Sensory irritation by toluene diisocyanate in single and repeated exposures

The effects of single and repeated exposures to toluene diisocyanate (TDI) at concentrations ranging from 0.007 to 2 ppm were investigated using an animal model to detect the level of sensory irritation caused by this chemical. Time-response relationships showed the slow development of the response with exposure duration and a very slow recovery following 3 hr of exposure. Concentration-response relationships also showed that the level of response was not only dependent upon exposure concentration, but also on duration of exposure and that TDI is the most potent sensory irritant tested so far. Repeated exposures to TDI at or above 0.023 ppm resulted in cumulative effects. On the basis of a prior prediction proposed from the results obtained with this animal model, it is suggested that the Threshold Limit Value (TLV) for industrial exposure be reduced to 0.006 ppm as a time weighted average (TWA) and no exposure above 0.02 ppm be permitted, even for short exposures.     

Effects of single and repeated exposures to abate on rat behavior and cholinesterase activity.

Rats were injected i.p. with the organophosphate insecticide ABATE and tested over the next 16 days. Animals given 1000 mg/kg showed impaired performance of a previously conditioned avoidance response 6 days after injection but not 2, 8, 10, or 16 days after injection. No behavioral changes were observed in animals given 316 or 562 mg/kg. A subsequent experiment showed that the avoidance impairment in animals given 1000 mg/kg was accompanied by significant erythrocyte, plasma, and brain cholinesterase activity inhibition and decreased spontaneous motor activity. If administration of the same ABATE dose was distributed over 6 days (167 mg/kg/day), cholinesterase and motor activity depression was still evident but conditioned avoidance performance was unimpaired. The results were interpreted as differential behavioral adaption to repeated injections of ABATE.     

MK-801 induced retrieval, but not acquisition, deficits for passive avoidance conditioning

Two experiments using a state-dependent retention (SDR) design determined whether MK-801 blocked the acquisition and retention of an avoidance response. In Experiments 1 and 2, rats were trained and tested 30 min after injections of either saline or MK-801 (0.05 and 0.10 mg/kg, respectively). Two minutes after training, subjects were immediately tested, and in both experiments, the avoidance response was acquired. The 24-h retention tests for Experiment 1 revealed that the data marginally supported a SDR interpretation. In Experiment 2, the dose of MK-801 was increased to 0.10 mg/kg, and the results showed that MK-801 rendered passive avoidance (PA) state-dependent. These experiments indicate that neither the 0.05 nor 0.10 mg/kg doses of MK-801 prevented acquisition of the avoidance response and that the latter dose rendered memory for PA training state-dependent. It is suggested that doses of MK-801 that did not impair PA learning can function as a cue state and influence expression of memory for PA.     

软骨藻酸对神经胶质细胞的氧化损伤及HO-1表达的影响

软骨藻酸（domoicaeid，DA）是多列型尖刺拟菱形硅藻产生的可严重危害人畜健康的兴奋性神经生物毒素，作用于中枢神经系统，导致中毒患者出现短时和永久记忆力丧失等神经症状。在我国香港海域的赤潮中发现尖刺拟菱形硅藻的存在，随着赤潮发生频率日益增多，软骨藻酸势必对人类健康和环境造成严重威胁。超氧化物歧化酶（SOD）能清除超氧阴离子自由基保护细胞免受损伤。     

Potentiation of ethanol in spatial memory deficits induced by some benzodiazepines

Triazolam caused no significant increase in the total error at 0.05 and 0.1 mg/kg. However, at 0.2 mg/kg, it caused a significant increase in total error. Almost the same findings were observed with brotizolam and rilmazafone. That is, at 0.2 and 0.5 mg/kg of brotizolam, 0.5 and 1.0 mg/kg of rilmazafone caused no significant increase in the total error. However, brotizolam at 1.0 mg/kg and rilmazafone at 2.0 mg/kg caused a significant increase in total error. Triazolam (0.05 mg/kg) and ethanol (1.0 g/kg) showed no significant effect on the numbers of errors when used alone separately, but the simultaneous use of triazolam and ethanol caused a significant increase in total error. Almost the same findings were observed with the coadministration of brotizolam (0.2 mg/kg) or rilmazafone (0.5 mg/kg) with ethanol. These results clearly indicate that all the short-acting benzodiazepines used in the study showed potentiation by ethanol in spatial memory deficits in mice.     

蛇床子素减轻脂多糖诱导的大鼠学习记忆减退

目的观察蛇床子素对脂多糖诱导的大鼠学习记忆减退的作用,并初探其可能的作用机制。方法 40只雄性SD大鼠随机分为假手术组、模型组、阳性药组及蛇床子素组。阳性药组、蛇床子素组分别每日1次灌胃布洛芬、蛇床子素40 mg.kg-1,连续12 d,假手术组、模型组灌胃等体积的生理盐水,3 d后侧脑室注射脂多糖诱导大鼠的神经炎症模型,制模后d 5开始Morris水迷宫检测大鼠的空间记忆能力,连续5 d。Morris水迷宫检测结束后,处死大鼠,HE染色观察大鼠海马神经元损伤情况,real time RT-PCR法测定海马肿瘤坏死因子α(Tnf-α)、白细胞介素-1β(Il-1β)、诱导型一氧化氮合酶(Nos2)及环氧合酶-2(Cox-2)的mRNA表达。结果侧脑室注射脂多糖后,大鼠在定向航行实验中的逃避潜伏期显著增加(P<0.05),空间探索实验中的校正逃避潜伏期缩短(P<0.05),海马神经元明显受损,且海马Tnf-α、Il-1β、Nos2及Cox-2的mRNA表达增加(P<0.05);然而,蛇床子素及布洛芬明显缩短了大鼠的定向航行实验中的逃避潜伏期(P<0.05),延长了空间探索实验中的校正逃避潜伏期(P<0.05),减轻了海马神经元损伤,且降低海马Tnf-α、Il-1β、Nos2及Cox-2的mRNA表达。结论蛇床子素可减轻脂多糖诱导的大鼠学习记忆减退及海马神经元损伤,其机制与抑制炎症相关基因的mRNA表达有关。     

Short-term individual housing induced social deficits in female Mongolian gerbils: attenuation by chronic but not acute imipramine

Mongolian gerbils are highly sensitive to manipulations of their social environments. Housing females individually for short periods (in the order of 7-21 days) has been shown to produce robust and reliable impairments of their subsequent social behaviour. These effects are typified by a marked reduction in the social investigation of an unfamiliar male in a neutral arena and/or a marked increases in levels of freezing whilst and only whilst they are being socially investigated (Immobile in contact). These responses demonstrate housing induced impaired motivation to socially interact. These effects have also been shown to be sensitive to treatment with chronic (but not acute) administration of the selective serotonin reuptake inhibitor (SSRI) fluoxetine. It was therefore of interest to know if similar effects would be produced by treatment with the tricyclic antidepressant Imipramine. This mixed NA/5-HT reuptake inhibitor first developed in the 1950's is a commonly used standard in animal models of depression and remains in clinical use today. Female gerbils were individually housed for 7 days or maintained in single-sex groups of 4 for the same period. All animals were then randomly allocated to be administered with either 0, 10 or 20 mg/kg imipramine. Acute administration did not reverse the social impairments produced by the individual housing but did produce non-specific stimulant effects on locomotion in both housing conditions. These social impairments were however reduced after a further 14 days chronic treatment with 10 or 20 mg/kg imipramine and stimulant effects were no longer seen. Following chronic administration in group-housed animals locomotor stimulation was replaced with sedation, which resulted in a reduction in social behaviour. That is, opposite to the effect seen in Individual housed animals. It is therefore concluded that chronic treatment with imipramine serves to increase social behaviour but only in those animals with a pre-existing social deficit.     

Glutathione levels modulate domoic acid induced apoptosis in mouse cerebellar granule cells.

Exposure of mouse cerebellar granule neurons (CGNs) to domoic acid induced cell death, either by apoptosis or by necrosis, depending on its concentration. Necrotic damage predominated in response to domoic acid above 0.1 microM. In contrast, cell injury with apoptotic features (assessed by Hoechst staining and DNA laddering assay) was evident after exposure to lower concentrations of domoic acid (< or = 0.1 microM). The AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)/kainate receptor antagonist 2,3-dihydroxy-6-nitro-sulfamoylbenzo [f] quinoxaline, but not the N-methyl-D-aspartate receptor antagonist MK-801, prevented domoic acid-induced apoptosis. To evaluate the role of oxidative stress in domoic acid-induced apoptosis, experiments were carried out in CGNs isolated from wild-type mice (Gclm (+/+)) and mice lacking the modifier subunit of glutamate-cysteine ligase, the first and rate-limiting step of glutathione (GSH) biosynthesis (Gclm (-/-)). CGNs from Gclm (-/-) mice have very low levels of GSH and were more sensitive to domoic acid-induced apoptosis and necrosis than Gclm (+/+) CGNs. The antioxidant melatonin (200 microM) and the membrane-permeant GSH delivery agent GSH ethyl ester (2.5 mM) prevented domoic acid-induced apoptosis. Domoic acid increased formation of reactive oxygen species but did not affect intracellular GSH levels. Domoic acid also increased cytosolic and mitochondrial calcium levels, increased oxidative stress in mitochondria, and altered mitochondrial membrane potential, which ultimately caused cytochrome c release, activation of caspase-3, and degradation of poly (ADP-ribose) polymerase. These results indicate that low concentrations of domoic acid cause apoptotic neuronal cell death mediated by oxidative stress.     

Changes in sleep and wakefulness following single and repeated exposures to toluene vapor in rats

Male rats with indwelling electrodes for electroencephalographic (EEG), electromyographic (EMG) and electrooculographic (EOG) recordings were exposed via inhalation to 900 ppm and 2700 ppm toluene vapor continuously for a 8-h period or repeatedly for 3 weeks at a rate of 8 h/day and 5 days/week. Rats exposed to a clean airstream under the same exposure schedules served as controls. Polygraphic recordings were made on 3 consecutive days after cessation of the single 8-h and repeated 3-week exposures to 900 ppm and 2700 ppm toluene vapor or clean airstream. Amounts of time spent in wakefulness (W), slow-wave sleep (SWS) and paradoxical sleep (PS) were quantified by visual inspection of the polygraphic records. Single exposure to toluene produced a prolonged PS latency and a long-lasting increase in SWS at the expense of depressed W, whereas repeated exposures prolonged both SWS and PS latencies, abolished the initial increase of SWS and increased the light-phase level of W on Days 1 and 2. The prolonged PS latency and the decreased light-phase PS on Day 2 induced by single exposure to toluene still persisted after repeated exposures. There were no statistically significant differences in attenuation of brain and blood toluene levels between single and repeated exposures to toluene vapor of 900 ppm and 2700 ppm.     

The behavioural response to intrathecal serotonin is changed by acute but not by repeated treatment with zimelidine or metergoline.

The behavioural response to intrathecal serotonin (5-HT) was examined in mice after acute and after withdrawal of repeated treatment with the 5-HT uptake inhibitor zimelidine or the 5-HT receptor antagonist metergoline. Intrathecal 5-HT elicits a response consisting of biting or licking of the lower part of abdomen and reciprocal hindlimb scratching, indicative of nociceptive stimulation. Acute injection of zimelidine (20 mg/kg) significantly increased the response to intrathecal 5-HT (0.25-1 micrograms) whereas a single dose of metergoline (5 mg/kg) completely blocked the response to intrathecal 5-HT (2 micrograms). The behavioural response to intrathecal 5-HT (0.25-2 micrograms) was not significantly changed 48 hr after withdrawal of repeated treatment with zimelidine (2 x 10 mg/kg/day for 14 days) or metergoline (2 x 2.5 mg/kg/day for 14 days). In the present experiments acute zimelidine appeared to increase nociceptive responsiveness, whereas metergoline had the opposite effect. This study does not provide evidence that long-term treatment with zimelidine or metergoline leads to adaptive changes in the response to spinal cord 5-HT receptor stimulation.     

血红素氧化酶在软骨藻酸对细胞DNA损伤中的作用

目的　　研究血红素氧化酶 (hemeoxygenase ,HO)系统在软骨藻酸 (domoicacid ,DA)对H4细胞DNA损伤中的作用。方法　应用单细胞凝胶电泳法 (SCGE)分别测定 0、0 0 64、0 64和 6 4μmol/LDA单独及与HO系统的活性阻断剂ZnPP 9(10 - 5mol/L)联合作用于H4细胞 6、12、2 4和 48h后彗星拖尾细胞率及拖尾尾长。结果　彗星拖尾细胞率 :中剂量和高剂量组各时间点均比对照组高 ,差异有显著性 (P <0 0 5 )。中剂量 +阻断剂组各时间点均相应高于中剂量组 ,差异有显著性 (P <0 0 5 )。彗星拖尾尾长 :中剂量组 12、2 4和 48h比对照组长 ,2 4、48h比低剂量组长 ,差异均有显著性 (P<0 0 5 )。高剂量组各时间点均比对照组、低剂量组和中剂量组长 ,差异有显著性 (P <0 0 5 )。高剂量 +阻断剂组和中剂量 +阻断剂组 2 4、48h分别高于高剂量和中剂量组 ,差异有显著性 (P <0 0 5 )。尾长 时间作Regression分析 ,各剂量组r差异值均有显著性 (P <0 0 1)。结论　软骨藻酸能诱导H4细胞DNA损伤 ,HO系统对这种损伤有一定的保护作用。     

Mechanisms of the spatial memory deficits induced by injection of okadaic acid into the Meynert nucleus basalis of rats

We previously reported that the injection of okadaic acid (OA) into the Meynert nucleus basalis of rats induced spatial memory deficits. The present study was designed to further explore the underlying mechanisms. We found that the level of acetylcholine (Ach) in the hippocampus significantly decreased 24 h after injection of OA into the Meynert nucleus basalis of rats. Simultaneously, spatial memory deficit, PP-2A inhibition and tau hyperphosphorylation at Ser-198/Ser-199/Ser-202 (Tau-1 epitope) and Ser-396/Ser-404 (PHF-1 epitope) were observed. With the restoration of hippocampus Ach to normal levels at 48 and 72 h after the injection, the spatial memory deficits, PP-2A inhibition and tau hyperphosphorylation were reversed. It is suggested that injection of OA into the Meynert nucleus basalis of rats may impair the hippocampus-dependent spatial memory through damaging the cholinergic projection between the Meynert nucleus basalis and the hippocampus and the selective inhibition of PP-2A and tau hyperphosphorylation may be at least part of the underlying mechanisms.     

Multiple exposures to sarin vapor result in parasympathetic dysfunction in the eye but not the heart.

Several studies in conscious animals have reported parasympathetic dysfunction in the eyes following exposure to cholinesterase inhibitors. Given the similarities between the autonomic innervation in the eye and the heart, it is possible that parasympathetic dysfunction could also occur in the heart. Therefore, the present study assessed time domain indices of heart rate variability in conscious rats surgically implanted with telemetric transmitters to investigate the hypothesis that multiple exposures to the nerve agent sarin would result in muscarinic receptor desensitization and parasympathetic dysfunction in the heart. Animals exposed to sarin vapor on multiple occasions developed parasympathetic dysfunction in the eye characterized by an attenuated response to light and a diminished miotic response to sarin vapor exposure. However, the same dose of sarin vapor failed to produce any effects on either time domain indices of HRV or the magnitude of the tachycardia induced by atropine, suggesting that autonomic control in the heart was not affected. It is possible that the dose of sarin used in the present study was insufficient to inhibit cardiac acetylcholinesterase (AChE). Additional studies utilizing higher doses of sarin may be able to inhibit cardiac AChE, producing overstimulation of cardiac muscarinic receptors, ultimately resulting in desensitization and parasympathetic dysfunction.     

Chronic tryptophan deprivation attenuates gating deficits induced by 5-HT1A,but not 5-HT2 receptor activation

The neurotransmitter serotonin (5-hydroxytryptamine; 5-HT) exerts a multifaceted function in the modulation of information processing, through the activation of multiple receptor families. In particular, stimulation of 5-HT_1A and 5-HT_2A receptors leads to sensorimotor gating impairments and perceptual perturbations. Previous evidence has shown that chronic deprivation of l-tryptophan (TRP), the precursor of 5-HT, results in marked reductions of 5-HT brain levels, as well as neuroplastic alterations in 5-HT_1A and 5-HT_2A expression and/or signaling. Building on these premises, in the present study we tested whether a prolonged TRP deprivation may differentially impact the roles of these receptors in the regulation of the prepulse inhibition (PPI) of the acoustic startle reflex, a dependable index of gating. Male Sprague-Dawley rats were fed for 14 days with either a regimen with negligible TRP content (TR?) or the same diet supplemented of TRP (TR+). At the end of this schedule, rats were treated with the prototypical 5-HT_1A receptor agonist 8-OH-DPAT (62.5–250 μg/kg, subcutaneous, s.c.) or the 5-HT₂ receptor agonist DOI (0.25–1 mg/kg, s.c.). Notably, the PPI deficits induced by 8-OH-DPAT in TR? rats were significantly milder than those observed in their TR+ counterparts; these effects were fully prevented by the 5-HT_1A antagonist WAY-100135 (10 mg/kg, intraperitoneal). Conversely, TRP deprivation did not affect the PPI-disrupting properties of DOI. These findings suggest that prolonged 5-HT depletion attenuates the influence of 5-HT_1A, but not 5-HT₂ receptors on sensorimotor gating, confirming the distinct mechanisms of these two targets in PPI regulation.     

白藜芦醇减轻慢性神经炎症所致的大鼠空间学习记忆减退

目的:考察白藜芦醇对慢性炎症所致大鼠空间学习记忆减退的保护作用,探讨其作用机制。方法:雄性SD大鼠ip给予脂多糖20 mg·kg-1,每周1次,连续4周制备大鼠慢性神经炎症模型,同时ig给予白藜芦醇10,20,40 mg·kg-1·d-1,阳性组ig给予布洛芬40 mg·kg-1,连续26 d。给药d22行Morris水迷宫测定大鼠的空间学习记忆能力,连续5 d。实时定量PCR法测定大鼠海马组织肿瘤坏死因子α(TNF-α)、白细胞介素-1β(IL-1β)、诱导型一氧化氮合酶(iNOS)及环氧合酶-2(COX-2)mRNA的表达。结果:连续4周注射脂多糖(LPS)后,大鼠在定向航行实验中的逃避潜伏期明显增加,空间探索实验中的校正逃避潜伏期明显缩短,且海马组织中TNF-α,IL-1β,NOS2及COX-2基因的mRNA表达水平增加;白藜芦醇和布洛芬组大鼠定向航行实验中的逃避潜伏期明显缩短,空间探索实验中的校正逃避潜伏期延长,海马组织中TNF-α,IL-1β,NOS2及COX-2基因的mRNA表达水平降低。结论:白藜芦醇可减轻慢性神经炎症诱导的大鼠记忆能力减退,其机制可能与降低海马组织中TNF-α,IL-1β,NO...     

From sanddabs to blue whales: the pervasiveness of domoic acid.

Domoic acid (DA) is a potent food web transferred algal toxin that has caused dramatic mortality events involving sea birds and sea lions. Although no confirmed DA toxicity events have been reported in whales, here we present data demonstrating that humpback and blue whales are exposed to the toxin and consume DA contaminated prey. Whale fecal samples were found to contain DA at levels ranging from 10 to 207microg DA g(-1) feces via HPLC-UV methods. SEM analysis of whale feces containing DA, collected from krill-feeding whales, revealed the presence of diatom frustules identified as Pseudo-nitzschia australis, a known DA producer. Humpback whales were observed feeding on anchovies and sardines that contained DA at levels ranging from 75 to 444microg DA g(-1) viscera. DA contamination of whale feces and fish occurred only during blooms of toxic Pseudo-nitzschia. Additionally, several novel fish species collected during a toxic diatom bloom were tested for DA. Fish as diverse as benthic sanddabs and pelagic albacore were found to contain the neurotoxin, suggesting that DA permeates benthic as well as pelagic communities.     

Spatial memory deficits induced by perinatal treatment of rats with PCP and reversal effect of D-serine.

It has been suggested that perinatal treatment with the noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist phencyclidine (PCP) induces transient neurodegeneration in the limbic and cortical structures of rats. Since dysfunction of these structures is associated with cognitive deficits in patients with schizophrenia, we studied the effects of subchronic treatment with PCP in perinatal rats with respect to spatial reference, reversal, and spatial working memories using the Morris water maze task in adulthood. In addition, we investigated the effect of D-serine, which has clinical relevance for the treatment of cognitive deficits in patients with schizophrenia. Our goal was to develop a neurodevelopmental model with predictive validity for the cognitive dysfunction described in patients with schizophrenia. Male and female Sprague-Dawley rats were treated with either saline or PCP (8.7 mg/kg s.c.) on days 7, 9, and 11, postnatal, and the long-term behavioral effects were investigated in adulthood. Male PCP-treated rats were slightly impaired during the spatial reference memory task, but strongly impaired during the reversal and spatial working memory tasks. Female rats were not significantly affected by this treatment. This cognitive deficit was reversed by chronic treatment with D-serine. We suggest that this model mimics some of the cognitive deficits of patients with schizophrenia and might be appropriate for the screening of putative antipsychotic agents for the treatment of these cognitive deficits.     

Species differences in impairment and recovery of alveolar macrophage functions following single and repeated ozone exposures.

Effects of single (0.4 ppm for 3, 6, or 12 hr) and repeated (0.4 ppm, 12 hr/day for 3 or 7 days) in vivo ozone exposures on rat and mouse alveolar macrophage functions and cell number were investigated. Single ozone exposure of rats resulted in a small (approximately 15%) decrease in Fc-receptor-mediated phagocytosis and phorbol ester-induced superoxide production by the alveolar macrophages and was followed by recovery above control levels within 12 hr of exposure. Repeated exposures of rats for up to 7 days did not alter alveolar macrophage functions, with the exception of the effects of 3 days of exposure on superoxide production (71 +/- 9% as compared with the controls). In mice, significant changes in alveolar macrophage functions were not observed until 12 hr of exposure (at that timepoint phagocytosis was 74 +/- 2%). Repeated ozone exposures of mice did not cause a further decrease in phagocytosis (at Day 7, 74 +/- 14%). Both after 3 and 7 days of repeated ozone exposure of mice, superoxide production by the alveolar macrophages was inhibited approximately 50%. In rats and mice, repeated ozone exposures led to an increase in the number of alveolar macrophages. In mice, this increase appeared at a later time point (at Day 7 vs Day 3) and was less pronounced (at Day 7, 139 +/- 9% vs 179 +/- 17%) as compared with rats. In summary, our data show that rat and mouse alveolar macrophages have different susceptibilities to both single and repeated in vivo ozone exposures.