No abstract

Impaired cognitive function and enhanced activity of the hypothalamic-pituitary-adrenocortical system are among the cardinal symptoms of major depression in humans that resolve after successful antidepressant treatment. We used a transgenic mouse model expressing antisense RNA complementary to that of glucocorticoid receptor (GR) mRNA to test the hypothesis that reduced GR function can cause these clinical disturbances. The transgenic mice show profound behavioural changes in a number of animal tests that are indicative of cognitive impairment. These mice also have elevated plasma corticotropin concentrations in response to stress. After long-term treatment with moclobemide, a reversible inhibitor of monoamine oxidase type A that acts clinically as an antidepressant, both the behavioural deficits and the hormonal alterations disappeared. These observations suggest that a transgenic mouse with GR dysfunction may be a useful model for investigation of drug effects on the cognitive and neuroendocrine aspects of depression.

The effects of the tricyclic antidepressant amitriptyline on the rat hypothalamic-pituitary-adrenocortical (HPA) system were studied. The time-course experiments showed that amitriptyline, given via the drinking water (4.5 mg/kg.day), produces significant decreases (P < 0.05) in adrenal weight after 5 (-20%) and 7 weeks (-21%) of treatment. Hippocampal mineralocorticoid receptor (MR) levels were down-regulated at days 3 (-27%) and 7 (-20%), and transiently up-regulated at 2 (+40%), 5 (+74%), and 7 (+18%) weeks of treatment. Hippocampal glucocorticoid receptor (GR) levels were slightly down-regulated at days 3 (-8%) and 7 (-17%), transiently up-regulated by 26% at 5 weeks, and indistinguishable from controls after 7 weeks of treatment. MR levels were unchanged in the hypothalamus and neocortex, whereas hypothalamic GR concentrations were elevated and neocortical receptor levels were not altered. Dose-response experiments showed significant decreases in adrenal weight when rats were treated with 4.5 (-14%), 8.8 (-16%) and 14.5 (-13%) mg/kg.day antidepressant, but this applied only for the 4.5- (-14%) and 8.8- (-12%) mg/kg.day doses when the ratio of adrenal weight to body weight was considered. The dose-response relationship regarding hippocampal GR content displayed an inverted U-shaped curve, whereas this was less marked for MR levels. A dose of 4.5 mg/kg.day appeared to be optimal for the rise in MR as well as GR. Concerning the neuroendocrine implications of chronic antidepressant treatment, amitriptyline (5 weeks, 4.5 mg/kg.day) produced significant decreases in basal (ACTH, -47%; corticosterone, -31%) as well as stress (30 min novel environment)-induced plasma ACTH (-38%) and corticosterone (-57%) levels. Previous experiments have forwarded a role of limbic MR in the tonic control of basal HPA activity. Based on the present data, we hypothesize that during amitriptyline treatment a rise in limbic MR may be the initial phenomenon in a successively adjusting HPA system, as evidenced by the decreasing plasma hormone concentrations, declining adrenal size, and up-regulation of GR in particular brain regions.

We investigated whether non-abortive maternal infections would compromise fetal brain development and alter hypothalamic-pituitary-adrenocortical (HPA) axis functioning when adult. To study putative teratogenic effects of a T cell-mediated immune response versus an endotoxic challenge, 10-d-pregnant rats received a single intraperitoneal injection of 5 X 10i human red blood cells (HRBC) or gram-negative bacterial endotoxin (Escherichia coli LPS: 30 ag/kg). The adult male progeny (3 mo old) of both experimental groups showed increased basal plasma corticosterone levels. In addition, after novelty stress the HRBC group, but not the LPS group, showed increased AC'H and corticosterone levels. Both groups showed substantial decreases in mineralocorticoid (MR) and glucocorticoid receptor (GR) levels in the hippocampus, a limbic brain structure critical for HPA axis regulation, whereas GR concentrations in the hypothalamus were unchanged and in anterior pituitary were slightly increased. HRBC and LPS indeed stimulated the maternal immune system as revealed by specific anti-HRBC antibody production and enhanced IL-1ft mRNA expression in splenocytes, respectively. This study demonstrates that a T cell-mediated immune response as well as an endotoxic challenge during pregnancy can induce anomalies in HPA axis function in adulthood. Clinically, it may be postulated that disturbed fetal brain development due to prenatal immune challenge increases the vulnerability to develop mental illness involving inadequate responses to stress. (J. Clin. Invest. 1994.

A transgene expressing antisense RNA complementary to a fragment of the glucocorticoid receptor cDNA was incorporated into the mouse genome and resulted in a transgenic animal that has decreased glucocorticoid receptor function. The transgenic mice showed basal plasma ACTH and corticosterone levels similar to those of the normal control animals. We have further investigated changes in HPA axis regulation by use of different neuroendocrine challenge tests including a dexamethasone suppression test (DST). In comparison to normal mice, a tenfold higher dose of dexamethasone (i.e. 20 µg/100 g body weight) was required to suppress the basal corticosterone levels of transgenic mice. Dexamethasone (2 µg/100 g body weight) produced a long-lasting suppression of plasma ACTH and corticosterone levels in control mice, whereas in transgenic animals only a short-lasting decrease in ACTH levels was apparent. Corticotropin-releasing hormone (CRH) administration resulted in an enhanced response in plasma ACTH levels in transgenic mice, whereas the corticosterone response was markedly reduced. The discrepancy between ACTH and corresponding corticosterone secretions in transgenic mice could be attributed, in part, to a reduced sensitivity of the adrenal gland to stimulation by ACTH. Pituitaries of transgenic mice contained about 50% less proopiomelanocortin (POMC) mRNA than those of control animals. No significant differences were noted in the ACTH or protein contents of normal and transgenic mice pituitary glands although a slight increase in protein content of the transgenic mouse adrenal gland was apparent. In conclusion, transgenic mice with impaired GR function show major disturbances in HPA axis regulation which seem to be caused by the primary defect in conjunction with secondary modifications in, amongst others, pituitary CRH receptor system(s), sympathetic output and adrenal development. This mouse is therefore a useful model to study the consequences of life-long defective GR function and HPA axis regulation in general.

No abstract

Brain corticosteroid receptors, the type 1 mineralocorticoid receptor (MR) and the type 2 glucocorticoid receptor (GR), are involved in the regulation of neuroendocrine and behavioral responses during ongoing and stressful conditions. To further investigate the role of MR in these responses, we treated male Wistar rats intracerebroventricularly (icv) for 1 week with an 18-base end-capped phosphorothioate-protected antisense oligodeoxynucleotide (ODN) directed against MR mRNA (MR-AS). A mixed bases sequence (MR-MB) and vehicle (0.9% saline) served as controls. The ODN solution was administered by continuous infusion (1 µg/0.5 µl/h) via an icv cannula connected with polyethylene tubing to a subcutaneously implanted Alzet miniosmotic pump. No nonspecific effects of the ODNs, such as signs of sickness behavior or loss of body weight, were observed at any time during the treatment. The MR-AS treatment produced a 21 % decline in hippocampal MR concentrations. Hippocampal GR levels were not affected by the treatment. MR and GR levels after MR-MB treatment were similar to those found after treatment with the vehicle. In situ hybridization experiments using an [³⁵S]-labeled antisense MR probe showed that hippocampal MR mRNA levels were increased in MR-AS-treated rats. No changes were found in basal early morning levels of plasma ACTH and corticosterone which is consistent with the lack of any changes in adrenal and thymus weight. When rats were socially defeated for 10 min by a male and female resident and then placed for 5 min in the elevated plusmaze, no changes in the anxiety-like behavior were observed in MR-AS-treated animals. However, MR-AS-treated rats killed immediately after the behavioral test had markedly higher plasma ACTH, but not corticosterone, levels than the MR-MB and saline controls. In conclusion, down-regulation of the brain MR produces an enhanced responsiveness of ACTH to stressful situations which appears to be accompanied by a reduced sensitivity of the adrenal gland to ACTH.