Deep Underground Laboratory Measurement of

The ^{13}C(α,n)^{16}O reaction is the main neutron source for the slow-neutron-capture process in asymptotic giant branch stars and for the intermediate process. Direct measurements at astrophysical energies in above-ground laboratories are hindered by the extremely small cross sections and vast cosmic-ray-induced background. We performed the first consistent direct measurement in the range of E_{c.m.}=0.24 to 1.9 MeV using the accelerators at the China Jinping Underground Laboratory and Sichuan University. Our measurement covers almost the entire intermediate process Gamow window in which the large uncertainty of the previous experiments has been reduced from 60% down to 15%, eliminates the large systematic uncertainty in the extrapolation arising from the inconsistency of existing datasets, and provides a more reliable reaction rate for the studies of the slow-neutron-capture and intermediate processes along with the first direct determination of the alpha strength for the near-threshold state.

Direct Measurement of the Astrophysical

Fluorine is one of the most interesting elements in nuclear astrophysics, where the ^{19}F(p,α)^{16}O reaction is of crucial importance for Galactic ^{19}F abundances and CNO cycle loss in first generation Population III stars. As a day-one campaign at the Jinping Underground Nuclear Astrophysics experimental facility, we report direct measurements of the essential ^{19}F(p,αγ)^{16}O reaction channel. The γ-ray yields were measured over E_{c.m.}=72.4-344 keV, covering the Gamow window; our energy of 72.4 keV is unprecedentedly low, reported here for the first time. The experiment was performed under the extremely low cosmic-ray-induced background environment of the China JinPing Underground Laboratory, one of the deepest underground laboratories in the world. The present low-energy S factors deviate significantly from previous theoretical predictions, and the uncertainties are significantly reduced. The thermonuclear ^{19}F(p,αγ)^{16}O reaction rate has been determined directly at the relevant astrophysical energies.

Canadian global village reality: anthropometric surrogate cutoffs and metabolic abnormalities among Canadians of East Asian, South Asian, and European descent.

OBJECTIVE: To test the appropriateness of body mass index (BMI) and waist circumference (WC) cutoff points derived in largely white populations (ie, those of European descent) for detecting obesity-related metabolic abnormalities among East Asian and South Asian Canadians. DESIGN: Cross-sectional survey. SETTING: Primary care and community settings in Ontario. PARTICIPANTS: Canadians of East Asian (n = 130), South Asian (n = 113), and European (n = 111) descent. MAIN OUTCOME MEASURES: Variables for metabolic syndromes, including BMI, WC, body fat percentage, blood pressure, lipid profile, and fasting blood glucose and insulin levels, were measured. Receiver operating characteristics curve analysis was used to generate BMI and WC cutoff points based on various criteria for metabolic syndromes. RESULTS: Adjusting for sex and age, East Asian Canadians had a significantly lower mean BMI (23.2 kg/m(2)) and mean WC (79.6 cm) than did those of South Asian (26.1 kg/m(2) and 90.3 cm) and European (26.5 kg/m(2) and 89.3 cm) descent (P < .05). The BMI cutoffs for an increased risk of metabolic abnormalities ranged from 23.1 to 24.4 kg/m(2) in East Asian Canadians; 26.6 to 26.8 kg/m(2) in South Asian Canadians; and 26.3 to 28.2 kg/m(2) in European Canadians. Waist circumference cutoffs for increased risk of metabolic abnormalities were relatively low in East Asian men (83.3 to 85.2 cm) and women (74.1 to 76.7 cm), compared with South Asian men (98.8 cm) and women (90.1 to 93.5 cm), as well as European men (91.6 to 95.2 cm) and women (82.8 to 88.3 cm). CONCLUSION: The BMI and WC cutoffs used for defining risk of metabolic abnormalities should be lowered for East Asian Canadians but not for South Asian Canadians. The World Health Organization ethnic-specific BMI and WC cutoffs should be used with caution, particularly with Asian migrants who have resided in Canada for a long period of time.

Effect of 5-HT agonists on rats fed single diets with varying proportions of carbohydrate and protein.

Low doses of 5-HT agonists have been shown to selectively suppress carbohydrate intake in rats given dietary choices. To investigate further the relationship between dietary macronutrient composition and 5-HT-induced anorexia, the present study examined the effects of three 5-HT agonists on rats fed single isocaloric diets containing varying proportions of carbohydrate (CHO) and protein (PRO). Rats were habituated to eat one of the three diets (73.5% CHO--10% PRO, 58.5% CHO--25% PRO or 43.5% CHO--40% PRO) during the dark period (1900-0700 h). Saline or 5-HT agonists (fluoxetine, RU 24969 and dexfenfluramine) were administered intraperitoneally at 1845 hours, 15 min prior to food access. At the doses used, food intake was significantly affected only during the first hour of eating. All 5-HT agonists caused dose-dependent decreases in food intake (P < 0.01). The magnitude of decrease, however, was significantly influenced by diet composition. Reduction in intake was greatest in rats fed the 73.5% CHO--10% PRO diet. Thus, rats chronically fed a diet high in carbohydrate content were more sensitive to the anorectic effect of 5-HT agonists than rats fed diets containing moderate to low levels of carbohydrate.

Food intake and selection pattern of rats treated with dexfenfluramine, fluoxetine and RU 24969.

The effects of two indirect (dexfenfluramine and fluoxetine) and one direct (RU 24969) serotonergic agonists on diet selection over a 12-hr period were examined. Rats were habituated to eat, during the dark period, from two isoenergetic diets that differed in carbohydrate and protein content. Drugs were injected intraperitoneally at 1845 hr, 15 min prior to food access. The drugs exerted their effects mainly during the first hour of feeding (1900-2000 hr). At this time, a selective suppression in intake of the high carbohydrate-low protein diet was the most prominent characteristic of all three serotonergic agonists. This macronutrient specific effect was particularly strong at low dosages (dexfenfluramine, fluoxetine and RU 24969: 0.5, 2.0 and 1.0 mg/kg, respectively). With time, as the effect of drugs wore off, diet selection pattern became more variable. The fact that both indirect 5-HT agonists and a direct selective 5-HT receptor agonist share a specific behavioral effect provides additional support for the role of serotonin in the control of macronutrient specific appetites.

Buspirone-induced carbohydrate feeding is not influenced by route of administration and nutritional status.

Rats were habituated to ad lib food intake from two isoenergetic diets that differed in carbohydrate and protein content. To examine the route of administration effect, buspirone (0.6, 1.0, and 1.4 mg/kg) was injected into satiated rats either subcutaneously or intraperitoneally. Overall, no route of administration effect was observed; however, when results of the lowest dose were analyzed separately, the subcutaneous route was more effective than the intraperitoneal route. Regardless of route of administration, buspirone increased food intake over the first 2 h of food presentation in a dose-dependent manner. Moreover, the increase was entirely attributed to increases in intake from the high carbohydrate diet. In the subsequent experiment, the effect of buspirone (0.6 mg/kg) was examined in both satiated (early light period) and nonsatiated rats (early dark period). Both groups responded to buspirone with an increase in carbohydrate intake. Despite differences in baseline intake, the absolute increase was similar between satiated and nonsatiated rats. These data suggest that both sensitivity and selectively of buspirone-induced feeding are neither influenced by route of administration nor nutritional status of rats.

Brain mechanisms and the quantitative and qualitative aspects of food intake.

The brain receives a large number of signals from the ingestion of food. They provide the brain with information on both the adequacy of energy ingested and the macronutrient composition of the food. From this information brain feeding control systems are able to respond and direct the animal to make appropriate food choices so that both the quantitative (energy) needs as well as the qualitative (nutrient) needs are met. An understanding of brain mechanisms regulating feeding will only emerge if their dual purposes are recognized.

5-Hydroxytryptamine : a modulator of food composition but not quantity?

After a meal of protein, in contrast to a meal of carbohydrate (CHO) at 1915 hr, rats allowed to choose from high carbohydrate and high protein diets during 2000-2100 hr prefer CHO (1). Thus the hypothesis that this regulation of macronutrient selection involves brain 5-hydroxytryptamine (5-HT) metabolism was tested. Compared to three baseline days during which rats (250- 300g ) consumed 1 g CHO, rats fed tryptophan (TRP, 5-HT precursor; 15 mg in 1 g CHO) selected meals higher in protein concentration (35.4% vs 46.6%, F (1,12) = 20.05, p less than 0.001) from 10% and 60% casein diets during 2000-2100 hr. Associated with the higher protein selection was an elevated brain 5-HT turnover in rats killed 30 minutes after consuming CHO + TRP. Pretreating rats with p-chlorophenylalanine, an inhibitor of TRP hydroxylase, blocked this effect of TRP (36.3% vs 37.0%). Fenfluramine (1 and 2 mg/kg i.p. at 1945 hr), which transiently enhances neuronal 5-HT release, increased the rat's relative preference for protein from 28.8% to 37.5% (2 mg/kg, t = 3.21, p less than 0.025) during 2000-2100 hr. These rats, also exhibited a selective preference for CHO between 3-12 hrs post injection which paralleled the known subsequent depletion of 5-HT by fenfluramine. We conclude that the relative proportion of protein and carbohydrate selected in a meal is controlled, at least in part, by prior food effects on brain 5-HT metabolism.

Selective increase in carbohydrate intake by rats treated with 8-hydroxy-2-(di-n-propylamino)-tetraline or buspirone.

Both 8-hydroxy-2-(di-n-propylamino)-tetraline (8-OH-DPAT) and buspirone (BUSP) were found to induce food intake in free-feeding, self-selecting young rats. The hyperphagia was macronutrient specific. In rats given simultaneous access to two diets which differed in carbohydrate and protein content, 8-OH-DPAT and BUSP selectively increased intake from the diet with high carbohydrate content during a two hour test. This specific behavioral effect is dose-dependent and is opposite to that induced by serotonin releasers or reuptake inhibitors. In a separate experiment, the selective decrease in carbohydrate intake after fluoxetine (FLX) was blocked by 8-OH-DPAT co-administration. These results further support a role for the serotonergic system in the control of feeding and macronutrient specific appetites.

Meal composition influences subsequent food selection in the young rat.

Food selection one-half hour after the ingestion (2 g) of either a protein containing or a protein-free (carbohydrate) diet was studied in young rats. Following a 12 hr fast the rats were allowed 15 minutes to consume the meal (premeal). Thirty minutes later, they had access to two isocaloric diets that differed only in protein and carbohydrate content. During the first hour of ad lib feeding, protein intake and protein concentration selected were lower in the 45% casein prefed group compared to the carbohydrate group. A further reduction in protein intake and protein concentration occurred when the protein content of the premeal was increased to 70% from 45% casein. Rats prefed with the 70% casein diet significantly reduced their daily total food intake (12 hr) compared to either the 45% casein or carbohydrate prefed group. It is concluded that both quantity and composition of food selected is influenced by the composition of the preceding meal.

Food intake and selection after peripheral tryptophan.

Two studies investigated the effects of peripheral (IP) administration of the dietary indispensible amino acid tryptophan, on food intake and macronutrient selection in rats adapted to a 12 hr nocturnal feeding period and a choice of 10% and 60% casein diets. In a dose-response study (35, 55, 75, 95, 115 mg/kg), the threshold dose of 75 mg/kg produced a significant reduction in total food intake (3.6 to 2.3 g, p less than 0.05) during the first hour of feeding. The reduction in carbohydrate intake (2.1 vs. 1.2 g, p less than 0.05) was greater than that for protein intake (1.6 vs. 1.1 g, p less than 0.05). Twelve hr total food intake was also decreased (20.9 to 19.5 g, p less than 0.05) and this was attributable to decreased carbohydrate intake (13.2 to 11.8 g, p less than 0.05). In a second study designed to determine if tryptophan's effects were mediated by the central nervous system, brain tryptophan uptake was blocked by co-injecting valine with tryptophan. The significant reduction in first hour total food intake by tryptophan was not prevented by co-injection of an equal quantity of valine (3.5 to 1.8 g, p less than 0.05). Again the suppression of carbohydrate intake (2.0 to 0.9 g p less than 0.05) was greater than that for protein intake (1.5 to 0.9 g, p less than 0.05). This dose of valine significantly reduced brain tryptophan uptake by 16% (21.3 to 17.8 micrograms/g, p less than 0.05) and when administered alone did not affect first hour total food intake (3.1 vs 3.2 g).(ABSTRACT TRUNCATED AT 250 WORDS)

Dual-energy X-ray absorptiometry for body composition estimation in Chinese women.

OBJECTIVE: To determine whether dual-energy X-ray absorptiometry (DXA) is a valid method for body composition assessment of obese and non-obese subjects. DESIGN: Cross-sectional study. SUBJECTS: Chinese women living in Hong Kong; 66 of 91 subjects had body mass index (BMI) of >25 kg/m2. MEASUREMENTS: Anthropometrics, including body weight, body height, waist and hip girth. Percentage body fat (%BF) and fat-free mass (FFM) from DXA (Hologic 2000 plus, Enhanced Array Whole Body Version 5.63) were compared with that based on a tracer dose of deuterium oxide for the determination of total body water (TBW). RESULTS: In both obese and non-obese subjects, FFMDXA was similar to FFMTBW. The Bland and Altman-type analysis indicated that comparable between-methods differences (mean bias) and limits of agreement were obtained in obese and non-obese subjects for FFM (0.4, between -4.4 and 5.2 kg vs 0.5, between -3.1 and 4.1 kg) and %BF (-0.6, between -7.6 and 6.4% vs -1.2, between -8.6 and 6.2%). The %BF bias was independent of age, BMI, hip circumference, and waist-to-hip ratio, but correlated with waist girth (r=0.24, P=0. 021). CONCLUSION: The sources of bias are methodological and anthropometric in nature. The between-methods differences, however, are small and clinically insignificant. DXA is a valid method for assessing the body composition of obese patients. SPONSORSHIP: This study was supported by a HKU-CRCG grant.

Effects of repeated administration of serotonergic agonists on diet selection and body weight in rats.

Food intake, diet selection and body weight gain were examined in three separate experiments in which rats received saline or one of three serotonergic agonists, dexfenfluramine, RU 24969 and fluoxetine. In all experiments, food was available only in the dark period during which time rats were given simultaneous access to two isoenergetic diets which differed in their protein and carbohydrate content. After habituation to this feeding paradigm and intraperitoneal injections, rats were assigned to control or drug group. Saline or a serotonergic agonist was given to the same rat once daily, 15 min prior to feeding, for six consecutive days. All three agonists (1.5 mg/kg for dexfenfluramine and RU 24969; 3 mg/kg for fluoxetine) caused immediate (first two h of feeding) hypophagia which was accounted for by the selective suppression in intake of the high-carbohydrate-low-protein diet. This selective shift in diet choice was sustained upon repeated exposure. Although the effects of these agonists on daily (12-h) feeding was less pronounced, appetite suppression was due entirely to reduced intake of the high-carbohydrate-low-protein diet. Of the three agonists tested, partial tolerance was observed only after dexfenfluramine. Nevertheless, all three agonists caused comparable declines in weight gain. These results suggest that repeated administration of serotonergic agonists has sustained impacts on food intake, diet choice and weight gain.

A role for vagus nerve in regulation of protein and carbohydrate intake.

The effects of vagotomy on long-term protein and carbohydrate selection or on short-term food selection following cholecystokinin octapeptide (CCK-8) injections, protein, or carbohydrate premeals and on brain 5-hydroxytryptamine (5HT) and catecholamine metabolism were examined in adult rats. Vagotomy was followed by a reduction in daily protein intake that by 3 wk had fallen to 50% of preoperative levels. A corresponding increase in carbohydrate intake occurred so that total food intake was maintained at approximately 93% of that consumed by the sham-operated controls. These changes in day-to-day macronutrient selection from a choice of high- and low-protein diets were associated with a vagotomy-induced decreased turnover of 5HT in the hypothalamus. In meal consumption studies vagotomy prevented a further reduction in meal size by CCK-8 but did not block decreased consumption of total food or of protein preference of the rats in meals taken subsequent to a protein meal. It was concluded that the vagus nerve plays a role in regulating long-term protein and carbohydrate preferences but not in the relationships among meal-to-meal composition and intake.

Food intake and choice in lean and obese Zucker rats after intragastric carbohydrate preloads.

Feeding behavior in response to a carbohydrate preload was determined in lean and obese Zucker rats. Rats were adapted to a schedule of feeding during a 12-h daily dark period. Carbohydrate preloads (cornstarch in water) were given by intragastric intubation 30 min before rats had access to a choice of two diets that differed in their protein and carbohydrate contents. Behavioral responses of lean rats to carbohydrate preloads were prompt and selective. In the first hour of feeding, reduction in intake, mainly of the high carbohydrate-low protein diet, more than compensated for the energy content of the preload. In contrast, obese rats failed to achieve a similar degree of compensation to the energy surplus from the carbohydrate preload during the first hour of feeding. Also, their decreases in food intake were nonselective. In general, it took obese rats two or more hours to adjust their feeding behavior in response to a carbohydrate preload. Increasing the size of the preload did not improve the overall response of obese rats, but an extra 30-min lapse between preload and food access led to selective suppression in first-hour intake from the high carbohydrate-low protein diet. These findings suggest that altered food intake and selection behavior of the obese Zucker rat may be, in part, due to a delay in response to physiologic and metabolic changes arising from carbohydrate ingestion.

Self-selected meal composition, circadian rhythms and meal responses in plasma and brain tryptophan and 5-hydroxytryptamine in rats.

Relationship among food composition, plasma and brain tryptophan and 5-hydroxytryptamine (5-HT) were studied by measuring both carcadian feeding and meal responses in self-selecting rats. Under ad libitum feeding conditions in which young rats were given a choice between two isocaloric diets (0 and 60% casein) and groups were killed at 3-hour intervals throughout the day, several circadian rhythms become apparent. Protein and carbohydrate energy, the plasma tryptophan:neutral amino acid ratio (TRP:NAA) and brain TRP, but not 5-HT concentrations showed statistically significant circadian variations. During the dark hours of plasma TRP:NAA ratio and brain TRP concentrations were inversely associated with the protein concentration of meals previously selected. In meal response studies, rats were similarly given a choice of diets, but were killed 20 minutes after their selected meals. Plasma TRP:NAA ratios, brain TRP and 5-hydroxyindole levels were inversely correlated with the protein concentration of the meals selected. Absolute quantities of protein, but not carbohydrate, fat or total energy, were inversely related to the plasma TRP:NAA ratio and brain TRP concentration. It is concluded that the circadian changes in the plasma TRP:NAA ratio and in brain TRP amd 5-hydroxyindole concentrations are under the continual influences of food choices made during spontaneous feeding activity.