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Chronically elevated levels of corticotropin-releasing hormone (CRH) are implicated in human stress-related and affective disorders, including generalized anxiety disorder and major depression. To gain more insight into the relationship between hyperactivity of the CRH system and associated neuroendocrine, autonomic, physiological, and behavioral changes, we have developed a transgenic mouse model of CRH overproduction (CRHOE). In this study, we explored the behavioral consequences of chronic CRH overproduction in mice of the two available transgenic lines (CRH-OE2122 and CRH-OE2123) in paradigms measuring behavioral aspects of stress, anxiety, and depression. These paradigms include tasks based on free exploration of novel environments (unfamiliar homecage and unfamiliar open field), stress-induced hyperthermia, tests associated with anxiety- related behavior (elevated plus maze and light-dark box), and paradigms in which (anti-)depressant-like behaviors can be detected (tail suspension test and forced swim test). The only relatively consistent finding, although not always significant, was reduced locomotor activity in CRH-OE2122 mice, corresponding well with the known effects of CRH on locomotion. Contrary to our predictions, CRH-OE mice did not show an altered response to stress, and a phenotype indicative of increased anxiety and/or depression was not evident in CRH-OE mice.

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. [ABSTRACT FROM AUTHOR]

The behavioral effects of corticotropin-releasing hormone (CRH) appear to depend on the baseline state of arousal of the animal. In this study, this hypothesis was tested using a 4-min maternal separation procedure in 7-day-old male and female mouse pups (outbred CFW strain). Two intensities of stress were used to assess the effects of intracerebroventricularly administered r/hCRH: a mild stress condition where the ambient temperature was close to nest temperature (30 °C) and rates of maternal separation-induced ultrasonic vocalizations (USVs) were relatively low (ca. 25/4 min), and a more stressful condition where the temperature was 19 °C and the rates of USVs were high (ca. 250/4 min). Differential effects of CRH on vocalization rate and locomotor behavior were observed to be dependent on the level of stress. In the more stressful 19 °C condition, r/hCRH dose-dependently reduced the number of USVs without affecting motor behavior, as indexed by grid crossings. In contrast, in the 30 °C condition, only the highest dose of r/hCRH reduced calling while r/hCRH activated motor behavior over a wider range of doses. These effects were independent of hypothalamus–pituitary–adrenal (HPA) axis activity, as measured by plasma corticosterone levels. The present study indicates that in mouse pups, the effects of CRH administration depend on baseline levels of arousal and that the behavioral effects of CRH administration can be dissociated under mild and more stressful conditions. [Copyright &y& Elsevier]