Food intake suppression by histidine

Side Effects of Amino Acid Supplements

The aim of the article is to examine side effects of increased dietary intake of amino acids, which are commonly used as a dietary supplement. In addition to toxicity, mutagenicity and carcinogenicity, attention is focused on renal and gastrointestinal tract functions, ammonia production, and consequences of a competition with other amino acids for a carrier at the cell membranes and enzymes responsible for their degradation. In alphabetic order are examined arginine, β-alanine, branched-chain amino acids, carnosine, citrulline, creatine, glutamine, histidine, β-hydroxy-β-methylbutyrate, leucine, and tryptophan. In the article is shown that enhanced intake of most amino acid supplements may not be risk-free and can cause a number of detrimental side effects. Further research is necessary to elucidate effects of high doses and long-term consumption of amino acid supplements on immune system, brain function, muscle protein balance, synthesis of toxic metabolites, and tumor growth and examine their suitability under certain circumstances. These include elderly, childhood, pregnancy, nursing a baby, and medical condition, such as diabetes and liver disease. Studies are also needed to examine adaptive response to a long-term intake of any substance and consequences of discontinuation of supplementation.

Targeting Histamine and Histamine Receptors for the Precise Regulation of Feeding

Histamine has long been accepted as an anorexigenic agent. However, lines of evidence have suggested that the roles of histamine in feeding behaviors are much more complex than previously thought, being involved in satiety, satiation, feeding motivation, feeding circadian rhythm, and taste perception and memory. The functional diversity of histamine makes it a viable target for clinical management of obesity and other feeding-related disorders. Here, we update the current knowledge about the functions of histamine in feeding and summarize the underlying molecular and neural circuit mechanisms. Finally, we review the main clinical studies about the impacts of histamine-related compounds on weight control and discuss insights into future research on the roles of histamine in feeding. Despite the recent progress in histamine research, the histaminergic feeding circuits are poorly understood, and it is also worth verifying the functions of histamine receptors in a more spatiotemporally specific manner.

Bilberry (Vaccinium myrtillus L.) Extracts Comparative Analysis Regarding Their Phytonutrient Profiles, Antioxidant Capacity along with the In Vivo Rescue Effects Tested on a Drosophila melanogaster High-Sugar Diet Model

Bilberries (Vaccinium myrtillus L.) have been reported to hold a plentitude of health-promoting properties beyond basic nutrition, mainly attributed to their anthocyanin content and antioxidant activity. In this article, we built the phytochemical profile of three wild bilberry fruit extract formulations (aqueous, methanolic, and hydro-methanolic) using UHPLC-ESI-MS/MS putative analysis, identifying 88 individual phytochemicals, mainly flavonoids (total content 8.41 ± 0.11 mg QE/g dw), free amino acids, polyphenols (total content 21.68 ± 0.19 mg GAE/g dw), carboxylic acids, and vitamins. Furthermore, the antioxidant activity of the extract was assessed, reaching 78.03 ± 0.16% DPPH free radical scavenging activity, comparable to literature values determined for bilberry extracts of other origin. Due to the increased prevalence of metabolic syndrome and based on the reviewed benefits of bilberries, we tested the most potent formulation of our bilberry extracts in this biological context. The in vivo rescue effect of a bilberry extract supplemented diet on Drosophila melanogaster was assessed by monitoring biochemical and genomic markers. Hemolymph trehalose levels were halved upon addition of 3% hydro-methanolic bilberry extract to a high-sugar (1.5 M sucrose) diet, as compared to the non-supplemented high-sugar diet. Noteworthy, the rescue seen for flies kept on the bilberry extract supplemented high-sugar diet appeared to parallel the trehalose levels observed in the case of the control diet (50 mM sucrose) flies. Moreover, next to the trehalose-lowering type of in vivo effects, other gene expression related rescues were also detected for genes such as InR, Akh, AstA, AstC, Irk, Npc2g, and CCHa2 upon supplementation of the high-sugar diet with our hydro-methanolic bilberry fruit extract. Our findings suggest that such a bilberry fruit extract could generate physiological and genomic type of compensatory mechanisms so that further translational approaches would advance the understanding of some human specific pathological conditions.

Influence of Histidine Administration on Ammonia and Amino Acid Metabolism: A Review

Histidine (HIS) is an essential amino acid investigated for therapy of various diseases, used for tissue protection in transplantation and cardiac surgery, and as a supplement to increase muscle performance. The data presented in the review show that HIS administration may increase ammonia and affect the level of several amino acids. The most common are increased levels of alanine, glutamine, and glutamate and decreased levels of glycine and branched-chain amino acids (BCAA, valine, leucine, and isoleucine). The suggested pathogenic mechanisms include increased flux of HIS through HIS degradation pathway (increases in ammonia and glutamate), increased ammonia detoxification to glutamine and exchange of the BCAA with glutamine via L-transporter system in muscles (increase in glutamine and decrease in BCAA), and tetrahydrofolate depletion (decrease in glycine). Increased alanine concentration is explained by enhanced synthesis in extrahepatic tissues and impaired transamination in the liver. Increased ammonia and glutamine and decreased BCAA levels in HIS-treated subjects indicate that HIS supplementation is inappropriate in patients with liver injury. The studies investigating the possibilities to elevate carnosine (β-alanyl-L-histidine) content in muscles show positive effects of β-alanine and inconsistent effects of HIS supplementation. Several studies demonstrate HIS depletion due to enhanced availability of methionine, glutamine, or β-alanine.

Histidine: A Systematic Review on Metabolism and Physiological Effects in Human and Different Animal Species

Histidine is an essential amino acid (EAA) in mammals, fish, and poultry. We aim to give an overview of the metabolism and physiological effects of histidine in humans and different animal species through a systematic review following the guidelines of PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). In humans, dietary histidine may be associated with factors that improve metabolic syndrome and has an effect on ion absorption. In rats, histidine supplementation increases food intake. It also provides neuroprotection at an early stage and could protect against epileptic seizures. In chickens, histidine is particularly important as a limiting factor for carnosine synthesis, which has strong anti-oxidant effects. In fish, dietary histidine may be one of the most important factors in preventing cataracts. In ruminants, histidine is a limiting factor for milk protein synthesis and could be the first limiting AA for growth. In excess, histidine supplementation can be responsible for eating and memory disorders in humans and can induce growth retardation and metabolic dysfunction in most species. To conclude, the requirements for histidine, like for other EAA, have been derived from growth and AA composition in tissues and also have specific metabolic roles depending on species and dietary levels.

Histidine in Health and Disease: Metabolism, Physiological Importance, and Use as a Supplement

L-histidine (HIS) is an essential amino acid with unique roles in proton buffering, metal ion chelation, scavenging of reactive oxygen and nitrogen species, erythropoiesis, and the histaminergic system. Several HIS-rich proteins (e.g., haemoproteins, HIS-rich glycoproteins, histatins, HIS-rich calcium-binding protein, and filaggrin), HIS-containing dipeptides (particularly carnosine), and methyl- and sulphur-containing derivatives of HIS (3-methylhistidine, 1-methylhistidine, and ergothioneine) have specific functions. The unique chemical properties and physiological functions are the basis of the theoretical rationale to suggest HIS supplementation in a wide range of conditions. Several decades of experience have confirmed the effectiveness of HIS as a component of solutions used for organ preservation and myocardial protection in cardiac surgery. Further studies are needed to elucidate the effects of HIS supplementation on neurological disorders, atopic dermatitis, metabolic syndrome, diabetes, uraemic anaemia, ulcers, inflammatory bowel diseases, malignancies, and muscle performance during strenuous exercise. Signs of toxicity, mutagenic activity, and allergic reactions or peptic ulcers have not been reported, although HIS is a histamine precursor. Of concern should be findings of hepatic enlargement and increases in ammonia and glutamine and of decrease in branched-chain amino acids (valine, leucine, and isoleucine) in blood plasma indicating that HIS supplementation is inappropriate in patients with liver disease.

Safety and efficacy of l-histidine monohydrochloride monohydrate produced by fermentation with Escherichia coli (NITE BP-02526) for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-histidine monohydrochloride monohydrate produced by fermentation with Escherichia coli (NITE BP-02526) when used as a nutritional additive or as a feed flavouring compound in feed and water for drinking for all animal species. The product under assessment is l-histidine HCl H2O produced by fermentation with a genetically modified strain of E. coli (NITE BP-02526). The production strain and its recombinant DNA were not detected in the final products. l-Histidine HCl H2O does not give rise to any safety concern to the production strain. The use of l-histidine HCl H2O is safe for the target species when used to supplement the diet in appropriate amounts. It is safe at the proposed use level of 25 mg/kg when used as a flavouring compound for all animal species. The use of l-histidine HCl H2O in animal nutrition raises no safety concerns for consumers of animal products. The additive is not irritating to the skin or eyes and is not a skin sensitiser. There is a risk for persons handling the additive from the exposure to endotoxins by inhalation. The use of l-histidine as a feed additive does not represent a risk to the environment. The additive l-histidine HCl H2O is regarded as an effective source of the amino acid l-histidine when used as a nutritional additive. For the supplemental l-histidine to be as efficacious in ruminants as in non-ruminant species, it requires protection against degradation in the rumen. It is also considered efficacious as a feed flavouring compound under the proposed conditions of use.

Safety and efficacy of l-histidine monohydrochloride monohydrate produced using Corynebacterium glutamicum KCCM 80172 for all animal species

Following a request from the European Commission, the Panel on Additives and Products or Substances used in Animal Feed (FEEDAP) was asked to deliver a scientific opinion on l-histidine monohydrochloride (HCl) monohydrate produced by fermentation using Corynebacterium glutamicum KCCM 80172 when used as a nutritional additive in feed and water for drinking for all animal species. The production strain is genetically modified. The production strain and its recombinant DNA were not detected in the final product. l-Histidine HCl monohydrate manufactured by fermentation using C. glutamicum KCCM 80172 does not give rise to any safety concern regarding the genetic modification. The use of l-histidine HCl monohydrate produced by fermentation using C. glutamicum KCCM 80172 is safe for the target species when used as a nutritional additive to supplement the diet in appropriate amounts to cover the requirements, depending on the species, the physiological state of the animal, the performance level, the environmental conditions, the background amino acid composition of the unsupplemented diet and the status of some essential trace elements such as copper and zinc. l-Histidine HCl monohydrate produced using C. glutamicum KCCM 80172 supplemented at levels appropriate for the requirements of the target species is considered safe for the consumer. l-Histidine HCl monohydrate produced using C. glutamicum KCCM 80172 is not irritant to skin, is a mildly irritant to eyes, and it is not a skin sensitiser. The additive does not pose a risk to users by inhalation. The use of l-histidine HCl monohydrate produced by C. glutamicum KCCM 80172 in animal nutrition is not expected to represent a risk to the environment. l-Histidine HCl monohydrate is considered an efficacious source of the essential amino acid l-histidine for non-ruminant animal species. For the supplemental l-histidine to be as efficacious in ruminants as in non-ruminant species, it would require protection against degradation in the rumen.

Effects of standardized ileal digestible histidine to lysine ratio on growth performance of 7- to 11-kg nursery pigs

Histidine may be the sixth limiting amino acid (AA) in practical nursery diets supplemented with high amounts of feed-grade AA. Therefore, 2 experiments were conducted to determine the standardized ileal digestible (SID) His:Lys ratio requirement estimate for growth performance of 7- to 11-kg nursery pigs. A total of 360 and 350 pigs (DNA 241 × 600, Columbus, NE; initially 7.1 ± 0.31 and 6.6 ± 0.36 kg) were used in Exp. 1 and 2, respectively. There were 5 pigs per pen with 12 replicates per treatment in Exp. 1 and 10 replicates per treatment in Exp. 2. After weaning, pigs were fed a common pelleted diet for 10 d in Exp. 1 and 7 d in Exp. 2. Then, pens were assigned to treatments in a randomized complete block design with body weight (BW) as the blocking factor. Dietary treatments consisted of SID His:Lys ratios of 24%, 28%, 32%, 36%, 40%, and 44% in Exp. 1 and 24%, 28%, 30%, 32%, 34%, 36%, and 42% in Exp. 2. Experimental diets were fed in pellet form for 10 or 14 d in Exp. 1 and 2, followed by a common mash diet for 15 or 14 d, respectively. Data were analyzed using the GLIMMIX and NLMIXED procedures of SAS, fitting data with heterogeneous variance when needed. The competing statistical models utilized were quadratic polynomial, broken-line linear (BLL), and broken-line quadratic. In Exp. 1, increasing SID His:Lys ratio increased (quadratic, P = 0.001) ADG, ADFI, G:F, and day 10 BW. In Exp. 2, ADG, G:F, and day 14 BW increased (quadratic, P = 0.001), and ADFI increased linearly (P = 0.001) with increasing SID His:Lys ratio. The best-fitting model for all response variables analyzed was the BLL. In Exp. 1, requirement estimates were 29.7%, 29.1%, and 29.8% SID His:Lys ratio for ADG, ADFI, and G:F, respectively. In Exp. 2, the SID His:Lys ratio requirement estimates were 31.0% for ADG and 28.6% for G:F. These results suggest that the SID His requirement estimate for growth performance is no more than 31% of Lys and that the NRC (2012) SID His requirement of 34% of Lys may be overestimated for 7- to 11-kg pigs.

Effects of intraperitoneally administered L-histidine on food intake, taste, and visceral sensation in rats

To evaluate relative factors for anorectic effects of L-histidine, we performed behavioral experiments for measuring food and fluid intake, conditioned taste aversion (CTA), taste disturbance, and c-Fos immunoreactive (Fos-ir) cells before and after i.p. injection with L-histidine in rats. Animals were injected with saline (9 ml/kg, i.p.) for a control group, and saline (9 ml/kg, i.p.) containing L-histidine (0.75, 1.5, 2.0 g/kg) for a L-histidine group. Injection of L-histidine decreased the average value of food intake, and statistically significant anorectic effects were found in animals injected with 1.5 or 2.0 g/kg L-histidine but not with 0.75 g/kg L-histidine. Taste abnormalities were not detected in any of the groups. Animals injected with 2.0 g/kg L-histidine were revealed to present with nausea by the measurement of CTA. In this group, a significant increase in the number of Fos-ir cells was detected both in the area postrema and the nucleus tractus solitarius (NTS). In the 0.75 g/kg L-histidine group, a significant increase in the number of Fos-ir cells was detected only in the NTS. When the ventral gastric branch vagotomy was performed, recovery from anorexia became faster than the sham-operated group, however, vagotomized rats injected with 2.0 g/kg L-histidine still acquired CTA. These data indicate that acute anorectic effects induced by highly concentrated L-histidine are partly caused by induction of nausea and/or visceral discomfort accompanied by neuronal activities in the NTS and the area postrema. We suggest that acute and potent effects of L-histidine on food intake require substantial amount of L-histidine in the diet.

The histaminergic system as a target for the prevention of obesity and metabolic syndrome

The control of food intake and body weight is very complex. Key factors driving eating behavior are hunger and satiety that are controlled by an interplay of several central and peripheral neuroendocrine systems, environmental factors, the behavioral state and circadian rhythm, which all concur to alter homeostatic aspects of appetite and energy expenditure. Brain histamine plays a fundamental role in eating behavior as it induces loss of appetite and has long been considered a satiety signal that is released during food intake (Sakata et al., 1997). Animal studies have shown that brain histamine is released during the appetitive phase to provide a high level of arousal preparatory to feeding, but also mediates satiety. Furthermore, histamine regulates peripheral mechanisms such as glucose uptake and insulin function. Preclinical research indicates that activation of H1 and H3 receptors is crucial for the regulation of the diurnal rhythm of food consumption; furthermore, these receptors have been specifically recognized as mediators of energy intake and expenditure. Despite encouraging preclinical data, though, no brain penetrating H1 receptor agonists have been identified that would have anti-obesity effects. The potential role of the H3 receptor as a target of anti-obesity therapeutics was explored in clinical trials that did not meet up to the expectations or were interrupted (clinicaltrials.gov). Nonetheless, interesting results are emerging from clinical trials that evaluated the attenuating effect of betahistine (an H1 agonist/H3 antagonist) on metabolic side effects associated with chronic antipsychotics treatment. Aim of this review is to summarize recent results that suggest the clinical relevance of the histaminergic system for the treatment of feeding disorders and provide an up-to-date summary of preclinical research. This article is part of the Special Issue entitled 'Histamine Receptors'.

Proxyfan acts as a neutral antagonist of histamine H3 receptors in the feeding-related hypothalamic ventromedial nucleus

BACKGROUND AND PURPOSE

Centrally acting histamine H(3) receptor ligands are proposed as potential treatments for obesity, although the value of inverse agonists at these receptors is still debated. Functional inhibition of H(3) autoreceptors activates neurones in a hypothalamic 'satiety' centre. The H(3) receptor antagonist, proxyfan was used as a tool to assess the action of histaminergic compounds in this model.

EXPERIMENTAL APPROACH

We compared the actions of histamine on feeding with those of an H(3) receptor agonist (imetit) and inverse agonist (thioperamide) in rats and mice. Sites of action were identified by immunohistochemistry and the hypothalamic ventromedial nucleus (VMN) was investigated using electrophysiological techniques.

KEY RESULTS

Central histamine or thioperamide decreased fast-induced feeding, whereas imetit increased feeding. Systemic thioperamide entered the brain to activate hypothalamic feeding centres and to reduce feeding without causing any adverse behaviours. Thioperamide activated neurones in the VMN through an action on histamine autoreceptors, whilst imetit had the opposite effect. Proxyfan administered alone did not affect either feeding or electrical activity. However, it blocked the actions of both thioperamide and imetit, acting as a neutral antagonist in this system.

CONCLUSIONS AND IMPLICATIONS

The H(3) receptor inverse agonist, thioperamide, potently reduced appetite without adverse behavioural effects. This action was blocked by proxyfan, acting as a neutral antagonist in this model and, therefore, this compound is useful in determining the selectivity of H(3) receptor-directed drugs. A major action of thioperamide is through presynaptic autoreceptors, inducing stimulation by endogenous histamine of postsynaptic H(1 ) receptors on anorectic hypothalamic neurones.

Integrative role of the histaminergic system in feeding and taste perception

Feeding behavior is regulated by a complex interplay of many endogenous substances, such as peptides and neurotransmitters in the central nervous system. Histamine is a neurotransmitter which expresses an anorectic effect on food intake via histamine H(1) receptors. The histaminergic system exists downstream of leptin, a satiety factor secreted from white adipose tissue. Because direct stimulation of the histaminergic system by histamine H(3)-inverse agonists or antagonists can normalize the obese phenotype in which animal models with exogenous leptin resistance, which resembles human obesity, the potential roles of histamine H(3) receptors as a therapeutic target now draw attention. Histaminergic activity is enhanced during feeding, and an oral somatic sensation is thought to affect histaminergic activity while blood glucose levels do not. In addition, gustatory information can modulate histaminergic activity by two mechanisms: by physiological excitation of the chorda tympani nerve, one of the taste nerves and by emotions elicited by taste perception, i.e., taste palatability. Particularly, aversive and hazardous taste stimuli tonically facilitate histaminergic activity, suggesting that the histaminergic system is involved in the response to harmful stimuli. Together with recent findings, it is postulated that the histaminergic system responds to both mechanical and chemical sensory input from the oral cavity during feeding and is exerted as a part of the danger response system.

Possible involvement of serotonin 5-HT2 receptor in the regulation of feeding behavior through the histaminergic system

The central histaminergic system has been proven to be involved in several physiological functions including feeding behavior. Some atypical antipsychotics like risperidone and aripiprazole are known to affect feeding behavior and to antagonize the serotonin (5-HT) receptor subtypes. To examine the possible neural relationship between the serotonergic and histaminergic systems in the anorectic effect of the antipsychotics, we studied the effect of a single administration of these drugs on food intake and hypothalamic histamine release in mice using in vivo microdialysis. Single injection of risperidone (0.5mg/kg, i.p.) or aripiprazole (1mg/kg, i.p.), which have binding affinities to 5-HT(1A, 2A, 2B) and (2C) receptors decreased food intake in C57BL/6N mice with concomitant increase of hypothalamic histamine release. However, a selective D(2)-antagonist, haloperidol (0.5mg/kg, i.p.), did not have effects on food intake or histamine release. Furthermore, in histamine H(1) receptor-deficient mice, there was no reduction of food intake induced by atypical antipsychotics, although histamine release was increased. Moreover, selective 5-HT(2A)-antagonists, volinanserin (0.5, 1mg/kg, i.p.) and ketanserin (5, 10mg/kg, i.p.), significantly increased histamine release and 5-HT(2B/2C) -antagonist, SB206553 (2.5, 5mg/kg, i.p.), slightly increased it. On the contrary, 5-HT(1A) -selective antagonist, WAY100635 (1, 2mg/kg), did not affect the histaminergic tone. These findings suggest that serotonin tonically inhibits histamine release via 5-HT(2) receptors and that antipsychotics enhance the release of hypothalamic histamine by blockade of 5-HT(2) receptors resulting in anorexia via the H(1) receptor.

The histamine H3 receptor and eating behavior

Interest in the histaminergic system as a potential target for the treatment of feeding disorders is driven by the unsatisfactory history of the pharmacotherapy of obesity. Eating behavior is regulated by a complex interplay of central neurotransmitter systems, peripheral endocrine stimuli, the circadian rhythm, and environmental cues, all factors that change the behavioral state and alter homeostatic aspects of appetite and energy expenditure. Key factors driving eating behavior are appetite and satiety that are regulated through different mechanisms. Brain histamine has long been considered a satiety signal in the nervous system. Recent observations, however, indicate that histamine does not meet the criteria for being a satiety signal, because augmented histamine release accompanies the appetitive phase of feeding behavior rather than food consumption and satiety. The appetitive phase requires a high and yet optimal arousal state, and the histaminergic system is crucial for sustaining a high degree of arousal during motivated behavior. Histamine H(1) receptors in the brain are crucial for the regulation of the diurnal rhythm of food intake and the regulation of obesity; however, from a therapeutic standpoint, no brain-penetrating H(1) receptor agonists have been identified that would have antiobesity effects. Despite conflicting preclinical data, insights are emerging into the potential role of histamine H(3) receptors as a target of antiobesity therapeutics. The aim of this review is to outline the relevance of the histaminergic system in controlling feeding behavior and evaluate the potential therapeutic use of histaminergic ligands for the treatment of eating disorders.

The effect of hardness of food on amygdalar histamine release in rats

When animals eat food, the oral cavity receives a variety of sensory information from food. The hardness of food, which elicits somatic sensation, is thought to affect feeding behavior, however, the details of neuronal mechanism are unclear. The histaminergic system is known to be involved in feeding behavior, and our previous studies indicated that gustatory information activates the histaminergic system, and that palatability of tastants influences its activity. From these findings, we hypothesized that the hardness of food may affect the histaminergic system. Thus, in the present study, we examined the effect of the hardness of food on histamine release in the central nucleus of amygdala when rats consumed either of two types of pellets composed of similar ingredients but having different degrees of hardness: hard and soft pellets. Histamine release was significantly increased in the rat fed with hard pellets. By contrast, histamine release was not enhanced in soft pellets-fed rats. There were no significant differences between the hard and soft pellet intakes during the experimental period. When rats acquired a conditioned aversion to soft pellets, histamine release was increased during feeding, in sharp contrast to no change of histamine release pattern seen during unconditioned soft pellet intake. These observations indicate that the amygdalar histaminergic system is modulated by oral somatic sensation from food, and by palatability of food texture.

Cerebrospinal fluid concentrations of large neutral and basic amino acids in Macaca mulatta: diurnal variations and responses to chronic changes in dietary protein intake

In rats, dietary protein intake influences brain concentrations of tryptophan, tyrosine, and other large neutral amino acids (LNAAs) and the neurotransmitters to which they are linked. Few experiments have examined these dietary protein-amino acid relationships in nonhuman primates, in relation to time of day or dietary protein content. We therefore examined the effect in monkeys of changes in chronic protein intake on 24-hour plasma and cerebrospinal fluid (CSF) concentrations of LNAAs (tyrosine, phenylalanine, branched-chain amino acids) and basic amino acids. Juvenile male monkeys (Macaca mulatta) consumed for sequential 4-week periods diets differing in protein content (approximately 23% --> approximately 16% --> approximately 10% --> approximately 6% protein [percentage of energy]). The daily ration was presented as a morning meal of fruit and an afternoon meal of fruit and a commercial diet to mimic feeding patterns in the wild. During week 4 on each diet, blood and CSF were sampled repeatedly over a 48-hour period via indwelling catheters. Plasma and CSF LNAA concentrations varied markedly with time of day and dietary protein content, showing up to 4-fold variations. Diurnal variations in plasma and CSF basic amino acids were smaller in magnitude and generally not strongly linked to dietary protein content. A measure of the competitive transport of LNAAs across the blood-brain barrier, calculated using plasma concentrations of the LNAAs and their blood-brain barrier kinetic constants, predicted the observed CSF concentration of each LNAA examined remarkably well, except for phenylalanine. Based on observations in rats, the variations in the CSF concentrations of the LNAAs in monkeys may be large enough to influence metabolic and signaling pathways in brain to which they have been linked.

Histamine in the nervous system

Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.

Histamine and the regulation of body weight

Energy intake and expenditure is regulated by a complex interplay between peripheral and central factors. An exhaustive list of peptides and neurotransmitters taking part in this complex regulation of body weight exists. Among these is histamine, which acts as a central neurotransmitter. In the present article we review current evidence pointing at an important role of histamine in the regulation of appetite and metabolism. Studies using both knockout mouse models as well as pharmacological studies have revealed that histamine acts as an anorexigenic agent via stimulation of histamine H(1) receptors. One effect of histamine in the regulation of appetite is to act as a mediator of the inhibitory effect of leptin on appetite. It seems that histamine may attenuate and delay the development of leptin resistance in high-fat-diet-induced obesity. Furthermore, histamine may also act to accelerate lipolysis. Based on the current evidence of the involvement of histamine in the regulation of body weight, the histaminergic system is an obvious target for the development of pharmacological agents to control obesity. At present, H(3) receptor antagonists that stimulate the histaminergic system may be the most promising histaminergic drugs for antiobesity therapy.

Evidence for tolerance following repeated dosing in rats with ciproxifan, but not with A-304121

Blockade of presynaptic histamine H(3) receptors with potent and selective ligands improves cognitive function in rodents and there is significant interest in developing such drugs for long-term symptomatic treatment of CNS disorders such as attention deficit hyperactivity disorder (ADHD). Unfortunately, little is known about the effects of repeated exposure to H(3) receptor antagonists/inverse agonists. We therefore investigated the effects of acute and repeated daily administration of two potent, brain penetrating H(3) receptor antagonists/inverse agonists, ciproxifan and A-304121, on rat body weight, food and water intake, core temperature and locomotor activity, as well as H(3) receptor density and gene expression levels. Methylphenidate, used clinically for the treatment of ADHD, was included as an additional comparator. Ciproxifan, an imidazole-based compound, decreased food intake over the first 10 days and locomotor activity acutely, but these effects were lost after further repeated administration. The ex vivo binding studies revealed increased H(3) receptor density in rats following repeated administration of ciproxifan for 10 or 15 days; however, H(3) receptor gene expression was not changed. In contrast, rats treated with the non-imidazole, A-304121, did not differ from controls on any measure during the observation period, while rats treated with methylphenidate exhibited hyperthermia and hyperactivity. The implications for potential long-term treatment with H(3) receptor antagonists in CNS disorders such as ADHD are discussed.

New targets in the treatment of anorexia nervosa

The pathophysiology of anorexia nervosa (AN) is complex and involves alterations of serotonin, dopamine and histamine neurotransmitters. In addition, receptor activity is disturbed, presumably in response to the neurotransmitter changes. These alterations are reviewed in relation to symptomatology and outcome of AN. Neuropeptide and peripheral orexigenic and satiety peptide research is in its infancy but holds much promise to shed light on the pathophysiological mechanisms involved in this illness. Current drug therapies have not demonstrated the efficacy desired in the treatment of AN. Current therapies are reviewed and new drug targets are explored. Compounds that interact with serotonin, histamine and dopamine receptors may offer unique treatment opportunities. In the future, the manipulation of peptides may add to the therapeutic potential of pharmacotherapy.

CENTRAL EFFECT OF HISTAMINE AND PERIPHERAL EFFECT OF HISTIDINE ON THE FORMALIN-INDUCED PAIN RESPONSE IN MICE

1. The present study was designed to investigate the role of brain histamine in modulating pain transmission in mice. 2. In conscious mice implanted with an intracerebroventricular (i.c.v.) cannula, the effects of i.v.c. injections of normal saline (control) and low and high doses histamine (2 and 40 microg/mouse, respectively) were investigated on the duration of paw licking and biting induced by subcutaneous (s.c.) injection of formalin (20 microL; 5%) into the plantar surface of the left hindpaw. 3. To clarify the involvement of histidine in the pain response, the effects of intraperitoneal (i.p.) injections of low and high doses of histidine (50 and 1000 mg/kg, respectively) alone or before i.c.v. injection of histamine were also examined. 4. Intraplantar injection of formalin induced a biphasic pain response (first phase: 0-5 min after injection; second phase: 20-40 min after injection). 5. Histamine (2 microg/mouse, i.c.v.) had no effect on the first phase of the pain response, but suppressed the second phase. The higher dose of histamine (40 microg/mouse, i.c.v.) suppressed both phases of the pain response. 6. Histidine, at 50 mg/kg, i.p., had no effect on the pain response, but the higher dose (1000 mg/kg, i.p.) suppressed the both phases of the pain response. 7. Pretreatment with the low dose of histidine (50 mg/kg, i.p.) prior to administration of 2 microg/mouse, i.c.v., histamine did not change the antinociception induced by low-dose histamine. However, pretreatment with the high dose of histidine (1000 mg/kg, i.p.) prior to 2 microg/mouse, i.c.v., histamine produced antinociception that resembled that seen following administration of the high dose of either histidine or histamine. Pretreatment with the low dose of histidine (50 mg/kg, i.p.) prior to administration of 40 microg/mouse, i.c.v., histamine has no effect on the pain response following high-dose histamine. Pretreatment with 1000 mg/kg, i.p., histidine prior to administration of 40 microg/mouse, i.c.v., histamine strongly suppressed both phases of the formalin-induced pain response, particularly the second phase. 8. The results of the present study indicate that: (i) activation of brain histamine produces antinociception in the mouse formalin test; (ii) peripheral loading with a high dose of histidine (1000 mg/kg, i.p.) alone exerts the same effect as that seen following 40 microg/mouse, i.c.v., histamine; and (iii) pretreatment with a high dose of histidine potentiates central histamine-induced antinociception.

Effect of central administration of carnosine and its constituents on behaviors in chicks

Even though their contents in the brain are high, the function of brain carnosine and its constituents has not been clarified. Both carnosine and anserine inhibited food intake in a dose dependent fashion when injected intracerebroventricularly. The constituents of carnosine, beta-alanine (beta-Ala) and l-histidine (His), also inhibited food intake, but their effects were weaker than carnosine itself. Co-administration with beta-Ala and His inhibited food intake similar to carnosine, but also altered other behaviors. Injection of carnosine induced hyperactivity and increased plasma corticosterone level, whereas beta-Ala plus His induced hypoactivity manifested as sleep-like behavior. This later effect seemed to be derived from beta-Ala, not His. These results suggest that central carnosine may act in the brain of chicks to regulate brain function and/or behavior in a manner different from its constituents.

1. Appetite suppressant activity of supplemental dietary amino acids and subsequent compensatory growth of broilers

This study was conducted to take advantage of the appetite-suppressant effect of excessive dietary amino acids in reducing feed intake and, in turn, restricting the early rapid growth of broilers to minimize metabolic disorders. Dietary amino acids were supplemented to a basal diet to yield a total of 1.57, 2.57, and 3.57% His; 2.7, 4.3, and 5.9% Lys; 1.36, 2.16, and 2.96% Met; 2.8, 3.8, and 4.8% Thr; and 1.27, 2.27, and 3.27% Trp and were fed to 408 chicks from 4 to 11 d of age. Fifteen dietary treatments of His, Lys, Met, Thr, and Trp were compared to the basal diet. Feed consumption was measured daily. Body weight measurements were taken at 0, 4, 7, 11, 14, and 21 d. At 21 d, pectoralis major and minor muscles, liver, and abdominal fat pad were weighed. High levels of Met and His caused the greatest depression in appetite from 4 to 11 d, and Thr, Trp, and Lys were found to be less potent. The exponential growth rate (EGR) of birds from 4 to 11 d of age was significantly reduced by the intermediate and high levels of the amino acid supplementation. From 11 to 14 d, EGR was greatest with high levels of Met or Trp, indicating more potential compensatory growth realized with these treatments. The high level of His decreased the percentage of pectoralis minor muscle yield, whereas the high level of Lys and Met increased the percentage of liver compared to those fed the basal diet. These results indicate that it is possible to use excessive individual amino acids in diets to suppress the appetite and early rapid growth to alleviate or minimize metabolic disorders.

The physiology of brain histamine

Histamine-releasing neurons are located exclusively in the TM of the hypothalamus, from where they project to practically all brain regions, with ventral areas (hypothalamus, basal forebrain, amygdala) receiving a particularly strong innervation. The intrinsic electrophysiological properties of TM neurons (slow spontaneous firing, broad action potentials, deep after hyperpolarisations, etc.) are extremely similar to other aminergic neurons. Their firing rate varies across the sleep-wake cycle, being highest during waking and lowest during rapid-eye movement sleep. In contrast to other aminergic neurons somatodendritic autoreceptors (H3) do not activate an inwardly rectifying potassium channel but instead control firing by inhibiting voltage-dependent calcium channels. Histamine release is enhanced under extreme conditions such as dehydration or hypoglycemia or by a variety of stressors. Histamine activates four types of receptors. H1 receptors are mainly postsynaptically located and are coupled positively to phospholipase C. High densities are found especially in the hypothalamus and other limbic regions. Activation of these receptors causes large depolarisations via blockade of a leak potassium conductance, activation of a non-specific cation channel or activation of a sodium-calcium exchanger. H2 receptors are also mainly postsynaptically located and are coupled positively to adenylyl cyclase. High densities are found in hippocampus, amygdala and basal ganglia. Activation of these receptors also leads to mainly excitatory effects through blockade of calcium-dependent potassium channels and modulation of the hyperpolarisation-activated cation channel. H3 receptors are exclusively presynaptically located and are negatively coupled to adenylyl cyclase. High densities are found in the basal ganglia. These receptors mediated presynaptic inhibition of histamine release and the release of other neurotransmitters, most likely via inhibition of presynaptic calcium channels. Finally, histamine modulates the glutamate NMDA receptor via an action at the polyamine binding site. The central histamine system is involved in many central nervous system functions: arousal; anxiety; activation of the sympathetic nervous system; the stress-related release of hormones from the pituitary and of central aminergic neurotransmitters; antinociception; water retention and suppression of eating. A role for the neuronal histamine system as a danger response system is proposed.

Dietary protein content affects the profiles of extracellular amino acids in the medial preoptic area of freely moving rats

This study examined the effect of protein consumption on extracellular amino acid concentrations in the medial preoptic area (MPOA) of rats. Rats were given free access to diets containing 0, 25 or 50 % protein for 3-h duration, starting from the onset of dark cycle (1800 h). The microdialysis probe was implanted into the MPOA at 1500 h. Dialysates were collected every 20 min from 1700 h to 2100 h. Amino acid concentrations in dialysate samples were determined by reverse phase-HPLC. Extracellular amino acid concentrations in the MPOA were elevated by protein consumption within 20 to 40 min following the start of the meal. The 50 % protein diet resulted in increased (p<0.05) alanine, glutamine, isoleucine, leucine, methionine, tyrosine and valine concentrations, when compared with both baseline and the 0% protein diet. When the 25 % protein diet was fed, amino acid concentrations in the MPOA were between those after the 0 and 50% protein diets. The ratio of tryptophan to the total branched-chain amino acids in extracellular fluid was highest after the 0% protein diet and increased with time. We conclude that extracellular amino acid profiles in the MPOA are affected by dietary protein content.

Effects of intracerebroventricularly infused histamine and selective H1, H2 and H3 agonists on food and water intake and urine flow in Wistar rats

The actions of intracerebroventricularly-infused histamine and selective histamine H1, H2 and H3 receptor agonists on food and water intake and urine flow were studied in rats. It was found that 100-800 nmoles of histamine significantly suppressed feeding. The H1 agonist 2-(3- trifluoromethylphenyl)histamine (FMPH) decreased food intake, whereas the H2 agonist dimaprit was without effect. Histamine- and FMPH-induced suppressions of feeding were attenuated by blockade of H1 but not by H2 receptors. The results clearly demonstrate that activation of brain H1 receptors decreases food intake. In subsequent studies, we found that both metoprine and thioperamide, which increase histaminergic activity through different mechanisms, also reduced food intake. This finding indicates that the brain histaminergic system is associated with feeding behavior. The same is true with body water homeostasis. Histamine caused a long-lasting diuresis. Also dimaprit and metoprine increased urine flow and the blockade of H2 receptors abolished the diuretic responses to histamine and dimaprit. On the other hand, the H3 agonist (R)-alpha-methylhistamine elicited drinking and this effect could be prevented by thioperamide pretreatment. The results imply that activation of H3 receptors predominantly provokes drinking, whereas central H2 receptors mediate the diuretic effect of histamine.

The blockade of H1 receptors attenuates the suppression of feeding and diuresis induced by inhibition of histamine catabolism

Metoprine elevates brain histamine content by blocking the conversion of histamine to methylhistamine. It suppresses food intake, increases water intake. and induces diuresis in rats. In the present experiment, to study which receptors were involved in these metoprine-induced changes, H1, H2, and H3 receptor blockers were administered to metoprine (10 mg/kg IP)-treated rats. The food and water consumption and urine excretion were measured at 10 and 24 h after the drug administration. It was found that systemic administration of the H3 receptor antagonist, thioperamide (5 mg/kg IP), supplemented the feeding suppressive effect of metoprine. In addition to this, the H1 receptor antagonist mepyramine (20 mg/kg IP) antagonized the suppression of feeding in metoprine-treated rats, whereas the H2 receptor antagonist, ranitidine (100 mg/kg IP), had no effect. Mepyramine also decreased the diuretic response to metoprine, whereas ranitidine or thioperamide were virtually without effect. The present results show that elevation of brain histamine content by inhibiting the catabolism of histamine suppresses food intake, and this effect of metoprine can be abolished by pretreatment with antihistamines. Although the blockade of H1 receptors also attenuates the diuretic response to metoprine, further studies are needed to understand the mechanisms that mediate the effects of metoprine on water balance.

Evidence for histamine involvement in the effect of histidine loads on food and water intake in rats

We examined the hypothesis that histidine is a regulator of short-term food and water intake in rats and that this control is through histidine's action as a precursor for histamine. The primary objectives were to measure food and water intake after histidine monohydrochloride monohydrate (His-HCl) given by intragastric (IG) and intraperitoneal (IP) routes of administration and to measure feeding and drinking responses to histidine when given after blockade of the histaminergic pathway by chlorpheniramine (CPA) and alpha-fluoromethylhistidine (FMH). Eight experiments were conducted using a back-to-back design. Rats were given treatment by IP or IG administration, and food and water intake was measured during time periods of 0-1, 1-2, 2-3 and 3-14 h. Histidine consistently reduced food intake with the sensitivity to IP much greater than to the IG route. The effect of histidine given by IP or IG on water intake was similar, generally causing an increase at least in the first hour. Histidine's action was not accounted for by its energy, pH or nitrogen content. Because FMH, which blocks the enzyme converting histidine to histamine, partially reversed the effect of histidine on food and water intake, these results support the hypothesis that histidine regulates food and water intake, at least in part, through its precursor control of histamine.

Dietary induced anorexia: a review of involvement of the histaminergic system

This review examines possible relationships between anorexia, dietary intake and central nervous system histaminergic activity. The hypothesis being reviewed is that one component of normal or pathophysiological neuroregulation of food intake involves histaminergic activity in the central nervous system, as influenced by concentrations and bioperiodicities of histamine and/or histamine receptors. Changes in concentrations of receptors are gender specific. Low protein quality or quantity diets elevate both central histamine and histamine receptors (H1) in rats while significantly decreasing their food intake. When injected with histaminergic antagonists, rats fed low protein diets increase food intake and have improved efficiency of weight gain. This review supports a dual hypotheses: central histaminergic activity is involved in the regulation of food intake, but food intake patterns (including dietary composition or energy content) can modify central histaminergic activity. This review also suggests that modified histamine and/or H1 receptor concentrations are potential mechanisms for elevated central histaminergic activity in food intake-related pathophysiological states. Thus, dietary interventions (clinically- or self-imposed) which modify food intake or diet composition have the potential of affecting the histaminergic system. Also, drugs with antihistaminergic properties have the potential of affecting food intake/weight gain patterns by interfering with normal neurochemical signals.

The effect of metoprine on glucoprivic feeding induced by 2-deoxy-D-glucose

Metoprine is a histamine N-methyltransferase inhibitor that elevates endogenous histamine (HA) levels. Because the histaminergic mechanism may be involved in the regulation of feeding behavior as well as in body glucose homeostasis, the effect of metoprine on glucoprivic feeding was studied in Wistar rats. Although metoprine treatment (10 and 20 mg/kg, IP) decreased feeding, the rats still responded to the administration of 400 mg/kg of 2-deoxy-D-glucose (2-DG) by increasing their feed intake. No difference was seen in the 6-h cumulative feed intake after administration of 2-DG between the metoprine- and solvent-treated rats. However, the response was delayed, and with 20 mg/kg metoprine the feed intake was significantly reduced during 2 h after 2-DG application. Both 2-DG and metoprine elevated plasma glucose concentration despite their opposite effects on feeding. Hypothalamic HA or its metabolite levels were not affected by 2-DG. The results suggest that the effects of metoprine and 2-DG are largely independent of each other, and that the feeding modulating function of HA is on such a level that it does not prevent the glucoprivic emergency response.

Role of histamine in rodent antinociception

1. Effects of substances which are able to alter brain histamine levels on the nociceptive threshold were investigated in mice and rats by means of tests inducing three different kinds of noxious stimuli: mechanical (paw pressure), chemical (abdominal constriction) and thermal (hot plate). 2. A wide range of i.c.v. doses of histamine 2HCl was studied. Relatively high dose were dose-dependently antinociceptive in all three tests: 5-100 micrograms per rat in the paw pressure test, 5-50 micrograms per mouse in the abdominal constriction test and 50-100 micrograms per mouse in the hot plate test. Conversely, very low doses were hyperalgesic: 0.5 microgram per rat in the paw pressure test and 0.1-1 microgram per mouse in the hot plate test. In the abdominal constriction test no hyperalgesic effect was observed. 3. The histamine H3 antagonist, thioperamide maleate, elicited a weak but statistically significant dose-dependent antinociceptive effect by both parenteral (10-40 mg kg-1) and i.c.v. (1.1-10 micrograms per rat and 3.4-10 micrograms per mouse) routes. 4. The histamine H3 agonist, (R)-alpha-methylhistamine dihydrogenomaleate was hyperalgesic, with a rapid effect (15 min after treatment) following i.c.v. administration of 1 microgram per rat and 3 microgram per mouse, or i.p. administration of 100 mg kg-1 in mice. In rats 20 mg kg-1, i.p. elicited hyperalgesia only 4 h after treatment. 5. Thioperamide-induced antinociception was completely prevented by pretreatment with a non-hyperalgesic i.p. dose of (R)-alpha-methylhistamine in the mouse hot plate and abdominal constriction tests. Antagonism was also observed when both substances were administered i.c.v. in rats. 6. L-Histidine HCl dose-dependently induced a slowly occurring antinociception in all three tests. The doses of 250 and 500 mg kg-1, i.p. were effective in the rat paw pressure test, and those of 500 and 1500 mg kg-1, i.p. in the mouse hot plate test. In the mouse abdominal constriction test 500 and 1000 mg kg-1, i.p. showed their maximum effect 2 h after treatment. 7. The histamine N-methyltransferase inhibitor, metoprine, elicited a long-lasting, dose-dependent antinociception in all three tests by both i.p. (10-30 mg kg-1) and i.c.v. (50-100 micrograms per rat) routes. 8. To ascertain the mechanism of action of the antinociceptive effect of L-histidine and metoprine, the two substances were also studied in combination with the histamine synthesis inhibitor (S)-alpha-fluoromethylhistidine and with (R)-alpha-methylhistamine, respectively. L-Histidine antinociception was completely antagonized in all three tests by pretreatment with (S)-alpha-fluoromethylhistidine HCl (50 mg kg-1, i.p.)administered 2 h before L-histidine treatment. Similarly, metoprine antinociception was prevented by(R)-alpha-methylhistamine dihydrogenomaleate 20 mg kg-1, i.p. administered 15 min before metoprine. Both(S)-alpha-fluoromethylhistidine and (R)-alpha-methylhistamine were used at doses which did not modify the nociceptive threshold when given alone.9. The catabolism product, 1-methylhistamine, administered i.c.v. had no effect in either rat paw pressure or mouse abdominal constriction tests.10. These results indicate that the antinociceptive action of histamine may take place on the postsynaptic site, and that its hyperalgesic effect occurs with low doses acting on the presynaptic receptor. This hypothesis is supported by the fact that the H3 antagonist, thioperamide is antinociceptive and the H3 agonist, (R)-alpha-methylhistamine is hyperalgesic, probably modulating endogenous histamine release.L-Histidine and metoprine, which are both able to increase brain histamine levels, are also able to induce antinociception in mice and rats. Involvement of the histaminergic system in the modulation of nociceptive stimuli is thus proposed.

FMH-induced decrease in central histamine levels produces increased feeding and body weight in rats

The present study tested the long-term effects of the histamine (H) synthesis inhibitor alpha-fluoromethylhistidine (FMH) on feeding and body weight in rats. FMH (administered via 2-week osmotic minipumps) increased feeding significantly throughout the test period. Body weights were also significantly increased toward the end of the test period. Hypothalamic H assays, performed at the end of the study, confirmed that FMH-treated rats had significantly lower H levels than controls. In general, the results suggest that H activity and feeding are inversely related.

Histamine: a neurotransmitter that influences food intake?

Brain histamine levels in rats in various states of water balance were raised by blocking histamine catabolism with metoprine. Acute administration of this drug caused a significant reduction in food intake. This finding suggests a possible role of histamine in the regulation of food intake.

Differential effects of psychotropic drugs on feeding in rats: is histamine blockade involved?

The present animal studies tested the hypothesis that drug-induced blockade of histamine-1 receptors leads to appetite stimulation. Test agents included the antipsychotic promazine which has very potent antihistaminic effects, as well as the antipsychotic haloperidol and the antidepressant desipramine which both have negligible antihistaminic effects. In support of the hypothesis, significant appetite stimulation occurred only with promazine, while the other two test agents did not increase feeding, and even produced some suppression in food intake.

Feed intake after inhibition of histamine catabolism

It has been reported that histamine and its precursor histidine have a feeding-suppressing effect. The present study shows that metoprine (20 mg/kg i.p.), which increases brain histamine levels by inhibiting its catabolism, also significantly decreases daily feed intake in rats. The reduced feed consumption is evident in different states of water balance. These results agree with an involvement of histaminergic systems in the regulation of feeding behaviour.

Responses of hypothalamic paraventricular neurons in vitro to norepinephrine and other feeding-relevant agents

To investigate paraventricular hypothalamic neuronal actions responsible for the effects of neurotransmitters on feeding, and to test the notion that a single population of cells there could account for feeding effects, hypothalamic slices containing the paraventricular nucleus (PVN) were prepared from rats. Electrophysiological responses of individual PVN neurons to feeding-inducing agents norepinephrine (NE) and gamma-aminobutyric acid (GABA), and to anorexic agents serotonin (5-HT) and histamine (Hist) were examined. NE inhibited neuronal activity through alpha 2-adrenergic receptors, and excited through alpha 1-receptors. alpha 2-receptors are known to mediate the behavioral effect of NE. NE inhibited most clearly those neurons that otherwise fired continuously in this type of in vitro preparation. GABA affected the activity of 37% of the neurons tested, primarily by inhibition. The inhibitory action of GABA can be related to its feeding-inducing effect. GABA in PVN can also attenuate excitatory responses and enhance inhibitory responses to NE or 5-HT. 5-HT caused excitatory and inhibitory responses with the former action outnumbering the latter by approximately 3 to 1. Since this would result in a net excitation, it appears that 5-HT in PVN inhibits feeding mainly by exciting neuronal activity. Hist excited 72% and inhibited only 2% of PVN neurons. The excitation was blocked by H1-antagonists, which have been shown to mediate Hist effect on feeding. Comparing across neurons, the inhibitory response to NE was correlated with that to GABA, but not with any responses to 5-HT or Hist. The excitatory responses to Hist correlated with 5-HT responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Prostaglandins, brown fat and weight loss

In obesity, a situation is created in which energy intake exceeds energy expenditure. The three components of energy expenditure are resting metabolism, physical activity, and thermogenesis. Increasing attention is being paid to the role of impaired energy expenditure in obesity. Evidence indicates that impairment in activity of the sympathetic nervous system, which stimulates thermogenic processes, contributes to the etiology of obesity. In addition, insulin resistance, a well-recognized metabolic consequence of obesity, appears to interfere with feeding-related, insulin-mediated increases in thermogenesis in brown adipose tissue. This thermogenic defect results in reduced energy buffering by brown adipose tissue leading to deficient energy expenditure and an increased efficiency in weight gain. A unique weight loss program, The Princeton Metabolic Diet Program, is presented. The Program stimulates metabolism by stimulating the sympathetic nervous system and correcting insulin resistance, thereby enhancing thermogenesis in brown adipose tissue. Methods include: 1) alternating diet composition and caloric intake and, 2) the use of nutritional metabolic stimulants. This type of non-toxic therapy, directed at correcting biochemical defects, will enhance metabolic mechanisms and induce weight loss.

Antihistaminic drugs increase feeding, while histidine suppresses feeding in rats

The present studies tested the hypothesis that histamine blockade stimulates appetite, while increases in histamine levels suppress appetite. Results show that the classical antihistamines cyproheptadine and promethazine both produced significant and long-lasting increases in food intake. Pronounced appetite stimulation was also seen following the administration of doxepin, the most potent antihistamine among the antidepressants. In contrast, administration of the histamine precursor histidine produced a profound suppression in food intake. The results thus suggest that an inverse relationship may exist between histamine and food intake.

Behavioural effects of histamine and its antagonists: a review

This review focuses on the behavioural effects of histamine and drugs which affect histaminergic function, particularly the H1- and H2-receptors antagonists. Research in this area has assumed considerable importance with increasing interest in the role of brain histamine, the clinical use of both H1 and H2 antagonists and evidence of nonmedical use of H1 antagonists. Results from a number of studies show that H1 and H2 antagonists have clear, but distinct subjective effects and that H1 antagonists have discriminative effects in animals. While H1 antagonists are reinforcers in certain conditions, histamine itself is a punisher. Moderate doses of H1 antagonists affect psychomotor performance in some situations, but the results are variable. The exceptions are terfenadine and astemizole, which do not seem to penetrate the blood-brain barrier readily. In studies of schedule-controlled behaviour, marked changes in response rate have been observed following administration of H1 antagonists, with the magnitude and direction dependent on the dose and the baseline behaviour. Histamine reduces avoidance responding, an effect mediated via H1-receptors. Changes in drinking and aggressive behaviour have also been observed following histamine administration and distinct roles for H1- and H2-receptors have been delineated. Separate H1- and H2-receptor mechanisms have also been suggested to account for changes in activity level. While the H2 antagonists do not always have strong behavioural effects when administered peripherally, there is evidence that cimetidine has a depressant effect on sexual function. These and other findings reveal an important role for histaminergic systems in a wide range of behaviour.