Observations on predicted brain influx rates of neurotransmitter precursors. Effects of tumor, operative stress with tumor removal, and postoperative TPN of varying amino acid compositions

Acute heat stress up-regulates neuropeptide Y precursor mRNA expression and alters brain and plasma concentrations of free amino acids in chicks

Heat stress causes an increase in body temperature and reduced food intake in chickens. Several neuropeptides and amino acids play a vital role in the regulation of food intake. However, the responses of neuropeptides and amino acids to heat-stress-induced food-intake regulation are poorly understood. In the current study, the hypothalamic mRNA expression of some neuropeptides related to food intake and the content of free amino acids in the brain and plasma was examined in 14-day-old chicks exposed to a high ambient temperature (HT; 40±1 °C for 2 or 5 h) or to a control thermoneutral temperature (CT; 30±1 °C). HT significantly increased rectal temperature and plasma corticosterone level and suppressed food intake. HT also increased the expression of neuropeptide Y (NPY) and agouti-signaling protein (ASIP) precursor mRNA, while no change was observed in pro-opiomelanocortin, cholecystokinin, ghrelin, or corticotropin-releasing hormone precursor mRNA. It was further found that the diencephalic content of free amino acids - namely, tryptophan, leucine, isoleucine, valine and serine - was significantly higher in HT chicks with some alterations in their plasma amino acids in comparison with CT chicks. The induction of NPY and ASIP expression and the alteration of some free amino acids during HT suggest that these changes can be the results or causes the suppression of food intake.

Hypothalamic integration of immune function and metabolism

The immune and neuroendocrine systems are closely involved in the regulation of metabolism at peripheral and central hypothalamic levels. In both physiological (meals) and pathological (infections, traumas and tumors) conditions immune cells are activated responding with the release of cytokines and other immune mediators (afferent signals). In the hypothalamus (central integration), cytokines influence metabolism by acting on nucleus involved in feeding and homeostasis regulation leading to the acute phase response (efferent signals) aimed to maintain the body integrity. Peripheral administration of cytokines, inoculation of tumor and induction of infection alter, by means of cytokine action, the normal pattern of food intake affecting meal size and meal number suggesting that cytokines acted differentially on specific hypothalamic neurons. The effect of cytokines-related cancer anorexia is also exerted peripherally. Increase plasma concentrations of insulin and free tryptophan and decrease gastric emptying and d-xylose absorption. In addition, in obesity an increase in interleukin (IL)-1 and IL-6 occurs in mesenteric fat tissue, which together with an increase in corticosterone, is associated with hyperglycemia, dyslipidemias and insulin resistance of obesity-related metabolic syndrome. These changes in circulating nutrients and hormones are sensed by hypothalamic neurons that influence food intake and metabolism. In anorectic tumor-bearing rats, we detected upregulation of IL-1beta and IL-1 receptor mRNA levels in the hypothalamus, a negative correlation between IL-1 concentration in cerebro-spinal fluid and food intake and high levels of hypothalamic serotonin, and these differences disappeared after tumor removal. Moreover, there is an interaction between serotonin and IL-1 in the development of cancer anorexia as well as an increase in hypothalamic dopamine and serotonin production. Immunohistochemical studies have shown a decrease in neuropeptide Y (NPY) and dopamine (DA) and an increase in serotonin concentration in tumor-bearing rats, in first- and second-order hypothalamic nuclei, while tumor resection reverted these changes and normalized food intake, suggesting negative regulation of NPY and DA systems by cytokines during anorexia, probably mediated by serotonin that appears to play a pivotal role in the regulation of food intake in cancer. Among the different forms of therapy, nutritional manipulation of diet in tumor-bearing state has been investigated. Supplementation of tumor bearing rats with omega-3 fatty acid vs. control diet delayed the appearance of tumor, reduced tumor-growth rate and volume, negated onset of anorexia, increased body weight, decreased cytokines production and increased expression of NPY and decreased alpha-melanocyte-stimulating hormone (alpha-MSH) in hypothalamic nuclei. These data suggest that omega-3 fatty acid suppressed pro-inflammatory cytokines production and improved food intake by normalizing hypothalamic food intake-related peptides and point to the possibility of a therapeutic use of these fatty acids. The sum of these data support the concept that immune cell-derived cytokines are closely related with the regulation of metabolism and have both central and peripheral actions, inducing anorexia via hypothalamic anorectic factors, including serotonin and dopamine, and inhibiting NPY leading to a reduction in food intake and body weight, emphasizing the interconnection of the immune and neuroendocrine systems in regulating metabolism during infectious process, cachexia and obesity.

Anorexia in space and possible etiologies: an overview

Space travelers experience a flight duration-dependent loss in weight and body mass while in a microgravity environment, despite the absence of increased energy expenditure. Anorexia in space can lead to in-flight caloric deficits of 1330 kcal per 70 kg astronaut per day in the presence of abundant food and has a critical effect on endurance and performance. Microgravity, alterations in the light-and-dark cycle, and exposure to radiation energy are the environmental stresses believed to influence appetite, food intake, and gastrointestinal function during space flight. Review of data and recent studies in rodents during microgravity showed a release of stress hormones and complex neuroendocrine and physiologic changes involving the modulation of hypothalamic activity, food intake-related hormones, and cytokines. The shift of dietary preference to carbohydrates, which occurs in astronauts, denotes a stress physiologic response and augments free-plasma tryptophan concentration in the brain, the precursor of the potent anorexic agent, serotonin (5-HT). Alterations of other neuroendocrine mediators, including corticotropin-releasing factor (CRF), coordinate the stress response, leading to a decrease in appetite and gastrointestinal function. Our laboratories used the antiorthostatic tail-suspension technique to successfully mimic some of these anorexia-related stress responses and to directly demonstrate the role of 5-HT in microgravity-related decreased food intake and delayed gastric emptying. Further rodent studies from our laboratories demonstrated the adverse effect of altered dark-and-light cycles on food intake and body weight. Radiation energy, through its documented effects on appetite, probably contributes to the decreased caloric intake by astronauts. Modulation of hypothalamic activity, 5-HT, and CRF play a critical role in anorexia related to microgravity and circadian rhythm alterations. Specific gene knockout mice (e.g., 5-HT or CRF and their respective receptors) may prove fruitful in defining the pathways by which anorexia in space occurs. An understanding of these pathophysiologic problems as they relate to appetite, food intake, gastric emptying and gastrointestinal function, sufficiently to derive successful practical solutions, may lead to a quantitative enhancement of physiologic well-being and performance status, serving as a productive countermeasure in space.

Hypothalamic dopamine and serotonin in the regulation of food intake

Because daily food intake is the product of the size of a meal and the frequency of meals ingested, the characteristic of meal size to meal number during a 24-h light-dark cycle constitutes an identifiable pattern specific to normal states and obesity and that occurs during early cancer anorexia. An understanding of simultaneous changes in meal size and meal number (constituting a change in feeding patterns) as opposed to an understanding of only food intake provides a more insightful dynamic picture reflecting integrated behavior. We have correlated this to simultaneous changes in dopamine and serotonin concentrations and to their postsynaptic receptors, focusing simultaneously on two discrete hypothalamic food-intake-related nuclei, in response to the ingestion of food. The relation between concentrations of dopamine and serotonin limited to the lateral hypothalamic area (LHA) and the ventromedial nucleus (VMN) as they relate to the influence of meal size and meal number during the hyperphagia of obesity and anorexia of cancer as measured in our experiments are discussed. Based on these data, conceptual models are proposed concerning: 1) an "afferent-efferent neurotransmitter unit," with facilitatory or inhibitory neuropeptide properties to generate an appropriate neuroendocrine and neuronal response that ultimately modifies food intake; 2) initiation and termination of a meal, thereby determining the number and size of a meal under normal conditions; and 3) a schema integrating the onset mechanism of cancer anorexia. Nicotine is used as a tool to further explore the relation of meal size to meal number, with a focus on simultaneous changes in dopamine and serotonin concentrations in the LHA and VMN with the onset of acute anorexia of nicotine infusion and acute hyperphagia of nicotine cessation. Data concerning the role of sex-related hormones on dopamine and serotonin with regard to the LHA and VMN in relation to the modulation of food intake are also presented.

Studies on the regulation of food intake using rat total parenteral nutrition as a model

Total parenteral nutrition (TPN) is essential for maintaining the nutritional status of patients who are unable to eat sufficiently to meet their metabolic needs. However, TPN suppresses appetite and ultimately diminishes food intake. Theories concerning the role(s) of peripheral metabolites as signals, acting via the liver and the hypothalamus, for the metabolic control of food intake, have been put forward to explain the anorectic effect of TPN. In addition, it is postulated that changes in peripheral metabolites during TPN may be translated into changes in the levels of brain neurotransmitters known to decrease food intake. This review summarizes studies concerning the effect of TPN on food intake. These studies have involved: (1) characterizing the changes in feeding activity due to TPN; (2) investigating the involvement of the central nervous system; and (3) investigating the role of the periphery and its metabolites in the regulation of food intake during TPN. Some insight into the mechanism of action of TPN on food intake is provided.

High-performance liquid chromatographic analysis with electrochemical detection of biogenic amines using microbore columns

High-performance liquid chromatography with electrochemical detection (HPLC-ED) is a popular method for measuring biogenic amines, owing to its simplicity, versatility, sensitivity, and specificity. Recent developments in microbore column HPLC-ED have been facilitated by miniaturization of solvent delivery, column packing, sample injection and micro-flow cell construction. The aim of this paper is to present an overview of recent developments in microbore column HPLC-ED, in terms of advantages and limitations. This paper covers the recent advancements and important factors of HPLC-ED analysis of biogenic amines using microbore columns. Particular emphasis is placed on applying this technique to microdialysis, for which great sensitivity is required. Its potential in future biomedical applications is also discussed.

The comparative effects of abrupt vs. stepwise discontinuation of TPN in rats

The comparative effects of discontinuing total parenteral nutrition (TPN: caloric ratio of glucose:fat:amino acid = 50:30:20) abruptly or in a stepwise manner on spontaneous food intake were investigated in two studies. Study 1: In 16 rats, TPN was given for 4 days, then stopped abruptly in eight rats. In the other eight rats, TPN was tapered; they received TPN at 75%, 50%, and 25% of their mean daily energy requirements per day for 3 consecutive days, and then switched to normal saline. Total parenteral nutrition induced a significant 60% reduction in spontaneous food intake (SFI) in both groups during the first TPN day. After 4 days of TPN, an 80% decrease in SFI had occurred in both groups. Resumption of SFI was significantly sooner in the abruptly-stopping group than in the stepwise-stopping group. But, in the latter group, there was a significantly greater cumulative caloric intake during the entire study. Study 2: In 32 rats, TPN providing either 100%, 50%, or 25% of their mean daily caloric requirements was given to three groups each of eight rats, for 3 days, then abruptly changed to normal saline; control rats received normal saline throughout. The TPN-induced decrease in SFI was proportional to the caloric density of the solution infused. Three days of 100%, 50%, or 25% TPN infusion led to an approximate 85%, 60%, or 35% decrease in SFI, respectively. Spontaneous food intake recovery was independent of the caloric density of TPN.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of anterior subdiaphragmatic vagotomy and TPN on rat feeding behavior

Total parenteral nutrition (TPN) inhibits food intake and feeding behavior. Whether caloric sensory function of the liver contributes to this food intake and feeding behavior regulation via vagal-afferent innervation was tested after performing anterior hepatic vagotomy or sham operation in rats infused with a TPN solution providing 100% of daily energy needs, given continuously for 4 days. Food intake, meal number, size, duration, meal and intermeal sniffs, and eating activity were measured using an automated computerized rat eater meter (ACREM). TPN infusion resulted in a significant decrease of food intake and feeding indexes in both groups. The vagotomized rats showed a significantly higher food consumption, achieved by greater meal frequency, larger meal size, and longer meal duration. Thus, vagotomized rats consumed more than their controls by eating larger meals more often and of longer duration. Data suggest that anterior hepatic vagotomy interrupts hepatic caloric sensory feedback loop, diminishing inhibitory vagal effects on food intake with TPN, leading to an overall increase in food intake.

Change in meal size, number and duration after neural isolation of liver and with TPN

The abundant neural connections between the liver and hypothalamus suggest that the liver contributes to spontaneous food intake (SFI) regulation. This hypothesis was tested in rats after total liver denervation (TLD) and infusing TPN. A sham operation (SO) or TLD was performed in Fischer rats, placed in metabolic cages fitted with an Eater Meter to measure SFI, meal number (MN), size (MZ), and duration (MD). Rats had free access to chow and water. After 22 days, a jugular catheter was placed and normal saline continuously infused for 10 days (days 22-32). Then TPN-100, providing 100% of rats daily energy needs, was infused for 3 days (days 32-35). During the post-SO/TLD and postjugular catheterization periods and during TPN-100, SFI was the same in SO controls and TLD group. However, TLD rats had decreased MZ and MD (interpreted as early satiety) and increased MN (interpreted as increased hunger) to maintain the same SFI as control rats. Although total SFI was not influenced by TLD, it significantly affected feeding pattern, suggesting that the neural isolation of the liver from the brain produces altered hypothalamic regulation of not only the onset of feeding, but also satiety.

Effects of continuous graded total parenteral nutrition on feeding indexes and metabolic concomitants in rats

The influence of graded amounts of total parenteral nutrition (TPN) on food intake and feeding indexes was investigated in 90 rats housed in Automated Computerized Rat Eater Meter metabolic cages with free access to water and chow. When food intake was stable after catheter placement, 10 control rats continued with the 3 ml/h normal saline used for catheter patency, whereas study rats were given graded TPN continuously for 3 days, amounting to the equivalent of 26% (TPN-26), 53% (TPN-53), 81% (TPN-81), or 114% (TPN-114) of their daily caloric needs. TPN consisted of glucose, fat, and amino acids in the caloric ratio of 50:30:20. In study rats, the graded TPN depressed food intake, meal number, meal size, and eventually food consumption rate, meal sniffs, and intermeal sniffs in a dose- and time-dependent manner. During graded TPN, rats decreased total food intake by eating fewer, smaller, shorter meals at a decreasing consumption rate; sniffing activities were correspondingly curtailed. Stopping TPN led to normalization of feeding indexes. Blood glucose did not change while plasma insulin rose with graded TPN. A decrease in hepatic glycogen and an increase in hepatic triglycerides occurred. Plasma valine, phenylalanine, and methionine rose in a TPN dose-dependent manner. TPN-26 and TPN-53 significantly decreased whole brain amino acids; with TPN-114 no change occurred. Brain influx of tryptophan remained unchanged, but a progressive decrease in brain influx of tyrosine occurred. Whole brain dopamine and serotonin were depressed with TPN-26 and TPN-81 but were normal with TPN-114.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of tryptophan and cyproheptadine on food intake

Whether tryptophan in the usual dose found in total parenteral nutrition (TPN) solutions caused a decrease in food intake was investigated in 16 adult male Fischer 344 rats. A jugular venous catheter was placed, and patency was maintained with a continuous infusion of normal saline at 3 ml/hr. After a 10-day recovery period, eight normal saline control rats were sacrificed and the remaining eight rats were given a parenteral nutrition solution (PN-50) at 3 ml/hr, providing 50% of the rat's daily energy requirement as 5% dextrose and 2% Intralipid. On day 14, study rats were further divided into two subgroups. Subgroup A received tryptophan (180 mg/day) added to the solution for 5 days. Subgroup B received the serotonin-receptor blocker, cyproheptadine 24 mg/kg/day, continuously for 5 days, and on day 16, tryptophan (0.25% = 180 mg/kg/day) was added to the solution for 3 days. Chow and water was continuously available and spontaneous food intake was measured daily. Study rats were sacrificed on day 19. Plasma amino acids and insulin and whole brain biogenic amines were compared with those in control rats using Student's t-test. With administration of PN-50, spontaneous food intake decreased to about 60% compared with the pre-PN level. The addition of tryptophan to the continuous infusion of PN-50 did not decrease spontaneous food intake further.(ABSTRACT TRUNCATED AT 250 WORDS)