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The biological mechanisms that determine cell-specific responses to glucocorticoid hormones may overlap with those that are associated with acquired glucocorticoid resistance. Cell and tIssue specificity can be brought about in many different ways. Studies on the brain, an important glucocorticoid target tIssue, may provide examples of regulatory mechanisms underlying response specificity at multiple levels. In this commentary a number of such mechanisms are discussed, with emphasis on regulation of glucocorticoid bio-availability by the efflux transporter P-glycoprotein and on the variable presence of nuclear proteins which modulate or interfere with gluco- and mineralocorticoid receptor-mediated transcription.

In the present study, we have investigated the role of the multidrug resistance (mdr) P-glycoprotein (Pgp) at the blood-brain barrier in hampering the access of the synthetic glucocorticoid, prednisolone. In vivo, a tracer dose of [(3)H]prednisolone poorly penetrated the brain of adrenalectomised wild-type mice, but the uptake was more than threefold enhanced in the absence of Pgp expression in mdr1a (-/-) mice. In vitro, in stably transfected LLC-PK1 monolayers the human MDR1 P-glycoprotein was able to transport prednisolone present at a micromolar concentration. A specific Pgp blocker, LY 335979, could block this polar transport of [(3)H]prednisolone. Human Pgp does not transport all steroids, as cortexolone was not transported at all and aldosterone was only weakly transported. The ability of Pgp to export the synthetic glucocorticoid, prednisolone, suggests that uptake of prednisolone in the human brain is impaired, leading to a discrepancy between central and peripheral actions. Furthermore, the ensuing imbalance in activation of the two types of brain corticosteroid receptors may have consequences for cognitive performance and mood.

A fundamental question in stress research is when the glucocorticoid stress hormone (cortisol in man) stops being neuroprotective and becomes harmful to the brain with negative consequences for cognition and mood. To address this question Section 1 focuses on the action mechanism of glucocorticoids. These hormones act via high and low affinity nuclear receptors, which regulate gene transcription in a coordinate manner. The receptors are expressed abundantly in hippocampus, amygdala and frontal cortex involved in cognitive processes. In Section 2 hypercortisolism is considered a potential disease factor for about 50% of the patients suffering from major depression. Recent data show that these patients recover within a few days when excess cortisol action is blocked with high doses of an antiglucocorticoid. Section 3 concerns animal models with ‘depression-like’ features of hypercorticism generated by manipulation of gene X environment inputs. Using gene expression profiling technology in the hippocampal transcriptome of these animals we identified about 700 potential targets for antidepressants out of 30 000 detectable gene products. One of our models is based on early life programming of the stress system. Rats exposed as pups to maternal deprivation display at senescence an enhanced individual difference in cognitive performance. The maternally deprived senescent animals age either successfully or become senile, at the expense of the average performance of non-deprived controls. The essay is concluded with the notion that the new generation of antidepressants ameliorates specific psychic dysfunctions (e.g. cognitive performance) linked to aberrant stress hormone action in discrete brain regions.

A fundamental question in stress research is when the glucocorticoid stress hormone (cortisol in man) stops being neuroprotective and becomes harmful to the brain with negative consequences for cognition and mood. To address this question Section 1 focuses on the action mechanism of glucocorticoids. These hormones act via high and low affinity nuclear receptors, which regulate gene transcription in a coordinate manner. The receptors are expressed abundantly in hippocampus, amygdala and frontal cortex involved in cognitive processes. In Section 2 hypercortisolism is considered a potential disease factor for about 50% of the patients suffering from major depression. Recent data show that these patients recover within a few days when excess cortisol action is blocked with high doses of an antiglucocorticoid. Section 3 concerns animal models with ‘depression‐like’ features of hypercorticism generated by manipulation of gene X environment inputs. Using gene expression profiling technology in the hippocampal transcriptome of these animals we identified about 700 potential targets for antidepressants out of 30 000 detectable gene products. One of our models is based on early life programming of the stress system. Rats exposed as pups to maternal deprivation display at senescence an enhanced individual difference in cognitive performance. The maternally deprived senescent animals age either successfully or become senile, at the expense of the average performance of non‐deprived controls. The essay is concluded with the notion that the new generation of antidepressants ameliorates specific psychic dysfunctions (e.g. cognitive performance) linked to aberrant stress hormone action in discrete brain regions.