytocin (OXT) in several species. Less is known about the modulatory influence of OXT on the neural and emotional responses to human interpersonal touch. The present randomized placebo (PLC)-controlled within-subject pharmaco-functional magnetic resonance imaging (fMRI) study was designed to test the hypothesis that a single intranasal dose of synthetic OXT (24 IU) would facilitate both neural and emotional responses to interpersonal touch in a context- (female vs male touch) and trait- (autistic trait load) specific manner. Specifically, the experimental rationale was to manipulate the reward value of interpersonal touch independent of the intensity and type of actual cutaneous stimulation administered. Thus, 40 heterosexual males believed that they were touched by either a man or a woman, although in fact an identical pattern of touch was always given by the same female experimenter blind to condition type. Our results show that OXT increased the perceived pleasantness of female, but not male touch, and associated neural responses in insula, precuneus, orbitofrontal, and pregenual anterior cingulate cortex. Moreover, the behavioral and neural effects of OXT were negatively correlated with autistic-like traits. Taken together, this is the first study to show that the perceived hedonic value of human heterosexual interpersonal touch is facilitated by OXT in men, but that its behavioral and neural effects in this context are blunted in individuals with autistic traits.

The role of oxytocin in familiarization-habituation responses to social novelty

Stress or arousal responses to novel social contexts ease off when individuals get familiar with the social context. In the present study we investigated whether oxytocin is involved in this process of familiarization-habituation as oxytocin is known to increase trust and decrease anxiety. Fifty-nine healthy female subjects took part in the same experimental procedure in two sessions separated by 4 weeks. In the first (novelty) session state trust scores were significantly positively correlated with salivary oxytocin levels while in the second (familiarity) session state trust scores were significantly negatively correlated with salivary oxytocin levels. In a path model oxytocin was associated with increased trust in the novelty session and trust was associated with decreased oxytocin levels in the familiarity session. The results are consistent with the idea that oxytocin decreases stress-to-novelty responses by promoting familiarization to novel social contexts.