Abstracts / Appetite 52 (2009) 815–868 837 Plasma levels of ‘adiposity signals’ do not reflect adiposity in rats compensating for under- or over-weight J.J.G. HILLEBRAND * , V. GLOY, W. LANGHANS, N. GEARY Physiology and Behaviour Group, ETH Zurich, Schwerzenbach, Switzerland Leptin and insulin are proposed to signal adiposity and play cru- cial roles in the regulation of energy balance, yet little is known about their responses after manipulations of body weight (BW). Here we measured leptin and insulin levels and fat pad mass in male LE rats recovering from forced underweight (UW) or overweight (OW). UW were restricted to 60% of baseline food intake until BW was 75% of ad lib-fed, normal weight (NW) rats, and OW were overfed (up to 190kcal/d) by gastric infusions until BW was 125% of NW. Manipulations were then stopped. Rats were equipped with jugular vein catheters for recurring blood sampling. Basal plasma leptin and insulin were assayed by radioimmunoassay. Fat pad mass was periodically estimated by computerized tomography. At 75% of NW BW, UW had only 35% of NW fat pad mass and reduced lep- tin and insulin levels. At 125% of NW BW, OW had 380% of NW fat pad mass and increased hormone levels. During recovery these variables all moved towards NW levels, but at different rates. UW leptin and insulin levels did not differ significantly (ns) from NW on d 4, whereas fat pad mass was still 75% of NW on d 30. OW leptin levels were ns versus NW from d 17 on, whereas fat pad mass was still 145% of NW on d 40. OW insulin levels were ns versus NW on d 1–5, and less than NW from d 8 on. These data are inconsistent with the hypotheses that plasma leptin and insulin reflect adiposity and suggest that changes in these hormone levels under our conditions reflect energy balance flux rather than state, i.e., adiposity per se. doi:10.1016/j.appet.2009.04.094 Intra-abdominal and subcutaneous fat pad measurements by computerized tomography in rats and mice J.J.G. HILLEBRAND * , W. LANGHANS, N. GEARY Physiology and Behaviour Group, ETH Zurich, Schwerzenbach, Switzerland Computerized tomography (CT) scanners for in vivo imaging of laboratory rodents have recently become available. One, the LaTheta scanner (LCT-100, Aloka, Tokyo, Japan), includes software for automated determination of intra-abdominal (IA) and subcu- taneous (SC) fat. To establish the accuracy and sensitivity of this system, we performed cross-sectional scans in male Long Evans rats (200–550 g) and C57Bl6 mice (12–35 g) and used the manufac- turer’s software or post-mortem dissection to quantify IA and SC fat. Scanned total and dissected IA or SC fat pads were linearly corre- lated in rats (r = 0.99/r = 0.99, n = 6) and mice (r = 0.97/r = 0.97, n = 11). Whole body fat pad mass was not a linear function of body weight. Dissected fat pad samples of 0.5–3 g for rats and 10–100 mg for mice were placed IA or SC in other rodents that were scanned before and after. Percent recoveries (mean ± SD) of the smallest samples in rats were 100.9 ± 0.5% for IA and 106.0 ± 5.4% for SC; recoveries in mice were 97.5 ± 2.7% for IA and 103.3 ± 13.8% for SC. Scans of IA and SC fat between lumbar vertebrae 1 and 6 (L1–L6) were well correlated with whole body IA ( = 0.99, n =19) and SC fat ( = 0.99, n = 19) in rats and with whole body IA fat ( = 0.96, n = 29), but less so with SC fat ( = 0.67, n = 29) in mice. In conclusion, CT can accurately and sensitively measure IA and SC fat in rats and mice over a wide range of BW, making it a valuable tool for experimental analyses of rodent obesity models. doi:10.1016/j.appet.2009.04.095 Endocannabinoids regulate energy balance in Siberian hamsters J.M. HO * , G.E. DEMAS Indiana University, Bloomington, IN, USA Siberian hamsters undergo marked seasonal changes in body mass and food intake, and this natural fluctuation serves as an important model for understanding human states of obesity and leanness. Transfer of animals to short, winter-like photoperiods (SD) results in ∼30% loss in body mass, and this decrement is regained upon return to long summer-like photoperiods (LD). The neuroendocrine mechanisms responsible for seasonal changes in adiposity are not well understood; gene expression profiles of “clas- sic” regulatory peptides cannot fully explain these effects. The endocannabinoid (EC) system affects appetite and energy balance, and empirical data support the involvement of hypothalamic CB1 receptors in cannabinoid-induced feeding. To determine whether ECs are involved in mediating seasonal changes in energy balance in Siberian hamsters, we examined EC signaling across photoperiods. Specifically, we transferred animals from LD to SD and compared levels of central CB1 receptors to those of LD controls at 0, 2, 6, and 12 weeks (n = 5 per group). Effects of CB1 stimulation or block- ade on food intake and body mass were also examined in SD- and LD-acclimated animals by administering daily i.p. injections of a CB1 agonist (ACEA) or antagonist (SR141716) for five days (n = 7 per group). Immunocytochemical analysis revealed CB1 staining in sev- eral CNS regions including the hypothalamus; ongoing analyses will determine seasonal and sex differences in CB1 labeling. Blockade of CB1 reduced food intake in LD and SD hamsters. Collectively, these findings suggest that ECs affect energy balance and may regulate photoperiodic changes in adiposity. doi:10.1016/j.appet.2009.04.096 Plasma endocrine profiles during and following maintenance on a ketogenic diet M.A. HONORS * , B.M. DAVENPORT, K.P. KINZIG Department of Psy- chological Sciences and Ingestive Behavior Research Center, Purdue University West Lafayette, IN, USA Low-carbohydrate, high-fat ketogenic diets have been pop- ularized for weight loss in recent years. We have previously demonstrated that maintenance on a ketogenic diet (KD) affects multiple neuroendocrine systems involved in energy homeosta- sis. The present experiments explored the development of these changes over time and the endocrine effects of returning to a chow diet (CH) following 8 weeks of KD consumption. Eighty- eight male Long Evans rats were maintained on KD or CH 8 weeks, after which KD rats were placed on CH for 8 additional weeks. Samples were collected following 1, 4, and 8 weeks of KD feeding, and 1, 4, and 8 weeks after the switch to CH (9, 12, and 16 total weeks). Following 1 week on KD, leptin was significantly increased as compared to CH (CH: 2.6 ± 0.3 ng/mL, KD: 3.8 ± 0.4 ng/mL, p <0.05), as was insulin (CH: 1.4 ± 0.1 ng/mL, KD: 2.5 ± 0.1 ng/mL, p < 0.05). At 8 weeks, increased leptin (CH: 7.8 ± 1.3, KD: 14.9 ± 2.2 ng/mL, p < 0.01) and decreased insulin (CH: 2.2 ± 0.3 ng/mL, KD: 1.4 ± 0.2 ng/mL, p < 0.05) were present in KD rats. The switch to CH in KD rats produced a significant increase in caloric intake at week 16, as compared to CH (CH: 77.3 ± 4.3 kcal, KD: 92.3 ± 3.9 kcal, p < 0.05), and significantly increased ghrelin 1 week after the dietary switch and increased insulin 8 weeks after the switch. Collectively, these data demonstrate that maintenance on KD followed by a return to chow results in hyperphagia and enduring endocrine effects. doi:10.1016/j.appet.2009.04.097