Oxytocin, but not arginine vasopressin is involving in the antinociceptive role of hypothalamic supraoptic nucleus

Effects of intranasal oxytocin on pain perception among human subjects: A systematic literature review and meta-analysis

INTRODUCTION

Oxytocin (OXT) is a peptide hormone produced in the hypothalamus that plays a neuromodulatory role in emotion, stress, and anxiety. Due to its multidimensional role, OXT is a promising target for therapeutic interventions to treat pain.

OBJECTIVE

Perform a systematic literature review, followed by a meta-analysis to identify the effects of intranasal OXT on the self-perception of clinical and experimental pain among human subjects.

METHOD

A systematic review was conducted in the PubMed, PsycINFO, Scielo, Lilacs, and Web of Science databases, using the keywords Oxytocin, Pain, Analgesia, and Nociception.

RESULTS

Fifteen papers were included in the meta-analysis. None of the outcomes presented statistical significance in terms of the interventions' effect size: pain intensity (SMD = -0.02 (CI 95 %: -0.14 to 0.10; p = 0.76)) and pain unpleasantness (SMD = -0.15 (CI 95 %: -0.34 to 0.04; p = 0.12)). No meta-analysis was performed for pain threshold or tolerance because few papers address these outcomes.

CONCLUSION

There was no statistically significant effect of intranasal OXT administration on pain perception, considering equivalence limits between (-0.2 and 0.2). However, it must be considered that the study designs may not have been sensitive enough to detect minor analgesic effects of OXT, which, being weak, may also not be perceived at a conscious level. Additionally, OXT effects possibly depend on specific characteristics of the painful condition, such as pain complexity, intensity, and duration, contextual variables like the presence of social and affective support, and individual characteristics.

The Comprehensive Neural Mechanism of Oxytocin in Analgesia

Oxytocin (OXT) is a nine amino acid neuropeptide hormone that has become one of the most intensively studied molecules in the past few decades. The vast majority of OXT is synthesized in the periventricular nucleus and supraoptic nucleus of the hypothalamus, and a few are synthesized in some peripheral organs (such as the uterus, ovaries, adrenal glands, thymus, pancreas, etc.) OXT modulates a series of physiological processes, including lactation, parturition, as well as some social behaviors. In addition, more and more attention has recently been focused on the analgesic effects of oxytocin. It has been reported that OXT can relieve tension and pain without other adverse effects. However, the critical role and detailed mechanism of OXT in analgesia remain unclear. This review aims to summarize the mechanism of OXT in analgesia and some ideas about the mechanism.

Protective effect of HCN2-induced SON sensitization on chronic visceral hypersensitivity in neonatal-CRD rat model

Abnormal brain-gut interactions contribute to the development of chronic visceral hypersensitivity (CVH), which is the pivotal feature of irritable bowel syndrome (IBS). Despite the consensus with respect to the vital role of hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) channels in promoting painful symptoms in the peripheral nervous system, we identified that the upregulation of HCN2 in supraoptic nucleus (SON) was involved in the modulation of CVH in rat model of neonatal colorectal distention (n-CRD). Specifically, colorectal distention (CRD) upregulated the expression of c-Fos in SON in adult CVH rats, indicating the involvement of SON sensitazation in visceral sensation. Moreover, the administration of ZD7288 (the pan-HCN channel inhibitor) rather than 8-Br-cAMP (the non-specific HCN channel agonist) aggravated the CVH symptoms and reduced the phosphorylation level of CaMKII-CREB cascade. Together, the findings indicated that the upregulation of supraoptic HCN2 contributed to the sensitization of SON, which had protective effects on the modulation of CVH with the involvement of CaMKII-CREB cascade in n-CRD rat model.

Oxytocin in the periaqueductal gray mainly comes form the hypothalamic supraoptic nucleus to participate in pain modulation

Oxytocin (OXT) that effects the nociception process is mainly synthesized and secreted in the hypothalamic supraoptic nucleus (SON). Although the periaqueductal gray (PAG) hardly synthesizes OXT, OXT in PAG also plays a role in pain regulation. The communication investigates whether OXT in the PAG comes from SON to influence pain modulation. RT-PCR was used to analyze OXT mRNA expression and radioimmunoassay to measure OXT concentration. The results showed that (1) pain stimulation enhanced OXT mRNA expression in the SON at 10 min (268.1 ± 39.2%, p < 0.001) and 20 min (135.4±37.9%, p < 0.05) treatment and did not change in the PAG; (2) OXT level increase in SON perfusion liquid during pain stimulation [236.7±22.1% at 10 min (p < 0.001), 223.1±12.4% at 20 min (p<0.001), 56.1 ± 15.7% at 30 min (p < 0.01) and 11.2±14.2% at 40 min] was earlier than that in PAG perfusion liquid [17.8±9.7% at 10 min, 375.6±35.1% at 20 min (p <  0.001), 123.2±17.7% at 30 min (p <  0.001) and 52.7±22.4% at 40 min (p < 0.05)]; (3) SON excitation (L-glutamate sodium microinjection) induced OXT level increase in PAG perfusion liquid in a dose-dependent manner; (4) the bilateral SON cauterization completely controlled and the right SON cauterization partly reversed the pain stimulation induced-OXT concentration increase in PAG perfusion liquid. The data suggested that OXT in PAG came from SON, which might influence the pain process.

Epigenetic modification of DRG neuronal gene expression subsequent to nerve injury: etiological contribution to complex regional pain syndromes (Part II)

Cumulating evidence indicated that nerve injury-associated cellular and molecular changes play an essential role in contributing to the development of pathological pain, and more recent findings implicated the critical role of epigenetic mechanisms in pain-related sensitization in the DRG subsequent to nerve injury. In this part of the dyad review (Part II), we reviewed and paid special attention on the etiological contribution of DGR gene expression modulated by epigenetic mechanisms of CRPS. As essential effectors to different molecular activation, we first discussed the activation of various signaling pathways that subsequently from nerve injury, and in further illustrated the fundamental and functional underpinnings of nerve injury-induced pain, in which we argued for the potential epigenetic mechanisms in response to sensitizing stimuli or injury. Therefore, understanding the specific mediating factors that influence individual epigenetic differences contributing to pain sensitivity and responsiveness to analgesics possesses crucial clinical implications.

Effect of oxytocin on the behavioral activity in the behavioral despair depression rat model

Oxytocin (OXT), a nonapeptide posterior hormone of the pituitary, is mainly synthesized and secreted in the hypothalamic paraventricular nucleus (PVN) and supraoptic nucleus (SON). The present study was to investigate in which level, brain or periphery, OXT effecting on the behavioral activity in the behavioral despair depression rat model. The results showed that (1) either the forced swimming or the tail suspension significantly increased OXT concentration in the brain (PVN, SON, frontal cortex, hippocampus, amygdala, lumbar spinal cord) and in the periphery (posterior pituitary and serum); (2) intraventricular injection (icv) of OXT decreased the animal immobility time, whereas OXT receptor antagonist-desGly-NH2, d(CH2)5[D-Tyr2, Thr-sup-4]OV (icv) increased the animal immobility time in a dose-dependent manner in forced swimming test (FST) and in tail suspension test (TST); (3) neither OXT nor OXT receptor antagonist (intravenous injection) influenced the animal immobility time in FST and in TST. OXT levels were increased in several areas of the brain and in the periphery following the behavioral despair, one stressor, yet pre-treatment with OXT appeared to be beneficial in term of reducing immobility time. The data suggested that behavioral despair could enhance OXT synthesis and secretion not only in the brain but also in the periphery, and OXT in the brain rather than the periphery played a role in the behavioral despair depression.

Nonsocial functions of hypothalamic oxytocin

Oxytocin (OXT) is a hypothalamic neuropeptide composed of nine amino acids. The functions of OXT cover a variety of social and nonsocial activity/behaviors. Therapeutic effects of OXT on aberrant social behaviors are attracting more attention, such as social memory, attachment, sexual behavior, maternal behavior, aggression, pair bonding, and trust. The nonsocial behaviors/functions of brain OXT have also received renewed attention, which covers brain development, reproduction, sex, endocrine, immune regulation, learning and memory, pain perception, energy balance, and almost all the functions of peripheral organ systems. Coordinating with brain OXT, locally produced OXT also involves the central and peripheral actions of OXT. Disorders in OXT secretion and functions can cause a series of aberrant social behaviors, such as depression, autism, and schizophrenia as well as disturbance of nonsocial behaviors/functions, such as anorexia, obesity, lactation failure, osteoporosis, diabetes, and carcinogenesis. As more and more OXT functions are identified, it is essential to provide a general view of OXT functions in order to explore the therapeutic potentials of OXT. In this review, we will focus on roles of hypothalamic OXT on central and peripheral nonsocial functions.

The interaction between the oxytocin and pain modulation in headache patients

Oxytocin (OXT), a nonapeptide hormone of posterior pituitary, reaches the central nervous system from systemic blood circulation with a difficulty because of the blood-brain barrier (BBB). The interest has been expressed in the use of the nasal route for delivery of OXT to the brain directly, exploiting the olfactory pathway. Our previous study has demonstrated that OXT in the central nervous system rather than the blood circulation plays an important role in rat pain modulation. The communication tried to investigate the interaction between the OXT and pain modulation in Chinese patients with headache to understand the OXT effect on human pain modulation. The results showed that (1) intranasal OXT could relieve the human headache in a dose-dependent manner; (2) OXT concentration in both plasma and cerebrospinal fluid (CSF) increased significantly in headache patients in relation with the pain level; and (3) there was a positive relationship between plasma and CSF OXT concentration in headache patients. The data suggested that intranasal OXT, which was delivered to the central nervous system through olfactory region, could treat human headache and OXT might be a potential drug of headache relief by intranasal administration.

Oxytocin affects nitric oxide and cytokine production by sepsis-sensitized macrophages

BACKGROUND/AIM

Oxytocin (OXT) secretion during cecal ligation puncture (CLP)-induced sepsis has not yet been examined. Although immune properties have been attributed to OXT, its effect on CLP-sensitized macrophages has never been investigated. We analyzed OXT secretion during CLP and its effect in CLP-sensitized macrophage cultures.

METHODS

Male Wistar rats were decapitated 4, 6 or 24 h after CLP surgery or sham operation and blood, brain and neurohypophyses were collected for OXT measurements. In another set of animals we studied the effect of OXT on nitrite, tumor necrosis factor (TNF-α), interleukin (IL)-1β and IL-10 production of peritoneal macrophages harvested at 6 and 24 h after CLP.

RESULTS

In the early phase of sepsis (4-6 h), OXT levels increased in plasma and decreased in hypothalamus and neurohypophysis. In the late phase (24 h), plasma and neurohypophyseal levels remained basal. In the paraventricular, the OXT content remained low, but in the supraoptic increased. Macrophages of the early phase of sepsis pretreated with OXT and stimulated with lipopolysaccharide showed decreased nitrite, TNF-α and IL-1β levels, but no alteration in IL-10 production. In the late phase, they showed reduction only on IL-1β.

CONCLUSIONS

OXT secretion during sepsis may represent a neuroendocrine response contributing to the overall host response to infection by decreasing the proinflammatory response and oxidative stress.

Central administration of oxytocin receptor ligands affects cued fear extinction in rats and mice in a timepoint-dependent manner

RATIONALE

Oxytocin (OXT) has been proposed as a potential therapeutic agent for post-traumatic stress disorder (PTSD).

OBJECTIVES

We aimed to verify whether pharmacological manipulation of the brain OXT system affects cued fear conditioning and fear extinction.

METHODS

Male rats and mice were intracerebroventricularly administered synthetic OXT (rats, 0.1 or 1.0 μg/5 μl; mice, 0.1 or 0.5 μg/2 μl) and/or an OXT receptor antagonist (OXTR-A; rats, 0.75 μg/5 μl) either prior to fear conditioning or extinction training.

RESULTS

Preconditioning administration of OXT did not affect fear conditioning in rats, but decreased fear expression and facilitated fear extinction. In contrast, preconditioning blockade of OXT neurotransmission by OXTR-A did not affect fear conditioning or fear expression, but impaired fear extinction. When administered before extinction training, OXT impaired fear extinction in both rats and mice, indicating that the effects of OXT on fear extinction are conserved across species. This impairment was OXTR-mediated, as the inhibitory effect of OXT on fear extinction was abolished by prior treatment with OXTR-A. The impaired fear extinction was not a result of reduced locomotion in rats, whereas an apparent decrease in fear expression and facilitation of fear extinction with the higher OXT dose in mice was the result of behavioral hyperactivity.

CONCLUSIONS

These results suggest that increasing OXT neurotransmission during traumatic events is likely to prevent the formation of aversive memories. In contrast, OXT treatment before fear extinction training, which would be the comparable timepoint for psychotherapy in PTSD patients, rather delays fear extinction and, therefore, caution is needed before recommending OXT for the treatment of PTSD.