Satiated Rats Research Articles

Assessment of help value affects reciprocation in Norway rats.

Wild-type Norway rats reciprocate help received in a well-replicated experimental food-giving task, but the criteria to appraise the received help's value are unclear. We tested whether quality or quantity of received help is more important when deciding to return help, and whether partner familiarity and own current need affect this evaluation. We experimentally varied recipients of help's hunger state, and familiar or unfamiliar partners provided either higher caloric food (enhanced quantity; carrots) or food higher in protein and fat (enhanced quality; cheese). Reciprocation of received help was our criterion for the rats' value assessment. Familiarity, food type and hunger state interacted and affected help returned by rats. Rats returned less help to familiar partners than to unfamiliar partners. With unfamiliar partners, rats returned more help to partners that had donated preferred food (cheese) than to partners that had donated less preferred food (carrots), and they returned help earlier if they were satiated and had received cheese. With familiar partners, food-deprived rats that had received cheese returned more help than satiated rats that had received carrots. Our results suggest that Norway rats assess the received help's value based on its quality, their current need and partner familiarity before reciprocating received help.

Fasting alters p75NTR and AgRP mRNA expression in rat olfactory bulb and hippocampus

Classic non-homeostatic structures involved in food intake regulation are reciprocally influenced by metabolic signals. Orexigenic peptides expressed in the olfactory bulb (OB) and hippocampus (HP) modulate olfactory processing and memory, respectively. Hypothalamic circuits also modulate feeding behavior by activating and releasing Agouti-related peptide (AgRP) in response to orexigenic signals. An adequate response to fasting requires the expression of p75 neurotrophin receptor (p75NTR) in AgRP neurons. The present study aimed to determine whether there is a role for p75NTR and AgRP in the OB and HP on the feeding behavior of fasted rats. A group of fasted rats (FG) was confronted with a decision-making paradigm in a T-maze containing a standard chow pellet (CP), and the same pellet coated with a phenolic-rich avocado paste extract (AVO) on either end; their OB and HP were then analyzed with histological and molecular tools. FG rats had briefer feeding latencies, as compared to control rats fed ad libitum (median latencies: 55.4 vs 191.7 min, p = 0.032). They also had reduced cell counts in both brain structures, as compared to satiated rats. AgRP mRNA was not expressed in the HP of either group, however, it was found in the OB. p75NTR mRNA was expressed in both brain structures of FG rats. These results suggest that contrasting metabolic states (fasted or satiated) motivate different feeding responses, which are influenced by p75NTR and AgRP mRNA expression in non-homeostatic food intake brain structures.

Endocannabinoids Released in the Ventral Tegmental Area During Copulation to Satiety Modulate Changes in Glutamate Receptors Associated With Synaptic Plasticity Processes.

Endocannabinoids modulate mesolimbic (MSL) dopamine (DA) neurons firing at the ventral tegmental area (VTA). These neurons are activated by copulation, increasing DA release in nucleus accumbens (NAcc). Copulation to satiety in male rats implies repeated ejaculation within a short period (around 2.5 h), during which NAcc dopamine concentrations remain elevated, suggesting continuous neuronal activation. During the 72 h that follow copulation to satiety, males exhibit long-lasting changes suggestive of brain plasticity processes. Enhanced DA neuron activity triggers the synthesis and release of endocannabinoids (eCBs) in the VTA, which participate in several long-term synaptic plasticity processes. Blockade of cannabinoid type 1 receptors (CB1Rs) during copulation to satiety interferes with the appearance of the plastic changes. Glutamatergic inputs to the VTA express CB1Rs and contribute to DA neuron burst firing and synaptic plasticity. We hypothesized that eCBs, released during copulation to satiety, would activate VTA CB1Rs and modulate synaptic plasticity processes involving glutamatergic transmission. To test this hypothesis, we determined changes in VTA CB1R density, phosphorylation, and internalization in rats that copulated to satiety 24 h earlier as compared both to animals that ejaculated only once and to sexually experienced unmated males. Changes in glutamate AMPAR and NMDAR densities and subunit composition and in ERK1/2 activation were determined in the VTA of males that copulated to satiety in the presence or absence of AM251, a CB1R antagonist. The CB1R density decreased and the proportion of phosphorylated CB1Rs increased in the animals that copulated compared to control rats. The CB1R internalization was detected only in sexually satiated males. A decrease in α-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor (AMPAR) density, blocked by AM251 pretreatment, and an increase in the proportion of GluA2-AMPARs occurred in sexually satiated rats. GluN2A- N-methyl-D-aspartate receptor (NMDAR) expression decreased, and GluN2B-NMDARs increased in these animals, both of which were prevented by AM251 pre-treatment. An increase in phosphorylated ERK1/2 emerged in males copulating to satiety in the presence of AM251. Results demonstrate that during copulation to satiety, eCBs activate CB1Rs in the VTA, producing changes in glutamate receptors compatible with a reduced neuronal activation. These changes could play a role in the induction of the long-lasting physiological changes that characterize sexually satiated rats.

Injections of the α-2 adrenoceptor agonist clonidine into the dorsal raphe nucleus increases food intake in satiated rats

The present study aimed to evaluate the effects of pharmacological manipulation of α-adrenergic agonists in the dorsal raphe nucleus (DR) on food intake in satiated rats. Adult male Wistar rats with chronically implanted cannula in the DR were injected with adrenaline (AD) or noradrenaline (NA) (both at doses of 6, 20 and 60 nmol), or α-1 adrenergic agonist phenylephrine (PHE) or α-2 adrenergic agonist clonidine (CLO) (both at doses of 6 and 20 nmol). The injections were followed by the evaluation of ingestive behaviors. Food and water intake were evaluated for 60 min. Administration of AD and NA at 60 nmol and CLO at 20 nmol increased food intake and decreased latency to start consumption in satiated rats. The ingestive behavior was not significantly affected by PHE treatment in the DR. CLO treatment increased Fos expression in the arcuate nucleus (ARC) and paraventricular nucleus of the hypothalamus (PVN) in rats that were allowed to eat during the experimental recording (AF group). However, when food was not offered during the experiment (WAF group), PVN neurons were not activated, whereas, neuronal activity remained high in the ARC when compared to control group. Noteworthy, ARC POMC neurons expressed Fos in the AF group. However, double-labeled POMC/Fos cells were absent in the ARC of the WAF group, although an increase in Fos expression was observed in non-POMC cells after CLO injections in the WAF group. In conclusion, the data from the present study highlight that the pharmacological activation of DR α-adrenoceptors affects food intake in satiated rats. The feeding response evoked by CLO injections into DR was similar to that induced by NA or AD injections, suggesting that the hyperphagia after NA or AD treatment depends on α-2 adrenoceptors activation. Finally, we have demonstrated that CLO injections into DR impact neuronal activity in the ARC, possibly evoking a homeostatic response toward food intake.

Nitric oxide and l-arginine have mixed effects on mammalian feeding in condition of a high motivation to feed

Feeding inhibition caused by satiation in rats is partially mediated by the unconventional neurotransmitter nitric oxide (NO). Thus, in satiated rats blocking NO production increases feeding, and treatment with the NO precursor l-arginine or with an NO donor reduces feeding beyond that caused by satiation. Do NO and l-arginine also inhibit feeding when feeding motivation is high? When feeding motivation in satiated animals was hedonically increased by offering a highly attractive food, blocking NO production reduced the quantity eaten, rather than increasing it, indicating that hedonic aspects of food are partially mediated by NO. Increasing NO via an NO donor or l-arginine did not further increase the quantity eaten, indicating a ceiling effect. The NO donor, but not l-arginine, also decreased some motivation-dependent parameters of feeding. When feeding motivation was increased by hunger, quantities of food eaten were unaffected by an NO donor, blocker or precursor, with only the blocker of NO production affecting feeding patterning. We also examined effects on feeding of dissolving l-arginine in drinking water over 3 weeks. Chronic l-arginine administration had different effects during the first and in subsequent weeks, increasing feeding at first, but not later. The data indicate that NO has complex, state dependent effects on both the quantity of food eaten, and on patterns of feeding, probably reflecting different sites and mechanisms of action in the nervous system.

Endogenous NUCB2/Nesfatin-1 Regulates Energy Homeostasis Under Physiological Conditions in Male Rats.

Nesfatin-1 is the proteolytic cleavage product of Nucleobindin 2, which is expressed both in a number of brain nuclei (e. g., the paraventricular nucleus of the hypothalamus) and peripheral tissues. While Nucleobindin 2 acts as a calcium binding protein, nesfatin-1 was shown to affect energy homeostasis upon central nervous administration by decreasing food intake and increasing thermogenesis. In turn, Nucleobindin 2 mRNA expression is downregulated in starvation and upregulated in the satiated state. Still, knowledge about the physiological role of endogenous Nucleobindin 2/nesfatin-1 in the control of energy homeostasis is limited and since its receptor has not yet been identified, rendering pharmacological blockade impossible. To overcome this obstacle, we tested and successfully established an antibody-based experimental model to antagonize the action of nesfatin-1. This model was then employed to investigate the physiological role of endogenous Nucleobindin 2/nesfatin-1. To this end, we applied nesfatin-1 antibody into the paraventricular nucleus of satiated rats to antagonize the presumably high endogenous Nucleobindin 2/nesfatin-1 levels in this feeding condition. In these animals, nesfatin-1 antibody administration led to a significant decrease in thermogenesis, demonstrating the important role of endogenous Nucleobindin 2/nesfatin-1in the regulation of energy expenditure. Additionally, food and water intake were significantly increased, confirming and complementing previous findings. Moreover, neuropeptide Y was identified as a major downstream target of endogenous Nucleobindin 2/nesfatin-1.

The smell of hunger: Norway rats provision social partners based on odour cues of need.

When individuals exchange helpful acts reciprocally, increasing the benefit of the receiver can enhance its propensity to return a favour, as pay-offs are typically correlated in iterated interactions. Therefore, reciprocally cooperating animals should consider the relative benefit for the receiver when deciding to help a conspecific. Norway rats (Rattus norvegicus) exchange food reciprocally and thereby take into account both the cost of helping and the potential benefit to the receiver. By using a variant of the sequential iterated prisoner’s dilemma paradigm, we show that rats may determine the need of another individual by olfactory cues alone. In an experimental food-exchange task, test subjects were provided with odour cues from hungry or satiated conspecifics located in a different room. Our results show that wild-type Norway rats provide help to a stooge quicker when they receive odour cues from a hungry rather than from a satiated conspecific. Using chemical analysis by gas chromatography-mass spectrometry (GC-MS), we identify seven volatile organic compounds that differ in their abundance between hungry and satiated rats. Combined, this “smell of hunger” can apparently serve as a reliable cue of need in reciprocal cooperation, which supports the hypothesis of honest signalling.

Diet as connecting factor: Functional brain connectivity in relation to food intake and sucrose tasting, assessed with resting-state functional MRI in rats.

Eating disorders and obesity form a major health problem in Western Society. To be able to provide adequate treatment and prevention, it is necessary to understand the neural mechanisms underlying the development of eating disorders and obesity. Specific brain networks have been shown to be involved in feeding behavior. We therefore hypothesized that functional connectivity in neural networks involved in feeding behavior is dependent on the status of homeostatic energy balance, thus on being hungry or satiated. To test our hypothesis, we measured functional connectivity and amplitudes of neural signals within neural networks in relation to food intake and sucrose tasting in rats. Therefore, 16 male Wistar rats, of which eight were food‐restricted and eight were satiated, underwent resting‐state functional magnetic resonance imaging (rs‐fMRI) at 9.4 T. Subsequently, half of these animals underwent a sucrose tasting procedure followed by a second rs‐fMRI scan. Functional connectivity and amplitude of low‐frequency signal fluctuations were statistically analyzed in a linear mixed model. Although we did not detect a significant effect of food intake on functional connectivity before sucrose tasting, there was a trend toward interaction between group (satiated vs. hungry) and treatment (sucrose tasting). Functional connectivity between feeding‐related regions tended to decrease stronger upon sucrose tasting in satiated rats as compared to food‐restricted rats. Furthermore, rs‐fMRI signal amplitudes decreased stronger upon sucrose tasting in satiated rats, as compared to food‐restricted rats. These findings indicate that food intake and sucrose tasting can affect functional network organization, which may explain the specific patterns in feeding behavior.

Endocannabinoids Interact With the Dopaminergic System to Increase Sexual Motivation: Lessons From the Sexual Satiety Phenomenon.

In male rats, copulation to satiety induces a long-lasting sexual inhibitory state, considered to rely on a decreased sexual motivation. Dopaminergic transmission at the mesolimbic system plays a central role in the regulation of male sexual motivation. Endocannabinoids (eCBs) modulate the activity of the mesolimbic system and both dopamine (DA) and cannabinoid receptor activation reverses the sexual inhibition that characterizes sexually satiated rats. The eCB anandamide reverses sexual satiety when systemically administered or infused into the ventral tegmental area (VTA), the region where the activity of mesolimbic dopaminergic neurons is regulated. Thus, it could be thought that sexual motivation is diminished during the long-lasting sexual inhibition of sexually satiated rats and that eCBs reverse that inhibition through the modulation of the dopaminergic system. To test this hypothesis, we assessed the motivational state of sexually satiated male rats and determined if 2-arachidonoylglycerol (2-AG), the most abundant eCB and a full cannabinoid receptor agonist, also reversed the sexual inhibitory state. To establish the possible interaction between 2-AG and anandamide with the dopaminergic system for the reversal of sexual satiety, we analyzed the effects of the co-administration of each eCB and DA receptor agonists or antagonists. Results showed that 24-h after copulation to satiety, when the sexual inhibition is well established, the males’ sexual motivation is diminished as measured in the sexual incentive motivation test. 2-AG, similarly to anandamide, reverses sexual satiety through the activation of CB1 receptors and both eCBs interact with the dopaminergic system to reverse the sexual inhibitory state. 2-AG effects are mediated by the modulation of the D2-like DA receptor family, whereas anandamide’s effects are clearly mediated by the modulation of the D1-like DA receptor family and the activation of D2-like DA receptors. Present results evidence that a reduced sexual motivation underlies the sexual inhibitory state of sexually satiated rats and support the notion that eCBs reverse sexual satiety by modulating dopaminergic transmission, presumably at the mesolimbic system. Anandamide and 2-AG have a different interaction with D1-like and D2-like DA receptor families. Altogether present data endorse the association of the eCB system with the regulation of the motivational tone at the mesolimbic system.

Merkezi ve periferik olarak enjekte edilen CDP-kolin’in sıçanlarda plazma nesfatin-1 seviyesi üzerine etkisi

Nesfatin-1 has a role in appetite control and energy balance. The activity of the cholinergic system also is able to affect feeding behavior. Moreover, the central cholinergic system interacts with central nesfatinergic systems. The main goal of the study was to determine the effect of intracerebroventricular (icv) and intravenous (iv) administrated CDP-choline (0.5 ve 1 μmol; icv ve 250 mg / kg; iv) on levels of plasma nesfatin-1 in the homogeneous number of male and female fasted and the satiated Wistar albino rats. The polyethylene cannula was inserted into the carotid artery and jugular vein of the rats anesthetized with sevoflurane (2–4%/100% O2) to collect blood samples and to make iv injection, respectively. For icv treatment, the lateral ventricle of rats was cannulated with guide cannula. The basal levels of plasma nesfatin-1 in the satiated rats were higher than those observed in the fasted animals. While 0.5 and 1 μmol dose of icv and/or 250 mg/kg dose of iv injected CDP-choline increased the level of plasma nesfatin-1 in the satiated rats, plasma nesfatin-1 level of the fasted animals decreased after the same dose and route of CDP-choline injection. The current findings show that CDP-choline can influence the level of plasma nesfatin-1 in the rats. The effect of the drug was different according to the food intake of the rats. These data might suggest a potential role in CDP-choline on plasma nesfatin-1 concentration.

Effect of central and peripheral injected nesfatin-1 on electrocardiography in rats

Nesfatin-1 is an anorexic nucleobindin-2 -derived peptide and it has directly and centrally effect on the heart. The current study was designed to determine the effect of centrally and peripherally administered nesfatin-1 on electrocardiography (ECG) of healthy both fasted rats for 12 h and satiated rats fed ad libitum. In order to record ECG, the electrodes were placed limbs of at lead II under ketamine (50 mg/kg; im) and xylazine (20 mg/kg; im) anesthesia mix. Centrally administered different doses of nesfatin-1 (100 and 200 pmol; icv) resulted in dose- and time-dependently a statistically significant increase (p <0.05) in T wave, Q-T interval, and R-R interval duration without changing in ECG waves’ amplitude in both satiated and fasted rats. In similar way, peripheral administration of nesfatin-1 (80 μg/kg; iv) in satiated rats prolonged statistically significant (p <0.05) T wave, Q-T interval, and R-R interval without producing a change in ECG waves’ amplitude. Moreover, icv administered nesfatin-1 in fasted and satiated rats, and iv injected nesfatin-1 in satiated rats induced statistically significant decrease in heart rate (p <0.05). In conclusion, our findings suggest that centrally and peripherally administrated nesfatin-1 caused a delay in T wave, Q-T interval and two R-waves interval duration in ECG so that leading to a bradycardic effect in heart rate.

Fat, carbohydrate and protein by oral gavage in the rat can be equally effective for satiation

This study aimed to determine the relative efficacy of the macronutrients, protein, fat and carbohydrate to induce satiation and satiety in rats in relation to macronutrient activation of neurons in the nucleus of the solitary tract (NTS). Male Sprague Dawley rats were schedule-fed twice a day for 2 h, receiving 100% of daily ad-libitum energy intake. On test day 1, 30 min before the first scheduled meal of the day, rats were gavaged with an 8 kcal isocaloric, isovolumetric solution of a glucose, lipid or peptone macronutrient solution or a non-caloric saline solution. To assess satiation, thirty minutes later rats were given access to food for 2 h and food intake determined. A second 2 h food access period 3 h later was used for assessment of satiety. On the second test day, rats were gavaged as before and killed 90 min after food presentation. Blood was collected for measurement of circulating metabolic markers. Brains were removed for analysis of c-Fos expression by in situ hybridization in the NTS.Rats which received saline consumed a similar amount of food compared to pre-gavage intakes. However, rats gavaged with a caloric macronutrient solution all reduced food intake by 18-20 kcal. Interestingly, the reduction in caloric intake was greater than the caloric value of the macronutrient solution gavaged and was sustained following the second scheduled meal. Quantification by in situ hybridization of c-Fos mRNA expression in the NTS 90 min post-gavage, showed a significant increase with each macronutrient, but was 24–29% higher with a lipid or peptone gavage compared to a glucose gavage. In conclusion, when delivered directly to the stomach, all macronutrients can be equally effective in inducing satiation with significant neuronal activation in the NTS of the hindbrain.

Influence of the fat/carbohydrate component of snack food on energy intake pattern and reinforcing properties in rodents.

Hedonic intake of strongly rewarding foods is independent from biological needs and, thus, a common cause of obesity. The effect of potato chips on energy intake in a snacking model could be explained by their fat/carbohydrate content (FCHc). The present study investigated if the FCHc shapes energy intake patterns and reward processing of satiated rodents. Modulation of energy intake patterns was studied in an established snacking model offering FCHc rich food for 3 × 10 min/day to satiated rats. Reward processing was analyzed by a previously established conditioned place preference tests in satiated mice. The limited access to FCHc rich food led to higher daily energy intake compared to days without access (110 ± 10 vs. 96 ± 5 kcal/day) indicating that fat/carbohydrate intake was not fully compensated by reducing standard chow intake during the rest of the day. Furthermore, fat/carbohydrate snacking led to binge eating episodes with up to 55% of the daily energy intake consumed during limited access. Forced withdrawal from fat/carbohydrate snacking opportunities for six weeks increased the total daily energy intake and the relative amount of energy consumed by FCHc after reintroducing fat/carbohydrate snacking. Snack food and fat/carbohydrate food were powerful food reinforcers in satiated mice in contrast to standard chow. Altogether, these data suggest that the FCHc of snack food has strong reinforcing properties, which are probably responsible for the significant modulation of the amount and pattern of food intake in ad libitum fed animals.

Nucleus accumbens dopamine increases sexual motivation in sexually satiated male rats.

The influence of the main dopaminergic brain regions controlling copulation, the medial preoptic area (mPOA) and the nucleus accumbens (NAcc), on male rat sexual behavior expression has not been fully established. This work analyzes the sexual effects of dopamine (DA) receptor activation in the mPOA or the NAcc of sexually active male rats, with an intact (sexually experienced) or a reduced (sexually exhausted) sexual motivation. The non-specific DA receptor agonist apomorphine and the D2-like receptor agonist quinpirole were infused into the mPOA or the NAcc of sexually experienced or sexually exhausted male rats and their sexual behavior recorded. DA receptor activation neither in the mPOA nor in the NAcc modified the copulatory behavior of sexually experienced male rats. DA receptor stimulation in the NAcc, but not in the mPOA, reversed the characteristic sexual inhibition of sexually satiated rats, and D2-like receptors were found to participate in this effect. The optimal sexual performance of sexually experienced male rats cannot be further improved by DA receptor activation at either brain region. In sexually satiated rats, which are sexually inhibited and have a diminished sexual motivation, NAcc DA receptor stimulation appears to play a key role in their capacity to respond to a motivational significant stimulus, the receptive female, with the participation of D2-like receptors. Activation of DA receptors with the same drug, at the same dose and in the same brain region, produces different effects on copulatory behavior that depend on the animal's sexual motivational state.

Nitric oxide and l-arginine regulate feeding in satiated rats

Nitric Oxide (NO) and its precursor l-arginine were found to inhibit feeding in rats with a low motivation to eat, as they do in Aplysia. In rats that are relatively satiated, treatment with an NO blocker increased feeding, and treatment with an NO donor or with either of 2 doses of l-arginine inhibited feeding. NO and l-arginine modulated several parameters of feeding, such as the total duration of appetitive behaviors, the time spent feeding, the quantity of food eaten and the number of feeding bouts. The inhibitory effect of l-arginine on feeding could not be attributed to changes in locomotion. These data indicate that satiation is partially mediated by increased production of NO. NADPH-Diaphorase histochemical staining, which is specific for tissues actively producing NO, showed significantly greater staining in satiated compared to hungry rats in all 4 hypothalamic nuclei (paraventricular and arcuate nuclei, lateral and ventromedial hypothalamus) that were examined. l-arginine may act as a regulator of feeding by controlling NO production in several hypothalamic nuclei, specifically under condition of a low feeding motivation.

Pituitary adenylate cyclase-activating polypeptide (PACAP) acts in the nucleus accumbens to reduce hedonic drive.

Obesity develops, in part, due to frequent overconsumption. Therefore, it is important to identify the regulatory mechanisms that promote eating beyond satiety. Previously, we have demonstrated that an acute microinjection of the neuropeptide PACAP into the nucleus accumbens (NAcc) attenuates palatable food consumption in satiated rats. To better understand the mechanism by which intra-NAcc PACAP selectively blocks palatable food intake, the current work employed a rodent taste reactivity paradigm to assess the impact of PACAP on the hedonic processing of a 1% sucrose solution. Our results revealed that bilateral intra-NAcc PACAP infusions significantly reduced appetitive orofacial responses to sucrose. Interestingly, the effect of PACAP on the expression of aversive responses to sucrose were dependent on the rostral-caudal placement of the microinjection. In a separate group of rats, PACAP was microinjected into the hypothalamus (a region of the brain in which PACAP does not attenuate palatable feeding). Here we found that PACAP had no effect on the hedonic perception of the sucrose solution. Taken together, this dataset indicates that PACAP acts in specific subregions of the NAcc to attenuate palatability-induced feeding by reducing the perceived hedonic value of palatable food.

Chronic refined low-fat diet consumption reduces cholecystokinin satiation in rats.

Reduced ability of cholecystokinin (CCK) to induce satiation contributes to hyperphagia and weight gain in high-fat/high-sucrose (HF/HS) diet-induced obesity, and has been linked to altered gut microbiota. Rodent models of obesity use chow or low-fat (LF) diets as control diets; the latter has been shown to alter gut microbiota and metabolome. We aimed to determine whether LF-diet consumption impacts CCK satiation in rats and if so, whether this is prevented by addition of inulin to LF diet. Rats (n = 40) were fed, for 8 weeks, a chow diet (chow) or low-fat (10%) or high-fat/high-sucrose (45 and 17%, respectively) refined diets with either 10% cellulose (LF and HF/HS) or 10% inulin (LF-I and HF/HS-I). Caecal metabolome was assessed by 1H-NMR-based metabolomics. CCK satiation was evaluated by measuring the suppression of food intake after intraperitoneal CCK injection (1 or 3µg/kg). LF-diet consumption altered the caecal metabolome, reduced caecal weight, and increased IAP activity, compared to chow. CCK-induced inhibition of food intake was abolished in LF diet-fed rats compared to chow-fed rats, while HF/HS diet-fed rats responded only to the highest CCK dose. Inulin substitution ameliorated caecal atrophy, reduced IAP activity, and modulated caecal metabolome, but did not improve CCK-induced satiety in either LF- or HF/HS-fed rats. CCK signaling is impaired by LF-diet consumption, highlighting that caution must be taken when using LF diet until a more suitable refined control diet is identified.

Melanin-concentrating hormone and orexin systems in rat nucleus incertus: Dual innervation, bidirectional effects on neuron activity, and differential influences on arousal and feeding

The rat nucleus incertus (NI) contains GABA/peptide-projection neurons responsive to orexin (hypocretin)/orexin receptor-2 (OX2) signalling. Melanin-concentrating hormone (MCH) and orexin neurons often innervate and influence common target areas. Therefore, we assessed the relationship between these hypothalamic peptidergic systems and rat NI, by investigating the presence of an MCH innervation and MCH receptor-1 (MCH1) expression, and neurophysiological and behavioural effects of MCH c.f. orexin-A (OXA), within the NI. We identified lateral hypothalamus (LH), perifornical and sub-zona incerta MCH neurons that innervate NI, and characterised the rostrocaudal distribution of MCH-containing fibres in NI. Single-cell RT-PCR detected MCH1 and OX2 mRNA in NI, and multiplex, fluorescent in situ hybridisation revealed distinct co-expression patterns of MCH1 and OX2 mRNA in NI neurons expressing vesicular GABA transporter (vGAT) mRNA. Patch-clamp recordings revealed 34% of NI neurons tested were hyperpolarised by MCH (1 μM), representing a distinct population from OXA-sensitive NI neurons (35%). Intra-NI OXA infusion (600 pmol) in satiated rats during the light/inactive phase produced increased locomotor activity and food (standard chow) intake, whereas intra-NI MCH infusion (600 pmol) produced only a trend for decreased locomotor activity and no effect on food intake. Furthermore, in satiated or pre-fasted rats tested during the dark/active phase, intra-NI infusion of MCH did not alter the elevated locomotor activity or higher food intake observed. However, quantification of neuropeptide-immunostaining revealed differential diurnal fluctuations in orexin and MCH trafficking to NI. Our findings identify MCH and orexin inputs onto divergent NI populations which may differentially influence arousal and motivated behaviours.

Acute orexigenic effect of agmatine involves interaction between central α2-adrenergic and GABAergic receptors

Agmatine and GABA have been abundantly expressed in brain nuclei involved in regulation of energy homeostasis and promoting stimulation of food intake in rodents. However, their mutual interaction, if any, in the elicitation of feeding behavior is largely remains unclear. The current study provides experimental evidence for the possible interaction of agmatine, adrenergic and GABAergic systems in stimulation of feeding in satiated rats.Satiated rats fitted with intracerebroventricular (i.c.v.) cannulae and were administered agmatine, alone or jointly with (a) GABAA receptor agonist, muscimol, diazepam or antagonist bicuculline and flumazenil, GABAA positive modulator, allopregnanolone or negative modulator of GABAA receptor, dehydroepiandrosterone (b) In view of the high affinity of agmatine for α2-adrenoceptors and the close association between α2-adrenoceptors and GABAergic system, the effect of their modulators on feeding elicited by agmatine/GABAergic agonists were also examined. I.c.v. administration of agmatine (40–80μg/rat) induces the significant orexigenic effect in satiated rats. The orexigenic effect of agmatine was potentiated by muscimol (25ng/rat, i.c.v.); diazepam (0.5mg/kg, i.p.); allopregnanolone (0.5mg/kg, s.c.) and blocked by bicuculline (1mg/kg, i.p.) and dehydroepiandrosterone (4mg/kg,s.c.). However, it remained unaffected in presence of flumazenil (25ng/rat, i.c.v.). The orexigenic effect of agmatine and GABAergic agonists was potentiated by a α2-adrenoceptors agonist, clonidine (10ng/rat, i.c.v.) and blocked by its antagonist, yohimbine (5μg/rat, i.c.v.). Yohimbine also blocked the hyperphagic effect elicited by ineffective dose combination of agmatine (5μg/rat, i.c.v.) with muscimol (25ng/rat, i.c.v.) or diazepam (0.5mg/kg, i.p.) or allopregnanolone (0.5mg/kg,s.c.). The results of the present study suggest that agmatine induced α2-adrenoceptors activation might facilitate GABAergic activity to stimulate food intake in satiated rats.

Pharmacological activation of RXFP3 is not orexigenic in C57BL/6J mice.

The neuropeptide relaxin-3 and its cognate G-protein-coupled receptor, RXFP3, have been implicated in the control of feeding behaviour in rats. For example, relaxin-3-positive projections and RXFP3 are present within hypothalamic feeding circuits, and icv injection of human relaxin-3 (-0.2 to 1.0 nmol) robustly increases feeding behaviour in satiated rats. To explore whether this action is conserved in other experimental species, the present study examined feeding behaviour in C57BL/6J mice following RXFP3 modulation, as mice display near identical regional distribution patterns of relaxin-3/RXFP3, and relaxin-3/RXFP3 signalling has been shown to modulate behavioural arousal in both species. Central injection of the RXFP3 agonists R3/I5 or H3 relaxin (0.5 nmol, icv) did not alter chow consumption in satiated mice relative to vehicle controls, during the 60 min after treatment. Furthermore, relaxin-3 knockout mice displayed similar basal 24-h chow consumption and 1-h palatable food consumption to wildtype littermate controls; although further studies involving acute pharmacological antagonism of RXFP3 in WT mice are required to eliminate the likelihood of compensation in these life-long relaxin-3 deficient mice. Taken together, these findings are in contrast to the potent orexigenic effects of RXFP3 activation observed in rats, and may reflect differential RXFP3 expression within hypothalamic neuron populations in the rat and mouse, or differences in signalling upstream or downstream of relaxin-3/RXFP3 networks in these two species.