Evidence for the Role of Hinbrain Orexin-1 Receptors in the Control of Meal Size

• Other Authors: Parise, Eric Michael (authoraut)
• Format: Others
• Language: English; English
• Published: Florida State University
• Subjects: Psychology; Neurosciences
• Online Access: http://purl.flvc.org/fsu/fd/FSU_migr_etd-7209

Hypothalamic orexin neurons project to the hindbrain, and 4th-intracerebroventricular (4th-icv) orexin-A treatment increases food intake. Here, we assessed the effects of hindbrain orexin-A and the selective orexin-1-receptor antagonist SB334867 on meal pattern in rats consuming standard chow. When injected 4th-icv shortly before dark onset, lower doses of orexin-A increased food intake over a 2-h period by significantly increasing the size of the first meal relative to vehicle, whereas the highest dose increased food intake by causing the second meal to be taken sooner. Conversely, hindbrain orexin-1-receptor blockade significantly reduced food intake by decreasing the size of the first meal of the dark phase. We also examined the effects of 4th-icv orexin-A and SB334867 on locomotor activity. Only the highest dose of orexin-A increased activity, and SB334867 had no effect. These data support the suggestion that endogenous hindbrain orexin-A acts to limit satiation. Both orexin-A and the pancreatic satiation hormone amylin require an intact Area Postrema (AP) to affect food intake, so we asked whether 4th-icv orexin-A impairs the satiating effect of peripheral amylin treatment. Amylin significantly reduced the size of the first meal of the dark cycle when rats were pre-treated with 4th-icv saline, yet amylin was ineffective after 4th-icv orexin-A pre-treatment. Using double-label immunohistochemistry, we determined that some orexin-A fibers in the AP are located in proximity to amylin-responsive neurons. We conclude that hindbrain orexin-A may increase food intake in part by reducing the ability of rats to respond to amylin during a meal. === A Thesis submitted to the Department of Psychology in partial fulfillment of the requirements for the degree of Master of Arts. === Summer Semester, 2011. === May 18, 2011. === Includes bibliographical references. === Diana L. Williams, Professor Directing Thesis; James Michael Overton, Committee Member; Pam Keel, Committee Member.