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Randy J Seeley

Publications and source records attributed to Randy J Seeley.

At least 55 records · Page 3Linked to original sources
PubMed2003

Neuropeptide Y and lipid increase apolipoprotein AIV gene expression in rat hypothalamus.

Apolipoprotein AIV (apo AIV) is a circulating signal released from intestinal cells in response to lipid feeding and contributes to the anorectic effect of a lipid meal. We have demonstrated that apo AIV is also synthesized in the hypothalamus, and that hypothalamic apo AIV gene expression is regulated physiologically. Neuropeptide Y (NPY) is a hypothalamic neuropeptide with broad regulatory actions in the central nervous system. In the present studies, the effects of intracerebroventricular (i.v.t.) administration of NPY and of intraduodenal lipid infusion on hypothalamic apo AIV gene expression were determined using competitive RT-PCR in fasted rats. I.v.t. injection of NPY alone significantly increased apo AIV mRNA levels in the hypothalamus in a dose-dependent manner. Intraduodenal infusion of lipid also stimulated the gene expression of hypothalamic apo AIV, but no further significant increment occurred when i.v.t. injection of NPY was combined with lipid infusion. These results suggest that NPY and lipid may regulate apo AIV gene expression in the rat hypothalamus.

Analysis of Variance↗
PubMed2003

7-OH-DPAT selectively reduces intake of both chow and high fat diets in different food intake regimens.

Mesolimbic dopaminergic system activation correlates with ingestive behavior in numerous feeding regimens. DA release is enhanced by food intake following deprivation, amount of food consumed, and the palatability of the food consumed. The dopamine-3 receptor (D3-R) has a limited expression pattern that is restricted largely to the mesolimbic dopaminergic system. The D3-R has been hypothesized to inhibit DA-mediated reward, locomotion and motivation. To test the potential for an inhibitory role of the D3-R on food intake, we administered the D3-R agonist 7-OH-DPAT (5, 10 and 50 microg/kg ip) to rats that had ad libitum access to standard rodent chow (3.41 kcal/gm, 0.51 kcal/gm from fat) or a preferable, high fat (HF) (4.4 kcal/gm, 1.71 kcal/gm from fat). In the second set of experiments we administered 7-OH-DPAT (10, 50 and 100 microg/kg) to rats that had access to chow or HF diet for only 3 h per day (meal fed). In the third set of experiments we administered 7-OH-DPAT (10 and 50 microg/kg) to rats that had access to chow or HF diet after a 21-h food restriction. The 10 and 50 microg/kg doses significantly, but equally reduced intake of chow and HF diet in animals that were ad libitum fed. In animals that were meal-fed the dose response was effectively shifted to the right and the 10 microg/kg dose was ineffective at reducing intake. The 50 and 100 microg/kg doses significantly but equally reduced intake of both diets. In animals that were 21-h restricted and had access to chow both the 10 and 50 microg/kg doses were ineffective at reducing intake. However, in animals that had access to HF diet, 7-OH-DPAT dose-dependently reduced intake. These results support a potential role for the D3-R in ingestive behavior particularly in situations that involve a significant learned component.

Animals↗
PubMed2003

Expression of biologically active rat apolipoprotein AIV in Escherichia coli.

Rat apolipoprotein AIV (apo AIV) is a 43-kDa intestinal apolipoprotein that is important in lipid metabolism and the suppression of food intake. In this study, a full-length rat apo AIV was expressed in Escherichia coli and purified in a bioactive form. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometric analysis revealed that the isolated recombinant protein has a molecular mass of approximately 43 kDa, similar to that of natural rat apo AIV. Immunoblot analysis and N-terminal amino acid sequencing confirmed the identity of the recombinant apo AIV protein as natural rat apo AIV. The recombinant protein was functional in lipoprotein binding assays. Biological activity was assessed behaviorally in that the recombinant protein suppressed food intake of fasted rats comparably to natural rat apo AIV. Neither native nor recombinant apo AIV elicited a conditioned taste aversion (CTA) at doses that suppress feeding. These results indicate that the recombinant apo AIV is structurally and functionally indistinguishable from rat natural apo AIV, making this overexpression and purification scheme a powerful tool for future structure and function studies.

Amino Acid Sequence↗
PubMed2003

Two novel paradigms for the simultaneous assessment of conditioned taste aversion and food intake effects of anorexic agents.

The conditioned taste aversion (CTA) is routinely used to assess the aversive consequences of anorexic agents, including potential pharmacological therapies for obesity. In a typical CTA paradigm, rats briefly sampling a novel tastant (e.g., saccharin) are acutely administered with toxin (e.g., lithium chloride, LiCl). After as few as one taste-toxin pairing, rats will reliably avoid the novel tastant. This paradigm is frequently used for the assessment of possible aversive consequences of drugs that are candidates for pharmacological therapies. The degree to which the drug supports development of a CTA is interpreted as an index of its aversive properties. Difficulties with previous work include the inability to assess affects on food intake and CTA simultaneously, particularly during chronic drug administration. We report here two novel CTA paradigms for the assessment of appetitive and aversive consequences of anorexic agents, simultaneously. In the first experiment, animals receive an intraoral infusion of a novel and highly palatable tastant immediately prior to administration of increasing doses of LiCl. In the second experiment, rats were implanted intraperitoneally with osmotic minipumps that chronically delivered a low dose of LiCl for 7 days. LiCl did not affect short or long term food intake in either experiment. However, LiCl did support the development of a CTA in both paradigms. These results suggest that both the appetitive and aversive consequences of anorexic agents can be assessed simultaneously during either acute or chronic drug administration.

Animals↗
PubMed2003

Altered feeding responses in mice with targeted disruption of the dopamine-3 receptor gene.

Dopamine signaling has been implicated in the control of food intake and body weight. In particular, dopamine is important in the control of meal size and number and is thought to mediate the response to metabolic deprivation states. In the present experiments, the authors assessed the role of the dopamine-3 receptor (D3R) in the feeding responses to 2-deoxy-D-glucose, mercaptoacetate, and peripheral insulin. All 3 compounds increased food intake in wild-type mice, but the hyperphagic responses were blunted in D3R-/- mice. In other experiments, D3R-/- mice were hyperresponsive to the administration of amylin and leptin relative to wild-type mice. These results support the hypothesis that D3Rs chronically inhibit the effects of adiposity hormones, thereby contributing to a net anabolic state.

Animals↗
PubMed2003

Ethanol consumption in mice with a targeted disruption of the dopamine-3 receptor gene.

Considerable evidence suggests that the mesolimbic dopaminergic system is an important substrate for the rewarding effects of ethanol consumption. Previous data have demonstrated that pharmacological agents that alter dopamine signaling also influence the self-administration of ethanol. The present experiments were designed to assess the role of the dopamine-3 receptor (D3-R) on voluntary ethanol consumption in C57BL/6 mice. Mice with targeted disruption of the D3-R gene (D3-R - /-) were compared to wild-type controls in an ethanol intake paradigm. In Experiment 1, mice had 24-hour access to ethanol each day in a two-bottle choice paradigm for a period of 7 days per concentration. The concentrations tested were 3, 6, 10 and 15%. In Experiment 2, mice had I hour of access to ethanol each day in a two-bottle paradigm for a period of 7 days per concentration. The same concentrations in Experiment I were compared in Experiment 2. In Experiment 3 we sought to test the development of a conditioned taste aversion (CTA) after receiving an intraperitoneal (ip.) injection of 2.0 g/kg ethanol. In Experiment 4, blood ethanol levels where assessed following a 2.0 g/kg ip.injection of ethanol. Experiment 5 assessed taste preference for saccharine and quinine in wild-type and D3-R -/- mice. Contrary to our predictions, both D3-R -/- and wild-types on a CS57BL/6 background had similar intakes of ethanol, at all concentrations tested, in the 24-hour and 1-hour intake paradigms. Wild-type and D3-R -/- mice respond to injected ethanol similarly by developing a conditioned taste aversion. Metabolic analysis revealed mutant mice are slower in metabolizing a bolus injection of ethanol. Lastly, wild-type and D3-R -/- mice showed similar consumption to increasing concentration of both sweet and bitter tastes. These data suggest that deletion of the D3-R gene does not increase ethanol consumption above that found on the C57BL/6 genetic background. Furthermore, the D3-R -/- mice adequately learn a CTA to ethanol and do not ham differing taste reactivity to saccharin or quinine. However, D3-R -/- mice do appear to have a slower rate of ethanol metabolism.

Alcohol Drinking↗
PubMed2003

A controlled high-fat diet induces an obese syndrome in rats.

The prevalence of obesity is increasing. Although the etiology of obesity is complex, dietary factors, particularly the consumption of a high-fat (HF) diet, is considered a risk factor for its development. Nonetheless, a causal role of dietary fat has never been definitively documented, in part because of inadequate animal models. We developed a rat model of diet-induced obesity that will be a powerful tool for assessment of this issue. In four experiments, Long-Evans rats ate ad libitum a synthetic semipurified diet containing 20 g (HF) or 4 g [low-fat (LF)] of fat/100 g of diet or a nonpurified diet. Other rats ate ad libitum the HF diet in amounts matched to the energy intake of the LF rats. When compared over 10 wk of free feeding, HF rats weighed 10% more (P < 0.01) than LF rats and had 50% more body fat (P < 0.01), as well as significant hyperleptinemia and insulin resistance. Compared with rats fed the nonpurified diet, the HF rats had even more marked differences in these variables. The rats fed the HF diet to match the rats fed the LF diet had similar body weights but significantly more adipose tissue than LF rats, suggesting that diet composition and/or energy density of the diet affects fat deposition. This dietary regimen has reproducible effects on body size and composition, and these are similar in male and female rats. This model of diet-induced obesity will be a useful tool for studying the mechanisms by which dietary fat influences the regulation of energy balance.

Animals↗
PubMed2003

Syndecan-3 modulates food intake by interacting with the melanocortin/AgRP pathway.

Syndecan-3, expressed in the developing nervous system and adult brain, alters feeding behavior through its interaction with the CNS melanocortin system, which provides critical tonic inhibition of both food intake and body adipose stores. A variety of both in vitro and transgenic data supports the hypothesis that syndecan-3 modulates melanocortin activity via syndecan-3 facilitation of agouti-related protein (AgRP), a competitive antagonist of alpha-melanocyte-stimulating hormone (alpha-MSH) at the melanocortin-3 and -4 receptors. Consistent with this hypothesis, mice lacking syndecan-3, which therefore would be predicted to have less effective AgRP, are more sensitive to inhibition of food intake by the melanocortin agonist MTII. Additionally, we took advantage of the fact that syndecan-3 facilitation of AgRP is limited to when it is bound to the cell membrane. Pharmacologic inhibition of the enzyme that cleaves syndecan-3 from the cell membrane leads to increased food intake in fasted rats, which have elevated levels of AgRP. Furthermore, the shedding process appears to be regulated under physiologic conditions, because a putative inhibitor of the shedding process, tissue inhibitor of metalloprotease-3 (TIMP-3), is increased by food deprivation. These observations contribute to the hypothesis that syndecan-3 regulation of melanocortin signaling contributes to the normal control of energy balance. Collectively, the data suggest that the modulation of melanocortin regulation of energy balance by syndecan-3 is modulated by the action of a TIMP-3-sensitive metalloprotease.

Agouti-Related Protein↗
PubMed2003

Intraventricular melanin-concentrating hormone stimulates water intake independent of food intake.

The lateral hypothalamus (LH) has a critical role in the control of feeding and drinking. Melanin-concentrating hormone (MCH) is an orexigenic peptidergic neurotransmitter produced primarily in the LH, and agouti-related protein (AgRP) is an orexigenic peptidergic neurotransmitter produced exclusively in the arcuate (ARC), an area that innervates the LH. We assessed drinking and eating after third ventricular (i3vt) administration of MCH and AgRP. MCH (2.5, 5, and 10 micro g i3vt) significantly increased food as well as water intake over 4 h when administered during either the light or the dark portion of the day-night cycle. When MCH (5 micro g) was administered to rats with access to water but no food, they drank significantly more water than when given the vehicle. AgRP (7 micro g i3vt), on the other hand, increased water intake but only in proportion to food intake during the dark and the light, and water intake was not increased after i3vt AgRP in the absence of food. Hence, in contrast to AgRP, MCH elicits increased water intake independent of food intake. These results are consistent with historical data linking activity of the LH with water as well as food intake.

Agouti-Related Protein↗
PubMed2003

Increased dietary fat attenuates the anorexic effects of intracerebroventricular injections of MTII.

The hypothalamic melanocortin (MC) system provides a critical inhibitory control on food intake and body weight. Because access to high-fat (HF) diets is associated with the development of obesity, we hypothesized that increased dietary fat attenuates signaling through the MC system. To evaluate this hypothesis, we compared the efficacy of the MC3/4 receptor agonist, MTII, to reduce food intake in rats fed carefully matched HF or low-fat (LF) diets for 12 wk. Rats given the HF diet ad libitum were significantly more obese than rats given the LF diet, and had significantly higher plasma insulin and leptin levels. MTII given into the third cerebral ventricle in doses of 0.1, 0.3, and 1.0 nmol was less effective at reducing food intake in HF rats than in LF rats. Whole-hypothalamic expression of the MC agonist precursor gene, proopiomelanocortin, the MC antagonist agouti-related protein, and the MC4 receptor, were not different between the HF and LF groups. These results indicate that consumption of a HF diet decreases signaling through the melanocortin system, an abnormality that could contribute to diet-induced obesity.

Agouti-Related Protein↗
PubMed2003

A randomized trial comparing a very low carbohydrate diet and a calorie-restricted low fat diet on body weight and cardiovascular risk factors in healthy women.

Untested alternative weight loss diets, such as very low carbohydrate diets, have unsubstantiated efficacy and the potential to adversely affect cardiovascular risk factors. Therefore, we designed a randomized, controlled trial to determine the effects of a very low carbohydrate diet on body composition and cardiovascular risk factors. Subjects were randomized to 6 months of either an ad libitum very low carbohydrate diet or a calorie-restricted diet with 30% of the calories as fat. Anthropometric and metabolic measures were assessed at baseline, 3 months, and 6 months. Fifty-three healthy, obese female volunteers (mean body mass index, 33.6 +/- 0.3 kg/m(2)) were randomized; 42 (79%) completed the trial. Women on both diets reduced calorie consumption by comparable amounts at 3 and 6 months. The very low carbohydrate diet group lost more weight (8.5 +/- 1.0 vs. 3.9 +/- 1.0 kg; P < 0.001) and more body fat (4.8 +/- 0.67 vs. 2.0 +/- 0.75 kg; P < 0.01) than the low fat diet group. Mean levels of blood pressure, lipids, fasting glucose, and insulin were within normal ranges in both groups at baseline. Although all of these parameters improved over the course of the study, there were no differences observed between the two diet groups at 3 or 6 months. beta- Hydroxybutyrate increased significantly in the very low carbohydrate group at 3 months (P = 0.001). Based on these data, a very low carbohydrate diet is more effective than a low fat diet for short-term weight loss and, over 6 months, is not associated with deleterious effects on important cardiovascular risk factors in healthy women.

Adipose Tissue↗
PubMed2003

Insulin and the blood-brain barrier.

Although several possible mechanisms exist by which the pancreatic hormone, insulin, could enter the brain from the blood, most evidence suggests that the majority of it enters primarily by a receptor-mediated transport process. Many factors influence the rate of entry, including fasting and refeeding and several pathological conditions. Within the brain insulin acts on specific receptors to influence a number of behaviors, and especially caloric homeostasis and cognition.

Animals↗
PubMed2003

Learned meal initiation attenuates the anorexic effects of the melanocortin agonist MTII.

The central melanocortin system is critically involved in the control of food intake and body weight. Administration of melanocortin agonists reduces food intake and adiposity, and the central melanocortin system is demonstrated to mediate the anorexic effects of both leptin and insulin. An important unanswered question has been whether melanocortin agonists would also reduce food intake that is driven by factors other than homeostatic mechanisms (e.g., conditioned eating). In the first experiment, we identified that long-term maintenance on a meal-feeding schedule attenuated rats' sensitivity to central administration of the melanocortin agonist MTII. The results from a second experiment demonstrate that the attenuation of the MTII-induced anorexia was due to learned schedules of food intake rather than food deprivation per se. Results from the final experiment suggest that this attenuation of MTII-induced anorexia may be independent of the decreased sensitivity caused by a high-fat diet. These results support the hypothesis that meal-feeding schedules can lead to anticipatory physiological responses that attenuate the anorexic effects of exogenous melanocortin agonists.

Animals↗
PubMed2003

Adrenalectomy alters the sensitivity of the central nervous system melanocortin system.

Removal of adrenal steroids by adrenalectomy (ADX) reduces food intake and body weight in rodents and prevents excessive weight gain in many genetic and dietary models of obesity. Thus, glucocorticoids appear to play a key role to promote positive energy balance in normal and pathological conditions. By comparison, central nervous system melanocortin signaling provides critical inhibitory tone to regulate energy balance. The present experiments sought to test whether glucocorticoids influence energy balance by altering the sensitivity to melanocortin receptor ligands. Because melanocortin-producing neurons are hypothesized to be downstream of leptin in a key weight-reducing circuit, we tested rats for their sensitivity to leptin and confirmed reports that the hypophagic response to third ventricular (i3vt) leptin is increased in ADX rats and is normalized by glucocorticoid replacement. Next we tested rats for their sensitivity to the melanocortin agonist melanotan II and found that, as for leptin, ADX enhanced the hypophagic response via a glucocorticoid-dependent mechanism. The central nervous system melanocortin system is unique in that it includes the endogenous melanocortin receptor antagonist, AgRP. The orexigenic effect of i3vt AgRP was absent in ADX rats and restored by glucocorticoid replacement. We conclude that the potent weight-reducing effects of ADX likely involve heightened responsiveness to melanocortin receptor stimulation.

Adrenalectomy↗
PubMed2003

Insulin activation of phosphatidylinositol 3-kinase in the hypothalamic arcuate nucleus: a key mediator of insulin-induced anorexia.

In peripheral tissues, insulin signaling involves activation of the insulin receptor substrate (IRS)-phosphatidylinositol 3-kinase (PI3K) enzyme system. In the hypothalamus, insulin functions with leptin as an afferent adiposity signal important for the regulation of body fat stores and hepatic glucose metabolism. To test the hypothesis that hypothalamic insulin action involves intracellular PI3K signaling, we used histochemical and biochemical methods to determine the effect of insulin on hypothalamic IRS-PI3K activity. Here, we report that insulin induces tyrosine phosphorylation of the insulin receptor and IRS-1 and -2, increases binding of activated IRS-1 and -2 to the regulatory subunit of PI3K, and activates protein kinase B/Akt, a downstream target of PI3K. Using an immunohistochemical technique to detect PI 3,4,5-triphosphate, the main product of PI3K activity, we further demonstrate that in the arcuate nucleus, insulin-induced PI3K activity occurs preferentially within cells that contain IRS-2. Finally, we show that the food intake- lowering effects of insulin are reversed by intracerebroventricular infusion of either of two PI3K inhibitors at doses that have no independent feeding effects. These findings support the hypothesis that the IRS-PI3K pathway is a mediator of insulin action in the arcuate nucleus and, combined with recent evidence that leptin activates PI3K signaling in the hypothalamus, provide a plausible mechanism for neuronal cross-talk between insulin and leptin signaling.

Animals↗
PubMed2003

Is the energy homeostasis system inherently biased toward weight gain?

We describe a model of energy homeostasis to better understand neuronal pathways that control energy balance and their regulation by hormonal signals such as insulin and leptin. Catabolic neuronal pathways are those that both reduce food intake and increase energy expenditure (e.g., melanocortin neurons in the hypothalamic arcuate nucleus) and are stimulated by input from insulin and leptin. We propose that in the basal state, catabolic effectors are activated in response to physiological concentrations of leptin and insulin, and that this activation is essential to prevent excessive weight gain. In contrast, anabolic pathways (e.g., neurons containing neuropeptide Y) are those that stimulate food intake and decrease energy expenditure and are strongly inhibited by these same basal concentrations of insulin and leptin. In the basal state, therefore, catabolic effector pathways are activated while anabolic effector pathways are largely inhibited. The response to weight loss includes both activation of anabolic and inhibition of catabolic pathways and is, thus, inherently more vigorous than the response to weight gain (stimulation of already-activated catabolic pathways and inhibition of already-suppressed anabolic pathways). Teleological, molecular, physiological, and clinical aspects of this hypothesis are presented, along with a discussion of currently available supporting evidence.

Adipose Tissue↗