Submitted on April 6, 2007
Accepted on May 29, 2007
Growth Hormone-Releasing Hormone: Cerebral Cortical Sleep-related EEG Actions and Expression
Éva Szentirmai1, Tadanobu Yasuda2, Ping Taishi1, Mingxiang Wang1, Lynn Churchill1, Stewart Bohnet1, Paul Magrath1, Bálint Kacsóh3, Lissette Jimenez1, and James M. Krueger1*
1 Department of VCAPP, Washington State University, Pullman, Washington, United States
2 Department of Anesthesiology, University of Hirosaki School of Medicine, Hirosaki, Japan
3 Division of Basic Medical Sciences and Department of Pediatrics, Mercer University School of Medicine, Macon, Georgia, United States
* To whom correspondence should be addressed. E-mail: krueger{at}vetmed.wsu.edu.
Growth hormone-releasing hormone (GHRH), its receptor (GHRHR) and other members of the somatotropic axis are involved in non-rapid eye movement sleep (NREMS) regulation. Previously, studies established the involvement of hypothalamic GHRHergic mechanisms in NREMS regulation, but cerebral cortical GHRH mechanisms in sleep regulation remained uninvestigated. Here we show that unilateral application of low doses of GHRH to the surface of the rat somatosensory cortex ipsilaterally decreased electroencephalogram (EEG) delta wave power while higher doses enhanced delta power. These actions of GHRH on EEG delta wave power occurred during NREMS but not during rapid eye movement sleep. Further, the cortical forms of GHRH and GHRHR were identical to those found in the hypothalamus and pituitary respectively. Cortical GHRHR mRNA and protein levels did not vary across the day-night cycle, whereas cortical GHRH mRNA increased with sleep deprivation. These results suggest that cortical GHRH and GHRHR have a role in the regulation of localized EEG delta power that is state-dependent as well as in their more classic hypothalamic role in NREMS regulation.
