Effects of vasopressin and oxytocin on evoked dorsal horn cell activity in an isolated segment of spinal cord

During experiments on an isolated segment of the spinal cord of 2- to 3-week-old rats, a study was made of the effects of vasopressin and oxytocin on the activity of dorsal horn cells produced by stimulating the afferent root. Both field and action potentials were recorded in single cells. It was established that vasopressin and oxytocin produced reversible inhibition of the postsynaptic component of field potentials. The amplitude of potentials was reduced by 33–39% by vasopressin and by 12–34% using oxytocin. The effect of the test substances depended on the concentration used and the duration of their action on the brain. Both vasopressin and oxytocin reversibly depressed discharges of single dorsal horn cells evoked by stimulating the dorsal root. These two neuropeptides prolonged latency, and reduced the number of evoked potentials or completely suppressed response. A facilitatory effect was recorded in a small number of cells. We deduced from our findings that their hypothalamospinal neurohormonal system inhibits transmission of afferent impulses at the level of interneurons of the dorsal horn.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 5, pp. 634–640, September–October, 1985.     

Pharmacological doses of oxytocin affect plasma hormone levels modulating glucose homeostasis in normal man

Pharmacological doses of oxytocin administered in basal conditions evoked a rapid surge in plasma glucose and glucagon levels followed by a later increase in plasma insulin and adrenaline levels. The effects of oxytocin on plasma glucagon and adrenaline levels were potentiated by hypoglycemia. When the endogenous pancreas secretion was suppressed by cyclic somatostatin (150 micrograms/h) and exogenous glucagon (3.5 micrograms/h) and insulin (0.2 mU/kg.min) were both replaced, oxytocin (0.2 U/min) evoked a transient but significant increase in plasma glucose levels suppressing the glucose infusion rate (GIR) in the first 60 min. On the contrary at higher insulin infusion rate (0.6 mU/kg.min) plasma glucose levels and GIR remained unaffected throughout the study. Oxytocin seems also to potentiate glucose-induced insulin secretion as evidenced by hyperglycemic glucose clamp. In conclusion, pharmacological doses of oxytocin seem to exert a prevalent hyperglycemic effect by a combined action at the liver site (as glycogenolytic agent) and at the endocrine pancreas (as a stimulatory agent of A cell secretion).     

Substance P and NPY differentially potentiate ATP and adrenergic stimulated vasopressin and oxytocin release

The supraoptic nuclei are innervated by the A1 neurons of the caudal ventrolateral medulla. Substances colocalized in the A1 terminals include norepinephrine (NE), substance P (SP), ATP, and neuropeptide Y (NPY). ATP, acting at P(2x) receptors, caused rapid and unsustained stimulation of vasopressin (VP) and oxytocin (OT) release from perifused explants of the hypothalamo-neurohypophysial system. SP elicited a concentration-dependent stimulation of VP and OT release that was large and sustained compared with other stimuli. ATP, but not phenylephrine (PE, alpha(1)-adrenergic agonist), augmented the response to SP (1 microM). In contrast, NPY did not alter basal nor ATP-induced VP or OT release, but it did cause sustained potentiation of PE-induced VP and OT release. The Y(1)-agonist, [Leu(31),Pro(34)]-NPY, increased VP and OT release, suggesting that the ineffectiveness of NPY reflects opposing actions at pre- and postsynaptic receptors. However, [Leu(31),Pro(34)]-NPY did not potentiate hormone responses to ATP or PE. The differential responses to these colocalized neurotransmitters and neuropeptides illustrate the range of potential responses that stimulation of this pathway might elicit from supraoptic neurons.     

Effects of interleukins on plasma arginine vasopressin and oxytocin levels in conscious, freely moving rats.

To elucidate whether interleukins are involved in vasopressin or oxytocin release during cytokine-related stressful conditions, we examined the effects of human interleukin-1 beta and interleukin-6 on plasma vasopressin and oxytocin levels in rats. Interleukin-1 beta administrated intravenously stimulated both the vasopressin and oxytocin secretion in dose-dependent manners. Neither hormone release was observed following interleukin-6 administration. Pretreatment with aspirin significantly attenuated the effects of interleukin-1 beta on both the vasopressin and oxytocin levels. SC-19220, a prostaglandin E2 receptor antagonist, did not affect the interleukin-1 beta-induced increase of plasma oxytocin levels, but almost completely abolished its effect on plasma vasopressin levels. These results suggest that under certain stressful conditions which accompany the stimulation of cytokine production, interleukin-1 is involved in the increase of plasma vasopressin and oxytocin levels and, moreover, different kinds of prostaglandins are suggested to participate in these interleukin-1-induced hormone release.     

Effect of vasopressin and oxytocin on spontaneous unit activity of dorsal horn cells in the isolated spinal cord of young rats

The effect of vasopressin and oxytocin, added to the perfusion solution, on the spontaneous firing rate of single dorsal horn cells was studied in experiments on an isolated segment of spinal cord from rats aged 2–3 weeks. Both neuropeptides were found to have a mainly inhibitory action. Under the influence of vasopressin the spontaneous firing rate of 74% of cells (29 of 39 cells responding to vasopressin) fell, and only in 26% (10 of 39 cells) did it rise. Oxytocin inhibited spontaneous activity of 67% of cells (14 of 21 which responded) and excited 33% of neurons (seven of 21). The effects were dose-dependent and reversible. The cells either responded in the same way to vasopressin and oxytocin or they responded to application of one peptide but not of the other.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 3, pp. 314–320, May–June, 1985.     

Effects of beta-endorphin fragments on plasma levels of vasopressin

Plasma vasopressin levels are significantly decreased after intracerebroventricular (icv) administration of β-endorphin (βE), but not of des-tyrosine βE (DTβE). The βE induced decrease of vasopressin levels, which occurs in normal as well as in water deprivated rats, can partially be blocked by naltrexone. γ-Endorphin (γE), α-endorphin (αE), DTγE and DTαE did not affect basal levels of vasopressin, but γE and DTγE further increased the elevated vasopressin levels in water deprivated rats. Naltrexone antagonized this increase following γE administration, but not that induced by DTγE. The results suggest that the effects of βE and its fragments on plasma vasopressin levels are mediated by multiple opiate and non-opiate receptor systems.     

Segmental norepinephrine and dopamine levels in cat spinal cord

Tissue levels of norepinephrine in the uninjured cat were determined by a fluorimetric or enzymatic radiometric assay technique. There were no significant differences of NE levels between the two techniques. The highest concentrations of NE were found in the cervical (.170 ug/g) and lumbar (.232 ug/g) enlargements and appear to be related to the relative amount of grey and white matter present at these levels. Dopamine levels, as determined by the enzymatic radiometric assay technique, were found to be low in those spinal segments measured (less than 0.030 ug/g). DA appears to be similarly distributed as norepinephrine in the spinal segments. Barbiturate or nitrous oxide anesthetic agents did not result in significant differences in NE determinations at cervical or thoracic segments. Variability of reported NE and DA levels from other studies appears to be related to differences in assay technique.     

Chromosomal and comparative mapping of rat oxytocin, oxytocin receptor and vasopressin genes

Oxytocin and its receptor are potentially important for cardiovascular functions. In the present paper, we report their chromosome locations in the rat and their comparative mapping with the mouse and human. They are located in chromosome regions previously known to contain quantitative trait loci for blood pressure in various genetic crosses. Thus, they have become valid candidate genes for genetic hypertension.     

催产素和加压素与应激的关系

催产素和加压素是由下丘脑视上核和室旁核大细胞性神经内分泌细胞合成和分泌的一种神经垂体激素。各种应刺激都可以引起催产素和加压素神经元的活动。目前应激后引起的这类神经活动的变化与人类的某结疾病的病理生理相关联正在引起人们的关注。西文总结了近几年在这方面的研究进展。主要内容包括：（1）催产素和加压素神经元在应激中的反应;（2）在大细胞性催产素和加压素神经元的应激反应相关联的神经传递物质;（3）与应激相关联的精神疾病的关系。     

Distribution of vasopressin and oxytocin in rat brain

Arginine-vasopressin and oxytocin in various portions of rat brain were determined by radioimmunoassays. The hormones were extracted from tissue samples into 0.1 N HCl and then purified partially with acetone-petroleum ether extraction. The non-equilibration method was used for the assays. In this method recovery rates of arginine-vasopressin and oxytocin were 73.0 +/- 4.4% and 75.0 +/- 3.8%, respectively. Sensitivities of the assays were 1 pg of arginine-vasopressin and 0.75 pg (0.3 microU) of oxytocin per assay tube. The higher concentrations of arginine-vasopressin and oxytocin were confirmed in the hypothalamo-neurohypophyseal system, where these hormones are synthesized, transported and stored. Relatively high concentrations of these hormones, especially oxytocin, were detected in spinal cord. Amygdala, hippocampus, limbic forebrain and pineal body contained a certain amount of arginine-vasopressin (2-20 pg/mg protein). Oxytocin (1-7 pg/mg protein) was also detected in amygdala, pons and medulla oblongata, pineal body and midbrain. The low concentrations of these hormones were also found in cerebral cortex and cerebellum.     

Quantitativein situ hybridization to measure single-cell changes in vasopressin and oxytocin mRNA levels after osmotic stimulation

1. The measurement of cellular mRNA content by quantitative in situ hybridization is a valuable approach to the study of gene expression in brain since this tissue exhibits a high degree of phenotypic heterogeneity. 2. The cellular content of vasopressin and oxytocin mRNA in hypothalamo-neurohypophysial system neurons was altered by maintaining rats for 24 hr on 2% sodium chloride water. 3. Statistical and graphical techniques were then used to analyze cell by cell how mRNA levels were altered as a result of osmotic stimulation. We propose that the negative binomial probability distribution is a suitable model to describe how mRNA content varies across a defined cell population. For both measures of oxytocin and vasopressin mRNA levels, maximum-likelihood estimation indicated that this model adequately described empirical findings obtained from rats drinking tap water or salt water. 4. Both graphical and statistical analyses suggested how the defined neural system responds to osmotic stimulation: mRNA content was altered as a multiplicative function of "initial state." The utility and limitations of the quantitative approach are discussed.     

Norepinephrine and dopamine levels in normal dog and monkey spinal cord

Levels of norepinephrine (NE) and dopamine (DA) were determined for normal spinal cord of dog and monkey. Mean levels for both NE and DA in monkey were about twice those found in dog. Both NE and DA increased with descending cord levels. NE levels were highest in lower cervical and lumbosacral regions and showed a direct correlation without the amount of gray matter present in the segment. DA levels increased gradually from cervical to lumbosacral regions and did not show localized increases. NE levels were similar in isolated gray matter from each region indicating that total cord values are related to gray and white ratios.