Here is an interesting new study about orexin (aka hypocretin). Recall that orexin was first identified as an appetite stimulating molecule. It was then tied to narcolepsy (through stuides of a well-defined colony of narcoleptic dogs). It is involved in sleep/wake, and orexin deficient mice (and dogs and people) move from wake to sleep abnormally easily.
Orexin is very low in narcolepsy, and also is often low in PWS – FPWR is currently funding a study to look at this connection more closely. Note that it is somewhat counterintuitive that orexin (an appetite stimulant) is low in both of these populations, which are characterized by obesity.
Recently, orexin was linked to reward seeking, and here it is linked to addiction and craving (of cocaine).
Orexin A in the VTA is critical for the induction of synaptic plasticity and behavioral sensitization to cocaine. Borgland SL, Taha SA, Sarti F, Fields HL, Bonci A. Neuron. 2006 Feb 16;49(4):589-60