Effects of fluvoxamine on food intake during rebound hyperphagia in rats

Modeling energy intake by adding homeostatic feedback and drug intervention

Energy intake (EI) is a pivotal biomarker used in quantification approaches to metabolic disease processes such as obesity, diabetes, and growth disorders. Eating behavior is however under both short-term and long-term control. This control system manifests itself as tolerance and rebound phenomena in EI, when challenged by drug treatment or diet restriction. The paper describes a model with the capability to capture physiological counter-regulatory feedback actions triggered by energy imbalances. This feedback is general as it handles tolerance to both increases and decreases in EI, and works in both acute and chronic settings. A drug mechanism function inhibits (or stimulates) EI. The deviation of EI relative to a reference level (set-point) serves as input to a non-linear appetite control signal which in turn impacts EI in parallel to the drug intervention. Three examples demonstrate the potential usefulness of the model in both acute and chronic dosing situations. The model shifts the predicted concentration-response relationship rightwardly at lower concentrations, in contrast to models that do not handle functional adaptation. A fourth example further shows that the model may qualitatively explain differences in rate and extent of adaptation in observed EI and its concomitants in both rodents and humans.

The effect of vertical sleeve gastrectomy on food choice in rats

Objective

Diets high in fat are implicated in the development and maintenance of obesity, and obese individuals display greater preferences for high-fat foods than do their lean counterparts. Weight-reduction bariatric surgery is associated with changes in food choice. In particular, after Roux-en-Y Gastric Bypass (RYGB), humans and rodents select or prefer foods which are lower in fat content. We asked whether a bariatric surgical procedure limited to the stomach, Vertical Sleeve Gastrectomy (VSG), causes a similar reduction of fat intake/preference.

Research Design and Methods

Rats received VSG or Sham surgery or remained surgically naïve, and were assessed for food preference using three diet-choice paradigms. Using progressive-ratio and conditioned taste aversion paradigms, we further asked whether surgically-induced changes in food choice are secondary to changes in the reward value of food and/or to the formation of a food aversion. Finally, food choice was compared between VSG and RYGB-operated rats.

Results

VSG rats decreased their intake of dietary fat, and shifted their preference toward lower caloric-density foods. This change in food choice was not associated with changes in motivated responding on a progressive-ratio schedule for either a fat or a carbohydrate food reinforcer. When VSG and RYGB were compared directly, both procedures caused comparable changes in food choice. The conditioned taste aversion paradigm revealed that VSG rats form an aversion to an intra-gastric oil administration whereas RYGB rats do not.

Conclusions

VSG and RYGB, two anatomically-distinct bariatric procedures, produce similar changes in food choice.

Fluvoxamine attenuated endoplasmic reticulum stress-induced leptin resistance

Increasing evidence indicates that endoplasmic reticulum stress (ER stress) is involved in the development of metabolic syndrome. However, pharmacological treatments targeting ER stress are not well understood. In the present study, we found that fluvoxamine, a selective serotonin reuptake inhibitor used for depression, can attenuate ER stress-induced "leptin resistance," i.e., insensitivity to the anti-obesity hormone leptin. Treatment with tunicamycin, an ER stress-inducing reagent, caused cell death which was significantly inhibited by fluvoxamine. Leptin activates JAK2-STAT3 signaling. ER stress caused an impairment of leptin-induced STAT3 phosphorylation which was reversed by fluvoxamine. Fluvoxamine would be a novel leptin-sensitizing drug, which targets ER stress.

A serotoninergic basis for hyperphagic eating changes in Alzheimer's disease

Hyperphagia and associated eating changes occur frequently in Alzheimer's disease (AD) and lead to considerable morbidity. However, the neurochemical basis for these neuropsychiatric behaviours is at present unclear. In this study, we measured serotonin transporters, 5-HT(1A), 5-HT(2A), and 5-HT(4) receptors using radioligand binding assays in the postmortem temporal cortex of a cohort of controls and AD patients longitudinally assessed for hyperphagia. We found significant decreases in 5-HT(4) receptor densities in the hyperphagic, but not normophagic, AD group. Our data suggest that 5-HT(4) receptor deficits may be a specific neurochemical correlate of hyperphagia, and point to the potential pharmacotherapeutic utility of 5-HT(4) agonists for these behaviours in AD.

The selective serotonin reuptake inhibitor fluvoxamine suppresses post-feeding hyperactivity induced by food restriction in rats

Previous studies demonstrated that rats allowed access to running wheel with food restriction schedules run excessively. This hyperactivity consisted of a pre-feeding activity (an increase in running activity before the feeding time, also termed food-anticipatory activity: FAA) and a post-feeding activity (an increase in running activity after the feeding time, succeeding activity: SA). Here we evaluated the effect of fluvoxamine, a selective serotonin reuptake inhibitor, on food restriction-induced hyperactivity in rats. Furthermore, the effect of fluvoxamine on each of the FAA and the SA was also investigated. Rats were individually housed in a running-wheel cage under food restriction for 3 h per day, and running activity was measured for 7 consecutive days. This restricted feeding significantly increased the running activity and decreased body weight. Simultaneous administration of fluvoxamine (50 mg/kg/day, p.o.) for 7 days suppressed the increase in running activity (P<0.05) with no modification of the decrease in body weight or food intake. Analysis of each activity revealed that fluvoxamine's efficacy was observed only in the SA (p<0.01). These results suggest that repeated treatment with fluvoxamine attenuates the hyperactivity, which is exclusively dependent on the substantial reduction in the SA.

Reduction of anxiety after restricted feeding in the rat: implication for eating disorders

BACKGROUND

Eating-disorder patients exhibit not only abnormal eating attitudes but also pathologic anxiety-like behaviors. The specific nature of the relationship between dieting and anxiety-like behavior is unknown.

METHODS

To investigate the adaptational changes that resulted from chronic restricted scheduled feeding (2-hour access per day for 2 weeks) and subsequent free refeeding, longitudinal changes in the microstructure of feeding behavior were studied in male rats. To study the relationship between restricted feeding and anxiety-like behavior, separate rats were tested in the elevated plus-maze under the following conditions: 1) free feeding; 2) acute food restriction (2-hour access for 1 day); 3) chronic food restriction (for 10 days); or 4) postrecovery (after 10 days of free feeding subsequent to chronic food restriction).

RESULTS

The effects of chronic food restriction on meal structure diminished within a few days after refeeding. Decreased anxiety-like behavior was seen during acute and chronic food restriction and did not reflect nonspecific behavioral activation. Anxiolytic-like effects persisted after 10 days of refeeding.

CONCLUSIONS

Chronic food restriction produced reductions in anxiety-like behavior that persisted beyond the normalization of food intake patterns. The findings might have etiologic and pathophysiologic relevance for the restrained eating pattern in eating-disorder patients with comorbid anxious symptoms.

Prefrontal and striatal dopamine metabolism during enhanced rebound hyperphagia induced by space restriction--a rat model of binge eating

BACKGROUND

Several lines of evidence indicate that abnormalities in brain dopamine and serotonin metabolism may play an important role in bulimia nervosa. However, the regional neurochemical mechanism of the binge eating is poorly understood. Our purpose was to elucidate brain neurochemical mechanisms of binge eating using a rat model.

METHODS

The dopamine release and metabolism in the prefrontal cortex (PFC) and in the ventrolateral striatum (VLS) of rats were studied using microdialysis during enhanced rebound hyperphagia induced by space restriction (an animal model of binge eating).

RESULTS

The rats showed rebound hyperphagic state when they were released from scheduled feeding (2 hours/day feeding for 7 days). The hyperphagia was further enhanced when they were put in a space-restricted cage where their mobility was restricted. Dopamine release and metabolism were increased both in the PFC and in the VLS during the enhanced rebound hyperphagia.

CONCLUSIONS

These results tentatively suggest that increased dopamine release and metabolism in the PFC and in the VLS may be related to space restriction and to activation of motor function involved in feeding behavior, respectively. The enhanced rebound hyperphagia induced by space restriction may be useful as an animal model of binge eating.