EnglandThe orexins (A and B) are neuropeptides synthesized by neurons in the lateral hypothalamus. Initial experiments suggested that these peptides are important in the regulation of appetite. Orexin Ahmunoreactivity (orexin A-IR) was measured in the rat brain and found to be highest in the hypothalamus, thalamus, septum, amygdala, midbrain, pons and medulla. Interestingly, unlike prepro-orexin mRNA, which is upregulated with rdarvation, brain orexin A-IR levels were unaltered with starvation. Hypothalamic orexin A-IR was unaltered after exposure to a high fat diet. Orexin A-IR and prepro-orexin mRNA were measured in brain regions of obese Zucker rats, which lack leptin receptor action. There was no difference in prepro-orexin mRNA and orexin A-IR levels between
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