The actions of corticotropin-releasing hormone (Crh), a mediator of endocrine and behavioural responses to stress, and the related hormone urocortin (Ucn) are coordinated by two receptors, Crhr1 (encoded by Crhr) and Crhr2. These receptors may exhibit distinct functions due to unique tissue distribution and pharmacology. Crhr-null mice have defined central functions for Crhr1 in anxiety and neuroendocrine stress responses. Here we generate Crhr2-/- mice and show that Crhr2 supplies regulatory features to the hypothalamic-pituitary-adrenal axis (HPA) stress response. Although initiation of the stress response appears to be normal, Crhr2-/- mice show early termination of adrenocorticotropic hormone (Acth) release, suggesting that Crhr2 is involved in maintaining HPA drive. Crhr2 also appears to modify the recovery phase of the HPA response, as corticosterone levels remain elevated 90 minutes after stress in Crhr2-/- mice. In addition, stress-coping behaviours associated with dearousal are reduced in Crhr2-/- mice. We also demonstrate that Crhr2 is essential for sustained feeding suppression (hypophagia) induced by Ucn. Feeding is initially suppressed in Crhr2-/- mice following Ucn, but Crhr2-/- mice recover more rapidly and completely than do wild-type mice. In addition to central nervous system effects, we found that, in contrast to wild-type mice, Crhr2-/- mice fail to show the enhanced cardiac performance or reduced blood pressure associated with systemic Ucn, suggesting that Crhr2 mediates these peripheral haemodynamic effects. Moreover, Crhr2-/- mice have elevated basal blood pressure, demonstrating that Crhr2 participates in cardiovascular homeostasis. Our results identify specific responses in the brain and periphery that involve Crhr2.

Toll-like receptor (TLR) proteins mediate cellular activation by microbes and microbial products. To delineate the role of TLR proteins in the development of host immune responses against mycobacteria, wild-type and TLR-deficient mice were infected with nonpathogenic Mycobacterium bovis bacillus Calmette-Guerin (BCG). Two weeks after intraperitoneal challenge with BCG, few bacilli were present in the lungs of wild-type and TLR4(-/-) mice, whereas bacterial loads were tenfold higher in the lungs of infected TLR2(-/-) mice. BCG challenge in vitro strongly induced proinflammatory cytokine secretion by macrophages from wild-type and TLR4(-/-) mice but not by TLR2(-/-) macrophages. In contrast, intracellular uptake, intracellular bacterial growth, and suppression of intracellular bacterial growth in vitro by interferon-gamma (IFN-gamma) were similar in macrophages from all three mouse strains, suggesting that BCG growth in the lungs of TLR2(-/-) mice was a consequence of defective adaptive immunity. Antigenic stimulation of splenocytes from infected wild-type and TLR4(-/-) mice induced T cell proliferation in vitro, whereas T cells from TLR2(-/-) mice failed to proliferate. Unexpectedly, activated CD4(+) T cells from both TLR-deficient mouse strains secreted little IFN-gamma in vitro compared with control T cells. A role for TLR4 in the control of bacterial growth and IFN-gamma production in vivo was observed only when mice were infected with higher numbers of BCG. Thus, TLR2 and TLR4 appear to regulate distinct aspects of the host immune response against BCG.

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In mammals, the release of pituitary ACTH is stimulated by CRF. Two related peptides exist in nonmammalian vertebrates, sauvagine from frog skin and urotensin-I from the urophysis of teleost fish. Their related structures (approximately 50%) and capacity to stimulate the release of ACTH from mammalian and fish pituitaries has led to the proposal that sauvagine and urotensin-I are homologs of mammalian CRF. However, sauvagine does not appear to stimulate ACTH release in amphibians, although mammalian CRF (ovine) induces a potent response from amphibian pituitaries. This could indicate that the main function of sauvagine does not involve ACTH regulation and suggests that an additional CRF-like peptide exists in Amphibia. We report here the isolation of two highly homologous CRF-like genes from the frog, Xenopus laevis. Analysis of the expression pattern of these CRF-like genes revealed mRNA in splenic tissue and in the preoptic nucleus and paraventricular organ of the brain. The amino acid sequence of the mature peptide regions (1-41) of both X. laevis genes is strikingly conserved, sharing more than 93% homology with mammalian CRFs, yet only 50% homology with sauvagine. In view of the fact that these new amphibian CRF-like genes share far greater homology with mammalian CRF than that exhibited by sauvagine, we propose that the new Xenopus CRF-like genes are the amphibian counterparts to mammalian CRF. Thus, two members of the CRF family have now been identified in the Amphibia, namely CRF and sauvagine.

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