Zhong-Jin Yang

Correlation between food intake and CSF IL-1 alpha in anorectic tumor bearing rats

Postulating that central IL-1 is involved in the pathogenesis of cancer anorexia we measured IL-1 alpha in cerebrospinal fluid (CSF) from anorectic tumor bearing (TB) rats and non-tumor bearing controls, and correlated their CSF IL-1 alpha with food intake and tumor weight. Food intake in controls was significantly higher than that in anorectic TB rats. Eight of the 13 anorectic TB rats had detectable CSF IL-1 alpha; no CSF IL-1 alpha was detected in controls. In anorectic TB rats a negative correlation existed between CSF IL-1 alpha and food intake and a positive correlation between CSF IL-1 alpha and tumor weight. Data suggest a link between CSF IL-1 alpha and the pathogenesis of cancer anorexia.

Eating induced rise in LHA-dopamine correlates with meal size in normal and bulbectomized rats

Dopaminergic function in the lateral hypothalamic area (LHA) is important for processing intrinsic and extrinsic feeding related information. Brain microdialysis was used to examine if dopamine release in the LHA correlates with meal size in normal and bulbectomized rats. Food-deprived bulbectomized rats ate significantly less food (1.7 +/- 0.1 g) than food-deprived sham operated rats (3.1 +/- 0.5 g, p < 0.05), accompanied by a lesser increase in LHA-dopamine release (150.6 +/- 4.9% vs. 195.1 +/- 13.9, p < 0.02). LHA-dopamine release was significantly higher in rats which ate a full meal (2.9 +/- 0.1 g) than in rats which ate half a meal (1.5 +/- 0.1 g, p < 0.05), being 155.9 +/- 7.8% vs. 131.0 +/- 4.9% (p < 0.05) in food-deprived normal rats. Data suggest that dopamine release in the LHA correlates to the quantity of food consumed during a meal.

Dopamine and serotonin VMN release is related to feeding status in obese and lean Zucker rats.

Study of neurotransmitter role in food intake regulation in a leptin signaling deficient model, such as the Zucker rat, would benefit in the understanding of mechanisms of human obesity, in which leptin resistance is a common syndrome. We studied dopamine (DA) and serotonin (5-HT) concentrations in vivo in the ventromedial nucleus (VMN) of the hypothalamus, as they relate to eating after food deprivation in obese and lean 9-week-old male Zucker rats. DA and 5-HT concentrations were measured by HPLC via microdialysis before and during refeeding in 24-h food-deprived rats. Before food was provided, mean baseline DA and 5-HT levels were lower in obese than in lean rats (9.2 ± 0.9 vs 15.1 ± 1.9 pg/10 μl, p < 0.01, and 0.68 ± 0.05 vs 1.17 ± 0.02 pg/10 μl, p < 0.001, respectively). Food intake was accompanied by a decrease in DA levels in both obese and lean rats to 64% (p < 0.01) and 65% (p < 0.02) of their baseline levels respectively. 5-HT levels were significantly increased during eating by 41% in obese and 35% in lean rats (p < 0.01) from the baseline levels. Thus in obese rats with altered leptin signaling we found an unaltered pattern of DA and 5-HT release associated with food deprivation and refeeding, but with presence of their low levels. This points to an impaired postsynaptic monoaminergic action to produce an adequate metabolic response in obese Zucker rats in response to feeding state.

Effect of estradiol and progesterone on daily rhythm in food intake and feeding patterns in Fischer rats

The product of meal number x meal size, over time, is food intake. Because estrogens modulate feeding activity via their action on the hypothalamus, and because there is a diurnal rhythm in the expression of cytoplasmic estrogen receptors and in estrogen binding activity, the present study examined the effects of ovariectomy and later hormone therapy on acute changes in body weight, and on the meal number-to-meal size relationship as reflected by food intake in the dark/light feeding patterns, in adult female rats in the intact state and after ovariectomy. Twelve female Fischer rats were randomized into ovariectomy and sham operation groups. A rat eater meter measured the feeding indexes for 15 days before and 25 days after ovariectomy, and later for 35 days with hormone therapy. We report: (a) mean body weight gain was linear before and up to ovariectomy, while exponential after ovariectomy; (b) increase in daily food consumption is mainly via an increase in food intake during the light phase; (c) light phase meal number remains unchanged, meal size significantly increases, with the resultant increase in overall food intake; (d) during the dark phase, meal size also significantly increases, but is accompanied by a proportional decrease in meal number, resulting in unchanged dark-phase food intake; and (e) estrogen restoration with either estradiol valerate or estradiol-progesterone combination, reversed the above changes. Data show that in the female Fischer 344 rat: (a) changes in daily rhythm in food intake are brought about by differential effects of the hormones on both meal size and meal number in both the total daily levels as well as in the dark-to-light distribution; (b) estadiol appears to have a tonic inhibitory effect on the light phase meal size and a phasic effect on the dark phase meal size and number, but no significant effect on the light-phase meal number; and (c) in the Fischer rats, progesterone augments estradiols effect on these indicies.

Infusion of Nicotine Into the LHA Enhances Dopamine And 5-HT Release and Suppresses Food Intake

Nicotine administration induces hypophagia. Because of the involvement of hypothalamic neurotransmitters in food intake control, we hypothesized that increased activity of the lateral hypothalamic dopamine (LHA-DA) and/or serotonin (LHA-5-HT) may be responsible for nicotine-induced hypophagia. Either 4 mM nicotine or vehicle was administered via reverse microdialysis technique into the LHA of overnight food-deprived rats for 60 min; then food was provided for 40 min. The LHA-DA, 5-HT and their intermediate metabolites, DOPAC and 5-HIAA, were continuously measured during 20-min intervals before, during, and after nicotine administration. Continuous nicotine administration for 60 min increased LHA-DA and DOPAC concentrations during the first 40 min, and induced a long-lasting increase in LHA-5-HT release, until 120 min after the start nicotine administration, even when nicotine administration was stopped. The food intake during the 40-min refeeding period was significantly lower when rats received nicotine. Eating induced a significant and short-lasting increase in the LHA-DA and a long-lasting increase in the LHA-5-HT. These findings indicate that nicotine enhances dopaminergic and serotonergic activity in the LHA, and that the enhanced LHA-5-HT activity may contribute to nicotine-induced hypophagia.

LHA dopaminergic activity in obese and lean Zucker rats.

&NA; Microdialysis was performed to quantitate lateral hypothalamic dopamine (LHA DA) release before, during and after a single meal in food‐deprived obese and lean Zucker rats to examine our hypothesis that an abnormally high dopamine activity may exist in the LHA of obese Zucker rats. Food consumption after food deprivation, was significantly greater in obese than in lean rats (4.1 ± 0.2 and 2.3 ± 0.4 g, respectively; (p < 0.05). Mean basal dopamine level was significantly higher in obese than in lean rats (12.0 ± 0.3 and 10.5 ± 0.3 pg in 10 &mgr;l dialysates, respectively; p < 0.05). Dopamine release during eating was greater in obese than in lean rats (159.1 ± 6.8% and 135.4 ± 3.6% of baseline level, respectively; p < 0.05). After eating, the dopamine level returned to that before (105.6 ± 4.5% in obese rats and 101.9 ± 4.0% in lean rats) within the first 20 min sample. Data suggest that there may exist an inherently higher LHA DA ‘threshold’ level in obese Zucker rats and that until it is reached, food intake continues. This higher ‘threshold’ level may be responsible for their unique feeding behavior and is probably a contributory factor to their development of obesity.

AUTOMATED COMPUTERIZED RAT EATER METER : DESCRIPTION AND APPLICATION

A real-time Automated Computerized Rat Eater Meter was developed by modifying commercially available metabolic cages. Food access via a feeding tunnel was monitored by photocells. Food consumption was measured by an electronic scale. The signals thus generated were processed by a computer. This allowed us to continuously measure the spontaneous feeding behavior of free-feeding nondeprived Fischer rats for a sum total of 35 study days. Based on our data, we defined a meal as an episode of food consumption preceded and followed by at least 5 minutes of no feeding. Fischer rats showed periodic nychthemeral eating behavior. Food consumption, number of meals, meal sniffs, intermeal sniffs, and, consequently, eating activity were greater during the dark cycle than the light cycle. Meal duration, meal size, and thus food consumption rates remained constant throughout both cycles. Our modification of commercially available metabolic cages provides unique data for continuously monitoring rat feeding patterns over prolonged periods of time.

The early cancer anorexia paradigm: changes in plasma free tryptophan and feeding indexes.

Tumor growth is accompanied by an anorexia mediated by humoral factors that appear to influence appetitive mechanisms in the brain. Because tumor resection is followed by resumption of normal food intake, the circulating anorexigenic substance(s) are produced either by the neoplastic tissue or by the host in response to the tumor. Increased levels of plasma free tryptophan and plasma ammonia have been proposed to mediate cancer anorexia. With animal models, it is often difficult to ascertain whether changes in food intake depend upon metabolic changes or the progressively increasing tumor mass per se. The feeding patterns and biochemical changes that occur during tumor growth were evaluated in 96 male Fischer rats that were inoculated with 10(6) methylcholanthrene sarcoma cells or saline (controls). Rats were placed into metabolic cages equipped with an Automated Computerized Rat Eater Meter to continuously determine meal size and meal number. Plasma free tryptophan and ammonia were evaluated 6, 10, 16, 18, 22, and 26 days after tumor inoculation. Anorexia developed by day 17-18, when food intake started to decrease via a decrease in meal size but not meal number and reached 60% of control by day 26. However, long before anorexia developed, free tryptophan was significantly higher 6 days after tumor inoculation, and the greatest increase occurred after 18 days. Ammonia did not differ from control at any time. Data confirm tumor-associated increases in plasma free tryptophan that occurred before the manifestation of anorexia and support a possible role of brain serotonin in cancer anorexia.

Bilateral hypothalamic dopamine infusion in male Zucker rat suppresses feeding due to reduced meal size.

Lateral hypothalamic area dopamine activity (LHA-DA) appears to play a contributory role in regulating food intake, in particular, meal size. In this study we examined our hypothesis that bilateral LHA-DA injection induced depression of food intake via reduced meal size. Dopamine (11 mg/ml) or vehicle was infused into bilateral LHA at 0.5 microliter/h via two osmotic minipumps in six study or six control obese male Zucker rats for 13 days, respectively. Meal size, meal number, as well as food intake were continuously measured before, during, and after dopamine infusion. Intra-LHA-DA infusion significantly depressed food intake. The decreased food intake was solely caused by a significant and profound reduction in meal size. There was a modest compensatory rise in meal number that gradually increased food intake so that it reached control level on 10th dopamine infusion day. However, feeding pattern did not normalize until dopamine infusion ceased. The findings support our hypothesis that LHA-DA may participate in regulating meal size. Data also demonstrate that meal size and meal number are regulated in a reciprocal and independent manner to compensate for each other.

Interleukin-1α Injection Into Ventromedial Hypothalamic Nucleus of Normal Rats Depresses Food Intake and Increases Release of Dopamine and Serotonin

A microdialysis injector probe administered IL-1alpha into ventromedial hypothalamus (VMN) and concurrently measured release of dopamine (DA), DOPAC, 5-HT, and 5-HIAA. After baseline dialyses, six rats received 2-ng IL-1alpha and six rats received vehicle (1 microl saline) into VMN. Sixty minutes later, food was provided for 40 min while VMN monoamines were measured every 20 min. Vehicle had no significant effect on monoamines, their metabolites, or food intake. Food intake was significantly lower in IL-1alpha rats vs. controls (p < 0.01). Baseline levels of VMN monoamines (pg/10 microl dialysate) in IL-1alpha and vehicle groups were similar. DA and 5-HT rose immediately on injecting IL-1alpha and remained higher (p < 0.05) than basal during the first 60 min and 40 min sampling period, respectively. Levels of 5-HIAA also increased (p < 0.01). Eating decreased VMN DA in controls, and decreased VMN DOPAC in IL-1alpha-treated rats. During eating, VMN 5-HT in control rats significantly increased while increasing VMN 5-HIAA occurred in IL-1alpha rats. Findings show that an IL-1alpha pathophysiological dose injected into the VMN was associated with anorexia and significantly increased dopaminergic and serotonergic activities and suggest that enhanced VMN DA and 5-HT activities may be part of an IL-1alpha-initiated cascade involved in IL-1alpha-associated anorexia.