Effect of corticosterone on CART peptide levels in rat blood

We have recently demonstrated that CART peptides display a diurnal rhythm in blood that depends partly on glucocorticoids levels. This study extends previous findings by directly testing the effects of acute administration of corticosterone and metyrapone on CART peptide levels in blood. Acute treatment with corticosterone augmented CART levels, while metyrapone administration prevented the increase in CART in the evening hours. These results further support the hypothesis that glucocorticoids play a role in the regulation of CART levels in blood.     

Effect of oxytocin and naloxone on the plasma levels of corticosterone in the rat

The effect of two doses of oxytocin (2 or 4 UI/kg i.p.) has been studied in the male Wistar rats, either preceded or not by a naloxone administration (10 mg/kg i.p.), on the response of the hypothalamus-pituitary-adrenal system, the latter being valued by changes produced in the plasmatic corticosterone levels. Oxytocin produced significant increases of the plasmatic corticosterone levels, this effect being stronger and longer lasting after the superior dose. Naloxone alone produced the same effect, but not as intense and stable as that of oxytocin. Pretreatment with naloxone modified the response of the hypothalamus-pituitary-adrenal system to oxytocin, producing partial blockade. The results suggest that the oxytocin action on the hypothalamus-pituitary-adrenal axis might be mediated by the endogenous opiates.     

Maternal influences on the sexual behavior and reproductive success of the female rat

In many species, including humans, there is evidence for parental effects on within-sex variations in reproductive behavior. In the present studies we found that variations in postnatal maternal care were associated with individual differences in female sexual behavior in the rat. Females born to and reared by dams that showed enhanced pup licking/grooming (i.e., High LG mothers) over the first week postpartum showed significantly reduced sexual receptivity and alterations in the pacing of male mounting (i.e., longer inter-intromission intervals) observed in a paced mating test. There were minimal effects on the sexual behavior of the male offspring. The female offspring of High LG mothers showed a reduced lordosis rating, a decreased mount:intromission ratio, received fewer ejaculations and were less likely to achieve pregnancy following mating in the paced mating context. The data suggest maternal influences on the sexual development of the female rat that are functionally relevant for reproductive success. Together with previous studies these findings imply that maternal care can ‘program’ reproductive strategies in the female rat.     

Increased corticosterone levels in mice subjected to the rat exposure test

In recent years, there has been a notable interest in studying prey-predator relationships to develop rodent-based models for the neurobehavioral aspects of stress and emotion. However, despite the growing use of transgenic mice and results showing important differences in the behavioral responses of rats and mice, little research has been conducted regarding the responses of mice to predators. The rat exposure test (RET), a recently developed and behaviorally validated prey-predator (mouse-rat)-based model, has proven to be a useful tool in evaluating the defensive responses of mice facing rats. To further validate the RET, we investigated the endocrine and behavioral responses of mice exposed to this apparatus. We first constructed a plasma corticosterone secretion curve in mice exposed to a rat or to an empty cage (control). Rat-exposed mice showed a pronounced rise in corticosterone levels that peaked 15 min from the beginning of the predator exposure. The corticosterone levels and behavioral responses of mice exposed to a rat or to a toy in the RET apparatus were then measured. We observed high plasma corticosterone levels along with clear avoidance behaviors represented by decreases in tunnel and surface area exploration and increases in risk assessment behaviors and freezing. This strongly suggests that the test elicits a repertoire of behavioral responses compatible with an aversion state and indicates that it is a promising model for the evaluation of prey-predator interactions. However, more physiological, neurochemical, and pharmacological studies are needed to further validate the test.     

Maternal methamphetamine administration during pregnancy influences on fetal rat heart development. [corrected

Methamphetamine (MAP) is one of the most abused drugs in Japan. The rate of MAP abuse by young women has recently reached more than 50 percent in adolescents. A major health concern is that these women will continue to use MAP during pregnancy. The purpose of this study was to investigate whether MAP administered to the mother during pregnancy would change the expression of α- and β- myosin heavy chain (MHC) mRNA in rat neonatal hearts, as detected by quantitative RT-PCR. In addition, morphological changes in the rat neonatal ventricles were examined. Pregnant rats were injected intraperitoneally with MAP (1 mg/kg/day) starting at day 0 of gestation and ending at day 21. There was a significant increase in α-MHC mRNA expression in the neonatal ventricular muscle in the experimental group compared with the control at postnatal day (P) 0 and 5. α-MHC mRNA expression in both groups was similar after P9. β-MHC mRNA expression was similar in both groups at P0. Postnatal β-MHC mRNA expression decreased rapidly, but significant alteration was not detected. Neonatal rats at P0 exhibited some cardiac changes, including hypertrophy, degeneration, and disarrangement of myofibers, but these lesions disappeared by P14. We conclude that chronic maternal administration of MAP changes the α- and β-MHC mRNA expression pattern in fetal and neonatal hearts, correlating with abnormal development, plasma level of hormones, and myocardial damage. At the same time, it is indicated that neonatal cardiomyocytes have reversibility.     

Effect of clorgyline and of alpha-methyl-p-tyrosine on the plasma levels of corticosterone in the rat

The effect of a type A MAO inhibitor, clorgyline, injected alone or with alpha-methyl-p-tyrosine (aMpT) on the plasmatic corticosterone levels estimated at 9 a.m. and 5 p.m. has been studied in male Wistar rats. The clorgyline injected alone produced significant decreases in corticosterone values, especially at 5 p.m., determining a variation lack between the morning and the afternoon levels. When alpha-MpT is associated to IMAO, increases at both points of the day considered in this experiment take place. The amount of NA and 5-HT in the brain was also estimated; clorgyline high increases in Na and 5-HT contents, 5-HT; aMpT reduces the effect of clorgyline, especially as regards content. The results are discussed in relation to this highly specific MAO inhibitor and with the role of these amines as modulators of ACTH secretion. In view of the changes introduced by the aMpT injection, the modifications produced by clorgyline alone are related to NA, but to 5-HT, when the NA synthesis has been interrupted by the tyrosine hydroxylase inhibitor.     

Effect of endogenous corticosterone on the determination of dexamethasone receptor levels in rat liver cytosol

The effect of endogenous corticosterone on the quantitative measurement of dexamethasone receptors in liver cytosols from developing rats has been studied. Liver cytosols from adrenalectomized rats were preincubated with increasing concentrations of nonlabeled corticosterone and the levels of detectable dexamethasone receptors were subsequently determined either directly or after removal of unbound corticosterone. Corticosterone concentrations of 50 nM or lower had no significant effect on the specific binding of labeled dexamethasone. Higher concentrations of corticosterone resulted in under-estimation of dexamethasone receptor levels. The mean levels of endogenous corticosterone in liver cytosols from 19.5- to 21.5- day fetuses, 22-day fetuses, 6-day-old immature rats and adult rats were 27.40, 11.91, 0.81 and 4.05 nM, respectively. It is concluded that variations in the levels of circulating corticosterone in the rat under normal physiological conditions have no significant effect on the quantitative measurement of total (occupied and unoccupied) receptor sites for dexamethasone in liver cytosol. This is supported by the finding that prior treatment of liver cytosols, from rats at different stages of development, with charcoal to remove unbound steroids has no effect on the amount of detectable dexamethasone receptors.     

Effect of estrus cycle, ovariectomy and lactation on variations of basal corticosterone levels or agression stress levels in rats]

In the Rat, the estrous cycle induces a rhythm of plasmatic corticosterone level : the fluctuations of basal or stress corticosteronemy are significantly superior during the periods of high estradiol secretion, proestrus and estrus, that during metaestrus and diestrus. Ovariectomy, performed at 60 days of age, is without effect on resting corticosteronemy, but reduces significantly the response to stress. Weaning unaffects the basal level of plasmatic corticosterone which remains comparable to diestrus level ; however, stress response decreased during lactation returns to normal level at the end of the first ovarian cycle (diestrus).     

Maternal influences on placental development

Epidemiological evidence suggests that size at birth may affect health in later life. The growth of the fetus may be adversely affected by a suboptimal maternal environment. Understanding placental development and function will help unravel the mechanisms controlling fetal growth. This article poses the problem: how does the maternal environment (uterine or systemic) influence placental development? Critical human placental functions include remodelling maternal uterine spiral arteries to increase the flow of blood to the maternofetal interface, and transferring oxygen and nutrients into the fetal vasculature, all processes involving trophoblast. Gene ablations that affect pregnancy outcome in mice lead to some interesting hypotheses.     

Skeletal ontogeny in basal scleractinian micrabaciid corals

The skeletal ontogeny of the Micrabaciidae, one of two modern basal scleractinian lineages, is herein reconstructed based on serial micro‐computed tomography sections and scanning electron micrographs. Similar to other scleractinians, skeletal growth of micrabaciids starts from the simultaneous formation of six primary septa. New septa of consecutive cycles arise between septa of the preceding cycles from unique wedge‐shaped invaginations of the wall. The invagination of wall and formation of septa are accompanied by development of costae alternating in position with septa. During corallite growth, deepening invagination of the wall results in elevation of septa above the level of a horizontal base. The corallite wall is regularly perforated thus invaginated regions consist of pillars inclined downwardly and outwardly from the lower septal margins. Shortly after formation of septa (S2 and higher cycles) their upper margins bend and fuse with the neighboring members of a previous cycle, resulting in a unique septal pattern, formerly misinterpreted as “septal bifurcation.” Septa as in other Scleractinia are hexamerally arranged in cycles. However, starting from the quaternaries, septa within single cycles do not appear simultaneously but are inserted in pairs and successively flank the members of a preceding cycle, invariably starting from those in the outermost parts of the septal system. In each pair, the septum adjacent to older septa arises first (e.g., the quinaries between S2 and S4 before quinaries between S3 and S4). Unique features of micrabaciid skeletal ontogeny are congruent with their basal position in scleractinian phylogeny, which was previously supported by microstructural and molecular data. J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Circadian influences on feeding-induced changes in ACTH and corticosterone secretion in rats.

Food ingestion has a variable influence on pituitary-adrenal hormone secretion depending on the species studied and/or the experimental design. In this study, changes in plasma concentrations of ACTH and corticosterone following 30 min of food ingestion were compared in both 24 h fasted and ad libitum fed rats tested during either the early light cycle or the early dark cycle. In the dark, food ingestion caused significant decreases in both ACTH (to 80% of control) and corticosterone (to 32% of control) in both fasted and ad libitum fed rats. In contrast, in the light, food ingestion by the fasted animal resulted in a doubling of corticosterone concentrations. Such a response was not seen in ad libitum fed animals; however, these animals ate very little during the test. There were no significant changes in ACTH during the light phase. These data indicate that time of day has a significant impact on the responses of the pituitary-adrenal system to food ingestion. This circadian effect may be due to the influence of the endogenous levels of ACTH/corticosterone existing at the time of food ingestion.     

Effect of olfactory bulbectomy on plasma levels of glucose, lipids and corticosterone in the rat

The effect of bilateral olfactory bulbs removal on the peripheral glucose, lipids and corticosterone levels has been studied in Wistar male rats. After 30 days of the olfactory bulbectomy there was found: an increase in the basal values of plasmatic glucose, a significant increase in peripheral levels of the free fatty acids, and a notorius decrease in plasmatic corticosterone at 9 a.m. Other biochemical parameters, such as free glycerol, triglycerides and phospholipids, went unaltered. These after bulbectomy variations, especially the increase in free fatty acids, are discussed in relation to a possible role of the olfactory bulbs on the nutritional, endocrine and nervous factors, which are closely related to the mechanisms involved in the regulation of cellular lypolisis.     

Differential effect of adrenalectomy on rat liver metallothionein mRNA levels in basal and stress conditions.

Liver metallothionein (MT) mRNA and serum MT levels of adrenalectomized (ADX) and sham-ADX rats in basal and stress (1, 3 or 6 h of restraint) conditions have been measured. Serum MT levels were overall lower in ADX than in sham-ADX rats. Basal liver MT mRNA levels were increased in ADX rats, suggesting that glucocorticoids have an inhibitory role on the regulation of liver MT synthesis. In contrast, liver MT mRNA levels were increased by stress in sham-ADX but not in ADX rats, suggesting a stimulatory role for glucocorticoids. These results suggest that glucocorticoids have a different role in liver MT regulation depending on the physiological situation.     

Adrenal and plasma corticosterone levels in the pregnant, foetal and neonatal rat, in the perinatal period.

A group of pregnant control rats was sacrificed before parturition, in the morning, afternoon and evening of day 20 and 21 and in the morning of day 22. Another group was sacrificed during parturition, when 2 to 8 foetuses had been expelled. The onset of parturition occurred for the first rat in the afternoon of day 21 and for the last rat in the afternoon of day 22. Corticosterone was extracted from maternal, foetal and neonatal adrenals and plasma, and was assayed by a fluorometric procedure. The maternal adrenal and plasma corticosterone levels, before parturition, were lower in the morning than in the afternoon excepting day 22 when morning values were as high as those in the afternoon of day 21. Adrenal and plasma corticosterone concentrations were elevated during parturition in the mother but not the foetus. Plasma corticosterone values were raised in the newborn compared to their littermates in utero.     

Effects of dimaprit, an H2 receptor agonist, on blood levels of corticosterone in the rat

These experiments were performed in order to further clarify the role played by hystamine in the control of hypothalamus-hypophisis-adrenal axis. To this aim we evaluated the effect of Dimaprit, a H2 agonist on plasma corticosterone levels. This drug was administered intraperitoneally or i.c.v. at the doses of 25, 50 and 100 mg/kg or 100 gamma/animal respectively. The administration i.p. at the dose of 100 mg/kg increased plasma-corticosterone levels whereas Dimaprit, injected intraventricularly did not modify plasma-corticosterone levels. These results seem to suggest that Dimaprit stimulates corticosterone secretion at a peripheral level.     

Evoked potential correlates of early conditioning in the rat ontogeny.

In rats aged 2-8 weeks cortical EP to CS (20 flash - tone combinations, 0,9/sec, reinforced since the 10th application by electric shocks to the hind leg) were studied within different kinds of behavioral responses during avoidance learning and extinguishing. In contrast to our results in freely moving rats no developmental trend was found in this kind of avoidance (lifting of the hind leg). Average EP within reinforced trials (with escape or no reactions) differed in isolated application of CS from those when both CS and US were acting together. In younger animals the EP to CS combined with US were characterized by an evident late negative wave which shifted later (5-6 weeks toward the early negative complex. The EP changes in the auditory cortex were more pronounced, whereas visual EP with CS-US combination were rather decreased. In the youngest animals (2 weeks) the auditory EP within trials with avoidance were characterized by a distinct short latency deflection of the first positive wave, whereas in EP to extinguished CS the second deflection of the first positive wave prevailed. Also in these phenomena, the typical changes were clearly revealed in the auditory cortex. At later developmental stages (starting the 3rd, more prominently the 4th and 5th week) the wave following primary positive - negative complex was shifted toward the negativity if the animal responded by an avoidance; on the contrary an ample positive, often a double-peak wave arose if the response was extinguished. The stimulus and reaction dependence in the cortical EP showed the role of not yet fully mature cerebral cortex in avoidance learning. Both, fast as well as with some delay running processes participated in the observed phenomena during the ontogenetical development.     

The effect of transdermal corticosterone application on plasma corticosterone levels in pregnant Lacerta vivipara

Relationships between hormones and behaviour can be explored by altering endogenous hormone levels, often through implantation of silastic tubing or osmotic pumps filled with a hormone or its agonists or antagonists. However, organisms in sensitive life-history stages (such as pregnancy) may be adversely affected by the surgical procedures associated with these manipulations, necessitating use of non-invasive techniques. We demonstrate that the application of a sesame oil-corticosterone mixture to the skin of pregnant female common lizards (Lacerta vivipara) elevates plasma levels of the hormone. Pregnant female L. vivipara were captured and treated daily for 1-20 days with the sesame oil-corticosterone mixture (experimental group) or with vehicle only (control group). Blood samples were collected and analyzed for corticosterone by radioimmunoassay. Baseline plasma corticosterone levels were elevated within 1 h in the experimental group. Similar levels ( approximately 145 ng/ml) were found over the subsequent 2 days, and by day 5 had risen significantly higher ( approximately 281.9 ng/ml), where they remained for the duration of the experiment. These increases are comparable to those found in other species using related techniques. No significant changes in plasma corticosterone levels occurred in the control group. Finally, corticosterone levels also were determined for untreated females that were captured, held overnight, sampled, and released to access to the natural range of basal corticosterone levels. Basal plasma levels of corticosterone in pregnant females varied among individuals independently of female body size or corpulence.     

Effects of methamphetamine on daily rhythms of hypothalamic norepinephrine, serotonin and plasma corticosterone levels in the rat

The relationship between daily rhythms of hypothalamic norepinephrine (NE) and serotonin (5HT) contents and the circadian rhythm of plasma corticosterone (Comp. B) levels was studied in the rat. It was found that levels of hypothalamic NE, 5HT and plasma Comp. B exhibited distinct daily flucturations in the control condition. In animals treated with methamphetamine, the daily rhythms of hypothalamic 5HT contents and plasma Comp. B levels remained unchanged, whereas the daily rhythm of hypothalamic NE contents was completely abolished. As a result, it was suggested that the daily rhythm of hypothalamic NE is not functionally related to the circadian change of pituitary-adrenocortical activity.