Hippocampal synaptic plasticity is modulated by theta rhythm in the fascia dentata of adult and aged freely behaving rats

A modulatory role for the hippocampal theta rhythm in synaptic plasticity is suggested by the observations that theta occurs during exploratory behaviors, spatial learning is impaired when the theta rhythm is disrupted, and excitation of hippocampal principal cells is phase-coupled to the theta wave. The theta phase affects the nature of the plasticity induced in urethane-anesthetized rats and in the carbachol-treated in vitro slice preparation, but these oscillations are phenomenologically different from natural theta, and the effects of theta phase on plasticity under natural conditions have not been reported. We therefore examined the effects of theta phase on the magnitude of long-term potentiation (LTP) in awake rats running on a linear track for a food reward. Twelve adult and 10 aged F344 male rats were implanted with a stimulating electrode in the perforant path and a recording electrode in the hilus of the fascia dentata. Stimuli were delivered at the peak or trough of the hilar theta rhythm. In both adult and aged, memory-impaired rats, LTP lasting at least 48 h was induced when stimuli were delivered at the positive theta peak, whereas LTP was not induced when stimuli were delivered at the negative troughs. Consistent with the finding that the threshold for LTP induction is increased at this synapse in old rats, the magnitude of LTP induced at the peak of theta rhythm was significantly lower in old animals. These data confirm that LTP can be modulated by locomotion-induced theta, and that this modulation is at least qualitatively preserved across age.

High throughput studies of gene expression using green fluorescent protein-oxidative stress promoter probe constructs: the potential for living chips

Green fluorescent protein fusions were constructed with several oxidative stress promoters from Escherichia coli. These promoters were chosen for their induction by reactive oxygen species (ROS) such as superoxide, hydrogen peroxide, and hydroxyl radicals. When exposed to various free radical insults, the cells fluoresced with great specificity based on the corresponding ROS. In this work, we propose a way in which these constructs could be used to study the mode of action of a variety of antitumor drugs. This approach offers the possibility of complementing gene chip technology by the creation of living chips for high throughput screening as well as studying differential gene expression.

Enhancement of organophosphorus hydrolase yield in Escherichia coli using multiple gene fusions

It was previously shown that organophosphorus hydrolase (OPH) expression and purification could be tracked by fluorescence of green fluorescent protein (GFP) when synthesized as an N-terminal fusion with GFP (Cha et al., 2000; Wu et al., 2000). In order to enhance OPH productivity while utilizing the advantage of the reporter protein (GFP), two copies of OPH were cloned in tandem following the gfp(uv) gene (e.g., GFP-OPH(n=2)). Both anti-GFP and anti-OPH Western blots demonstrated that a higher yield was achieved in comparison to the one copy fusion (GFP-OPH). Importantly, the fusion protein was still fluorescent as determined via microscopy. In contrast, a fusion containing two copies of OPH without GFP, and an operon fusion of two OPHs with two independent ribosomal binding sites, did not result in a higher yield than one OPH expressed alone.

Cystatin C is an independent predictor of fasting and post-methionine load total homocysteine concentrations among stable renal transplant recipients

BACKGROUND

An increased prevalence of hyperhomocysteinemia with an increased incidence of cardiovascular disease events has been reported among stable renal transplant recipients (RTRs). Preliminary studies in a small number of these individuals have shown that serum creatinine and cystatin C, both markers of kidney function and glomerular filtration rate, are independent determinants of fasting tHcy concentrations; however, determinants of tHcy concentrations after a methionine load have not been studied.

METHODS

We determined the prevalence of both fasting and 4-h post-methionine load (PML) tHcy concentrations in 78 stable RTRs and compared the role of cystatin C with the role of serum creatinine as determinants of fasting and PML tHcy.

RESULTS

Of the 78 RTRs, 21 (26.9%) had fasting and PML tHcy within the respective reference intervals, and 57 (73.1%) had increased plasma tHcy. Of these 57 RTRs, 22 had fasting hyperhomocysteinemia, 9 had PML hyperhomocysteinemia, and 26 had combined hyperhomocysteinemia (both fasting and PML). Unadjusted Pearson correlations showed that fasting plasma tHcy correlated with both cystatin C (r = 0.564; P <0.001) and creatinine (r = 0.519; P <0.001) and that increases in PML tHcy modestly correlated with cystatin (r = 0.205; P = 0.072), but not creatinine (r = 0.057; P = 0.624). General linear regression modeling with stepwise analysis of covariance showed that both cystatin C (partial R = 0.554; P <0.001) and creatinine (partial R = 0.535; P <0.001) were independent predictors of fasting tHcy, but of the two, only cystatin C (partial R = 0.242; P = 0.035) was an independent predictor of increased PML tHcy.

CONCLUSIONS

Clinically stable RTRs have an excess prevalence of moderate hyperhomocysteinemia, and additional cases can be detected by methionine loading. Both creatinine and cystatin C are independent predictors of fasting tHcy in these individuals; however, only cystatin C is a determinant of tHcy concentration after a methionine load, probably because cystatin C is a more sensitive marker of glomerular filtration rate than serum creatinine.

Post discharge dropout of alcoholics - a naturalistic study in a general hospital setting

In a naturalistic longitudinal design 133 consecutive inpatients with alcohol dependence syndrome were followed up for one year following discharge from the hospital. 59 patients (group 1) paid follow up visit at regular intervals whereas 28 subjects (group 2)never returned despite three consecutive postal intimations. Rest of the patient were irregular in follow up. The individuals in group 1 were compared with those in group 2 on various sociodemographic and clinical variables with the aim of delineating the characteristics that could define the alcoholics who dropped out following discharge. It was found that such patient were relatively younger with lower level of education, less frequently married, had earlier onset of problem drinking with poor social support and higher rates of mental problems. It was concluded that post discharge attrition of alcoholics could be a social as well as a clinical problem in any setting rendering long treatment for alcoholism.

Insulin resistance syndrome

Insulin resistance can be linked to diabetes, hypertension, dyslipidemia, cardiovascular disease and other abnormalities. These abnormalities constitute the insulin resistance syndrome. Because resistance usually develops long before these diseases appear, identifying and treating insulin-resistant patients has potentially great preventive value. Insulin resistance should be suspected in patients with a history of diabetes in first-degree relatives; patients with a personal history of gestational diabetes, polycystic ovary syndrome or impaired glucose tolerance; and obese patients, particularly those with abdominal obesity. Present treatment consists of sensible lifestyle changes, including weight loss to attain healthy body weight, 30 minutes of accumulated moderate-intensity physical activity per day and increased dietary fiber intake. Pharmacotherapy is not currently recommended for patients with isolated insulin resistance.

Low-cost microbioreactor for high-throughput bioprocessing

The design of a microbioreactor is described. An optical sensing system was used for continuous measurements of pH, dissolved oxygen, and optical density in a 2 mL working volume. The K(L)a of the microbioreactor was evaluated under different conditions. An Escherichia coli fermentation in both the microbioreactor and a standard 1 L bioreactor showed similar pH, dissolved oxygen, and optical density profiles.%The low cost of the microbioreactor, detection system, and the small volume of the fermentation broth provide a basis for development of a multiple-bioreactor system for high-throughput bioprocess optimization.

Purification of recombinant green fluorescent protein using chromatofocusing with a pH gradient composed of multiple stepwise fronts

Green fluorescent protein (GFP), which fluoresces in the green region of the visible spectrum and is widely used as a reporter for gene expression and regulation, was overexpressed in the JM105 strain of Escherichia coli transformed with pBAD-GFP. A two-step chromatofocusing procedure was used to purify GFP starting from cell lysate, with each step employing a pH gradient extending from pH 5.5 to 4.0. The first chromatofocusing step was performed using a low-pressure column in which a retained stepwise pH front formed by adsorbed buffering species was used to capture GFP directly from clarified cell lysate and selectively focus it into a chromatographic band. The second step utilized a high-performance column under mass overloaded conditions where a similar pH front acted as a protein displacer and led to the formation of a highly concentrated rectangular band of GFP. The overall procedure yielded a 50-fold increase in purity, a 20-fold volume reduction, and a recovery and purity for GFP of 60% and 80%, respectively. Because the method employs a strong-base ion-exchange column packing and low-cost buffers formed with formic and acetic acids instead of the proprietary column packings and polyampholyte elution buffers more generally used for chromatofocusing, it appears to be a practical alternative for the preparative ion-exchange chromatography of GFP in particular and for the recovery of recombinant proteins from cell lysate in general. A discussion is also given concerning the choice of appropriate buffers for the rational design of pH gradients involving retained, stepwise pH fronts that span a given pH range and of the use of the fluorescence properties of GFP for flow visualization and chromatographic process development.

Is there a benefit of preoperative meningioma embolization?

OBJECTIVE

To evaluate the effect of preoperative embolization of meningiomas on surgery and outcomes.

METHODS

In a prospective study, 60 consecutive patients with intracranial meningiomas who were treated in two neurosurgical centers were included. In Center A, embolization was performed for none of the patients (n = 30). In Center B, 30 consecutive patients with embolized meningiomas were treated. Preoperatively, tumor size and location, neurological status, and Barthel scale score were recorded. In Center B, the extent of tumor devascularization was evaluated using angiography and postembolization magnetic resonance imaging. Intraoperatively, blood loss, the numbers of blood units transfused, and the observations of the neurosurgeon concerning hemostasis, tumor consistency, and intratumoral necrosis were recorded. Postoperatively, the neurological status and duration of hospitalization were recorded. Six months after surgery, the outcomes were assessed using the Barthel scale and neurological examinations.

RESULTS

The mean tumor sizes were 22.9 cc in Center A and 29.6 cc in Center B (P > 0.1). The mean blood losses did not differ significantly (646 ml in Center A versus 636 ml in Center B; P > 0.5). However, for a subgroup of patients with subtotal devascularization (>90% of the tumor) on postembolization magnetic resonance imaging scans in Center B, blood loss was less, compared with the entire group in Center A (P < 0.05). The observations of the neurosurgeon regarding hemostasis, tumor consistency, and intratumoral necrosis did not differ significantly. There were no surgery-related deaths in either center. The rates of surgical morbidity, with permanent neurological worsening, were 20% (n = 6) in Center A and 16% (n = 5) in Center B. There was one permanent neurological deficit (3%) caused by embolization.

CONCLUSION

In this preliminary study, only complete embolization had an effect on blood loss. The value of preoperative embolization for all meningiomas must be reconsidered, especially in view of the high costs and risks of embolization.

All solid-state GFP sensor

An all-solid-state green fluorescent protein (GFP) sensor for GFP measurement was developed. It is immune to interference from ambient light and works with standard flow-through cuvettes. The sensor is practically insensitive to the scattered excitation light encountered in microbial suspensions. It has a range of 0.0002-1 g/L (7.4 x 10(-9) - 3.7 x 10(-5) M) with limit of detection 0.00019 g/L (7.0 x 10(-9) M). The sensor could be used with a UV or blue light emitting diode (LED) as a light source, depending on required sensitivity, selectivity, and background levels. Its very low cost makes it useful in a variety of applications. This article describes the construction and validation of the sensor both off- and on-line in fermentation processes.

Green fluorescent protein in Saccharomyces cerevisiae: real-time studies of the GAL1 promoter

Green fluorescent protein (GFP) was used to study the regulation of the galactose-inducible GAL1 promoter in yeast Saccharomyces cerevisiae strains. GFP was cloned into the pGAL110 vector and transformed into the yeast strains. Time course studies comparing culture fluorescence intensity and GFP concentration were conducted along with on-line monitoring of GFP expression. Our results demonstrated that GFP fluorescence could be used as a quantifiable on-line reporter gene in yeast strains. The effect of an integrated GAL10p-GAL4 transcription cassette was investigated. Induction time studies showed that there was no significant difference in GFP expression level by adding galactose at different culture times. A wide range of galactose concentrations was used to study the initial galactose concentration effect on GFP expression kinetics. A minimum of 0.05 g/L galactose doubled the GFP fluorescence signal as compared to the control, whereas 0.1 g/L gave the highest specific GFP yield. A simple analytical model was proposed to describe GFP expression kinetics based on the experimental results. In addition, this GFP-based approach was shown to have potential use for high-throughput studies. The use of GFP as a generic tool provided important insights to the GAL expression system and has great potential for further process optimization applications.

Histologic evaluation of the inflammatory response around implanted hollow fiber membranes

Hollow fiber membranes are enjoying widespread use as barrier materials in many implanted applications. In order to predict in vivo device behavior, it is important to understand and quantify the changes to the membrane and to the tissue immediately surrounding it that occur following implantation. We have considered a range of commercially available hollow fiber membranes for their suitability as candidates for subcutaneously implanted applications. Through analysis of excised tissue sections by light microscopy, membranes were screened at 3, 6, and 12 weeks post-implantation for the ability to maintain integrity, foreign-body reaction, and thickness of the external fibrotic capsule layer. The polysulfone microfiltration membranes and cellulose diacetate membranes investigated were found to be unsuitable owing to extensive degradation. All membranes exhibited typical foreign body reaction with fibrotic capsule formation. The thinnest capsules were observed on the regenerated cellulose microdialysis membranes and the polysulfone ultrafiltration membranes. Extensive cellular penetration into the membrane matrix of the latter was observed, but did not appear to affect the foreign body reaction. A heat-sealing method was also considered for thermoplastic membranes and found to effectively prevent cellular penetration into the lumen of the hollow fiber for the duration of the 12-week implantation.

LTP induction threshold change in old rats at the perforant path--granule cell synapse

Old, memory-deficient rats do not show a change in the threshold for long-term potentiation (LTP) induction in hippocampal region CA1. This observation suggests that defective NMDA receptor mechanisms at the Schaffer collateral-CA 1 pyramidal cell synapse cannot explain age-related LTP induction deficits that are observed under some stimulation protocols. The effects of aging on functional electrophysiology are not, however, identical between hippocampal subregions. In fact, at the perforant path-granule cell synapse of rats NMDA receptor-mediated responses are reduced, suggesting a possible change in the threshold for LTP induction at this synapse. This hypothesis was tested in the present experiment. We found that when weak orthodromic stimulation of medial perforant path fibers is paired with intracellular current injection of granule cells, the threshold for LTP induction is elevated in aged, spatial memory-impaired rats compared to middle-aged and young controls. Thus, in addition to there being fewer total medial perforant path synaptic contacts in old rats, greater depolarization and input convergence is required before durable modification of synaptic strength can be induced.

[Tumor surgery of the upper cervical spine]

Our own series of tumors of the upper cervical spine was analyzed retrospectively. The standard treatment strategies were reevaluated. A total of nine patients (mean age 61 years, metastasis 4, plasmocytoma 3, chordoma 1, histiocytosis 1) were treated between 1/92 and 2/99. A total of 12 operations were carried out. One-step procedures (6): Three extraoral, one transoral, one dorsal and in one case combined dorsal and extraoral tumor removal were performed. Three dorsal occipitocervical or atlantoaxial stabilizations, one ventral plating and two combined ventral plating plus dorsal three-point fixations, and four vertebral body replacements were carried out. Two-step procedures (3): three extraoral tumor removals with ventral plating plus dorsal three-point fixation, in combination with vertebral body replacement in two cases. The neurological status and the quality of life (Karnofsky performance status, pain levels) were analyzed preoperatively and at the follow-up outpatient examinations (mean follow-up: 18 months). Flexion-extension radiographs were performed at the follow-up. There was no operative mortality. The transient morbidity was 11%. The operative intervention improved the quality of life in all patients. Three patients died within 27 months of operation. Tumor resection at the upper cervical spine using individually modified surgical strategies over an approach corresponding to the tumor location, stabilization and vertebral body replacement increases significantly the time of survival and quality of life with an acceptable surgical risk for complications.

Framework for online optimization of recombinant protein expression in high-cell-density Escherichia coli cultures using GFP-fusion monitoring

A framework for the online optimization of protein induction using green fluorescent protein (GFP)-monitoring technology was developed for high-cell-density cultivation of Escherichia coli. A simple and unstructured mathematical model was developed that described well the dynamics of cloned chloramphenicol acetyltransferase (CAT) production in E. coli JM105 was developed. A sequential quadratic programming (SQP) optimization algorithm was used to estimate model parameter values and to solve optimal open-loop control problems for piecewise control of inducer feed rates that maximize productivity. The optimal inducer feeding profile for an arabinose induction system was different from that of an isopropyl-beta-D-thiogalactopyranoside (IPTG) induction system. Also, model-based online parameter estimation and online optimization algorithms were developed to determine optimal inducer feeding rates for eventual use of a feedback signal from a GFP fluorescence probe (direct product monitoring with 95-minute time delay). Because the numerical algorithms required minimal processing time, the potential for product-based and model-based online optimal control methodology can be realized.

[A study of HSP70 and NF in brain contusion timing]

The changes of HSP70 and NF after brain contusion were studied by the immunohistochemistry method. HSP70 and NF were seen at 30 min after injury around the wound area, but faded away after 12-24 h. The result suggests that these two proteins could be used to estimate brain contusion time, to diagnose brain wound and to distinguish antemortem and postmortem brain contusion.

A green fluorescent protein fusion strategy for monitoring the expression, cellular location, and separation of biologically active organophosphorus hydrolase

Organophosphorus hydrolase (OPH) is capable of degrading a variety of pesticides and nerve agents. We have developed a versatile monitoring technique for detecting the amount of OPH during the expression and purification steps. This involves fusion of the gene for green fluorescent protein (GFP) to the 5' end of the OPH gene and subsequent expression in Escherichia coli. The synthesized fusion protein was directly visualized due to the optical properties of GFP. Western blot analyses showed that the correct fusion protein was expressed after IPTG-induction. Also, the in vivo GFP fluorescence intensity was proportional to the OPH enzyme activity. Moreover, the OPH, which forms a dimer in its active state, retained activity while fused to GFP. Enterokinase digestion experiments showed that OPH was separated from the GFP reporter after purification via immobilized metal affinity chromatography, which in turn was monitored by fluorescence. The strategy of linking GFP to OPH has enormous potential for improving enzyme production efficiency, as well as enhancing field use, as it can be monitored at low concentrations with inexpensive instrumentation based on detecting green fluorescence.

Ratiometric oxygen sensing: detection of dual-emission ratio through a single emission filter

A new method and device for the ratiometric measurement of oxygen concentration are presented. They are based on the use of a dual-emission oxygen-sensitive dye. The method allows the exclusion of the influence of emission overlap. The detection of the dual-emission ratio is performed using a single long-pass emission filter. The device described is simpler than the widely used lifetime instruments and could easily be a stand-alone low-cost instrument.

Observations of green fluorescent protein as a fusion partner in genetically engineered Escherichia coli: monitoring protein expression and solubility

We have constructed three plasmid vectors for the expression of green fluorescent protein (GFP) fusion proteins using the following motif: (His)(6)-GFP-EK-X, where X represents chloramphenicol acetyl-transferase (CAT), human interleukin-2 (hIL-2), and organophosphorous hydrolase (OPH), respectively, (His)(6) represents a histidine affinity ligand for purification, and EK represents an enterokinase cleavage site for recovering the protein-of-interest from the fusion. The CAT and OPH fusion products ( approximately 63 kDa GFP/CAT and approximately 70 kDa GFP/OPH) were expressed at 4.85 microg/mL (19.9 microg/mg-total protein) and 1.42 microg/mL (4.2 microg/mg-total protein) in the cell lysis supernatant, and, in both cases, enzymatic activity was retained while coupled to GFP. In the case of hIL-2 fusion ( approximately 52 kDa), however, the GFP fluorescence was significantly reduced and most of the fusion was retained in the cell pellet. Linear relationships between GFP fluorescence and CAT or OPH concentration, and with enzymatic activity of CAT or OPH, indicated, for the first time, that in vivo noninvasive quantification of proteins-of-interest, was made possible by simple measurement of GFP fluorescence intensity. The utility of GFP as a reporter was not realized without disadvantages however, in particular, an incremental metabolic cost of GFP was found. This could be offset by many benefits foreseen in expression and purification efficiencies.

Age-related decrease in the Schaffer collateral-evoked EPSP in awake, freely behaving rats

Synaptic response size in the CA1 region of the hippocampus in aged rats is reduced for a given stimulus intensity, compared with that elicited in young rats. Consistent with the in vitro findings of reduced Schaffer collateral-evoked CA1 EPSPs in old rats, the population currents evoked to iontophoretically applied AMPA are also smaller relative to the presynaptic fiber potential amplitude. On the other hand, the size of the presynaptic fiber potential and amplitude of unitary intra-cellularly recorded EPSP responses do not change across age in the CA1 region. These electrophysiological findings are consistent with the hypothesis that old rats have fewer functional synaptic contacts per Schaffer collateral axon than do young rats. The possibility that this age change arises as a result of a differential tissue recovery response to in vitro preparation was examined in the present study. CA1 presynaptic fiber potential and EPSP amplitudes evoked by the stimulation of Schaffer collateral afferents were studied in intact, freely behaving young and old rats. We confirmed in vivo the pattern of electrophysiophysiological results previously reported in vitro and found significant correlations between the synaptic response amplitudes and the accuracy of spatial behavior in the Morris swim task. The data suggest that changes in functional connectivity of old rats may be a significant contributor to cognitive changes during aging.