Metabolic inhibition increases feeding and brain Fos-like immunoreactivity as a function of diet

The role of liver fructose-1,6-bisphosphatase in regulating appetite and adiposity

Liver fructose-1,6-bisphosphatase (FBPase) is a regulatory enzyme in gluconeogenesis that is elevated by obesity and dietary fat intake. Whether FBPase functions only to regulate glucose or has other metabolic consequences is not clear; therefore, the aim of this study was to determine the importance of liver FBPase in body weight regulation. To this end we performed comprehensive physiologic and biochemical assessments of energy balance in liver-specific transgenic FBPase mice and negative control littermates of both sexes. In addition, hepatic branch vagotomies and pharmacologic inhibition studies were performed to confirm the role of FBPase. Compared with negative littermates, liver-specific FBPase transgenic mice had 50% less adiposity and ate 15% less food but did not have altered energy expenditure. The reduced food consumption was associated with increased circulating leptin and cholecystokinin, elevated fatty acid oxidation, and 3-β-hydroxybutyrate ketone levels, and reduced appetite-stimulating neuropeptides, neuropeptide Y and Agouti-related peptide. Hepatic branch vagotomy and direct pharmacologic inhibition of FBPase in transgenic mice both returned food intake and body weight to the negative littermates. This is the first study to identify liver FBPase as a previously unknown regulator of appetite and adiposity and describes a novel process by which the liver participates in body weight regulation.

Conditioned flavor aversion and brain Fos expression following exposure to arsenic

Recent advances in the knowledge of the cellular effects of arsenic have provided insights into the molecular mechanisms of arsenic-associated carcinogenesis, immunotoxicity and cardiovascular disease. In the present experiments we tested the hypothesis that the arrival of arsenic to the gastrointestinal (GI) tract is detected by the gut-brain axis, which includes hindbrain and forebrain nuclei activated by GI stimulation. As a marker of neuronal activation we measured Fos expression using immunohistochemistry. Because Fos expression in these nuclei is closely linked to the development of conditioned flavor aversion (CFA) we also tested the effect of arsenic on CFA. Our experiments indicate that arsenic ingestion is readily detected by the brain, as shown by increased Fos expression after oral administration of arsenic. Furthermore, the vagus nerve, which supplies information from the GI tract to the brain, is not involved in this response because a complete subdiaphragmatic vagotomy did not reduce the effect of arsenic on brain Fos expression, but enhanced this response. In parallel, arsenic ingestion is associated with a robust, dose-dependent CFA, which started at doses as low as 0.1 mg/kg body weight. In summary, these data indicate that arsenic given by oral administration is detected by the brain in low concentrations, and activates specific nuclei, which might trigger behavioral responses, such as CFA.

Baclofen reduces fat intake under binge-type conditions

The GABA-B agonist baclofen reduces drug self-administration in rats and has shown promise clinically in the treatment of substance abuse. Baclofen generally does not reduce food intake in non-binge feeding protocols. In this study, baclofen was tested in a fat-binge protocol. Thirty male rats were divided into three groups (B: binge; FM: fat-matched; C: chow). B received a bowl of vegetable shortening for 2 h on Monday, Wednesday, and Friday (MWF) and continuous access to powdered chow (regular chow) in all phases. FM had continuous access to a regular chow+shortening mixture (FM chow) that provided the same proportion of shortening and regular chow that the B rats consumed in all phases. In addition, FM had the following: phase 1: no separate bowl of shortening; phase 2: 2-h MWF access to a separate bowl of shortening; phase 3, daily 2-h access to a separate bowl of shortening; C rats had continuous access to the regular chow in all phases. In addition, C had the following: phase 1: no separate bowl of shortening; phase 2: 2-h MWF access to a separate bowl of shortening; in phase 3, daily 2-h access to a separate bowl of shortening. Baclofen (1.0, 1.8 mg/kg, i.p.) reduced shortening intake regardless of access condition. Baclofen had no effect on, or stimulated, FM and regular chow intake. These results demonstrate that baclofen can reduce fat intake in rats under binge-type conditions. Furthermore, these results indicate that bingeing, as modeled in our protocol, is different from other forms of food intake and may share similarities with substance abuse.

Social recognition memory requires two stages of protein synthesis in mice

Olfactory recognition memory was tested in adult male mice using a social discrimination task. The testing was conducted to begin to characterize the role of protein synthesis and the specific brain regions associated with activity in this task. Long-term olfactory recognition memory was blocked when the protein synthesis inhibitor anisomycin was injected 20 min before, immediately after, or 6 h after sampling. No effect was observed when anisomycin was administered 3 h or 18 h after sampling. Immunohistochemical analysis of Fos expression revealed that sampling-like exposure to a juvenile increased the activity of a subset of cells in the accessory olfactory bulb and the brain areas that are associated with it. Additionally, increased Fos expression was measured in the main olfactory bulb and the piriform cortex, whereas no signs of activation were seen in the cortical nucleus of the amygdala, all components of the main olfactory system. No increases in Fos immunoreactivity were observed after 4 h. Our data suggest that long-lasting olfactory recognition memory requires two stages of protein synthesis. The first stage takes place within 1-2 h and the second stage between 6-7 h after sampling. The first but not the second stage is paralleled by an increase in the number of Fos-immunoreactive cells in brain areas associated with both the main and accessory olfactory systems. It therefore appears that the role of the second stage of protein synthesis in recognition memory depends on the integrity of the first stage of protein synthesis.

High-fat diet prevents eating response and attenuates liver ATP decline in rats given 2,5-anhydro-D-mannitol

Administration of the fructose analog 2,5-anhydro-D-mannitol (2,5-AM) stimulates eating in rats fed a low-fat diet but not in those fed a high-fat diet that enhances fatty acid oxidation. The eating response to 2,5-AM treatment is apparently triggered by a decrease in liver ATP content. To assess whether feeding a high-fat diet prevents the eating response to 2,5-AM by attenuating the decrease in liver ATP, we examined the effects of the analog on food intake, liver ATP content, and hepatic phosphate metabolism [using in vivo 31P-NMR spectroscopy (NMRS)]. Injection (intraperitoneal) of 300 mg/kg 2,5-AM increased food intake in rats fed a high-carbohydrate/low-fat diet, but not in those fed high-fat/low-carbohydrate (HF/LC) food. Liver ATP content decreased in all rats given 2,5-AM compared with saline, but it decreased about half as much in rats fed the HF/LC diet. NMRS on livers of anesthetized rats indicated that feeding the HF/LC diet attenuates the effects of 2,5-AM on liver ATP by reducing phosphate trapping. These results suggest that rats consuming a high-fat diet do not increase food intake after injection of 2,5-AM, because the analog is not sufficiently phosphorylated and therefore fails to decrease liver energy status below a level that generates a signal to eat.

Metabolic inhibitors synergistically decrease hepatic energy status and increase food intake

Previous studies indicate that administration of the metabolic inhibitor, 2,5-anhydro-D-mannitol (2,5-AM) or methyl palmoxirate (MP), induces feeding behavior in rats by lowering hepatic energy status. Combined treatment with these agents synergistically increases food intake. The present study was designed to investigate whether combined treatment also has a synergistic effect on hepatic energy status. Rats treated with both inhibitors increased feeding behavior compared with the controls, whereas those treated with 2, 5-AM or MP alone did not. Although 2,5-AM alone lowered hepatic ATP content regardless of MP treatment, only the combination resulted in decreases in hepatic ATP/ADP ratio and phosphorylation potential. MP treatment did not affect the uptake of 2,5-AM into liver. These results suggest that a reduction in hepatic energy status is the common triggering signal for eating behavior induced by 2,5-AM and MP and provide additional evidence for an integrated metabolic control of food intake.