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First published online on March 7, 2003.
 Copyright © 2003 by The Physiological Society
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Received December 31, 2002
Accepted after revision February 5, 2003

Intravenously administered hypocretin-1 alters brain amino acid release: an in vivo microdialysis study in rats

Joshi John1, Ming-Fung Wu1, Tohru Kodama1, and J. M. Siegel2*

1 Neurobiology Research (151A3), Veterans Affairs Greater Los Angeles Health Care System, North Hills, CA 91343 and Department of Psychiatry and Brain Research Institute, University of California at Los Angeles, Los Angeles, CA 91020, USA
2 UCLA/Neurobiology Research (151A3), Sepulveda VAMC, 16111 Plummer Street, North Hills, CA 91343, USA

* To whom correspondence should be addressed. E-mail: jsiegel{at}ucla.edu.

We have reported that intravenous administration of hypocretin (Hcrt or orexin) reverses the symptoms of narcolepsy in genetically narcoleptic dogs. We have also reported that the onset of symptoms in canine genetic narcolepsy is accompanied by degenerative changes in forebrain regions, particularly the septal nucleus and amygdala. In the present in vivo microdialysis study we have investigated the effect of intravenous administration of Hcrt-1 (orexin-A) to anaesthetized rats on glutamate and GABA release in the amygdala, a region with moderate Hcrt innervation, and in the cerebellar cortex, a region with sparse or no Hcrt innervation. We found that intravenous Hcrt administration caused a marked (> 60 %) and sustained (> 50 min) increase in glutamate release within the amygdala, but no change in release in the cerebellar cortex. We did not detect a significant change in GABA release. When calcium-free artificial cerebrospinal fluid was used as the microdialysis perfusate, Hcrt-1 no longer produced an increase in glutamate release. Hcrt may act via the calcium-dependent regulation of glutamate release in the central nervous system.




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