Glucocorticoid antagonists and the role of glucocorticoids at the resting and stress state

Neuroanatomical pathways underlying the effects of hypothalamo-hypophysial-adrenal hormones on exploratory activity

When injected via the intracerebroventricular route, corticosterone-releasing hormone (CRH) reduced exploration in the elevated plus-maze, the center region of the open-field, and the large chamber in the defensive withdrawal test. The anxiogenic action of CRH in the elevated plus-maze also occurred when infused in the basolateral amygdala, ventral hippocampus, lateral septum, bed nucleus of the stria terminalis, nucleus accumbens, periaqueductal grey, and medial frontal cortex. The anxiogenic action of CRH in the defensive withdrawal test was reproduced when injected in the locus coeruleus, while the amygdala, hippocampus, lateral septum, nucleus accumbens, and lateral globus pallidus contribute to center zone exploration in the open-field. In addition to elevated plus-maze and open-field tests, the amygdala appears as a target region for CRH-mediated anxiety in the elevated T-maze. Thus, the amygdala is the principal brain region identified with these three tests, and further research must identify the neural circuits underlying this form of anxiety.

Leptin mediates Clostridium difficile toxin A-induced enteritis in mice

BACKGROUND & AIMS

Leptin regulates energy homeostasis and participates in the regulation of the hypothalamic-pituitary-adrenal axis. Although hyperleptinemia is described in experimental colitis, its role in the pathophysiology of enterotoxin-mediated diarrhea and inflammation remains unclear. We examined the role of leptin in the inflammatory diarrhea induced by toxin A from Clostridium difficile, the causative agent of antibiotic-related colitis.

METHODS

Toxin A (10 microg) or buffer were administered in ileal loops of leptin-deficient (ob/ob), leptin-resistant (db/db), or wild-type mice and enterotoxic responses were measured.

RESULTS

In toxin A-treated wild-type mice, circulating leptin and corticosterone levels were increased compared with buffer-injected animals. Toxin A also stimulated increased mucosal expression of the Ob-Rb at the messenger RNA (mRNA) and protein level. Ob/ob and db/db mice were partially protected against toxin A-induced intestinal secretion and inflammation, and this effect was reversed by leptin administration in ob/ob, but not db/db, mice. Basal- and toxin A-stimulated plasma corticosterone levels in ob/ob and db/db mice were higher compared with toxin A-treated wild-type mice. To assess whether the effect of leptin in intestinal inflammation is mediated by corticosteroids we performed adrenalectomy experiments in db/db and wild-type mice. Our results suggested that the diminished intestinal response to toxin A in db/db mice was related only in part to increased levels of corticosteroids.

CONCLUSIONS

Leptin plays an important role in regulating the severity of enterotoxin-mediated intestinal secretion and inflammation by activating both corticosteroid-dependent and -independent mechanisms.

Effects of the circadian rhythm of corticosteroids on leukocyte-endothelium interactions in the AM and PM

Circadian rhythms are responsible for a number of key cycles within the body. In vivo microscopy was used to investigate the hypothesis that the circadian rhythm of corticosterone in rats produces different leukocyte-endothelium interactions throughout the day. The data indicate that corticosterone levels range from 12 ng/ml in the AM to 260 ng/ml in the PM. In contrast, the number of circulating polymorphonuclear leukocytes (PMNs) yields peak values in the AM (630 PMNs/microl) and trough values in the PM (262 PMNs/microl). During surgical stress there is a significant increase in the number of circulating PMNs in the PM but little change in the AM. Furthermore, there is significantly greater leukocyte-endothelium adhesion in the PM (5.2 cells/100 microm) than in the AM (2.9 cells/100 microm). Addition of the chemoattractant FMLP increased adhesion 125% in the AM but only 62% in PM. Both exogenous glucocorticoid supplementation for 2 weeks and bilateral adrenalectomy abolished the circadian rhythms of circulating PMNs, the number of sticking white blood cells and the initial stages of an acute inflammatory response. These findings suggest that the circadian rhythm of corticosterone alters leukocyte-endothelium interactions throughout the day.