Distribution of orexin/hypocretin in the rat median eminence and pituitary

We determined the: distribution of orexin-A and orexin-B (also known as hypocretin-1 and hypocretin-2) and their receptors in the rat median eminence and pituitary using sensitive radioimmunoassays coupled with high-performance liquid chromatography, immunohistochemistry, and in situ hybridization. Orexin-A and -B were present in the median eminence, adenohypophysis, and neurohypophysis. Orexin fibers were abundant in the median eminence, and a few fibers projected to the neurohypophysis. Both the orexin(1)- and orexin(2)-receptor mRNAs were expressed robustly in the pituitary intermediate lube, whereas in the anterior lobe, the orexin(1) receptor was more markedly expressed than the orexin(2) receptor. These: two receptor mRNAs were also found in the posterior lube. These findings may implicate orexin's involvement in additional as yet undefined physiological functions in the hypothalamo-hypophyseal tract. (C) 2000 Elsevier Science B.V. All rights reserved.