Changes in hippocampal histamine receptors in rats after treatment with Trimeresurus albolabris venom

BACKGROUND： It has been demonstrated that histamine and its receptors in the hippocampus play an important role in memory and/or learning behaviors.OBJECTIVE： To investigate the expression levels of the histamine receptor gene and protein in the hippocampi of rats prior to and after administration of Trimeresurus albolabris venom using reverse transcription-polymerase chain reaction （RT-PCR） and Western blot techniques. DESIGN, TIME AND SETTING： A controlled observation based on cellular protein level was performed in the College of Life Sciences, Chongqing Normal University between March 2005 and April 2007. MATERIALS： Eighty adult male Sprague-Dawley rats were provided by the Laboratory Animal Center of the Third Military Medical University of Chinese PLA. The lyophilized powder of Trimeresurus albolabris venom was collected from Jin-Hu-Shan in Chongqing, China. METHODS： Twenty rats were randomly and evenly divided into an experimental group and a control group The experimental group was subcutaneously injected with 0.65 mg/mL Trimeresurus albolabris venom, 0.5 mL for each rat. The control group was subcutaneously injected with an equal amount of 0.9% physiological saline. Prior to and after injection, rats from these two groups were placed in the Morris Water Maze for recording of path length and escape latency. The remaining 60 rats were randomly allocated to another experimental group （n = 50） and another control group （n = 10）. Rats were correspondingly injected as described above. At different time points （0.1, 0.5, 1, 2, and 3 hours after injection）, rats were decapitated and bilateral hippocampal tissues were dissociated （approximately 100 mg for each sample）. Then, the acquired hippocampal tissue was immediately preserved at -70 ℃ for subsequent experiments. MAIN OUTCOME MEASURES： （1） The levels of histamine receptor （including H1R, H2R, and H3R） mRNA and protein in the hippocampi of rats were measured prior to and after injection of Trimeresurus albolabris venom using RT-PCR and Western Blot techniques. （2） Escape latency （namely, time to reach a platform） and path length were examined by Morris Water Maze testing. RESULTS： All 80 rats were included in the final analysis. In the experimental group, the level of mRNA for H3R receptor in rat hippocampi was just slightly changed, but the level of H3R receptor protein was significantly down-regulated compared with that in the control group （P 〈 0.05）. Both mRNA and protein levels for H1R receptor were initially downregulated and then recovered to normal levels. Expression of H2R receptor mRNA was initially upregulated, then downregulated, and finally restored to the control level. The level of H2R receptor protein showed a tendency for downregulation. In the Morris Water Maze testing, escape latency and path length were significantly longer in the experimental group than in the control group （P 〈 0.05）. CONCLUSION： Within three hours of injection with Trimeresurus albolabris venom, mRNA and protein levels of most histamine receptors in rat hippocampi were downregulated. Such changes possibly contribute to an impairment of memory and/or learning behaviors in rats following injection of Trimeresurus albolabris venom.

Thioperamide treats neonatal hypoxic-ischemic encephalopathy by postsynaptic H1 receptors

Thioperamide, a selective histamine H3 receptor antagonist, can increase histamine content in the brain, improve brain edema, and exert a neuroprotective effect. This study aimed to examine the mechanism of action of thioperamide during brain edema in a rat model of neonatal hypoxic ischemic encephalopathy. Our results showed that thioperamide significantly decreased brain water content and malondialdehyde levels, while significantly increased histamine levels and superoxide dismutase activity in the hippocampus. This evidence demonstrates that thioperamide could pre vent oxidative damage and attenuate brain edema following neonatal hypoxicischemic encepha Iopathy. We further observed that changes in the above indexes occurred after combined treatment of thioperamide with the H1 receptor antagonist, pyrilamine, and the H2 receptor antagonist, ci metidine. Experimental findings indicated that pyrilamine reversed the effects of thioperamide; however, cimetidine had no significant influence on the effects of thioperamide. Our present findings suggest that thioperamide can increase brain histamine content and attenuate brain edema and oxidative damage by acting in combination with postsynaptic H1 receptors in a rat model of neo natal hypoxicischemic encephalopathy.

Histamine H2 receptor deletion in glutamatergic neurons causes schizophrenia-like pheno⁃ types

OBJECTIVE Genetic variation in histamine H2 receptor(H2R)and H2R ligands are linked to schizophrenia,however little is known about how H2R contributes to pathogenesis of schizophrenia.Here,we detected a decreased expression of H2R in medial prefrontal cortex(mPFC)glutamatergic neurons in schizophrenia patients.METHODS AND RESULTS Selective knockout of H2R gene(Hrh2)in glutamatergic neurons induced schizophrenia-like behaviors including sensorimotor gating deficit,increased locomotor activity,social withdrawal and anhedo⁃nia in behavior tests,as well as reduced sponta⁃neous firing of mPFC glutamatergic neurons in electrophysiological tests.Selective deletion of the Hrh2 in mPFC glutamatergic neurons but not hippocampus glutamatergic neurons also induced such schizophrenia-like behaviors.Patch-clamp electrophysiology establishes that H2R deficiency reduced the intrinsic excitability of glutamatergic neurons by up-regulation of hyperpolarization activated cyclic nucleotide-gated channels.Fur⁃thermore,either overexpression of H2R in gluta⁃matergic neurons or activation of H2R in the mPFC reversed the MK-801-induced schizophrenia-like symptoms.CONCLUSION H2R can serve as a novel drug target given that functional deficiency of this receptor in mPFC glutamatergic neurons may be crucial for the pathogenesis of schizo⁃phrenia.H2R agonists can be viewed as drug candidates for the treatment of schizophrenia.

Comparative study of therapeutic effects of PPI and H2RA on ulcers during continuous aspirin therapy

AIM:To compare the therapeutic effects of proton pump inhibitors(PPI) and histamine 2 receptor antagonists(H2RA) on gastroduodenal ulcers under continuous use of low-dose aspirin.METHODS:Sixty patients who had a gastroduodenal ulcer on screening endoscopy but required continuous use of low-dose aspirin were randomly assigned to receive PPI(lansoprazole 30 mg,n = 30) or H2RA(famotidine 40 mg or if famotidine had been administered before assignment,ranitidine 300 mg,n = 30).The therapeutic effects were evaluated by endoscopy after 8-wk treatment.The presence or absence of Helicobacter pylori(H.pylori) was determined by urea breath test before treatment.Abdominal symptoms were compared with the gastrointestinal symptom rating scale(GSRS) questionnaire before and after treatment.RESULTS:Twenty-six patients in the PPI group and 26 patients in the H2RA group,excluding dropouts,were analyzed.There were no significant differences in median age,sex,underlying disease,smoking status,H.pylori infection,prevalence of ulcers before treatment,and lesion site between the two groups.The therapeutic effects were endoscopically evaluated as healed in 23 patients(88.5%) and not healed in 3 patients in the PPI group and as healed in 22 patients(84.6%) and not healed in 4 patients in the H2RA group.Abdominal symptoms before treatment were uncommon in both groups;the GSRS scores were not significantly reduced after treatment as compared with before treatment.CONCLUSION:The healing rate of gastroduodenal ulcers during continuous use of low-dose aspirin was greater than 80% in both the PPI group and the H2RA group,with no significant difference between the two groups.

Loss of Hrh2 on dopaminergic neurons leads to mania-like behavior in mice

OBJECTIVE Dysfunction of the dopaminergic(DA)neurons is implicated in the pathogenesis of bipolar disorder(BPD).Hista⁃mine receptor 2(Hrh2)is highly expressed in DA neurons,and its antagonists have been reported to induce mania phase of BPD.However,whether Hrh2 on DA neurons contributes to BPD patho⁃genesis is unclear.The present study aims to explore the role of hrh2 on DA neurons in the pathology of BPD.METHODS AAV-FLEX-shHrh2 was injected into a targeted brain area of DAT-Cre mice,leading to a selective brain-regional loss of Hrh2 on DA neurons.A series of behavior tests were used to measure the sponta⁃neous activity,anxiety and depression level of Hrh2-deficient mice.RESULTS①In the open field test and home-cage activity test,Hrh2-defi⁃cient mice displayed increased spontaneous activity.②Hrh2-deficient mice showed reduced depression level in the tail suspension test,forced swimming test and sucrose preference test.③The anxiety level of Hrh2-deficient mice was decreased in the open field test.CONCLU⁃SION Hrh2 on DA neurons is closely related with mania-like behavior.

Effects of splice sites on the intron retention in histamine H_3 receptors from rats and mice

In the alternative splicing, intron retention, of histamine H3 receptors in rats and mice, the short transcript isoforms that are excised alternatively spliced introns are easily detected in a very low level in rats and are undetectable in mice using the regular PCR protocol. The retained introns have common 5＇ splice site and different 3＇ splice sites. The detailed mechanism for the special alternative splicing remains largely unclear. In this study, we developed a minigene splicing system to recapitulate natural alternative splicing of the receptors and investigated the effects of 5＇ and 3＇ splice sites on intron retention in HeLa cells. Mutating weak 5＇ and 3＇ splice sites of the alternatively spliced introns toward the canonical consensus sequences promoted the splicing of the corresponding introns in rat and mouse minigenes. The effect of splice site strength was context-dependent and much more sigiaificant for the 3＇ splice site of the longer alternative intron than for the 3＇ splice site of the shorter alternative intron and the common 5＇ splice sites; it was also more significant in the rat minigene than in the mouse minigene. Mutating the 3＇ splice site of the longer alternative intron resulted in almost complete splicing of the intron and made the corresponding isoform to become the nearly exclusive transcript in the rat minigene.