Corticotropin-releasing hormone links pituitary adrenocorticotropin gene expression and release during adrenal insufficiency.

Corticotropin-releasing hormone (CRH)-deficient (KO) mice provide a unique system to define the role of CRH in regulation of the hypothalamic-pituitary-adrenal (HPA) axis. Despite several manifestations of chronic glucocorticoid insufficiency, basal pituitary proopiomelanocortin (POMC) mRNA, adrenocorticotrophic hormone (ACTH) peptide content within the pituitary, and plasma ACTH concentrations are not elevated in CRH KO mice. The normal POMC mRNA content in KO mice is dependent upon residual glucocorticoid secretion, as it increases in both KO and WT mice after adrenalectomy; this increase is reversed by glucocorticoid, but not aldosterone, replacement. However, the normal plasma levels of ACTH in CRH KO mice are not dependent upon residual glucocorticoid secretion, because, after adrenalectomy, these levels do not undergo the normal increase seen in KO mice despite the increase in POMC mRNA content. Administration of CRH restores ACTH secretion to its expected high level in adrenalectomized CRH KO mice. Thus, in adrenal insufficiency, loss of glucocorticoid feedback by itself can increase POMC gene expression in the pituitary; but CRH action is essential for this to result in increased secretion of ACTH. This may explain why, after withdrawal of chronic glucocorticoid treatment, reactivation of CRH secretion is a necessary prerequisite for recovery from suppression of the HPA axis.

Distinct regional and subcellular localization of adenylyl cyclases type 1 and 8 in mouse brain.

Adenylyl cyclases (ACs) convert ATP to cAMP and therefore, subserve multiple regulatory functions in the nervous system. AC1 and AC8 are the only cyclases stimulated by calcium and calmodulin, making them uniquely poised to regulate neuronal development and neuronal processes such as learning and memory. Here, we detail the production and application of a novel antibody against mouse AC1. Along with AC8 immunohistochemistry, these data reveal distinct and partially overlapping patterns of protein expression in brain during murine development and adulthood. AC1 protein increased in abundance in the neonatal hippocampus from postnatal days 7-14. By adulthood, abundant AC1 protein expression was observed in the mossy fiber tract in the hippocampus and the molecular layer in the cerebellum, with diffuse expression in the cortex and thalamus. AC8 protein levels were abundant during development, with diffuse and increasing expression in the hippocampus that intensified in the CA1/CA2 region by adulthood. AC8 expression was weak in the cerebellum at postnatal day 7 and decreased further by postnatal day 14. Analysis of synaptosome fractions from the adult brain demonstrated robust expression of AC1 in the postsynaptic density and extrasynaptic regions, while expression of AC8 was observed in the presynaptic active zone and extrasynaptic fractions. These findings were confirmed with localization of AC1 and/or AC8 with PSD-95, tau, synaptophysin and microtubule-associated protein-2 (MAP-2) expression throughout the brain. Together, these data provide insight into the functional roles of AC1 and AC8 in mice as reflected by their distinct localization in cellular and subcellular compartments.

Altered stress-induced anxiety in adenylyl cyclase type VIII-deficient mice.

Stress results in alterations in behavior and physiology that can be either adaptive or maladaptive. To define the molecular pathways involved in the response to stress further, we generated mice deficient (KO) in the calcium-stimulated adenylyl cyclase type VIII (AC8) by homologous recombination in embryonic stem cells. AC8 KO mice demonstrate a compromise in calcium-stimulated AC activity in the hippocampus, hypothalamus, thalamus, and brainstem. Hippocampal slices derived from AC8 KO mice fail to demonstrate CA1-region long-term depression after low-frequency stimulation, and AC8 KO mice also fail to activate CRE-binding protein in the CA1 region after restraint stress. To define the behavioral consequences of AC8 deficiency, we evaluated AC8 KO mice in the elevated plus-maze and open field. Although naive AC8 KO mice exhibit indices of anxiety comparable with that of wild-type mice, AC8 KO mice do not show normal increases in behavioral markers of anxiety when subjected to repeated stress such as repetitive testing in the plus-maze or restraint preceding plus-maze testing. These results demonstrate a novel role for AC8 in the modulation of anxiety.

Substrate and inhibitor specificity of the lactate carrier of human neutrophils.

The substrate and inhibitor specificity of the lactic acid (Lac) transport system of human neutrophils was investigated. The ability of a variety of compounds to inhibit the influx of [14C]lactate, presumably reflecting competition by substrate analogues for binding at the external translocation site, was taken as an index of affinity for the Lac carrier. pH-state techniques were utilized to assess transportability. Results indicate a relatively low order of selectivity, the neutrophil H+(+)lactate- cotransport system demonstrating a broad acceptance of short-chain unsubstituted and substituted alkyl monocarboxylates as well as aromatic monocarboxylates. There was a slight preference for oxo, Cl, and OH substituents over other groups at the two-position of short chain alkyl fatty acids: all were readily transported across the plasma membrane at rates approaching that of L-lactate itself. Aromatic acids were not transported inward by the carrier although these compounds did permeate via simple nonionic diffusion. The neutrophil Lac carrier can be blocked by a number of cyanocinnamate derivatives, the classical inhibitors of monocarboxylate transport in mitochondria, and by dithiol compounds and sulfhydryl-reactive agents. This constellation of biochemical properties is similar to the features that characterize other well described H+(+)lactate- cotransport systems in red blood cells, Ehrlich ascites tumor cells, hepatocytes, and cardiac sarcolemmal vesicles, although significant differences exist when comparisons are made to the Na(+)-dependent lactate transporter of the kidney proximal tubule.

Use of tributyltin to probe contribution of Cl(-)-HCO3- exchange to regulation of steady-state pHi in human neutrophils.

Organotin derivatives represent a class of artificial ionophores that mediate Cl(-)-OH- exchange and thereby facilitate the chemical equilibrium distribution of Cl- and H+ across biological membranes. Imposing different pH and Cl- gradients by varying extracellular pH (pHo) and extracellular [Cl-] in the presence of 1 microM tributyltin validated the above assumptions in human neutrophils. Under relatively alkaline conditions [intracellular pH (pHi) greater than or equal to 7.10 and pHo greater than or equal to 7.40], the cell's natural Cl(-)HCO3- exchanger mimicked the actions of the tributyltin compound and was the principal factor controlling steady-state pHi. However, with increasing extracellular acidification, there was a progressive deviation from the predicted equilibrium distribution in the case of the normal Cl(-)-HCO3- transport system, whereas tributyltin-treated cells followed theoretical expectations. Exposure of neutrophils to a number of inhibitors of Cl(-)-HCO3- exchange led to a fall in pHi, apparently confirming the impression that a net HCO3- influx through Cl(-)-HCO3- countertransport was chiefly responsible for maintaining steady-state pHi. However, this intracellular acidification could be satisfactorily ascribed to proton movements through a parallel pathway, namely nonionic diffusion of the free acid form of the drugs. These results imply that Cl(-)-HCO3- exchange is the dominant pH regulatory device only under relatively alkaline conditions and that other mechanisms in addition to Na(+)-H+ exchange are likely to play an important role in recovery from acidification and in maintaining steady-state pHi. The possibility that the lactate carrier may function in this capacity is discussed.

Interleukin-6 is an essential, corticotropin-releasing hormone-independent stimulator of the adrenal axis during immune system activation.

Glucocorticoids play a critical role in control of the cytokine response after immune challenge. Conversely, cytokines modulate glucocorticoid production by the hypothalamic-pituitary-adrenal axis. To define the potency and mechanism of interleukin-6 (IL-6) for augmentation of adrenal function, we exploited mice deficient in corticotropin-releasing hormone (CRH), IL-6, or both. Mice deficient in CRH action demonstrate severely impaired glucocorticoid production in response to psychological and metabolic challenge, but near normal responses to stressors that activate the immune system. In this paper, we demonstrate that IL-6 is essential for activation of the hypothalamic-pituitary-adrenal axis during immunological challenge in the absence of hypothalamic input from CRH. IL-6 receptors are present on pituitary corticotrophs and adrenocortical cells, consistent with the ability of IL-6 to bypass CRH in augmentation of adrenal function. Plasma corticosterone levels after bacterial lipopolysaccharide injection in mice deficient in CRH or IL-6 were significantly lower than in wild-type mice but significantly greater than in mice deficient in both CRH and IL-6. A second model of immune system activation using 2C11, an antibody to the T cell receptor, demonstrated a normal corticosterone response in mice deficient in CRH or IL-6, but a markedly decreased response in mice deficient in both CRH and IL-6. Surprisingly, the relative contribution of IL-6 for modulation of the adrenal response to stress is greater in female than in male mice. This gender-specific difference in IL-6 action in mice suggests the utility of further analysis of IL-6 in determining the female predominance seen in many human inflammatory/autoimmune diseases.

Pituitary-adrenal axis regulation in CRH-deficient mice.

Corticotropin-releasing hormone (CRH)-deficient (knockout (KO)) mice demonstrate severely impaired adrenal responses to restraint, ether, and fasting, and lack the normal diurnal glucocorticoid (GC) rhythm. Here, we summarize recent studies determining the role of CRH in augmenting plasma adrenocorticotrophic hormone (ACTH) concentration after glucocorticoid withdrawal and pituitary-adrenal axis stimulation in the context of inflammation. Even though GC insufficient, basal pituitary proopiomelanocortin (POMC) mRNA, ACTH peptide content within the pituitary, and plasma ACTH concentrations are not elevated in CRH KO mice. POMC mRNA content in CRH KO mice increases following adrenalectomy, and this increase is reversed by GC, but not aldosterone, replacement. In marked contrast to the increase in POMC mRNA, plasma ACTH does not increase in the CRH KO mice following adrenalectomy. Administration of CRH to adrenalectomized CRH KO mice results in acute, robust ACTH secretion. Thus, loss of GC feedback can increase POMC gene expression in the pituitary, but CRH action is essential for increased secretion of ACTH into the circulation. While GC secretion is impaired in CRH KO mice after most stimuli, we have found near-normal GC responses to inflammation and systemic immune challenge. Studies in mice with CRH and IL-6 deficiency reveal that IL-6 is essential for activation of the pituitary-adrenal axis during inflammatory and other stressors in the absence of CRH.

Oxytocin modulates the onset of murine parturition by competing ovarian and uterine effects.

Recent analysis of mice deficient in both oxytocin (OT) and cyclooxygenase-1 has shown that OT exerts significant effects on both the ovarian corpus luteum and the uterine myometrium during pregnancy. To better define the roles of OT during pregnancy, we evaluated OT action and OT receptor regulation in wild-type and OT-deficient knockout (KO) mice. Continuous infusion of OT revealed that OT can either delay labor at low doses or initiate preterm labor at high doses. The infusion rates of OT necessary for these effects were reduced in OT KO mice. The dose of OT that delayed labor also delayed the normal decrease in plasma progesterone late in gestation, implicating a primary effect on the corpus luteum. Consistent with this hypothesis, luteal OT receptor expression exceeded that of the myometrium until luteolysis occurred. We propose that the downregulation of OT receptors in the corpus luteum and induction of OT receptors in the myometrium serve to shift the predominant consequence of OT action during murine pregnancy from labor inhibition to labor promotion.

Knock-ins and conditional knockouts: in vivo analysis of glucocorticoid receptor regulation and function.

To determine the cellular targets for glucocorticoid (GC) action, we have generated mice in which a green fluorescent protein-glucocorticoid receptor (GFP-GR) fusion gene is knocked into the endogenous GR locus. We found that GFP-GR function is indistinguishable from endogenous GR on both a cellular and systemic level. Furthermore, the green fluorescence intensity of the GFP-GR protein is proportional to its expression, allowing quantitation of GR expression in single living cells. We initiated our analysis of GR regulation in the thymus. Using multicolor flow cytometry, we found that GR expression is uniform among embryonic thymocyte subpopulations, but gradually "matures" over a three-week period after birth. In the adult, analysis of GFP-GR expression on RAG2-/- and HY T cell receptor (TCR) transgenic genetic backgrounds, showed that GR is induced to high levels in immature CD25+ CD4- CD8- thymocytes and down-regulated by activation of the pre-TCR during positive but not negative selection. Additionally, relative GR expression is dissociated from GC-induced apoptosis in vivo. These results implicate pre-TCR signaling as a mechanism for GR down-regulation and separate receptor abundance from susceptibility to apoptosis across thymocyte populations.

Inhibition of cyclooxygenase-2 prevents inflammation-mediated preterm labor in the mouse.

Prostaglandins (PGs) have proven important during parturition, but inhibition of PG production treating preterm labor (PTL) results in significant maternal and fetal side effects. We hypothesize that specific inhibition of either cyclooxygenase (COX)-1 or -2 may result in separation of therapeutic and toxic effects. We demonstrate that COX-2, but not COX-1, is induced during inflammation-mediated PTL caused by lipopolysaccharide (LPS) administration. A two- to threefold increase in uterine and ovarian PG concentrations coincides with this induction of COX-2. The COX-2-selective inhibitor SC-236 proved effective in stopping preterm delivery and the increases in PGs. The COX-1-selective inhibitor SC-560 also attenuated uterine and ovarian PG production after LPS but did not inhibit PTL as efficiently as SC-236. COX-1-deficient mice, which show delay in the onset of term labor, exhibited no delay in onset of PTL after LPS. These findings suggest that the mechanisms for initiation of inflammation-mediated PTL and term labor differ and that selective COX-2 inhibition may provide a means of stopping inflammation-induced PTL in humans.

The 5'-flanking region of the mouse adenylyl cyclase type VIII gene imparts tissue-specific expression in transgenic mice.

The calcium-stimulated adenylyl cyclases (ACs) play a central role in stimulus-dependent modification of synaptic function. The type VIII AC (AC8) is one of three mammalian calcium-stimulated isoforms, each of which is expressed in a region-specific manner in the CNS. To delineate the DNA sequences responsible for appropriate targeting of AC8 expression, we report here the complete structure of the AC8 gene and define the pattern of expression of the full-length cDNA and its splice variants. In addition to expression within the brain, robust expression of AC8 was also found in the lung. By in situ hybridization, we have found the highest expression of AC8 mRNA within the olfactory bulb, thalamus, habenula, cerebral cortex, and hypothalamic supraoptic and paraventricular nuclei. By generating transgenic mice whose expression of beta-galactosidase is controlled by the AC8 5'-flanking DNA sequences, we demonstrate that the DNA sequences within the 10 kb preceding exon 1 are critical for establishment of this region-specific pattern. This spectrum of sites of production is unique to AC8 among the calcium-stimulated adenylyl cyclases and suggests nonredundant functions with other adenylyl cyclases in neuroendocrine regulation and/or behavior.

Oxytocin mediates stress-induced analgesia in adult mice.

As a neurohormone and as a neurotransmitter, oxytocin has been implicated in the stress response. Descending oxytocin-containing fibres project to the dorsal horn of the spinal cord, an area important for processing nociceptive inputs. Here we tested the hypothesis that oxytocin plays a role in stress-induced analgesia and modulates spinal sensory transmission. Mice lacking oxytocin exhibited significantly reduced stress-induced antinociception following both cold-swim (10 degrees C, 3 min) and restraint stress (30 min). In contrast, the mice exhibited normal behavioural responses to thermal and mechanical noxious stimuli and morphine-induced antinociception. In wild-type mice, intrathecal injection of the oxytocin antagonist dOVT (200 microM in 5 microl) significantly attenuated antinociception induced by cold-swim. Immunocytochemical staining revealed that, in the mouse, oxytocin-containing neurones in the paraventricular nucleus of the hypothalamus are activated by stress. Furthermore, oxytocin-containing fibres were present in the dorsal horn of the spinal cord. To test whether descending oxytocin-containing fibres could alter nociceptive transmission, we performed intracellular recordings of dorsal horn neurones in spinal slices from adult mice. Bath application of oxytocin (1 and 10 microM) inhibited excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. This effect was reversed by the oxytocin antagonist dOVT (1 microM). Whole-cell recordings of dorsal horn neurones in postnatal rat slices revealed that the effect of oxytocin could be blocked by the addition of GTP-gamma-S to the recording pipette, suggesting activation of postsynaptic oxytocin receptors. We conclude that oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission.

Opposing actions of prostaglandins and oxytocin determine the onset of murine labor.

Prostaglandins (PGs) have been recently proven essential for parturition in mice. To dissect the contributions of the two cyclooxygenase (COX) isoforms to the synthesis of PGs during pregnancy, we have characterized the parturition phenotype of COX-1-deficient mice. We find that mice with targeted disruption of the COX-1 gene have delayed parturition resulting in neonatal death. Results of matings of COX-1-deficient females with COX-1 intact males, and blastocyst transfer of COX-1-deficient or -intact embryos into wild-type foster mothers, proved necessity and sufficiency of maternal COX-1 for the normal onset of labor. COX-1 expression is induced in gravid murine uterus and by in situ hybridization; this induction is localized to the decidua. Measurement of uterine PGs further confirmed that COX-1 accounted for the majority of PGF2alpha production. To evaluate the interaction of PGs with oxytocin during murine labor, we generated mice deficient in both oxytocin and COX-1. Surprisingly, the combined oxytocin and COX-1-deficient mice initiated labor at the normal time. COX-1-deficient mice demonstrated impaired luteolysis, as evidenced by elevated serum progesterone concentration and ovarian histology late in gestation, and delayed induction of uterine oxytocin receptors. In contrast, simultaneous oxytocin and COX-1 deficiency restored the normal onset of labor by allowing luteolysis in the absence of elevated PGF2alpha production. These findings demonstrate that COX-1 is essential for normal labor in the mouse, with a critical function being to overcome the luteotrophic action of oxytocin in late gestation.

Proliferation and differentiation defects during lung development in corticotropin-releasing hormone-deficient mice.

Corticotropin-releasing hormone-deficient (CRH-KO) mice, which as a consequence are also glucocorticoid-insufficient, exhibit neonatal lethality when derived from CRH-KO mothers. Death is due to respiratory insufficiency as a result of abnormal pulmonary development, and can be prevented by prenatal administration of glucocorticoids. In the study described here, we used CRH-KO mice as a model of genetically altered in utero glucocorticoid action to elucidate the role of endogenous glucocorticoids in lung maturation. The histologic appearance of the lungs of these mice is normal until Day 17.5 of gestation, at which point failure of septal thinning and air-space formation is observed. These morphologic alterations in the CRH-KO mouse lung are the result of continued cell division in cellular compartments that by this time in gestation have ceased proliferating in wild-type mice, rather than the result of a failure of apoptosis. In accord with this observation, the CRH-KO lung exhibits delayed induction of type II pneumocyte biochemical parameters, such as messenger RNAs (mRNAs) for surfactant protein-A (SP-A) and SP-B, and fatty acid synthase, as well as delayed Clara cell maturation. In contrast, surfactant phospholipid synthesis is not impaired during CRH-KO lung development. Our findings indicate that an essential role of endogenous glucocorticoids in pulmonary maturation in utero is to stimulate a developmental program in late gestation that affects epithelial and mesenchymal cell proliferation and differentiation throughout the parenchyma.