Bupropion and naltrexone combination alters high fructose corn syrup self-administration and gene expression in rats

Neural mechanisms underlying the role of fructose in overfeeding

Fructose consumption has been linked with metabolic syndrome and obesity. Fructose-based sweeteners like high fructose corn syrup taste sweeter, improve food palatability, and are increasingly prevalent in our diet. The increase in fructose consumption precedes the rise in obesity and is a contributing driver to the obesity epidemic worldwide. The role of dietary fructose in obesity can be multifactorial by promoting visceral adiposity, hypertension, and insulin resistance. Interestingly, one emergent finding from human and animal studies is that dietary fructose promotes overfeeding. As the brain is a critical regulator of food intake, we reviewed the evidence that fructose can act in the brain and elucidated the major brain systems underlying fructose-induced overfeeding. We found that fructose acts on multiple interdependent brain systems to increase orexigenic drive and the incentive salience of food while decreasing the latency between food bouts and reducing cognitive control to disinhibit feeding. We concluded that the collective actions of fructose may promote feeding behavior by producing a hunger-like state in the brain.

Understanding the appetite modulation pathways: The role of the FFA1 and FFA4 receptors

Pharmaconutrition is an area of current interest, especially concerning the advances in the pharmacology of nutrient-sensing receptors, as have been accomplished in the last 20 years. The family of free fatty acid (FFA) receptors is composed of four members, sequentially named as FFA1 to FFA4, which are activated by the short to long-chain fatty acids. The affinity of the FFA1 and FFA4 receptors for the omega-3 polyunsaturated fatty acids prompted pre-clinical and clinical investigations regarding their involvement in metabolic diseases. The main studies have been focused on the receptors' expression analyses, the featuring of knockout mice, and the assessment of selective synthetic ligands. These clearly have indicated a relevant role for FFA1 and FFA4 in the peripheral and central circuits for the regulation of energetic metabolism. This review article aimed to discuss the relevance of the FFA1 and FFA4 receptors in appetite-related complications, mainly related to obesity, cancer cachexia, and anorexia in the elderly, emphasizing whether their pharmacological modulation might be useful for the management of these disorders.

Evidence of hypoglycemic anhedonia and modulation by bupropion in rats

BACKGROUND

Disorders characterized by dysfunction of glucose metabolism are often comorbid with depression. The current study investigated whether a hypoglycemic state caused by 2-deoxy-d-glucose (2-DG) can result in anhedonic behaviors responsive to stimulation of monoamine activity.

METHODS

In experiment 1, male Sprague-Dawley rats were tested for maintenance of intra-oral self-administration (IOSA) of a sweet solution after pre-treatment with 300 or 500 mg/kg 2-DG, a blocker of glucose metabolism. Experiment 2 determined whether exposure to an environment previously paired with the effects of 2-DG (0, 200 or 300 mg/kg) can influence IOSA, and whether 2-DG can modify taste reactivity to same sweet solution. Finally, experiment 3 examined whether 0 or 30 mg/kg bupropion, a monoamine-reuptake blocker, would attenuate the effect of 300 mg/kg 2-DG on IOSA and taste reactivity.

RESULTS

It was found that 2-DG produced a sustained decrease in IOSA when animals were tested drug-free. This decrease in IOSA did not appear linked to place conditioning or to alterations in taste reactivity, and it was partially normalized by pre-treatment with bupropion.

CONCLUSIONS

Taken together, these results in rats suggest that rapid hypoglycemia can induce an anhedonic state characterized by impaired consummatory responses to nutritional incentive stimuli and that can be alleviated by the antidepressant bupropion.

The Role of Melanocortin Plasticity in Pain-Related Outcomes After Alcohol Exposure

The global COVID-19 pandemic has shone a light on the rates and dangers of alcohol misuse in adults and adolescents in the US and globally. Alcohol exposure during adolescence causes persistent molecular, cellular, and behavioral changes that increase the risk of alcohol use disorder (AUD) into adulthood. It is established that alcohol abuse in adulthood increases the likelihood of pain hypersensitivity and the genesis of chronic pain, and humans report drinking alcohol to relieve pain symptoms. However, the longitudinal effects of alcohol exposure on pain and the underlying CNS signaling that mediates it are understudied. Specific brain regions mediate pain effects, alcohol effects, and pain-alcohol interactions, and neural signaling in those brain regions is modulated by neuropeptides. The CNS melanocortin system is sensitive to alcohol and modulates pain sensitivity, but this system is understudied in the context of pain-alcohol interactions. In this review, we focus on the role of melanocortin signaling in brain regions sensitive to alcohol and pain, in particular the amygdala. We also discuss interactions of melanocortins with other peptide systems, including the opioid system, as potential mediators of pain-alcohol interactions. Therapeutic strategies that target the melanocortin system may mitigate the negative consequences of alcohol misuse during adolescence and/or adulthood, including effects on pain-related outcomes.

Endogenous Opiates and Behavior: 2018

This paper is the forty-first consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2018 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (2), the roles of these opioid peptides and receptors in pain and analgesia in animals (3) and humans (4), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (5), opioid peptide and receptor involvement in tolerance and dependence (6), stress and social status (7), learning and memory (8), eating and drinking (9), drug abuse and alcohol (10), sexual activity and hormones, pregnancy, development and endocrinology (11), mental illness and mood (12), seizures and neurologic disorders (13), electrical-related activity and neurophysiology (14), general activity and locomotion (15), gastrointestinal, renal and hepatic functions (16), cardiovascular responses (17), respiration and thermoregulation (18), and immunological responses (19).

Effects of high fructose corn syrup on ethanol self-administration in rats

OBJECTIVE

The addition of sweeteners to alcoholic beverages is thought to facilitate heavy alcohol consumption, and this may be of particular concern when the additive is high fructose corn syrup (HFCS).

METHODS

Four experiments in male Sprague-Dawley rats were performed to investigate whether the addition of 25% HFCS to ethanol (5%, 10%, and 20% v/v ethanol) would alter its intraoral operant self-administration, palatability, and sensitivity to food deprivation stress.

RESULTS

As anticipated, HFCS drastically increased ethanol intake, and this effect appeared driven by its caloric value. Importantly, HFCS increased the persistence of operant responding following extinction in animals trained to self-administer the combination, and the addition of HFCS to ethanol changed subsequent responses to ethanol, including increased palatability and intake.

CONCLUSIONS

These results in rats suggest that the addition of HFCS to the list of ingredients in sweetened alcoholic beverages could play a significant role in the harmful consumption of ethanol-containing beverages.

Sex differences in the effect of bupropion and naltrexone combination on alcohol drinking in mice

A fixed dose combination of bupropion (BPP) and naltrexone (NTX), Contrave®, is an FDA approved pharmacotherapy for the treatment of obesity. A recent study found that combining BPP with low-dose NTX reduced alcohol drinking in alcohol-preferring male rats. To explore potential pharmacological effects of the BPP + NTX combination on alcohol drinking, both male and female C57Bl/6J mice were tested on one-week drinking-in-the dark (DID) and three-week intermittent access (IA) models. Neuronal proopiomelanocortin (POMC) enhancer knockout (nPE^-/-) mice with hypothalamic-specific deficiency of POMC, and its bioactive peptides melanocyte stimulating hormone and beta-endorphin, were used as a genetic control for the effects of the BPP + NTX. A single administration of BPP + NTX (10 mg/kg + 1 mg/kg) decreased alcohol intake after DID in C57Bl/6J males, but not females. Also in C57Bl/6J males, BPP + NTX reduced intake of the caloric reinforcer sucrose, but not the non-caloric reinforcer saccharin. In contrast, BPP + NTX had no effect on alcohol DID in nPE^-/- males. Pretreatment with the selective melanocortin 4 receptor (MC4R) antagonist HS014 reversed the anti-dipsogenic effect of BPP + NTX on alcohol DID in C57Bl/6J males. In the 3-week chronic IA model, single or repeated administrations for four days of BPP + NTX reduced alcohol intake and preference in C57Bl/6J males only. The behavioral measures observed in C57Bl/6J mice provide clear evidence that BPP + NTX profoundly reduced alcohol drinking in males, but the doses tested were not effective in females. Furthermore, our results suggest a hypothalamic POMC/MC4R-dependent mechanism for the observed BPP + NTX effects on alcohol drinking in male mice.