Rapid membrane effect of estrogens on stimulation of corticotropin-releasing hormone.

BACKGROUND: Classic nuclear-initiated estrogen signaling stimulates corticotropin-releasing hormone (CRH) gene expression as a transcription factor. However, the possible mechanism by which membrane-initiated estrogen signaling (MIES) influences CRH expression remains unclear. There are indications that MIES may upregulate nitric oxide (NO) production through the phosphatidylinositol 3-hydroxy kinase (PI3K) and potentially through the mitogen-activated protein kinase (MAPK) pathway. OBJECTIVES: We investigated the effect of MIES-mediated kinase pathways on CRH expression with or without NO synthesis. METHOD: In SK-N-SH cell culture, estradiol-bovine serum albumin (E2-BSA) was used as the specific membrane estrogen receptor activator, with a specific NO donor, and/or inhibitors for NO synthase (NOS), PI3K, MAPK, protein kinase A (PKA), and protein kinase C (PKC). RESULTS: E2-BSA significantly increased NO and CRH levels in the medium and NOS1-mRNA levels in the cells. In addition, NO donor up-regulated CRH expression, while NOS-inhibitor down-regulated it. When the inhibitor of MAPK and/or the inhibitor of PI3K was added to the medium, only the latter appeared to significantly block the stimulating effect of E2-BSA on NO synthesis, and this was accompanied by an increased CRH expression in the medium. We further studied the effect of the MIES-PKC-mediated pathway on CRH expression, with or without NOS-inhibitor, while the MIES-PKA(-PI3K) pathway served as a control. We found that MIES-PKC upregulated CRH expression independent of NO synthesis. CONCLUSION: MIES can efficiently upregulate CRH expression via various intracellular kinase pathways and may thus be a crucial component in the stress response.

Sex hormones affect acute and chronic stress responses in sexually dimorphic patterns: Consequences for depression models.

BACKGROUND: Alterations in peripheral sex hormones may play an important role in sex differences in terms of stress responses and mood disorders. It is not yet known whether and how stress-related brain systems and brain sex steroid levels fluctuate in relation to changes in peripheral sex hormone levels, or whether the different sexes show different patterns. We aimed to investigate systematically, in male and female rats, the effect of decreased circulating sex hormone levels following gonadectomy on acute and chronic stress responses, manifested as changes in plasma and hypothalamic sex steroids and hypothalamic stress-related molecules. METHOD: Experiment (Exp)-1: Rats (14 males, 14 females) were gonadectomized or sham-operated (intact); Exp-2: gonadectomized and intact rats (28 males, 28 females) were exposed to acute foot shock or no stressor; and Exp-3: gonadectomized and intact rats (32 males, 32 females) were exposed to chronic unpredictable mild stress (CUMS) or no stressor. For all rats, plasma and hypothalamic testosterone (T), estradiol (E2), and the expression of stress-related molecules were determined, including corticotropin-releasing hormone, vasopressin, oxytocin, aromatase, and the receptors for estrogens, androgens, glucocorticoids, and mineralocorticoids. RESULTS: Surprisingly, no significant correlation was observed in terms of plasma sex hormones, brain sex steroids, and hypothalamic stress-related molecule mRNAs (p > 0.113) in intact or gonadectomized, male or female, rats. Male and female rats, either intact or gonadectomized and exposed to acute or chronic stress, showed different patterns of stress-related molecule changes. CONCLUSION: Diminished peripheral sex hormone levels lead to different peripheral and central patterns of change in the stress response systems in male and female rats. This has implications for the choice of models for the study of the different types of mood disorders which also show sex differences.

Effect of pentobarbital and isoflurane on acute stress response in rat.

BACKGROUND: Anesthesia administration before sacrificing animals is a common practice in stress-related studies, but the effect of anesthesia on the results remains understudied. We aimed to reveal the interference of different anesthetics, i.e. intraperitoneal (i.p.) sodium-pentobarbital injection or isoflurane inhalation, with the acute stress responses in rats. METHODS: Rats were randomly divided into foot shock (FS) and non-stressed control groups, and further grouped according to the sacrificing procedure: direct decapitation, decapitation after i.p. sodium-pentobarbital injection, or isoflurane inhalation. There was also a non-stressed group sacrificed by decapitation following i.p. saline injection. Plasma levels of corticosterone (CORT), testosterone and estradiol, hypothalamic stress-related molecule mRNA expression of corticotropin-releasing hormone, arginine vasopressin and oxytocin, and frontal lobe stress-related molecule mRNA expression of NMDA receptor subunit NR2B, GABAA receptor and the neuronal-type nicotinic acetylcholine receptor were measured. RESULTS: FS significantly increased plasma CORT levels in direct decapitation and isoflurane groups, while this stress response 'disappeared' following i.p. sodium-pentobarbital injection. In control animals, both the injection of saline and pentobarbital caused a significant increase of plasma CORT. Neither the sex hormone levels nor the mRNA expression of stress-related molecules in the brain showed significant differences among the groups. CONCLUSION: The injection of the anesthetic compound rather than the compound itself may cause extra stress which interferes with the plasma CORT levels, but not with plasma sex hormone levels nor with the brain mRNA expression. Isoflurane inhalation leaves the stress response intact and is also optimal from an ethical point of view.

Sex differences in the stress response in SD rats.

Sex differences play an important role in depression, the basis of which is an excessive stress response. We aimed at revealing the neurobiological sex differences in the same study in acute- and chronically-stressed rats. Female Sprague-Dawley (SD) rats were randomly divided into 6 groups: chronic unpredictable mild stress (CUMS), acute foot shock (FS) and controls, animals in all 3 groups were sacrificed in proestrus or diestrus. Male SD rats were randomly divided into 3 groups: CUMS, FS and controls. Comparisons were made of behavioral changes in CUMS and control rats, plasma levels of corticosterone (CORT), testosterone (T) and estradiol (E2), and of the hypothalamic mRNA-expression of stress-related molecules, i.e. estrogen receptor α and ß, androgen receptor, aromatase, mineralocorticoid receptor, glucocorticoid receptor, corticotropin-releasing hormone, arginine vasopressin and oxytocin. CUMS resulted in disordered estrus cycles, more behavioral and hypothalamic stress-related molecules changes and a stronger CORT response in female rats compared with male rats. Female rats also showed decreased E2 and T levels after FS and CUMS, while male FS rats showed increased E2 and male CUMS rats showed decreased T levels. Stress affects the behavioral, endocrine and the molecular response of the stress systems in the hypothalamus of SD rats in a clear sexual dimorphic way, which has parallels in human data on stress and depression.