Participation of corticotropin-releasing factor type 2 receptors in the acute, chronic and withdrawal actions of nicotine associated with feeding behavior in rats

Pathophysiological and therapeutic implications of neuropeptide S system in neurological disorders

Neuropeptide S (NPS) is a 20 amino acids-containing neuroactive molecule discovered by the reverse pharmacology method. NPS is detected in specific brain regions like the brainstem, amygdala, and hypothalamus, while its receptor (NPSR) is ubiquitously expressed in the central nervous system (CNS). Besides CNS, NPS and NPSR are also expressed in the peripheral nervous system. NPSR is a G-protein coupled receptor that primarily uses Gq and Gs signaling pathways to mediate the actions of NPS. In animal models of Parkinsonism and Alzheimer's disease, NPS exerts neuroprotective effects. NPS suppresses oxidative stress, anxiety, food intake, and pain, and promotes arousal. NPSR facilitates reward, reinforcement, and addiction-related behaviors. Genetic variation and single nucleotide polymorphism in NPSR are associated with depression, schizophrenia, rheumatoid arthritis, and asthma. NPS interacts with several neurotransmitters including glutamate, noradrenaline, serotonin, corticotropin-releasing factor, and gamma-aminobutyric acid. It also modulates the immune system via augmenting pro-inflammatory cytokines and plays an important role in the pathogenesis of rheumatoid arthritis and asthma. In the present review, we discussed the distribution profile of NPS and NPSR, signaling pathways, and their importance in the pathophysiology of various neurological disorders. We have also proposed the areas where further investigations on the NPS system are warranted.

Chronic Nicotine Consumption and Withdrawal Regulate Melanocortin Receptor, CRF, and CRF Receptor mRNA Levels in the Rat Brain

Alterations in the various neuropeptide systems in the mesocorticolimbic circuitry have been implicated in negative effects associated with drug withdrawal. The corticotropin-releasing factor (CRF) and α-melanocyte-stimulating hormone are two peptides that may be involved. This study investigated the regulatory effects of chronic nicotine exposure and withdrawal on the mRNA levels of melanocortin receptors (MC3R, MC4R), CRF, and CRF receptors (CRFR1 and CRFR2) expressed in the mesocorticolimbic system. Rats were given drinking water with nicotine or without nicotine (control group) for 12 weeks, after which they continued receiving nicotine (chronic exposure) or were withdrawn from nicotine for 24 or 48 h. The animals were decapitated following behavioral testing for withdrawal signs. Quantitative real-time PCR analysis demonstrated that nicotine exposure (with or without withdrawal) increased levels of CRF and CRFR1 mRNA in the amygdala, CRF mRNA in the medial prefrontal cortex, and CRFR1 mRNA in the septum. Nicotine withdrawal also enhanced MC3R and MC4R mRNA levels in different brain regions, while chronic nicotine exposure was associated with increased MC4R mRNA levels in the nucleus accumbens. These results suggest that chronic nicotine exposure and withdrawal regulate CRF and melanocortin signaling in the mesocorticolimbic system, possibly contributing to negative affective state and nicotine addiction.

Epigallocatechin Gallate Ameliorates Nicotine Withdrawal Conditions-Induced Somatic and Affective Behavior Changes in Mice and Its Molecular Mechanism

In nicotine withdrawal (NW) conditions, molecular changes, such as increasing corticotropin-releasing factor (CRF) in the amygdala, and melanocortin signaling in the hypothalamus, can occur in the brain, leading to increased feeding behavior and body weight as somatic changes as well as high anxiety-like behavior as an affective changes. Therefore, this research aimed to investigate the effect of epigallocatechin gallate (EGCG), the largest component in green tea, on CRF, pro-opiomelanocortin (POMC), and melanocortin four receptor gene expression in the brain under NW conditions. The 24 Balb/c male mice used were randomly divided into four groups. The doses used included normal saline 1.0 mL/kg as a control group, and nicotine 3.35 mg/kg that was administered subcutaneously three times a day. After NW conditions, EGCG 50 mg/kg was administered intraperitoneally two times a day. Behavior evaluation was performed to measure somatic and affective changes, and the animal was sacrificed for molecular analysis. The results showed that NW conditions significantly increased food intake, body weight, and anxiety-like behavior compared with the normal group. Meanwhile, EGCG significantly decreased food intake, body weight, and anxiety-like behavior compared with NW conditions in mice without EGCG. The polymerase chain reaction results also showed that EGCG decreased the CRF mRNA expression in the amygdala and increased the POMC. This indicated that EGCG improved somatic and affective behavior in NW conditions by decreasing CRF mRNA expression in the amygdala and increasing POMC mRNA expression in the hypothalamus.

Nicotine' actions on energy balance: Friend or foe?

Obesity has reached pandemic proportions and is associated with severe comorbidities, such as type 2 diabetes mellitus, hepatic and cardiovascular diseases, and certain cancer types. However, the therapeutic options to treat obesity are limited. Extensive epidemiological studies have shown a strong relationship between smoking and body weight, with non-smokers weighing more than smokers at any age. Increased body weight after smoking cessation is a major factor that interferes with their attempts to quit smoking. Numerous controlled studies in both humans and rodents have reported that nicotine, the main bioactive component of tobacco, exerts a marked anorectic action. Furthermore, nicotine is also known to modulate energy expenditure, by regulating the thermogenic activity of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT), as well as glucose homeostasis. Many of these actions occur at central level, by controlling the activity of hypothalamic neuropeptide systems such as proopiomelanocortin (POMC), or energy sensors such as AMP-activated protein kinase (AMPK). However, direct impact of nicotine on metabolic tissues, such as BAT, WAT, liver and pancreas has also been described. Here, we review the actions of nicotine on energy balance. The relevance of this interaction is interesting, because considering the restricted efficiency of obesity treatments, a possible complementary approach may focus on compounds with known pharmacokinetic profile and pharmacological actions, such as nicotine or nicotinic acetylcholine receptors signaling.

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.

Changes in striatal dopamine release and locomotor activity following acute withdrawal from chronic nicotine are mediated by CRF1, but not CRF2, receptors

The aim of the present study was to investigate the participation of corticotropin-releasing factor (CRF) receptors (CRF1 and CRF2) in the alterations of the dorsal and ventral striatal dopamine release and the vertical and horizontal locomotor activity observed in rats following chronic nicotine treatment and consequent acute withdrawal. In this purpose, male Wistar rats were exposed to repeated intraperitoneal (ip) injection with nicotine or saline solution for 7 days. On the 8th day or the 9th day the rats were injected intracerebroventricularly (icv) with selective CRF1 antagonist antalarmin or selective CRF2 antagonist astressin_2B or saline solution. Thirty minutes after the icv injection the changes of the horizontal and vertical locomotor activity were recorded in an in vivo conducta system. Immediately after the behavioral recordings the changes of the dorsal and ventral striatal dopamine release were determined in an in vitro superfusion system. On the 8th day, the horizontal and vertical locomotor activities and the dorsal and ventral striatal dopamine releases increased significantly in nicotine-treated rats, compared to the saline-treated ones. On the 9th day, the horizontal locomotor activity and the dorsal striatal dopamine release increased significantly, whereas the vertical locomotor activity and the ventral striatal dopamine release decreased significantly in nicotine-treated rats, compared to the saline-treated ones. All the changes observed were attenuated significantly by antalarmin, but not astressin_2B. The present study demonstrates that the changes of striatal dopamine release and locomotor activity observed following chronic nicotine treatment and consequent acute withdrawal are mediated by CRF1, but not CRF2, receptor.

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.

Pharmacotherapy in smoking cessation: Corticotropin Releasing Factor receptors as emerging intervention targets

Smoking represents perhaps the single most important health risk factor and a global contributor to mortality that can unquestionably be prevented. Smoking is responsible for many diseases, including various types of cancer, chronic obstructive pulmonary disease, coronary heart disease, peripheral vascular disease and peptic ulcer, while it adversely affects fetal formation and development. Since smoking habit duration is a critical factor for mortality, the goal of treatment should be its timely cessation and relapse prevention. Drug intervention therapy is an important ally in smoking cessation. Significant positive steps have been achieved in the last few years in the development of supportive compounds. In the present review, we analyze reports studying the role of Corticotropin Releasing Factor (CRF), the principle neuroendocrine mediator of the stress response and its two receptors (CRF1 and CRF2) in the withdrawal phase as well as in the abstinence from nicotine use. Although still in pre-clinical evaluation, therapeutic implications of these data were investigated in order to highlight potential pharmaceutical interventions.

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.

Epigenetic-Imprinting Changes Caused by Neonatal Fasting Stress Protect From Future Fasting Stress

Unfavourable nutritional conditions during the neonatal critical period can cause both acute metabolic disorders and severe metabolic syndromes in later life. These phenomena have been tightly related to the epigenetic modification controlling the balance between satiety and hunger in the hypothalamus. In the present study, we investigated epigenetic modification associated with both the fasting stress effects and the short-term resilience to fasting stress in the hypothalamic paraventricular nucleus (PVN) of chicks. Fasting for 24 h at 3 days of age (D) (i.e. D3) significantly increased global methylation at lysine 27 of histone 3 (H3K27) and its specific histone methyltransferase (HMT) expression level in the PVN. Because global methylation could not fully reveal the changes at specific genes, the regulation of the gene for brain-derived neurotrophic factor (Bdnf), which was recently also found to have an anorexigenic effect, was evaluated as a potential target. Chromatin immunoprecipitation assay analysis revealed that tri- (me3) and di-methylated (me2) H3K27 exhibited an instant (on D4 only) and latent increase (on both D11 and D41), respectively, at the putative promoter of Bdnf after 24 h of fasting on D3. This indicated that fasting could regulate energy-expenditure-related genes via modifying methylation at H3K27, which we suspected might be a protective mechanism for keeping the inner environment homeostatic. To test this hypothesis, a short-term repetitive fasting stress was applied to chickens, which were fasted for 24 h either on D10 only or on both D3 and D10. It was found that pre-existing fasting on D3 could induce a short-term fasting resilience, which rescued the reduction of Bdnf expression from future fasting on D10. We call this phenomenon the ‘molecular memory’, which was mainly conducted by HMTs and H3K27me2/me3 in the PVN. In conclusion, chicks respond to fasting with dynamic methylation at H3K27 in the PVN during the neonatal critical period. This allows the PVN to form a ‘molecular memory’, which keeps the individual inner environment homeostatic and resilient to future fasting over the short term.

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.

A mechanistic hypothesis of the factors that enhance vulnerability to nicotine use in females

Women are particularly more vulnerable to tobacco use than men. This review proposes a unifying hypothesis that females experience greater rewarding effects of nicotine and more intense stress produced by withdrawal than males. We also provide a neural framework whereby estrogen promotes greater rewarding effects of nicotine in females via enhanced dopamine release in the nucleus accumbens (NAcc). During withdrawal, we suggest that corticotropin-releasing factor (CRF) stress systems are sensitized and promote a greater suppression of dopamine release in the NAcc of females versus males. Taken together, females display enhanced nicotine reward via estrogen and amplified effects of withdrawal via stress systems. Although this framework focuses on sex differences in adult rats, it is also applied to adolescent females who display enhanced rewarding effects of nicotine, but reduced effects of withdrawal from this drug. Since females experience strong rewarding effects of nicotine, a clinical implication of our hypothesis is that specific strategies to prevent smoking initiation among females are critical. Also, anxiolytic medications may be more effective in females that experience intense stress during withdrawal. Furthermore, medications that target withdrawal should not be applied in a unilateral manner across age and sex, given that nicotine withdrawal is lower during adolescence. This review highlights key factors that promote nicotine use in females, and future studies on sex-dependent interactions of stress and reward systems are needed to test our mechanistic hypotheses. Future studies in this area will have important translational value toward reducing health disparities produced by nicotine use in females. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Urocortin I inhibits the effects of ghrelin and neuropeptide Y on feeding and energy substrate utilization

The corticotropin releasing hormone-related ligand, urocortin-I (UcnI), suppresses food intake when injected into multiple hypothalamic and extrahypothalamic areas. UcnI also alters energy substrate utilization, specifically via enhanced fat oxidation as reflected in reductions in respiratory quotient (RQ). In the present study we compared the feeding and metabolic effects of ghrelin and NPY following pretreatment with UcnI. Direct PVN injections of NPY (50 pmol) and ghrelin (50 pmol) were orexigenic while UcnI (10-40 pmol) reliably suppressed food intake. Both ghrelin and NPY increased RQ, indicating enhanced utilization of carbohydrates and the preservation of fat stores. UcnI alone suppressed RQ responses. PVN UcnI attenuated the effects of both ghrelin and NPY on food intake and energy substrate utilization. While ghrelin (5 pmol) potentiated the effect of NPY (25 pmol) on RQ and food intake, these responses were inhibited by pretreatment with UcnI (10 pmol). In conclusion, PVN NPY and ghrelin stimulate eating and promote carbohydrate oxidation while inhibiting fat utilization. These effects are blocked by UcnI which alone suppresses appetite and promotes fat oxidation. Overall these findings are consistent with a possible interactive role of PVN NPY, ghrelin and urocortin in the modulation of appetite and energy metabolism.

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.

Tolerance to ethanol sedation and withdrawal hyper-excitability is mediated via neuropeptide Y Y1 and Y5 receptors

AIMS

Neuropeptide Y (NPY) is widely distributed throughout the brain and has been implicated in some of the actions of ethanol. The aim of the present study was to characterize the subtypes of NPY receptors in ethanol induced sedation, tolerance and withdrawal hyper-excitability.

MAIN METHODS

The loss of righting reflex paradigm was used to record the sleep duration in mice.

KEY FINDINGS

The acute administration of ethanol (3-4g per kg, i.p., 20%v/v) resulted in marked sedation. While prolonged ethanol consumption led to the development of tolerance, the mice showed hyper-excitability following ethanol withdrawal. Prior acute intracerebroventricular (i.c.v.) injection of NPY (5-20 ng per mouse) or NPY Y1 and Y5 receptors agonist [Leu(31), Pro(34)]-NPY (0.02-0.2 ng per mouse) potentiated ethanol induced sedation. On the other hand, administration of selective NPY Y1 receptor antagonist BIBP3226 (5 ng per mouse, i.c.v.) inhibited ethanol induced sedation. Chronic concomitant treatment of NPY (20 ng per mouse, i.c.v.) or [Leu(31), Pro(34)]-NPY (0.2 ng per mouse, i.c.v.) to ethanol-fed groups prevented the development of tolerance and attenuated withdrawal hyper-excitability. Moreover, acute treatment of NPY (5 ng per mouse, i.c.v.) or [Leu(31), Pro(34)]-NPY (0.02 ng per mouse, i.c.v.) reversed the peak ethanol withdrawal hyper-excitability.

SIGNIFICANCE

The results underscore a role for NPY Y1 and Y5 receptors in the ethanol induced sedation, tolerance and withdrawal hyper-excitability. We suggest that modulation of NPY Y1 and Y5 receptors may be a strategy to address the ethanol withdrawal conditions.