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  • American Physiological Society  (12)
  • 1995-1999  (12)
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  • American Physiological Society  (12)
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  • 1995-1999  (12)
Year
  • 1
    Online Resource
    Online Resource
    Potency of naloxone's anorectic effect in rats is dependent on diet preference
    American Physiological Society ; 1996
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 271, No. 1 ( 1996-07-01), p. R217-R221
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 271, No. 1 ( 1996-07-01), p. R217-R221
    Abstract: Modulation of feeding behavior by neuropeptide Y (NPY) and opioids is well established, but the possibility that these neural influences provoke specific appetites, NPY for carbohydrate and opioids for fat, has also been considered. In other studies, intake of standard chow after NPY stimulation can be blocked by naloxone, indicating an interaction between these systems in the regulation of feeding. The present experiments examined the nature of NPY-opioid interactions in diet selection. Rats were administered NPY and naloxone concurrently, then chose between high-fat and high-carbohydrate diets. Subcutaneous administration of naloxone (0.01-0.3 mg/kg) potently reduced intake of the preferred diet, but not the nonpreferred diet. A similar pattern of selection was seen in a separate experiment where the same doses of naloxone were administered after 24-h food deprivation. These data support the idea that the opioid system mediates the “rewarding” aspects of feeding.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1996.271.1.R217
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1996
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 2
    Online Resource
    Online Resource
    Cold-induced alterations in uncoupling protein and its mRNA are seasonally dependent in ground squirrels
    American Physiological Society ; 1995
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 269, No. 2 ( 1995-08-01), p. R357-R364
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 269, No. 2 ( 1995-08-01), p. R357-R364
    Abstract: We were interested in determining whether season affects the ability of cold exposure to increase brown adipose tissue (BAT) thermogenic function in 13-lined ground squirrels after acute and chronic cold (4 degrees C) exposure. Tissues were collected from animals in April and September after cold exposure for 12, 24, or 48 h. Animals chronically exposed to the cold (10 days) were killed in early May and mid-August. We found that mitochondrial uncoupling protein (UCP) concentrations varied seasonally, with concentrations in control animals (at 23 degrees C) higher in late summer (mid-August and September) than in the spring (April and early May). Cold exposure in late summer did not induce further increases in UCP concentrations. In contrast, when animals were cold exposed in the spring, UCP concentrations and total UCP increased. Surprisingly, 10 days at 4 degrees C did not cause a greater increase in UCP concentrations than did 24 h at 4 degrees C. Chronic cold exposure increased the UCP mRNA-to-beta-actin mRNA ratio 48% in May, whereas a fivefold increase occurred in August. GDP binding was increased after 12 h at 4 degrees C in April; in contrast, animals attempted to hibernate when placed in the cold in September, and no increase in GDP binding was observed. Chronic cold exposure caused GDP binding to increase at both times. These results indicate that mitochondrial UCP concentrations are seasonally regulated in the 13-lined ground squirrel.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1995.269.2.R357
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1995
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 3
    Online Resource
    Online Resource
    Role of lipid type on morphine-stimulated diet selection in rats
    American Physiological Society ; 1999
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 277, No. 5 ( 1999-11-01), p. R1345-R1350
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 277, No. 5 ( 1999-11-01), p. R1345-R1350
    Abstract: Administration of morphine is said to increase fat consumption among rats allowed to self-select nutrients. However, fats represent a diverse group of molecules, differing in metabolic and sensory properties. Despite this, lipid has yet to be manipulated as a variable in drug-stimulated nutrient selection studies. To determine whether lipid source can impact daily and morphine-stimulated (1, 3, and 10 mg/kg) diet intake, rats were provided with a choice between a high-fat and high-carbohydrate diet in three regimens in which the source of fat was varied between vegetable shortening, lard, or corn oil. Daily and morphine-stimulated diet selections were determined under all conditions. Under daily feeding conditions, rats ate more of the high-lipid diet compared with the high-carbohydrate diet when vegetable shortening or lard was the main lipid alternative, but lipid and carbohydrate intake did not differ when corn oil was the main lipid alternative. When rats were stimulated with morphine, the percentage of lipid increased relative to baseline intake only when the lipid diets were the preferred alternatives (i.e., vegetable shortening or lard). When preference between lipid and carbohydrate diets was neutral (i.e., corn oil condition), morphine did not enhance lipid consumption. These results indicate that morphine increases consumption of total energy or preferred diets and not lipid per se.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1999.277.5.R1345
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1999
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 4
    Online Resource
    Online Resource
    Effect of naloxone on intake of cornstarch, sucrose, and polycose diets in restricted and nonrestricted rats
    American Physiological Society ; 1996
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 270, No. 6 ( 1996-06-01), p. R1183-R1188
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 270, No. 6 ( 1996-06-01), p. R1183-R1188
    Abstract: We studied the effect of the opioid receptor antagonist naloxone on intake of three isocaloric diets containing cornstarch, sucrose, or Polycose as the predominant carbohydrate in ad libitum-fed and food-restricted rats. A large body of evidence suggests that opioids affect palatability (reward)-rater than hunger (energy deficit)-driven food intake. We expected food intake to be driven by both energy needs and palatability in ad libitum-fed rats, whereas in food-restricted rats we expected intake to be driven by energy needs with a relatively small palatability component in the preferred sucrose and Polycose diet groups. In the ad libitum-fed rats, naloxone significantly reduced nocturnal intake of all three diets at doses of 0.3, 1.0, and 3.0 mg/kg. In contrast, naloxone failed to alter intake of the cornstarch diet in chronically food-restricted rats. However, naloxone decreased intake of the sucrose diet in food-restricted rats at doses of 0.3, 1.0, and 3.0 mg/kg and decreased intake of the Polycose diet at the 3 mg/kg dose. These data lend further support to the notion that opioids are involved in some other component of feeding than that induced by energy needs.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1996.270.6.R1183
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1996
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 5
    Online Resource
    Online Resource
    Role of carbohydrate type on diet selection in neuropeptide Y-stimulated rats
    American Physiological Society ; 1997
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 273, No. 6 ( 1997-12-01), p. R2040-R2045
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 273, No. 6 ( 1997-12-01), p. R2040-R2045
    Abstract: We tested whether carbohydrate source (corn starch, sucrose, Polycose) influences the choice between a high-fat and high-carbohydrate diet in spontaneously feeding rats and in rats stimulated to eat by neuropeptide Y (NPY) administration or food deprivation. Rats were tested under three diet options: 1) a high-fat diet versus a high-corn starch diet; 2) a high-fat diet versus a high-sucrose diet; and 3) a high-fat diet versus a high-Polycose diet. During daily and stimulated feeding rats ate more of the high-carbohydrate diet than the fat diet when the source of carbohydrate was sucrose or Polycose; however, when corn starch was provided as the carbohydrate source rats ate more of the high-fat diet. Food-deprived rats increased intake of both the high-fat and the high-carbohydrate diets, with the proportion of energy ingested from each of the diets resembling that noted during 3 days of spontaneous feeding. NPY-injected rats ate more of both the high-fat and high-carbohydrate diets during diet options 1 and 3, but not during option 2 when the high-sucrose and high-fat diets were offered concurrently. In that case, rats did not significantly increase their intake of the high-fat diet. Although carbohydrate source and NPY administration each influenced diet selection, altering the source of carbohydrate had a more marked effect.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1997.273.6.R2040
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1997
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 6
    Online Resource
    Online Resource
    Naloxone blocks that portion of feeding driven by sweet taste in food-restricted rats
    American Physiological Society ; 1995
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 268, No. 1 ( 1995-01-01), p. R248-R252
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 268, No. 1 ( 1995-01-01), p. R248-R252
    Abstract: We evaluated the potency of naloxone on intake of normal and sweet chow in food-deprived and schedule-fed rats. We found that naloxone's anorectic potency was dependent on the type of chow presented to the rats and the deprivation schedule utilized to stimulate food intake. In 24-h and 48-h deprived rats, naloxone decreased intake of normal rat chow at doses ranging from 0.3 to 3 mg/kg. In chronically deprived rats (80% of normal body wt), these doses of naloxone failed to decrease intake of normal chow. Rats eating sweet chow ate more when energy deprived and were more sensitive than rats eating normal chow to naloxone-induced limitations in food intake, both in acute and chronic food-deprived groups. Thus naloxone decreased intake of sweet chow much more effectively than normal chow even when rats were chronically food deprived. We also found that an extremely low dose of naloxone (0.03 mg/kg) decreased intake of sweet chow by almost 50% in satiated rats.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1995.268.1.R248
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1995
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 7
    Online Resource
    Online Resource
    Naltrexone induces arcuate nucleus neuropeptide Y gene expression in the rat
    American Physiological Society ; 1996
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 271, No. 1 ( 1996-07-01), p. R289-R294
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 271, No. 1 ( 1996-07-01), p. R289-R294
    Abstract: Neuropeptide Y (NPY) has potent effects on several components of energy metabolism, including increased feeding and decreased brown fat thermogenesis. Negative energy balance, such as food deprivation, increases NPY mRNA in hypothalamic arcuate nucleus (ARC). Naltrexone (NLTX), an opioid receptor antagonist, decreases NPY-induced feeding. We hypothesized that NLTX would alter ARC NPY mRNA and change NPY effects on brown fat. Osmotic minipumps prefilled with either saline or NLTX (70 micrograms/h) were implanted subcutaneously in 32 male Sprague-Dawley rats. One-half of the rats were food deprived and one-half were allowed food ad libitum for 48 h. Food intake was measured at 24 and 48 h. At 48 h, ARC NPY mRNA and brown fat uncoupling protein (UCP) mRNA levels were determined using cDNA probes. Forty-eight-hour food intake was significantly decreased by 24% after NLTX infusion. Food deprivation and NLTX treatment significantly and independently increased ARC NPY mRNA and decreased UCP mRNA levels in brown fat, suggesting a complex interaction between hypothalamic NPY and endogenous opioids in the regulation of energy balance.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1996.271.1.R289
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1996
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 8
    Online Resource
    Online Resource
    Opioids in the nucleus of the solitary tract are involved in feeding in the rat
    American Physiological Society ; 1997
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 272, No. 4 ( 1997-04-01), p. R1028-R1032
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 272, No. 4 ( 1997-04-01), p. R1028-R1032
    Abstract: We evaluated the effect of selective opioid peptides and naltrexone on feeding when injected into the nucleus of the solitary tract (NTS). Doses of 0, 1, 2, 4, and 8 nmol of [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO, mu-agonist), dynorphin A-(1-17) (DynA-(1-17), kappa-agonist), and [D-Ser2] leucine enkephalin-thr, (delta-agonist) were injected into the NTS in satiated male rats, and food intake was measured at 1, 2, and 4 h. Only DAMGO significantly increased feeding above control levels at doses of 2, 4, and 8 nmol. Doses of 10 and 50 microg naltrexone in the NTS significantly decreased 18-h deprivation-induced feeding. These data suggest that NTS opioid receptors (primarily mu) may be involved in the regulation of feeding.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1997.272.4.R1028
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1997
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 9
    Online Resource
    Online Resource
    Neural site of leptin influence on neuropeptide Y signaling pathways altering feeding and uncoupling protein
    American Physiological Society ; 1998
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 275, No. 2 ( 1998-08-01), p. R478-R484
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 275, No. 2 ( 1998-08-01), p. R478-R484
    Abstract: Inhibition of a signal that produces positive energy balance involving neuropeptide Y (NPY) projection from arcuate nucleus (Arc; site of NPY synthesis) to paraventricular nucleus (PVN; site of NPY release) is one potential mechanism of leptin action. NPY in the PVN increases feeding and decreases uncoupling protein (UCP) activity in brown fat, whereas leptin decreases NPY biosynthesis in the Arc, which presumably decreases PVN NPY. It is hypothesized that decreased NPY activity is necessary for the satiety and thermogenic effects of leptin. To test this, we first determined the effect of leptin on feeding in two paradigms: satiated rats and food-deprived rats. Leptin was effective in decreasing feeding in the satiated rats but ineffective in the food-deprived rats. Next, we determined that leptin decreases NPY and increases UCP gene expression. Finally, we injected leptin intracerebroventricularly before specific PVN NPY microinjection. We found that repletion of NPY in PVN by specific NPY microinjection reverses the feeding-inhibitory and thermogenic effects of centrally administered leptin, the first functional evidence indicating that leptin acts on the Arc-PVN feeding-regulatory pathway.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1998.275.2.R478
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1998
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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  • 10
    Online Resource
    Online Resource
    STZ-induced diabetes decreases and insulin normalizes POMC mRNA in arcuate nucleus and pituitary in rats
    American Physiological Society ; 1999
    In:  American Journal of Physiology-Regulatory, Integrative and Comparative Physiology Vol. 276, No. 5 ( 1999-05-01), p. R1320-R1326
    Details
    In: American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, American Physiological Society, Vol. 276, No. 5 ( 1999-05-01), p. R1320-R1326
    Abstract: Effects of streptozotocin (STZ)-induced diabetes and insulin on opioid peptide gene expression were examined in rats. In experiment 1, three groups were administered STZ (75 mg/kg ip single injection). Two groups were killed at either 2 or 4 wk. In the third group, insulin treatment (7.0 IU/kg × 1 day for 3 wk) was initiated 1 wk after STZ injection. STZ induced hyperphagia and reduced weight gain. Insulin decreased food intake and increased body weight relative to diabetes. Proopiomelanocortin (POMC) mRNA in arcuate nucleus (Arc) and pituitary decreased in diabetes and normalized after insulin treatment. Prodynorphin (proDyn) mRNA increased in diabetes and normalized in the pituitary after insulin but not in the Arc. Diabetes did not alter proenkephalin (proEnk) expression in the Arc or pituitary, nor dynorphin A 1–17 or β-endorphin in paraventricular nucleus (PVN). α-Melanocyte-stimulating hormone (α-MSH) peptide levels were decreased in the PVN and normalized following insulin treatment. Diabetes increased Arc neuropeptide Y mRNA, and insulin suppressed this increase. In experiment 2, insulin (2.5 IU/kg sc) daily for 1 wk in normal rats increased Arc POMC mRNA, but not proDyn and proEnk mRNA. These results suggest that Arc POMC expression and PVN α-MSH peptide levels decrease in diabetes. Also, insulin may influence Arc and pituitary POMC activity in neurons that regulate energy metabolism.
    Type of Medium: Online Resource
    ISSN: 0363-6119 , 1522-1490
    URL: Article
    DOI: 10.1152/ajpregu.1999.276.5.R1320
    Language: English
    Publisher: American Physiological Society
    Publication Date: 1999
    detail.hit.zdb_id: 1477297-8
    SSG: 12
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