The hypothalamus is a very small part of the brain, lying just behind the eyes.  Although it represents only about 1% of brain weight, it is absolutely critical to maintain life.  Hypothalamic neurons play a critical role in regulating feeding, drinking, sleeping, and reproduction, as well as the response to external threat.  Because these functions are so basic, many of the circuits used to control these functions are preserved throughout the mammalian line, from rodents to humans.  Thus, it has been possible to identify and manipulate these circuits in animals, to determine their function, but it is also possible to demonstrate many of the same circuits in human brains.

            A key example has been the findings over the last few years concerning hypothalamic circuits that regulate wake-sleep cycles and feeding behavior.  Animal models have been created which explain some human disorders of wake-sleep control and feeding and body weight.  We will discuss in particular the nerve cells in the lateral hypothalamus, which are known to contain two different neurotransmitters, orexin and melanin-concentrating hormone.  Nerve cells containing these two neurotransmitters receive many of the same inputs, and they collaborate on some aspects of regulation, but have very distinct roles, as damage to the orexin neurons causes the disease known as narcolepsy, while loss of melanin-concentrating hormone produces loss of appetite and low body weight.

(C. Saper)