Central nervous system: a conductor orchestrating metabolic regulations harmed by both hyperglycaemia and hypoglycaemia.

Recent evidence suggests that the brain has a key role in the control of energy metabolism, body fat content and glucose metabolism. Neuronal systems, which regulate energy intake, energy expenditure, and endogenous glucose production, sense and respond to input from hormonal and nutrient-related signals that convey information regarding both body energy stores and current energy availability. In response to this input, adaptive changes occur that promote energy homeostasis and the maintenance of blood glucose levels in the normal range. Defects in this control system are implicated in the link between obesity and type 2 diabetes mellitus. The central nervous system may be considered the conductor of an orchestra involving many peripheral organs involved in these homeostatic processes. However, the brain is mainly a glucose-dependent organ, which can be damaged by both hypoglycaemia and hyperglycaemia. Hypoglycaemia unawareness is a major problem in clinical practice and is associated with an increased risk of coma. Stroke is another acute complication associated with diabetes mellitus, especially in elderly people, and the control of glucose level in this emergency situation remains challenging. The prognosis of stroke is worse in diabetic patients and both its prevention and management in at-risk patients should be improved. Finally, chronic diabetic encephalopathies, which may lead to cognitive dysfunction and even dementia, are also recognized. They may result from recurrent hypoglycaemia and/or from chronic hyperglycaemia leading to cerebral vascular damage. Functional imaging is of interest for exploring diabetes-associated cerebral abnormalities. Thus, the intimate relationship between the brain and diabetes is increasingly acknowledged in both research and clinical practice.