The hypophagic factor oleoylethanolamide differentially increases c-fos expression in appetite regulating centres in the brain of wild type and histamine deficient mice.

Histaminergic neurons in the hypothalamic tuberomamillary nucleus (TMN) establish connections with virtually all brain areas. Recent evidence suggests that feeding-related motivation is correlated with the activation of a subpopulation of histamine neurons in the ventral TMN that project to hypothalamic and subcortical areas controlling feeding behaviour. Oleoylethanolamide (OEA) is a hypophagic lipid-amide released by the small intestine in response to daily fat intake that indirectly activates hypothalamic oxytocin-neurons in the paraventricular (PVN) and supraoptic (SON) nuclei. We recently showed that OEA requires the integrity of neuronal histamine to fully display its hypophagic effect. Here we aimed to investigate if differences exist in OEA-induced c-Fos expression in several brain regions of fasted, histidine decarboxylase (HDC)-KO mice that do not synthesize histamine, and wild type (WT) littermates. All the brain regions examined receive histaminergic innervation and are involved in different aspects of feeding behaviour. We found that OEA increased c-Fos expression in the SON, arcuate nucleus (ARC) and the amygdala of WT mice, but not HDC-KO mice, whereas neither genotype nor treatment differences were observed in the lateral and dorsomedial hypothalamus. Furthermore, oxytocin-immunostaining was markedly increased in the neurohypophysis of WT and not in HDC-KO mice. Of note, OEA increased c-Fos expression in the nucleus of solitary tract of both genotypes. Our findings suggest that the TMN serves as a relay station to elaborate peripheral signals that control homeostatic and adaptive behavioural responses.

Satiety factor oleoylethanolamide recruits the brain histaminergic system to inhibit food intake.

Key factors driving eating behavior are hunger and satiety, which are controlled by a complex interplay of central neurotransmitter systems and peripheral stimuli. The lipid-derived messenger oleoylethanolamide (OEA) is released by enterocytes in response to fat intake and indirectly signals satiety to hypothalamic nuclei. Brain histamine is released during the appetitive phase to provide a high level of arousal in anticipation of feeding, and mediates satiety. However, despite the possible functional overlap of satiety signals, it is not known whether histamine participates in OEA-induced hypophagia. Using different experimental settings and diets, we report that the anorexiant effect of OEA is significantly attenuated in mice deficient in the histamine-synthesizing enzyme histidine decarboxylase (HDC-KO) or acutely depleted of histamine via interocerebroventricular infusion of the HDC blocker α-fluoromethylhistidine (α-FMH). α-FMH abolished OEA-induced early occurrence of satiety onset while increasing histamine release in the CNS with an H3 receptor antagonist-increased hypophagia. OEA augmented histamine release in the cortex of fasted mice within a time window compatible to its anorexic effects. OEA also increased c-Fos expression in the oxytocin neurons of the paraventricular nuclei of WT but not HDC-KO mice. The density of c-Fos immunoreactive neurons in other brain regions that receive histaminergic innervation and participate in the expression of feeding behavior was comparable in OEA-treated WT and HDC-KO mice. Our results demonstrate that OEA requires the integrity of the brain histamine system to fully exert its hypophagic effect and that the oxytocin neuron-rich nuclei are the likely hypothalamic area where brain histamine influences the central effects of OEA.

Identification of a histaminergic circuit in the caudal hypothalamus: an evidence for functional heterogeneity of histaminergic neurons.

It is well established that histaminergic neurons in the posterior hypothalamus make connections with whole brain areas and regulate several functions. Recent evidence indicates that histaminergic neurons are heterogeneous cell group and organized into distinct circuits. However, functional circuits of histaminergic neurons have not been fully mapped so far. To address this issue, we have investigated antihistamine-sensitive neuronal activation in the hypothalamus to determine the hypothalamic region primarily innervated by histaminergic neurons. Here we review our recent findings showing the existence of the heterogeneous subpopulations of histaminergic neurons in the TMN that innervated distinct regions to regulate particular functions. We have identified the caudal part of the arcuate nucleus of hypothalamus (cARC) as a target region of histaminergic neurons in food-restricted rats by assessing suppression of c-Fos expression by pretreatment with antihistamines. Histaminergic neurons in the tuberomammillary nucleus (TMN) are morphologically subdivided into five groups (E1-E5). Among the subdivisions, the E3 group was found to be activated corresponding to the activation of cARC neurons. Our findings suggest that this subpopulation selectively innervate cARC neurons. Accumulating reports have also described c-Fos expression in other TMN subpopulations. Various stress challenge induced c-Fos expression primarily in E4 and E5 subpopulations. Motivation- and drug-induced arousal elicited in common activation of ventrolateral part of the TMN containing E1 and E2 subdivisions, which receive projections from wake-active orexin neurons and sleep-active GABA neurons. These lines of evidence support the hypothesis that there are heterogeneous subpopulations in the TMN that innervated distinct regions to regulate particular functions.

Deprivation of anticipated food under scheduled feeding induces c-Fos expression in the caudal part of the arcuate nucleus of hypothalamus through histamine H1 receptors in rats: potential involvement of E3 subgroup of histaminergic neurons in tuberomammillary nucleus.

It is well established that histaminergic neurons densely innervate the anterior hypothalamus and regulate several functions through histamine H(1) receptor (H1R). However, functional innervations of histaminergic neurons in the caudal hypothalamus have been poorly investigated. Recently, we have demonstrated that c-Fos, a marker of neuronal activation, was significantly induced by food deprivation under scheduled feeding in H1R-expressing cells in the caudal part of the arcuate nucleus of hypothalamus (cARC) of rats and histaminergic neurons innervating this area. In this study, we have examined the functional involvement of histaminergic neurons in the food deprivation-induced c-Fos expression in the cARC under scheduled feeding. The c-Fos expression in the cARC by food deprivation was significantly suppressed by pretreatment with antihistamines. After food deprivation, the number of c-Fos-histidine decarboxylase (HDC) double-positive neurons was mostly increased in the E3 subdivision of the tuberomammillary nucleus (TM). Under the restricted feeding schedule, significant expressions of c-Fos were detected in the TM and cARC only when rats strongly anticipated feeding, compared with a slight c-Fos induction in both nuclei when they were satiated. These findings suggest that the histaminergic neurons in the E3 subdivision of the TM are selectively activated by deprivation of an anticipated food under scheduled feeding and functionally innervate the H1R-expressing neurons in the cARC.

Suplatast tosilate inhibits histamine signaling by direct and indirect down-regulation of histamine H1 receptor gene expression through suppression of histidine decarboxylase and IL-4 gene transcriptions.

Allergic rhinitis (AR) is an inflammatory disorder typified by symptoms such as sneezing, congestion, and rhinorrhea. Histamine plays important roles in eliciting AR symptoms. Up-regulation of the histamine H(1) receptor (H1R) and histidine decarboxylase (HDC) mRNAs was observed in AR patients. Th2 cytokines are also involved in the pathogenesis of AR. We examined the effect of suplatast tosilate on nasal symptoms, and H1R, HDC, and IL-4 gene expression using toluene-2,4-diisocyanate (TDI)-sensitized rats and HeLa cells expressing endogenous H1R. Provocation with TDI increased nasal symptoms, HDC activity, the histamine content of nasal lavage fluid, and the expression of H1R, HDC, and IL-4 mRNAs in TDI-sensitized rats. Pretreatment with suplatast for 2 wk significantly suppressed TDI-induced nasal symptoms and elevation of H1R, HDC, and IL-4 mRNAs. Suplatast also suppressed HDC activity in the nasal mucosa and the histamine content of the nasal lavage fluid. Bilateral injection of IL-4 into the nasal cavity of normal rats up-regulated H1R mRNA, while intranasal application of histamine up-regulated IL-4 mRNA. Suplatast suppressed IL-4-induced up-regulation of H1R mRNA in HeLa cells. However, it did not inhibit histamine-induced H1R mRNA elevation. These results suggest that suplatast alleviates nasal symptoms by inhibiting histamine signaling in TDI-sensitized rats through the suppression of histamine- and IL-4-induced H1R gene expression by the inhibitions of HDC and IL-4 gene transcriptions, respectively.

Kujin suppresses histamine signaling at the transcriptional level in toluene 2,4-diisocyanate-sensitized rats.

Kujin, the dried root of Sophorae flavescensis, has been used in Chinese folklore medicine against allergy. Evaluation of its anti-allergic potential as well as its mechanism of action has rarely been established. We investigated the effect of Kujin on toluene-2,4-diisocyanate (TDI)-induced allergic behavior and related histamine signaling including mRNA levels of histamine H(1) receptor (H1R) and histidine decarboxylase (HDC), H1R and HDC activities, and histamine content in rat nasal mucosa. We also investigated the effect of Kujin on the mRNA levels of helper T cell type 2 (Th2)-cytokine genes closely related to histamine signaling. TDI provocation caused acute allergic symptoms accompanied with up-regulations of H1R and HDC mRNAs and increases in HDC activity, histamine content, and [(3)H]mepyramine binding activity in the nasal mucosa, all of which were significantly suppressed by pretreatment with Kujin for 3 weeks. Kujin also suppressed the TDI-induced IL-4 and IL-5 mRNA elevations. These data suggest that oral administration of Kujin showed anti-allergic activity through suppression of histamine signaling by the inhibition of TDI-induced H1R and HDC mRNA elevations followed by decrease in H1R, HDC protein level, and histamine content in the nasal mucosa of TDI-sensitized rats. Suppression of Th2-cytokine signaling by Kujin also suggests that it could affect the histamine-cytokine network.

Effects of hypergravity on histamine H1 receptor mRNA expression in hypothalamus and brainstem of rats: implications for development of motion sickness.

CONCLUSION: The study findings suggest that histamine was released from the axon terminals in the hypothalamus and brainstem and the released histamine activated post-synaptic H1 receptors there, resulting in the development of motion sickness. OBJECTIVES: We first examined which subtype of post-synaptic histaminergic receptor was responsible for the development of motion sickness. We then examined whether H1 receptors were up-regulated in various areas of the rat brain after 2 G hypergravity load, because the stimulation of H1 receptor was reported to up-regulate the level of H1 receptor protein expression through augmentation of H1 receptor mRNA expression. MATERIALS AND METHODS: For this purpose, we used an animal model of motion sickness, using pica (eating non-nutritive substances such as kaolin), as a behavioral index in rats. RESULTS: After 2 G hypergravity load, rats ate a significant amount of kaolin, indicating that they suffered from motion sickness. The hypergravity-induced kaolin intake was suppressed by mepyramine, but not by terfinadine or zolantizine. This finding indicates that cerebral post-synaptic H1 but not H2 or peripheral H1 receptors play an important role in the development of motion sickness. The expression of H1 receptor mRNA was up-regulated in the hypothalamus and brainstem, but not in the cerebral cortex after 2 G hypergravity load in rats.

Sho-seiryu-to suppresses histamine signaling at the transcriptional level in TDI-sensitized nasal allergy model rats.

BACKGROUND: The therapeutic use of Kampo medicine, Sho-seiryu-to (SST) in allergic disorders is well known. As histamine plays a central role in allergic diseases, it is possible that SST affects the allergy-related histamine signaling. In this study, we investigated the effect of SST on allergy-related histamine signaling in the nasal mucosa of toluene 2, 4-diisocyanate (TDI)-sensitized nasal allergy model rats. METHODS: Six-week-old male, Brown Norway rats were sensitized for 2 weeks with 10 microl of 10% TDI, and after a 1 week interval, provocation was initiated with the same amount of TDI. SST (0.6g/rat) was given orally 1 hour before TDI treatment began for a period of 3 weeks. Nasal symptoms were scored for 10 minutes immediately after TDI-provocation. The genes expression in nasal mucosa was determined using real-time quantitative RT-PCR. RESULTS: SST significantly suppressed TDI-induced nasal allergy-like symptoms. TDI provocation showed a significant up-regulation of histamine H(1) receptor (H1R) and histidine decarboxylase (HDC) gene expressions. Prolonged pre-treatment of SST significantly suppressed the mRNA levels of H1R and HDC that was up-regulated by TDI. SST also suppressed TDI-induced interleukin (IL)-4 and IL-5 mRNA elevation. However, SST showed no significant effect for TDI-induced mRNA elevation of IL-13. CONCLUSIONS: These results demonstrate that SST alleviates nasal symptoms by the inhibition of histamine signaling through suppression of TDI-induced H1R and HDC gene up-regulation. SST also suppresses cytokine signaling through suppression of IL-4 and IL-5 gene expression. Suppression of histamine signaling may be a novel mechanism of SST in preventing allergic diseases.

Repeated pre-treatment with antihistamines suppresses [corrected] transcriptional up-regulations of histamine H(1) receptor and interleukin-4 genes in toluene-2,4-diisocyanate-sensitized rats.

Antihistamines are effective for treatment of seasonal nasal allergy. Recently, prophylactic treatment with antihistamines in patients with pollinosis was reported to be more effective when started before the pollen season. The administration with antihistamines from 2 to 6 weeks before onset of the pollen season is recommended for management of allergic rhinitis in Japan. To determine the reason for the effectiveness of prophylactic treatment with antihistamines, the effects of repeated pre-treatment with antihistamines before provocation with toluene 2,4-diisocyanate (TDI) on their nasal allergy-like behavior and up-regulations of histamine H(1) receptors (H1R) and interleukin (IL)-4 mRNAs in their nasal mucosa were examined. Provocation with TDI induced sneezing and up-regulations of H1R and IL-4 mRNAs in the nasal mucosa of TDI-sensitized rats. Repeated pre-treatments with antihistamines including epinastine, olopatadine, or d-chlorpheniramine for 1 to 5 weeks before provocation with TDI suppressed TDI-induced sneezing and the up-regulations of H1R and IL-4 mRNAs in the nasal mucosa more than their administrations once or for 3 days before TDI provocation. Our data indicate that repeated pre-treatment with antihistamines before provocation with TDI is more effective than their single treatment in reducing nasal allergy-like behavior by causing additional suppression of up-regulations of H1R and IL-4 mRNAs in the nasal mucosa.

Evaluation of efficacy and sedative profiles of H(1) antihistamines by large-scale surveillance using the visual analogue scale (VAS).

BACKGROUND: H(1) antihistamines are widely used as therapeutics for allergic diseases. Sedation is a well-known side effect of H(1) antihistamines and sometimes it is life-threatening for patients. Thus it is important to evaluate the sedative properties of H(1) antihistamines to avoid side effects. For this purpose, histamine H(1) receptor (H1R) occupancy and proportional impairment ratios (PIR) are now being used. However, it is not easy to obtain these parameters. Here, we sought to evaluate the sedative properties of H(1) antihistamines by means of a large-scale surveillance at health insurance pharmacies. METHODS: The survey was conducted at 37 health insurance pharmacies. The therapeutic efficacy and the degree of sleepiness were quantified through a questionnaire using the visual analog scale (VAS) directly from 1742 patients who received H(1) antihistamines. RESULTS: The degree of sleepiness caused by the first-generation antihistamines was significantly higher than that of the second-generation antihistamines. The high VAS score in case of efficacy was found in d-chlorpheniramine, olopatadine, and ebastine. Among the mean values of efficacy, all second-generation antihistamines except for loratadine, bepotastine, and mequitazine were significantly higher than that of clemastine. Regarding the degree of sleepiness, clemastine scored the highest VAS score, and significantly lower scores were obtained in all second-generation antihistamines. CONCLUSIONS: The sedative properties of the H(1) antihistamines obtained from VAS analysis were very similar to those of H1R occupancy from positron emission tomography (PET) studies and PIR from meta-analysis. Our results indicate that large-scale surveillance using VAS might be useful to evaluate the profiles of H(1) antihistamines.

Suppression of histamine signaling by probiotic Lac-B: a possible mechanism of its anti-allergic effect.

It has been shown that probiotic bacteria are effective for the treatment of allergic diseases. As histamine plays a central role in allergic diseases, it is possible that probiotic bacteria affect the allergy-related histamine signaling. Here, we investigated the effect of Lac-B, a mixture of freeze-dried Bifidobacterium infantis and Bifidobacterium longum, on the allergy-related histamine signaling. In the nasal allergy model rats made by sensitization and provocation with toluene 2,4-diisocyanate (TDI) for 3 weeks, TDI provocation caused acute allergy-like behaviors along with significant up-regulation of histamine H(1) receptor (H1R) and histidine decarboxylase (HDC) mRNA expression, increased HDC activity, histamine content, and [(3)H]mepyramine binding activity in nasal mucosa. Prolonged treatment with Lac-B (40 mg/rat, p.o.) significantly suppressed both the allergy-like behaviors and all of the above mentioned factors involved in histamine signaling. Our findings indicate that oral administration of Lac-B showed significant anti-allergic effect through suppression of both H1R and HDC gene expression followed by decrease in H1R, HDC protein level, and histamine content. Suppression of histamine signaling may be a novel target of probiotics in preventing allergic diseases.

Down-regulation of histamine H1 receptors by beta2-adrenoceptor-mediated inhibition of H1 receptor gene transcription.

Histamine H1 receptor (H1R) levels vary under various pathological conditions, and these changes may be responsible for some pathogenesis such as in allergic rhinitis. Several stimulants, including histamine, muscarinic agonists and platelet-activating factor, have now been shown to regulate H1R levels and may have roles in regulating the H1R level in physiological and pathological conditions. Results for beta2-adrenoceptor (beta2AR) stimulation are conflicting, however.beta2AR up-regulated H1R in bovine tracheal smooth muscle, but down-regulated human H1R expressed in Chinese hamster ovary (CHO) cells. It is possible that this discrepancy comes from the differences in the preparations used for each study: the former cell expressed bovine H1R and the latter cell expressed human H1R. Moreover, CHO cells have been shown to be inadequate for studying the effects on H1R gene expression, because the cells express non-endogenous stably transfected H1R under the control of the SV40 promoter. Therefore, in this study, we have investigated the role of beta2AR stimulation in H1R gene regulation using human U373 astrocytoma cells that express endogenous H1R and transfected beta2AR. Stimulation of beta2AR significantly reduced H1R promoter activity and H1R mRNA levels. H1R mRNA stability was slightly reduced by beta2AR stimulation, although this was not significant. The decrease of H1R mRNA by beta2AR stimulation was blocked by the protein kinase A (PKA) inhibitor KT5720, suggesting the involvement of PKA. These results indicate that the beta2AR is involved in the down-regulation of human H1R by inhibiting H1R gene transcription through a PKA-dependent process.