The role of brain insulin in the neurophysiology of serious mental disorders: review.

The purpose of this review is to indicate the role insulin plays in normal brain neurophysiology, together with the role insulin may play in the regulation of regional cerebral blood flow (rCBF). The relationship between sustained elevation of the inflammatory cytokines and brain insulin dysregulation, with respect to the serious mental disorders, is also discussed. It has been observed that, as the inflammatory cytokines increase, they exert a synergistic influence on insulin and somatostatin, by initially increasing and then decreasing insulin secretion. In the brain, increased levels of insulin result in increased glucose utilization and over-stimulation of the autonomic nervous system (ANS), while the inhibition of insulin secretion results in decreased glucose utilization and dysregulation of the hypothalamo-pituitary-adrenal (HPA) axis. It will further be argued that these alterations in brain insulin influence rCBF in the serious mental disorders such as schizophrenia and the affective disorders. It is hypothesized that insulin regulates rCBF either directly, or indirectly via GLUT4 in the hypothalamus now considered the glucose-sensing, insulin-sensing mechanism of the brain and the body. Thus, we shall propose that insulin plays an important role in normal neurophysiology and that sustained elevation of the inflammatory cytokines dysregulates insulin secretion, rCBF, ANS and the HPA-axis in serious mental disorders.