Ann-Marie Torregrossa

Determining biological tissue turnover using stable isotopes: the reaction progress variable.

The reaction progress variable is applied to stable isotope turnover of biological tissues. This approach has the advantage of readily determining whether more than one isotope turnover pool is present; in addition, the normalization process inherent to the model means that multiple experiments can be considered together although the initial and final isotope compositions are different. Consideration of multiple isotope turnover pools allows calculation of diet histories of animals using a time sequence of isotope measurements along with isotope turnover pools. The delayed release of blood cells from bone marrow during a diet turnover experiment can be quantified using this approach. Turnover pools can also be corrected for increasing mass during an experiment, such as when the animals are actively growing. Previous growth models have been for exponential growth; the approach here can be used for several different growth models.

Maintenance on a high-fat diet impairs the anorexic response to glucagon-like-peptide-1 receptor activation

Previous data suggests that the adiposity signal leptin reduces food intake in part by enhancing sensitivity to short-term signals that promote meal termination, including glucagon-like peptide 1 (GLP-1). We hypothesized that maintenance on a high-fat (HF) diet, which causes resistance to leptin, would impair GLP-1s ability to reduce food intake. To test this hypothesis, we examined the anorexic responses to intraperitoneal injection of 100 μg/kg GLP-1 and 1 μg/kg exendin-4 (Ex-4), the potent, degradation resistant GLP-1 receptor agonist, in Wistar rats maintained on a low-fat (10%; LF) or HF (60%) diet for 4-6 weeks. Rats maintained on each of these diets were tested twice, once while consuming LF food and once while consuming HF food, to distinguish between effects of acute vs. chronic consumption of HF food. LF-maintained rats tested on LF diet reduced 60-min dark phase intake in response to GLP-1, but HF-maintained rats failed to respond to GLP-1 whether they were tested on HF or LF diet. LF-maintained rats tested on HF diet also showed no response, suggesting that even brief exposure to HF diet can impair sensitivity to GLP-1 receptor activation. Both LF- and HF-maintained rats showed significant anorexic responses to Ex4 at 4h post-treatment, but only LF-maintained rats had significantly reduced intake and body weight 24h after injections. To determine whether the ability of endogenous GLP-1 to promote satiation is impaired by HF maintenance, we examined the response to exendin 3 (9-39) (Ex9), a GLP-1 receptor antagonist. In LF-maintained rats, Ex9 increased intake significantly, but HF-maintained rats reduced food intake in response to Ex9. These data support the suggestion that maintenance on HF diet reduces the anorexic effects of GLP-1 receptor activation, and this phenomenon may contribute to overconsumption of high-fat foods.

Estradiol acts in the medial preoptic area, arcuate nucleus, and dorsal raphe nucleus to reduce food intake in ovariectomized rats.

Estradiol (E2) exerts an inhibitory effect on food intake in a variety of species. While compelling evidence indicates that central, rather than peripheral, estrogen receptors (ERs) mediate this effect, the exact brain regions involved have yet to be conclusively identified. In order to identify brain regions that are sufficient for E2s anorectic effect, food intake was monitored for 48 h following acute, unilateral, microinfusions of vehicle and two doses (0.25 and 2.5 μg) of a water-soluble form of E2 in multiple brain regions within the hypothalamus and midbrain of ovariectomized rats. Dose-related decreases in 24-h food intake were observed following E2 administration in the medial preoptic area (MPOA), arcuate nucleus (ARC), and dorsal raphe nucleus (DRN). Within the former two brain areas, the larger dose of E2 also decreased 4-h food intake. Food intake was not influenced, however, by similar E2 administration in the paraventricular nucleus, lateral hypothalamus, or ventromedial nucleus. These data suggest that E2-responsive neurons within the MPOA, ARC, and DRN participate in the estrogenic control of food intake and provide specific brain areas for future investigations of the cellular mechanism underlying estradiols anorexigenic effect.

Two effects of high-fat diets on the satiating potency of cholecystokinin-8.

Chronic ingestion of diets containing 34% or 54% fat have been reported [Peptides 19 (1998) 1407] to decrease the inhibitory effect on food intake of doses of cholecystokinin-8 (CCK-8) less than 1 microg/kg i.p. We attempted to replicate this phenomenon in three experiments by comparing the effect of high-fat and low-fat diets on the threshold dose of CCK-8 for inhibition and on the dose-response function for doses of CCK-8 that ranged from 0.125 to 2.0 microg/kg. The first experiment tested rats five times per week. Rats on a 34% fat diet had a higher threshold (1.0 microg/kg) than rats on a 5% fat diet (0.25 microg/kg). The dose-response functions, however, were not significantly different. This result replicated the earlier report [Peptides 19 (1998) 1407]. The second experiment tested rats maintained on the same diets every other day as in the original report. It failed, however, to replicate the results of the first experiment or the earlier report because the threshold doses and the dose-response functions of CCK-8 were not significantly different between rats on 34% and 5% fat diets. The third experiment compared the potency of CCK-8 in rats on a 60% fat diet with the potency in rats on a 5% fat diet. CCK-8 was significantly more potent in the rats on the 60% fat diet because the threshold dose of these rats was lower (0.125 microg/kg) than in rats on the 5% fat diet (0.25 microg/kg), and the dose-response function in rats on the 60% fat diet was significantly more potent than in rats on the 5% fat diet. Thus, we observed two effects of the chronic ingestion of high-fat diets on the inhibitory potency of CCK-8: (1). A 34% fat diet increased the threshold dose of CCK-8 without changing the dose-response function in one of two experiments. (2). A 60% fat diet increased the potency of CCK-8 because it decreased the threshold dose and increased the dose-response function significantly.

Rats Display a Robust Bimodal Preference Profile for Sucralose

Female Sprague-Dawley rats display considerable variability in their preference for the artificial sweetener sucralose over water. While some rats can be classified as sucralose preferrers (SP), as they prefer sucralose across a broad range of concentrations, others can be classified as sucralose avoiders (SA), as they avoid sucralose at concentrations above 0.1 g/L. Here, we expand on a previous report of this phenomenon by demonstrating, in a series of 2-bottle 24-h preference tests involving water and an ascending series of sucralose concentrations, that this variability in sucralose preference is robust across sex, stage of the estrous cycle, and 2 rat strains (Long-Evans and Sprague-Dawley). In a second experiment involving a large sample of rats (n = 50), we established that the ratio of SP to SA is approximately 35-65%. This bimodal behavioral response to sucralose appears to be driven by taste because rats display a similar bimodal licking response to a range of sucralose solutions presented during brief-access tests. Finally, we have shown that sucralose avoidance is extremely robust as 23-h water-deprived SA continue to avoid sucralose in 1-h single-bottle intake tests. Based on their reduced licking responses to sucralose during brief-access (taste driven) tests, and the fact that their distaste for sucralose cannot be overcome by the motivation to rehydrate, we conclude that SA detect a negative taste quality of sucralose that SP are relatively insensitive to.

Caching as a Behavioral Mechanism to Reduce Toxin Intake

Abstract We hypothesized that caching could be a mechanism to remove volatile secondary compounds from a plant-based diet. This mechanism has been demonstrated in 1 herbivore and has been hypothesized as a widespread mechanism for reduction of intake of toxins. We examined this hypothesis in both the field and the laboratory by documenting the ability of herbivorous rodents to manipulate alpha-pinene, the major terpene in juniper (Juniperus osteosperma). First, we dismantled middens of Neotoma albigula and found that cached plant material was devoid of alpha-pinene, whereas surrounding trees contained alpha-pinene. In laboratory trials, we examined the ability of woodrat species (N. albigula, N. lepida, and N. bryanti) to reduce toxin intake by storing food before consumption. Each species responded differently when offered terpene-treated pellets. N. albigula controlled terpene intake by increasing reliance on the terpene-free cache. N. lepida controlled terpene intake by decreasing total intake but did not change cache consumption. N. bryanti did not regulate terpene intake. All 3 species abandoned more food in the foraging cage when the food contained terpene. In an additional laboratory trial with N. albigula, we determined that increased abandonment was not related to cache size.

Testing the diet-breadth trade-off hypothesis: differential regulation of novel plant secondary compounds by a specialist and a generalist herbivore

Specialist herbivores are predicted to have evolved biotransformation pathways that can process large doses of secondary compounds from the plant species on which they specialize. It is hypothesized that this physiological specialization results in a trade-off such that specialists may be limited in ability to ingest novel plant secondary compounds (PSCs). In contrast, the generalist foraging strategy requires that herbivores alternate consumption of plant species and PSC types to reduce the possibility of over-ingestion of any particular PSC. The ability to behaviorally regulate is a key component of this strategy. These ideas underpin the prediction that in the face of novel PSCs, generalists should be better able to maintain body mass and avoid toxic consequences compared to specialists. We explored these predictions by comparing the feeding behavior of two herbivorous rodents: a juniper specialist, Neotoma stephensi, and a generalist, Neotoma albigula, fed diets with increasing concentrations of phenolic resin extracted from the creosote bush (Larrea tridentata), which produces a suite of PSCs novel to both species. The specialist lost more mass than the generalist during the 15-day trial. In addition, although the specialist and generalist both regulated phenolic resin intake by reducing meal size while on the highest resin concentration (4%), the generalist began to regulate intake on the 2% diet. The ability of the generalist to regulate intake at a lower PSC concentration may be the source of the generalist’s performance advantage over the specialist. These data provide evidence for the hypothesis that the specialist’s foraging strategy may result in behavioral as well as physiological trade-offs in the ability to consume novel PSCs.

Hematologic iron analyte values as an indicator of hepatic hemosiderosis in callitrichidae

Hepatic hemosiderosis is one of the most common postmortem findings in captive callitrichid species. Noninvasive evaluation of hematologic iron analytes has been used to diagnose hepatic iron storage disease in humans, lemurs, and bats. This study evaluated the relationship between hematologic iron analyte values (iron, ferritin, total iron binding capacity, and percent transferrin saturation) and hepatic hemosiderosis in callitrichids at the Wildlife Conservation Societys Central Park and Bronx Zoos. Results revealed that both ferritin and percent transferrin saturation levels had strong positive correlations with hepatic iron concentration (P<0.001, r=0.77, n=20; P<0.001, r=0.85, n=10, respectively). Serum iron levels positively correlated with hepatic iron concentration (P=0.06, r=0.56, n=11), but this finding was not significant. Serum total iron binding capacity did not significantly correlate with hepatic iron concentration (P=0.47, r=0.25, n=10). Both ferritin and hepatic iron concentration positively correlated with severity of hepatic iron deposition on histology (P<0.05, r=0.49, n=21; P<0.001, r=0.67, n=21, respectively). This study suggests that ferritin, serum iron concentration, and percent transferrin saturation are convenient, noninvasive, antemortem methods for assessing severity of hemosiderosis in callitrichids. Am. J. Primatol. 70:629–633, 2008.

Water Restriction and Fluid Temperature Alter Preference for Water and Sucrose Solutions

The role of diet temperature in ingestive behavior is poorly understood. We examined the importance of stimulus temperature and water-restriction state on the preference for and intake of water and sucrose. Using custom-designed equipment that allows us to monitor and maintain solution temperatures during testing (±0.1 °C), we conducted a series of 2-bottle preference tests (10 °C water vs. sucrose 10-40 °C) and brief access tests (10-40 °C water and sucrose). Water-restricted rats preferred cold water over any sucrose concentration (0.0-1.0 M) if the sucrose was 30 or 40 °C, whereas the same rats preferred sucrose at all concentrations and temperatures when unrestricted suggesting that the water-restriction state interacts with temperature preference. In a series of brief-access tests using a Davis Rig (MS-180), rats reduced licking to cold sucrose compared with 20 °C sucrose, suggesting that unlike water, cold temperature reduced the palatability of sucrose.

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.