Detection of Burkholderia pseudomallei in rice fields with PCR-based technique

Burkholderia pseudomallei Ara- in rice fields was detected using PCR-based techniques with 16S RNA and flagella gene primer sets. The sensitivity of these PCRs was at least 1 CFU/mL of B. pseudomallei Ara- preincubated into Ashdown's medium for 6 h. B. pseudomallei Ara- DNA from watery soil were more detectable than from dry soil. The distribution of this DNA was mainly found at a depth of 300-600 mm under crop-covered fields, but not detected in the location of soil close to the land surface. The results suggest that PCR based on 16S RNA and flagella gene primer sets can be applied to investigate the presence of B. pseudomallei Ara- in contaminated soil of rice fields.

Enhanced PCE dechlorination by biobarrier systems under different redox conditions

The industrial solvent tetrachloroethylene (PCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to evaluate the (1) feasibility of enhancing PCE biodegradation using cane molasses and sludge cakes as the primary substrates under methanogenic and iron reducing conditions, and (2) potential of installation a sludge cake/cane molasses biobarrier to clean up PCE-contaminated aquifers. The biodegradability of sludge cake (from secondary wastewater treatment system) and cane molasses was tested using bioavailability experiments. Results show that biodegradable materials were released from sludge cake/cane molasses and utilized by microbial consortia. Based on the chemical oxygen demand (COD) tests, approximately 28 and 248 mg of biodegradable COD can be released from 1g of sludge cake and 1g of cane molasses under anaerobic conditions, which have the potential to convert 70 and 620 mg of PCE to ethylene (ETH), respectively. Reductive dechlorination was evaluated using microcosms containing primary substrates (sludge cake/cane molasses) and inocula (aquifer sediments). Results indicate that sludge cake and cane molasses can serve as the diffusion sources of primary substrates, and enhance the reductive dechlorination of PCE under methanogenic processes. However, results from this study were not sufficient enough to show that reductive dechlorination of PCE would occur under iron-reducing conditions. This indicates that more studies need to be performed to further evaluate the role of iron reduction on the PCE dechlorination. Results reveal that it is feasible and applicable to install a sludge cake or cane molasses biobarrier to clean up PCE contaminated aquifers. From an engineering point of view, the sludge cake/cane molasses biobarrier has the potential to become an environmentally and economically acceptable technology for PCE bioremediation.

Effects of soil pH, temperature and water content on the growth of Burkholderia pseudomallei

Optimum conditions were determined for the growth of Burkholderia pseudomallei in natural soils or waters. It grows better in paddy soil, crop-covered and fallow field than in fresh and salty water. Although the optimal temperature and pH for the growth were 37 or 42 degrees C, and 6.5 or 7.5 in an environmental-mimicking soil medium, this bacterium can still grow at 4 degrees C, which was suggested to be related with the occurrence of melioidosis in some cold areas. In soil media with water content < 15. B. pseudomallei did not grow until 60 d of incubation, suggesting that water contents of soils in which it dwelled would be one important factor in determining the growth rate.

Adsorption characteristics of benzene on biosolid adsorbent

This study selected biosolids from a petrochemical wastewater treatment plant as the raw material. The sludge was immersed in 0 to 5 mol l(-1) of ZnCl2 solutions and pyrolyzed at different temperatures. When the sludge was pyrolyzed for 30 min at temperatures of 400, 500, 600, and 700 degrees C, the corresponding surface area of the biosolid adsorbent was 46, 401, 921, and 727 m2/g, respectively. Pore size analysis indicated that the mesopore (20 to 500 A) contributed more than the macropore and micropore in the sludge pyrolytic residue. When the benzene influent concentration was 800 ppmv, the adsorption capacity ranged from 59 to 164 mg/g for different biosolid adsorbents. A larger BET surface area and smaller average pore diameter yielded a larger benzene adsorption capacity.

Remediation of PCE-contaminated aquifer by an in situ two-layer biobarrier: laboratory batch and column studies

The industrial solvent tetrachloroethylene (PCE) is among the most ubiquitous chlorinated compounds found in groundwater contamination. The objective of this study was to develop an in situ two-layer biobarrier system consisting of an organic-releasing material layer followed by an oxygen-releasing material layer. The organic-releasing material, which contained sludge cakes from a domestic wastewater treatment plant, is able to release biodegradable organics continuously. The oxygen-releasing material, which contained calcium peroxide, is able to release oxygen continuously upon contact with water. The first organic-releasing material layer was to supply organics (primary substrates) to reductively dechlorinate PCE in situ. The second oxygen-releasing material layer was to release oxygen to aerobic biodegrade or cometabolize PCE degradation byproducts from the first anaerobic layer. Batch experiments were conducted to design and identify the components of the organic and oxygen-releasing materials, and evaluate the organic substrate (presented as chemical oxygen demand (COD) equivalent) and oxygen release rates from the organic-releasing material and oxygen-releasing materials, respectively. The observed oxygen and COD release rates were approximately 0.0368 and 0.0416 mg/d/g of material, respectively. A laboratory-scale column experiment was then conducted to evaluate the feasibility of this proposed system for the bioremediation of PCE-contaminated groundwater. This system was performed using a series of continuous-flow glass columns including a soil column, an organic-releasing material column, two consecutive soil columns, and an oxygen-releasing material column, followed by two other consecutive soil columns. Anaerobic acclimated sludges were inoculated in the first four columns, and aerobic acclimated sludges were inoculated in the last three columns to provide microbial consortia for contaminant biodegradation. Simulated PCE-contaminated groundwater with a flow rate of 0.25 L/d was pumped into this system. Effluent samples from each column were analyzed for PCE and its degradation byproducts. Results show that up to 99% of PCE removal efficiency was obtained in this passive system. Thus, the biobarrier treatment scheme has the potential to be developed into an environmentally and economically acceptable remediation technology for the in situ treatment of PCE-contaminated aquifer.

Concomitant conus medullaris arteriovenous malformation and sacral dural arteriovenous fistula of the filum terminale

SUMMARY

A patient with a spinal intradural arteriovenous malformation (AVM) at the conus medullaris concomitant with a sacral dural arteriovenous fistula (AVF) of the filum terminale is reported. A 44-year-old-male presentied with bilateral leg weakness and urinary incontinence for several months. Spinal angiography demonstrated two lesions: one was spinal intradural AVM at the conus medullaris supplied by the anterior spinal artery; the other was sacral dural AVF of the filum terminale supplied by the middle sacral artery. Although multifocal spinal cord AVMs have been reported, this is the first case report of two different types of vascular malformations coexisting in one patient. The arterial supply of the dural AVF of the filum by the middle sacral artery is also first demonstrated in the literature. The patient was treated successfully by surgical approach for both lesions in the same operation.

Tuberous sclerosis complex with an unruptured intracranial aneurysm: manifestations of contiguous gene syndrome

SUMMARY

With the advancement of molecular genetics, the deletion of the TSC2/PKD1 gene at chromosome 16p13.3 has been discovered to be responsible for the tuberous sclerosis complex sharing some of the clinical manifestations of autosomal dominant adult polycystic kidney disease such as multiple renal cysts and intracranial aneurysms. The unruptured aneurysm in tuberous sclerosis complex is far beyond the meaning it has in general population. The risk of aneurysmal hemorrhage in tuberous sclerosis complex may be higher than that in autosomal dominant adult polycystic kidney disease due to the synergistic effect of gene deletion and certainly much higher than that in the general population. For such high-risk patients with intracranial aneurysms doomed to subarachnoid hemorrh age, magnetic resonance angiography plays an important role in screening and follow-up, especially more critically for patients with contiguous gene syndrome. Endovascular coil embolization should be the first choice of treatment for un ruptured intracranial aneurysms.

Analysis of the drude model in metallic films

A method, believed to be new, to simulate Drude parameters for collective oscillation of the free carriers in metallic films is proposed. Plasma resonance frequency and relaxation were simulated simultaneously from both the real and the imaginary parts of the dielectric function of a metallic film after consideration of their correlation in the Drude model. As examples, the contributions of the electrons in Ag films and of the free carriers in metallic silicide, NbSi(2) and TaSi(2), films have been studied.

Directed evolution to produce an alkalophilic variant from a Neocallimastix patriciarum xylanase

The catalytic domain of a xylanase from the anaerobic fungus Neocallimastix patriciarum was made more alkalophilic through directed evolution using error-prone PCR. Transformants expressing the alkalophilic variant xylanases produced larger clear zones when overlaid with high pH, xylan-containing agar. Eight amino acid substitutions were identified in six selected mutant xylanases. Whereas the wild-type xylanase exhibited no activity at pH 8.5, the relative and specific activities of the six mutants were higher at pH 8.5 than at pH 6.0. Seven of the eight amino acid substitutions were assembled in one enzyme (xyn-CDBFV) by site-directed mutagenesis. Some or all of the seven mutations exerted positive and possibly synergistic effects on the alkalophilicity of the enzyme. The resulting composite mutant xylanase retained a greater proportion of its activity than did the wild type at pH above 7.0, maintaining 25% of its activity at pH 9.0, and its retention of activity at acid pH was no lower than that of the wild type. The composite xylanase (xyn-CDBFV) had a relatively high specific activity of 10128 micromol glucose x min(-1) x (mg protein)(-1) at pH 6.0. It was more thermostable at 60 degrees C and alkaline tolerant at pH 10.0 than the wild-type xylanase. These properties suggest that the composite mutant xylanase is a promising and suitable candidate for paper pulp bio-bleaching.

Importance of injection solution composition for LC-MS-MS methods

For the first time, the influence of the injection solution composition on the quality of LC-MS-MS methods, in terms of column efficiency and peak shape, was systematically investigated. Various types of compounds, including polar ionic acidic, polar ionic basic and non-polar neutral compounds, were prepared in different solutions ranging from 100% water to 100% acetonitrile. Different volumes of these solutions were injected onto either C18 or silica columns connected to tandem mass spectrometry. The mobile phases consisted of acetonitrile, water, and small amounts of volatile acid or buffer. On silica columns, the influence of injection solution on the peak shape and column efficiency was straightforward. The sharpest peaks and the highest column efficiency were obtained with 100% acetonitrile as the injection solvent. On C18 columns, this type of influence was less clear due to the dual retention mechanism of the bonded phase and of the residual silanol groups. On C18 column, retention due to residual silanol groups was significant even with a mobile phase containing less than 50% acetonitrile. Poor peak shape was observed when the injection solution had a stronger eluting strength than mobile phase, particularly for early eluting peaks.

Growth inhibition of cultured smooth muscle cells by corrosion products of 316 L stainless steel wire

The potential cytotoxicity on vascular smooth muscle cells of corrosion products from 316 L stainless steel, one of most popular biomaterials of intravascular stents, has not been highlighted. In this investigation, 316 L stainless steel wires were corroded in Dulbecco's modified eagle's medium with applied constant electrochemical breakdown voltage, and the supernatant and precipitates of corrosion products were prepared as culture media. The effects of different concentrations of corrosion products on the growth of rat aortic smooth muscle cells were conducted with the [3H]-thymidine uptake test and cell cycle sorter. Both the supernatant and precipitates of corrosion products were toxic to the primary culture of smooth muscle cells. The growth inhibition was correlated well with the increased nickel ions in the corrosion products when nickel concentration was above 11.7 ppm. The corrosion products also changed cell morphology and induced cell necrosis. The cell growth inhibition occurred at the G0/G1 to S transition phase. Similar to our recent study of nitinol stent wire, the present investigation also demonstrated the cytotoxicity of corrosion products of 316 L stainless steel stent wire on smooth muscle cells, which might affect the poststenting vascular response.

Salvianolic acid B attenuates VCAM-1 and ICAM-1 expression in TNF-alpha-treated human aortic endothelial cells

Attachment to, and migration of leukocytes into the vessel wall is an early event in atherogenesis. Expression of cell adhesion molecules by the arterial endothelium may play a major role in atherosclerosis. It has been suggested that antioxidants inhibit the expression of adhesion molecules and may thus attenuate the processes leading to atherosclerosis. In the present study, the effects of a potent water-soluble antioxidant, salvianolic acid B (Sal B), and an aqueous ethanolic extract (SME), both derived from a Chinese herb, Salvia miltiorrhiza, on the expression of endothelial-leukocyte adhesion molecules by tumor necrosis factor-alpha (TNF-alpha)-treated human aortic endothelial cells (HAECs) were investigated. When pretreated with SME (50 and 100 microg/ml), the TNF-alpha-induced expression of vascular adhesion molecule-1 (VCAM-1) was notably attenuated (77.2 +/- 3.2% and 80.0 +/- 2.2%, respectively); and with Sal B (1, 2.5, 5, 10, and 20 microg/ml), 84.5 +/- 1.9%, 78.8 +/- 1.2%, 58.9 +/- 0.4%, 58.7 +/- 0.9%, and 57.4 +/- 0.3%, respectively. Dose-dependent lowering of expression of intercellular cell adhesion molecule-1 (ICAM-1) was also seen with SME or Sal B. In contrast, the expression of endothelial cell selectin (E-selectin) was not affected. SME (50 microg/ml) or Sal B (5 microg/ml) significantly reduced the binding of the human monocytic cell line, U937, to TNF-alpha-stimulated HAECs (45.7 +/- 2.5% and 55.8 +/- 1.2%, respectively). SME or Sal B significantly inhibited TNF-alpha-induced activation of nuclear factor kappa B (NF-kappaB) in HAECs (0.36- and 0.48-fold, respectively). These results demonstrate that SME and Sal B have anti-inflammatory properties and may explain their anti-atherosclerotic properties. This new mechanism of action of Sal B and SME, in addition to their previously reported inhibition of LDL, may help explain their efficacy in the treatment of atherosclerosis.

[Studies on polysaccharide alkaloids and minerals from Dendrobium moniliforme (L.) Sw]

OBJECTIVE

To explore contents of active substances in different part of Dendrobium monilifrome and the quality influenced by different drying processes.

METHOD

Contents of alkaloids and polysaccharides in upper, middle, lower-stem and root part of Dendrobium moniliforme were determined by uv-spectrophotometer method. Contents of essential trace elements were determined by ICP method.

RESULT

Contents of polysaccharides and alkaloids were highest in the upper-stem of D. montiliforme. Contents of active substances in different part of D. moniliforme were unequal. Distributions of polysaccharides and alkaloids in different parts were greatly influenced by drying procedures.

CONCLUSION

Dendrobium moniliforme has higher contents of active ingredients, such as essential tract elements, alkaloids and polysaccharides. The ideal drying process after harvesting is to be the way dried by fire at a high temperature and desiccated at a temperature of 60 degreeC.

Down-regulation of Fas-L in glioma cells by ribozyme reduces cell apoptosis, tumour-infiltrating cells, and liver damage but accelerates tumour formation in nude mice

Fas-L (CD95L, APO-1L) expresses in a variety of tumours and has been proposed to play a role in tumour formation and metastasis. The contribution of Fas-L to tumour growth, however, is not conclusive especially in systems using cells with over-expressed Fas-L. In this study we down-regulated the expression o Fas-L in human glioma cells by a hammerhead ribozyme (Fas-L(ribozyme)) targeting against Fas-L mRNA. Fas-L(ribozyme)-carrying cells exhibited slightly enhanced growth rate and less degree of spontaneous apoptosis in vitro as compared with vector controls. In nude mice, Fas-L(ribozyme)-carrying cells grew faster with lesser apoptosis, formed bigger tumour with significantly fewer infiltrating cells in the tumour area, and triggered relatively milder tumour-associated liver damage than vector controls did. Thus, down-regulation of Fas-L not only improved viability of glioma cells but also reduces local immune responses that may consequently affect tumour formation. Taken together, our findings imply that endogenous expression of Fas-L in malignant cells is not always growth promoting.

Visualization of laser-induced breakdown and ignition

Laser-induced gas breakdown and ignition of atmospheric pressure NH3/O2 mixtures are investigated. The nanosecond-pulsed, 1064-nm Nd:YAG laser is used to create the cascade-type optical breakdown. The post-breakdown plasma and ignition are studied using spectroscopic techniques that include spontaneous emission and NH planar laser-induced fluorescence (PLIF). These time-resolved two-dimensional images provide not only radiative and gas dynamic information but also the space-time loci of the temperature and transient species concentrations. The results provide an understanding of the plasma kernel dynamics and the flame development that is essential to verify on-going simulation modeling of laser-ignition.

Optimization of venous return tubing diameter for cardiopulmonary bypass

OBJECTIVE

To determine the optimal venous tubing diameter for adult cardiopulmonary bypass (CPB) to improve gravity drainage and to reduce priming volume.

METHODS

(A) Maximum bovine blood flow rates by gravity drainage were assessed in vitro for four different tubing diameters (1/2, 3/8, 5/16,1/4 inch) with three different lengths and various pre- and afterloads. Based on the results of (A) and multiple regression analyses, we developed equations to predict tubing sizes as a function of target flows. (C) The equations obtained in (B) were validated by ex vivo bovine experiments. (D) The clinically required maximal flows were determined retrospectively by reviewing 119 perfusion records at Zurich University. (E) Based on our model (B), the clinical patient and hardware requirements, the optimal venous tubing diameter was calculated. (F) The optimized venous tubing was evaluated in a prospective clinical trial involving 312 patients in Hangzhou.

RESULTS

For a mean body surface area of 1.83+/-0.2 m(2), the maximal perfusion flow rate (D) achieved with 1/2-inch (=1.27 cm(2)) venous tubing was 4.62+/-0.57 l/min (range: 2.50-6.24 l/min). Our validated model (B,C) predicted 1.0 cm(2) as optimal cross-sectional area for the venous line. New tubing packs developed accordingly were used routinely thereafter. The maximal flow rate was 4.93+/-0.58 l/min (range: 3.9-7.0) in patients with a mean body surface area of 1.62+/-0.21 m(2).

CONCLUSION

The new venous tubing with 1.0-cm(2) cross-sectional area improves the drainage in the vast majority of adult patients undergoing CPB and reduces the priming volume (-27 ml/m). Reduced hemodilution can prevent homologous transfusions if a predefined transfusion trigger level is not reached.

Application of tilt sensors in human-computer mouse interface for people with disabilities

This study describes the motivation and the design considerations of an economical head-operated computer mouse. In addition, it focuses on the invention of a head-operated computer mouse that employs two tilt sensors placed in the headset to determine head position and to function as simple head-operated computer mouse. One tilt sensor detects the lateral head-motion to drive the left/right displacement of the mouse. The other one detects the head's vertical motion to move up and down with respect to the displacement of the mouse. A touch switch device was designed to contact gently with operator's cheek. Operator may puff his cheek to trigger the device to perform single click, double clicks, and drag commands. This system was invented to assist people with disabilities to live an independent professional life.

Salvia miltiorrhiza inhibits intimal hyperplasia and monocyte chemotactic protein-1 expression after balloon injury in cholesterol-fed rabbits

Antioxidants that prevent low density lipoproteins (LDL) from oxidation may inhibit atherosclerosis and post-angioplasty restenosis. Salvia miltiorrhiza (SM) has been shown to inhibit LDL oxidation and reduce atherosclerosis in cholesterol-fed rabbits. The effects of SM on neointimal hyperplasia and monocyte chemotactic protein-1 (MCP-1) expression after balloon injury were studied. Male New Zealand white rabbits were fed a 2% cholesterol diet together with daily SM (4.8 gm/kg body wt.) treatment (SM; n=10) or without SM as a control (C; n=9) for 6 weeks. Probucol-treated (0.6 gm/kg body wt.) rabbits (P; n=9) were used as a positive control group. A balloon injury of the abdominal aorta was performed at the end of the third week. Aortas were harvested at the end of 6 weeks. The plasma cholesterol levels were lowered in SM group. The neointimal hyperplasia in abdominal aortas was significantly inhibited in SM group [neointima/media area ratio: 0.63+/-0.05 (SM) versus 0.78+/-0.05 (C); P < 0.05] and in P group [0.45+/-0.02 (P) versus 0.78+/-0.05 (C); P < 0.05] when compared with C group. SM treatment significantly reduced MCP-1 mRNA and protein expression in balloon-injured abdominal aorta. These inhibitory effects on intimal response after balloon injury might be attributed to antioxidant capacity and cholesterol lowering effect of SM. SM treatment may offer some protection against post-angioplasty restenosis.

Prothymosin alpha enhances protective immune responses induced by oral DNA vaccination against pseudorabies delivered by Salmonella choleraesuis

Previously, we showed that vaccination with the glycoprotein D (gD) gene of pseudorabies virus (PrV) delivered by Escherichia coli induced protective immune responses. In this study, we report that oral DNA vaccination with attenuated Salmonella choleraesuis carrying the PrV gD gene conferred protective immunity in mice against PrV. Moreover, co-delivery of the prothymosin alpha gene carried by S. choleraesuis enhanced the vaccine efficacy. Our results thus demonstrate for the first time, to our knowledge, the effectiveness of oral DNA vaccination using S. choleraesuis as a delivery vehicle and the potential usefulness of prothymosin alpha as a DNA vaccine adjuvant.

Spontaneous healing and complete disappearance of a giant basilar tip aneurysm in a child

SUMMARY

We report a rare case of spontaneous total thrombosis of a giant basilar tip aneurysm resulting in compression of the brainstem, diagnosed in a two-year-old child who presented with neurological deficits and third cranial nerve impairment. After conservative treatment, the giant aneurysm was completely thrombosed and the clinical symptoms were remarkably improved. MRI demonstrated dramatic shrinkage and ultimately complete disappearance of the giant aneurysm at seven month follow-up.

Synthesis and antibacterial evaluation of certain quinolone derivatives

A number of 7-substituted quinolone derivatives were synthesized and evaluated for antibacterial and cytotoxic activities. Preliminary results indicated that most compounds tested in this study demonstrated better activity against methicillin-resistant Staphylococcus aureus than norfloxacin. Among them, 1-(4-amino-2-fluorophenyl)-6-fluoro-1,4-dihydro-7-[4-[2-(4-methoxyphenyl)-2-hydroxyiminoethyl]-1-piperazinyl]-4-oxo-3-quinolinecarboxylic acid (11d) and its ketone precursor 10d exhibited significant activities against Klebsiella pneumoniae, methicillin-resistant S. aureus, erythromycin- and ampicillin-resistant Streptococcus pneumoniae, and vancomycin-resistant Enterococcus faecalis. Due to strong cytotoxicities of 11d (a mean log GI(50) of -5.40), compound 10d, with good antibacterial activities and low cytotoxicities (a mean log GI(50) of -4.67), is a more potential drug candidate.

Magnolol, a potent antioxidant from Magnolia officinalis, attenuates intimal thickening and MCP-1 expression after balloon injury of the aorta in cholesterol-fed rabbits

BACKGROUND

Restenosis is a common complication after balloon angioplasty. A number of cytokines, chemotactic factors and growth factors may be involved. Several antioxidants have been shown to inhibit intimal thickening after balloon injury in hyperlipidemic animals.

OBJECTIVES

The effects of magnolol on the expression of monocyte chemotactic protein-1 (MCP-1) and intimal response in balloon injured aorta of cholesterol-fed rabbits were investigated.

METHODS

Male New Zealand white rabbits were fed a 2% high cholesterol (HC) diet together with daily intramuscular injection of either 1 microg/kg B.W. of magnolol (HC-M, n = 10) or vehicle (propylene glycol) as a control (HC-C, n = 10) for a total of 6 weeks. Another 10 rabbits fed a regular diet also served as a control (C) group. A balloon denudation of abdominal aorta was performed in each group at the end of the third week. The aortas were harvested at the end of 6 weeks.

RESULTS

Magnolol treatment significantly inhibited Cu2+-induced LDL oxidation in cholesterol-fed rabbits and reduced atheroma formation [atheroma area ratio: 0.10 +/- 0.03 (HC-M) versus 0.33 +/- 0.07 (HC-C), p < 0.05] in thoracic aortas without lowering serum cholesterol. The intimal response was significantly attenuated in the HC-M rabbits when compared to those of the HC-C group [intimal thickness: 88.95 +/- 14.91 microm (HC-M) versus 198.02 +/- 20.35 microm (HC-C), p < 0.05; intimal area: 278.21 +/- 43.16 x 10(3) microm2 (HC-M) versus 642.70 +/- 65.01 x 10(3) microm2 (HC-C), p < 0.05]. The MCP-1 mRNA and protein expression were reduced in the HC-M group compared to the HC-C and C groups.

CONCLUSION

The inhibitory effects on intimal hyperplasia and MCP-1 expression might be attributed to the antioxidant capacity of magnolol instead of lowering serum cholesterol. Magnolol may offer some protection against postangioplasty restenosis.

Time-dependent reversal of long-term potentiation by low-frequency stimulation at the hippocampal mossy fiber-CA3 synapses

Using mouse hippocampal slices, we studied the induction of depotentiation of long-term potentiation (LTP) at the mossy fiber synapses onto CA3 pyramidal neurons. A long train of low-frequency (1 Hz/900 pulses) stimulation (LFS) induced a long-term depression of baseline synaptic transmission or depotentiation of previously established LTP, which was reversible and was independent of NMDA receptor activation. This LFS-induced depotentiation was observed when the stimulus was delivered 1 or 10 min after LTP induction. However, when LFS was applied at 30 min after induction, significantly less depotentiation was found. The induction of depotentiation on one input was associated with a heterosynaptic reverse of the LTP induced previously on a separate pathway. In addition, this LFS-induced depotentiation appeared to be mediated by the activation of group 2 metabotropic glutamate receptors (mGluRs), because it was mimicked by the bath-applied group 2 agonist (2S,2'R,3'R)-2-(2', 3'-dicarboxycyclopropyl) glycine and was specifically inhibited by the group 2 antagonists (S)-alpha-methyl-4-carboxyphenylglycine and (alphaS)-alpha-amino-alpha-(1S,2S)-2-carboxycyclopropyl-9H-xanthine-9-propanic acid. Moreover, the induction of depotentiation was entirely normal when synaptic transmission is blocked by glutamate receptor antagonist kynurenic acid and was associated with a reversal of paired-pulse facilitation attenuation during LTP expression. Pretreatment of the hippocampal slices with G(i/o)-protein inhibitor pertussis toxin (PTX) prevented the LFS-induced depotentiation. These results suggest that the activation of presynaptic group 2 mGluRs and in turn triggering a PTX-sensitive G(i/o)-protein-coupled signaling cascade may contribute to the LFS-induced depotentiation at the mossy fiber-CA3 synapses.

Modulations of Spinal Serotonin Activity Affect the Development of Morphine Tolerance

To test whether modulations of spinal serotonin (5-HT) levels would affect the development of morphine tolerance, we treated rats with either intrathecal 5-HT or 5,7-dihydroxytryptamine (5,7-DHT; a 5-HT neurotoxin) in addition to systemic infusion with morphine (2 mg x kg(-1) x h(-1)). Continuous infusion of 5-HT (10 microg x 6 microL(-1) x h(-1)) into the lumbar subarachnoid space of rats for 9 h accelerated the development of morphine tolerance. The area under the curve for the tail-flick latency test was 454.1 +/- 35.1 in the Sham Control group vs 327.6 +/- 41.0 in the 5-HT-Infused group. mu-opioid receptor binding in the lumbar spinal cord showed a decrease in the Bmax (maximal binding -46.5%), but not the binding affinity (Kd), in 5-HT-infused rats. However, intrathecal injection of 5,7-DHT (50 microg), which resulted in a 48% reduction in 5-HT and 51% reduction in 5-hydroxyindoleacetic acid concentrations, led to an attenuation of morphine tolerance (the area under the curve was 613.0 +/- 24.7 in the 5,7-DHT-Lesioned group). The binding study indicated that the affinity of lumbar micro-opioid receptors decreased 196% in 5-HT-depleted rats, whereas there was no effect on apparent binding. The infusion of 5-HT (10 microg x 6 microL(-1) x h(-1)) was not analgesic and the 5,7-DHT-induced lesion did not affect acute morphine-induced analgesia. We conclude that activity of spinal 5-HT-containing neurons plays a crucial role during the development of morphine tolerance.