Corticotropin-releasing factor decreases meal size by decreasing cluster number in Koletsky (LA/N) rats with and without a null mutation of the leptin receptor

Characterizing ingestive behavior through licking microstructure: Underlying neurobiology and its use in the study of obesity in animal models

Ingestive behavior is controlled by multiple distinct peripheral and central physiological mechanisms that ultimately determine whether a particular food should be accepted or avoided. As rodents consume a fluid they display stereotyped rhythmic tongue movements, and by analyzing the temporal distribution of pauses of licking, it is possible through analyses of licking microstructure to uncover dissociable evaluative and motivational variables that contribute to ingestive behavior. The mean number of licks occurring within each burst of licking (burst and cluster size) reflects the palatability of the consumed solution, whereas the frequency of initiating novel bouts of licking behavior (burst and cluster number) is dependent upon the degree of gastrointestinal inhibition that accrues through continued fluid ingestion. This review describes the analysis of these measures within a context of the behavioral variables that come to influence the acceptance or avoidance of a fluid, and the neurobiological mechanisms that underlie alterations in the temporal distribution of pauses of licks. The application of these studies to models of obesity in animals is also described.

Role of the corticotropin-releasing factor receptor type 2 in the control of food intake in mice: a meal pattern analysis

The actions of corticotropin-releasing factor (CRF) and related peptides are mediated by two receptors (CRF(1) and CRF(2)). The respective role of each subtype in the control of food intake remains poorly known. In the present study, we examined the quantity and microstructure of ingestive behavior of knockout (KO) mice lacking CRF(2) receptors and their wild-type (WT) littermates. Under basal conditions, CRF(2) KO mice showed increased nocturnal food intake, evident as an increased zenith in circadian cosinor analysis of food intake. Microstructure analysis revealed that this greater food intake reflected increased meal size, rather than meal frequency, suggesting a decreased satiating value of food. Following acute restraint stress, CRF(2) KO mice showed an intact immediate anorectic response with increased latency to eat and decreased meal size. However, CRF(2) deletion abolished the prolonged phase of restraint-induced anorexia. CRF(2) KO mice did not differ from WT controls in feeding responses to food deprivation or injection of ghrelin receptor agonists. Independent of genotype, food deprivation increased food intake, with dramatic changes in meal size, meal frequency, water : food ratio and eating rate. Acyl-ghrelin or BIM-28131, a potent ghrelin analog, dose-dependently stimulated food intake by increasing meal size (ghrelin, BIM-28131) and meal number (BIM-28131), while slowing the average eating rate (BIM-28131) similarly in WT and KO mice. These results suggest that the CRF(2) receptor is involved in the control of meal size during the active phase of eating and following acute exposure to stress.

Peripheral injection of CCK-8S induces Fos expression in the dorsomedial hypothalamic nucleus in rats

Peripheral cholecystokinin (CCK) plays a physiological role in the regulation of food intake. The dorsomedial hypothalamic nucleus (DMH) has been implicated in the brain regulation of food intake and satiety. The aim of this study was to determine if peripherally administered CCK affects neuronal activity in the DMH, as assessed by Fos expression. Density of Fos-positive neurons was determined in the DMH, paraventricular nucleus of the hypothalamus (PVN), arcuate nucleus of the hypothalamus (ARC) and ventromedial hypothalamic nucleus (VMH) in non-fasted Sprague-Dawley rats in response to intraperitoneally (ip) injection of CCK-8S (2 microg/kg, n=6) or vehicle (0.15 M NaCl; n=6). CCK-8S increased Fos immunoreactivity in the DMH (mean+/-SEM; cells/section: 108+/-10 versus 54+/-6, p<0.001) and PVN (120+/-12 versus 20+/-3, p<0.001) compared to the vehicle group while not influencing Fos expression in the ARC and VMH. Double labeling showed that 27.4+/-6.4% (n=3) of Fos-positive neurons induced by CCK-8S were positive for corticotropin-releasing factor immunoreactivity, that were mainly localized in the ventral part of the DMH, and encircled in a network of tyrosine-hydroxylase-immunoreactive positive fibers. These data indicate that in addition of the PVN, peripheral CCK increases neuronal activity in the DMH suggesting a possible role in this hypothalamic nucleus in the satiating effect of the peptide.

Orosensory stimulation is sufficient and postingestive negative feedback is not necessary for neuropeptide Y to increase sucrose intake

Although central administration of neuropeptide Y (NPY) has a potent orexic effect, it is not clear how NPY changes the potency of peripheral feedbacks from the gut to prolong eating and increase meal size. It has been suggested that NPY increases the stimulating effect of orosensory sweet stimuli or that it decreases the inhibitory effect of postingestive stimuli. To clarify this issue, we compared the orexic effect of NPY (2 microg) injected into the third ventricle of the brain on the volume and microstructure of intake of 0.8M sucrose during sham feeding (SF) and real feeding (RF) in male Sprague Dawley rats. The rationale for this comparison is that orosensory stimulation occurs in SF and RF, but postingestive negative feedback is present only in RF. NPY increased the volume ingested and the rate and number of clusters of licking significantly more in SF than in RF. This demonstrates that orosensory sucrose stimulation is sufficient and postingestive negative feedback is not necessary for the orexic effect of NPY under these experimental conditions.

Treatment with a CRH-1-receptor antagonist (R121919) does not affect weight or plasma leptin concentration in patients with major depression

Weight gain during treatment with psychotropic drugs is frequently observed and is assumed to be responsible for non-compliance and for an elevated risk to develop a number of somatic co-morbidities including cardiovascular disorders and type 2 diabetes. Absence of weight inducing effects is therefore a major objective for the development of new compounds. Recently, R121919, the first corticotropin releasing hormone receptor 1 (CRH1R) antagonist, was tested in major depression. Clinical efficacy, safety, and tolerability of this compound could be demonstrated. Since CRH is discussed to be involved in the regulation of appetite and weight, directly and via interaction with leptin, CRH1R antagonists are suspected to influence body weight. Effects of 30 days of treatment with the CRH1R antagonist R121919 on weight and leptin levels in 20 patients suffering from major depression were investigated. No significant weight changes during treatment with R121919 were observed. Furthermore, noeffects on plasma leptin concentrations were found. We conclude that treatment with the CRH1R antagonist R121919 does not affect weight or plasma leptin concentrations in patients with major depression. Together with previous findings indicating safety, tolerability, and clinical efficacy CRH1R antagonists are highly promising as a new treatment option in depression.

Dorsomedial hypothalamic corticotropin-releasing factor mediation of exercise-induced anorexia

Running wheel access and resulting voluntary exercise alter food intake and reduce body weight. The neural mechanisms underlying these effects are unclear. In this study, we first assessed the effects of 7 days of running wheel access on food intake, body weight, and hypothalamic gene expression. We demonstrate that running wheel access significantly decreases food intake and body weight and results in a significant elevation of CRF mRNA expression in the dorsomedial hypothalamus (DMH) but not the paraventricular nucleus. Seven-day running wheel access also results in elevated arcuate nucleus and DMH neuropeptide Y gene expression. To assess a potential role for elevated DMH CRF activity in the activity-induced changes in food intake and body weight, we compared changes in food intake, body weight, and hypothalamic gene expression in rats receiving intracerebroventricular (ICV) CRF antagonist alpha-helical CRF or vehicle with or without access to running wheels. During a 4-day period of running wheel access, we found that exercise-induced reductions of food intake and body weight were significantly attenuated by ICV injection of the CRF antagonist. The effect on food intake was specific to a blockade of activity-induced changes in meal size. Central CRF antagonist injection further increased DMH CRF mRNA expression in exercised rats. Together, these data suggest that DMH CRF play a critical role in the anorexia resulting from increased voluntary exercise.

Peptides that regulate food intake: separable mechanisms for dorsal hindbrain CART peptide to inhibit gastric emptying and food intake

We investigated whether dorsal hindbrain and/or peripheral cocaine- and amphetamine-regulated transcript peptide (CARTp) acts to suppress gastric emptying of a caloric stimulus. Furthermore, effects of dorsal hindbrain CARTp on sucrose consumption and licking microstructure was studied, as well as the possible contribution of corticotropin-releasing factor (CRF) receptors to mediate effects of CARTp downstream on emptying and sucrose intake. Rats bearing gastric fistulas received intragastric infusions (1.0 ml/min) of 12 ml 12.5% glucose. Gastric samples were withdrawn immediately after the intragastric infusion to reflect emptying during gastric fill. CARTp injected in the fourth ventricle intracerebroventricularly (0.5 and 1.0 microg) suppressed gastric emptying. CARTp reduced sucrose intake at similar doses and altered a variety of lick microstructure variables (no. of licks, bursts, clusters, licks/burst, licks/clusters, interlick interval, first meal size, and first meal duration). Pretreatment with the CRF antagonist alpha-helical CRF-(9-41) blocked the effect of 1.0 microg CARTp on gastric emptying but not on sucrose consumed or on any of the licking microstructure parameters. These data demonstrate differential mediation of the feeding and gastric inhibitory effects of CARTp and suggest that CARTp-induced inhibition of gastric emptying does not contribute to this peptide's ability to inhibit food intake.