Effects of pramlintide on energy intake and food preference in rats given a choice diet

From the pancreas to the amygdala: New brain area critical for ingestive and motivated behavior control exerted by amylin

Amylin, a pancreatic peptide, has a well-established role in feeding behavior control. Amylin analogues are clinically utilized in patients with diabetes and are under investigation as potential anti-obesity pharmacotherapies. The neural circuits underlying actions of amylin on behavior are not well understood. While amylin was found to bind to the central amygdala (CeA) of rodents and primates and we found that all components of amylin receptors are present in the CeA, their potential role in physiology or behavior remains unknown. Here, we investigated the impact of this potential pancreas - CeA amylin-mediated communication - on ingestive and motivated behaviors. Activation of CeA amylin receptors resulted in a robust hypophagia, reduced food-motivated behavior, and altered macronutrient preference in male and female rats. Clinically used amylin analogue, pramlintide, reduced meal size and frequency by acting on the CeA. Disruption of CeA amylin signaling led to hyperphagia and body weight gain in a sex divergent manner. Importantly, CeA amylin signaling was required for appetite suppression induced by peripherally applied amylin, highlighting translational relevance of this brain site. Our data indicate the CeA is a critical neural substrate for amylin signaling.

Synergistic-like decreases in alcohol intake following combined pharmacotherapy with GLP-1 and amylin in male rats

BACKGROUND AND PURPOSE

The limited effectiveness of current pharmacological treatments for alcohol use disorder (AUD) highlights the need for novel therapies. These may involve the glucagon-like peptide-1 receptor or the amylin receptor, as treatment with agonists targeting either of these receptors lowers alcohol intake. The complexity of the mechanisms underlying AUD indicates that combining agents could enhance treatment efficacy. While a combination of amylin receptor and GLP-1 receptor agonists reduced food intake and body weight synergistic-like, its influence on alcohol intake is unknown.

EXPERIMENTAL APPROACH

Effects of a range of dose-combinations of GLP-1 receptor (dulaglutide) and amylin receptor (salmon calcitonin; sCT) agonists on alcohol intake were explored in male and female rats. We used dose combinations that either lowered alcohol intake as monotherapy (0.1 mg·kg-1 + 5 μg·kg-1), or that did not affect alcohol consumption per se (0.075 mg·kg-1 + 2 μg·kg-1).

KEY RESULTS

Acute administration of dulaglutide and sCT (0.1 mg·kg-1 + 5 μg·kg-1) reduced alcohol intake in males, but not in females. When higher doses were evaluated in female rats, a decrease in alcohol intake was observed. Furthermore, the low dose combination (0.075 mg·kg-1 + 2 μg·kg-1) decreased, in in a synergistic-like manner, alcohol intake and prevented abstinence-induced drinking without affecting kaolin intake in males. However, tolerance developed during sub-chronic treatment.

CONCLUSION AND IMPLICATIONS

Collectively, these findings show that the combination of dulaglutide and sCT decreased, in in a synergistic-like manner, alcohol consumption in male rats. Contrarily, higher doses are required for females.

Chronic pramlintide decreases feeding via a reduction in meal size in male rats

Amylin, a pancreatic hormone, is well-established to suppress feeding by enhancing satiation. Pramlintide, an amylin analog that is FDA-approved for the treatment of diabetes, has also been shown to produce hypophagia. However, the behavioral mechanisms underlying the ability of pramlintide to suppress feeding are unresolved. We hypothesized that systemic pramlintide administration in rats would reduce energy intake, specifically by reducing meal size. Male rats were given b.i.d. administration of intraperitoneal pramlintide or vehicle for 1 week, and chow intake, meal patterns, and body weight were monitored throughout the test period. Consistent with our hypothesis, pramlintide decreased chow intake mainly via suppression of meal size, with corresponding reductions in meal duration on several days. Fewer effects on meal number or feeding rate were detected. Pramlintide also reduced weight gain over the 1-week study. These results highlight that the behavioral mechanisms by which pramlintide produces hypophagia are similar to those driven by amylin itself, and provide important insight into the ability of this pharmacotherapy to promote negative energy balance over a period of chronic administration.

Amylin Modulates a Ventral Tegmental Area-to-Medial Prefrontal Cortex Circuit to Suppress Food Intake and Impulsive Food-Directed Behavior

BACKGROUND

A better understanding of the neural mechanisms regulating impaired satiety to palatable foods is essential to treat hyperphagia linked with obesity. The satiation hormone amylin signals centrally at multiple nuclei including the ventral tegmental area (VTA). VTA-to-medial prefrontal cortex (mPFC) projections encode food reward information to influence behaviors including impulsivity. We hypothesized that modulation of VTA-to-mPFC neurons underlies amylin-mediated decreases in palatable food-motivated behaviors.

METHODS

We used a variety of pharmacological, behavioral, genetic, and viral approaches (n = 4-16/experiment) to investigate the anatomical and functional circuitry of amylin-controlled VTA-to-mPFC signaling in rats.

RESULTS

To first establish that VTA amylin receptor (calcitonin receptor) activation can modulate mPFC activity, we showed that intra-VTA amylin decreased food-evoked mPFC cFos. VTA amylin delivery also attenuated food-directed impulsive behavior, implicating VTA amylin signaling as a regulator of mPFC functions. Palatable food activates VTA dopamine and mPFC neurons. Accordingly, dopamine receptor agonism in the mPFC blocked the hypophagic effect of intra-VTA amylin, and VTA amylin injection reduced food-evoked phasic dopamine levels in the mPFC, supporting the idea that VTA calcitonin receptor activation decreases dopamine release in the mPFC. Surprisingly, calcitonin receptor expression was not found on VTA-to-mPFC projecting neurons but was instead found on GABAergic (gamma-aminobutyric acidergic) interneurons in the VTA that provide monosynaptic inputs to this pathway. Blocking intra-VTA GABA signaling, through GABA receptor antagonists and DREADD (designer receptor exclusively activated by designer drugs)-mediated GABAergic neuronal silencing, attenuated intra-VTA amylin-induced hypophagia.

CONCLUSIONS

These results indicate that VTA amylin signaling stimulates GABA-mediated inhibition of dopaminergic projections to the mPFC to mitigate impulsive consumption of palatable foods.