Satiation and masticatory function modulated by brain histamine in rats

Effect of mastication evaluation and intervention on body composition and biochemical indices in female patients with obesity: a randomized controlled trial

BACKGROUND

A limited number of studies have evaluated the masticatory indices of individuals with obesity who only chew their food a few times and for shorter duration or who were provided with an instructional intervention. This study aimed to examine the effects of a 6-month instructional mastication intervention on the body composition and biochemical indices in female patients with obesity.

METHODS

Female patients with obesity were randomly classified into a conventional treatment group (CTG; 12 individuals), which only received normal nutritional and exercise guidance, and a mastication intervention group (MIG; 16 individuals), which received an additional mastication guidance. The MIG received guidance on foods requiring increased number of chews and chewing duration, eating techniques, and the proper method of cutting foods.

RESULTS

Changes in the masticatory, body composition, and biochemical indices were compared before and after the 6-month intervention. The values of body composition indices decreased significantly in both groups; however, the rate of change in body mass index significantly decreased in the MIG. In addition, the values of biochemical indices were significantly decreased in the MIG compared with that in the CTG, which is attributed to the addition of mastication instruction to female patients with obesity.

CONCLUSION

Increasing the number of chews and duration of chewing times for carbohydrates, which are staple foods, possibly contributed to weight loss and improvement of glucose metabolism.

TRIAL REGISTRATION

UMIN, UMIN000025875. Registered on 27 Jan 2017.

Masticatory dysfunction in patients with diabetic neuropathy: A cross-sectional study

Introduction

Chewing well is essential for successful diet therapy and control of blood glucose level in patients with diabetes. In addition, long-term hyperglycemia is a risk factor for microvascular complications, which are the main cause of morbidity and mortality in these patients. Hence, it is plausible that masticatory disorder may be relevant to diabetic microvascular complications which is caused by long-term hyperglycemia. The aim of this study was to investigate whether masticatory disorders are relevant to diabetic microvascular complications.

Methods

This cross-sectional study included 172 patients with type 2 diabetes who underwent educational hospitalization in the Department of Endocrinology and Diabetic Medicine, Hiroshima University Hospital, from April 2016 to March 2020. Masticatory efficiency was determined quantitatively by using the GLUCO SENSOR GS-Ⅱ. Multivariable linear regression models were constructed to examine which factors were related to masticatory efficiency. Statistical significance was defined as a two-sided p value of < 0.05.

Results

According to the bivariable analysis, masticatory efficiency was significantly correlated with duration of diabetes (p = 0. 049), number of remaining teeth (p < 0.0001), the number of moving teeth (p = 0.007) and condition of diabetic neuropathy (p < 0.0001). Moreover, the number of remaining teeth (p < 0.0001) and diabetic neuropathy (p = 0.007) remained significantly correlated with masticatory efficiency in the multivariable analysis.

Conclusions

For the first time, we demonstrated that patients with type 2 diabetes who developed diabetic neuropathy had significantly reduced masticatory efficiency. Effective mastication is an important factor in successful diet therapy for diabetes. To prevent the progression of diabetic complications, especially in patients with diabetic neuropathy, it may be necessary to combine individualized therapies from dentists and nutritionists with consideration for the level of masticatory dysfunction.

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.

Trigeminal, Visceral and Vestibular Inputs May Improve Cognitive Functions by Acting through the Locus Coeruleus and the Ascending Reticular Activating System: A New Hypothesis

It is known that sensory signals sustain the background discharge of the ascending reticular activating system (ARAS) which includes the noradrenergic locus coeruleus (LC) neurons and controls the level of attention and alertness. Moreover, LC neurons influence brain metabolic activity, gene expression and brain inflammatory processes. As a consequence of the sensory control of ARAS/LC, stimulation of a sensory channel may potential influence neuronal activity and trophic state all over the brain, supporting cognitive functions and exerting a neuroprotective action. On the other hand, an imbalance of the same input on the two sides may lead to an asymmetric hemispheric excitability, leading to an impairment in cognitive functions. Among the inputs that may drive LC neurons and ARAS, those arising from the trigeminal region, from visceral organs and, possibly, from the vestibular system seem to be particularly relevant in regulating their activity. The trigeminal, visceral and vestibular control of ARAS/LC activity may explain why these input signals: (1) affect sensorimotor and cognitive functions which are not directly related to their specific informational content; and (2) are effective in relieving the symptoms of some brain pathologies, thus prompting peripheral activation of these input systems as a complementary approach for the treatment of cognitive impairments and neurodegenerative disorders.

Short-Term Effects of Chewing on Task Performance and Task-Induced Mydriasis: Trigeminal Influence on the Arousal Systems

Trigeminal input to the ascending activating system is important for the maintenance of arousal and may affect the discharge of the noradrenergic neurons of the locus coeruleus (LC), whose activity influences both vigilance state and pupil size, inducing mydriasis. For this reason, pupil size evaluation is now considered an indicator of LC activity. Since mastication activates trigeminal afferent neurons, the aims of the present study, conducted on healthy adult participants, were to investigate whether chewing a bolus of different hardness may: (1) differentially affect the performance on a cognitive task (consisting in the retrieval of specific target numbers within numerical matrices) and (2) increase the dilatation of the pupil (mydriasis) induced by a haptic task, suggesting a change in LC activation. Results show that chewing significantly increased both the velocity of number retrieval (without affecting the number of errors) and the mydriasis associated with the haptic task, whereas simple task repetition did not modify either retrieval or mydriasis. Handgrip exercise, instead, significantly decreased both parameters. Effects were significantly stronger and longer lasting when subjects chewed hard pellets. Finally, chewing-induced improvements in performance and changes in mydriasis were positively correlated, which suggests that trigeminal signals enhanced by chewing may boost the cognitive performance by increasing LC activity.

Association between Mastication, the Hippocampus, and the HPA Axis: A Comprehensive Review

Mastication is mainly involved in food intake and nutrient digestion with the aid of teeth. Mastication is also important for preserving and promoting general health, including hippocampus-dependent cognition. Both animal and human studies indicate that mastication influences hippocampal functions through the end product of the hypothalamic-pituitary-adrenal (HPA) axis, glucocorticoid (GC). Epidemiologic studies suggest that masticatory dysfunction in aged individuals, such as that resulting from tooth loss and periodontitis, acting as a source of chronic stress, activates the HPA axis, leading to increases in circulating GCs and eventually inducing various physical and psychological diseases, such as cognitive impairment, cardiovascular disorders, and osteoporosis. Recent studies demonstrated that masticatory stimulation or chewing during stressful conditions suppresses the hyperactivity of the HPA axis via GCs and GC receptors within the hippocampus, and ameliorates chronic stress-induced hippocampus-dependent cognitive deficits. Here, we provide a comprehensive overview of current research regarding the association between mastication, the hippocampus, and HPA axis activity. We also discuss several potential molecular mechanisms involved in the interactions between mastication, hippocampal function, and HPA axis activity.

Anti-Obesity Actions of Mastication Driven by Histamine Neurons in Rats

Implications of mastication in energy intake and expenditure regulated by histamine (HA) neurons were investigated in rats. Depletion of neuronal HA from the mesencephalic trigeminal sensory nucleus (Me5) reduced eating speed, but that from a satiety center of the ventromedial hypothalamus (VMH) increased both meal size and its duration leaving eating speed unaffected. Turnover of neuronal HA in the Me5 was elevated at the early phase of feeding and that in the VMH was at the later phase. This elevated turnover was abolished by gastric intubations of an isocaloric liquid diet or an equivolume of water. Mastication-induced activation of HA neurons suppressed physiological food intake through H1-receptor in the hypothalamic paraventricular nucleus (PVN) and the VMH. On the other hand, the HA neurons activation accelerated lipolysis particularly in the visceral adipose tissues and up-regulated mRNA expression of uncoupling protein family through sympathetic efferent nerve. Mastication thus plays an important role as a potent input signal to activate HA neurons. Our recent findings have evidently shown how tightly and elegantly HA neurons are concordant with leptin signaling system through a negative feedback loop.

Effectiveness of a Nutrition Education Program to Improve Children's Chewing Habits

This quasi-experimental study determined whether the nutrition education program we developed to promote chewing food properly influenced children's chewing habits successfully. Four kindergarten classes in Japan (150 children, aged 5-6 years) were studied; one class received the educational program in the classroom and at home (Group A) and three classes received the program in the classroom only (Group B). The educational program was integrated into the classes' daily curriculum for five weeks. It included storytelling with large picture books, chewing consciously while eating lunch, singing a song with gestures, and greetings before and after meals (both groups). Group A also used a paper textbook and was provided information by the leaflet to encourage guardians to implement the program at home. Chewing habits before and after intervention were evaluated: (1) guardians completed seven questionnaire items related to chewing habits and chewing movement and (2) the number of chews and time spent eating the test meal were measured by a portable chewing sensor. Both approaches improved the children's chewing habits; however, no difference was found between the two groups. We concluded that this intervention could be used to improve chewing habits in young children even without active involvement of their guardians.

Chronic Powder Diet After Weaning Induces Sleep, Behavioral, Neuroanatomical, and Neurophysiological Changes in Mice

The purpose of this study is to clarify the effects of chronic powder diet feeding on sleep patterns and other physiological/anatomical changes in mice. C57BL/6 male mice were divided into two groups from weaning: a group fed with solid food (SD) and a group fed with powder food (PD), and sleep and physiological and anatomical changes were compared between the groups. PD exhibited less cranial bone structure development and a significant weight gain. Furthermore, these PD mice showed reduced number of neurogenesis in the hippocampus. Sleep analysis showed that PD induced attenuated diurnal sleep/wake rhythm, characterized by increased sleep during active period and decreased sleep during rest period. With food deprivation (FD), PD showed less enhancement of wake/locomotor activity compared to SD, indicating reduced food-seeking behavior during FD. These results suggest that powder feeding in mice results in a cluster of detrimental symptoms caused by abnormal energy metabolism and anatomical/neurological changes.

Mastication as a Stress-Coping Behavior

Exposure to chronic stress induces various physical and mental effects that may ultimately lead to disease. Stress-related disease has become a global health problem. Mastication (chewing) is an effective behavior for coping with stress, likely due to the alterations chewing causes in the activity of the hypothalamic-pituitary-adrenal axis and autonomic nervous system. Mastication under stressful conditions attenuates stress-induced increases in plasma corticosterone and catecholamines, as well as the expression of stress-related substances, such as neurotrophic factors and nitric oxide. Further, chewing reduces stress-induced changes in central nervous system morphology, especially in the hippocampus and hypothalamus. In rodents, chewing or biting on wooden sticks during exposure to various stressors reduces stress-induced gastric ulcer formation and attenuates spatial cognitive dysfunction, anxiety-like behavior, and bone loss. In humans, some studies demonstrate that chewing gum during exposure to stress decreases plasma and salivary cortisol levels and reduces mental stress, although other studies report no such effect. Here, we discuss the neuronal mechanisms that underline the interactions between masticatory function and stress-coping behaviors in animals and humans.

Involvement of histaminergic inputs in the jaw-closing reflex arc

Histamine receptors are densely expressed in the mesencephalic trigeminal nucleus (MesV) and trigeminal motor nucleus. However, little is known about the functional roles of neuronal histamine in controlling oral-motor activity. Thus, using the whole-cell recording technique in brainstem slice preparations from Wistar rats aged between postnatal days 7 and 13, we investigated the effects of histamine on the MesV neurons innervating the masseter muscle spindles and masseter motoneurons (MMNs) that form a reflex arc for the jaw-closing reflex. Bath application of histamine (100 μM) induced membrane depolarization in both MesV neurons and MMNs in the presence of tetrodotoxin, whereas histamine decreased and increased the input resistance in MesV neurons and MMNs, respectively. The effects of histamine on MesV neurons and MMNs were mimicked by an H1 receptor agonist, 2-pyridylethylamine (100 μM). The effects of an H2 receptor agonist, dimaprit (100 μM), on MesV neurons were inconsistent, whereas MMNs were depolarized without changes in the input resistance. An H3 receptor agonist, immethridine (100 μM), also depolarized both MesV neurons and MMNs without changing the input resistance. Histamine reduced the peak amplitude of postsynaptic currents (PSCs) in MMNs evoked by stimulation of the trigeminal motor nerve (5N), which was mimicked by 2-pyridylethylamine but not by dimaprit or immethridine. Moreover, 2-pyridylethylamine increased the failure rate of PSCs evoked by minimal stimulation and the paired-pulse ratio. These results suggest that histaminergic inputs to MesV neurons through H1 receptors are involved in the suppression of the jaw-closing reflex although histamine depolarizes MesV neurons and/or MMNs.

The effects of bilateral lesions of the mesencephalic trigeminal sensory nucleus on nocturnal feeding and related behaviors in mice

AIMS

The mesencephalic trigeminal sensory nucleus (Me5), which receives signals originating from oral proprioceptors and projects its fibers to the hypothalamus, regulates mastication and modulates satiation. Because the Me5 neurons display circadian rhythms in circadian mPer1 gene expression and bilateral Me5 lesions change feeding and exploratory behavior profiles, we speculated that Me5 may influence the daily timing of feeding. Therefore, we explored the effects of bilateral caudal Me5 lesions on the circadian profiles of feeding and its related behaviors.

MAIN METHODS

We measured the activities of feeding, drinking, and locomotion for 24h using an automated feeding behavior measurement apparatus and analyzed the mRNA expression levels of hypothalamic orexigenic and anorexigenic signaling molecules in both Me5-lesioned and sham-operated mice.

KEY FINDINGS

Food and water intake and locomotor activity decreased significantly in Me5-lesioned mice during the dark phase without affecting these total indexes when measured over the entire day. Analysis of the mRNA expression levels of hypothalamic orexigenic and anorexigenic signaling molecules showed that prepro-orexin (orexin) mRNA in the perifornical area was significantly decreased during the dark phase only in Me5-lesioned mice.

SIGNIFICANCE

Bilateral caudal Me5 lesions alter the nocturnal properties of food and water intake and locomotor activity in mice and decrease the mRNA expression level of orexin in the perifornical area during the dark phase. These results suggest that Me5 activity may influence the nocturnal properties of feeding and its related behaviors by adjusting the activity of orexin neurons in the perifornical area.

Effects of mastication on glucose metabolism in rats, with emphasis on differences in properties of food consumed whilst breeding

OBJECTIVE

In this study, to elucidate the effects of preferred properties of food that affect the daily masticatory habits on the onset of lifestyle-related disease, we investigated whether groups of rats continuously fed with diet having distinct properties show differences in glucose metabolism.

DESIGN

Thirty-six male Wistar rats aged 4 weeks were divided into two groups; only the pellet type feed was given to one (solid diet group), and the powdered feed to the other (powder diet group). The oral glucose tolerance test (OGTT) was performed to measure glucose metabolism. For the determination of statistical significance (p<0.05), blood glucose level and areas under the blood glucose response curve (AUC) were analysed using the Mann-Whitney U-test.

RESULTS

The AUC values were significantly different between the two diet groups when the animals were 45 and 51 weeks of age. The median blood glucose level in 45-week-old rats fed with the powder diet was significantly higher than those in age-matched rats fed with solid diet 45 and 120 min after glucose load. Similarly, the median blood glucose level in the 51-week-old rats in the powder diet group was significantly higher than those in the solid diet group at 30, 45, 60, and 120 min after glucose load.

CONCLUSIONS

We showed that the rats which had been fed with solid diet and therefore had been masticating the feed plentifully enhanced glucose metabolism. This can suggest the possible use of masticatory and dietary intervention, which promotes sufficient mastication of hard food, in the prevention and cure of human lifestyle-related diseases.

Bilateral lesions of the mesencephalic trigeminal sensory nucleus stimulate hippocampal neurogenesis but lead to severe deficits in spatial memory resetting

The mesencephalic trigeminal sensory nucleus (Me5), which receives signals originating from oral proprioceptors, becomes active at weaning and contributes to the acquisition of active exploratory behavior [Ishii, T., Furuoka, H., Kitamura, N., Muroi, Y., and Nishimura, M. (2006) Brain Res. 1111, 153-161]. Because cognitive functions play a key role in animal exploration, in the present study we assessed the role of Me5 in spatial learning and memory in the water maze. Mice with bilateral Me5 lesions exhibited severe deficits in both a reversal learning and a reversal probe test compared with sham-operated mice. In spite of these reversal tests, Me5 lesions had no effect on a hidden platform test. These results suggest that Me5-lesioned mice show a perseveration of the previously learned spatial strategy rather than an inability to learn a new strategy, resulting in reduced spatial memory resetting. Moreover, adult neurogenesis in the dentate gyrus of the hippocampus, which has been proposed to have a causal relationship to spatial memory, was stimulated in Me5-lesioned mice. Thus, a stimulation of hippocampal neurogenesis observed after Me5 lesions may lead to a rigidity and perseverance of the previously learned strategy because of inferential overuse of past memories in a novel situation. These results suggest that Me5 contributes to spatial memory resetting by controlling the rate of hippocampal neurogenesis through an ascending neuronal pathway to the hippocampus.

Occlusion and brain function: mastication as a prevention of cognitive dysfunction

Research in animals and humans has shown that mastication maintains cognitive function in the hippocampus, a brain area important for learning and memory. Reduced mastication, an epidemiological risk factor for the development of dementia in humans, attenuates spatial memory and causes hippocampal neurons to deteriorate morphologically and functionally, especially in aged animals. Active mastication rescues the stress-attenuated hippocampal memory process in animals and attenuates the perception of stress in humans by suppressing endocrinological and autonomic stress responses. Active mastication further improves the performance of sustained cognitive tasks by increasing the activation of the hippocampus and the prefrontal cortex, the brain regions that are essential for cognitive processing. Abnormal mastication caused by experimental occlusal disharmony in animals produces chronic stress, which in turn suppresses spatial learning ability. The negative correlation between mastication and corticosteroids has raised the hypothesis that the suppression of the hypothalamic-pituitary-adrenal (HPA) axis by masticatory stimulation contributes, in part, to preserving cognitive functions associated with mastication. In the present review, we examine research pertaining to the mastication-induced amelioration of deficits in cognitive function, its possible relationship with the HPA axis, and the neuronal mechanisms that may be involved in this process in the hippocampus.

Influência de alimentos líquidos e sólidos no controle do apetite

Este trabalho discute o papel dos alimentos líquidos e sólidos na ingestão alimentar, fundamentando-se em uma revisão crítica sobre o assunto. Utilizaram-se os principais bancos de dados nacionais e internacionais em saúde, entre eles, Medline/PubMed, Web of Science, Lilacs, SciELO. A busca bibliográfica compreendeu o período de 1980 a 2008. Os resultados atuais das pesquisas indicam que o estado físico do alimento pode influenciar o consumo alimentar, tanto a curto quanto a longo prazo, e que os alimentos líquidos exercem um menor poder sacietógeno, em comparação aos sólidos. Os possíveis mecanismos envolvidos nesse fraco controle do apetite pelos líquidos são: falta de mastigação, fase cefálica da ingestão menos pronunciada, esvaziamento gástrico mais rápido e fatores cognitivos. Conclui-se que o uso de alimentos líquidos, em especial bebidas energéticas, deve ser moderado tanto na prevenção como no tratamento da obesidade.

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.

Food components inhibiting recombinant human histidine decarboxylase activity

Histidine decarboxylase (HDC) catalyzes histamine formation from histidine. Histamine is a bioactive amine acting as a neurotransmitter as well as a chemical mediator. Phenolic food components have been tested for their ability to inhibit recombinant human HDC. Epicatechin gallate (ECG) was found to be a potent inhibitor as it inhibited HDC activity in a competitive manner with Ki = 10 muM against l-histidine. Epigallocatechin gallate (EGCG) showed time-dependent inhibition which disappeared under anaerobic conditions. It is probable that time-dependent inhibition could be due to the result of autoxidation of EGCG. The initial burst observed for EGCG suggests that EGCG itself is involved in HDC inhibition as observed for ECG. Our present results have shown that the tested food components can inhibit HDC activity. This inhibition likely affects histamine biosynthesis and possibly leads to controlling the biological action induced by histamine. Therefore, those food components exhibiting HDC inhibitory activity might be potentially useful in controlling histamine-induced biological actions.

The mesencephalic trigeminal sensory nucleus is involved in acquisition of active exploratory behavior induced by changing from a diet of exclusively milk formula to food pellets in mice

Post-weaning mice fed exclusively milk display low-frequency exploratory behavior [Ishii, T., Itou, T., and Nishimura, M. (2005) Life Sci. 78, 174-179] compared to mice fed a food pellet diet. This low-frequency exploratory behavior switched to high-frequency exploration after a switch from exclusively milk formula to a food pellet diet. Acquisition of the high-frequency exploratory behavior was irreversible. Recently, we demonstrated that the mesencephalic trigeminal nucleus (Me5) is involved in the control of feeding and exploratory behavior in mice without modulating the emotional state [Ishii, T., Furuoka, H., Itou, T., Kitamura, N., and Nishimura, M. (2005) Brain Res. 1048, 80-86]. We therefore investigated whether the Me5 is involved in acquisition of high-frequency exploratory behavior induced by the switch in diet from an exclusively milk formula to food pellets. Mouse feeding and exploratory behaviors were analyzed using a food search compulsion apparatus, which was designed to distinguish between the two behaviors under standard living conditions. Immunohistochemical analysis of immediate early genes indicated that the Me5, which receives signals from oral proprioceptors, is transiently activated after the diet change. The change from low-frequency to high-frequency exploratory behavior was prevented in milk-fed mice by bilateral lesion of the Me5. These results suggest that the Me5 is activated by signals associated with mastication-induced proprioception and contributes to the acquisition of active exploratory behavior.

Selective expression of histamine receptors in rat mesencephalic trigeminal neurons

The perikarya of sensory neurons of the mesencephalic trigeminal nucleus (MTN) receive dense histaminergic hypothalamic innervation. In this study, we examine the yet unknown expression and localization of histamine receptors in the rat MTN using immunohistochemistry with subtype-specific antibodies. Same as the masticatory muscle spindle somata H1 receptors were located along the entire MTN, whereas H3 receptors were detected in the caudal pontine part of the nucleus, which receives input from periodontal afferents. Most of the immunostained cell bodies were surrounded by histidine decarboxylase-, histamine- or vesicular monoamine transporter 2-containing pericellular varicose fibers and terminals in a basket-like manner. Our results suggest that rat MTN neurons are directly influenced by histaminergic descending projections from the hypothalamus. It can be inferred that processing of proprioceptive information at the level of the MTN is controlled via histamine H1 and H3 receptors through different postsynaptic mechanisms.

Influence of a selective histamine H3 receptor antagonist on hypothalamic neural activity, food intake and body weight

OBJECTIVE

This study was conducted to elucidate whether antagonistic targeting of the histamine H3 receptor increases hypothalamic histamine levels, in parallel with decreases in food intake and body weight.

METHODS

The competitive antagonist potency of a recently synthesized histamine H3 receptor antagonist, NNC 38-1049, was studied in intact HEK293 cells expressing human or rat histamine H3 receptor, in which NNC 38-1049 was allowed to antagonize the effect of the H3 receptor agonist R-alpha-methylhistamine on isoprenaline-induced accumulation of cAMP. The affinity of NNC 38-1049 for a number of variants of the histamine receptor was also determined. Following single dosing of normal rats with NNC 38-1049, hypothalamic histamine levels were assessed by means of microdialysis. Plasma and brain levels of NNC 38-1049 and acute effects on food intake and energy expenditure were followed after oral doses of 3-60 mg/kg. Potential side effects were examined with rat models of behaviour satiety sequence (BSS), pica behaviour and conditioned taste aversion (CTA). Intakes of food and water together with body weight were recorded for 15 days during daily dosing of dietary obese rats.

RESULTS

NNC 38-1049 was found to be a highly specific and competitive antagonist towards both human and rat histamine H3 receptors, and measurable amounts of NNC 38-1049 were found in the plasma of rats following single oral doses of 3-60 mg/kg and in the brain after 15-60 mg/kg. Following single intraperitoneal injections of NNC 38-1049 (20 mg/kg), significant increases in extracellular histamine concentrations were observed. The same dose did not change BSS or pica behaviour acutely, nor did it induce CTA following repeated administration for 7 days. Reductions in food intake were seen very soon after administration, and occurred in a dose-dependent fashion. Energy expenditure was unchanged, but the respiratory quotient (RQ) tended to decrease at higher doses, indicating an increase in lipid oxidation. Twice daily administration of 20 mg/kg of NNC 38-1049 in old and dietary obese rats resulted in sustained reduction of food intake throughout a 2-week study, and was associated with a highly significant (P<0.01) decrease in body weight compared with controls (-18.4+/-3.4 vs +0.4+/-2.7 g). The same dose of NNC 38-1049 produced an acute decrease of water intake, but 24 h intakes were not significantly changed.

CONCLUSIONS

The results of this study strongly support the idea that an increase in the hypothalamic concentration of histamine produces a specific reduction of food intake and that this effect can be translated into a decrease in body weight.

The mesencephalic trigeminal sensory nucleus is involved in the control of feeding and exploratory behavior in mice

The mesencephalic trigeminal nucleus (Me5), which receives input from oral proprioceptors and projects to higher brain regions, is involved in mastication-induced modulation of satiation. To investigate how the Me5 is involved in the control of feeding and exploratory behavior, we examined the effect of bilateral electrolytic lesions of the Me5 on feeding and exploratory behavior in mice. Mouse feeding and exploratory behaviors were analyzed using a food-search-compulsion-apparatus (FSCA), which was designed to distinguish between the two behaviors under standard living conditions. To assess anxiety in mice in an unfamiliar environment, exploratory activity was analyzed in an automated hole-board apparatus. Mice with bilateral Me5 lesions had unique feeding and exploratory behavior profiles in the FSCA compared with sham-operated mice. Me5-lesioned mice spent more time in the food chamber during each trial in the FSCA, but the number of entries into the food chamber was decreased by 40% compared to sham-operated mice. Moreover, Me5 lesions markedly inhibited exploratory behavior, manifested as low-frequency exploration. In spite of the low-frequency exploration in the FSCA, Me5 lesions had no effect on various exploratory activities analyzed in the hole-board apparatus, i.e., total locomotor activity, frequency and duration of rearing and head-dipping, and latency to the first head-dipping. These results suggest that the Me5 is involved in the control of feeding and exploratory behavior through its ascending neuronal pathways in mice without modulating the emotional state.

Food texture differences affect energy metabolism in rats

Dietary factors such as taste and nutrients are known to affect satiety and energy balance. We hypothesized that food texture might contribute to the regulation of energy metabolism through the process of mastication in the oral cavity as well. The effects of long-term feeding of different-textured pellets on body weight gain, adiposity, and thermogenesis were assessed. From weaning at 4 wks, rats were divided into 2 groups fed on either standard (controls) or soft pellets (soft-fed) that required less chewing with the same nutritional composition. At 26 wks, the soft-fed rats showed greater adiposity than did the controls. Daily food intake did not differ between the 2 groups. The increase in body temperature following feeding was significantly lower in the soft-fed rats. These results suggested that food texture affected energy metabolism by changing post-prandial thermogenesis. The long-term deficiency of thermogenesis associated with soft foods resulted in a greater tendency toward obesity.

Comparative analysis of the chemical neuroanatomy of the mammalian trigeminal ganglion and mesencephalic trigeminal nucleus

A characteristic peculiarity of the trigeminal sensory system is the presence of two distinct populations of primary afferent neurons. Most of their cell bodies are located in the trigeminal ganglion (TG) but part of them lie in the mesencephalic trigeminal nucleus (MTN). This review compares the neurochemical content of central versus peripheral trigeminal primary afferent neurons. In the TG, two subpopulations of primary sensory neurons, containing immunoreactive (IR) material, are identified: a number of glutamate (Glu)-, substance P (SP)-, neurokinin A (NKA)-, calcitonin gene-related peptide (CGRP)-, cholecystokinin (CCK)-, somatostatin (SOM)-, vasoactive intestinal polypeptide (VIP)- and galanin (GAL)-IR ganglion cells with small and medium-sized somata, and relatively less numerous larger-sized neuropeptide Y (NPY)- and peptide 19 (PEP 19)-IR trigeminal neurons. In addition, many nitric oxide synthase (NOS)- and parvalbumin (PV)-IR cells of all sizes as well as fewer, mostly large, calbindin D-28k (CB)-containing neurons are seen. The majority of the large ganglion cells are surrounded by SP-, CGRP-, SOM-, CCK-, VIP-, NOS- and serotonin (SER)-IR perisomatic networks. In the MTN, the main subpopulation of large-sized neurons display Glu-immunoreactivity. Additionally, numerous large MTN neurons exhibit PV- and CB-immunostaining. On the other hand, certain small MTN neurons, most likely interneurons, are found to be GABAergic. Furthermore, NOS-containing neurons can be detected in the caudal and the mesencephalic-pontine junction portions of the nucleus. Conversely, no immunoreactivity to any of the examined neuropeptides is observed in the cell bodies of MTN neurons but these are encircled by peptidergic, catecholaminergic, serotonergic and nitrergic perineuronal arborizations in a basket-like manner. Such a discrepancy in the neurochemical features suggests that the differently fated embryonic migration, synaptogenesis, and peripheral and central target field innervation can possibly affect the individual neurochemical phenotypes of trigeminal primary afferent neurons.

[Monoaminergic anorectic agents]

Catecholamine, dopamine, serotonine (5HT) and neuronal histamine are anorectic monoamines and act as anorectic neurotransmitters. The anorectic agents as modulators of these monoamines inhibit appetite by activating release together with suppressing reuptake of those monoamines. The anorectic agents were classified in clinical use into either alpha 1, beta-adrenergic receptor agonists or 5HT-receptor agonist. Dexfenfluramine, a 5HT-receptor agonist, was inhibited in clinical use because of its cardiac complications including pulmonary hypertension and valvelar disease. Mazindol is an adrenergic agonist and the solitary anti-obesity drug used clinically in Japan. Sibutramine shows the effects of both beta-adrenergic and serotonergic receptor agonists. Sibutramine induces not only appetite suppression but also acceleration of peripheral energy expenditure. No histaminergic anorectics have been employed in the clinical situation to date. L-Histizine, precursor amino acid of endogenous neuronal histamine, is useful for suppression of food intake, lipolytic acceleration of peripheral adipose tissues and enhanced energy expenditure in both animals and humans. L-Histizine thus inspires development of more effective and safer anorectics that can be used without suffering from the rebound phenomenon of body weight.

Occlusal function associated with body composition in premenopausal Japanese women

OBJECTIVES

The goal of the present study was to investigate the relationship between occlusal function and body composition in 108 premenopausal healthy Japanese women aged 20-45 years.

METHODS

Pressure-sensitive sheets were used to measure occlusal function. Whole fat mass and lean mass, fat-free mass, and whole-bone mineral content were measured by dual-energy X-ray absorptiometry (DXA).

RESULTS

After being adjusted for age and the square of height, the whole lean mass and grip strength of the large occlusal contact-area group were found to be significantly higher than those of the small occlusal area groups (p<0.05, respectively). In the 1-year follow-up study, changes in weight in the small-occlusal contact-area group and the low-occlusal force group were significantly larger than other occlusal-contact area or occlusal-force groups. The mean occlusal-contact area and occlusal force were both significantly smaller in subjects with partial dentures than in those without (p<0.05).

CONCLUSION

Large occlusal contact-area, high occlusal force, and no dentures may be associated with some good health conditions in premenopausal Japanese women.

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.

Masticatory function and its effects on general health

One of the main goals of dentistry is to preserve a lifelong healthy masticatory function. Recent studies have shown that mastication is of great importance, not only for the intake of food but also for the systemic, mental and physical functions of the body. The purpose of this review is to compile the latest scientific information concerning the relationship between mastication and general health.