Hypothalamic 2-Arachidonoylglycerol Regulates Multistage Process of High-Fat Diet Preferences

In this study, we examined alterations in the hypothalamic reward system related to high-fat diet (HFD) preferences. We previously reported that hypothalamic 2-arachidonoylglycerol (2-AG) and glial fibrillary acid protein (GFAP) were increased after conditioning to the rewarding properties of a HFD. Here, we hypothesized that increased 2-AG influences the hypothalamic reward system.The conditioned place preference test (CPP test) was used to evaluate HFD preferences. Hypothalamic 2-AG was quantified by gas chromatography-mass spectrometry. The expression of GFAP was examined by immunostaining and western blotting.Consumption of a HFD over either 3 or 7 days increased HFD preferences and transiently increased hypothalamic 2-AG levels. HFD consumption over 14 days similarly increased HFD preferences but elicited a long-lasting increase in hypothalamic 2-AG and GFAP levels. The cannabinoid 1 receptor antagonist O-2050 reduced preferences for HFDs after 3, 7, or 14 days of HFD consumption and reduced expression of GFAP after 14 days of HFD consumption. The astrocyte metabolic inhibitor Fluorocitrate blocked HFD preferences after 14 days of HFD consumption.High levels of 2-AG appear to induce HFD preferences, and activate hypothalamic astrocytes via the cannabinoid system. We propose that there may be two distinct stages in the development of HFD preferences. The induction stage involves a transient increase in 2-AG, whereas the maintenance stage involves a long lasting increase in 2-AG levels and activation of astrocytes. Accordingly, hypothalamic 2-AG may influence the development of HFD preferences

Effects of the CB₁ receptor antagonist O-2050 on HFD preferences.

<p>(a) Mice were given HFD for 3 days before CPP test. O-2050 (10 mg/kg i.p.) was administrated 1 h before the test. n = 8 for each. Results are expressed as the mean ± S.E.M. ^*<i>p</i><0.05 vs. Vehicle (Student's t-test). (b) Mice were given HFD for 14 days before CPP test. O-2050 (10 mg/kg i.p.) was administrated 1h before the test (test day) or for 14 days before the CPP test (14 days). n = 8 for each (CPP test). n = 6 for each (western blotting). Results are expressed as the mean ± S.E.M. Scale bar: 100 μm. ^*<i>p</i><0.05 vs. Vehicle (Student's t-test).</p

Effects of FC on preferences for a HFD.

<p>Results are expressed as the mean ± S.E.M. (a) The mice were fed a HFD for 3 days before the CPP test. (Vehicle, n = 10; 0.1 nmol/site, n = 10; 1.0 nmol/site, n = 11). (b) The mice were fed a HFD for 14 days before the CPP test. (Vehicle, n = 14; 0.1 nmol/site, n = 12; 1.0 nmol/site, n = 16). ^*p<0.05 vs. Vehicle (Tukey-Kramer tests).</p

Preference scores and hypothalamic 2-AG after SD or HFD consumption.

<p>(a) Filled circles represent the preference score in HFD intake mice. Open circles represent the preference score in SD intake mice. Preference score represents the mean change in time (s) spent in the HFD-paired side in pre-test and test sessions. n = 8 for each. Results are expressed as the mean ± S.E.M. *<i>p</i><0.05 vs. SD consumption group (Student's t-test were performed following two-way ANOVA). (b) Mice were given HFD (+) or SD (-) before the CPP test. Hypothalamic 2-AG were quantified by GC-MS. Filled squares represents the hypothalamic 2-AG after test. Open squares represents the hypothalamic 2-AG before test. n = 8 for each. Results are expressed as the mean ± S.E.M.</p