Neuropeptides

Neuropeptides are small, protein-like signaling molecules (amino acid chains) synthesized and released by neurons in the central (CNS) and peripheral (PNS) nervous systems. They regulate diverse brain and bodily functions, such as mood, stress, sleep, appetite, pain, and memory. Neuropeptides either function as neurotransmitters (directly affecting synapses) or as neuromodulators (altering the effect of other neurotransmitters). Beyond the brain, many act as hormones or signaling molecules in the immune, endocrine, and digestive systems. Examples include oxytocin, endorphins, neuropeptide Y, and substance P. Another key example is orexin-A and orexin-B (also known as hypocretin), produced in the lateral hypothalamus to regulate arousal, wakefulness, appetite, and energy homeostasis. Lack of orexin causes narcolepsy. Also see Circadian Rhythms

Neuropeptides were discovered by two groups around the same time, so they have two interchangeable names within the scientific community One group took the name orexin from the Greek “orexis,” meaning appetite. The other group called them hypocretins because they were discovered in the hypothalamus. Each type is now called orexin-A and orexin-B. Also see Circadian Rhythms