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 microl, p < 0.01, and 0.68 +/- 0.05 vs 1.17 +/- 0.02 pg/10 microl, 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.

From food to nutritional support to specific nutraceuticals: a journey across time in the treatment of disease

Hospitalized patients who are unable to eat or cannot eat enough to meet their metabolic needs are given parenteral or enteral nutritional support. This form of therapy is now also given to patients at home. Nutritional support is a recent development, prior to which the value of food was recognized for its medicinal benefits as nutraceuticals. The value of such "alternative" therapy is now being rediscovered by many patients who enhance their dietary intake with these traditional remedies. In Western culture, conventional medicine until recently has largely rejected the use of such "alternative" therapeutic intervention. Based on an increasing database, though, insight has been gained concerning the scientific validity of many previously termed established nutraceuticals. We focus here on the effects of honey, green tea, ginseng, and vitamin supplementation on the immune system. Honey has proven antimicrobial activity. Green tea enhances humoral and cell-mediated immunity while decreasing the risk of certain cancers and the risk of cardiovascular disease. Ginseng enhances production of macrophages, B and T cells, natural killer cells, and colony-forming activity of bone marrow. Vitamin supplementation is associated with increased antibody titer response to both hepatitis B and tetanus vaccines as a result of macrophage and T cell stimulation. Because of these findings, nutraceuticals are becoming more widely accepted as an adjunct to conventional therapies for enhancing general well-being.

VMN dopaminergic graft and feeding pattern in obese Zucker rats

OBJECTIVE

To study the role of dopamine in the ventromedial hypothalamus (VMN) in the regulation of meal size and meal number during obesity.

METHODS

Embryonic mesencephalic cells rich in dopaminergic neurons from lean rats were grafted into the VMN of obese Zucker rats. Since food intake is the product of meal size and number, these variables were measured using a rat 'eater meter'. Dopamine and serotonin concentrations in the VMN were assayed in grafted and control rats via in vivo microdialysis and HPLC two months after transplantation.

RESULTS

Food intake increased in grafted rats due to an increase of both meal size and meal number 2 weeks after implantation and to an increase of meal size with insufficient compensatory decrease of meal number 2 months after transplantation. Grafted rats showed higher absolute dopamine and lower serotonin concentrations in the VMN.

CONCLUSION

It would appear that an increase of dopamine and a decrease of serotonin in the VMN of grafted obese rats may correlate with increase in meal number and meal size, respectively. Since obese Zucker rats usually display an enlarged meal size, we deduce from the data that chronically elevated VMN dopamine and low serotonin are involved in producing the large meal size observed during obesity.

VMN hypothalamic dopamine and serotonin in anorectic septic rats

During sepsis, catabolism of proteins and associated changes in plasma amino acids occur. Tryptophan and tyrosine, and their derivatives serotonin (5-HT) and dopamine (DA), influence hypothalamic feeding-related areas and are associated with the onset of anorexia. We hypothesized that anorexia of sepsis is associated with changes in serotonin and dopamine in the ventromedial nucleus (VMN) of the hypothalamus. The aim of this study was to test our hypothesis by measuring intra-VMN changes of these two neurotransmitters at the onset of anorexia during sepsis. Fischer 344 male rats had an intracerebral guide cannula stereotaxically implanted into the VMN. Ten days later, in awake, overnight-food-deprived rats, a microdialysis probe was inserted through the in situ VMN cannula. Two hours thereafter, serial baseline serotonin and dopamine concentrations were measured. Then cecal ligation and puncture to induce sepsis or a control laparotomy was performed under isoflurane anesthesia. VMN microdialysis samples were serially collected every 30 min for 8 h after the surgical procedure to determine 5-HT and DA changes in response to sepsis. During the hypermetabolic response to sepsis, a strong association occurred between anorexia and a significant reduction of VMN dopamine concentration (P < 0.05; constant rate of dopamine decrease in the Study group of 0.99 pg per 2 h); no changes occurred in 5-HT in association with anorexia of sepsis. Six hours after operation, a single meal was offered for 20 min to assess the response of neurotransmitters to food ingestion. Food intake was minimal in anorectic septic rats (mean size of the after food-deprived meal in the Septic group was 0.03+/-0.01 g, that of the Control group was 1.27+/-0.14 g; P = 0.0001), while Control rats demonstrated anticipated changes in neurotransmitters in response to eating. We conclude that the onset of anorexia in septic rats is associated with a reduction in VMN dopamine.

Effects of intra-VMN mianserin and IL-1ra on meal number in anorectic tumor-bearing rats

BACKGROUND

Tumor growth in animals and humans is associated with the onset of anorexia and reduced food intake. We previously demonstrated that the ventromedial nucleus of hypothalamus (VMN) plays a contributory role in mediating cancer anorexia. Because serotonin and interleukin-1 (IL-1) are putative mediators of cancer anorexia, we hypothesized that their influence on food intake during tumor growth might occur via their action within the VMN.

METHODS

To test this hypothesis, 12 Fischer rats injected subcutaneously with 10(6) viable MCA sarcoma cells (TB rats) and their nontumor-bearing controls (NTB, n = 13) were studied. When anorexia developed, TB and NTB rats received bilateral intra-VMN microinjections of the serotonin antagonist mianserin (200 nmol) or the IL-1 receptor antagonist (IL-1ra, 25 ng). Food intake and its determinants of meal number and size were continuously recorded via a computerized device.

RESULTS

In NTB rats, intra-VMN mianserin did not affect food intake, whereas after IL-1ra or vehicle a momentary decrease in food intake due to a predominant reduction of meal size occurred. In TB rats, intra-VMN mianserin or IL-1ra selectively increased meal number, leading to improved food intake.

CONCLUSIONS

Data suggest that intra-VMN serotonin and IL-1 are involved in influencing cancer related anorexia.

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 estradiol's effect on these indicies.

Hypophysial and meningeal melanocytes in the Zucker rat

Melanocytes have not been described in the pituitary of mammals or in the meninges of the rat. In this paper, we report the presence of the cluster of melanocytes in the intermediate lobe of the pituitary and around the median eminence of the hypothalamus forming an 'infundibulo-hypophysial circle', and also describe the characteristics of meningeal melanocytes in Zucker rats. In the leptomeninges, numerous melanocytes were found on the ventrolateral surface of cerebral hemisphere in the area of the middle cerebral artery. Pigment granules were also observed in the surrounding tissue outside the melanocytes as well as incorporated in the cytoplasm of neural and epithelial cells. Electron microscopy revealed that melanosomes in hypophysial and meningeal melanocytes were in different (II-IV) stages of maturity. In the leptomeninges of Zucker rats, HMB-45 immunoreactivity was found in round non-melanosome-containing cells, while no HMB-45 reaction was found in the leptomeninges of the albino rat. We conclude that both obese and lean Zucker rats possess functionally active melanocytes in the meninges and the pituitary and transfer pigment granules to neighboring cells. The distributions of melanocytes in proximity to blood vessels in the leptomeninges and in the 'infundibulo-hypophysial circle' suggest an endocrine secretory function.

The normal breast epithelium of women with breast cancer displays an aberrant response to estradiol

Breast epithelial response to estradiol may play an important role in breast cancer etiology. We have examined the relationship between serum estradiol and progesterone levels and normal breast epithelial expression of estrogen receptor (ER) alpha, progesterone receptor (PgR), and epithelial proliferation (as reflected by the Ki-67 labeling index) in 121 women (50 newly diagnosed breast cancer cases and 71 benign breast disease controls). Simultaneous samples of grossly normal breast tissue and venous blood were obtained from women undergoing breast surgery. Serum estradiol and progesterone levels were measured by radioimmunoassay; breast epithelial ER, PgR, and Ki-67 expression was measured by immunohistochemistry. Linear regression, controlled for patient age and ductal and lobular composition of the tissue, showed that the breast epithelium of control women displayed an inverse correlation between serum estradiol and ER-alpha, which was not seen in case women (P for the difference in regression slopes = 0.001). PgR expression displayed a significant positive correlation with serum estradiol in cases, but not in controls. Epithelial proliferation had no relationship to either estradiol or progesterone in both cases and controls but showed an inverse relationship with ER in controls and a direct relationship in cases (P for the difference in regression slopes = 0.066). These results suggest a dysregulation of hormonal response in the normal breast epithelium of high-risk women, with lack of regulation of ER by estradiol, increased estrogen responsiveness as reflected by PgR expression, and a dissociation of ER expression and proliferative response.

Use of TPN in terminally ill cancer patients

Total parenteral nutrition (TPN) is often used as an adjunct to cancer therapy. However, it is increasingly being used in terminally ill cancer patients without clearly defined reasons. To determine the validity of the use of TPN in terminally ill cancer patients, 26 patients with limited life expectancy due to end-stage cancer were given TPN by their physicians, and the validity of its use was evaluated using the criteria of 1) quality of life, and 2) ultimate outcome. Patients were divided into two groups according to the use of TPN. Group I = TPN as adjunct of medical therapy, n = 15 (eight male, seven female), mean age 32 y. Group II = TPN for in-hospital supportive care, n = 11 (two male, nine female), mean age 56 y. Nutritional status on admission, quality of life (assessed by extent of daily activities, pain, and ability to sustain oral intake), and ultimate treatment outcome were determined. Mean weight loss in patients in Group I was 8.6 kg, 11 patients out of 15 were malnourished; mean weight loss in patients in Group II was 21 kg, and all of the 11 patients belonging to this group were malnourished. Two patients of Group I improved their quality of life, while 6 declined and 7 died; in Group II, 3 improved their quality of life, 4 declined, and 4 died. We conclude that when TPN was given either as an adjunct to in-hospital aggressive therapy for cancer or for in-hospital supportive care, quality of life did not improve in the majority of patients; nor did it influence ultimate outcome. These objective data, thus, raise the question of the validity of the use of TPN in terminally ill cancer patients. However, barring the cost factor, it is recognized that subjective reasons for giving TPN to terminally ill cancer patients persist and include compassionate, ethical, religious, or emotional reasons.

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.

Use of recombinant human soluble TNF receptor in anorectic tumor-bearing rats

With progression of tumor growth, rats demonstrate anorexia and reduced food intake, a function of meal number and meal size. Tumor necrosis factor-alpha (TNF-alpha), a recognized anorectic agent, reacts with two different receptors (type I: 55 kDa; type II: 75 kDa). We used a dimeric, pegylated 55-kDa TNF receptor construct to test its effects on food intake, meal number, and meal size, which were continuously measured with a rat eater meter in 16 Fischer 344 male rats injected with 10(6) viable methylcholanthrene cells. When anorexia developed, rats received a subcutaneous injection of either 0.25 mg/kg body wt of soluble TNF receptor construct (study) or vehicle (tumor-bearing control). Before TNF inhibitor injection, no differences were observed in food intake, meal number, or meal size between the two groups. After the TNF inhibitor injection, study vs. control rats significantly improved food intake as a result of an increase in meal number and meal size. Rats also showed a significant improvement in body weight. These data suggest that TNF-alpha, in addition to other cytokines, contributes to the anorexia of tumor growth, probably mediated via the hypothalamus.

Nicotine's effect on hypothalamic neurotransmitters and appetite regulation

BACKGROUND

Tobacco smoking reduces appetite and body weight. Cessation of smoking leads to hyperphagia and weight gain. Food intake is a function of meal number (MN) and meal size (MZ) (i.e., Food intake = MN x MZ). The effect of nicotine on these feeding components and their relationships to dopamine and serotonin in the lateral hypothalamic area (LHA) were determined.

METHODS

In Fischer-344 rats the effect of 7 days of systemic nicotine infusion on the feeding patterns was measured by rat eater meter and changes in serotonin (5HT) and dopamine (DA) in the LHA were measured by in vivo microdialysis.

RESULTS

Nicotine infusion caused hypophagia through a significant decrease in MN with a smaller decrease in MZ, resulting in a body weight reduction. 5HT and DA concomitantly increased in LHA. Stopping nicotine resulted in hyperphagia by a significant increase in MZ. Body weight normalized. 5HT and DA in LHA decreased after nicotine was stopped.

CONCLUSION

Nicotine's hypophagic effect was associated with increased 5HT and DA in LHA, whereas hyperphagia after nicotine cessation was accompanied by decreased concentrations of the neurotransmitters. These findings suggest that nicotine affects appetite regulation, in part by modulation of LHA-DA and 5HT.

Differential feeding patterns induced by tumor growth and by TPN

The effects of anorexia induced by early tumor, and anorexia induced by total parenteral nutrition (TPN) on food intake and the indexes of food intake, were investigated in rats infused with saline after jugular catheter placement and concomitant inoculation with methylcholanthrene (MCA)-induced tumor cells on day 0, and in rats without catheters receiving tumor only. Tumor became palpable around day 10 and increased to represent 6-8% of host body weight by day 26. On day 18, food intake started to decrease. Catheter-bearing rats were then randomized to saline controls (n = 9) for 11 d or to TPN-100 (n = 9) for 4 d providing 100% of daily caloric needs. Both then received saline until day 26. Food intake and feeding indexes were continuously measured using the Automated Computerized Rat Eater Meter (ACREM) and data was analyzed using ANOVA and regression analysis. In controls (both with and without catheter) the tumor induced a specific feeding pattern which consisted of a significant (P < 0.01) decrease in food intake via a significant (P < 0.05) decrease in meal size. A non-significant decrease in meal number and meal duration occurred. Two other feeding-related activities, meal consumption rate and intermeal sniffs, also decreased. Infusion of TPN-100 into the already anorectic rat led to a further significant (P < 0.0001) decrease in food intake via a significant decrease in both meal size (P < 0.0001) and in meal number (P < 0.0001). A decrease in all other feeding indexes also occurred, resulting in a different feeding pattern. After stopping TPN-100, the TPN-100-induced feeding pattern returned to that of the tumor-induced feeding pattern. That the tumor-induced feeding pattern differs from the TPN-100-induced feeding pattern suggests that the mechanisms whereby these two factors induce anorexia may also differ.

Lack of influence of hysterectomy on meal size and meal number in Fischer-344 rats

Based on our previous observation that, when eating the same amount of food per 100 g b.wt., male rats gain five to seven times more weight than females who have an estrous cycle every 4 to 5 days, we questioned whether lower weight gain seen in female rats could be the result of increased energy cost in preparing endometrium for anticipated fertilization. Because the uterus modulates estrogenic effects on other hormone-dependent behaviors, for example, sexual receptivity and lordosis, we performed this study to determine if estrogen-mediated cyclical changes in food intake and feeding pattern occur after hysterectomy. Fifteen female Fischer 344 rats were randomized during the estrous phase to either hysterectomy with ovarian preservation or sham operation. A rat eater meter was used to continuously measure food intake, meal number, and meal size for two estrous cycles before and four cycles after surgery. Both groups showed the estrous phase linked cycling in meal number, meal size, and food intake. No differences existed between the two groups in these indices either before or after surgery. No differences existed between groups in rate of body weight gain after surgery, 0.95 +/- 0.13 g/day in hysterectomized and 0.77 +/- 0.1 g/day in sham-operated rats. We conclude that hysterectomy has no effect on rate of weight gain, food intake, and estrus linked cyclical feeding pattern in Fischer 344 rats.