Growth hormone and IGF-1 actions in the brain and neuropsychiatric diseases.

Growth hormone (GH) is secreted by the anterior pituitary gland under the control of hypothalamic neuroendocrine neurons that express somatostatin or growth hormone-releasing hormone (GHRH). Ghrelin, originating primarily in the stomach, is also an important GH secretagogue. GH stimulates the hepatic secretion of insulin-like growth factor-1 (IGF-1) and the expression of IGF-1 in extra-hepatic tissues, including the brain. Many regions of the brain express receptors for GH, IGF-1, and ghrelin. In recent decades, evidence from both human and animal studies has indicated that GH, IGF-1, and ghrelin regulate numerous brain functions. Alterations in the secretion or sensitivity to these hormones may represent risk factors for developing neurodegenerative diseases (e.g., Alzheimer's and Parkinson's) and neuropsychiatric conditions (such as depression, anxiety, posttraumatic stress disorder, schizophrenia, and bipolar disorder). Additionally, classical neurodevelopmental disorders such as autism spectrum and attention-deficit hyperactivity disorder may also be influenced by somatotropic hormones. This review aims to summarize and discuss the emerging role of GH and IGF-1 in influencing brain function and the predisposition to brain diseases and neuropsychiatric disorders.