Body energy homeostasis results from balancing energy intake and energy expenditure. Central nervous system administration of pituitary adenylate cyclase activating polypeptide (PACAP) dramatically alters metabolic function, but the physiologic mechanism of this neuropeptide remains poorly defined. PACAP is expressed in the mediobasal hypothalamus (MBH), a brain area essential for energy balance. Ventromedial hypothalamic nucleus (VMN) neurons contain, by far, the largest and most dense population of PACAP in the medial hypothalamus. This region is involved in coordinating the sympathetic nervous system in response to metabolic cues in order to re-establish energy homeostasis. Additionally, the metabolic cue of leptin signaling in the VMN regulates PACAP expression. We hypothesized that PACAP may play a role in the various effector systems of energy homeostasis, and tested its role by using VMN-directed, but MBH encompassing, AAV Cre injections to ablate Adcyap1 (gene coding for PACAP) in mice (Adcyap1MBHKO mice). Adcyap1  MBHKO mice rapidly gained body weight and adiposity, becoming hyperinsulinemic and hyperglycemic. Adcyap1  MBHKO mice exhibited decreased oxygen consumption (VO2), without changes in activity. These effects appear to be due at least in part to BAT dysfunction, and we show that PACAP-expressing cells in the MBH can stimulate BAT thermogenesis. While we observed disruption of glucose clearance during hyperinsulinemic/euglycemic clamp studies in obese Adcyap1  MBHKO mice, these parameters were normal prior to the onset of obesity. Thus, MBH PACAP plays important roles in the regulation of metabolic rate and energy balance through multiple effector systems on multiple time scales, which highlight the diverse set of fuctions for PACAP in overall energy homeostasis.

Body energy homeostatic mechanisms dynamically balance energy expenditure with energy intake, and the brain plays a critical role in this process. However, the specific circuits responsible for controlling energy expenditure are only superficially understood. Because Ventromedial Hypothalamic (VMN)-specific expression of pituitary adenylate cyclase-activating polypeptide (PACAP) decreases with both under-nutrition and loss of leptin action, we tested the hypothesis that VMN PACAP controls energy expenditure. Since PACAP is expressed in the periphery, we administered a VMN-targeted injection of AAVcre in PACAPflox mice to remove VMN PACAP (PACAPVMNKO), which resulted in a near complete bilateral ablation of PACAP mRNA in the VMN without interfering with PACAP mRNA in nearby sites (e.g., preoptic area (POA) and medial amygdala). In both male and female mice, PACAPVMNKO induced massive obesity and more than a two-fold increase in adipose mass. This induced obesity, similar to other VMN loss of function studies, is due to chronically suppressed energy expenditure because VO2, but not activity, was decreased in these mice. PACAPVMNKO mice were also hyperinsulinemic, hyperglycemic, and exhibited impaired glucose clearance in the hyperinsulinemic/hyperglycemic clamp. However, PACAPVMNKO mice were normoglycemic 4 weeks post-injection (prior to obesity), indicating that glycemic effects were secondary to obesity. Because the VMN does not contain directly pre-autonomic neurons, PACAP must activate a circuit via a downstream site to stimulate energy expenditure. PAC1r cells primarily overlay with VMN projections in the POA and to a lesser extent in the periaqueductal grey and bed nucleus of the stria terminalis. VMN PACAP, as well as associated signaling targets, are critical components to the control of energy balance by activating energy expenditure. Disclosure D.Q. Johnson: None. J. Flak: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-17-INI-15 to J.F.); National Institutes of Health (DK020572)

Body energy homeostatic mechanisms dynamically balance energy expenditure with energy intake, and the brain plays a critical role in this process. While mediobasal hypothalamic (MBH) signaling is essential for natural elevations in energy expenditure, the downstream anatomical mechanisms are not clear at this point. The MBH contains several important nuclei for energy expenditure control, such as the Ventromedial Hypothalamus (VMN). Because VMN-specific expression of pituitary adenylate cyclase-activating polypeptide (PACAP) decreases with both under-nutrition and loss of leptin action, we tested the hypothesis that MBH PACAP controls energy expenditure. To test this hypothesis, we administered local AAVCre injections into Adcyap1flox (gene that encodes for PACAP) mice. While our approach ensured that peripheral PACAP expression was completely intact, AAV injections did spread into nearby hypothalamic regions, resulting in a MBH loss of function (PACAPMBHKO), rather than a purely VMN knockout. However, all mice exhibited a near complete bilateral ablation of PACAP mRNA in the VMN without interfering with PACAP mRNA in nearby populations that highly express PACAP (e.g., preoptic area (POA) and medial amygdala). In both male and female mice, PACAPMBHKO induced obesity and more than a two-fold increase in adipose mass. VO2, expressed as a function of lean mass, was decreased particularly in the first few hours of the dark cycle, when the mice consume food. Because MBH PACAP cells do not directly project to the spinal cord, PACAP must activate a circuit via a downstream site to stimulate energy expenditure. PAC1r cells primarily overlay with VMN, the primary MBH site containing PACAP, projections in the POA and to a lesser extent in the periaqueductal grey and bed nucleus of the stria terminalis. MBH PACAP, as well as associated signaling targets, are critical components to the control of energy balance by activating energy expenditure. Disclosure D. Q. Johnson: None. R. Basu: None. J. Flak: None. Funding American Diabetes Association/Pathway to Stop Diabetes (1-17-INI-15 to J.F.); Indiana University