Brain estrogen production and the encoding of recent experience

Abstract

The vertebrate central nervous system integrates cognition and behavior, and it also acts as both a source and target for steroid hormones like estrogens. Recent exploration of brain estrogen production in the context of learning and memory has revealed several common themes. First, across vertebrates, the enzyme that synthesizes estrogens is expressed in brain regions that are characterized by elevated neural plasticity and is also integral to the acquisition, consolidation, and retrieval of recent experiences. Second, measurement and manipulation of estrogens reveal that the period following recent sensory experience is linked to estrogenic signaling in brain circuits underlying both spatial and vocal learning. Local brain estrogen production within cognitive circuits may therefore be important for the acquisition and/or consolidation of memories, and new directions testing these ideas will be discussed.

Figure 1. Aromatase is typically expressed in brain regions crucial for cognition among vertebrates

Aromatase expression is abundantly expressed within the hippocampus, auditory cortex/forebrain, and amygdala of several representative species across a wide range of classes. Black stripped-filled brain regions indicate no reported presence of aromatase, whereas maroon-filled brain regions indicate detectable presence of aromatase as assessed through various techniques. Briefly, 1) hippocampus - humans: [22,23]; rhesus macaques: [24]; mice: not seen in hippocampus [19,20]; but see [25]; birds: [26,27]; reptiles (medial cortex): [28,29]; fish (dorsolateral telencephalon): [30,31]; 2) auditory cortex/forebrain – humans: [32,33]; rhesus macaques: [24]; birds (caudomedial nidopallium; NCM [34]): [26,27]; reptiles (anterior dorsal ventricular ridge; ADVR [34]): [28]; fish (posterior portion of the ventral telencephalon; Vp): [30,35,36]; 3) amygdala - humans: [37]; rhesus macaques: [38]; mice: [19]; birds (nucleus taenia; TnA): [27]; reptiles: [28,29,39,40]; fish (supracommissural nucleus of the ventral telencephalon; Vs [41,42]): [30,36].