Neurohumoral and endocrine control of feeding

Anthropogenic Noise Aggravates the Toxicity of Cadmium on Some Physiological Characteristics of the Blood Clam Tegillarca granosa

Widespread applications of cadmium (Cd) in various products have caused Cd contamination in marine ecosystems. Meanwhile, human activities in the ocean have also generated an increasing amount of noise in recent decades. Although anthropogenic noise and Cd contaminants could be present simultaneously in marine environments, the physiological responses of marine bivalve mollusks upon coexposure to anthropogenic noise and toxic metal contaminants, including Cd remain unclear. Therefore, the combined effects of anthropogenic noise and Cd on the physiological characteristics of the blood clam Tegillarca granosa were investigated in this study. The results showed that 10 days of coexposure to anthropogenic noise and Cd can enhance adverse impacts on metabolic processes, as indicated by the clearance rate, respiration rate, ammonium excretion rate, and O:N ratio of T. granosa. In addition, both the ATP content, ATP synthase activity and genes encoding important enzymes in ATP synthesis significantly declined after coexposures to anthropogenic noise and Cd, which have resulted from reduced feeding activity and respiration. Furthermore, the expressions of neurotransmitter-related genes (MAO, AChE, and mAChR3) were all significantly down-regulated after coexposure to anthropogenic noise and Cd, which suggests an enhanced neurotoxicity under coexposure. In conclusion, our study demonstrated that anthropogenic noise and Cd would have synergetic effects on the feeding activity, metabolism, and ATP synthesis of T. granosa, which may be due to the add-on of stress responses and neurotransmitter disturbances.

A pathophysiologic approach to growth problems in children with attention-deficit/hyperactivity disorder

In recent years there has been an increasing trend in the diagnosis and treatment of children with attention-deficit/hyperactivity disorder (ADHD) worldwide. One of the most frequently discussed side effects of these treatments is related to problems of growth. In order to better understand what ADHD is and the mechanisms by which it could affect growth, this article reviews relevant data from a clinical and neurophysiologic perspective to improve understanding of this controversial issue.

Impairment of albuterol-induced suppression of food intake in diabetes mellitus

Albuterol (salbutamol), a beta 2 adrenoreceptor agonist, produced a dose-dependent decrease in food intake in Sprague-Dawley male control rats. This phenomenon appeared to be impaired in streptozotocin (STZ) diabetic rats. The density of beta 2 adrenoreceptors in the ventromedial hypothalamic nucleus was increased as a function of diabetes. In contrast, a decrease in the ventromedial hypothalamic 5-hydroxyindoleacetic acid (5-HIAA) concentration, an indicator of serotonin (5-hydroxytryptamine; 5-HT) release or turnover rate, was observed in this disease state. Neither the beta 2 adrenoreceptor level nor 5-HT turnover rate was altered in the periventricular hypothalamic nucleus of STZ diabetic rats. The concentrations of 5-HT in both hypothalamic nuclei were unchanged in these animals. Neurochemical and behavioral abnormalities featured in the diabetic state were reversed with institution of insulin therapy. These data conclude that diabetes-related impairment in the anorexic action of albuterol may be due to derangements in ventromedial hypothalamic beta 2 adrenoreceptor function.

Immunomodulators and feeding regulation: a humoral link between the immune and nervous systems

Cells of the nervous and immune systems have specific receptors for humoral substances that originate in both systems. These elements establish a bidirectional information exchange network between the nervous and immune systems. In particular, neuroregulators (neurotransmitters and neuromodulators) can modulate specific immune system function(s) and immunoregulators (immunomodulators) can modulate specific nervous system function(s). Modulation of immune functions by neuroregulators has been receiving considerable attention; however, modulation of nervous system functions by immunomodulators has been little studied. The presence of immunomodulators in the brain and cerebrospinal fluid may represent local synthesis by astrocytes, microglia, endothelial cells, intrinsic macrophages and blood-derived lymphocytes which cross the blood-brain barrier, or the concentration of substances derived from the peripheral blood. Acute and chronic inflammatory processes, malignancy, and immunological reactions stimulate the synthesis and release of immunomodulators in various cell systems. These immunomodulators have pivotal roles in the coordination of the host defense mechanisms and repair and induce a series of endocrine, metabolic, and neurologic responses. This paper focuses on the effects of immunomodulators (interleukins, tumor necrosis factor, tuftsin, platelet activating factor, and others) on the central nervous system (CNS), in particular, on feeding regulation. It is proposed that an immunomodulatory system regulates food intake by a direct action in the CNS through a specific neuro-immuno interaction. This regulatory system may be operative during acute and chronic disease.

Growth factors, feeding regulation and the nervous system

A variety of growth factors and their receptors are present in the nervous system. Growth factors can modulate specific nervous system functions others than those related to growth, development, and tissue repair. The presence of growth factors in the brain and cerebrospinal fluid is the result of local synthesis (by neuronal, glial, vascular, and mononuclear phagocyte components), and uptake from the peripheral blood through the blood-brain barrier (in specific cases) and circumventricular organs. This paper focuses on the effects of a heterogeneous group of growth factors (acidic and basic fibroblast growth factors, insulin-like growth factors, epidermal growth factor, platelet-derived growth factor, interleukin-1 and others) on the central nervous system (CNS), in particular, on feeding regulation. Recent evidence supporting participation of growth factors in the regulation of feeding by a direct action at the level of the CNS is reviewed. Various growth factors have the ability to suppress short- and long-term food intake (FI), whereas others affect only short-term FI, or do not affect FI. Acute and chronic pathological processes stimulate the synthesis and release of growth factors in various cellular systems, and monitoring of growth factors by the CNS could be part of the regulatory signals that induce FI suppression frequently accompanying acute and chronic disease. Thus, it is proposed that a system regulating FI through growth factor-dependent mechanisms may be operative during specific physiological or pathological conditions.

Neuropharmacology of drugs affecting food intake

The importance of the central monoamines NE, DA and 5-HT in ingestive behavior has inevitably resulted in considerable effort being expended in attempting to implicate these monoamines in the mechanism of action of anorectic drugs. The statements that amphetamine-induced anorexia is unlikely to be due to central serotoninergic systems and that central noradrenergic and dopaminergic systems are not implicated in the appetite suppressant effect of fenfluramine are in all probability correct. However, to attribute the ability of drugs to decrease food intake unequivocally to a specific effect on central monoaminergic systems is almost certainly an oversimplification, due to the fact that other putative neurotransmitters, such as GABA and peptides, play a critical role in eating. This can be achieved either directly or by modulating the release of other transmitters. An added complication in attempting to correlate a specific neurochemical process to a behavioral effect, such as anorexia, is the complexity of the central actions of the drug. At best, a predominant but not an exclusive process can be identified. Perhaps the in-built constraint of attempting to correlate a specific neurochemical effect to the desired action of a drug is accountable for the absence of a second generation of centrally acting anorectic drugs. Dramatic progress has been made in elucidating the factors involved in ingestive behavior over the last 5-10 years. This information should, and must, provide the catalyst for more efficacious anorectic drugs because obesity represents one of the few major diseases for which adequate drug therapy does not exist.

Selection for growth alters the feeding response to injections of biogenic amines

Two experiments were conducted to determine if selection for growth altered the response to intracerebroventricular (ICV) injections of methoxamine and 5-hydroxytryptamine (5-HT). Lines of chickens divergently selected over 25 generations for 8-week body weight were used. The ICV injection of methoxamine into fully fed birds significantly increased food intake in the high-weight line but had no effect on food intake in the low-weight line. Conversely, the ICV injection of 5-HT had no effect in fully fed birds but significantly decreased food intake in 24-hr fasted birds in both weight-lines. Food intake was affected by 5-HT for a much longer period in the high-weight line than in the low-weight line. These results suggest that selection for growth alters the brain response to biogenic amines.

Circannual variations of GABA content in cytosolic and crude synaptosomal fractions in some brain areas of the European hamster

In the European hamster, Cricetus cricetus, a common hibernator, over a year, the gamma-aminobutyric acid (GABA) content has been followed, in the cytosolic and crude synaptosomal fractions of the olfactory bulbs, hypothalamus and cerebellum. In these 3 areas, the GABA content shows circannual variations of endogenous origin: in this period, in both fractions two peaks can be observed, at the beginning of spring and in autumn. These circannual variations do not follow the circannual variation of food intake or body weight.

Energy balance and play in juvenile rats

These experiments systematically analyzed the relationship between energy balance and play in the juvenile rat. As expected, depriving pups of food for 24 hours or more resulted in a reliable reduction in levels of play, with a single meal being sufficient to return play to baseline levels. Consumption of saccharin did not reverse deprivation-induced reductions of play. It is proposed that the food-induced restoration of play in food-deprived pups is perhaps reflective of normal satiety and may be useful in screening putative "satiety agents." Naloxone, cholecystokinin and bombesin, all putative satiety agents, were tested for their ability to reverse deprivation-induced reduction of play. Only bombesin was marginally effective in increasing play of food deprived rats.

Autonomic and endocrine factors in the regulation of food intake

Destruction of the ventromedial hypothalamus produces hyperphagia, hyperinsulinemia and hypertriglyceridemia. These changes appear to be partly the result of increased firing rate of the vagus nerve and reduced firing rate of the sympathetic nerves. These reciprocal changes in the function of the autonomic nervous system appear to provide an adequate explanation for the hyperinsulinemia in this syndrome, and for the reduced heat expenditure. Destruction of the lateral hypothalamus, has effects opposite to those of the ventromedial hypothalamus with a reduction in food intake, a decrease in body fat, and an increase in the activity of the sympathetic nervous system. These reciprocal functions of the hypothalamus are associated with different adrenergic receptors. A medial hypothalamic alpha-adrenergic system mediates the epinephrine stimulation of feeding, and a beta-adrenergic system mediates the lateral hypothalamic inhibition of eating. Peptides from the endorphin family can stimulate food intake, but most other peptides are inhibitory. Growth hormone and thyroid hormone stimulate food intake under appropriate conditions. Insulin and adrenal steroids appear to play the most important role of all the hormones in regulating food intake. Deficiency of adrenal glucocorticoids is associated with decreased food intake and a wasting of body flesh. Increased levels of glucocorticoids, on the other hand, produce a variety of truncal obesity. In animals with ventromedial hypothalamic lesions and obesity, adrenalectomy will reverse the obesity. In genetically obese rats and mice, adrenalectomy will attenuate the progression of the syndrome. These effects appear to be through a reduction of food intake, and an increase in energy expenditure. Injections of insulin will stimulate food intake and may lead to obesity.(ABSTRACT TRUNCATED AT 250 WORDS)

Food intake control in birds

The regulation of food intake has been a topic of intense investigation for several decades. Most investigators have used the rat in such studies while considerably fewer studies have been conducted using birds. Research concerned with the control of food intake in birds is discussed herein. In most instances, birds and mammals have similar control mechanisms. The alimentary tract and the liver are peripheral structures which function in the control of feeding in birds but much remains to be studied as to their role. Many brain loci, including the lateral hypothalamus, ventromedial hypothalamus, striatum and olfactory bulbs are also involved in controlling food intake. Studies with birds have revealed marked breed and line differences in the response to factors modulating food intake. The bird appears to provide an excellent model for studies designed to investigate how selection for growth can alter the mechanisms involved in food intake control.

Effects of serotonin-depleting midbrain lesions on the defense of hypothalamic obesity

Previous research has suggested that lesions of the midbrain dorsal and median raphe nuclei may lower the level at which body weight is regulated in hypothalamic obesity. To test this possibility further, we examined the ability of adult female rats made obese by medial hypothalamic (MH) lesions to regain weight lost due to food deprivation after midbrain raphe lesions. We first verified that obese MH-lesioned rats would regain the weight lost during a one-week fast in the same manner as non-lesioned control rats. However, when raphe lesions were produced in both groups after a second week of fasting, the weight regain of MH-lesioned rats was impaired over a full month of access to standard laboratory chow. This deficit could not be attributed to generalized impairments in feeding or capacity to gain weight since MH + raphe-lesioned rats became hyperphagic and gained almost four times more weight than controls when subsequently allowed to consume a high fat diet. Terminal assays of forebrain serotonin, norepinephrine and dopamine revealed that raphe lesions depleted only serotonin. Furthermore, the magnitude of serotonin depletion correlated inversely with the number of days required by MH + raphe-lesioned rats to regain the deprivation-induced weight loss. These findings complement earlier observations that serotonin-depleting midbrain injury can impede the development of obesity induced by subsequent hypothalamic lesions. Both findings are compatible with the possibility that raphe lesions mitigate the elevation of body weight in hypothalamic obesity.

Suppression of feeding by sodium depletion in food-deprived rats

Food-deprived rats were depleted of sodium peritoneal dialysis (pd) against 5.0% glucose solution and offered food 24 h later. Food intake was suppressed compared with fasting sham-dialyzed controls, or controls dialyzed against Ringer-Tyrode. Sodium depletion by subcutaneous formalin also suppressed feeding. Measurements of osmolality and sodium chloride (NaCl) concentrations of the ascitic fluid showed that osmolality increased 19% mainly due to NaCl diffused 96.2 +/- 7.23 mEq/l. Consequently serum sodium concentration fell significantly (5.5% below control value). Serum potassium concentration did not change. Measurements of blood glucose levels showed that 1.87 g/l of glucose had been absorbed while it was in the peritoneum. Twenty four hours after sodium depletion, blood glucose levels of fasting sodium-depleted animals did not differ from nondepleted controls. Stomach load of glucose, in the same amount given for pd, did not suppress feeding in fasting rats 24 h later. Fasting sodium-depleted rats, offered 0.3 M NaCl to drink instead of food, drank as much as non-fasting sodium-depleted controls, ruling out the possibility of impaired behavior. Suppression of feeding was reversed in fasting sodium-depleted animals which were allowed to replace their sodium deficit by free-drinking or by stomach loading of sodium solutions. These results provide the first demonstration that depletion of sodium suppresses feeding in food-deprived rats.

GABA and endorphin mechanisms in relation to the effects of benzodiazepines on feeding and drinking

Behavioural actions of benzodiazepines have a number of significant characteristics. Anxiolytic effects are demonstrable both clinically and experimentally; in addition, there is excellent evidence for a reinforcing effect of these compounds, and a direct involvement in ingestional responses. This review focusses on the effects of benzodiazepines on the latter feeding and drinking responses. A necessary mediator of benzodiazepine action in the central nervous system appears to be the facilitation of inhibitory GABAergic neurotransmission. It follows, therefore, that behavioural consequences of benzodiazepine action may depend crucially on enhanced GABAergic activity in the brain. Evidence for some involvement of GABAergic mechanisms in the control of feeding and drinking responses is reviewed. Only a few data are so far available to link benzodiazepines effects on ingestional behaviour directly to GABAergic transmission. A major current theme in the psychopharmacology of feeding and drinking behaviour is the possible involvement of endogenous opioid peptides. There is a strong suggestion in the experimental data that there are links between benzodiazepine and endorphinergic mechanisms in relation to ingestional responses. A promising future line of approach appears to be a delineation of benzodiazepine-GABA-endorphin interrelations in the control of food and water consumption.

The role of norepinephrine in feeding behavior

When dopamine-beta-hydroxylase is inhibited with FLA-63 (10 mg/kg) free feeding behavior is disrupted in satiated rats. While the average number of meals taken was not different from vehicle injected controls, meal size was decreased 58% in the first 9 hr after treatment with FLA-63. In starved animals, FLA-63, when given alone, produced little effect on feeding behavior, even though norepinephrine depletion was in excess of 40%. When given in combination with RO4-1284 (5 mg/kg), a vesicular reuptake inhibitor, feeding was reduced to 16% of control intake and norepinephrine was specifically depleted 99%. Feeding was reliably reinstated in animals which received FLA-63 plus RO4-1284 with either dl-threo-DOPs, a metabolic precursor to NE, or direct intrahypothalamic injections of NE. These findings suggest that the feeding inhibition observed after treatment with FLA-63 plus RO4-1284 is due to disruption of transmission in brain NE systems. A non-anorectic dosage of L110-140 (3.73 mg/kg), a specific FLA-63. Taken collectively, these findings suggest that the primary role of NE in feeding is maintenance of the consummatory response and that these effects are expressed in relation to activity in other neurochemical systems.

THIP inhibits feeding behavior in fasted rats

The effects of 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridin-3-ol (THIP) were compared with those of d-amphetamine and GABA in fasted rats. Intravenously-administered THIP produced a dose-dependent decrease in food consumption (ED50 congruent to 1.5 mg/kg) by an action that was not reversed by prior subcutaneous or simultaneous intravenous (IV) injection of bicuculline. d-Amphetamine-SO4 also produced a decrease in food consumption in this model (ED50 congruent to 0.2 mg/kg, IV). Unlike THIP, GABA (in doses up to 100 mg/kg, IV) did not produce a marked anorexigenic effect. These results provide further evidence that THIP can penetrate the "blood-brain barrier", and that central GABA-ergic systems are involved in controlling food intake.

Feeding and drinking response of young chicks to injections of serotonin into the lateral ventricle of the brain

The effects of serotonin [5-hydroxytryptamine (5-HT)] on food intake and water consumption were investigated in young broiler chicks. Artificial cerebrospinal fluid containing either 0, 33, 67, or 100 microgram of 5-HT/10 microliter was injected into the lateral ventricle of either 24-hr fasted or fully fed chicks maintained in a thermoneutral environment with continuous lighting. Neither cannulation per se nor injection of 10 microliter of artificial cerebrospinal fluid had an effect on food intake or water consumption. Furthermore, food intake was not affected by 5-HT in fasted chicks. In fully fed chicks, however, food intake was significantly decreased by 67 and 100 microgram of 5-HT. Water consumption was affected by 5-HT injection in fully fed chicks. Results with fasted chicks remain equivocal. Data suggest that 5-HT may be involved in the neurohumoral control of food intake.

Influence of depression and antidepressants on weight

Depression is often combined with loss of appetite and weight. Treatment with some psychotropic drugs, especially many of the tricyclic antidepressives, causes weight gain. Zimelidine, an antidepressive drug with selective inhibitory effect on the reuptake of 5-hydroxytryptamine (5-HT) causes no weight gain in treated patients. As even weight loss is seen it can be discussed whether the drug has an inhibitory effect on feeding behaviour. This would be theoretical interest as animal experiments show that 5-HT may be an anorectic transmitter. It is also of practical importance as then the embarrassing side effect of weight gain might be avoided in antidepressive treatment.