GABAA receptors in nucleus accumbens shell mediate the hyperphagia and weight gain following haloperidol treatment in rats

Activation of Calcium-Sensing Receptor in the Area Postrema Inhibits Food Intake via Glutamatergic and GABAergic Signaling Pathways

SCOPE

A high-protein diet has become a popular way to lose weight. Calcium-sensing receptor (CaSR) is activated by amino acids in addition to calcium ions. CaSR shows dense expression in the area postrema (AP), which participates in feeding regulation. The effect of CaSR in the AP on food intake and the potential mechanism involved is investigated.

METHODS AND RESULTS

Male C57BL/6 mice are used to observe the effect of R568 (agonist of CaSR) on food intake. Enzyme-linked immunosorbent assay, immunofluorescence staining, and chemogenetics are used to explore the neural signaling involved. CaSR activation in the AP inhibited acute feeding; R568 increases the content of glutamate and γ-aminobutyric acid (GABA) in the AP, whereas only glutamatergic neurons mediate the effect of R568. GABA-A receptor and ionic glutamate receptor (N-methyl-D-aspartate receptor [NMDAR]) in the paraventricular nucleus of hypothalamus (PVN) are involved in the effect of R568. Promotion of oxytocin (OT) synthesis in the PVN also participates in the effect of R568, and this mechanism is mediated by NMDAR in the PVN.

CONCLUSION

CaSR activation in the AP suppresses feeding, and AP-PVN glutamatergic and GABAergic signaling pathways are involved.

Role of the striatal dopamine, GABA and opioid systems in mediating feeding and fat intake

Food intake, which is a highly reinforcing behavior, provides nutrients required for survival in all animals. However, when fat and sugar consumption goes beyond the daily needs, it can favor obesity. The prevalence and severity of this health problem has been increasing with time. Besides covering nutrient and energy needs, food and in particular its highly palatable components, such as fats, also induce feelings of joy and pleasure. Experimental evidence supports a role of the striatal complex and of the mesolimbic dopamine system in both feeding and food-related reward processing, with the nucleus accumbens as a key target for reward or reinforcing-associated signaling during food intake behavior. In this review, we provide insights concerning the impact of feeding, including fat intake, on different types of receptors and neurotransmitters present in the striatal complex. Reciprocally, we also cover the evidence for a modulation of palatable food intake by different neurochemical systems in the striatal complex and in particular the nucleus accumbens, with a focus on dopamine, GABA and the opioid system.

Nucleus Accumbens Functional Connectivity with the Frontoparietal Network Predicts Subsequent Change in Body Mass Index for American Children

Background: Nucleus accumbens (NAc) is a brain structure with a well-established role in the brain reward processing system. Altered function of the NAc is shown to have a role in the development of food addiction and obesity. However, less is known about sex differences in the role of NAc function as a predictor of children’s change in body mass index (BMI) over time. Aim: We used the Adolescent Brain Cognitive Development data (version 2.01) to investigate sex differences in the predictive role of the NAc functional connectivity with the frontoparietal network on children’s BMI change over a one-year follow-up period. Methods: This 1-year longitudinal study successfully followed 3784 9–10-year-old children. Regression models were used to analyze the data. The predictor variable was NAc functional connectivity with the frontoparietal network measured using resting-state functional magnetic resonance imaging (fMRI). The primary outcome was BMI at the end of the 1-year follow up. Covariates included race, ethnicity, age, socioeconomic factors, and baseline BMI. Sex was the effect modifier. Results: NAc functional connectivity with the frontoparietal network was predictive of BMI changes over time. This association remained significant above and beyond all covariates. The above association, however, was only significant in female, not male children. Conclusion: The epidemiological observation that NAc functional connectivity is associated with BMI changes in children is an extension of well-controlled laboratory studies that have established the role of the NAc in the brain reward processing. More research is needed on sex differences in the brain regions that contribute to childhood obesity.

Stronger Association between Nucleus Accumbens Density and Body Mass Index in Low-Income and African American Children

BACKGROUND

The nucleus accumbens' (NAc) size, function, and density influence individuals' body mass index (BMI). However, little is known about racial and socioeconomic status (SES) differences in the role of NAc density as a predictor of childhood BMI.

OBJECTIVES

We used the Adolescent Brain Cognitive Development (ABCD) data to investigate racial and SES differences in the effect of NAc density on childhood BMI.

METHODS

This cross-sectional study included 9497 children between ages 9 and 10. Mixed-effects regression models were used to analyze the data. The predictor variable was NAc density measured using diffusion MRI (dMRI). The outcome variable was BMI, operationalized as a continuous variable. Covariates included sex, age, ethnicity, family structure, and parental education. Race (White, African American, Asian, and Other/mixed) and household income (< 50k, 50-100 k, and 100+ k) were the moderators.

RESULTS

High NAc diffusion tension (density) was predictive of higher BMI, net of covariates. However, the positive association between NAc density and BMI was stronger in African Americans than in White, and in low-income than in high-income children.

CONCLUSIONS

Our findings suggest that although high NAc has implications for children's BMI, this effect varies across racial and SES groups. More research should be performed on the role of obesogenic environments in altering the effect of NAc on childhood BMI.

Involvement of neuropeptide CART in the central effects of insulin on feeding and body weight

While insulin secreted from pancreas plays a pivotal role in the control of glucose homeostasis, it also interacts with hypothalamic sites and negatively influences the energy balance. The present study was undertaken to reveal the functional interaction between cocaine- and amphetamine-regulated transcript (CART), a well-known anorexic peptide, and insulin within the framework of hypothalamus in the regulation of feeding behavior and body weight. Insulin was administered daily by intracerebroventricular (icv) route, alone or in combination with CART (icv) for a period of seven days. Immediately thereafter, preweighed food was offered to the animals at the commencement of the dark phase. The food intake and body weight were measured daily just prior to next injection. Furthermore, brains of insulin-treated rats were processed for the immunohistochemical analysis of CART-containing elements in the hypothalamus. Treatment with insulin (6 mU, icv) for a period of 7 days caused a significant decrease in food intake and body weight as compared to control. Concomitant administration of CART (0.5 μg, icv) potentiated insulin-induced anorexia and weight loss. Insulin administration resulted in a significant increase in CART immunoreactivity in the hypothalamic arcuate, paraventricular, dorsomedial and ventromedial nuclei. We suggest that increased CART contents in the hypothalamus may be causally linked with anorexia and weight loss induced by insulin.

A role of neuropeptide CART in hyperphagia and weight gain induced by olanzapine treatment in rats

Although olanzapine is highly efficacious and most widely used second generation antipsychotic drug, the success of treatment has been hampered by its propensity to induce weight gain. While the underlying neuronal mechanisms are unclear, their elucidation may help to target alternative pathways regulating energy balance. The present study was undertaken to define the role of cocaine- and amphetamine-regulated transcript (CART), a well-known anorexic peptide, in olanzapine-induced hyperphagia and body weight gain in female rats. Olanzapine was administered daily by intraperitoneal route, alone or in combination with CART (intracerebroventricular) for a period of two weeks. Immediately after drug administrations, preweighed food was offered to the animals at the commencement of the dark phase. The food intake and body weight were measured daily just prior to next injection. Furthermore, the brains of olanzapine-treated rats were processed for the immunohistochemical analysis of CART-containing elements in the hypothalamus. Treatment with olanzapine (0.5 mg/kg) for the duration of 14 days produced a significant increase in food intake and body weight as compared to control. However, concomitant administration of CART (0.5 µg) attenuated the olanzapine-induced hyperphagia and weight gain. Olanzapine administration resulted in a significant reduction in CART immunoreactivity in the hypothalamic arcuate, paraventricular, dorsomedial and ventromedial nuclei. We suggest that decreased CART contents in the hypothalamus may be causally linked with the hyperphagia and weight gain induced by olanzapine.

Evidence for the involvement of neuropeptide Y in the antidepressant effect of imipramine in type 2 diabetes

Depression is a major comorbidity factor of diabetes and the outcome of one disorder influences the other. Our aim is to scrutinize the link between the two, if any. Since neuropeptide Y (NPY) system plays an important role in regulating central glucose sensing mechanisms, and also depression-related behavior, we test the involvement of NPY in the modulation of depression in type 2 diabetic mice. The mice were fed on high-fat diet and administered with low dose of streptozotocin to induce type 2 diabetes. These animals showed augmented plasma glucose and increased immobility time in tail suspension test (TST) suggesting induction of diabetes and depression. Intracerebroventricular (icv) treatment with NPY or NPY Y1 receptor agonist [Leu(31), Pro(34)]-NPY and intraperitoneal treatment with imipramine decreased immobility time. However, opposite effect was produced by NPY Y1 receptor antagonist BIBP3226 (icv). Moreover, reduced immobility time by imipramine was potentiated by NPY and [Leu(31), Pro(34)]-NPY, but attenuated by BIBP3226. Immunohistochemical analysis of the different nuclei of the extended amygdala, the region primarily involved in affective disorders, was undertaken. A significant reduction in NPY immunoreactivity in the central nucleus of amygdala, nucleus accumbens shell and lateral division of bed nucleus of stria terminalis of the diabetic mice was noticed; the response was ameliorated in imipramine treated animals. The results suggest that decreased NPY expression in the extended amygdala might be causally linked with the depression induced following type 2 diabetes and that the antidepressant action of imipramine in diabetic mice might be mediated by NPY-NPY Y1 receptor system.

Involvement of hypothalamic neuropeptide Y in pentazocine induced suppression of food intake in rats

The potent orexigenic peptide neuropeptide Y (NPY) has been considered as a possible endogenous ligand for a subpopulation of sigma receptors (SigR). However, their mutual interaction with reference to feeding behavior remains poorly understood. In the present study, we explored the possible interaction between sigma1 receptors (Sig1R) agonist, pentazocine, and NPY on food intake in satiated rats. While pentazocine dose-dependently reduced the food intake, NPY significantly increased it at 2, 4 and 6h post injection time points. In combination studies, pretreatment with NPY (0.1 nmol/rat, intra-PVN) normalized the inhibitory effect of pentazocine (60 μg/rat, intra-PVN) on food intake. Similarly, pre-treatment with pentazocine (30 μg/rat, intra-PVN) significantly antagonized the orexigenic effect of NPY (0.5 and 1.0 nmol/rat, intra-PVN). Moreover, pentazocine treatment decreased NPY immunoreactivity in arcuate (ARC), paraventricular (PVN), dorsomedial (DMH) and ventromedial (VMH) nuclei of hypothalamus. However, no change was observed in lateral hypothalamus (LH). Study implicates the reduced NPY immunoreactivity for the anorectic effect observed following pentazocine injections. Therefore, the concomitant activation of the NPYergic system along with the Sig1R agonist treatment may serve a useful purpose in the management of the unwanted side effects related to energy homeostasis.

Food hoarding, but not food intake, is attenuated by acute diazepam treatment in female Mongolian gerbils (Meriones unguiculatus)

This article is part of a Special Issue "Energy Balance". Effects of γ-aminobutyric acid (GABA) on food hoarding are unknown in rodents, and the effects of energy balance and GABA have not been evaluated in females. To evaluate the role of food deprivation and GABA on food hoarding, female Mongolian gerbils were given i.p. injection of diazepam (1mg/kg and 3mg/kg, respectively), a GABAA receptor agonist. Among food-deprived females, there was a bimodal pattern in the frequency of gerbils with different levels of food hoarding. High food hoarding (HFH) and low food hoarding (LFH) gerbils were analyzed. Diazepam blocked food deprivation-induced food hoarding in HFH gerbils, but not in LFH gerbils. This blockade was associated with increased cellular activation in selected brain areas, such as the nucleus accumbens (NAcc), caudate putamen (CP) and ventral tegmental area (VTA), which suggested that direct activation of GABA in the brain reward circuitry decreased food hoarding in HFH females. Moreover, diazepam increased Fos expression in field CA2 and CA3 of the hippocampus, but had no significant effect on Fos expression in field CA1 and dentate gyrus (DG) of the hippocampus, indicating that the hippocampus has area-specific effects on food hoarding in HFH gerbils. Diazepam did not alter food intake in both HFH and LFH gerbils. In addition, serum corticosterone concentrations were higher in the HFH than in the LFH ones. Together, these data indicated that food deprivation increased food hoarding in female gerbils, diazepam reduced food deprivation-induced food hoarding in HFH gerbils, and that GABA might influence food hoarding via classical reward circuitry via the mesolimbic dopamine system and specific hippocampal areas.

Lesions of nucleus accumbens affect morphine-induced release of ascorbic acid and GABA but not of glutamate in rats

Our previous studies have shown that local perfusion of morphine causes an increase of extracellular ascorbic acid (AA) levels in nucleus accumbens (NAc) of freely moving rats. Lines of evidence showed that glutamatergic and GABAergic were associated with morphine-induced effects on the neurotransmission of the brain, especially on the release of AA. In the present study, the effects of morphine on the release of extracellular AA, γ-aminobutyric acid (GABA) and glutamate (Glu) in the NAc following bilateral NAc lesions induced by kainic acid (KA) were studied by using the microdialysis technique, coupled to high performance liquid chromatography with electrochemical detection (HPLC-ECD) and fluorescent detection (HPLC-FD). The results showed that local perfusion of morphine (100 µM, 1 mM) in NAc dose-dependently increased AA and GABA release, while attenuated Glu release in the NAc. Naloxone (0.4 mM) pretreated by local perfusion to the NAc, significantly blocked the effects of morphine. After NAc lesion by KA (1 µg), morphine-induced increase in AA and GABA were markedly eliminated, while decrease in Glu was not affected. The loss effect of morphine on AA and GABA release after KA lesion could be recovered by GABA agonist, musimol. These results indicate that morphine-induced AA release may be mediated at least by µ-opioid receptor. Moreover, this effect of morphine possibly depend less on the glutamatergic afferents, but more on the GABAergic circuits within this nucleus. Finally, AA release induced by local perfusion of morphine may be GABA-receptor mediated and synaptically localized in the NAc.

Agmatine in the hypothalamic paraventricular nucleus stimulates feeding in rats: involvement of neuropeptide Y

BACKGROUND AND PURPOSE

Agmatine, a multifaceted neurotransmitter, is abundantly expressed in the hypothalamic paraventricular nucleus (PVN). Our aim was to assess (i) the effect of agmatine on feeding behaviour and (ii) its association, if any, with neuropeptide Y (NPY).

EXPERIMENTAL APPROACH

Satiated rats fitted with intra-PVN cannulae were administered agmatine, alone or jointly with (i) α₂-adrenoceptor agonist, clonidine, or antagonist, yohimbine; (ii) NPY, NPY Y₁ receptor agonist, [Leu³¹, Pro³⁴]-NPY, or antagonist, BIBP3226; or (iii) yohimbine and NPY. Cumulative food intake was monitored at different post-injection time points. Furthermore, the expression of hypothalamic NPY following i.p. treatment with agmatine, alone or in combination with yohimbine (i.p.), was evaluated by immunocytochemistry.

KEY RESULTS

Agmatine robustly increased feeding in a dose-dependent manner. While pretreatment with clonidine augmented, yohimbine attenuated the orexigenic response to agmatine. Similarly, NPY and [Leu³¹, Pro³⁴]-NPY potentiated the agmatine-induced hyperphagia, whereas BIBP3226 inhibited it. Moreover, yohimbine attenuated the synergistic orexigenic effect induced by the combination of NPY and agmatine. Agmatine increased NPY immunoreactivity in the PVN fibres and in the cells of the hypothalamic arcuate nucleus (ARC) and this effect was prevented by pretreatment with yohimbine. NPY immunoreactivity in the fibres of the ARC, dorsomedial, ventromedial and lateral nuclei of the hypothalamus was not affected by any of the above treatments.

CONCLUSIONS AND IMPLICATIONS

The orexigenic effect of agmatine is coupled to increased NPY activity mediated by stimulation of α₂-adrenoceptors within the PVN. This signifies the importance of agmatine or α₂-adrenoceptor modulators in the development of novel therapeutic agents to treat feeding-related disorders.

New approaches to the pharmacological treatment of obesity: can they break through the efficacy barrier?

In this review we assess the range of centrally active anorectics that are either in human clinical trials, or are likely to be so in the near future. We describe their weight loss efficacy, mode of action at both pharmacological and behavioural levels, where understood, together with the range of side effects that might be expected in clinical use. We have however evaluated these compounds against the considerably more rigorous criteria that are now being used by the Federal Drugs Agency and European Medicines Agency to decide approvals and market withdrawals. Several trends are evident. Recent advances in the understanding of energy balance control have resulted in the exploitation of a number of new targets, some of which have yielded promising data in clinical trials for weight loss. A second major trend is derived from the hypothesis that improved weight loss efficacy over current therapy is most likely to emerge from treatments targeting multiple mechanisms of energy balance control. This reasoning has led to the development of a number of new treatments for obesity where multiple mechanisms are targeted, either by a single molecule, such as tesofensine, or through drug combinations such as qnexa, contrave, empatic, and pramlintide+metreleptin. Many of these approaches also utilise advances in formulation technology to widen safety margins. Finally, the practicality of peptide therapies for obesity has become better validated in recent studies and this may allow more rapid exploitation of novel targets, rather than awaiting the development of orally available small molecules. We conclude that novel, more efficacious and better tolerated treatments for obesity may become available in the near future.