Fig. 1.

Models representing the acute and chronic effects of GC on function in the HPA axis. The canonical effects occur rapidly, within minutes to a few hours after stress; GCs act directly on brain and pituitary probably through nongenomic mechanisms. The new model requires ≈24 h, after elevation of GC into stress concentrations. Then, the direct action of GCs on brain is stimulatory, and the negative feedback inhibition of function in the HPA axis is a consequence of metabolic effects of GC increasing abdominal energy stores.