Neonatal exposure to a high level of ACTH4-10 impairs adult learning performance

Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties

Semax is a heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) that encompasses the sequence 4-7 of N-terminal domain of the adrenocorticotropic hormone and a C-terminal Pro-Gly-Pro tripeptide. N-terminal amino group acetylation (Ac-Semax) modulates the chemical and biological properties of parental peptide, modifying the ability of Semax to form complex species with Cu(II) ion. At physiological pH, the main complex species formed by Ac-Semax, [CuLH_-2]^2-, consists in a distorted CuN₃O chromophore with a weak apical interaction of the methionine sulphur. Such a complex differs from the Cu(II)-Semax complex system, which exhibits a CuN₄ chromophore. The reduced ligand field affects the [CuLH_-2]^2- formal redox potential, which is more positive than that of Cu(II)-Semax corresponding species. In the amino-free form, the resulting complex species is redox-stable and unreactive against ascorbic acid, unlike the acetylated form. Semax acetylation did not protect from Cu(II) induced toxicity on a SH-SY5Y neuroblastoma cell line, thus demonstrating the crucial role played by the free NH₂ terminus in the cell protection. Since several brain diseases are associated either to Cu(II) or Zn(II) dyshomeostasis, here we characterized also the complex species formed by Zn(II) with Semax and Ac-Semax. Both peptides were able to form Zn(II) complex species with comparable strength. Confocal microscopy imaging confirmed that peptide group acetylation does not affect the Zn(II) influx in neuroblastoma cells. Moreover, a punctuate distribution of Zn(II) within the cells suggests a preferred subcellular localization that might explain the zinc toxic effect. A future perspective can be the use of Ac-Semax as ionophore in antibody drug conjugates to produce a dysmetallostasis in tumor cells.

Endogenous cortisol suppression with metyrapone enhances acoustic startle in healthy subjects

Previous human studies have shown that excess cortisol sufficient to fully occupy central nervous system (CNS) corticosteroid receptors may reduce startle eye blink. The present study tested whether cortisol depletion and the resulting reduction in activity of CNS corticosteroid receptors has the opposite effect. In a single-blind, placebo-controlled, randomized study, eye blink EMG responses to 105 dB acoustic startle stimuli were assessed in 25 healthy subjects who received oral metyrapone (1500 mg) to suppress endogenous cortisol production, while 24 controls received oral placebo. As expected, metyrapone significantly reduced salivary cortisol, indicating effective endogenous cortisol suppression. Startle eye blink responses were significantly increased in the metyrapone group. Short-term habituation of the startle reflex was not different between groups. Our results suggest that startle is enhanced during depletion of cortisol. This effect may be mediated by CNS mechanisms controlling cortisol feedback.

The impact of corticosteroids on the developing animal

Infants are subjected to both endogenous and exogenous corticosteroids in the pre- and postnatal periods. Stress to the mother before birth, or to the child postpartum, can give rise to high, chronic endogenous corticosteroid levels caused by activation of the hypothalamic-pituitary-adrenal (HPA) axis. Physician-administered exogenous corticosteroids are also used in the management of a wide spectrum of pre- and postnatal conditions. The long-term effects of corticosteroids in developing humans are not well known. Studies in animals, however, indicate that both natural stress and exogenous corticosteroids can have long-lasting and deleterious effects on the body, brain, behavior, and hypothalamic-pituitary-adrenal axis of developing infants. These data suggest that exogenous corticosteroids should be administered with caution, after careful benefit/risk analyses, and that, as far as possible, the developing brain should be protected against the effects of pre- and postnatal stress.

Exogenous cortisol exerts effects on the startle reflex independent of emotional modulation

Exogenous cortisol's modulation of the acoustic startle reflex (ASR) was tested alone and during exposure to affectively valenced photographs in healthy men and women. During nonmodulated startle, oral hydrocortisone had a biphasic dose effect, with 5 mg increasing and 20 mg decreasing, eyeblink reflex magnitude compared to placebo. During emotion modulation, 20 mg of hydrocortisone reduced reflex magnitude without affecting the usual pattern of modulation across positive, neutral, and negatively affective slides. Gender differences were not found in either relationship. These findings illustrate dose-dependent effects of cortisol on the startle pathway independent of emotional state and consistent across genders.

Decreased postnatal testosterone and corticosterone concentrations in rats following acute intermittent prenatal hypoxia without alterations in adult male sex behavior

The prenatal and postnatal testosterone surges in the male rat are associated with neurobehavioral sexual differentiation of the brain. Both surges can be attenuated by maternal stress or other environmental factors that activate the maternal and/or fetal hypothalamic/pituitary/adrenal (HPA) axis during the last week of gestation. Since hypoxia is known to activate the HPA axis, we studied its effect during gestation on sexual differentiation in the male rat. We examined the influence of intermittent hypoxic exposure during gestation with respect to the postnatal testosterone surge and corticosterone levels, and subsequent development of adult reproductive and nonreproductive sexually dimorphic behaviors. Plasma testosterone and corticosterone concentrations of male neonates were measured after maternal exposure to acute, intermittent, prenatal hypoxia (9% O2 6 h/day from Day 15 to 21 of gestation). Relative to normoxic controls, acute, intermittent, prenatal hypoxia significantly attenuated the postnatal testosterone surge. Postpartum plasma corticosterone levels in these animals were also suppressed. In adulthood, prenatally hypoxic animals exhibited normal masculine sex behavior. Lordosis behavior in response to estrogen and progesterone priming was not significantly different between treatment groups. Saccharin preference, a nonreproductive, sexually dimorphic behavior, was not significantly influenced by prenatal hypoxic exposure. These results demonstrate that in the male acute intermittent prenatal hypoxia attenuates the postnatal testosterone surge. However, this reduction failed to result in significant alterations in the expression of sex related behaviors in adulthood.

Altered adult sexual behavior in the male rat following chronic prenatal hypoxia

The last week of gestation is a critical period for the sexual differentiation of the brain in the rat. Exposure to prenatal stress during this period has been shown to demasculinize and/or feminize adult male sexual behavior. Many of the neurochemical and endocrine responses to hypoxia are similar to that observed under stressful conditions such as restraint stress. Therefore, we examined the postnatal consequences on reproductive and nonreproductive sexually dimorphic behaviors in male offspring of dams exposed to chronic hypoxia during the last week of gestation. In addition, we examined sensorimotor development in offspring of both sexes. Pregnant Sprague-Dawley dams were exposed to continuous hypoxia (10.5% O2 from gestational day 15 to 21). Offspring were weaned at 22 days of age and group housed. Behavioral tests were conducted with littermate representatives. In adulthood, male rats prenatally exposed to hypoxia had significantly delayed initiation latencies of masculine sexual behavior and decreased number of ejaculations, but did not display a significant increase in feminine sex behavior potentials. Developmentally, animals exposed to prenatal hypoxia did not differ significantly from controls with respect to day of eye or ear opening, or the in times of righting reflex, negative geotaxis or cliff avoidance. Wire hanging latencies in hypoxic exposed animals were significantly greater than controls around the time of eye opening, but did not differ at earlier or later ages. A significant effect of hypoxia was detected on stride length at 95 days of age, but other aspects of gait patterns were similar to controls. No group differences in gait patterns were observed at 17 or 45 days of age. In addition, no significant differences were observed in open field activity, circadian locomotor activity, saccharin preference, or Morris water maze test. This hypoxia regimen did not influence the occurrence of the prenatal or postnatal surge of plasma testosterone. Overall, these results provide some evidence that, in males, mild, chronic prenatal hypoxia may result in incomplete masculinization of adult reproductive behavior in the absence of overt changes in perinatal testosterone surges.

Behavioral sequelae in young rats of acute intermittent antenatal hypoxia

Several studies have examined behavioral sequelae of acute or chronic pre- or postnatal hypoxia. However, few of these tested a large battery of behavioral functions, particularly those following relatively mild, intermittent hypoxia. Also, in few studies were the hypoxic pups cross-fostered or the experimenter blinded as to experimental group. In addition, in almost no studies were concomitant hypoxic-induced brain biochemicals measured. The present study tested the hypotheses that mild, intermittent antenatal hypoxia can lead to long-term alterations in neurobehavioral development, as well as neurochemical changes.

Prenatal inhibition of hypothalamic sex steroid uptake by cocaine: effects on neurobehavioral sexual differentiation in male rats

Several adrenergically active drugs have been shown to prevent the masculinizing and/or defeminizing effects of testosterone on brain sexual differentiation. We examined the ability of the neuronal norepinephrine uptake blocker, cocaine, to produce similar effects. The ability of cocaine to inhibit sex steroid incorporation into the hypothalamus during a critical period for sexual differentiation of the brain was examined in females treated at birth with testosterone. Sixty minutes after administration, cocaine was observed to inhibit both testosterone and estradiol incorporation into the hypothalamus by approximately 50%. Long-term consequences of prenatal cocaine exposure were studied by injecting Sprague-Dawley dams twice daily with 3, 10 or 30 mg/kg of cocaine hydrochloride on days 15 through 20 of gestation and examining the offspring. In adulthood, cocaine-exposed males, but not females were found to exhibit significantly less marking behavior than controls. Cocaine-exposed males in the 10 mg/kg group tested for sex behavior exhibited demasculinization in some aspects of the behaviors tested. Measurement of plasma hormone levels in this group revealed elevated levels of plasma LH, but normal levels of FSH and testosterone. No differences were observed in cocaine-exposed males with respect to sex organ or adrenal weights, but thymus was approximately 25% smaller compared to control males at 80 days of age. In a separate experiment, dams were treated with 3 mg/kg of cocaine twice daily from days 15 through 21 of gestation and half of the male pups received additional injections twice a day for the first 5 days postnatally.(ABSTRACT TRUNCATED AT 250 WORDS)

Pre- and postnatally administered ACTH, Organon 2766 and CRF facilitate or inhibit active avoidance task performance in young adult mice

This study investigated the effect of learning/memory-related neuropeptides on behavioral task performance in later life. A 1 mg/kg dosage of adrenocorticotropic hormone 4-9, Organon 2766, ACTH/MSH 4-10, ACTH 1-24, CRF, or diluent was subcutaneously injected into either pregnant females or into newborn pups during specific neural developmental windows. Each of the progeny was trained in an active-avoidance task and tested for acquisition on postpartum days 35-37. The mice were then tested for memory task performance and reacquisition on days 42-44 postpartum using the identical experimental paradigm as that used in the training sessions. Prenatal treatment with these memory-related neuropeptides resulted in significant facilitation of learning/memory task performance in male and female mice treated with Organon 2766 (p less than 0.001), and a significant inhibition of learning/memory task performance in males and females treated with ACTH 1-24 (p less than 0.01). Additional sex-specific performance facilitations and inhibitions resulted from the pre- or postnatal administration of the various neuropeptides used in this study. These results suggest that neuropeptides, when available in increased amounts during specific neural developmental windows, can significantly improve or suppress related behavioral performance capability in later life.

Alpha-melanocyte-stimulating hormone infusions during pregnancy in the rat: effects on offspring weight, pain reactivity and sexual behavior

Pregnant rats treated during the last third of pregnancy with a continuous infusion of alpha-melanocyte-stimulating hormone (alpha-MSH) produced offspring that weighed less at birth and in adulthood. These offspring of the alpha-MSH treated mothers were less sensitive to pain and as adults showed a reduced analgesic response to morphine. Male offspring of alpha-MSH treated mothers and of control animals responded similarly in sexual performance tests, except that the treated animals significantly shifted their pattern of responding when they encountered a new testing arena or experienced defeat. The offspring of alpha-MSH treated mothers were influenced more by changes in their environment than were control offspring. These effects are similar to those reported following perinatal treatment with opiate drugs or peptides.