Oxytocinergic activity is linked to lower blood pressure and vascular resistance during stress in postmenopausal women on estrogen replacement

Estrogen administration results in increased release of the oxytocin (OT) prohormone reflected by increases in oxytocin intermediate peptide (OT Int) in both animal models and humans, and sequential treatment of ovariectomized rats with estrogen/progesterone then progesterone withdrawal leads to increased hypothalamic OT mRNA. Blood pressure (BP) reductions have been related to increased exogenous and endogenous OT in rats and to higher endogenous OT activity in premenopausal women, but not previously in postmenopausal women. Thus, we used plasma obtained at rest and during a speech stressor from 54 postmenopausal women who participated in a 6-month randomized trial of oral conjugated estrogens vs. placebo to examine effects of estrogen replacement therapy (ERT) on plasma OT and OT Int levels and their relationships to changes in BP during the trial. ERT alone and with progesterone (but not placebo) led to significant increases in plasma levels of OT Int, but no change in plasma OT levels. Women showing greater increases in OT Int during treatment showed greater decreases in BP and total vascular resistance during a series of behavioral stressors compared to women with moderate or no increases in OT Int, even after controlling for effects related to treatment condition or to changes in plasma estradiol. The findings suggest that enhanced oxytocinergic activity may contribute to BP decreases associated with ERT in more responsive postmenopausal women.     

Enhanced corticosterone concentrations and attenuated Fos expression in the medial amygdala of female oxytocin knockout mice exposed to psychogenic stress

Centrally released oxytocin (OT) is believed to attenuate the response of the hypothalamic-pituitary-adrenal (HPA) axis to psychogenic stress. To test this hypothesis, we measured plasma corticosterone concentrations and Fos-immunoreactive protein in the paraventricular nucleus of the hypothalamus (PVN) and limbic brain areas of female wild-type and OT knockout mice that were exposed to a shaker platform, a predominantly psychogenic stress. Plasma corticosterone concentrations after shaker stress were higher in female OT knockout mice than wild-type mice. Genotypic differences in the corticosterone response after shaker stress persisted across all stages of the estrous cycle and when mice were conditioned to repeated shaker stress. Shaker stress activated Fos in OT-positive neurons of wild-type mice and corticotropin-releasing hormone-positive, but not vasopressin-positive, neurons within the PVN of wild-type and OT knockout mice. Fos expression was also increased after shaker stress in the bed nucleus of the stria terminalis, medial and central nuclei of the amygdala, medial preoptic area, and the paraventricular nucleus of the thalamus of wild-type and OT knockout mice. However, Fos expression in the medial amygdala was significantly lower in female OT knockout mice than wild-type mice. Our findings indicate heightened stress-induced corticosterone release in female OT knockout mice. Therefore, the results suggest that OT pathways play a role in attenuating the HPA axis response to psychogenic stress in female mice.     

Enhanced initial and sustained intake of sucrose solution in mice with an oxytocin gene deletion

Laboratory mice drink little sucrose solution on initial exposure, but later develop a strong preference for sucrose over water that plateaus after a few days. Both the initial neophobia and later plateau of sucrose intake may involve central oxytocin (OT) signaling pathways. If so, then mice that lack the gene for OT [OT knockout (KO)] should exhibit enhanced initial and sustained sucrose intake compared with wild-type (WT) cohorts. To test this hypothesis, female OT KO and WT mice (11-13 mo old) were given a two-bottle choice between 10% sucrose and water available ad libitum for 4 days. On the first day, sucrose intake was 20-fold greater in OT KO mice compared with WT cohorts. The avid sucrose consumption by OT KO mice increased further on day 2 and was sustained at significantly higher levels than intake by WT mice. Enhanced initial and sustained sucrose intake also was observed in 5- to 7-mo-old male OT KO mice. The effect of genotype was observed over a range of sucrose concentrations and was maintained over at least 8 days of continual exposure. However, there was no effect of genotype on daily intake of sucrose-enriched powdered chow. These findings indicate that the genetic absence of OT in mice is associated with enhanced initial and sustained intake of sucrose solutions. Thus central OT pathways may normally participate in limiting initial intake of novel ingesta and may also participate in limiting intake of sweet, highly palatable familiar ingesta.     

Dehydration anorexia is attenuated in oxytocin-deficient mice

Evidence in rats suggests that central oxytocin (OT) signaling pathways contribute to suppression of food intake during dehydration (i.e., dehydration anorexia). The present study examined water deprivation-induced dehydration anorexia in wild-type and OT -/- mice. Mice were deprived of food alone (fasted, euhydrated) or were deprived of both food and water (fasted, dehydrated) for 18 h overnight. Fasted wild-type mice consumed significantly less chow during a 60-min refeeding period when dehydrated compared with their intake when euhydrated. Conversely, fasting-induced food intake was slightly but not significantly suppressed by dehydration in OT -/- mice, evidence for attenuated dehydration anorexia. In a separate experiment, mice were deprived of water (but not food) overnight for 18 h; then they were anesthetized and perfused with fixative for immunocytochemical analysis of central Fos expression. Fos was elevated similarly in osmo- and volume-sensitive regions of the basal forebrain and hypothalamus in wild-type and OT -/- mice after water deprivation. OT-positive neurons expressed Fos in dehydrated wild-type mice, and vasopressin-positive neurons were activated to a similar extent in wild-type and OT -/- mice. Conversely, significantly fewer neurons within the hindbrain dorsal vagal complex were activated in OT -/- mice after water deprivation compared with activation in wild-type mice. These findings support the view that OT-containing projections from the hypothalamus to the hindbrain are necessary for the full expression of compensatory behavioral and physiological responses to dehydration.     

Acyclic tetraprenyltoluquinols from Cystoseira sauvageuana and their possible role as biogenetic precursors of the cyclic cystoseira metabolites

From the brown alga Cystoseira sauvageuana two novel tetraprenyltoluquinols with an acyclic terpenoid side chain have been isolated. Their chemical transformation into compounds containing a cyclopentane ring provides a clue to the biogenesis of the cyclic Cystoseira metabolites.     

Tetraprenyltoluquinols from the brown alga Cystoseira jabukae

The chloroform extract of the brown alga Cystoseira jabukae afforded two new tetraprenyltoluquinols and two tetraprenyltoluquinones. The structures were determined by spectral analysis and chemical correlations. The quinones are possibly artifacts formed by oxidation of the corresponding quinols in the isolation procedure.     

Effects of antihelminthic treatment on cell-mediated immunity in Gentoo penguin chicks

Intestinal parasites suppose a cost to hosts as they compete directly for nutritional resources. Therefore, hosts must defend themselves against intestinal parasites by mounting an immune response. Many penguin species acquire parasites through their diet and transfer these parasites to their chicks when feeding them. High parasite loads in penguin chicks could have effects on their growth and body condition, and ultimately on their survival. Here, we evaluated the effect of parasites on the cell-mediated immune system in Gentoo penguin (Pygoscelis papua) chicks at Stranger Point (25 de Mayo/King George Island, South Shetland Islands). To this end, 12 chicks were experimentally deparasitized with a mixture of anthelminthic drugs (albendazole and praziquantel), whereas 10 others were kept as control. We measured cutaneous cell-mediated immunity in response to immunization with phytohemagglutinin (PHA). We also analyzed the leukocyte profile in both treated and control groups before and after the treatment. After the treatment, deparasitized birds showed larger foot-web swelling in response to PHA injection than control birds. Deparasitized penguins also showed lower eosinophil and monocyte counts than controls, whereas heterophils, lymphocytes, and total white blood cell counts did not differ between groups. Our results suggest that Gentoo penguin chicks parasitized with intestinal parasites suffer a cost in terms of reduced cell-mediated immune responses that could ultimately affect their survival.     

Post-dispersal seed predation in Patagonia temperate forest depends on habitat patchiness and seed species

Plant Ecology - Post-dispersal seed predation is a key process regulating plant population dynamics and community composition. Because food preference (i.e., seed species selection) can interact...     

Effect of white and far-red light on betalain formation

Light-induced betalain synthesis has been studied in three species of Amaranthaceae. The results obtained suggest that the response to short-term irradiation with white light is mediated by phytochrome, while the effects of prolonged illumination are controlled by the photosynthetic system. Betalain accumulation stimulated by prolonged far-red irradiation is controlled chiefly by the photosynthetic system, the participation of phytochrome being of minor importance.