NADPH diaphorase activity in the posterior pituitary: relation to neuronal function

Magnocellular neurons of the paraventricular and supraoptic nuclei, fibers of the medial basal hypothalamus, and the posterior pituitary gland all stain histochemically for NADPH diaphorase activity (NADPHd). Following 8 days of salt loading to stimulate the hypothalamo-neurohypophyseal system, NADPHd activity, as determined by a spectrophotometric assay, is markedly increased in the posterior pituitary gland but not in the hypothalamus of rats. Therefore, NADPHd activity in this system correlates with neuronal function and may provide a convenient method for the assessment of neuronal activity in selected neuronal populations.     

A role of central oxytocin in autonomic functions: Its action in the motor nucleus of the vagus nerve

Neurones located in the dorsal motor nucleus of the vagus nerve were shown, in slices from the rat brainstem, to respond to oxytocin by a concentration-dependent increase in rate of firing. A newly available oxytocin antagonist suppressed the excitatory effect of oxytocin on single neurones, this antagonism was partially reversible. Further evidence that neurones located in the dorsal motor nucleus of the vagus nerve possess oxytocin receptors was obtained from in vitro light microscopical autoradiography using [¹²⁵I]-labelled oxytocin antagonist. In conjunction with data by others which showed that oxytocin antagonist microinjected into the dorsal motor nucleus of the vagus nerve blocks gastric and cardiac effects caused by stimulation of the hypothalamic paraventricular nucleus, our results suggest a role for central oxytocin in autonomic efferent activity.     

Methylation of the oxytocin receptor gene in clinically depressed patients compared to controls: The role of OXTR rs53576 genotype

The emerging field of epigenetics provides a biological basis for gene-environment interactions relevant to depression. We focus on DNA methylation of exon 1 and 2 of the oxytocin receptor gene (OXTR) promoter. The research aims of the current study were to compare OXTR DNA methylation of depressed patients with healthy control subjects and to investigate possible influences of the OXTR rs53576 genotype. The sample of the present study consisted of 43 clinically depressed women recruited from a psychosomatic inpatient unit and 42 healthy, female control subjects – mean age 30 years (SD = 9). DNA methylation profiles of the OXTR gene were assessed from leukocyte DNA by means of bisulfite sequencing. Depressed female patients had decreased OXTR exon 1 DNA methylation compared to non-depressed women. The association between depression and methylation level was moderated by OXTR rs53576 genotype. Exon 2 methylation was associated with OXTR rs53576 genotype but not with depression. Our findings suggest exon-specific methylation mechanisms. Exon 1 methylation appears to be associated with depressive phenotypes whereas exon 2 methylation is influenced by genotype. Previously reported divergent associations between OXTR genotype and depression might be explained by varying exon 1 methylation. In order to further understand the etiology of depression, research on the interplay between genotype, environmental influences and exon-specific methylation patterns is needed.     

Intracerebroventricular injection of choline increases plasma oxytocin levels in conscious rats

In the present study, we examined the effect of intracerebroventricularly (i.c.v.) injected choline on both basal and stimulated oxytocin release in conscious rats. I.c.v. injection of choline (50–150 μg) caused time- and dose-dependent increases in plasma oxytocin levels under normal conditions. The increase in plasma oxytocin levels in response to i.c.v. choline (150 μg) was greatly attenuated by the pretreatment of rats with atropine (10 μg; i.c.v.), muscarinic receptor antagonist. Mecamylamine (50 μg; i.c.v.), a nicotinic receptor antagonist, failed to suppress the effect of 150 μg choline on oxytocin levels. Pretreatment of rats with 20 μg of hemicholinium-3 (HC-3), a specific inhibitor of choline uptake into nerve terminals, greatly attenuated the increase in plasma oxytocin levels in response to i.c.v. choline injection. Osmotic stimuli induced by either oral administration of 1 ml hypertonic saline (3 M) following 24-h dehydration of rats (type 1) or an i.c.v. injection of hypertonic saline (1 M) (type 2) increased plasma oxytocin levels significantly, but hemorrhage did not alter basal oxytocin concentrations. The i.c.v. injection of choline (50, 150 μg) under these conditions caused an additional and significant increase in plasma oxytocin concentrations beyond that produced by choline in normal conditions. These data show that choline can increase plasma oxytocin concentrations through the stimulation of central cholinergic muscarinic receptors by presynaptic mechanisms and enhance the stimulated oxytocin release.     

Differential regulation of oxytocin and vasopressin messenger ribonucleic acid levels by gonadal steroids in postpartum rats

We previously reported that sequential estradiol and progesterone exposure followed by progesterone withdrawal increases oxytocin (OT), but not arginine vasopressin (AVP), messenger ribonucleic acid (mRNA) in the hypothalamic paraventricular nucleus (PVN) of the rat. Substitution of testosterone for progesterone and subsequent testosterone withdrawal in the estrogen-primed rat increases PVN AVP mRNA levels. At the end of pregnancy (day 21), rats are exposed to high estrogen and declining progesterone and testosterone concentrations. Coincident with these changes in circulating gonadal steroid hormones are increases in OT and AVP mRNAs. If progesterone levels are sustained at term, OT levels are attenuated and if testosterone is sustained, AVP mRNA levels are attenuated. Immediately postpartum, however, OT and AVP mRNA levels decline compared to term levels. To further determine the role of estrogen in the regulation of OT and AVP mRNAs, we performed two experiments. In the first experiment, we administered estrogen during the peripartum period to determine if estrogen supplementation prevents the relative attenuation of OT and AVP mRNAs that is seen after parturition. Day 18 pregnant rats were given estradiol-filled or empty capsules and sacrificed on day 2 of lactation. By Northern analysis, significant differences in PVN AVP, but not OT, mRNA were found between the estrogen- and sham-treated lactational animals, P < 0.02. In the second experiment, we determined if sustaining estrogen after progesterone is removed in steroid-treated ovariectomized rats is essential for the increase in OT mRNA. Ovariectomized rats were given either empty capsules or sequential estradiol- and progesterone-filled capsules and both were sustained for 12 days. When progesterone-filled capsules were removed, estradiol-filled capsules were either removed or left in place, and the animals were sacrificed 48 h later. PVN OT mRNA was analyzed by Northern blot hybridization. OT mRNA was increased in both of the steroid-treated groups to the same degree, compared to sham-treated animals, P = 0.04. In summary, estrogen supplementation during early lactation prevents the attenuation of PVN AVP, but not OT, mRNA after parturition. In the estrogen-primed ovariectomized rat, it is not necessary to sustain estrogen to see the effects of progesterone withdrawal upon PVN OT mRNA.     

Adrenocorticotropin secretagog release: stimulation by frustration and paradoxically by reward presentation

Colchicine blockade of axonal transport from the paraventricular nucleus to the median eminence was used to indirectly infer adrenocorticotropin (ACTH) secretagog release in response to a reward presentation and the psychological stressor of frustration. After training rats to drink at the same time of day for 30 min for 2–3 weeks, basal arginine vasopressin (AVP), but not corticotropin-releasing factor (CRF) or oxytocin (OT), concentrations were elevated. The frustration of presenting empty water bottles resulted in increased corticosterone concentrations. Concordantly, CRF, AVP, and OT contents in the median eminence decreased compared to controls. All three secretagogs are thus apparently involved in the corticosterone response to frustration. As expected, water presentation decreased both ACTH and corticosterone. Paradoxically, however, CRF, AVP, and OT contents also decreased compared to controls. The discrepancy of ACTH and corticosterone concentrations declining despite release of secretagogs cannot be explained by decreased adrenal or pituitary sensitivities since both exogenous ACTH and CRF elevated corticosterone and ACTH, respectively, in rewarded rats. Secretagog release, therefore, may not always be associated with stimulation of ACTH release.     

Developmental consequences of oxytocin

This paper examines the developmental effects of the mammalian neuropeptide, oxytocin (OT). In adults, OT is the most abundant neuropeptide in the hypothalamus and serves integrative functions, coordinating behavioral and physiological processes. For example, OT has been implicated in parturition, lactation, maternal behavior and pair bond formation. In addition, OT is capable of moderating behavioral responses to various stressors as well as the reactivity of the hypothalamic-pituitary-adrenal (HPA) axis. Neonates may be exposed to hormones of maternal origin, possibly including peptides administered to the mother in the perinatal period to hasten or delay birth and in milk; however, whether peptide hormones from the mother influence the developing infant remains to be determined. In rodents, endogenous OT is first synthesized during the early postnatal period, although its functions at this time are not well known. Experiments in neonatal prairie voles have documented the capacity of OT and OT receptor antagonists to have immediate and lifelong consequences for social behaviors, including adult pair bonding and parental behaviors, as well as the reactivity of the HPA axis; most of these effects are sexually dimorphic. Possible mechanisms for such effects, including long-lasting changes in OT and vasopressin, are summarized.     

Effects of neonatal oxytocin treatment on aggression and neural activities in mandarin voles

Neonatal manipulation of oxytocin (OT) has long-term effects on behavior and physiology. Here we test the hypothesis that neonatal OT treatment can affect the subsequent expression of intrasexual aggression partly by reprogramming the neural activities of relevant brain regions. To test this hypothesis, mandarin voles (Lasiopodomys mandarinus) received OT or isotonic saline treatment within 24 h of birth. At about 75 days of age, aggressive behaviors and Fos expression in different brain regions were tested. The results indicate that the (1) level of intrasexual aggression was higher and other social contact was lower in SAL-treated sexually na?ve males than in females and; (2) OT-treated females showed a greater increase in aggressive behaviors and Fos expression only after exposure to a male than SAL-treated females, but there were no significant changes in aggressive behaviors in males. These results demonstrate a sexual difference in aggression, and that neonatal exposure to OT may increase aggression in female mandarin voles. These effects may be based on changes in neural activities of relevant brain regions including the bed nucleus of the stria terminalis (BNST), lateral septal nucleus (LS), medial preoptic area (MPOA), the paraventricular nucleus of the hypothalamus (PVN), supraoptic nucleus (SON), mediodorsal thalamic nucleus (MD), ventromedial nucleus of hypothalamic (VMH), the medial amygdala (MeA) and central amygdala (CeA).     

催产素减轻新生大鼠海马神经元缺氧缺血性损伤

目的:探讨催产素(oxytocin)对新生大鼠缺氧缺血性损伤后海马CA1区神经元的作用及机制。方法:采用氧糖剥夺(OGD)制备体外缺氧缺血模型,取8只7~10日龄新生大鼠的急性分离脑片(6~8片/只)随机分为4组,即对照组、OGD 20 min组、OGD 40 min组和OGD+oxytocin组,进行TO-PRO-3染色实验观察催产素对神经元的作用。另取20只新生大鼠脑片随机分为4组,分别是OGD组、OGD+oxytocin组、OGD+d VOT(催产素受体阻断剂)+oxytocin组和OGD+bicuculline(GABAA受体阻断剂)+oxytocin组,用全细胞膜片钳记录不同药物作用下海马神经元缺氧去极化的出现时间。结果:TO-PRO-3染色结果显示海马CA1区神经元死亡数量随着氧糖剥夺时间延长而增加,催产素能显著减少OGD所致的死亡神经元数目(P0.05)。全细胞膜片钳记录结果显示,催产素可使缺氧去极化时间显著延长;d VOT及bicuculline可以消除这种效应。结论:催产素能减轻新生大鼠海马CA1区神经元缺氧缺血性损伤,其机制可能是通过结合催产素受体,增强抑制性神经传递,从而产生神经保护作用。