Oxytocin mRNA Research Articles

Evaluation of the effect of Metformin on the inhibitory effect of oxytocin on Potassium chloride stimulated goat ileum

The posterior pituitary hormone, oxytocin is expressed in the myenteric and submucous ganglia and nerve fi bers along the entire human gastrointestinal (GI) tract. The role for oxytocin in the physiology and pathophysiology of the bowel remains to be clearly elucidated. Many 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 GI tract. In this study, we examined the responses of the posterior pituitary hormone, oxytocin on the contractile responses to KCl and the effect of metformin on these responses as it affects the glucose transport and causes monoamine release in the gut.

Different expression of PGE synthase, PGF receptor, TNF, Fas and oxytocin in the bovine corpus luteum of the estrous cycle and pregnancy

Functional differences between the corpus luteum (CL) of pregnancy and CL of the cycle in cows were examined. Messenger RNA and protein levels of prostaglandin (PG) E synthase (PGES), PGF2α receptor (PGFR), tumor necrosis factor-α (TNF) and Fas were found to be higher in the CL of pregnancy than in CL of the cycle. Oxytocin (OT) mRNA and protein levels were lower in the CL of pregnancy. Messenger RNA levels of progesterone receptor (PR), luteinizing hormone receptor (LHR), PGE2 receptor (PGER), PGF synthase (PGFS), TNF receptor type I (TNFRI) and TNF receptor type II (TNFRII) did not differ between the cycle and pregnancy. PGE2 and PGF2α production by cultured bovine endometrial tissues was decreased by a supernatant derived from the homogenized CL of pregnancy but not by that of the CL of the cycle, suggesting that specific substances in the CL of pregnancy affect endometrial PG production in cows. Collectively, PGES, PGFR, TNF, Fas or OT may contribute to differences between the CL of pregnancy and CL of the estrous cycle in cows.

Endoplasmic reticulum stress in vasopressin neurons of familial diabetes insipidus model mice: aggregate formation and mRNA poly(A) tail shortening

The immunoglobulin heavy chain binding protein (BiP) is an endoplasmic reticulum (ER) chaperone, which binds to newly synthesized secretory and transmembrane proteins to facilitate protein folding. BiP mRNA is expressed in the arginine vasopressin (AVP) neurons in the supraoptic nucleus of wild-type mice even in basal conditions, and the expression levels increase in response to dehydration. These data suggest that AVP neurons are subjected to ER stress. Familial neurohypophysial diabetes insipidus (FNDI) is caused by mutations in the gene locus of AVP. The mutant proteins could accumulate in the ER and possibly increase ER stress in the AVP neurons. We bred mice possessing a mutation causing FNDI, which manifested progressive polyuria, as do the patients with FNDI. Electron microscopic analyses demonstrated that aggregates accumulated in the ER of AVP neurons in FNDI mice. Despite polyuria, which could potentially induce dehydration, AVP mRNA expression was decreased in the supraoptic nucleus, and the AVP mRNA poly(A) tail length was shortened in FNDI mice compared with wild-type mice. Incubation of hypothalamic explants of wild-type mice with ER stressors caused shortening of the poly(A) tail length of AVP mRNA, accompanied by decreases in the expression. These data revealed a mechanism by which ER stress decreases poly(A) tail length of AVP mRNA, and this reduces the load of unfolded proteins that form the aggregates in ER of the AVP neurons in FNDI mice.

Blunted HPA axis response in lactating, vasopressin-deficient Brattleboro rats

Adaptation to stress is a basic phenomenon in mammalian life that is mandatorily associated with the activity of the hypothalamic-pituitary-adrenal (HPA) axis. An increased resting activity of the HPA axis can be measured during pregnancy and lactation, suggesting that these reproductive states lead to chronic load in females. In this study, we examined the consequences of the congenital lack of vasopressin on the activity of the HPA axis during lactation using vasopressin-deficient Brattleboro rats. Virgin and lactating, homozygous vasopressin-deficient rats were compared with control, heterozygous rats. In control dams compared with virgins, physiological changes similar to those observed in a chronic stress state (thymus involution, adrenal gland hyperplasia, elevation of proopiomelanocortin mRNA levels in the adenohypophysis, and resting plasma corticosterone levels) were observed. In vasopressin-deficient dams, adrenal gland hyperplasia and resting corticosterone level elevations were not observed. Corticotropin-releasing hormone (Crh) mRNA levels in the hypothalamic paraventricular nucleus were elevated in only the control dams, while oxytocin (OT) mRNA levels were higher in vasopressin-deficient virgins and lactation induced a further increase in both the genotypes. Suckling-induced ACTH and corticosterone level elevations were blunted in vasopressin-deficient dams. Anaphylactoid reaction (i.v. egg white) and insulin-induced hypoglycemia stimulated the HPA axis, which were blunted in lactating rats compared with the virgins and in vasopressin-deficient rats compared with the controls without interaction of the two factors. Vasopressin seems to contribute to the physiological changes observed during lactation mimicking a chronic stress state, but its role in acute HPA axis regulation during lactation seems to be similar to that observed in virgins. If vasopressin is congenitally absent, OT, but not the CRH, compensates for the missing vasopressin; however, the functional restitution remains incomplete.

Oxytocin and vasopressin levels are decreased in the plasma of male schizophrenia patients.

Impaired social functioning and autistic symptoms are characteristics of schizophrenia. The social hormones oxytocin (OT) and arginine-vasopressin (AVP) both modulate social interaction and therefore may be involved in the pathogenesis of schizophrenia. We investigated whether men with schizophrenia show altered OT and AVP levels compared with healthy controls (HC) and whether autism symptoms are associated with OT levels. Forty-one men with non-acute schizophrenia and 45 matched HC were enrolled. Schizophrenia was assessed with the Positive and Negative Syndrome Scale (PANSS). Blood samples were collected on 2 days, and plasma OT and AVP levels were measured by ELISA immunoassay. The schizophrenia patients had significantly lower plasma OT levels than the HC; a similar trend was found for AVP. Plasma OT levels were associated with severe life events, fewer important attached persons, and a higher score on the PANSS negative scale; the most dominant PANSS items were 'preoccupation', 'emotional withdrawal', and 'passive/apathetic social withdrawal'. These findings support an association between the social hormones OT and AVP and schizophrenia. We suggest that OT metabolism may be altered in schizophrenia, but other possible causes for decreased plasma OT levels in schizophrenia patients include decreased OT synthesis, mRNA expression, and translation. Especially the 'autistic' symptoms of schizophrenia seem to be closely linked to an altered metabolism of OT, the 'attachment' hormone.

Anandamide modulates the neuroendocrine responses induced by extracellular volume expansion

(1) The aim of the present study was to evaluate the effects of intracerebroventricular administration of anandamide (AEA), an inhibitor of fatty acid amide hydrolase activity (URB597) and a CB1 receptor (CB1 R) antagonist (AM251) on the homeostatic responses elicited by extracellular volume expansion (EVE) in male adult rats. (2) Pretreatment with AEA (100 ng/4 μL) significantly reduced the effect of hypertonic (H-) EVE on plasma concentrations of prolactin (PRL), oxytocin (OT) and corticosterone, but not vasopressin (AVP). Administration of URB597 (20 μg/5 μL) alone significantly reduced PRL, OT, AVP and corticosterone in the H-EVE group. Conversely, URB597 and AEA had no significant effect on basal hormone concentrations. Pretreatment with AM251 (200 ng/2 μL) potentiated OT but did not change AVP plasma levels in the H-EVE group. (3) Hypertonic EVE significantly increased AVP and OT mRNA expression in the supraoptic nucleus (SON), an effect that was blunted in AEA-pretreated rats. Pretreatment with AEA did not change the percentage of vasopressinergic or oxytocinergic neurons colocalizing c-Fos in the SON, but increased nitrate concentrations in the median eminence of animals subjected to H-EVE. (4) The present data suggest that: (i) vasopressinergic and oxytocinergic neurons may be differentially affected by AEA; (ii) activation of CB1 R may restrain the response of the neurohypophyseal system (NHS) to EVE; (iii) the hypothalamic-pituitary-adrenal axis, PRL and the NHS may still be sensitive to AEA after EVE, with these effects probably not dependent on AEA metabolism; and (iv) AEA and nitric oxide could interact in vivo as modulators to directly control stress-induced responses.

The satiety signal oleoylethanolamide stimulates oxytocin neurosecretion from rat hypothalamic neurons

The anandamide monounsaturated analogue oleoylethanolamide (OEA) acts as satiety signal released from enterocytes upon the ingestion of dietary fats to prolong the interval to the next meal. This effect, which requires intact vagal fibers and intestinal PPAR-alpha receptors, is coupled to the increase of c-fos and oxytocin mRNA expression in neurons of the paraventricular nucleus (PVN) and is prevented by the intracerebroventricular administration of a selective oxytocin antagonist, thus suggesting a necessary role of oxytocinergic neurotransmission in the pro-satiety effect of OEA. By brain microdialysis and immunohistochemistry, in this study we demonstrate that OEA treatment can stimulate oxytocin neurosecretion from the PVN and enhance oxytocin expression at both axonal and somatodendritic levels of hypothalamic neurons. Such effects, which are maximum 2h after OEA administration, support the hypothesis that the satiety-inducing action of OEA is mediated by the activation of oxytocin hypothalamic neurons.

Oxytocin in Brattleboro Rats: Increased Synthesis is Contrasted by Blunted Intrahypothalamic Release From Supraoptic Nucleus Neurones

Adult male Brattleboro rats were used to investigate the impact of the congenital absence of vasopressin on the release pattern of oxytocin (OXT) within the hypothalamic supraoptic nucleus (SON) in response to a 10-min forced swimming session and osmotic stimulation. Both immunohistochemical and in situ hybridisation data suggest that vasopressin-deficient animals have more oxytocin-synthesising neurones in the SON than homozygous wild-type controls. Unexpectedly, both forced swimming and peripheral osmotic stimulation resulted in a blunted release profile of oxytocin within the SON of vasopressin-deficient rats compared to controls. A similar intranuclear OXT response to direct osmotic stimulation of the SON by retrodialysis with hypertonic Ringer's solution in both genotypes confirmed the capability of SON neurones to locally release oxytocin in vasopressin-deficient rats, indicating an altered processing of information originating from multisynaptic inputs rather than a deficit in release capacity. Taken together with data obtained in previous studies, the present findings provide evidence suggesting that autocrine and paracrine signalling of magnocellular neurones differs within the paraventricular nucleus and the SON. Thus, significant alterations in intra-SON oxytocin mRNA levels cannot easily be extrapolated to intranuclear release profiles and the local signal intensity of this neuropeptide after physiological stimulation.

Oxytocin in the Central Amygdaloid Nucleus Modulates the Neuroendocrine Responses Induced by Hypertonic Volume Expansion in the Rat

The present study investigated the involvement of the oxytocinergic neurones that project into the central amygdala (CeA) in the control of electrolyte excretion and hormone secretion in unanaesthetised rats subjected to acute hypertonic blood volume expansion (BVE; 0.3 M NaCl, 2 ml/100 g of body weight over 1 min). Oxytocin and vasopressin mRNA expression in the paraventricular (Pa) and supraoptic nucleus (SON) of the hypothalamus were also determined using the real time-polymerase chain reaction and in situ hybridisation. Male Wistar rats with unilaterally implanted stainless steel cannulas in the CeA were used. Oxytocin (1 μg/0.2 μl), vasotocin, an oxytocin antagonist (1 μg/0.2 μl) or vehicle was injected into the CeA 20 min before the BVE. In rats treated with vehicle in the CeA, hypertonic BVE increased urinary volume, sodium excretion, plasma oxytocin (OT), vasopressin (AVP) and atrial natriuretic peptide (ANP) levels and also increased the expression of OT and AVP mRNA in the Pa and SON. In rats pre-treated with OT in the CeA, previously to the hypertonic BVE, there were further significant increases in plasma AVP, OT and ANP levels, urinary sodium and urine output, as well as in gene expression (AVP and OT mRNA) in the Pa and SON compared to BVE alone. Vasotocin reduced sodium, urine output and ANP levels, although no changes were observed in plasma AVP and OT levels or in the expression of the AVP and OT genes in both hypothalamic nuclei. The results of the present study suggest that oxytocin in the CeA exerts a facilitatory role in the maintenance of hydroelectrolyte balance in response to changes in extracellular volume and osmolality.

The Androgen Metabolite, 5α-Androstane-3β,17β-Diol (3β-Diol), Activates the Oxytocin Promoter Through an Estrogen Receptor-β Pathway

Testosterone has been shown to suppress the acute stress-induced activation of the hypothalamic-pituitary-adrenal axis; however, the mechanisms underlying this response remain unclear. The hypothalamic-pituitary-adrenal axis is regulated by a neuroendocrine subpopulation of medial parvocellular neurons in the paraventricular nucleus of the hypothalamus (PVN). These neurons are devoid of androgen receptors (ARs). Therefore, a possibility is that the PVN target neurons respond to a metabolite in the testosterone catabolic pathway via an AR-independent mechanism. The dihydrotestosterone metabolite, 5α-androstane-3β,17β-diol (3β-diol), binds and activates estrogen receptor-β (ER-β), the predominant ER in the PVN. In the PVN, ER-β is coexpressed with oxytocin (OT). Therefore, we tested the hypothesis that 3β-diol regulates OT expression through ER-β activation. Treatment of ovariectomized rats with estradiol benzoate or 3β-diol for 4 days increased OT mRNA selectively in the midcaudal, but not rostral PVN compared with vehicle-treated controls. 3β-Diol treatment also increased OT mRNA in the hypothalamic N38 cell line in vitro. The functional interactions between 3β-diol and ER-β with the human OT promoter were examined using an OT promoter-luciferase reporter construct (OT-luc). In a dose-dependent manner, 3β-diol treatment increased OT-luc activity when cells were cotransfected with ER-β, but not ER-α. The 3β-diol-induced OT-luc activity was reduced by deletion of the promoter region containing the composite hormone response element (cHRE). Point mutations of the cHRE also prevented OT-luc activation by 3β-diol. These results indicate that 3β-diol induces OT promoter activity via ER-β-cHRE interactions.

Sexual experience increases oxytocin receptor gene expression and protein in the medial preoptic area of the male rat

Oxytocin (OT) promotes social and reproductive behaviors in mammals, and OT deficits may be linked to disordered social behaviors like autism and severe anxiety. Male rat sexual behavior is an excellent model for OT regulation of behavior, as its pattern and neural substrates are well characterized. We previously reported that OT microinjected into the medial preoptic area (MPOA), a major integrative site for male sexual behavior, facilitates copulation in sexually experienced male rats, whereas intra-MPOA injection of an OT antagonist (OTA) inhibits copulation. In the present studies, copulation on the day of sacrifice stimulated OTR mRNA expression in the MPOA, irrespective of previous sexual experience, with the highest levels observed in first-time copulators. In addition, sexually experienced males had higher levels of OTR protein in the MPOA than sexually naïve males and first-time copulators. Finally, intra-MPOA injection of OT facilitated mating in sexually naive males. Others have reported a positive correlation between OT mRNA levels and male sexual behavior. Our studies show that OT in the MPOA facilitates mating in both sexually naive and experienced males, some of the behavioral effects of OT are mediated by the OTR, and sexual experience is associated with increased OTR expression in the MPOA. Taken together, these data suggest a reciprocal interaction between central OT and behavior, in which OT facilitates copulation and copulation stimulates the OT/OTR system in the brain.

Exposure to chronic isolation modulates receptors mRNAs for oxytocin and vasopressin in the hypothalamus and heart

The goal of our study was to explore the effect of social isolation stress of varying durations on the plasma oxytocin (OT), messenger ribonucleic acid (mRNA) for oxytocin receptor (OTR), plasma arginine vasopressin (AVP) and mRNA for V1a receptor of AVP (V1aR) expression in the hypothalamus and heart of socially monogamous female and male prairie voles (Microtus ochrogaster). Continuous isolation for 4 weeks (chronic isolation) increased plasma OT level in females, but not in males. One hour of isolation every day for 4 weeks (repeated isolation) was followed by a significant increase in plasma AVP level. Chronic isolation, but not repeated isolation, significantly decreased OTR mRNA in the hypothalamus and heart in both sexes. Chronic isolation significantly decreased cardiac V1aR mRNA, but no effect on hypothalamic V1aR mRNA expression. We did not find a gender difference within repeated social isolation groups. The results of the present study reveal that although chronic social isolation can down-regulate gene expression for the OTR in both sexes, the release of the OT peptide was increased after chronic isolation only in females, possibly somewhat protecting females from the negative consequences of isolation. In both sexes repeated, but not chronic, isolation increased plasma AVP, which could be permissive for mobilization and thus adaptive in response to a repeated stressor. The differential effects of isolation on OT and AVP systems may help in understanding mechanisms through social interactions can be protective against emotional and cardiovascular disorders.

Effects of Stresscopin on Rat Hypothalamic Paraventricular Nucleus Neurons In Vitro

The effects of stresscopin (SCP) on rat paraventricular nucleus (PVN) neurons were examined using whole-cell patch-clamp recordings and single-cell reverse-transcription multiplex polymerase chain reaction (SC-RT-mPCR) techniques. Under current-clamp conditions, bath application of SCP (100 nM) induced inhibition in 35.2% (37/105) of putative magnocellular neurons and 24.7% (20/81) of putative parvocellular neurons, and excitation in 5.7% (6/105) of putative magnocellular neurons and 18.5% (15/81) of putative parvocellular neurons. SCP-induced inhibition persisted in the presence of a mixture of TTX, a voltage-gated Na+ channel blocker, CNQX, an AMPA/kainate receptor antagonist and bicuculline, a GABAA receptor antagonist, whereas SCP-induced excitation of PVN neurons was reversed by the mixture. The SCP-induced inhibition of PVN neurons was abolished by bath application of antisauvagine-30, a selective CRF receptor 2 (CRF-R2) antagonist. Under voltage-clamp conditions, SCP evoked outward currents at the holding potential (−60 mV), which reversed near the potassium equilibrium potential. The SCP-evoked membrane currents were completely blocked by bath application of tertiapin-Q, a selective blocker of G protein-activated inwardly rectifying potassium (GIRK) channels. SC-RT-mPCR analysis indicated that all the SCP-sensitive PVN neurons (57 SCP-inhibited neurons, 21 SCP-excited neurons) expressed CRF-R1 and CRF-R2 mRNAs. Among SCP-hyperpolarized PVN neurons, oxytocin (OT) mRNA was detected in 91.8% of putative magnocellular neurons and 45.0% of putative parvocellular neurons. OT mRNA was also detected in 26.6% of SCP-depolarized parvocellular neurons, but not in SCP-depolarized magnocellular neurons. These results indicate that SCP inhibits a subpopulation of PVN neurons, especially OTergic magnocellular neurons, by enhancing the activity of GIRK channels via CRF-R2.

Diet-induced obesity induces endoplasmic reticulum stress and insulin resistance in the amygdala of rats

Insulin acts in the hypothalamus, decreasing food intake (FI) by the IR/PI3K/Akt pathway. This pathway is impaired in obese animals and endoplasmic reticulum (ER) stress and low-grade inflammation are possible mechanisms involved in this impairment. Here, we highlighted the amygdala as an important brain region for FI regulation in response to insulin. This regulation was dependent on PI3K/AKT pathway similar to the hypothalamus. Insulin was able to decrease neuropeptide Y (NPY) and increase oxytocin mRNA levels in the amygdala via PI3K, which may contribute to hypophagia. Additionally, obese rats did not reduce FI in response to insulin and AKT phosphorylation was decreased in the amygdala, suggesting insulin resistance. Insulin resistance was associated with ER stress and low-grade inflammation in this brain region. The inhibition of ER stress with PBA reverses insulin action/signaling, decreases NPY and increases oxytocin mRNA levels in the amygdala from obese rats, suggesting that ER stress is probably one of the mechanisms that induce insulin resistance in the amygdala.

Modulation of feeding by chronic rAAV expression of a relaxin-3 peptide agonist in rat hypothalamus

Relaxin-3 is a neuropeptide that is abundantly expressed by discrete brainstem neuron populations that broadly innervate forebrain areas rich in the relaxin-3 G-protein-coupled-receptor, RXFP3. Acute and subchronic central administration of synthetic relaxin-3 or an RXFP3-selective agonist peptide, R3/I5, increase feeding and body weight in rats. Intrahypothalamic injection of relaxin-3 also increases feeding. In this study, we developed a recombinant adeno-associated virus 1/2 (rAAV1/2) vector that drives expression and constitutive secretion of bioactive R3/I5 and assessed the effect of intrahypothalamic injections on daily food intake and body weight gain in adult male rats over 8 weeks. In vitro testing revealed that the vector rAAV1/2-fibronectin (FIB)-R3/I5 directs the constitutive secretion of bioactive R3/I5 peptide. Bilateral injection of rAAV1/2-FIB-R3/I5 vector into the paraventricular nucleus produced an increase in daily food intake and body weight gain (P<0.01, ~23%, respectively), relative to control treatment. In a separate cohort of rats, quantitative polymerase chain reaction analysis of hypothalamic mRNA revealed strong expression of R3/I5 transgene at 3 months post-rAAV1/2-FIB-R3/I5 infusion. Levels of mRNA transcripts for the relaxin-3 receptor RXFP3, the hypothalamic 'feeding' peptides neuropeptide Y, AgRP and POMC, and the reproductive hormone, GnRH, were all similar to control, whereas vasopressin and oxytocin (OT) mRNA levels were reduced by ~25% (P=0.051) and ~50% (P<0.005), respectively, in rAAV1/2-FIB-R3/I5-treated rats (at 12 weeks, n=9/8 rats per group). These data demonstrate for the first time that R3/I5 is effective in modulating feeding in the rat by chronic hypothalamic RXFP3 activation and suggest a potential underlying mechanism involving altered OT signalling. Importantly, there was no desensitization of the feeding response over the treatment period and no apparent deleterious health effects, indicating that targeting the relaxin-3-RXFP3 system may be an effective long-term therapy for eating disorders.

Peripheral chemoreceptors mediate training‐induced plasticity in paraventricular nucleus pre‐autonomic oxytocinergic neurons

We showed previously that sino-aortic denervation prevented training-induced plasticity in pre-autonomic oxytocinergic neurons and blocked the beneficial effects of training. In this study, we investigate the combined effect of training and removal of specific chemoreceptor afferents on both cardiovascular parameters and oxytocin (OT) gene and protein expression within the hypothalamic paraventricular nucleus (PVN). Wistar rats and spontaneously hypertensive rats (SHRs) underwent carotid body denervation or sham surgery and were trained or kept sedentary for 3 months. After haemodynamic measurements at rest, rats were anaesthetized for brain perfusion. Fresh (perfused with PBS) and fixed brains (perfused with 4% paraformaldehyde) were processed for PVN OT mRNA (real-time PCR) and OT immunoreactivity within PVN subnuclei. In sham-operated rats, training improved treadmill performance and reduced resting heart rate (Wistar, -8%; SHRs, -10%), with a reduction in blood pressure only in SHRs (-8%). Training was accompanied by increased PVN OT mRNA expression (twofold increase in sham-operated SHRs) and peptide density in the posterior, ventromedial and dorsal cap PVN subnuclei (on average 70% increase in both strains), with significant correlations between OT content and training-induced resting bradycardia in sham-operated groups. Carotid body denervation did not interfere with the performance gain, abolished chemoreflex activation (without changing baroreflex control) and blocked training-induced cardiovascular adaptations and training-induced changes in PVN OT content in both strains. After carotid body denervation, there was no correlation between OT mRNA or OT immunoractivity and resting heart rate. The chronic absence of chemoreceptor inputs uncovers an unknown role of chemoreceptor signalling in driving the plasticity/activity of PVN oxytocinergic pre-autonomic neurons, thus mediating training-induced cardiovascular adaptive responses.

Social interaction attenuates stress responses following chronic stress in maternally separated rats

Early life stress has been implicated as a risk factor for functional gastrointestinal (GI) disorders. Hypothalamic oxytocin (OXT) is well known to regulate social interactions and affiliative behaviors. We have shown that maternal separation (MS) induces GI dysmotility and impair hypothalamic OXT expression in response to chronic homotypic stress (CHS). We studied whether social interaction can improve GI dysmotility and OXT expression in MS rats. Male neonatal SD rats were exposed to MS for 180min from postnatal day (PND)-2 to PND-14. After weaning, 3MS rats were housed together (pure MS). In another group, 1MS rat was housed with 2 control rats (mixed MS). Anxiety-like behaviors were evaluated in elevated plus maze (EPM). Solid gastric emptying (GE) and colonic transit (CT) were measured following CHS loading. Expression of corticotropin releasing factor (CRF) and OXT in the paraventricular nucleus (PVN) were evaluated by real time RT-PCR and immunohistochemistry. Pure MS rats demonstrated increased anxiety-like behaviors, which were significantly reduced in mixed MS rats. Delayed GE (31.5±2.8%, n=6) and accelerated CT [Geometric center (GC) =8.9±0.8, n=6] observed in pure MS rats were restored in mixed MS rats (GE=67.8±3.8%, GC=6.7±1.2, n=6, P<0.05) following CHS. OXT mRNA expression was upregulated, while CRF mRNA expression was downregulated in mixed MS rats, compared to pure MS rats. The number of OXT-immunoreactive cells was significantly increased following CHS at the PVN in mixed MS rats. Our study may contribute to the treatment strategies for GI motility disorders associated with early life stress.

Carotid Body Artery Removal (CBX) Prevents Training‐ Induced Plasticity in Preautonomic Oxytocinergic Neurons of the Paraventricular Nucleus SHR

We observed that sinoaortic denervation prevents T‐induced plasticity in the OTergic preautonomic PVN neurons of SHR (Cavalleri et al., AJP, Regulatory, 2011). In the present study, we sought to investigate whether peripheral chemoreceptors participate in T‐induced OTergic plasticity in PVN subnuclei of SHR. CBX or SHAM were trained or kept sedentary (S) for 3 month. After cardiovascular records, rats were anesthetized and perfused (saline or PFA 4%). Tissue samples of PVN were processed for oxytocin (OT) mRNA expression (RT‐PCR) or for immunofluorescence (ir) staining with OT antibody (1:200.000). CBX abolished pressor and bradicardic responses to chemoreflex activation (KCN 40 μg, iv) in S and T rats. T induced increases in both OT mRNA (1.3±0.2 vs 2.6±0.4, ShamS vs ShamT) and OTir in PVN preautonomic subnuclei (dorsal cap, dc = 15±2 vs 23±1%; ventromedial, vm = 36±1 vs 44±1%; posterior, post = 9±1 vs 17±5 %, respectively). CBX did not change basal expression, but blocked T‐induced OT gene and protein expression (ShamT vs CBXT: PVN OT mRNA= 2.6±0.4 vs 1.4±0.6; OTir dc = 23±1 vs 15±2 %); OTir vm = 36±1 vs 22±3; OTir post = 17±2 vs 12±2%). Chemoreceptors are not tonic to drive preautonomic oxytocinergic neurons, but participate in the peripheral signaling to modulate T‐induced OTergic plasticity Financial Support: FAPESP, CNPq

Affiliative behavior attenuates stress responses of GI tract via up-regulating hypothalamic oxytocin expression

Hypothalamic oxytocin (OXT) has stress-attenuating effects. Social interaction in a positive environment continuously activates OXT release system. We have recently shown that pair housing restores delayed gastric emptying following chronic heterotypic stress, via up-regulation of OXT mRNA expression in rats. We tested the hypothesis that affiliative behavior attenuates stress responses via upregulating OXT expression. Adult male SD rats were divided into two groups: the rat with a stressed partner (RSP) and the rat with a non-stressed partner (RNSP). RSPs were pair housed with a partner that received different types of stress for 7 consecutive days (chronic heterotypic stress). RNSPs were pair housed with a partner who did not receive any stress. After each stress loading, the rats were returned to their home cages and the behaviors of RSPs and RNSPs toward their partners were videotaped. After the study completion, RSPs and RNSPs were loaded with acute restraint stress. Then, gastric emptying and colonic transit were measured. Corticotropin releasing factor (CRF) and OXT expression in the paraventricular nucleus (PVN) were evaluated by real time RT-PCR and immunohistochemistry. The time of affiliative behaviors toward their partners was increased in RSPs, compared to that of RNSPs. Delayed gastric emptying and accelerated colonic transit induced by acute restraint stress were significantly attenuated in RSPs, compared to RNSPs. CRF expression was reduced, while OXT expression was increased in RSPs in response to acute stress, compared to controls. It is suggested that affiliative behaviors may upregulate hypothalamic OXT expression, which in turn attenuates stress responses.

The effect of combination treatment with trenbolone acetate and estradiol-17β on skeletal muscle expression and plasma concentrations of oxytocin in sheep

Implantation of trenbolone acetate (TBA) in conjunction with estradiol-17β (E2) increases growth, feed conversion efficiency, and carcass leanness in cattle. Our previous study in Brahman steers suggested that the neuropeptide hormone oxytocin (OXT) may be involved in increasing muscle growth after TBA-E2 treatment. The present study aimed to determine whether OXT mRNA expression in the longissimus muscle (LM) is also up-regulated in TBA-E2-implanted wethers as has been found in steers. Real-time quantitative PCR was used to measure the expression of the gene encoding the OXT precursor, three genes with increased expression in the LM muscle of TBA-E2-treated steers, MYOD1 (muscle transcription factor), GREB1 (growth regulation by estrogen in breast cancer 1), and WISP2 (Wnt-1 inducible signaling pathway protein 2), and two genes encoding IGF pathway proteins, IGF1, IGFR, in the LM of both untreated and TBA-E2-treated wethers. The expression of OXT mRNA in wethers that received the TBA-E2 treatment was increased ∼4.4-fold (P = 0.01). TBA-E2 treatment also induced a 2.3-fold increase in circulating OXT (P = 0.001). These data, together with the observation that untreated wethers had much higher baseline concentrations of circulating OXT than previously observed in steers, suggest that wethers and steers have quite different OXT hormone systems. TBA-E2 treatment had no effect on the expression of IGF1, IGFR, and the muscle regulatory gene MYOD1 mRNA levels in wethers (P ≥ 0.15), but there was an increase in the expression of the two growth-related genes, GREB1 (P = 0.001) and WISP2 (P = 0.04). Both genes are common gene targets for both the estrogen and androgen signaling pathways. Consequently, their actions may contribute to the positive interaction between TBA and E2 on additive improvements on muscle growth.