Regulation of excitatory synapses and fearful memories by stress hormones

Abstract

Memories for emotionally arousing and fearful events are generally well retained. From the evolutionary point of view this is a highly adaptive behavioral response aimed to remember relevant information. However, fearful memories can also be inappropriately and vividly (re)expressed, such as in posttraumatic stress disorder. The memory formation of emotionally arousing events is largely modulated by hormones, peptides, and neurotransmitters which are released during and after exposure to these conditions. One of the core reactions in response to a stressful situation is the rapid activation of the autonomic nervous system, which results in the release of norepinephrine in the brain. In addition, stressful events stimulate the hypothalamus-pituitary-adrenal axis which slowly increases the release of glucocorticoid hormones from the adrenal glands. Here we will review how glucocorticoids and norepinephrine regulate the formation of fearful memories in rodents and humans and how these hormones can facilitate the storage of information by regulating excitatory synapses.

Keywords: AMPA; fear conditioning; glucocorticoids; norepinephrine.

Figure 1

Norepinephrine and glucocorticoids rapidly increase activity-dependent synaptic insertion of AMPA receptors. Slowly, corticosteroid hormones enhance AMPA receptor mediated synaptic transmission and reduce the ability to encode novel information. This might preserve and promote the retention of the original (fearful and relevant) memory trace (see text for details).