Steroidogenesis and neuroplasticity in the songbird brain

Abstract

The vertebrate brain is a source and target of steroid hormones. Songbirds have long provided an array of structural and behavioral endpoints towards understanding how steroid molecules affect neuroanatomy and neurophysiology. More recently, our conceptualization of the brain has expanded to include the CNS as a potent source of these very steroids. Here we review recent findings about the expression of steroidogenic enzymes in the songbird brain with particular emphasis upon the role of neurosteroidogenesis on the plasticity of brain circuits. We include examples of natural neuroplasticity in laboratory and field studies. Additionally, we discuss the role of neurosteroidogenesis on the outcomes of pathological brain damage. These two areas of research have provided novel and fundamentally restructured hypotheses as to the role of neurosteroidogenesis in brain function. Notable among recent findings from such studies, are the consideration of alternate substrates for steroidogenic enzymes, an expansion of the suite of enzymes found at sites of neuronal recruitment and the expression of these enzymes in additional cell types and ultrastructural compartments. The powerful link among ethology, physiology, anatomy and cell biology is exemplified in these vertebrates and renders the songbird an enduring model for the study of the role of de novo steroid synthesis on the plasticity of brain structure and function. © 2008 Springer Netherlands.