Figure 1.

A schematic diagram illustrating potential molecular and cellular mediators of HD pathogenesis, with a focus on serotonergic and neurotrophin signaling as well as the HPA-dysfunction which may give rise to depression and associated symptoms. The role of environmental enrichment in ameliorating specific aspects of molecular, cellular, and systems dysfunction is also illustrated. There are clearly many other molecular and cellular candidates implicated in HD pathogenesis which are not shown in this diagram, which outlines a specific hypothesis regarding the etiology of depression in HD. 5-HT, serotonin; BDNF, brain-derived neurotrophic factor; HD, Huntington’s disease; HPA-axis, hypothalamic-pituitary-adrenal axis.