Regular papersOrexin-A in the human brain and tumor tissues of ganglioneuroblastoma and neuroblastoma
Introduction
Orexins (hypocretins) are neuropeptides that have recently been discovered from rat brain and have a strong stimulatory effect on food consumption [8], [21]. The orexins consist of two peptides; orexin-A, a 33 amino acid peptide and orexin-B, a 28-amino acid peptide, which are derived from the same precursor by proteolytic processing [8], [21]. Orexin-A and -B share 46% identity. Studies by immunocytochemistry and in situ hybridization in the rat and human brain showed that orexin-A and -B positive cell bodies were restricted to the lateral and posterior hypothalamus, which is well known to be a feeding center in the hypothalamus [4], [7], [8], [9], [13], [21]. Both orexin-A and -B nerve fibers projected from the hypothalamus widely to various brain regions, such as the olfactory bulb, cerebral cortex, thalamus, and brain stem.
Intracerebroventricular administration of orexin-A or -B stimulated food consumption in rat [21] and gastric acid secretion [30]. Expression levels of orexin mRNA were up regulated by fasting [21] and down regulated in genetically obese mice [32]. The orexins modulated luteinizing hormone secretion in an ovarian steroid-dependent manner [18]. Canine narcolepsy is caused by a mutation in the orexin (hypocretin) receptor 2 gene [15], and orexin knockout mice exhibit a phenotype strikingly similar to human narcolepsy patients [5], indicating that orexin regulates sleep/wakefulness states. Consistent with these reports, orexin-A activated locus coeruleus cell firing and increased arousal and locomoter activity in rats [12]. Thus, the orexins are involved in regulating various brain and endocrine functions, such as feeding and arousal.
On the other hand, regional distribution of the orexins in the human brain and pituitary has not been studied. We therefore studied regional distribution of orexin-A-like immunoreactivity (orexin-A-LI) in human brain and pituitary by radioimmunoassay and expression of orexin mRNA by reverse transcriptase-PCR (RT-PCR).
It is known that adrenal medulla and neural crest-derived tumors, such as pheochromocytomas and neuroblastomas, produce various kinds of neuropeptides, e.g. neuropeptide Y (NPY) [2], calcitonin-gene-related peptide (CGRP) [17], pituitary adenylate cyclase activating polypeptide (PACAP) [27] and adrenomedullin [22]. However, there has been no report on the production of the orexins by tumors. We therefore examined tissue concentrations of orexin-A-LI in human adrenal glands and tumor tissues of pheochromocytomas, adrenocortical tumors, ganglioneuroblastomas, and neuroblastomas.
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Tissues
This study has been approved by the Ethics Committee of Tohoku University School of Medicine. Human brain tissues were obtained at autopsy performed at the Department of Pathology, Tohoku University Hospital within 4-h postmortem from 13 patients (nine male and four female, 20–75 years old). These patients had no neurologic or endocrinological diseases. Tumor tissues of pheochromocytomas (n = 15), ganglioneuroblastomas (n = 4), neuroblastomas (n = 6), aldosterone-producing adrenocortical
Results
A standard curve of orexin-A and dilution curves of human brain extracts are shown in Fig. 1. The dilution curves were parallel with a standard curve of orexin-A. Orexin-A-LI was detected in every region of human brain, but not in the pituitary (<0.220 pmol/g wet weight) (Fig. 2). The highest concentration of orexin-A-LI in the human brain was found in hypothalamus (17.8 ± 4.4 pmol/g wet weight, mean ± SEM, n = 7), followed by thalamus (12.1 ± 2.3 pmol/g wet weight, n = 7), medulla oblongata
Discussion
The present study has shown the wide distribution of orexin-A-LI in various human brain regions and the expression of orexin mRNA in the hypothalamus. Furthermore, the present study has shown the production of orexin-A in ganglioneuroblastomas and neuroblastomas. This is the first report on the production of orexin-A by tumors.
The findings in the human brain are consistent with previous studies by others using immunocytochemistry and in situ hybridization showing that orexin is produced only in
Acknowledgements
The authors are grateful to Ms Kikuchi for her technical assistance. This study has been supported in part by a Research Grant from the Takeda Science Foundation (to K. To.), by a Research Grant for the Renal Anemia Research (to K. To.), by the Mochida Memorial Foundation for Medical and Pharmaceutical Research (to K. Ta.), and a Grant-in-Aid for Scientific Research on Priority Areas (A) (to K. Ta.) from the Ministry of Education, Science, Sports, and Culture, Japan.
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