Chapter 19 Resolving a mystery: progress in understanding the function of adrenal steroid receptors in hippocampus

Publisher Summary This chapter discusses the significance of adrenal steroid action on the hippocampus. The first effects of adrenal steroids concerned destruction of neural tissue, but later findings pointed to the additional effects that protect neurons and enhance plasticity. The role of the hippocampus in learning and memory processes may be subject to regulation by circulating adrenal steroids over both short and long time periods. The adult hippocampus is the site of hormonally directed plasticity. Estradiol and progesterone regulate the cyclic formation and breakdown of excitatory synapses on CA1 pyramidal neurons. Excess thyroid hormone promotes a reduction in dendritic spines on CA1 pyramidal neurons, whereas the transient elevation of thyroid hormone neonatally produces a long-term increase of dendritic branching and spine density in the CA3 region of the hippocampal formation. The chapter discusses the interactive roles that are played by thyroid hormone balance, sex hormones, and gender, together with the actions of adrenal steroids, in determining the ability of the hippocampus to change its structure and function in response to the external environment.