Oxytocin increases and a specific oxytocin antagonist decreases pain threshold in male rats

Subcutaneous Oxytocin Injection Reduces Heat Pain: A Randomized-Controlled Trial

Oxytocin (OT) is a neuropeptide broadly implicated in social relationships and behavior. OT also exerts antinociceptive and pain-reducing effects in both humans and rodents. Recent research in rodents demonstrates that these effects can be peripheral and local. In human studies, intravenous OT has reduced visceral pain, and subcutaneous injection of OT has reduced postsurgical pain. However, the local effects of subcutaneous OT on experimental pain have not been studied. We conducted a 2-session crossover study during which healthy adults received a subcutaneous injection of synthetic OT (4 mcg/2 mL) or saline placebo (isotonic saline 2 mL), in a randomized and double-blinded manner. Eighteen participants completed full study procedures. We hypothesized that 10 minutes after injection, OT would reduce measures of acute mechanical pain, pressure pain, and heat pain perception. Subcutaneous OT significantly reduced ratings of heat pain intensity and unpleasantness (both P < .01), but did not alter mechanical pain, pressure pain, or heat pain threshold (all P > .05). Changes in heat pain were observed only on the injected arm and not on the contralateral arm, confirming a localized mechanism. These findings confirm the ability of OT in or near the skin to modulate nociceptive processes in cutaneous tissues in human adults, opening exciting avenues for further mechanistic research as well as potential clinical applications for acute pain. PERSPECTIVE: This randomized-controlled trial showed that a subcutaneous injection of OT could reduce perception of heat pain tested with a thermode. OT did not alter mechanical or pressure pain or thresholds for perceiving heat pain. These findings are relevant to scientists and clinicians seeking nonaddictive local drug treatments for pain.

Oxytocin receptors influence the development and maintenance of social behavior in zebrafish (Danio rerio)

Zebrafish are highly social teleost fish and an excellent model to study social behavior. The neuropeptide Oxytocin is associated different social behaviors as well as disorders resulting in social impairment like autism spectrum disorder. However, how Oxytocin receptor signaling affects the development and expression kinetics of social behavior is not known. In this study we investigated the role of the two oxytocin receptors, Oxtr and Oxtrl, in the development and maintenance of social preference and shoaling behavior in 2- to 8-week-old zebrafish. Using CRISPR/Cas9 mediated oxtr and oxtrl knock-out fish, we found that the development of social preference is accelerated if one of the Oxytocin receptors is knocked-out and that the knock-out fish reach significantly higher levels of social preference. Moreover, oxtr^−/− fish showed impairments in the maintenance of social preference. Social isolation prior to testing led to impaired maintenance of social preference in both wild-type and oxtr and oxtrl knock-out fish. Knocking-out either of the Oxytocin receptors also led to increased group spacing and reduced polarization in a 20-fish shoal at 8 weeks post fertilization, but not at 4. These results show that the development and maintenance of social behavior is influenced by the Oxytocin receptors and that the effects are not just pro- or antisocial, but dependent on both the age and social context of the fish.

The Role of Central Serotonin Neurons and 5-HT Heteroreceptor Complexes in the Pathophysiology of Depression: A Historical Perspective and Future Prospects

Serotonin communication operates mainly in the extracellular space and cerebrospinal fluid (CSF), using volume transmission with serotonin moving from source to target cells (neurons and astroglia) via energy gradients, leading to the diffusion and convection (flow) of serotonin. One emerging concept in depression is that disturbances in the integrative allosteric receptor–receptor interactions in highly vulnerable 5-HT1A heteroreceptor complexes can contribute to causing major depression and become novel targets for the treatment of major depression (MD) and anxiety. For instance, a disruption and/or dysfunction in the 5-HT1A-FGFR1 heteroreceptor complexes in the raphe-hippocampal serotonin neuron systems can contribute to the development of MD. It leads inter alia to reduced neuroplasticity and potential atrophy in the raphe-cortical and raphe-striatal 5-HT pathways and in all its forebrain networks. Reduced 5-HT1A auto-receptor function, increased plasticity and trophic activity in the midbrain raphe 5-HT neurons can develop via agonist activation of allosteric receptor–receptor interactions in the 5-HT1A-FGFR1 heterocomplex. Additionally, the inhibitory allosteric receptor–receptor interactions in the 5-HT1AR-5-HT2AR isoreceptor complex therefore likely have a significant role in modulating mood, involving a reduction of postjunctional 5-HT1AR protomer signaling in the forebrain upon activation of the 5-HT2AR protomer. In addition, oxytocin receptors (OXTRs) play a significant and impressive role in modulating social and cognitive related behaviors like bonding and attachment, reward and motivation. Pathological blunting of the OXTR protomers in 5-HT2AR and especially in 5-HT2CR heteroreceptor complexes can contribute to the development of depression and other types of psychiatric diseases involving disturbances in social behaviors. The 5-HTR heterocomplexes are novel targets for the treatment of MD.

The Effects of Frequency and Duration of Handling on the Development of Feline Upper Respiratory Infections in a Shelter Setting

Simple Summary

Stress in cats residing in a shelter environment is a significant contributor to the development of upper respiratory disease (URD). Previous studies have shown that positive interactions can reduce stress and enhance the immune system. However, little is known on how the frequency and duration of daily handling affects a cat’s likelihood of developing URD. The goal of this study was to record the daily frequency and duration of handling of clinically healthy cats that were relinquished at a closed admission shelter and determine if these parameters were associated with a statistically significant increased risk of developing URD. While no parameters were statistically significantly associated with an increased hazard of developing URD, we found that cats that did not develop URD were handled more frequently than cats that did develop URD. Our results suggest that increased frequency and duration of handling does not appear to increase the risk of URD signs and may reduce the incidence of URD development. These results are important for the shelter community in developing handling and hygiene protocols for shelter cats.

Abstract

Reducing stress is important to maintaining the health of shelter cats and decreasing the risk of upper respiratory disease (URD). The aim of this study was to determine if the frequency and/or duration of daily routine handling of shelter cats affects the likelihood of URD development. At a closed admission shelter, each cat free of URD on intake was given a cage card for recording handling data. These data included: date and times when the cat was handled, duration of handling, if and when the cat developed signs of URD, and the handler identity. Cox regression was used to determine the relationship between these factors and URD development. We found cats that did not develop URD were handled significantly more than cats that did (1.1 times per day vs. 0.7 times per day, p < 0.001). Increased frequency of handling had a borderline significant effect on the hazard of developing URD (HR 0.37; CI: 0.13–1.1; p = 0.066). No other parameters were significantly associated with the development of URD; however, small sample size may be responsible for this finding. A larger study is needed to elucidate the relationship between handling and URD development.

Effects of intranasal oxytocin on tactile perception

In addition to its role in childbirth labor and lactation, oxytocin is a well-known neurohormone, having several prosocial effects. Moreover, oxytocin seems to play a significant modulatory role in painful experiences, due to its participation in central and peripheral processing of nociceptive somatosensory information. Despite studies on oxytocin in pain modulation, there is a scarce literature investigating the role of oxytocin in tactile perception. Here we investigate the effects of 24 and 40 IU intranasal administration of oxytocin in the non-harmful mechanical tactile detection threshold in men. The data showed a significant increase in tactile perception in an experimental 40 IU oxytocin group. We suggest that this effect could be the basis for the oxytocin-bonding effect via touch.

The immediate effects of cervical spine manipulation on pain and biochemical markers in females with acute non-specific mechanical neck pain: a randomized clinical trial

Study Design: Randomized clinical trial with pre-test, post-test control group design.

Objectives: To examine the immediate effects of cervical spinal manipulation (CSM) on serum concentration of biochemical markers (oxytocin, neurotensin, orexin A, and cortisol).

Background: Several studies have found an association between spinal manipulation (SM) and pain perception. However, the mechanism by which SM modulates pain remains undefined.

Methods: Twenty-eight female subjects with non-specific mechanical neck pain were randomly assigned to one of two interventions (CSM versus sham CSM). Blood samples were drawn before and immediately after the respective interventions. Oxytocin, neurotensin, orexin A, and cortisol were measured from the blood and serum using the Milliplex Map Magnetic Bead Panel Immunoassay on the Luminex 200 Platform.

Results: In the CSM group, there were significant increases in pre- versus post-manipulation mean oxytocin (154.5 ± 60.1 vs. 185.1 ± 75.6, p = .012); neurotensin (116.0 ± 26.5 vs.136.4 ± 34.1, p < . 001); orexin A (52.2 ± 31.1 vs. 73.8 ± 38.8, p < .01) serum concentration; but no significant differences in mean cortisol (p = .052) serum concentration. In the sham group, there were no significant differences in any of the biomarkers (p > .05).

Conclusion: The results of the current study suggest that the mechanical stimuli provided through a CSM may modify neuropeptide expression by immediately increasing the serum concentration of nociception-related biomarkers (oxytocin, neurotensin, orexin A, but not cortisol) in the blood of female subjects with non-specific mechanical neck pain.

Changes in biochemical markers following spinal manipulation-a systematic review and meta-analysis

The aim of this meta-analysis was to determine the effectiveness of spinal manipulation in influencing various biochemical markers in healthy and or symptomatic population. Electronic databases (n = 10) were searched (from inception till September 2016) and eight trials (325 participants) that met the inclusion criteria were included in the meta-analysis. Two authors independently extracted and assessed the risk of bias in included studies. Standardised mean differences for outcome measures were used to calculate effect sizes. The Grading of Recommendations, Assessment, Development and Evaluation (GRADE) tool was used for assessing the quality of the body of evidence for each outcome of interest. There was moderate quality evidence that spinal manipulation influenced biochemical markers. There was moderate quality evidence of significant difference that spinal manipulation is better (SMD -0.46, 95% CI - 0.93 to 0) than control in eliciting changes in cortisol levels immediately after intervention. There was also a low quality evidence that spinal manipulation is better than control at post-intervention in increasing substance-P (SMD -0.48,95%CI-0.87 to -0.1), neurotensin (SMD -1.8,95%CI-2.56 to -1.04) and oxytocin levels (SMD -2.61,95%CI-3.5to-1.72). However, low quality evidence indicated that spinal manipulation did not influence epinephrine (SMD 0.1,95%CI- 0.56to0.75) or nor-epinephrine levels (SMD -0.06,95%CI-0.71to0.6). The current review found that spinal manipulation can increase substance-p, neurotensin, oxytocin and interleukin levels and may influence cortisol levels post-intervention. However, future trials targeting symptomatic populations are required to understand the clinical importance of such changes.

The influence of early life sexual abuse on oxytocin concentrations and premenstrual symptomatology in women with a menstrually related mood disorder

Oxytocin (OT), associated with affiliation and social bonding, social salience, and stress/pain regulation, may play a role in the pathophysiology of stress-related disorders, including menstrually-related mood disorders (MRMD's). Adverse impacts of early life sexual abuse (ESA) on adult attachment, affective regulation, and pain sensitivity suggest ESA-related OT dysregulation in MRMD pathophysiology. We investigated the influence of ESA on plasma OT, and the relationship of OT to the clinical phenomenology of MRMD's. Compared to MRMD women without ESA (n=40), those with ESA (n=20) displayed significantly greater OT [5.39pg/mL (SD, 2.4) vs. 4.36pg/mL (SD, 1.1); t (58)=-2.26, p=0.03]. In women with ESA, OT was significantly, inversely correlated with premenstrual psychological and somatic symptoms (r's=-0.45 to -0.64, p's<0.05). The relationship between OT and premenstrual symptomatology was uniformly low and non-significant in women without ESA. In women with ESA, OT may positively modulate MRMD symptomatology.

Self-soothing behaviors with particular reference to oxytocin release induced by non-noxious sensory stimulation

Oxytocin, a hypothalamic nonapeptide, is linked to increased levels of social interaction, well-being and anti-stress effects. The effects of oxytocin that is released by sensory stimulation during different kinds of interactive behaviors are often underestimated or even forgotten. In fact, many of the positive effects caused during interaction, such a wellbeing, stress reduction and even health promotion, are indeed linked to oxytocin released in response to activation of various types of sensory nerves. Oxytocin is released in response to activation of sensory nerves during labor, breastfeeding and sexual activity. In addition oxytocin is released in response to low intensity stimulation of the skin, e.g., in response to touch, stroking, warm temperature, etc. Consequently oxytocin is not only released during interaction between mothers and infants, but also during positive interaction between adults or between humans and animals. Finally oxytocin is also released in response to suckling and food intake. Oxytocin released in the brain in response to sensory stimulation as a consequence of these types of interactive behaviors, contributes to every day wellbeing and ability to handle stress. Food intake or sex may be used or even abused to achieve oxytocin-linked wellbeing and stress relief to compensate for lack of good relationships or when the levels of anxiety are high. The present review article will summarize the role played by oxytocin released by sensory (in particular somatosensory) stimulation, during various kinds of interactive behaviors. Also the fact that the anti-stress effects of oxytocin are particularly strong when oxytocin is released in response to “low intensity” stimulation of the skin will be highlighted.

Adolescent exposure to oxytocin, but not the selective oxytocin receptor agonist TGOT, increases social behavior and plasma oxytocin in adulthood

There are indications that exposing adolescent rodents to oxytocin (OT) may have positive "trait-changing" effects resulting in increased sociability and decreased anxiety that last well beyond acute drug exposure and into adulthood. Such findings may have relevance to the utility of OT in producing sustained beneficial effects in human psychiatric conditions. The present study further examined these effects using an intermittent regime of OT exposure in adolescence, and using Long Evans rats, that are generally more sensitive to the acute prosocial effects of OT. As OT has substantial affinity for the vasopressin V1a receptor (V1aR) in addition to the oxytocin receptor (OTR), we examined whether a more selective peptidergic OTR agonist - [Thr4, Gly7]-oxytocin (TGOT) - would have similar lasting effects on behavior. Male Long Evans rats received OT or TGOT (0.5-1mg/kg, intraperitoneal), once every three days, for a total of 10 doses during adolescence (postnatal day (PND) 28-55). Social and anxiety-related behaviors were assessed during acute administration as well as later in adulthood (from PND 70 onwards). OT produced greater acute behavioral effects than TGOT, including an inhibition of social play and reduced rearing, most likely reflecting primary sedative effects. In adulthood, OT but not TGOT pretreated rats displayed lasting increases in social interaction, accompanied by an enduring increase in plasma OT. These findings confirm lasting behavioral and neuroendocrine effects of adolescent OT exposure. However, the absence of such effects with TGOT suggests possible involvement of the V1aR as well as the OTR in this example of developmental neuroplasticity.

Modulation of early stress-induced neurobiological changes: a review of behavioural and pharmacological interventions in animal models

Childhood adversity alters the predisposition to psychiatric disorders later in life. Those with psychiatric conditions and a history of early adversity exhibit a higher incidence of treatment resistance compared with individuals with no such history. Modulation of the influence early stress exerts over neurobiology may help to prevent the development of psychiatric disorders in some cases, while attenuating the extent of treatment resistance in those with established psychiatric disorders. This review aims to critically evaluate the ability of behavioural, environmental and pharmacologic interventions to modulate neurobiological changes induced by early stress in animal models. Databases were systematically searched to locate literature relevant to this review. Early adversity was defined as stress that resulted from manipulation of the mother-infant relationship. Analysis was restricted to animal models to enable characterisation of how a given intervention altered specific neurobiological changes induced by early stress. A wide variety of changes in neurobiology due to early stress are amenable to intervention. Behavioural interventions in childhood, exercise in adolescence and administration of epigenetic-modifying drugs throughout life appear to best modulate cellar and behavioural alterations induced by childhood adversity. Other pharmacotherapies, such as endocannabinoid system modulators, anti-inflammatories and antidepressants can also influence these neurobiological and behavioural changes that result from early stress, although findings are less consistent at present and require further investigation. Further work is required to examine the influence that behavioural interventions, exercise and epigenetic-modifying drugs exert over alterations that occur following childhood stress in human studies, before possible translational into clinical practice is possible.

Changes in biochemical markers of pain perception and stress response after spinal manipulation

STUDY DESIGN

Controlled, repeated-measures, single-blind randomized study.

OBJECTIVES

To determine the effect of cervical or thoracic manipulation on neurotensin, oxytocin, orexin A, and cortisol levels.

BACKGROUND

Previous studies have researched the effect of spinal manipulation on pain modulation and/or range of movement. However, there is little knowledge of the biochemical process that supports the antinociceptive effect of spinal manipulation.

METHODS

Thirty asymptomatic subjects were randomly divided into 3 groups: cervical manipulation (n = 10), thoracic manipulation (n = 10), and nonmanipulation (control) (n = 10). Blood samples were extracted before, immediately after, and 2 hours after each intervention. Neurotensin, oxytocin, and orexin A were determined in plasma using enzyme-linked immuno assay. Cortisol was measured by microparticulate enzyme immuno assay in serum samples.

RESULTS

Immediately after the intervention, significantly higher values of neurotensin (P<.05) and oxytocin (P<.001) levels were observed with both cervical and thoracic manipulation, whereas cortisol concentration was increased only in the cervical manipulation group (P<.05). No changes were detected for orexin A levels. Two hours after the intervention, no significant differences were observed in between-group analysis.

CONCLUSION

The mechanical stimulus provided by spinal manipulation triggers an increase in neurotensin, oxytocin, and cortisol blood levels. Data suggest that the initial capability of the tissues to tolerate mechanical deformation affects the capacity of these tissues to produce an induction of neuropeptide expression. J

Multimodal postcesarean delivery analgesia

Cesarean deliveries can be associated with moderate to severe postoperative pain. Appropriate management of pain is important because it results in better patient satisfaction, earlier mobilization, and improved maternal-infant bonding. There are many individual options for treatment of pain; however, multimodal analgesic therapy has become the mainstay of treatment. In this article, the epidemiology of postcesarean delivery pain, pain mechanisms, and the multiple options available to providers for treatment of postoperative pain are discussed.

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.

Newborn behaviour to locate the breast when skin-to-skin: a possible method for enabling early self-regulation

AIM

The aim of this study was to provide a more detailed analysis of the infant's behavioural sequence that begins immediately after birth and terminates with grasping the nipple, suckling and then falling asleep.

METHOD

Twenty-eight full-term infants were videotaped immediately after birth. A video protocol was developed to examine infant behaviours identified from five random videotapes.

RESULTS

When birth crying had stopped, the babies showed a short period of relaxation and then successively became alert. They went through an 'awakening phase', an 'active phase' with movements of limbs, rooting activity and looking at the mother's face, a 'crawling phase' with soliciting sounds, a 'familiarization phase' with licking of the areola, and a 'suckling phase' and last a 'sleeping phase'. Five factors related to the time spent to locate the breast: more number of looks at the breast 10-20 min after birth (p < 0.0001); and exposure to meperidine (p = 0.0006) related to increased time. Early start of crawling (p = 0,0040); increased number of 'soliciting sounds' (p = 0.0022); and performing hand-breast-mouth movements (p = 0.0105) related to shorter time.

CONCLUSION

Inborn breastfeeding reflexes were depressed at birth, possibly because of a depressed sensory system. It is hypothesized that when the infant is given the option to peacefully go through the nine behavioural phases birth cry, relaxation, awakening, activity, crawling, resting, familiarization, suckling and sleeping when skin-to-skin with its mother this results in early optimal self-regulation.

Polymorphism in the oxytocin promoter region in patients with lactase non-persistence is not related to symptoms

Background

Oxytocin and the oxytocin receptor have been demonstrated in the gastrointestinal (GI) tract and have been shown to exert physiological effects on gut motility. The role for oxytocin in the pathophysiology of GI complaints is unknown. The aim of this study was to examine genetic variations or polymorphism of oxytocin (OXT) and its receptor (OXTR) genes in patients with GI complaints without visible organic abnormalities.

Methods

Genetic variants in the OXT promoter region, and in the OXTR gene in DNA samples from 131 rigorously evaluated patients with Irritable Bowel Syndrome (IBS), 408 homozygous subjects referred for lactase (LCT-13910 C>T, rs4988235) genotyping, and 299 asymptomatic blood donors were compared. One polymorphism related to the OXT gene (rs6133010 A>G) and 4 related to the OXTR gene (rs1465386 G>T, rs3806675 G>A, rs968389 A>G, rs1042778 G>T) were selected for genotyping using Applied Biosystems 7900 HT allele discrimination assays.

Results

There were no statistically significant differences in the genotype or allele frequencies in any of the SNPs when IBS patients were compared to healthy controls. Among subjects referred for lactase genotyping, the rs6133010 A>G OXT promoter A/G genotype tended to be more common in the 154 non-persistent (27.3%) subjects than in the 254 lactase persistant (18.1%) subjects and in the healthy controls (19.4%) (p = 0.08). When direct comparing, the A/G genotype was less common in the OXT promoter region in controls (p = 0.09) and in subjects with lactase persistence (p = 0.03) compared to subjects with lactase non-persistence. When healthy controls were viewed according to their own LCT-13910 genotypes, the C/C lactase non-persistent controls had a higher frequency for the OXT promoter A/G genotype than LCT-13910 T/T lactase persistent controls (41.2% vs 13.1%).

No significant differences in frequencies of the investigated OXTR SNPs were noted in this study.

Conclusion

The results suggest that polymorphism in the promoter region of the OXT gene is most common in subjects with lactase non-persistence. This polymorphism may not be related to GI symptoms, as it is related to lactase non-persistence also in healthy controls.

Hypothalamospinal oxytocinergic antinociception is mediated by GABAergic and opiate neurons that reduce A-delta and C fiber primary afferent excitation of spinal cord cells

Recent results implicate a new original mechanism involving oxytocin (OT), as a mediator via descending fibers of the paraventricular hypothalamic nucleus (PVN), in antinociception and analgesia. In rats electrical stimulation of the PVN or topical application of OT selectively inhibits A-delta and C fiber responses in superficial dorsal horn neurons, and this inhibition is reversed by a selective OT antagonist. However, little is known about the mechanisms and the spinal elements participating in this phenomenon. Here we show that topical application of bicuculline blocks the effects produced by PVN electrical stimulation or OT application. PVN electrical stimulation also activates a subpopulation of neurons in lamina II. These PVN-On cells are responsible for the amplification of local GABAergic inhibition. This result reinforces the suggestion that a supraspinal descending control of pain processing uses a specific neuronal pathway in the spinal cord in order to produce antinociception involving a GABAergic interneuron. Moreover, the topical administration of naloxone or a mu-opiate receptor antagonist beta-funaltrexamine only partially blocks the inhibitory effects produced by OT application or PVN electrical stimulation. Thus, this OT mechanism only involves opiate participation to a minor extent. The OT-specific, endogenous descending pathway represents an interesting mechanism to resolve chronic pain problems in special the neuropathic pain.

Ethnicity is associated with alterations in oxytocin relationships to pain sensitivity in women

It is well established that African Americans (AA) experience greater pain associated with a variety of clinical conditions, and greater pain sensitivity to experimental pain tasks relative to non-Hispanic Whites (W). Notably, African Americans do not show the same relationships involving endogenous pain regulatory mechanisms and pain sensitivity documented in Caucasians, including positive associations between blood pressure, norepinephrine, cortisol and greater pain tolerance.

OBJECTIVES

The purpose of this study was to examine the relationship between plasma oxytocin (OT) and pain sensitivity and to explore the relation of OT to other factors known to influence pain perception.

DESIGN

OT concentration and sensitivity to ischemic, cold pressor, and thermal pain tasks were assessed in African American (n=25) and non-Hispanic White (n=23) pre-menopausal women.

RESULTS

African American women demonstrated significantly lower pain tolerance across tasks compared with Whites (F(1,46)=6.31, p=0.0156) and also exhibited lower plasma OT levels (AA: 3.90, W: 7.05 pg/mL; p=0.0014). Greater OT levels were correlated with greater tolerance to ischemic pain (r=0.36, p=0.013) and accounted for a marginally significant portion of the ethnic difference in ischemic pain tolerance (B=+0.29, p=0.06). Greater OT was also correlated with greater tolerance of cold pressor pain (r=0.31, p=0.03); however, this association was no longer seen after the variance due to ethnicity was accounted for.

CONCLUSION

These data suggest that reduced oxytocinergic function may be one of multiple biological factors contributing to the greater sensitivity to experimental ischemic pain, and to the greater burden of some types of clinical pain experienced by African Americans compared with Whites.

Neuroanatomical and cellular substrates of hypergrooming induced by microinjection of oxytocin in central nucleus of amygdala, an experimental model of compulsive behavior

Oxytocin (OT) is a neurosecretory nonapeptide synthesized in hypothalamic cells that project to the neurohypophysis as well as to widely distributed sites in the central nervous system. Central OT microinjections induce a variety of cognitive, sexual, reproductive, grooming and affiliative behaviors in animals. Obsessive-compulsive disorder (OCD) includes a range of cognitive and behavioral symptoms that bear some relationship with OT. Here, we study the neuroanatomical and cellular substrates of the hypergrooming induced by administration of OT in the central nucleus of amygdala (CeA). In this context, this hypergrooming is considered as a model of compulsive behavior. Our data suggest a link between the CeA and the hypothalamic grooming area (HGA). The HGA includes parts of the paraventricular nucleus and the dorsal hypothalamic area. Our data on colocalization of OT (immunohistochemistry for peptide), OT receptor (binding assay) and its retrogradely labeled cells after Fluoro-Gold injection in the CeA suggest that CeA and connections are important substrates of the circuit underlying this OT-dependent compulsive behavioral pattern.

GABA-mediated oxytocinergic inhibition in dorsal horn neurons by hypothalamic paraventricular nucleus stimulation

In anaesthetized rats, we tested whether the unit activity of dorsal horn neurons that receive nociceptive input is modulated by electrical stimulation of the hypothalamic paraventricular nucleus (PVN). An electrophysiological mapping of dorsal horn neurons at L3-L4 let us choose cells responding to a receptive field located in the toes region of the left hindpaw. Dorsal horn neurons were classified according to their response properties to peripheral stimulation. Wide Dynamic Range (WDR) cells responding to electrical stimulation of the peripheral receptive field and presenting synaptic input of Adelta, Abeta, and C-fibers were studied. Suspected interneurons that are typically silent and lack peripheral receptive field responses were also analyzed. PVN electrical stimulation inhibits Adelta (-55.0+/-10.2%), C-fiber (-73.1+/-6.7%), and post-discharge (-75.0+/-8.9%) peripheral activation in WDR cells, and silent interneurons were activated. So, this last type of interneuron was called a PVN-ON cell. In WDR cells, the inhibition of peripheral responses caused by PVN stimulation was blocked by intrathecal administration of a specific oxytocin antagonist or bicuculline. However, PVN-ON cell activation was blocked by the same specific oxytocin antagonist, but not by bicuculline. Our results suggest that PVN stimulation inhibits nociceptive peripheral-evoked responses in WDR neurons by a descending oxytocinergic pathway mediated by GABAergic PVN-ON cells. We discuss our observation that the PVN electrical stimulation selectively inhibits Adelta and C-fiber activity without affecting Abeta fibers. We conclude that Adelta and C-fibers receive a presynaptic inhibition mediated by GABA.

Does regular massage from late pregnancy to birth decrease maternal pain perception during labour and birth?—A feasibility study to investigate a programme of massage, controlled breathing and visualization, from 36 weeks of pregnancy until birth

The present study was undertaken to produce a detailed specification of a programme of massage, controlled breathing and visualization performed regularly by birth partners, from 36 weeks gestation and assisted by a trained professional, following hospital admission during labour and birth. As current research on massage interventions for pain relief in labour is poorly characterized, we began by undertaking a feasibility study on an established massage programme [Goldstone LA. Massage as an orthodox medical treatment past and future. Complementary Therapies in Nursing & Midwifery. 2000;6:169-75]. The intervention was designed in light of experimental findings that repeated massage sessions over 14 days increases pain threshold, by an interaction between oxytocin and opioid neurons [Lund I, Yu L-C, Uvnas-Moberg K, Wang J, Yu C, Kurosawa M, et al. Repeated massage-like stimulation induces long-term effects on nociception: contribution of oxytocinergic mechanisms. European Journal of Neuroscience 2002;16:330-8]. A 4 week time-frame was selected to coincide with a physiological increase in maternal pain threshold [Cogan R, Spinnato JA. Pain and Discomfort Thresholds in Late Pregnancy. Pain 1986;27:63-8, Whipple B, Josimovich JB, Komisaruk BR. Sensory thresholds during the antepartum, intrapartum, and postpartum periods. International Journal of Nursing Studies 1990;27(3):213-21, Gintzler AR, Komisaruk BR. Analgesia is produced by uterocervical mechano-stimulation in rats: roles of afferent nerves and implications for analgesia of pregnancy and parturition. Brain Research 1991;566:299-302, Gintzler AR, Liu N-J. The maternal spinal cord: biochemical and physiological correlates of steroid-activated antinociceptive processes. In: Russell JA, Douglas AJ, Windle RJ, Ingram CD, editors., Progress in Brain Research. Volume 133. The Maternal Brain. Neurobiological and Neuroendocrine adaptation and disorders in pregnancy and postpartum. Amsterdam: Elsevier Science, 2001. p. 83-97]. The main objective was to measure the effects of the programme on maternal pain perception during labour and birth. To detect any effect of massage during labour, on maternal cortisol and catecholamines, cord venous blood was taken to measure plasma concentrations following birth. Twenty-five nulliparous (N) and 10 multiparous (M) women participated in the study. Cortisol values were similar to published studies following labour without massage but pain scores on a Visual Analogue Scale (VAS), at 90min following birth were significantly lower than scores recorded 2 days postpartum [Capogna G, Alahuhta S, Celleno D, De Vlieger H, Moreira J, Morgan B, et al. Maternal expectations and experiences of labour pain and analgesia: a multi-centre study of nulliparous women. International Journal of Obstetric Anaesthesia 1996;5:229-35]. The mean score was 6.6. Previous studies suggest that a reduction from 8.5 to 7.5 would significantly reduce pharmacological analgesia in labour [Capogna G, Alahuhta S, Celleno D, De Vlieger H, Moreira J, Morgan B, et al. Maternal expectations and experiences of labour pain and analgesia: a multi-centre study of nulliparous women. International Journal of Obstetric Anaesthesia 1996;5:229-35].

Oxytocin is expressed throughout the human gastrointestinal tract

BACKGROUND/AIM

Several studies have described that oxytocin exerts stimulatory or inhibitory effects on gut functions. Recently, mRNA for oxytocin and its receptor was found throughout the entire human gastrointestinal (GI) tract. The aim of this study was to examine the cellular localization and distribution of the corresponding proteins.

MATERIAL AND METHODS

Full-thickness biopsies from 24 patients, covering the entire GI tract, were collected during operations at the Department of Surgery in Malmö and Lund. The biopsies were taken from non_affected margins. The biopsies were fixed by immersion, rinsed in buffered sucrose, and kept frozen at 70 degrees C. Indirect immunofluorescence with primary antibodies to oxytocin and its receptor was used.

RESULTS

Oxytocin was expressed in nerve cell bodies and nerve fibres in the myenteric and submucous ganglia all along the GI tract. Immunoreactive nerve cell bodies in myenteric ganglia predominated in the proximal (antrum and duodenum) and distal gut, while those in the submucous ganglia were more numerous in the ileum and colon. The oxytocin receptor was not detectable by two different antibodies in any tissue in the GI tract.

CONCLUSION

Oxytocin is expressed in the myenteric and submucous ganglia and nerve fibres along the entire human GI tract. The role for oxytocin in the physiology and pathophysiology of the bowel remains to be settled.

Effects of long-term treatment with oxytocin in chronic constipation; a double blind, placebo-controlled pilot trial

BACKGROUND

Oxytocin and its receptor have been found throughout the gastrointestinal (GI) tract, where it affects gut function. Clinically, we have noticed an improvement of bowel habits during lactation in constipated women. The aim of this study was to examine whether oxytocin has an effect on bowel symptoms and psychological well being in women with refractory constipation.

METHODS

Fifty-nine women with refractory constipation were included in a double blind, multicentre study. After a 2-week run-in period, they were randomly allocated to nasal inhalation of either placebo or oxytocin treatment twice daily for 13 weeks, followed by a 2 weeks, posttreatment period. The patients completed a questionnaire every day concerning bowel habits, abdominal pain and discomfort, and Gastrointestinal Symptoms Rating Scale (GSRS) and Psychological General Well-being (PGWB) twice during the study; namely, during the baseline period and at the end of the treatment period.

RESULTS

Both oxytocin and placebo led to improvement of the constipation according to the GSRS and led to improvement in the sensation of incomplete evacuation and anorectal obstruction, without significant differences between the groups. Abdominal pain and discomfort responded weakly to oxytocin, with no effect of the placebo. In a subgroup of patients with IBS and concomitant depression, a weak improvement in depressed mood was observed after oxytocin administartion.

CONCLUSION

Nasal administration of oxytocin had no significant advantage over placebo concerning an effect on constipation. However, it seems to have a positive effect on abdominal pain and discomfort and depressed mood. These findings should be further explored.

[Acupuncture in the treatment of pain--hypothesis to adaptive effects]

A basic principle in conventional pain therapy is that the treatment should be tailored to the pathological mechanism of the disease. This is based on the knowledge of the effector mechanisms of the applied treatment modalities. Although for acupuncture the mode of action still remains elusive in many parts, evidence about its mechanisms in pain treatment is growing. A better understanding of the hypalgesic effects of acupuncture might lead to a more differentiated and mechanism guided application. The aim of this article is to evaluate the scientific data about the neurobiological mechanisms of acupuncture in the treatment of pain. Data are critically evaluated regarding their relevance for clinical practice. Possible mechanisms are differentiated in local and systemic effects and the question of point specificity is discussed. Additionally a comprehensive hypothesis is set up for the long-term effects of acupuncture in the treatment of chronic pain. In this context acupuncture is considered as a mode of repetitive, nociceptive stimulation, which induces adaptive processes on different physiological levels leading to an improved ability of the nociceptive system to cope with painful stimuli.

Why Does Social Exclusion Hurt? The Relationship Between Social and Physical Pain

The authors forward the hypothesis that social exclusion is experienced as painful because reactions to rejection are mediated by aspects of the physical pain system. The authors begin by presenting the theory that overlap between social and physical pain was an evolutionary development to aid social animals in responding to threats to inclusion. The authors then review evidence showing that humans demonstrate convergence between the 2 types of pain in thought, emotion, and behavior, and demonstrate, primarily through nonhuman animal research, that social and physical pain share common physiological mechanisms. Finally, the authors explore the implications of social pain theory for rejection-elicited aggression and physical pain disorders.

Inhibition of trigemino-hypoglossal reflex in rats by oxytocin is mediated by μ and κ opioid receptors

Recent studies showed that oxytocin plays an important role in the modulation of pain at different levels of the central nervous system. The present study was undertaken to investigate the effect of oxytocin on trigemino-hypoglossal reflex in rats. With the experimental settings used in this study, we have demonstrated that oxytocin showed significant analgesic effect after intracerebroventricular administration in rats, as assayed by the amplitude of the retractory movements of the tongue after tooth pulp stimulation. Antinociceptive effect of oxytocin was inhibited by subsequent perfusion of cerebral ventricles with oxytocin antagonist, [deamino-Cys1-D-Tyr(OEt)2-Thr4-Orn8]-oxytocin, atosiban. An involvement of opioid system in the oxytocin-induced analgesia was studied after intracerebroventricular administration of different opioid antagonists: non-selective naloxone, mu-selective beta-funaltrexamine, delta-selective naltrindole, and kappa-selective nor-binaltorphimine. It was shown that inhibition of antinociceptive effects was mediated through mu and kappa opioid receptors, indicating that there is a synergy between oxytocin and opioid systems in transmitting and modulating pain stimuli. Co-administration of oxytocin and a mu-selective endogenous opioid ligand endomorphin-2 did not significantly increase the antinociceptive activity of endomorphin-2.

Oxytocin stimulates colonic motor activity in healthy women

The effects of oxytocin in the gastrointestinal tract are unclear. The aim of this study was to examine the effect of infusion of oxytocin on colonic motility and sensitivity in healthy women. Fourteen healthy women were investigated twice. A 6-channel perfusion catheter, with three recording points (2 cm apart) proximally and three recording points distally to a barostat balloon, was inserted to the splenic flexure. An intestinal feeding tube was placed in the mid-duodenum. A 90-min duodenal lipid infusion of 3 kcal min(-1) was administered. Thirty minutes after the start of the lipid infusion, the subject randomly received either 20 or 40 mU min(-1) of oxytocin, or isotonic saline as intravenous infusions for 90 min. Meanwhile, the colonic motility was recorded. During the last 30 min of oxytocin and saline infusion, the visceral sensitivity to balloon distensions was examined. During lipid infusion the number of antegrade contractions per hour was 0.7 +/- 0.3 after saline and 3.9 +/- 1.4 after oxytocin (P = 0.03), indicating more pronounced lumen-occlusive contractile activity after oxytocin administration. Some of these consisted of high-amplitude (> 103 mmHg in amplitude) antegrade contractions. Lipid infusion evoked a decrease of the balloon volume, reflecting increased colonic tone, but there was no difference between saline and oxytocin. Sensory thresholds did not differ significantly between saline and oxytocin. Infusion of oxytocin stimulates antegrade peristaltic contractions in stimulated colon in healthy women. The effects of oxytocin on colonic motor activity deserve to be further explored, especially in patients with colonic peristaltic dysfunction.

Actions of oxytocin and interactions with glutamate on spontaneous and evoked dorsal spinal cord neuronal activities

Among the numerous pain control mechanisms that have been proposed, those acting at the spinal cord have been broadly studied, but little is known about how neuropeptides originating in supraspinal structures may relate to pain and analgesic mechanisms. Oxytocin (OT), in addition to its well known hormonal action, produces neuronal effects in various regions of the central nervous system. Indeed, some parvocellular neurons in the hypothalamic paraventricular nucleus (PVN) are oxytocinergic and project to the caudal part of the brain and the spinal cord. Moreover, the rat spinal cord shows a good overlap between the oxytocinergic hypothalamo-spinal neuron projections and the distribution of OT binding sites. However, the physiological significance of these binding sites is largely unknown. Extracellular unit activity of spinal cord neurons was recorded at the T13-L1 levels in male rats anesthetized with halotane. Somatic stimulation was applied to the inner and outer thigh of the ipsilateral hindpaw, and glutamate (GLU) and OT were locally delivered by pressure using pipettes coupled to recording electrodes. Our results show that spinal cord neurons, mainly located in the dorsal horn, in the intermediolateral cell column (IML) and in the intermediomedial gray matter (IMM), respond to the application of OT (71.5%) with activation (48%) or inhibition (52%). In some cases, opposite OT effects were observed during simultaneous recordings of two cells, suggesting OT activation of an inhibitory interneuron followed by the inhibition of the second recorded neuron. Increases in neuronal firing rate produced by GLU could be blocked by prior OT application. Finally, OT could reduce or partially block the responses to tactile and nociceptive somatic stimulation. We found that spinal cord neurons are sensitive to OT indicating that OT binding sites are functionally active. OT effects suggest the activation of inhibitory interneurons acting on a second order projecting cells to modulate afferent tactile and nociceptive information.

Effect of intrathecal and intravenous administration of oxytocin on amplitude of the reflex-evoked muscle action potential after electrical stimulation of the tooth pulp in anesthetized dogs

OBJECTIVE

To determine whether intrathecal (IT) or IV administration of oxytocin will diminish amplitude of the reflex-evoked muscle action potential (REMP) in the digastricus muscle during electrical stimulation of the tooth pulp in anesthetized dogs, thus suggesting an analgesic effect for oxytocin.

ANIMALS

6 male Beagles that were 2 to 6 years old.

PROCEDURE

Dogs were used in a crossover design with at least a 5-day washout period between treatments. Each dog received morphine, saline (0.9% NaCl) solution, and oxytocin by both the IT and IV routes of administration. Noninvasive dental dolorimetry was used to assess changes in pain threshold following administration of treatments. Effectiveness of analgesia was determined on the basis of change in REMP amplitude in the digastricus muscle.

RESULTS

Morphine administered IV significantly inhibited REMP amplitude, compared with IV administration of saline solution or oxytocin. There was not a significant change in REMP amplitude between saline solution and oxytocin administered IV. Intrathecal administration of morphine significantly inhibited REMP amplitude, compared with IT administration of saline solution or oxytocin. Intrathecal administration of oxytocin significantly increased REMP amplitude, compared with IT administration of saline solution or morphine.

CONCLUSIONS AND CLINICAL RELEVANCE

Although IV administration of oxytocin did not have an effect on REMP amplitude, compared with IV administration of saline solution, IT administration of oxytocin had the opposite effect of morphine and increased REMP amplitude of the digastricus muscle. These data do not support the use of oxytocin as an analgesic agent in dogs.

Repeated massage-like stimulation induces long-term effects on nociception: contribution of oxytocinergic mechanisms

Massage-like stroking induces acute antinociceptive effects that can be reversed by an oxytocin antagonist, indicating activation of oxytocin on endogenous pain controlling systems. We now demonstrate an increase in hindpaw withdrawal latencies (HWLs), in response to thermal and mechanical stimuli, which was present after six treatments of massage-like stroking every other day and which continued to increase through the remaining seven treatments. Repeated massage-like stroking also resulted in increased oxytocin-like immunoreactivity (oxytocin-LI) levels in plasma and periaquaductal grey matter (PAG). Furthermore, increases in HWLs were also present after injections of oxytocin into the PAG (0.1, 0.5 and 1.0 nmol). Intra-PAG oxytocin injection of 1 nmol followed by 1 or 20 nmol of naloxone attenuated the increments in HWL. Also, there was a dose-dependent attenuation of the oxytocin-induced antinociceptive effects following intra-PAG injection of the mu-opioid antagonist beta-funaltrexamine (beta-FNA) and the kappa-opioid antagonist nor-binaltorphimine (nor-BNI) but not the delta-antagonist naltrindole. The long-term antinociceptive effects of massage-like stroking may be attributed, at least partly, to the oxytocinergic system and its interaction with the opioid system, especially the mu- and the kappa-receptors in the PAG.

Oxytocin mediates stress-induced analgesia in adult mice

As a neurohormone and as a neurotransmitter, oxytocin has been implicated in the stress response. Descending oxytocin-containing fibres project to the dorsal horn of the spinal cord, an area important for processing nociceptive inputs. Here we tested the hypothesis that oxytocin plays a role in stress-induced analgesia and modulates spinal sensory transmission. Mice lacking oxytocin exhibited significantly reduced stress-induced antinociception following both cold-swim (10 degrees C, 3 min) and restraint stress (30 min). In contrast, the mice exhibited normal behavioural responses to thermal and mechanical noxious stimuli and morphine-induced antinociception. In wild-type mice, intrathecal injection of the oxytocin antagonist dOVT (200 microM in 5 microl) significantly attenuated antinociception induced by cold-swim. Immunocytochemical staining revealed that, in the mouse, oxytocin-containing neurones in the paraventricular nucleus of the hypothalamus are activated by stress. Furthermore, oxytocin-containing fibres were present in the dorsal horn of the spinal cord. To test whether descending oxytocin-containing fibres could alter nociceptive transmission, we performed intracellular recordings of dorsal horn neurones in spinal slices from adult mice. Bath application of oxytocin (1 and 10 microM) inhibited excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. This effect was reversed by the oxytocin antagonist dOVT (1 microM). Whole-cell recordings of dorsal horn neurones in postnatal rat slices revealed that the effect of oxytocin could be blocked by the addition of GTP-gamma-S to the recording pipette, suggesting activation of postsynaptic oxytocin receptors. We conclude that oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission.

Hypothalamic paraventricular axons projecting to the female rat lumbosacral spinal cord contain oxytocin immunoreactivity

Oxytocin-containing axons project from the hypothalamic paraventricular nucleus to the neurohypophysis and thoracic spinal cord to ultimately influence uterine contractions and autonomic activity, respectively. Whether or not oxytocin-immunoreactive axons project to the female rat lumbosacral spinal cord to influence autonomic outflow to pelvic organs has not been investigated. Thus, the present study was designed to investigate the presence, distribution, and origin of oxytocin-immunoreactive axons in the female rat lumbosacral spinal cord. Immunohistochemistry, spinal cord transections, and axonal tracing with Fluorogold, True Blue, and pseudorabies virus were used. Oxytocin-immunoreactive nerve fibers were present in the L6/S1 segments of the spinal cord. Prominent varicose axons were evident throughout the dorsal horn, along the lateral and medial collateral pathways, in the dorsal intermediate gray area, around the central canal in lamina X, and throughout the sacral parasympathetic nucleus. Injection of retrograde tracer into the L6/S1 spinal cord labeled neurons in the hypothalamic paraventricular nucleus. Transection of the thoracic spinal cord eliminated oxytocin-immunoreactive nerve axons in the L6/S1 spinal cord. In addition, transection of the thoracic spinal cord eliminated transport of retrograde axonal tracer from the L6/S1 spinal cord to the paraventricular nucleus. Pseudorabies virus, a transneuronal retrograde tracer, injected into the uterus and cervix marked uterine-related preganglionic neuronal cell bodies in the sacral parasympathetic nucleus and uterine-related neurons in the hypothalamic paraventricular nucleus. Double immuno-labeling of viral-infected spinal cord sections showed oxytocin-immunoreactive axons closely associated with viral labeled uterine-related preganglionic cell bodies of the sacral parasympathetic nucleus. The results of this study revealed that oxytocin-immunoreactive neurons of the hypothalamic paraventricular nucleus project axons to the lumbosacral spinal cord to areas involved in sensory processing and parasympathetic outflow to the uterus.

The hemodynamic effects of intrathecal oxytocin in normal dogs

OBJECTIVE

To evaluate the hemodynamic effects produced by intrathecal administration of oxytocin in healthy isoflurane-anesthetized dogs.

STUDY DESIGN

Prospective single-dose trial.

ANIMAL POPULATION

Six healthy purpose-bred adult dogs weighing between 7.3 and 14.5 kg.

METHODS

Dogs were anesthetized with isoflurane and instrumented. Oxytocin at a dosage of 1.6 microg/kg was administered intrathecally at the cisternal space at time 0. Hemodynamic data were recorded immediately before and at 1, 5, 15, 30, and 60 minutes after oxytocin administration. Statistical analysis included an analysis of variance (ANOVA) for repeated measures over time. A P < .05 was considered significant.

RESULTS

Baseline values +/- standard error of the mean for heart rate, mean arterial pressure, central venous pressure, cardiac output, systemic vascular resistance, mean pulmonary arterial pressure, pulmonary arterial occlusion pressure, and pulmonary vascular resistance were 101 +/- 11 beats/minute, 76 +/- 7 mm Hg, 4 +/- 4 mm Hg, 1.9 +/- 0.7 L/min, 3834 +/- 2556 dynes x sec/cm5, 14 +/- 3 mm Hg, 4 +/- 2 mm Hg, and 430 +/- 201 dynes x sec/cm5, respectively. Variations from the baseline values were seen in all parameters after intrathecal oxytocin administration, but no statistically significant differences were found.

CONCLUSION

The intrathecal injection of 1.6 microg/kg of oxytocin is associated with minimal hemodynamic effects during isoflurane anesthesia.

CLINICAL RELEVANCE

This study revealed no clinically significant deleterious effects from the intrathecal administration of oxytocin, and investigations into its use as a perioperative analgesic are therefore warranted.

Oxytocin content of the cerebrospinal fluid of dogs and its relationship to pain induced by spinal cord compression

OBJECTIVES

To determine whether oxytocin exists in the cerebrospinal fluid (CSF) of dogs and whether the amount of oxytocin in the CSF of dogs with neck or back pain caused by spinal cord compression is significantly different than that in the CSF of clinically normal dogs.

STUDY DESIGN

Prospective controlled study.

ANIMAL POPULATION

A total of 15 purpose-bred beagles and 17 client-owned dogs.

METHODS

CSF was collected by needle puncture of the cerebellar medullary cistern after induction of general anesthesia. Oxytocin levels within the samples were determined through radioimmunoassay.

RESULTS

Dogs with spinal cord compression had significantly more oxytocin in their CSF than the clinically normal dogs (13.76 +/- 2.0 pg/mL and 3.61 +/- 0.63 pg/mL, respectively; P < .0001). Dogs with chronic signs (>7 days) had significantly more oxytocin in their CSF than dogs with acute signs (<7 days) (21.60 +/- 0.86 pg/mL and 6.80 +/- 0.81 pg/mL, respectively; P < .0001). Both acutely and chronically affected dogs had significantly more oxytocin in their CSF than the controls (P < .005 and P < .0001 respectively).

CONCLUSIONS

Dogs with neck and back pain caused by spinal cord compression have significantly more oxytocin in their CSF than clinically normal dogs. Dogs with chronic clinical signs have significantly more oxytocin in their CSF than dogs with acute clinical signs.

CLINICAL RELEVANCE

In humans, intrathecal injection of oxytocin is effective in treating low back pain for up to 5 hours. Intrathecal oxytocin may be a logical choice for perioperative analgesia in dogs undergoing myelography because the intrathecal space is accessed for injection of contrast agent.

The organization of chemically characterized afferents to the perivascular neuronal groups of the hypothalamic magnocellular neurosecretory system in the rat

The hypothalamic magnocellular neurosecretory system consists of the paraventricular nucleus and supraoptic nucleus and a number of accessory nuclei. There is evidence that each of the accessory nuclei has a preferential source of afferents. Two of the accessory nuclei, namely the nucleus circularis (NC) and the lateral hypothalamic perivascular nucleus (LHPN), are particularly interesting due to their very close relationship with the blood vessels. The NC is composed of small dense clusters of neurons in the medial anterior hypothalamus. The groups of lateral hypothalamic neurons gathering around vascular branches are collectively called the LHPN. Their close topographical relationship with the blood vessels may indicate that the latter may serve as a source of input to these nuclei. As a part of the effort to investigate this issue, the present study examined in these two nuclei the distribution pattern of terminal-like elements containing 11 transmitters/modulators. Only a few, if any, terminal-like elements of the transmitters/modulators studied could be found distributed in the NC proper, although its immediate vicinity could be densely innervated. On the contrary, the LHPN proper was often densely innervated by fibers expressing the examined markers. These terminal patterns were found to be quite different from those of the paraventricular and supraoptic nuclei. The present findings further substantiate the notion of a functional differentiation among the subnuclei of the magnocellular neurosecretory system. The significance of the relationship of these two perivascular nuclei with the blood vessels is discussed.

Influences of fat and carbohydrate on postprandial sleepiness, mood, and hormones

Paired studies were conducted in 18 healthy volunteers (9 men, 9 women) to investigate whether differences in mood and daytime sleepiness induced by high-fat-low-carbohydrate (CHO) and low-fat-high-CHO morning meals were associated with specific hormonal responses. Plasma insulin concentrations were significantly higher after low-fat-high-CHO meals, and cholecystokinin (CCK) concentrations were significantly higher after high-fat-low-CHO meals. Subjects tended to feel more sleepy and less awake 2-3 h after the high-fat-low-CHO meal, and ratings of fatigue were significantly greater 3 h after the high-fat-low-CHO meal than after the low-fat-high-CHO meal. The results of the present study are consistent with the hypothesis that there is an association between the lassitude experienced after a meal and the release of CCK.

Integrative functions of lactational hormones in social behavior and stress management

For mammalian reproduction to succeed, self-defense and asociality must be subjugated to positive social behaviors, at least during birth, lactation, and sexual behavior. Perhaps the important task of regulating the interaction between social and agonistic behaviors is managed, in part, by interactions between two related neurochemical systems that incorporate oxytocin and vasopressin in their functions. The neuropeptides oxytocin and vasopressin participate in important reproductive functions, such as parturition and lactation, and homeostatic responses, including modulation of the adrenal axis. Recent evidence also implicates these hormones in social aspects of reproductive behaviors. For example, oxytocin is important for a variety of positive social behaviors, including the regulation of maternal-infant interactions. In adult animals, oxytocin may facilitate both social contact and selective social interactions associated with social attachment and pair bonding, and it participates in the regulation of parasympathetic functions. Vasopressin, in contrast, is associated with behaviors that might be broadly classified as "defensive" including enhanced arousal, attention, or vigilance, increased aggressive behavior, and a general increase in sympathetic functions. On the basis of the literature on the functions of these hormones and our own recent findings, we propose that dynamic interactions between oxytocin and vasopressin are components of a larger system which integrates the neuroendocrine and autonomic changes associated with mammalian social behaviors and the concurrent regulation of the stress axis. In addition, studies of lactating females provide a valuable model for understanding the more general neuroendocrinology of the stress axis. Peptide hormones, including oxytocin and vasopressin, do not readily cross the blood-brain barrier and must be administered centrally (i.c.v.) to reach the brain. Nasal sprays have been used to promote milk let down and have been used in some behavioral studies, but the extent to which such compounds reach the brain is not known. Therefore, virtually nothing is known regarding the effects in humans of centrally administered oxytocin. The study of human lactation, in conjunction with animal research, provides an opportunity to begin to develop viable hypotheses regarding the behavioral effects of oxytocin.

Oxytocin causes a long-term decrease of blood pressure in female and male rats

The aim of the present study was to investigate the long-term effects of oxytocin (OXY) on blood pressure (BP) and heart rate (HR) in conscious female and male rats. For this purpose, subcutaneous (SC) (0.01, 0.1, and 1 mg/kg) or intracerebroventricular (ICV) (1 microgram/kg) injections of OXY were given during 5-day periods. BP and HR were measured daily. A significant decrease in BP, without affecting HR, compared to saline-treated controls was seen in response to 0.1 (males: p < 0.01, females: p < 0.001) and 1 mg/kg (p < 0.001) of OXY given SC. BP gradually returned to preexperimental levels within 10 days after the last injection in male rats but, in females, the significant lowering of BP remained unchanged during this period. Also OXY ICV (1 microgram/kg) decreased BP (p < 0.05 after one day, p < 0.001 after 5 days of injections). This effect was still present 8 days after the last injection (p < 0.05). These results indicate that OXY may induce a long-term lowering of BP.

Oxytocin increases nociceptive thresholds in a long-term perspective in female and male rats

Oxytocin (0.1 and 1.0 mg/kg s.c.) given to male rats during 5 days, increased tail-flick latency when measured 1 (P < 0.05) and 7 days (0.1 mg/kg, P < 0.05; 1.0 mg/kg, P < 0.01) after the last injection. The effect was gone 2 weeks after the end of the treatment. If an additional injection of oxytocin was given 10 days after a previous 5 day treatment period, the significant difference persisted after 3 weeks (P < 0.05). Tail-flick latency was significantly delayed also in oxytocin-treated females when measured 1 week after the treatment period (P < 0.05). Naloxone, but not an oxytocin antagonist, temporarily antagonised the oxytocin induced delay in withdrawal latency. This indicates that oxytocin may act by increasing the activity of opioid mechanisms.

The oxytocin antagonist 1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin reverses the increase in the withdrawal response latency to thermal, but not mechanical nociceptive stimuli following oxytocin administration or massage-like stroking in rats

In this study the effect of exogenous oxytocin and of massage-like stroking on the withdrawal latency responses to heat and mechanical nociceptive stimulation were investigated in rats. A hot-plate test and the Randall-Selitto test were used to assess the withdrawal responses. Exogenous oxytocin (0.1-1 mg/kg) and stroking (a low frequency mechanical stimulation) significantly increased the withdrawal latencies in response to mechanical and to thermal nociceptive stimuli. The effect of oxytocin and of stroking in the hot-plate test was reversed by the oxytocin antagonist (1-deamino-2-D-Tyr-(Oet)-4-Thr-8-Orn-oxytocin) directed against the uterine receptor. In contrast, the antagonist did not affect the prolonged response latency in the mechanical nociceptive stimulation test following either exogenous oxytocin or stroking. These results support the view that (1) oxytocin administration affects directly or indirectly nociceptive related behaviour in response to heat stimulation, and (2) massage-like stroking may have an anti-nociceptive effect via activation of oxytocinergic mechanisms. Since the response to mechanical stimulation was not blocked by the antagonist the mechanisms mediating the withdrawal latency to heat and mechanical stimulation could be different.

Depressed concentrations of oxytocin and cortisol in children with recurrent abdominal pain of non-organic origin

The purpose of the present study was to measure plasma concentrations of oxytocin, cortisol and prolactin in children with recurrent abdominal pain of non-organic origin (RAP). Forty children with RAP and 34 controls, matched for age and sex, participated in the study. A blood sample was collected after an overnight fast in association with clinical examinations. Oxytocin, cortisol and prolactin levels were determined by radioimmunoassay (RIA). Oxytocin and cortisol concentrations in the children with RAP were found to be significantly reduced compared with those of the controls (approximately 24 versus 63 pmol/l for oxytocin and 160 versus 300 nmol/l for cortisol, respectively). The low oxytocin and cortisol levels persisted at a second examination 3 months later. No significant differences in the prolactin levels were observed between RAP and controls.

High doses of oxytocin cause sedation and low doses cause an anxiolytic-like effect in male rats

The aim of the present investigation was to explore dose relationships for effects of oxytocin on spontaneous motor activity in the rat. Oxytocin in doses from 1-1000 micrograms/kg was given SC to male Sprague-Dawley rats, and spontaneous motor behavior was measured by means of photocell-operated open-field observations. In the rats treated with low doses of oxytocin (1-4 micrograms/kg), there was a decrease in peripheral locomotor activity. With increasing doses (250-1000 micrograms/kg), there were clear signs of sedative effects as indicated by a suppression of locomotor activity and rearing. The time course for the effect of oxytocin on peripheral activity (1 microgram/kg) and rearing (1 mg/kg) was tested. A maximal effect was obtained within 1 h and, thereafter, the behavior gradually returned to normal within 24 h. This spectrum of effects caused by oxytocin was similar to that of midazolam but different from that induced by raclopride.