Leptin signaling pathways in the central nervous system: interactions between neuropeptide Y and melanocortins.

No other hormone has drawn more attention than leptin in recent studies on the control of appetite, body weight and obesity. This hormone is produced by adipose tissue and enters the brain via a saturable specific transport mechanism. Leptin acts in the hypothalamus to modulate food intake and heat production as well as several other neuroendocrine pathways. The mechanisms through which leptin exerts its central nervous effects are now better understood. Proopiomelanocortin- and neuropeptide Y-containing neurons in the hypothalamus have emerged as potent candidate mediators of leptin action. These two neuropeptides have been shown to exert opposing effects using different pathways. Recently, Cowley et al. (2001) described a new circuit in the regulation of neuronal activity by leptin with an interaction between these two pathways. These data add complexity to the mechanisms by which leptin achieves its effects in the central nervous system, but they also offer potential mechanisms to explain the phenomenon of leptin resistance observed in obesity.