Anatomy of hypothalamic CART neurons

Over the past 25 years the continuous discovery of novel neuropeptides has been a great aid in our understanding of central nervous system function. The neuropeptide CART was discovered in 1995 in a search for cocaine and amphetamine regulated transcripts in the striatum, but subsequently found to be expressed at much higher levels in the hypothalamus. Further studies on the distribution of both CART mRNA and CART immunoreactivity has added CART to the long list of neuropeptides expressed at high levels in several parts of the hypothalamus playing key roles in homeostasis and reproduction. Our extensive knowledge of hypothalamic function is due in great part to the high number of neuropeptides expressed in distinct hypothalamic cell groups, and naturally the discovery of CART led to myriad of papers examining possible roles played by CART peptides in different aspects of hypothalamic integration and reviewed elsewhere in this issue of Peptides. However, the rather widespread distribution of CART peptides in the brain certainly complicates the understanding of the role(s) played by this neurotransmitter and calls for careful interpretation of physiological/behavioral data. The aim of the present review is to focus attention on the rather complicated anatomy of the hypothalamic CART neurons, bearing in mind that a thorough understanding of brain function should be built on a solid anatomical foundation.