Dorsal medullary oxytocin, vasopressin, oxytocin antagonist, and TRH effects on gastric acid secretion and heart rate

Injections of oxytocin and TRH (11 picomoles), centered on the dorsal motor nucleus of the vagus, substantially increased gastric acid secretion. Additionally, oxytocin, but not TRH, simultaneously produced a consistent reduction in heart rate. Vasopressin injected into the same locus, at doses of 11 and 110 picomoles, had no effect on either function. Both the gastric and cardiac effects of oxytocin were eliminated by the central injections of oxytocin antagonist dEt₂Tyr(Et)Orn⁸Vasotocin (ETOV; 6 picomoles) or peripheral administration of atropine (300 μg/kg, IP). Application of oxytocin or TRH to the area postrema, at double the dosage (22 picomoles) yielded no consistent effects on either gastric secretion or heart rate. These findings indicate that oxytocin in the dorsal motor nucleus of the vagus may act as a regulator of vagally-mediated gastric and cardiovascular functions while TRH effects, in this medullary area, seem limited to the regulation of gastric function.     

Localization and osmotic regulation of vesicular glutamate transporter-2 in magnocellular neurons of the rat hypothalamus

In this report we present immunocytochemical and in situ hybridization evidence that magnocellular vasopressin and oxytocin neurons in the hypothalamic supraoptic and paraventricular nuclei express type-2 vesicular glutamate transporter, a marker for their glutamatergic neuronal phenotype. To address the issue of whether an increase in magnocellular neuron activity coincides with the altered synthesis of the endogenous glutamate marker, we have introduced a new dual-label in situ hybridization method which combines fluorescent and autoradiographic signal detection components for vasopressin and vesicular glutamate transporter-2 mRNAs, respectively. Application of this technique provided evidence that 2% sodium chloride in the drinking water for 7 days produced a robust and significant increase of vesicular glutamate transporter-2 mRNA in vasopressin neurons of the supraoptic nucleus. The immunocytochemical labeling of pituitary sections, followed by the densitometric analysis of vesicular glutamate transporter-2 immunoreactivity in the posterior pituitary, revealed a concomitant increase in vesicular glutamate transporter-2 protein levels at the major termination site of the magnocellular axons. These data demonstrate that magnocellular oxytocin as well as vasopressin cells contain the glutamatergic marker vesicular glutamate transporter-2, similarly to most of the parvicellular neurosecretory neurons examined so far. The robust increase in vesicular glutamate transporter-2 mRNA and immunoreactivity after salt loading suggests that the cellular levels of vesicular glutamate transporter-2 in vasopressin neurons are regulated by alterations in water–electrolyte balance. In addition to the known synaptic actions of excitatory amino acids in magnocellular nuclei, the new observations suggest novel mechanisms whereby glutamate of endogenous sources can regulate magnocellular neuronal functions.     

Oxytocin treatment immediately after calving does not reduce the incidence of retained fetal membranes or improve reproductive performance in crossbred Zebu cows

The objective was to determine the effect of oxytocin treatments after calving on the incidence of RFM and reproductive performance in dual purpose cows under tropical conditions. Five hundred thirty six pluriparous, crossbred Zebu cows were randomly assigned to two groups: Oxy (n = 280): cows were given 30 IU of oxytocin im immediately after normal unassisted calving, and again 6 h later; C (n = 256): control. Expulsion of fetal membranes was evaluated 24 h after delivery. After a 30-d voluntary waiting period, AI was done 12 h after cows were detected in estrus. Oxytocin had no effect on the incidence of RFM (4.6 vs. 3.1% for Oxy and C, respectively, P > 0.05). Cows in Oxy and C had similar first service and overall pregnancy rates (54.0 vs. 47.8% and 75.4 vs. 73.4%; respectively, P > 0.05). There were no differences between Oxy and C for calving to first estrus (83.6 ± 3.7 vs. 77.2 ± 3.8 d) and calving to conception intervals (113.6 ± 5.0 vs. 110.5 ± 5.2 d), as well as rates of anestrus (13.6 vs. 13.7%), repeat breeding (21.8 vs. 20.7%), and culling (15.7 vs. 16.4%). In conclusion, oxytocin treatment after normal unassisted calving did not significantly reduce the incidence of RFM or improve reproductive performance in crossbred Zebu cows under tropical conditions.     

Potentiated effect of systemic administration of oxytocin on hypertonic NaCl intake in food-deprived male rats

Subcutaneous administration of oxytocin (OT) increases water intake and sodium/urine excretion in food-deprived male rats. This study analyzes the effect of OT administration (at 0830 and 1430h) on the consumption of water and hypertonic NaCl (1.5%). In the first experiment, injections of OT increased the intake of hypertonic NaCl (but not of water) in food-deprived rats but not in ad lib-fed animals during the second 12 h (2030 to 0830) of the treatment day. The net concentration of the fluid consumed by OT/deprived animals was close to isotonic. In the second experiment, the initial effect of OT administration was an increase in urine volume and urinary sodium excretion and concentration by food-deprived animals during the first 12 h (0830 to 2030). These findings suggest that in food-deprived animals, systemic administration of OT induces NaCl intake as a consequence of previous urine loss and urinary sodium excretion.     

Sex differences and developmental effects of oxytocin on aggression and social behavior in prairie voles (Microtus ochrogaster)

Various hormones, including sex steroids and neuropeptides, have been implicated in aggression. In this study we examined (1) sex differences in intrasexual aggression in na?ve prairie voles; (2) the effects of developmental manipulations of oxytocin on intrasexual aggression; and (3) changes in patterns of intrasexual aggression after brief exposure to an animal of the opposite sex. Within 24 h of birth, infants were randomly assigned to receive either an injection of oxytocin (OT) or oxytocin antagonist (OTA) or to one of two control (CTL) groups receiving either isotonic saline or handling without injection. As adults, animals were tested twice in a neutral arena; before (Test 1) and 24 h after (Test 2) a 4-h exposure to an animal of the opposite sex. In Test 1, CTL males were more likely to show aggressive and less likely to show social behavior than CTL females. No significant treatment differences were observed within either sex in Test 1. In Test 2, after brief exposure to a male, females treated with OT became more aggressive and less social than OTA or CTL females. Male aggressive behavior did not change after exposure to a female. An increase in aggression and decline in social behavior toward other females, seen here in OT-treated females, is typically observed only following several days of female-male cohabitation. These findings demonstrate a sex difference in intrasexual aggression and suggest that neonatal exposure to OT may facilitate the onset of the mate-guarding component of pair bonding in female prairie voles.     

Serum oxytocinase activity is related to tumor growth parameters in N-methyl nitrosourea induced rat breast cancer

Oxytocinase has been reported to hydrolyse the peptide hormone oxytocin (OT). We have previously described changes in oxytocinase activity in human breast cancer, where a highly significant increase occurred in tumoral tissue. In the present work, we analysed oxytocinase activity in serum of rats with breast cancer induced by N-methyl-nitrosourea (NMU). We also correlated these data with the number and size of tumors and the body weight of the animals to evaluate the putative value of this activity as a biological marker of the disease. Our results confirm the involvement of OT in carcinogenesis and suggest a mayor role for oxytocinase activity in the development of breast cancer.     

雌雄同居对子午沙鼠情绪及下丘脑催产素表达的影响

雌雄同居是配偶关系形成的重要阶段,涉及到一系列生理和情绪的变化,对长期稳定的配偶关系形成具有重要意义。然而由于单配制动物模型较少,雌雄同居过程中的神经调控,尤其是两性差异仍不清楚。本研究以室内繁殖的子午沙鼠(Meriones meridianus)为研究对象,采用高架十字迷宫、强迫游泳和免疫组化法,探究雌雄同居对雌雄子午沙鼠的情绪变化及其相关脑区催产素表达的影响。结果表明：雌雄同居10 d后,在高架十字迷宫中,雌性沙鼠进入开放臂的频次显著减少(P <0.05),焦虑指数显著升高(P <0.05);在强迫游泳实验中,同居组雌性沙鼠停止游泳的频次和时间显著增加(P <0.05);同居组雌性沙鼠在下丘脑室旁核和视上核中的催产素表达水平显著升高(P <0.05)。然而同居组雄性的行为和催产素水平均没有出现显著变化,这可能与雌雄配偶关系形成过程中的两性不同步有关。综上,雌雄同居仅使得雌性子午沙鼠表现出焦虑样行为,且下丘脑催产素系统可能参与了该过程。