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Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine (S.B., K.A.S., T.H.M.), Baltimore, Maryland 21205; and Molecular Pharmacology Research Center, Department of Medicine, Tufts-New England Medical Center (A.S.K.), Boston, Massachusetts 02111
Address all correspondence and requests for reprints to: Dr. S. Bi, Department of Psychiatry and Behavioral Sciences, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Ross 618, Baltimore, Maryland 21205. E-mail: sbi{at}jhmi.edu.
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Although the satiety actions of peripheral CCK are well characterized, a role for brain CCK in the control of food intake has been controversial. Initial work reported that continuous picomole infusions of CCK into the cerebral ventricles of sheep suppressed feeding (12), but results in rodent models have been mixed. Although some studies have identified feeding inhibitory actions of central ventricular CCK administration, issues of dosage and access to peripheral sites have been raised (13, 14). Recently, Blevins et al. demonstrated that infusing smaller doses of CCK-8 into specific brain sites resulted in site-specific feeding inhibitory actions in the rat (15), and this anorexic dose of CCK-8 did not increase plasma CCK-8 levels sufficiently to suppress feeding by a peripheral mechanism (16).
Recent data from Otsuka Long-Evans Tokushima fatty (OLETF) rats (17), which have a 6.8-kb deletion of the CCK-AR gene resulting in the absence of CCK-AR (18), have suggested both peripheral and central roles for CCK acting through CCK-AR in the control of food intake (19). OLETF rats have a peripheral CCK satiety deficit. These rats have no feeding response to peripherally exogenous CCK administration (20). Consistent with the lack of an intact peripheral CCK satiety signaling, food intake in OLETF rats is characterized by significant and chronic increases in meal sizes. In response to this increase, meal number is decreased, but the decrease is not compensatory, and as a result, OLETF rats are hyperphagic (20). Although the increase in meal size in OLETF rats is consistent with the absence of peripheral CCK signaling, the overall hyperphagia and obesity were surprising. Pair-feeding OLETF rats to the intake of Long-Evans Tokushima Otsuka (LETO) control rats completely prevents their obesity, demonstrating that the increased body weight is secondary to the hyperphagia and does not depend on metabolic alterations. Pair-feeding not only prevented the increased body weight, but also normalized the elevated levels of leptin and insulin and the alterations in arcuate nucleus neuropeptide Y (NPY) and proopiomelanocortin (POMC) gene expression in OLETF rats (21). Pair-feeding also revealed what seems to be a primary deficit in dorsomedial hypothalamic (DMH) NPY mRNA expression in OLETF rats. DMH NPY mRNA expression was significantly elevated in pair-fed, normal weight OLETF rats, and this elevation was also found in 5-wk-old preobese OLETF rats (21). We have suggested that this dysregulation of DMH NPY gene expression may, in combination with the peripheral satiety deficit, contribute to the hyperphagia and obesity in OLETF rats (21).
CCK-AR knockout mice demonstrate a different phenotype from that of OLETF rats. In contrast to the OLETF rat, CCK-AR knockout mice have normal total daily food intake and maintain normal body weight well into adult life (22). Although these mice were insensitive to the feeding inhibitory action of peripheral exogenous CCK, this deficit did not appear to affect their overall food intake. These data were interpreted to suggest that CCK was not essential for controlling overall food intake nor was it involved in the long-term maintenance of body weight (22).
To investigate the basis underlying the different phenotypes in rats and mice lacking CCK-AR, we have characterized meal patterns in CCK-AR–/– mice and determined whether CCK-AR–/– mice demonstrated alterations in DMH NPY gene expression. The findings from these studies led us to compare the distribution of CCK-AR in mouse and rat brains and to determine the relationship between NPY and CCK-AR in rat DMH neurons. The data demonstrate that the distribution of CCK-AR differs in mice and rats, and this may account for the difference in phenotype between rats and mice lacking CCK-AR.
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Materials and Methods |
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In situ hybridization in mouse brain
Five-week-old male CCK-AR+/+ and CCK-AR–/– mice were decapitated, and brains were removed rapidly and frozen. Coronal sections (14 µm) were cut via a cryostat, mounted on SuperFrost Plus slides (Fisher Scientific, Fairlawn, NJ), and fixed with 4% paraformaldehyde. The full length of rat CCK-AR cDNA (24) was synthesized by RT-PCR, subcloned into pcDNA1 vector, and linearized by an appropriate restriction enzyme. The antisense or sense riboprobe of CCK-AR was labeled with [35S]UTP (Amersham Pharmacia Biotech, Piscataway, NJ) using in vitro transcription systems (Promega Corp., Madison, WI). As previously described (25), the 35S-labeled antisense riboprobe of NPY was transcribed from rat NPY precursor cDNA (26). Standard in situ hybridization was conducted. Brian sections over the paraventricular nucleus (PVN) and DMH regions (0.58–2.06 mm caudal to bregma) (27) were selected for examining CCK-AR mRNA expression. As well, brain sections over the DMH region (1.70–2.06 mm caudal to bregma) (27) were selected for examining NPY mRNA expression. Sections were treated with acetic anhydride and incubated in the standard hybridization buffer containing 108 cpm/ml 35S-labeled probe overnight. The incubation temperature was set at 55 C for NPY and 58 C for CCK-AR probe. After the hybridization, the sections were washed three times with 2x standard saline citrate (SSC), treated with 20 µg/ml ribonuclease A (Sigma-Aldrich Corp., St. Louis, MO) at 37 C for 30 min, rinsed in 2x SSC twice at 55 C for NPY or 58 C for CCK-AR, and finally washed twice in 0.1x SSC at 55 C for NPY or 58 C for CCK-AR for 15 min each time. Slides were dehydrated in gradient ethanol, air-dried, and exposed on BMR-2 film (Eastman Kodak Co., Rochester, NY) for 1–5 d. After autoradiography, slides were examined histologically by cresyl violet staining.
CCK binding assay in the wild-type mouse
The autoradiographic CCK binding assay was conducted as previously described (28). Adult male wild-type littermates of the CCK-AR–/– mice were killed by decapitation, and brains were removed and rapidly frozen in isopentane at –70 C. Coronal sections (20 µm) over the PVN (0.58–1.22 mm caudal to bregma) and DMH regions (1.46–2.06 mm caudal to bregma) were cut via a cryostat and mounted on cold gelatin-coated slides (27). To differentiate between CCK-AR and CCK-BR, we compared the ability of the CCK-AR antagonist devazepide and the CCK-BR agonist desulfated CCK-8 (dCCK) to displace the binding site of 125I-labeled CCK-8. If the binding was inhibited by devazepide, but not by dCCK, the binding was occurring to CCK-AR. In contrast, if the binding was inhibited by dCCK, but not by devazepide, the binding was occurring to CCK-BR. Thus, after preincubation in 50 mM Tris-HCl buffer (pH 7.4) containing 0.5% BSA for 20 min at 24 C, slides were incubated in the standard binding buffer containing 50 pM [125I]Bolton-Hunter-labeled CCK-8 (PerkinElmer, Boston, MA) for 2 h at 24 C, either alone or in the presence of 10 nM devazepide, 100 nM dCCK, or 100 µM sulfated CCK-8. After the incubation, slides were washed in ice-cold 50 mM Tris-HCl buffer (pH 7.4) containing 0.5% BSA six times for 10 min each time. Washed slides were completely air-dried and exposed on BMR-2 film (Eastman Kodak Co.) for 5–7 d.
Dual immunohistochemistry in the rat
Coronal sections (14 µm) from the brains of LETO and OLETF rats (obtained from Otsuka Pharmaceuticals, Otsuka, Japan) were prepared as described above and fixed with 4% paraformaldehyde. Dual immunohistochemistry was modified from the procedure previously described (29). Sections were incubated with the primary antibody mixtures containing 1:1000 mouse anti-NPY monoclonal antibody (a gift from Dr. Eric Grouzmann, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland) (30) and 1:2000 rabbit antirat CCK-AR antibody (the targeted amino acid sequence SHMSTSAPPP corresponding to the C-terminal of the rat CCK-AR, Accurate Chemical & Scientific Corp., Westbury, NY) at 4 C overnight. After three washes, secondary antibodies were added to the slides: goat antimouse conjugated to fluorescein (1 ng/µl; Roche, Indianapolis, IN) for detecting NPY peptide, and biotin-labeled goat antirabbit IgG (1:250; NEN Life Science Products, Inc., Boston, MA) for detecting CCK-AR. CCK-AR signal was further amplified by a TSA (tyramide signal amplification) Biotin System (NEN Life Science Products, Inc.) and stained with streptavidin-Texas Red conjugate (1:500; NEN Life Science Products, Inc.) according to the manufacturer’s protocol. Sections were examined on an LSM 410 confocal microscope (Zeiss, New York, NY) using the 488-nm laser to excite fluorescein and the 543-nm laser to excite Texas Red.
DMH cannulation and CCK-8 injection in the rat
Fifteen male Long-Evans rats (Charles River Laboratories, Wilmington, MA), weighing 275–300 g were implanted with chronic indwelling DMH cannulas. Animals were individually housed in hanging wire mesh cages maintained on a 12-h light, 12-h dark cycle with a feeding schedule in which regular chow food was removed from the cages 2 h before lights off and returned to the cages just before dark onset. Water was always available. At the time of surgery, the rats were anesthetized with an im mixture of ketamine (100 mg/kg) and xylazine (20 mg/kg) and placed in a stereotaxic device. A 26-gauge, stainless steel guide cannula (Plastic One, Wallingford, CT) was implanted into the DMH with the following coordinates: 3.3 mm caudal to bregma, 0.3 mm lateral to midline, and 8.1 mm ventral to skull surface (15, 31). These coordinates were chosen based on results with pilot experiments. A 33-gauge stainless steel obturator was inserted into the cannula to maintain patency. After surgery, rats were given penicillin (60,000 U, im) to prevent postoperative infection and banamine (1 mg/kg, im) for pain relief.
After 7 d of postoperative recovery, 15 cannulated rats were randomly divided into two groups. Just before lights off, one group of eight animals was injected with 0.3 µl artificial cerebrospinal fluid (aCSF; 147 mM Na+, 2.7 mM K+, 1.2 mM Ca2+, 0.85 mM Mg2+, and 153.8 mM Cl–), and the other group of seven animals was injected with 500 pmol CCK-8 (Bachem, Torrance, CA) in 0.3 µl aCSF. All DMH injections were made with a Gilmont’s micrometer syringe attached to polyethylene tubing and a 33-gauge stainless-steel injector (Plastic One). The tip of the injector extended 1.0 mm past the tip of the guide cannula. Injections were made over 10 s, and the injection remained in place for an additional 20 s before removal. Chow food was returned immediately after the injection. Food intakes were measured at 30 min, 1 h, 2 h, 4 h, and 22 h after returning food to the cages. After a 7-d period of recovery, all rats were given second DMH injections with aCSF or CCK-8 (500 pmol) treatment, i.e. the rat that had previously received CCK-8 administration was given an aCSF injection at this time and vice versa. Food intake was measured as described for the first injections. Thus, each rat received aCSF and CCK-8 administration and served as its own control for comparison of the CCK-8 feeding effect.
After feeding tests, 15 of these animals and 10 additional DMH-cannulated rats were body weight-matched and randomly divided into two groups, aCSF control (n = 12) and CCK-8 treatment (n = 13), for assessing whether CCK-8 injection into the DMH affected hypothalamic NPY mRNA expression. Animals were maintained on the same feeding schedule as described above, in which regular chow was removed from the cages 2 h before lights off and was returned to the cages just before dark onset, with access to water ad libitum. Again, rats received either aCSF or CCK-8 injections as described above, but without access to chow food after injections. Two hours after injections, rats were killed with an overdose of sodium pentobarbital, and brains were removed rapidly and frozen for subsequent analyses of hypothalamic NPY gene expression (25, 32, 33).
As described above, a series of 14-µm coronal brain sections ranging from 2.6–3.6 mm caudal to bregma were cut (31) and mounted on slides as a series of six (section 1, slide 1; section 2, slide 2; etc.; section 7, slide 1, etc.) and fixed with 4% paraformaldehyde. The site of the DMH injection in rats was anatomically examined via cresyl violet staining after the process of brain sections. Data from rats with incorrect cannula placements were excluded from subsequent statistical analyses.
The in situ hybridization determination of hypothalamic NPY mRNA expression was conducted as described above. Quantitative analysis of the in situ hybridization data was performed with NIH Scion Image software (NIH, Bethesda, MD). Autoradiographic images were first scanned using an EPSON Professional Scanner (EPSON, Long Beach, CA) and saved via computer for subsequent analyses with Scion image software using autoradiographic 14C microscales (Amersham Pharmacia Biotech) as a standard. Data for each animal were the mean of the product of hybridization area x density (background density was subtracted) obtained from four sections reflecting the level of gene expression in the region 3.2–3.4 mm posterior to bregma (for example, one section in 3.2 mm, one in 3.284 mm, one in 3.368, and one in 3.452 mm posterior to bregma) (31). Data from each group were normalized to aCSF-treated controls as 100%, and all data are presented as the mean ± SEM.
For statistical analysis, data were analyzed by t test for two groups of comparison. P < 0.05 was taken to be a statistically significant difference.
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Results |
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, CCK-AR–/– mice had slightly, but not significantly, increased total daily food intake compared with wild-type control mice. However, both the diurnal pattern of intake and the meal patterns were altered in CCK-AR–/– mice. Although both CCK-AR–/– and CCK-AR+/+ mice consumed the majority of their food intake in the dark period (83.1% of total intake in knockout and 75.8% in wild-type mice, respectively), CCK-AR–/– mice had significantly elevated food intake during the dark period (P < 0.05) and tended to decrease their food intake during the light period (P > 0.05) compared with wild-type mice. Meal pattern analysis revealed that CCK-AR–/– mice had a significant increase in overall average meal size compared with wild-type mice (Table 1). CCK-AR–/– mice consumed 35.3% more food per meal than wild-type mice. This alteration in meal patterns mainly occurred during the dark period, when the majority of food was consumed. Meal sizes were not elevated during the light period. Although meal frequency did not differ significantly between the two groups, CCK-AR–/– mice appeared to have slightly decreased meal numbers in the total daily and light periods compared with wild-type mice. Thus, similar to OLETF rats, the absence of CCK-AR in mice resulted in a dysregulation of the control of meal size. However, in contrast to OLETF rats, CCK-AR–/– mice were able to maintain their normal daily food intake. Whether this difference is due to the smaller magnitude of the meal size increase in CCK-AR–/– mice than that in OLETF rats (35% vs. 80%) (20) or has another explanation was addressed in the next series of experiments.
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, NPY mRNA expression was only evident in the arcuate nucleus in both CCK-AR–/– and CCK-AR+/+ mice. DMH NPY mRNA expression was not detectable in either CCK-AR–/– or CCK-AR+/+ mice at 5 wk of age (Fig. 1), when OLETF rats had elevated DMH NPY gene expression.
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, A–C), CCK-BR binding sites were found in the ventromedial hypothalamus (Fig. 2, E–G), but no CCK binding activity was detected in the DMH (Fig. 2, E–G). Consistent with these binding data, in situ hybridization histochemistry revealed that CCK-AR mRNA was highly expressed in the PVN (Fig. 3A), but was not expressed in the DMH in mice (Fig. 3B). There was some evidence of CCK-AR mRNA expression in the arcuate nucleus (Fig. 3B), although there was no CCK binding activity detected there (Fig. 2, E–G). Thus, neither CCK binding assay nor CCK-AR mRNA expression determination detected the presence of CCK-AR in the DMH of the mouse.
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, both LETO and OLETF DMH contained NPY immunostaining neurons (Fig. 4, A and D, green). CCK-AR immunostaining neurons were only detected in the DMH in LETO controls (Fig. 4B, red). The absence of CCK-AR immunoreactivity in OLETF rats (Fig. 4E), is consistent with the absence of CCK-AR in this model. Confocal microscopic analysis revealed that NPY and CCK-AR were colocalized in DMH neurons (Fig. 4, C and G, orange). As shown in high magnification in Fig. 4G, CCK-AR staining was found on the surface of NPY neurons.
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, NPY mRNA expression was significantly down-regulated by the parenchymal injection of CCK into the DMH. Exogenous CCK administration resulted in a 27% reduction of NPY mRNA expression in the ipsilateral compact subregion of the DMH (Fig. 5). We also found that, relative to controls, arcuate NPY mRNA expression was significantly reduced by 24% in CCK-injected rats (Fig. 5). These data confirm that CCK within the DMH is capable of directly regulating NPY gene expression.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The actions of peripheral CCK in the control of meal size are well characterized. Peripheral CCK produces dose-related suppression of meal size and results in the earlier appearance of a behavioral satiety sequence (11). These actions of the exogenous peptide appear to mimic a physiological role of endogenous CCK, because administration of CCK antagonists results in an increase in food intake. The feeding inhibitory actions of both exogenously administered and endogenously released CCK depend upon actions at the CCK-AR. CCK-mediated inhibition of food intake is blocked by CCK-AR antagonists, but is unaffected by CCK-BR antagonists (7). The current finding of increased meal size in CCK-AR–/– mice demonstrates an action of endogenous CCK in the control of meal size in mice that is consistent with prior data on antagonists and our previous findings in the OLETF rat that also lacks CCK-AR (10, 11, 20). Thus, these data provide additional molecular biological support for a physiological role for endogenous CCK in the short-term control of food intake. The magnitude of the change in meal size in CCK-AR–/– mice was quite a bit smaller than the 80% increase found in OLETF rats lacking CCK-AR. This difference may reflect a relative difference in the contribution of CCK to meal termination between rats and mice.
The current data demonstrate that CCK-AR–/– mice have altered diurnal feeding patterns. In OLETF rats lacking CCK-AR, increased food intake was characterized by increased meal size in both the dark and light periods. In response to their increased meal size, meal number was decreased in the dark period, but this decrease was not compensatory (20). However, analyses of feeding patterns in CCK-AR–/– mice revealed increased food intake in the dark period, characterized by an increase in meal size, and food intake tended to be decreased in the light period, characterized by a reduction in meal frequency, leading to the absence of significant changes in total food intake. These data suggest that CCK acting through CCK-AR plays a differential role in circadian activities between rats and mice.
Even though both rats and mice lacking CCK-AR have peripheral CCK satiety deficits, resulting in increased meal size, total daily food intake and body weight were normal in the CCK-AR–/– mice, whereas OLETF rats lacking CCK-AR have been shown to be hyperphagic and to become obese. Although this may reflect a differential ability to compensate for smaller rather than larger increases in meal size, the present data also suggest that this difference in phenotype may be the outcome of a different distribution of brain CCK-AR between rats and mice. The potential importance of this differential distribution derives from the findings that in intact rats, NPY and CCK-AR are colocalized in DMH neurons, and CCK plays a role in modulating DMH NPY; exogenous administration of CCK into the DMH down-regulates DMH NPY mRNA expression. These results are consistent our previous findings demonstrating that NPY gene expression is up-regulated in the DMH in OLETF rats that lack CCK-AR (21). Although pair-feeding OLETF rats prevented their increased body weight and normalized their altered arcuate NPY and POMC gene expression, pair-feeding resulted in significantly elevated NPY gene expression in the DMH. This elevation of NPY mRNA expression in the DMH was also documented in young preobese OLETF rats (21). Therefore, CCK acting through CCK-ARs in the DMH appears to suppress DMH NPY gene expression in the rat. Such a suppression inhibits energy intake, in that DMH CCK injection reduces food intake. The hyperphagic and obese OLETF rat has a deficit in this CCK-NPY signaling pathway resulting from the lack of CCK-AR production. CCK acting through CCK-AR does not appear to play a role in controlling DMH NPY in the mouse.
We failed to detect any NPY mRNA expression in the DMH in either CCK-AR–/– or CCK-AR+/+ mice by in situ hybridization determination. DMH NPY mRNA expression in ad libitum-fed rats is normally low and is only elevated in a few experimental situations, such as lactation (36) or in response to chronic food restriction (25). In the rat there are clear differences in the controls of DMH and arcuate nucleus NPY-expressing neurons. In the arcuate nucleus, NPY-containing neurons express Ob-RB, the long form of leptin receptors, and NPY expression is under leptin control (37). Elevated leptin levels reduce NPY mRNA expression, whereas food deprivation increases arcuate NPY gene expression. In contrast, DMH NPY-containing neurons do not express leptin receptors, and DMH NPY mRNA expression does not increase in response to acute food deprivation (25). Moreover, within the DMH, the region of altered NPY expression in response to a variety of treatments appears to differ. The current data demonstrating that the reduction of DMH NPY expression by CCK is localized to the compact subregion are consistent with our previous findings (21, 25). Whereas in lactating rats, Smith (36) had reported that although there was a very slight increase in NPY mRNA expression in the compact area, DMH NPY mRNA expression was mainly induced in the diffuse portion of the DMH. However, it is not yet clear whether NPY mRNA expression in different subregions of the DMH is differentially regulated. Controls of DMH NPY expression in the mouse have not been extensively investigated. Evidence that there are NPY-expressing neurons in the mouse comes from data demonstrating the induction of DMH NPY expression in several obesity models of disrupted melanocortin signaling: lethal agouti yellow (Ay), melanocortin 4 receptor knockout (MC4R–/–) mice (38), and diet-induced obese mice (39). Such data suggest interactions between melanocortin signaling and metabolic status in the control of DMH NPY functions in the mouse.
The finding of decreased arcuate as well as DMH NPY mRNA expression in response to DMH CCK injection was surprising. Consistent with previous studies in the rat (28, 34), we failed to identify any CCK-AR binding activity in the arcuate nucleus of the mouse. This absence of arcuate CCK receptors implies a DMH/arcuate interaction in the controls of arcuate NPY. Although the main hypothalamic output of the DMH is thought to be the PVN, projections from the DMH to the arcuate nucleus have been identified (40). These projections may be the basis for the arcuate NPY reduction in response to DMH CCK injection.
A role for the DMH in feeding control has long been suggested. Bellinger and colleagues (41) demonstrated that small DMH electrolytic or excitotoxic lesions (DMHL) result in hypophagia, hypodipsia, reduced body weight, and reduced linear growth in the rat. Pair-feeding experiments, in which one group of sham-operated rats was pair-fed by a computerized feeding system that presented food pellets in the same amount and pattern as their "yoked" DMHL rats, demonstrated that the altered body weight in DMHL rats was primarily a result of altered food intake (42). Despite findings such as these, the particular contribution of the DMH and how it interacts with other hypothalamic nuclei involved in energy balance has not been well understood. Our findings in the rat suggest that the basis of the DMHL-induced hypophagia may be the elimination of an NPY-ergic output, an output normally under the control of CCK acting through CCK-AR. Although the distribution and mediation of CCK-AR in human brain are unclear, data from other primates have demonstrated that the DMH contains CCK-AR binding site in the monkey (43), and central injection of the CCK-AR, but not the B receptor, agonist inhibits food intake in the baboon (44). Such findings as these suggest that the DMH CCK-AR may play a role in food intake control in humans. A polymorphism of the CCK-AR gene in patients with obesity and diabetes has been reported in various studies (45, 46, 47, 48), providing support for such a role.
We have interpreted the current data to support the view that the different phenotypes of OLETF rats and CCK–/– mice derive from a differential role for central CCK-AR in energy balance in rats and mice. OLETF rats are not a targeted deletion of CCK-AR, but arose a spontaneous mutation. It is quite possible that there are other genetic alterations in the OLETF rat that alone or in combination with the alterations in CCK-AR signaling account for the hyperphagia, obesity, or diabetes (49). However, such additional genetic defects are yet to be identified.
In summary, the present results suggest that although both rats and mice lacking CCK-AR demonstrate a deficit in meal size control, the differential distribution of CCK-AR in rat and mouse brains may determine the divergent effects of CCK-AR gene disruption. In the rat brain, CCK acting through CCK-AR appears to play a role in regulating DMH NPY gene expression. DMH CCK inhibits NPY mRNA expression and food intake. In the absence of CCK-AR, OLETF rats have a deficit in the control of DMH NPY gene expression, resulting in increased DMH NPY gene expression, increased food intake, and, eventually, obesity. In contrast, we found no evidence for the presence of CCK-AR in the DMH of the mouse. Thus, CCK-AR does not contribute to the control of DMH NPY gene expression, and in the absence of this central deficit, mice lacking CCK-AR are able to compensate for the absence of CCK satiety signaling and do not become hyperphagic and obese.
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Acknowledgments |
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Footnotes |
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Abbreviations: aCSF, Artificial cerebrospinal fluid; CCK-A, cholecystokinin A; CCK-AR, cholecystokinin A receptor; dCCK, desulfated cholecystokinin-8; DMH, dorsomedial hypothalamic; DMHL, DMH electrolytic or excitotoxic lesion; LETO, Long-Evans Tokushima Otsuka; NPY, neuropeptide Y; OLETF, Otsuka Long-Evans Tokushima fatty; POMC, proopiomelanocortin; PVN, paraventricular nucleus; SSC, standard saline citrate.
Received March 5, 2004.
Accepted for publication April 22, 2004.
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S. Bi, K. A. Scott, J. Hyun, E. E. Ladenheim, and T. H. Moran Running Wheel Activity Prevents Hyperphagia and Obesity in Otsuka Long-Evans Tokushima Fatty Rats: Role of Hypothalamic Signaling Endocrinology, April 1, 2005; 146(4): 1676 - 1685. [Abstract] [Full Text] [PDF]
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B. C. De Jonghe, A. Hajnal, and M. Covasa Increased oral and decreased intestinal sensitivity to sucrose in obese, prediabetic CCK-A receptor-deficient OLETF rats Am J Physiol Regulatory Integrative Comp Physiol, January 1, 2005; 288(1): R292 - R300. [Abstract] [Full Text] [PDF]
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