Attenuated Food Intake Research Articles

Melanin-concentrating hormone receptor 1 (MCH1-R) antagonism: Reduced appetite for calories and suppression of addictive-like behaviors

RationaleThe hypothalamic neuropeptide melanin-concentrating hormone and its MCH1 receptor have been implicated in regulation of feeding and energy homeostasis, as well as modulation of reward-related behaviors. Here, we examined whether the MCH system plays a role both in caloric and motivational aspects of sugar intake. Materials and methodsThe non-peptide MCH1-R antagonist GW803430 (3, 10, 30mg/kg, i.p.) was first tested on self-administration under a fixed ratio schedule of reinforcement of both a caloric (10% w/v sucrose) and a non-caloric (0.06% w/v saccharin) sweet solution. GW803430 was then tested for its ability to alter motivational properties and seeking of sucrose. Lastly, the drug was tested to concurrently examine its effects on the escalated consumption of both sugar and food in animals following intermittent sugar access. ResultsThe MCH1-R antagonist reduced sucrose- but not saccharin-reinforced lever pressing, likely reflecting a decreased appetite for calories in GW803430-treated rats. GW803430 reduced sucrose self-administration under a progressive ratio schedule, and suppressed cue-induced reinstatement of sucrose seeking, suggesting effects on rewarding properties of sucrose. GW803430 attenuated food intake in rats on intermittent access to sucrose at all doses examined (3, 10, 30mg/kg), while reduction of sugar intake was weaker in magnitude. ConclusionTogether, these observations support an involvement of the MCH system in regulation of energy balance as well as mediation of sucrose reward. MCH may be an important regulator of sugar intake by acting on both caloric and rewarding components.

Platycodon grandiflorum modifies adipokines and the glucose uptake in high-fat diet in mice and L6 muscle cells

Obesity and diabetes have become the most common human health problems worldwide. Obesity's contribution to type 2 diabetes might be due to dysregulation of adipokines and glucose uptake. In this study, we performed in-vivo and in-vitro studies to evaluate the effects of Platycodon grandiflorum extract (PGE) on adipokines and glucose uptake. Before study, platycodin D concentrations were analysed by HPLC in PGE prepared in water, in 50% ethanol and in 80% ethanol, and we selected the 80% ethanol extract as the PGE for this study based on the HPLC results. We found that inclusion of PGE in the high-fat diet (HFD) markedly attenuated food intake, body weight, epididymal fat weight, adipocyte size and blood glucose levels by the oral glucose tolerance test in mice, and maintained serum levels of adiponectin, resistin, leptin, fructosamine and triglycerides. Gene expression analysis revealed that PGE up-regulated adiponectin, and down-regulated TNF-α and leptin in fat tissue. In L6 muscle cells in vitro, PGE increased insulin-stimulated glucose uptake. We conclude that PGE may improve obesity in mice fed an HFD and glucose uptake in L6 muscle cells by modifying adipokines, and could offer clinical benefits as a supplement to treat obesity and diabetes.

Sida rhomboidea. Roxb Leaf Extract Down-Regulates Expression of PPARγ2 and Leptin Genes in High Fat Diet Fed C57BL/6J Mice and Retards in Vitro 3T3L1 Pre-Adipocyte Differentiation

Sida rhomboidea. Roxb leaf extract (SRLE) is being used by the populace of North-East India to alleviate symptoms of diabetes and obesity. We have previously reported its hypolipidemic and anti-diabetic properties. In this study, we report the effect of SRLE on (i) in vivo modulation of genes controlling high fat diet (HFD) induced obesity and (ii) in vitro 3T3L1 pre-adipocyte differentiation and leptin release. Supplementation with SRLE significantly prevented HFD induced increment in bodyweight, plasma lipids and leptin, visceral adiposity and adipocyte hypertrophy. Also, SRLE supplementation reduced food intake, down regulated PPARγ2, SREBP1c, FAS and LEP expressions and up-regulated CPT-1 in epididymal adipose tissue compared to obese mice. In vitro adipogenesis of 3T3L1 pre-adipocytes was significantly retarded in the presence of SRLE extract. Also decreased triglyceride accumulation, leptin release and glyceraldehyde-3-Phosphate dehydrogenase activity along with higher glycerol release without significant alteration of viability of 3T3L1 pre-adipocytes, was recorded. Our findings suggest that prevention of HFD induced visceral adiposity is primarily by down regulation of PPARγ2 and leptin gene expression coupled with attenuation of food intake in C57BL/6J mice. SRLE induced prevention of pre-adipocytes differentiation, and leptin release further substantiated these findings and scientifically validates the potential application of SRLE as a therapeutic agent against obesity.

Insulin detemir attenuates food intake, body weight gain and fat mass gain in diet-induced obese Sprague–Dawley rats

Objective:Initiation and intensification of insulin therapy commonly causes weight gain, a barrier to therapy. A contrasting body of evidence indicates that insulin functions as an adiposity negative feedback signal and reduces food intake, weight gain and adiposity via action in the central nervous system. Basal insulin analogs, detemir (Det) and glargine (Glar), have been associated with less hypoglycemia compared with neutral protamine hagedorn insulin, and Det with less weight gain, especially in patients with higher body mass index (BMI). We sought to determine whether insulin therapy per se causes body weight and fat mass gain when delivered via a clinically relevant subcutaneous (SC) route in the absence of hypoglycemia and glycosuria in non-diabetic lean and diet-induced obese rats.Materials and methods:Rats were exposed to either a low-fat diet (LFD; 13.5% fat) or high-fat diet (HFD; 60% fat), and received Det (0.5 U kg−1), Glar (0.2 U kg−1) or vehicle (Veh) SC once daily for 4 weeks. These dosages of insulin were equipotent in rats with respect to blood–glucose concentration and did not induce hypoglycemia.Results:As predicted by current models of energy homeostasis, neither insulin Det nor Glar therapy affected food intake and weight gain in LFD rats. Det treatment significantly attenuated food intake, body weight gain and fat mass gain relative to the Glar and Veh in high-fat fed animals, mirroring observations in humans.Conclusions:That neither insulin group gained excess weight, suggests weight gain with SC basal insulin therapy may not be inevitable. Our data further suggest that Det possesses a unique property to attenuate the development of obesity associated with a HFD.

The Peptidic GHS-R antagonist [D-Lys3]GHRP-6 markedly improves adiposity and related metabolic abnormalities in a mouse model of postmenopausal obesity

It was demonstrated that estrogen deficiency and consuming high fat (HF) diet enhanced orexigenic activity of ghrelin. Therefore, we hypothesized that antagonizing of ghrelin action would attenuate food intake and body weight in mice obese both from ovariectomy (OVX) and feeding a HF diet.Ghrelin receptor antagonist [D-Lys3]GHRP-6 after seven days of subcutaneous treatment markedly decreased food intake in OVX mice fed both HF and standard diets; furthermore, it reduced body weight and blood glucose, insulin and leptin, and increased β-hydroxybutyrate level and uncoupling-protein-1 mRNA in brown adipose tissue. Pair-feeding revealed that effect of [D-Lys3]GHRP-6 was primary anorexigenic. Estrogen supplementation reduced anorexigenic effects of [D-Lys3]GHRP-6. OVX [D-Lys3]GHRP-6 treatment in mice on HF diet resulted in markedly increased circulating level and liver expression of a major metabolic regulator, fibroblast growth factor 21.Our data suggest that ghrelin antagonists could be especially beneficial in individuals with common obesity combined with estrogen deficiency.

Chronic oestrogen replacement in ovariectomised rats attenuates food intake and augments c-Fos expression in the suprachiasmatic nucleus specifically during the light phase

Oestrogen replacement in ovariectomised (OVX) rats has been reported to attenuate food intake, especially during the light phase. To gain better insight into the central mechanism of oestrogen-induced reduction of food intake, we examined the effect of chronic oestrogen replacement in OVX rats on c-Fos expression in the suprachiasmatic nucleus (SCN) and on food intake during the light and dark phases. Eight-week-old female rats were ovariectomised and implanted with either an oestradiol (E2) or a vehicle pellet (Veh) subcutaneously. The animals were housed in an environment with a 12h light-12h dark cycle with the lights on at 07.00 hours. The amount of spontaneous food intake relative to each animal's body weight was significantly less for the E2 group than for the Veh group during the light phase, but there were no differences shown between these groups during the dark phase. There were no differences shown in the number of c-Fos-immunoreactive cells in the SCN in the E2 group compared with the Veh group during the early dark phase (22.00 hours; Zeitgeber time 15.00 (ZT15)), but the number was significantly higher than in the Veh group during the early light phase (10.00hours; ZT3). This finding suggests that chronic oestrogen replacement chronically enhances SCN activity, specifically during the light phase. The oestrogen-induced enhancement of SCN activity during the light phase is possibly involved in the light phase-specific attenuation of food intake by oestrogen replacement in OVX rats.

Attenuation of food intake in chicks by an inverse agonist of cannabinoid receptor 1 administered by either injection or ingestion in hydrocolloid carriers

The cannabinoid receptor (CB1) was studied primarily in mammals where it was found to comprise a link between reward processes and addictive behavior such as food consumption. The purpose of this study was twofold: first to characterize the effect of the chicken CB1 receptor inverse agonist AM251 on food intake, and second, to establish a stress-free approach for application of AM251 to birds using hydrocolloid carriers, which can be mixed with food. A single administration of AM251 by intravenous injection (at 0.85 or 5mgkg−1BW) or by ingestion of hydrocolloid carriers entrapping AM251 at a concentration of 5mgkg−1BW led to a transient attenuation of food intake. The consequent reduced cumulative food intake and BW were observed in the treated chicks for at least 7h post-administration, with no gender differences. Circulating levels of AM251, assessed by LC–MS following 48h of continuous feeding with hydrocolloid carriers containing 50mg AM251kg−1BWday−1, were physiologically significant at 186±73pmolml−1. It is concluded that unlike some other factors, which act differently in birds compared to mammals such as ghrelin, CB1 inverse agonists attenuate food intake in chicks similar to its effect in mammals. In addition, the new approach for administration of AM251 to birds in hydrocolloid carriers could provide a simple and stress-free tool for prolonged studies of this control mechanism in birds.

Weekly Exenatide Equals Daily Glargine Insulin for Glycemic Control

Exenatide (Byetta), an injectable glucagon-like peptide-1 (GLP-1) receptor agonist, is useful in managing patients with type 2 diabetes, because it stimulates glucose-dependent insulin secretion, reduces glucagon secretion, slows gastric emptying, and attenuates food intake. A once-weekly injectable form of exenatide is more effective than the currently FDA-approved twice-daily exenatide formulation …

Site-specific attenuation of food intake but not the latency to eat after hypothalamic injections of neuropeptide Y in dehydrated-anorexic rats

Anorexia that accompanies cellular dehydration in rats (DE-anorexia) offers a relatively simple model for investigating the functional organization of neural mechanisms that can suppress feeding during dehydration. Previous studies strongly suggest that the inputs that drive ingestive behavior control neurons in the paraventricular nucleus of the hypothalamus (PVH) and lateral hypothalamic area (LHA) remain active during DE-anorexia. Here we examine whether these two regions retain their sensitivity to neuropeptide Y (NPY). NPY is an important component in two major feeding-related inputs from the arcuate nucleus and the hindbrain. We found that intake responses to NPY injections in the LHA and PVH were suppressed in DE-anorexia, but the PVH remained less sensitive to the effects of NPY than the LHA in DE-anorexic animals. Indeed the higher dose of NPY (238 pmol) completely overcame shorter periods of DE-anorexia when injected into the LHA but not the PVH. However, the latency to eat after NPY injections remained unchanged from control animals, regardless of NPY dose, injection location, or intensity of anorexia. Furthermore, the onset and size of the strong and rapidly induced compensatory feeding that follows the return of water to DE-anorexic animals was also unaffected by any NPY injections. These data support the hypothesis that DE-anorexia develops as a consequence of the premature termination of regularly initiated meals, which perhaps involves processes that alter the sensitivity of satiety mechanisms downstream to the PVH and LHA.

Oxyntomodulin reduces expression of glucagon-like peptide 1 receptor in the brainstem of chickens

Oxyntomodulin (OXM) is a peptide released from the gut and attenuates food intake by acting on hypothalamus. However, its role at the molecular level is not well studied. In the first section of this study, we analysed the effect of OXM on food intake behaviour after injecting into the lateral ventricle of chickens. The outcome showed that food intake decreased significantly after administering 4 nmol of OXM. In the second part, the expression of glucagon-like peptide 1 receptor (GLP-1R) in the brainstem was analysed by real-time RT-PCR. The results showed that expression of GLP-1R was reduced to 27% and 16% at 30 and 90 mins after injection of OXM respectively. In saline-injected chickens, no reduction in GLP-1R was seen. It can be concluded that OXM has a down regulatory effect on the responding receptor, GLP-1R and OXM in chicks has the same reductive effect on food intake as in the mammals.

Estrogen attenuates food intake and perifornical orexinergic neuron′s activity during glucoprivation in ovariectomized rats

We examined the effect of estrogen (E2) replacement in ovariectomized rats on food intake and lateral hypothalamic neuron′s activity during glucoprivation induced by i.v. 2‐deoxy‐D‐glucose (2DG) administration. Rats were ovariectomized and implanted E2 or vehicle (cholesterol) subcutaneously. Two weeks after the replacement, rats were infused with 2DG (400 mg/kg) and food intake was measured for 3 hours. The same experiment was performed for immunohistochemical examination of c‐Fos, melanin concentrating hormone (MCH), and orexin A expression in the lateral hypothalamic area (LH) and arcuate nucleus (Arc). Glucoprivation induced c‐Fos expression in the orexin A neurons locating at the perifornical region of LH, but did not activate MCH neurons. Glucoprivation significantly induced food intake, and food intake in E2 replaced group was significantly lower than E2 deficit group. The number and fraction of c‐Fos expressed orexinergic neurons was significantly lower in E2 replaced group than E2 deficit group. The number of c‐Fos ir cells was less in E2 replaced group than E2 deficit rats. These data indicate that E2‐induced reduction of food intake induced by 2DG is possibly due to the reduced perifornical orexinergic neuron′s activity and to the reduced Arc neuron′s activity.

Pharmacological targeting of the serotonergic system for the treatment of obesity.

The attenuation of food intake as induced by an increase in serotonergic (5-hydroxytryptamine, 5-HT) efficacy has been a target of antiobesity pharmacotherapies. However, the induction of tolerance and/or side-effects limited the clinical utility of the earliest serotonin-related medications. With the global prevalence of obesity rising, there has been renewed interest in the manipulation of the serotonergic system as a point of pharmacological intervention. The serotonin(2C) receptor (5-HT(2C)R), serotonin(1B) (rodent)/serotonin(1Dbeta) (human) receptor (5-HT(1B/1Dbeta)R) and serotonin(6) receptor (5-HT(6)R) represent the most promising serotonin receptor therapeutic targets. Canonical serotonin receptor compounds have given way to a myriad of novel receptor-selective ligands, many of which have observable anorectic effects. Here we review serotonergic compounds reducing ingestive behaviour and discuss their clinical potential for the treatment of obesity.

Neuroendocrine, metabolic and pharmacological control of feeding behaviour – closing in on antiobesity treatment

Neuroendocrine, metabolic and pharmacological control of feeding behaviour – closing in on antiobesity treatment

Forebrain melanocortin signaling enhances the hindbrain satiety response to CCK-8

Melanocortin 4 receptors (MC4R) are hypothesized to mediate the central nervous system actions of leptin to enhance the satiety effects of cholecystokinin (CCK). To further elucidate this mechanism, we confirmed that peripheral administration of CCK-8 is less effective in producing this effect in MC4R-deficient mice (MC4R(-/-)). Whereas intraperitoneal (ip) CCK-8 at 0.75 nmol/kg lean body mass (lbm) suppressed food intake in wild-type mice, CCK-8 doses of 7.5 nmol/kg lbm were required to attenuate food intake in MC4R(-/-) mice. To determine whether melanocortin signaling in the hypothalamic paraventricular nucleus (PVN) participates in regulating this CCK satiety response, we administered the MC3/MC4R antagonist, SHU9119, into the PVN of rats before ip CCK-8 administration. PVN administration of SHU9119 attenuated the ability of CCK-8 to reduce 30-min food intake by 20%. To determine whether MC4R are expressed by PVN neurons that project directly to hindbrain nuclei involved in the satiety response to ip CCK-8, the retrograde tracer fluorescent cholera toxin subunit B was injected into the nucleus tractus solitarius (NTS) of the hindbrain. After 4 days, labeled PVN neurons were collected by laser capture microdissection and found to express MC4R mRNA by quantitative RT-PCR analysis. These data provide evidence for a neuroanatomical link between hypothalamic melanocortin signaling in the PVN and NTS neurons that regulate food intake. These findings highlight the contribution of melanocortin signaling in the PVN toward regulating the satiety effects of CCK-8 while acknowledging that melanocortin-dependent pathways in other brain regions and/or melanocortin-independent mechanisms are also important in this mechanism.

Short‐Term Anorexigenic Effects of Central Neuropeptide VF are Associated with Hypothalamic Changes in Chicks

The present study was designed to measure food and water intake, changes in hypothalamic chemistry, and other behaviour modifications after central injection of neuropeptide (NP) VF in broiler type chicks. In Experiment 1, chicks responded to central NPVF with a reduction in food intake for up to 90 min post injection. Water intake was unaffected. In Experiment 2, NPVF exerted a less potent and shorter duration of attenuated food intake than did the structurally related NPFF. In Experiment 3, 16.0 nmol NPVF reversed the prolactin-releasing peptide induced orexigenic effect. In Experiment 4, central NPVF treatment was associated with decreased c-Fos immunoreactivity in the lateral hypothalamus, whereas c-Fos immunoreactivity in the dorsomedial nucleus, infundibular nucleus (homologue to the mammalian arcuate nucleus) and ventromedial nucleus was increased. In Experiment 5, behaviours unrelated to ingestion including sit, stand, deep rest and locomotion were affected by central NPVF injection. Some of these behaviours are incompatible with ingestion and may contribute to hypothalamic associated perception of satiety after central NPVF. In conclusion, NVPF is a short-term regulator of appetite and its effects are associated with hypothalamic and behaviour changes in chicks.

The Role of the Vagus Nerve in Mediating the Long‐Term Anorectic Effects of Leptin

Leptin, the product of the obese (ob) gene, is mainly known for its regulatory role of energy balance by direct activation of hypothalamic receptors. Recently, its function in the acute control of food intake was additionally attributed to activation of the vagus nerve to regulate meal termination. Whether vagal afferent neurones are involved in longer term effects of leptin on food intake, however, remains undetermined. Using vagotomised (VGX) rats, we sought to clarify the contributions of vagal afferents in mediating the long-lasting effect of leptin on appetite suppression. Intraperitoneal (i.p.) injection of leptin (3.5 mg/kg) attenuated food intake at 4, 6, 8 and 24 h and body weight at 24 h postinjection in SHAM-operated rats; however, this response was not abrogated by vagotomy. In a separate study using immunohistochemistry, we observed leptin-induced Fos expression in the nucleus tractus solitarii, a brain structure where vagal afferent fibres terminate. This signal was not attenuated in VGX animals compared to the SHAM group. Moreover, leptin treatment led to a similar level of nuclear STAT3 translocation, a marker of leptin signalling, in the hypothalami of SHAM and VGX animals. In addition to the effects of leptin, vagotomy surgery itself resulted in a decrease of 24 h food intake. Analyses of brains from saline-treated VGX animals revealed a significant induction of Fos in the nucleus tractus solitarii and changes in agouti-related peptide and pro-opiomelanocortin mRNA expression in the hypothalamus compared to their SHAM counterparts, indicating that the vagotomy surgery itself induced a modification of brain activity in areas involved in regulating appetite. Collectively, our data suggest that vagal afferents do not constitute a major route of mediating the regulatory effect of leptin on food intake over a period of several hours.

Effect of cholecystokinin on feeding is attenuated in monosodium glutamate obese mice

Treatment of newborn mice with monosodium glutamate (MSG) is neurotoxic for hypothalamic arcuate nucleus (ARC) and causes obesity. In the MSG-treated 16-week-old NMRI mice, we detected specific ablation of ARC neuronal cells, 8 times higher fat to body mass ratio but unchanged body mass compared to controls, advanced hyperglycemia and hyperinsulinemia — both more pronounced in males, and hyperleptinemia — more severe in females. After fasting, the MSG-treated mice showed attenuated food intake compared to controls. Cholecystokinin octapeptide, which decreased food intake in a dose-dependent manner in 24 h fasted controls, did not significantly affect food intake in the MSG-treated animals. We propose that the obesity-related changes in the feeding behavior of the MSG-treated obese mice were the result of missing leptin and insulin receptors in ARC and consequent altered neuropeptide signaling. This makes the MSG model suitable for clarifying generally the central control of food intake.

Removal of norepinephrine and/or epinephrine signaling in the perifornical hypothalamus attenuates nicotine's hypophagic action

Previously we reported (Guan et al., Life Sci. 74:2725–2737, 2004) that intermittent nicotine (NIC) in the dark phase altered meal patterns, attenuated food intake and suppressed body weight. Infusion of the NIC receptor antagonist, mecamylamine (MEC), into the fourth ventricle attenuates the hypophagic action of i.p. administered NIC. One potential action of MEC is blocking NIC receptors on norepinephrine (NE)/epinephrine (EPI) producing C2/C3 neurons adjacent to the fourth ventricle. C2/C3 neurons project axons to the perifornical hypothalamus (PFH) region. We hypothesize that EPI released from C2/C3 neuronal axons binds adrenergic receptors in the PFH modulating neuronal activity that subsequently affects feeding. To test this hypothesis, bilateral PFH lesions were made using 4 μg of 6-OHDA hydrobromide (free base) in a volume of 0.3 μl. The animals were pretreated by injecting i.p. pargyline to enhance the lesion effect and bupropion HCl to protect dopamine neurons 30 minutes prior to 6-OHDA infusion. Controls received sham operations. Cannula placement and infusion was verified histochemically. After recovery of the pre-surgery body weights the animal's food intake was recorded before and after NIC injection. NIC injection altered meal patterns and attenuated body weight, but after lesioning the PFH NIC did not alter meal patterns or attenuate body weight. This suggests that the PFH is necessary, in part, for NIC to alter meal patterns and body weight.

Effects of selective estrogen receptor agonists on food intake and body weight gain in rats

Ovariectomized (OVX) rats eat more and gain weight more rapidly than sham-operated (SO) rats and estradiol (E 2) treatment attenuates food intake and body weight gain in OVX rats. Studies were designed to test the hypothesis that the alpha subtype of the estrogen receptor (ERα) mediates the attenuating effects of E 2 on food intake and body weight gain while the beta subtype (ERβ) mediates opposing actions that lead to increased food intake and body weight gain. Female rats were SO or OVX and treated daily with vehicle (dimethylsulfoxide, DMSO) or E 2 (10 μg/day), or the ERα−selective agonist, 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT, 0.5 mg/day), or the ERβ−selective agonist, 2,3-bis(4-hyroxyphenyl)-propionitrile (DPN, 0.5 mg/day) for 14 days. Total food intake was significantly reduced by E 2 and PPT, but not DPN. Total body weight gain was significantly increased in OVX rats compared to SO rats and treatment with E 2 or PPT, but not DPN, significantly decreased total body weight gain to levels that were not significantly different from SO rats. A dose–response study of PPT indicated that at 0.25 mg/day, PPT significantly reduced total 21-day food intake and body weight gain and, at 0.13 and 0.06 mg/day, PPT significantly reduced total body weight gain compared to OVX rats without significantly reducing total food intake. A dose–response study of DPN indicated that none of the three doses of DPN significantly altered total 21-day food intake or total body weight gain. These results suggest ERα mediates the attenuating effects of estrogens on food intake and body weight gain while ERβ has no effect on these variables.

Estrogenic effect on swelling and monocytic receptor expression in an arthritic temporomandibular joint model

Clinical presentation of temporomandibular joint (TMJ) disorders are more common in women and changes in the female hormone estrogen affect the level of swelling, pro-inflammatory cytokine release and pain in animal models of TMJ arthritis. Estrogen also modulates the expression of the CD16 receptor in vitro. This alters pro-inflammatory cytokine release in monocytes/macrophages when auto-antigens and arthritic factors bind the CD16 receptor. This study investigated the effects of various levels of estrogen on the intensity of inflammation and CD16 expression in a TMJ arthritic animal model. The experiments included rats that were intact or ovariectomized (OVX), eliminating the major source of estrogen output. A portion of the OVX animals had estrogen replaced with 17-β estradiol (E2) using Alzet ® pumps. In OVX animals E2 levels were administered for 10 days to create an artificial estrus cycle or to simulate pregnancy. Following E2 treatment the rats were given an intra-articular TMJ injection of saline or complete Freund's adjuvant (CFA). CFA injection significantly increased TMJ swelling, stress induced chromodacryorrhea and attenuated food intake, thus indicating the adjuvant induced TMJ pain/inflammation. Removing endogenous E2 through OVX reduced CFA induced TMJ inflammation, whereas CFA increased the number of TMJ monocytes expressing the CD14 receptor equally in all groups irrespective of plasma E2 levels. Paradoxically, higher levels of E2 reduced the number of TNF-α positive, CD16+ and double labeled CD14+/CD16+ cells. The findings indicate that reduced plasma E2 levels attenuated CFA induced TMJ inflammation, whereas increasing E2 levels enhanced TMJ swelling in a dose dependent manner. Estrogenic group differences in CFA induced swelling were independent of TMJ CD14+, CD14+/CD16+ or CD16+ cell numbers suggesting E2 action on the CFA immune response primarily excluded CD16 receptor action.