Neuromodulation of Orexin Neurons in the Lateral Hypothalamus Regulates Spontaneous Physical Activity, Energy Expenditure, and Diet-Induced Obesity

University of Minnesota Ph.D. dissertation. August 2015. Major: Neuroscience. Advisors: Catherine Kotz, Charles Billington. 1 computer file (PDF); vi, 60 pages.Spontaneous physical activity (SPA) is a promising therapeutic target for improving multiple clinical outcomes in obesity and metabolic syndrome. Low levels of the neuropeptide, orexin, are correlated with reduced SPA and pathological body weight in humans and animals. The dissertation research described here used a pharmacosynthetic approach (Designer Receptors Exclusively Activated by Designer Drugs; DREADDs) to modulate orexin neurons activity in adult male and female mice. Selective cellular and anatomic targeting was achieved by bilateral virus injection aimed at the lateral and caudal lateral hypothalamic area of transgenic mice expressing the DNA-recombinase, Cre, in orexin neurons. In the presence of Cre, viruses expressed the excitatory, Gq-coupled DREADD, hM3Dq, or the inhibitory, Gi-coupled DREADD, hM4Di. Expression and functional activation were validated via histology. A single systemic dose of the Designer Drug, Clozapine-N-Oxide (CNO; 5mg/kg; IP) induced cFos in the lateral hypothalamus, increased SPA, and energy expenditure (indirect calorimetry) 4hrs post-injection compared to vehicle. Females exhibited higher sensitivity to the lowest dose of CNO (1mg/kg) tested, leading to a significant sex-difference. However, no difference between sexes was observed at the dose (5mg/kg) selected for use in subsequent experiments. Under standard chow conditions, acute CNO treatment did not affect body weight. Eating and drinking patterns were altered in a complimentary fashion such that total food and water intake were unchanged. To test if elevated SPA protects against an obesogenic diet, males were housed on 45% high fat diet (HFD) and given repeated daily injections of CNO or vehicle. After 10d, adult mice (4.5M) showed significant weight loss and improved adiposity, while aged mice (9M) exhibited similar effects after only 5d. This study demonstrates the ability of SPA to counteract HFD-induced weight gain. Many medical conditions, in addition to obesity, stand to benefit from enhanced physical activity