The regulation of body weight: lessons from the seasonal animal

The hypothalamus is a major regulatory centre involved in the control of ma ny important physiological axes. One of these axes is the regulation of ing estive behaviour. Recent work using a combination of genetic-mutant mouse m odels together with targeted gene deletions has contributed much to our und erstanding of how neural pathways of the hypothalamus are involved in the r egulation of energy balance in animals. These pathways are also relevant to human energy homeostasis, as mutations in key genes are correlated with ob esity. Many of the genes identified mediate the effects of leptin, and are therefore primarily involved in sensing and responding to peripheral signal s. In seasonal animals, such as the Siberian hamster (Phodopus sungorus), t here is evidence for a higher level of regulation. The systems involved reg ulate body weight around an apparent 'set-point' through the action of phot operiod via the neurohormone, melatonin. The ability to manipulate energy b alance through photoperiod (and melatonin) in the seasonal-animal model off ers novel opportunities to identify further fundamental aspects of the cont rol mechanisms involved in the central control of energy homeostasis and bo dy weight.