No abstract

To gain a greater insight into the relationship between hyperactivity of the corticotropin-releasing hormone (CRH) system and autonomic and physiological changes associated with chronic stress, we developed a transgenic mouse model of central CRH overproduction. The extent of central and peripheral CRH overexpression, and the amount of bioactive CRH in the hypothalamus were determined in two lines of CRH-overexpressing (CRH-OE) mice. Furthermore, 24 h patterns of body temperature, heart rate, and activity were assessed using radiotelemetry, as well as cumulative water and food consumption and body weight gain over a 7-day period. CRH-OE mice showed increased amounts of CRH peptide and mRNA only in the central nervous system. Despite the presence of the same CRH transgene in their genome, only in one of the two established lines of CRH-OE mice (line 2122, but not 2123) was overexpression of CRH associated with increased levels of bioactive CRH in the hypothalamus, increased body temperature and heart rate (predominantly during the light (inactive) phase of the diurnal cycle), decreased heart rate variability during the dark (active) phase, and increased food and water consumption, when compared with littermate wildtype mice. Because line 2122 of the CRH transgenic mice showed chronic stress-like neuroendocrine and autonomic changes, these mice appear to represent a valid animal model for chronic stress and might be valuable in the research on the consequences of CRH excess in situations of chronic stress.

The pituitary melanotrope cell of Xenopus laevis displays cytosolic Ca2+ oscillations that arise for the interplay between the burst-like openings of voltage-operated Ca2+ channels and Ca2+-extrusion mechanisms. We have previously shown that Ca2+-extrusion rates increase with increases in [Ca2+]i, suggesting that Ca2+ itself plays a role in shaping the Ca2+ oscillations. The purpose of the present study was to test this hypothesis by manipulating the intracellular Ca2+ buffering capacity of the cell and determining the consequences of such manipulations for the shape of the Ca2+ oscillations. We manipulated the cytosolic buffering capacity by loading the fast Ca2+ chelator BAPTA into cells. During loading the [Ca2+]i was dynamically imaged with confocal laser scanning microscopy. The basal [Ca2+]i was reduced with BAPTA loading and this reduction was associated with lower Ca2+-extrusion rates, a broadening of the Ca2+ oscillations and declined oscillation frequencies. Short loading periods of the buffer led to new, stable patterns of Ca2+ signaling and to reduced but stable levels of peptide secretion. We propose that the cytosolic Ca2+ buffer capacity, and thus by inference the profile of intracellular Ca2+ buffering proteins, is an important factor in setting the frequency and shape of Ca2+ oscillations.