Stress hormones help firm up memories of emotional events so that we can avoid or deal with the challenge if it occurs again. For example, cortisol, produced by the adrenal glands, has receptors in many parts of the brain—especially the hippocampus, a nexus of emotion and memory.
Many disorders can result from improperly functioning cortisol, including anxiety, post-traumatic stress disorder, and some forms of depression. Scientists seeking treatments need a detailed picture of how cortisol works through its receptors to affect the brain. One player in the relay appears to be mitogen-activated protein kinase (MAPK), which previous studies show is activated in tandem with cortisol receptors.
In the May issue of Nature Neuroscience, Pier Vincenzo Piazza of the Bordeaux Institute for Neurosciences, France, and colleagues set out to establish cause and effect. They found that in cultured cells, activating cortisol receptors with the hormone increased levels of MAPK and the genes under its control.
In mice, the researchers found that the stress of being briefly restrained increased MAPK expression. When the mice were injected with a MAPK inhibitor, they lost the ability to form fear-related memories: in a conditioning test involving a mild shock to the foot, the treated mice showed none of the normal “freezing” behavior.
“Our data indicate a direct link between cortisol receptor activation, the MAPK signaling pathway and its target genes, and stress-induced enhanced memories of emotionally arousing experiences,” the researchers write.