Biomedical subjects

S Li

Publications and source records attributed to S Li.

At least 217 records · Page 12Linked to original sources

PubMed2001

Long-term survival of rat cardiac allografts by intrathymic plus portal venous injections of donor bone marrow cells and short-term tacrolimus immunosuppression.

Intrathymic (IT) or portal venous (PV) injection of donor antigens has been shown to prolong organ acceptance in low responder rat strain combinations. We determined whether a combination of these strategies would prolong cardiac allograft survival in high responder combinations. Wistar Furth rats received 1 x 10(8) ACI rat bone marrow cells (BMCs) via IT, intravenous (IV), PV, IV + PV, IT + IV or IT + PV route at the time of ACI cardiac transplantation. Without tacrolimus (FK), all grafts were acutely rejected. With FK immunosuppression (1.5 mg/kg per day, I. M., days 0-4), single BMC injection did not increase graft survival beyond 93 days, whereas 70% of grafts survived indefinitely ( > 150 days) when IT and PV BMCs were combined. Animals receiving IT and PV BMCs also had less allograft vasculopathy. Thus, IT and PV injections of donor BMCs under a brief course of FK synergistically improve cardiac allograft survival.

Animals↗

PubMed2001

In-situ separation of the matrix for the direct determination of traces of chromium, cobalt, and nickel in titanium dioxide powder by electrothermal atomic-absorption spectrometry with slurry sampling.

A novel method has been developed for the direct determination of traces of chromium, cobalt, and nickel in TiO2 powder; it entails slurry sampling and electrothermal atomic-absorption spectrometry (ETAAS) with a polytetrafluoroethylene (PTFE) slurry (6% m/v) as fluorinating reagent. The factors which could affect the vaporization of the matrix and analytes were studied in detail; the fluorinating vaporization behavior of the analyte both in the slurry and in solution were also investigated. Owing to the in-situ separation of the matrix, the matrix influences were reduced significantly. The proposed method has been applied to the direct determination of traces of chromium, cobalt, and nickel in high-purity TiO2 powder without chemical pretreatment. Under the optimum experimental conditions the detection limits of the analytes (Cr, Co, and Ni) were 1.9 ng g(-1), 2.4 ng g(-1) and 5.4 ng g(-1), respectively, the relative standard deviations (RSD) were 3.4% (n=6, c=7.0 ng mL(-1)), 2.9% (n=6, c=0.70 ng mL(-1)), and 7.6% (n=6, c=4.0 ng mL(-1)), again respectively, and the characteristic masses for Cr, Co, and Ni were 8.4 pg/ 0.0044A, 9.3 pg/0.0044A, and 40.0 pg/0.0044A, respectively.

Alloys↗

PubMed2001

Bilateral multifinger deficits in symmetric key-pressing tasks.

Maximal voluntary force during simultaneous bilateral and multifinger exertion has been shown to be smaller than the sum of unilateral or single-finger exertions. The goal of this study was to study the force deficit associated with bilateral multifinger tasks. Eight normal college students performed four types of maximal isometric key-pressing tasks: (1) unilateral single-finger, (2) bilateral single-finger, (3) unilateral multifinger, and (4) bilateral multifinger. Forces produced by the index (I), middle (M), ring (R), and little (L) fingers and surface electromyography (EMG) of extrinsic finger flexors were recorded. Multifinger deficit (MFD) was defined as the percentage difference between the force (or EMG) produced by a set of fingers and the sum of the forces (or EMGs) produced by the individual fingers in their unilateral single-finger tasks. Bilateral deficit (BLD) was defined as the percentage difference between the force (or EMG) produced by a set of fingers and the sum of the forces (or EMGs) produced by the finger subsets of the left and right hands. Significant BLD and MFD in force and EMG were found for all bilateral multifinger tasks and some of the bilateral single-finger tasks. Both BLD and MFD were dependent on the number of fingers involved. BLD ranged from 3% to 22.7% for force and from 8.9% to 31.0% for EMG, including bilateral single-finger and bilateral multifinger tasks. MFDs in force during bilateral I-, IM-, IMR-, and IMRL-finger tasks were 13.2%, 37.8%, 53.2%, 52.3%, respectively; and the corresponding MFDs in EMG were 11.7%, 51.3%, 67.6%, and 71.0%, respectively. BLD and MFD in EMG were found to vary in parallel with the corresponding force deficits. It was suggested that the neural ceiling effect remains the most plausible mechanism underlying the observed deficits. The central nervous system is unable to activate maximally a large number of muscle groups at the same time during tasks involving multiple body parts. During bilateral multifinger tasks, the ceiling effect may be organized hierarchically: (1) a certain limited neural drive is shared bilaterally, leading to a BLD; (2) at each hand, a certain limited neural drive is shared by multiple fingers, leading to MFD within a hand; (3) the deficits at bilateral and unilateral multifinger levels are cumulative during bilateral multifinger tasks, leading to a higher deficit associated with the tasks.

Adult↗

PubMed2001

Systemic administration of LPD prepared with CpG oligonucleotides inhibits the growth of established pulmonary metastases by stimulating innate and acquired antitumor immune responses.

Intravenous (i.v.) administration of a lipopolyplex consisting of a ternary complex of DOTAP:cholesterol cationic liposomes, protamine sulfate, and noncoding plasmid DNA (LPD-pDNA) is capable of stimulating a potent Th-1 cytokine response and inhibiting the growth of established tumors in mice. Both activities are mainly elicited by unmethylated CpG motifs in the plasmid DNA (pDNA) component, which are bacterial in origin. Since oligodeoxynucleotides (ODN) that possess a consensus immunostimulatory CpG motif of RRCpGYY (R is purine and Y is pyrimidine) can mimic the immunostimulatory actions of bacterial DNA, we hypothesized that i.v. administration of LPD prepared with GpG-ODN would mimic the ability of LPD-pDNA to stimulate Th-1 cytokines and antitumor activity and provide an improved vector for probing the immune mechanisms underlying the observed antitumor effects. These hypotheses were tested for the treatment of established 24JK experimental pulmonary metastases that are syngeneic in C57BL/6 mice. Mice treated with LPD containing 25 microg of the prototypical phosphodiester (PO) CpG-ODN 1668 (tccatGACGTTcctgatgct, motif capitalized) demonstrated a dramatic reduction in lung tumor burden (>80% inhibition, P<0.01) compared to dextrose-treated controls. The antitumor effect was dependent on the CpG dinulceotide and correlated with the ability to stimulate serum Th-1 cytokines (TNF-alpha, IL-12, and IFN-gamma). Both activities required assembly of CpG-ODN in a cationic liposome/DNA complex (lipoplex) or the LPD lipopolyplex. LPD delivery of both PO-1668 and phosphorothioated (PS)-1668 stimulated a greater cytokine response compared to delivery of free ODN. Furthermore, within the LPD complex, both PO- and PS-1668 had similar ability to stimulate Th-1 cytokines with respect to potency and duration of response, thus eliminating the need for the PS modification. In tumor cell lysis assays, LPD-CpG DNA stimulated development of an acquired, tumor-specific CD8+ cytotoxic T-lymphocyte (CTL) activity that was dependent on CpG DNA. LPD was also capable of stimulating NK activity; however, this was not dependent on CpG DNA. Only formulations that concomitantly stimulated NK activity and CpG-specific, Th-1 cytokine were capable of stimulating the development of tumor-specific CTL activity and significant inhibition of tumor growth. Thus, we propose a model where CpG DNA in complex with cationic liposome-based lipoplexes or lipopolyplexes stimulates antitumor NK activity and CpG-stimulated Th-1 cytokine production. The combination of these two activities of the innate immune system subsequently direct the development of an acquired, tumor-specific CTL response that in total are effective for inhibiting the growth of established tumors in mice.

Animals↗

PubMed2001

Targeted delivery of a peripheral benzodiazepine receptor ligand-gemcitabine conjugate to brain tumors in a xenograft model.

PURPOSE: Peripheral benzodiazepine receptors (PBRs) are overexpressed in brain tumors compared to normal brain, and could serve as a target to selectively increase anticancer drug delivery through a PBR ligand-drug conjugate system. We have previously synthesized PBR ligand-gemcitabine conjugates based on the model PBR ligand, PK11195. The goal of the current study was to examine this new drug delivery strategy in an intracerebral xenograft model by measurement of steady-state drug distribution following administration of gemcitabine (GEM) and PK11195-GEM. METHODS: In vitro PBR receptor binding and cytotoxicity assays were used to screen three different PK11195-GEM conjugates (GG01, GG02, GG03) in human SF126 glioma cells. Based on these findings and the favorable chemical stability of GG01, here referred as PK11195-GEM, pharmacokinetic investigations of PK11195-GEM and GEM were conducted in male rats. These studies consisted of single-dose and steady-state dosing regimen studies, the latter to assess drug distribution in normal brain and brain tumors. PK11195-GEM and GEM were measured in blood and tissue samples by HPLC. RESULTS: All PBR-GEM conjugates demonstrated appreciable receptor binding affinity and cytotoxicity with mean IC50 values ranging from 248 to 376 nM and 5.6 to 29.1 nM, respectively. The cytotoxicity of GEM was comparable with a mean IC50 value of 5.9 nM. Following administration of single 8 mg/kg doses of PK11195-GEM to rats (n=4), PK11195-GEM had a mean total clearance of 126.3 +/- 29.6 ml/min per kg, and a volume of distribution at steady-state of 1,261.9 +/- 31.05 ml/kg that resulted in a very short elimination half-life of 16.1 +/- 5.8 min. In comparison GEM had a similar volume of distribution (993.8 +/- 131.6 ml/kg), reduced clearance (3.4 +/- 0.8 ml/ min per kg), and longer half-life (235.6 +/- 26.7 min). In nude rats bearing intracerebral tumors, mean steady-state tumor/plasma, tumor/right brain, and tumor/left brain PK 11195-GEM concentration ratios were 1.75 +/- 0.46, 5.49 +/- 5.2, and 9.96 +/- 3.2, respectively. The analogous values following GEM administrations were 0.81 0.5, 3.67 1.57, and 5.21 +/- 1.95, respectively. These values indicate a minimum twofold increase in tumor target selectivity for the conjugate delivery system compared to GEM treatment. CONCLUSION: Targeting intracellular PBRs is a new drug delivery strategy based on the use of low molecular weight drug conjugates that can be administered systemically. It was demonstrated under steady-state conditions that PK11195-GEM possessed a twofold enhancement in brain tumor selectivity compared to GEM alone. This type of target selectivity would allow higher tumor concentrations to be achieved in conjunction with lower drug concentrations in normal or non-target tissues.

Animals↗

PubMed2001

High-resolution genetic mapping of the sucrose octaacetate taste aversion (Soa) locus on mouse Chromosome 6.

An acetylated sugar, sucrose octaacetate (SOA), tastes bitter to humans and has an aversive taste to at least some mice and other animals. In mice, taste aversion to SOA depends on allelic variation of a single locus, Soa. Three Soa alleles determine 'taster' (Soa(a)), 'nontaster' (Soa(b)), and 'demitaster' (Soa(c)) phenotypes of taste sensitivity to SOA. Although Soa has been mapped to distal Chromosome (Chr) 6, the limits of the Soa region have not been defined. In this study, mice from congenic strains SW.B6-Soa(b), B6.SW-Soa(a), and C3.SW-Soa(a/c) and from an outbred CFW strain were genotyped with polymorphic markers on Chr 6. In the congenic strains, the limits of introgressed donor fragments were determined. In the outbred mice, linkage disequilibrium and haplotype analyses were conducted. Positions of the markers were further resolved by using radiation hybrid mapping. The results show that the Soa locus is contained in an approximately 1-cM (3.3-4.9 Mb) region including the Prp locus.

Animals↗

PubMed2001

Histopathological identification of colon cancer with microsatellite instability.

Cancer with high levels of microsatellite instability (MSI-H) is the hallmark of hereditary nonpolyposis colorectal cancer syndrome, and MSI-H occurs in approximately 15% of sporadic colorectal carcinomas that have improved prognosis. We examined the utility of histopathology for the identification of MSI-H cancers by evaluating the features of 323 sporadic carcinomas using specified criteria and comparing the results to MSI-H status. Coded hematoxylin and eosin sections were evaluated for tumor features (signet ring cells; mucinous histology; cribriforming, poor differentiation, and medullary-type pattern; sponge-like mucinous growth; pushing invasive margin) and features of host immune response (Crohn's-like lymphoid reaction, intratumoral lymphocytic infiltrate, and intraepithelial T cells by immunohistochemistry for CD3 with morphometry). Interobserver variation among five pathologists was determined. Subjective interpretation of histopathology as an indication for MSI testing was recorded. We found that medullary carcinoma, intraepithelial lymphocytosis, and poor differentiation were the best discriminators between MSI-H and microsatellite-stable cancers (odds ratio: 37.8, 9.8, and 4.0, respectively; P = 0.000003 to < 0.000001) with high specificity (99 to 87%). The sensitivities, however, were very low (14 to 38%), and interobserver agreement was good only for evaluation of poor differentiation (kappa, 0.69). Mucinous histopathological type and presence of signet ring cells had low odds ratios of 3.3 and 2.7 (P = 0.005 and P = 0.02) with specificities of 95% but sensitivities of only 15 and 13%. Subjective interpretation of the overall histopathology as suggesting MSI-H performed better than any individual feature; the odds ratio was 7.5 (P < 0.000001) with sensitivity of 49%, specificity of 89%, and moderate interobserver agreement (kappa, 0.52). Forty intraepithelial CD3-positive lymphocytes/0.94 mm2, as established by receiver operating characteristic curve analysis, resulted in an odds ratio of 6.0 (P < 0.000001) with sensitivity of 75% and specificity of 67%. Our findings indicate that histopathological evaluation can be used to prioritize sporadic colon cancers for MSI studies, but morphological prediction of MSI-H has low sensitivity, requiring molecular analysis for therapeutic decisions.

CD3 Complex↗

PubMed2001

Comparative genome-scale analysis of gene expression profiles in T cell lymphoma cells during malignant progression using a complementary DNA microarray.

Using a cDNA microarray, we compared the expression of approximately 8000 genes between two unique, clonally related T cell lines derived from different stages of a progressive T cell lymphoma involving skin. A total of 180 genes was found to be differentially expressed at the RNA level by a factor of fivefold or greater. Compared with the cells from the earlier, clinically indolent stage of the lymphoma, 56 genes were up-regulated, whereas 124 genes were down-regulated in the cells from the advanced, clinically aggressive stage lymphoma. The functions of approximately 65% of these genes are currently unknown. The 22 genes with a known function that were up-regulated in the advanced lymphoma cells included several genes involved in promotion of cell proliferation and survival as well as drug resistance. The 42 functionally characterized genes that were down-regulated in the advanced lymphoma cells included negative regulators of cell activation and cell cycle, and mediators of cell adhesion, apoptosis, and genome integrity. The differential expression identified by the cDNA microarray analysis was confirmed for selected genes by reverse transcription-polymerase chain reaction and Northern blotting. The identified differences in gene expression may be related to the differences in behavior between the early and advanced stages of the T cell lymphoma and point to directions for further investigations into mechanisms of lymphoma progression.

Blotting, Northern↗

PubMed2001

A clinically relevant CTLA4-Ig-based regimen induces chimerism and tolerance to heart grafts.

BACKGROUND: We determined whether a nontoxic CTLA4-Ig-based conditioning regimen effected mixed chimerism and donor-specific tolerance when heart and bone marrow were transplanted simultaneously. METHODS: Fully mismatched rat strain combinations were used. Recipients received total-body irradiation (300 centigrays), bone marrow (10(8) cells), and cardiac transplants from the donor on day 0. Subsequently, recipient animals received CTLA4-Ig (2 mg/kg, every other day, x 5 doses), tacrolimus (1 mg/kg/day; days 0 to 9), and one dose (10 mg) of antilymphocyte serum on day 10. RESULTS: All bone marrow recipients (n = 7) developed mixed chimerism (mean = 25% +/- 9% at 1 year) and accepted cardiac allografts permanently (> 375 +/- 32 days). Recipients that received conditioning regimen but no bone marrow (n = 5) rejected donor hearts within 51 +/- 13 days (p < 0.01). Recipients that accepted heart grafts also permanently accepted (> 180 days) donor-specific skin grafts, but rapidly rejected (< 10 days) third-party skin grafts. CONCLUSIONS: A nontoxic CTLA4-Ig-based conditioning regimen effects mixed chimerism and donor-specific tolerance when heart and bone marrow are transplanted simultaneously. This regimen may have clinical application.

Abatacept↗

PubMed2001

Muscarinic agonists and antagonists in the treatment of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by cognitive impairment and personality changes. The development of drugs for the treatment of the cognitive deficits of AD has focused on agents which counteract loss in cholinergic activity. Although symptoms of AD have been successfully treated with acetylcholinesterase inhibitors (tacrine, donepezil. rivastigmine, galanthamine), limited success has been achieved with direct M1 agonists, probably due to their lack of selectivity versus other muscarinic receptor subtypes. Muscarinic M2 antagonists have been reported to increase synaptic levels of acetylcholine after oral administration to rats (e.g. BIBN-99, SCH-57790), but their selectivity versus other muscarinic receptor subtypes is modest. Exploration of a series of piperidinylpiperidines has yielded the potent and selective M2 antagonist SCH-217443. This antagonist has excellent bioavailability in rats and dogs and shows activity in a rat model of cognition.

Alzheimer Disease↗

PubMed2001

Taxane diterpenoids from the bark of Taxus yunnanensis.

Further investigation on the alcohol extract of the barks of Taxus yunnanensis led to the isolation of four taxoids, namely, 7beta-xylosyl-taxol D, taxuyunnanines P, Q and R, along with the known taxuyuntin G (2). Four are rearranged taxoids with an 11(15-->1)-abeotaxoid skeleton and an opened oxetane ring moiety. Structures were determined by spectroscopic and chemical means.

Diterpenes↗

PubMed2001

Cell biology of limb patterning.

Of vertebrate organ systems, the developing limb has been especially well characterized. Morphological studies have yielded a wealth of information describing limb outgrowth and have allowed for the identification of a multitude of important factors. In terms of the latter, key signaling pathways are known to control numerous aspects of limb development, including establishment of the early limb field, determination of limb identity, elongation of the limb bud, specification of digit pattern, and sculpting of the digits. Modification of underlying signaling pathways can thus result in dramatic alterations of the limb phenotype, accounting for many of the diverse limb patterns observed in nature. Given this, it is clear that signaling pathways regulate the highly orchestrated and tightly controlled sequence of cellular events necessary for limb outgrowth; however, exactly how molecular signals interface with the cell biology of limb development remains largely a mystery. In this review we first provide an overview of a number of the morphogenetic signaling pathways that have been identified in the developing limb and then review how a subset of these signals are known to modify cell behaviors important for limb outgrowth.

Animals↗

PubMed2001

Comparison of N2O- and chlordiazepoxide-induced behaviors in the light/dark exploration test.

Earlier research has demonstrated similarities in the behavioral effects of nitrous oxide (N2O) and benzodiazepine (BZ) drugs such as chlordiazepoxide (CP). The present research was conducted to compare the behavioral effects of N2O and CP in mice in the light/dark exploration test. When challenged with either N2O or CP, mice exhibited significant dose-dependent increases in the time spent in the light compartment and also in the number of transitions between the light and dark compartments. Pretreatment with BZ receptor antagonist flumazenil (FLU), the GABA(A) receptor antagonist SR-95531 or the selective neuronal nitric oxide (NO) synthase (nNOS) inhibitor 7-nitroindazole (7-NI) all antagonized anxiolytic effects of N20 and CP. Based on these findings, it was concluded that N20 and CP evoke similar behavioral effects in the light/dark exploration test that are similar in their interaction with BZ and GABA(A) receptor antagonists. There also appears to be a specific role for nNOS in generating the NO involved in mediation of these effects.

Analgesics, Non-Narcotic↗

PubMed2001

Protein release from physically crosslinked hydrogels of the PLA/PEO/PLA triblock copolymer-type.

A series of PLA/PEO/PLA triblock copolymers was prepared by ring opening polymerization of rac-lactide in the presence of various di-hydroxyl poly (ethylene glycol)s, using CaH2 as a biocompatible initiator. Hydrogels were prepared by a phase separation method consisting of introducing small amounts of water over solutions of the copolymers in a biocompatible organic solvent, namely tetraglycol [poly(ethylene glycol monotetrahydrofurfuryl ether)]. The resulting hydrogels appeared much more hydrophilic than the rather tough hydrogels formed by swelling of dry tablets or films processed from the same copolymers. The phase separation-derived hydrogels were soft enough to be injected through a trochar. Two proteins, namely bovine serum albumine (BSA) and fibrinogen, were physically entrapped in these hydrogels by mixing with the polymer solutions before gel formation. This procedure appeared to be protein-respecting according to circular dichroism analysis on the released BSA. Dramatically different release profiles were obtained for the two proteins. In the case of BSA, the release depended on the quantity of protein incorporated in the hydrogel and presented a parabolic-type profile, in agreement with the behaviors of diffusion-controlled monolitic drug delivery devices. In contrast, almost linear release profiles were observed in the case of fibrinogen, the hydrogels behaving like a reservoir drug delivery system. These findings are tentatively interpreted in terms of gel-protein compatibility in the case of BSA and gel-protein incompatibility in the case of fibrinogen.

Hydrogels↗

PubMed2001

A novel variant three-way translocation of inversion 16 in a case of AML-M4eo following low dose methotrexate therapy.

We report a case of acute myelomonocytic leukemia with eosinophilia (AML-M4eo) in a 65-year-old man following low dose methotrexate treatment for pemphigus vulgaris. Cytogenetic studies at diagnosis revealed a complex karyotype including a reciprocal translocation between 11q14.2 and 16q22, an inversion of chromosome 16(p13.1q22), and an apparently terminal deletion of 7q31. The presence of inv(16) was confirmed by reverse transcription-polymerase chain reaction which demonstrated a Type A fusion transcript derived from the core binding factor (CBF) beta and the smooth muscle myosin heavy chain (MYH11) genes. The patient was in complete hematologic and cytogenetic remission 6 months following intensive chemotherapy. Because AML-M4eo with inv(16) has a favorable prognosis, molecular studies should be performed in case the identification of inv(16) by conventional cytogenetics is difficult due to a complex karyotype.

Aged↗

PubMed2001

Combined host-conditioning with CTLA4-Ig, tacrolimus, anti-lymphocyte serum, and low-dose radiation leads to stable mixed hematopoietic chimerism.

The toxic dose of irradiation required to achieve stable mixed hematopoietic chimerism is the major limitation to its clinical application in transplantation and other nonmalignant conditions such as hemoglobinopathies. This study examines the additive effect of costimulatory blockage, to our previously described tacrolimus-based conditioning regimen, in further reducing the dose of total-body irradiation to achieve stable mixed chimerism in rats. Fully mismatched, 4- to 6-week-old ACI and Wistar Furth rats were used as donors and recipients, respectively. Recipients were administered CTLA4-Ig 2mg/kg/day (alternate days) in combination with tacrolimus 1 mg/kg/day (daily) from day 0 through day +10, anti-lymphocyte serum 10 mg at day +10 (single dose), and total-body irradiation ranging from 100-600 cGy, prior to bone marrow transplantation (day 0) with 100 x 10(6) of T-cell-depleted bone marrow cells. Levels of donor chimerism were determined over a period of 12 months. The short course of CTLA4-Ig, tacrolimus, and ALS led to dramatic engraftments at reduced doses of irradiation: 100% (5/5) and 93% (13/14) of the animals developed mixed chimerism at 400 cGy and 300 cGy, respectively. At 300 cGy, recipients exhibited durable, multilineage mixed chimerism at 365 days with donor cells ranging from 19-42% (mean 23.4%) with no evidence of graft-vs-host disease. These mixed chimeras exhibited in vitro (mixed lymphocyte reaction) and in vivo (skin grafts) donor-specific tolerance. This study suggests that addition of costimulatory blockade to a tacrolimus-based conditioning regimen reduces the dose of irradiation required to achieve stable multilineage chimerism in rats.

Abatacept↗

PubMed2001

Na(+)-K(+)-ATPase inhibition and depolarization induce glutamate release via reverse Na(+)-dependent transport in spinal cord white matter.

Excitotoxic mechanisms involving alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA)/kainate receptors play an important role in mediating cellular damage in spinal cord injury. However, the precise cellular mechanisms of glutamate release from non-synaptic white matter are not well understood. We examined how the collapse of transmembrane Na(+) and K(+) gradients induces reverse operation of Na(+)-dependent glutamate transporters, leading to glutamate efflux and injury to rat spinal dorsal columns in vitro. Compound action potentials were irreversibly reduced to 43% of control after ouabain/high K(+)/low Na(+) exposure (500 microM ouabain for 30 min to increase [Na(+)](i), followed by 1 h ouabain+high K(+) (129 mM)/low Na(+) (27 mM), to further reverse transmembrane ion gradients) followed by a 2 h wash. Ca(2+)-free perfusate was very protective (compound action potential amplitude recovered to 87% vs. 43%). The broad spectrum glutamate antagonist kynurenic acid (1 mM) or the selective AMPA antagonist GYKI52466 (30 microM) were partially protective (68% recovery). Inhibition of Na(+)-dependent glutamate transport with L-trans-pyrrolidine-2,4-dicarboxylic acid (1 mM) also provided significant protection (71% recovery), similar to that seen with glutamate receptor antagonists. Blocking reverse Na(+)-Ca(2+) exchange with KB-R7943 (10 microM) however, was ineffective in this paradigm (49% recovery). Semiquantitative glutamate immunohistochemistry revealed that levels of this amino acid were significantly depleted in axon cylinders and, to a lesser degree, in oligodendrocytes (but not in astrocytes) by ouabain/high K(+)/low Na(+), which was largely prevented by glutamate transport inhibition. Our data show that dorsal column white matter contains the necessary glutamate pools and release mechanisms to induce significant injury. When Na(+) and K(+) gradients are disrupted, even in the absence of reduced cellular energy reserves, reverse operation of Na(+)-dependent glutamate transport will release enough endogenous glutamate to activate AMPA receptors and cause substantial Ca(2+)-dependent injury. This mechanism likely plays an important role during ischemic and traumatic white matter injury, where collapse of transmembrane Na(+) and K(+) gradients occurs.

Animals↗

PubMed2001

Prolactin response to dl-fenfluramine challenge before and after treatment with paroxetine.

The prolactin response to dl-fenfluramine (an indirect central serotonin agonist) challenge has been used to assess serotonergic function and appears to be blunted in depressed patients. We used this method to determine whether the serotonergic deficit in depressed patients is corrected by treatment with paroxetine. Prior to treatment with paroxetine sixteen depressed patients received a placebo challenge followed by a dl-fenfluramine challenge the next day. The same two challenges were repeated after treatment. Prolactin baseline levels were measured before pill administration, and then hourly for 5 hours. Fenfluramine/norfenfluramine levels were assayed at each time point after drug administration. Treatment with paroxetine significantly increased the baseline prolactin level independently of treatment response but positively correlated with paroxetine dose. We found that pre-treatment prolactin response to dl-fenfluramine challenge did not predict clinical response to paroxetine, nor did the prolactin response change significantly after treatment. There was no significant difference in the post-treatment prolactin response between treatment responders and treatment non-responders. We found evidence of increased prolactin levels that may reflect effects of paroxetine in enhancing serotonin levels. Acute release of serotonin as measured by the prolactin response to fenfluramine is not altered by paroxetine treatment.

Aged↗