Regulation of the glial Na+-dependent glutamate transporters by cyclic AMP analogs and neurons

Sodium-dependent transport into astrocytes is critical for maintaining the extracellular concentrations of glutamate below toxic levels in the central nervous system. In this study, the expression of the glial glutamate transporters GLT-1 and GLAST was studied in primary cultures derived from cortical tissue. In primary astrocytes, GLAST protein levels were approximately one half of those observed in cortical tissue, but GLT-1 protein was present at very low levels compared with cortical tissue. Maintenance of these astrocytes in medium supplemented with dibutyryl-cAMP (dbcAMP) caused a dramatic change in cell morphology, increased GLT-1 and GLAST mRNA levels approximately 5-fold, increased GLAST protein approximately 2-fold, and increased GLT-1 protein >/=8-20-fold. These increases in protein expression were accompanied by 2-fold increases in the Vmax and Km values for Na+-dependent L-[3H]glutamate transport activity. Although GLT-1 is sensitive to inhibition by dihydrokainate in heterologous expression systems, no dihydrokainate sensitivity was observed in astrocyte cultures that expressed GLT-1. Biotinylation with a membrane-impermeant reagent, separation of the biotinylated/cell surface proteins, and subsequent Western blotting demonstrated that both GLT-1 and GLAST were present at the cell surface. Coculturing of astrocytes with neurons also induced expression of GLT-1, which colocalized with the glial specific marker, glial fibrillary acidic protein. Neurons induced a small increase in GLAST protein. Several studies were performed to examine the mechanism by which neurons regulate expression of the glial transporters. Three different protein kinase A (PKA) antagonists did not block the effect of neurons on glial expression of GLT-1 protein, but the addition of dbcAMP to mixed cultures of neurons and astrocytes did not cause GLT-1 protein to increase further. This suggests that neurons do not regulate GLT-1 by activation of PKA but that neurons and dbcAMP regulate GLT-1 protein through convergent pathways. As was observed with GLT-1, the increases in GLAST protein observed in cocultures were not blocked by PKA antagonists, but unlike GLT-1, the addition of dbcAMP to mixed cultures of neurons and astrocytes caused GLAST protein to increase approximately 2-fold. Neurons separated from astrocytes with a semipermeable membrane increased GLT-1 protein, indicating that the effect of neurons was mediated by a diffusible molecule. Treatment of cocultures with high concentrations of either N-methyl-D-aspartate or glutamate killed the neurons, caused GLT-1 protein to decrease, and caused GLAST protein to increase. These studies suggest that GLT-1 and GLAST protein are regulated independently in astrocyte cultures and that a diffusible molecule secreted by neurons induces expression of GLT-1 in astrocytes.     

On the bias of Huffcutt and Arthur's (1995) procedure for identifying outliers in the meta-analysis of correlations.

This study documents how the use of A. I. Huffcutt & W. A. Arthur's (1995) sample adjusted meta-analytic deviancy (SAMD) statistic for identifying outliers in correlational meta-analyses results in inaccuracies in mean r. Monte Carlo simulations found that use of the SAMD resulted in the overidentification of small relative to large correlations as outliers. Furthermore, this tendency to overidentify small correlations was found to increase as the magnitude of the population correlation increased and resulted in mean rs that overestimated the population correlation. The implications for meta-analysts are discussed, and 2 possible solutions are offered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rhabdomyosarcoma of the tongue in a dog

A lingual rhabdomyosarcoma was diagnosed in a six-year-old Staffordshire bull terrier with clinical signs of dysphagia. The unsuccessful response to initial chemotherapy, to surgical resection and subsequent surgical resection and radiation therapy is documented. The accurate diagnosis and prognosis of such tumours is also discussed. Lingual rhabdomyosarcoma has not previously been reported in the dog.     

Stereoselective actions of halothane at GABA(A) receptors

Isoflurane anesthesia exhibits stereoselectivity, and a corresponding stereoselectivity ((+)->(-)-isomer) has been reported at GABA(A) receptors in vitro. The objective of the present study was to determine if the positive modulatory actions of halothane at GABA(A) receptors exhibited a similar stereoselectivity. Both (R)- and (S)-halothane ((+)- and (-)- isomers, respectively) enhanced [3H]flunitrazepam binding to brain membranes in a concentration dependent manner without a significant difference in either potency (EC50) or efficacy (Emax). While both (R)- and (S)-halothane enhanced [3H]muscimol binding, the potency of the (+)-isomer was slightly greater than the corresponding (-)-isomer (0.91 +/- 0.17 versus 1.45 +/- 0.04% atmospheres, respectively (P < 0.02)). Thus, subtle structural differences between inhalational anesthetics can have a significant impact on the degree of stereoselectivity at the receptor level and may provide insights for the development of more specific drugs.     

Heated humidifiers. Structure and function

Humidity in the form of molecular water vapor is an essential requirement for intubated patients, and can be beneficial to nonintubated patients receiving CPAP or oxygen therapy. There are many different types of humidification devices but they generally consist of a humidity generator (or water reservoir) and humidity delivery system (or breathing circuit). Humidifiers that generate aerosols may provide adequate humidity, but they also provide a transport mechanism for contaminants and may deliver excess water to the airways. An ideal system generates the required amount of humidity, in the form of water vapor, at the correct temperature, and transports it to the patient without the loss of either heat or moisture. The most effective way to achieve this is to use a large heated water surface for the generator, and heating elements within the delivery system to prevent condensation. This system can be configured to provide optimal humidity for both intubated and nonintubated patients from the neonatal to the adult intensive care unit. Heated humidifiers have no contraindications and can be used on any patient requiring ventilatory assistance or supplemental oxygen.     

Role of axillary lymph node dissection after tumor downstaging with induction chemotherapy for locally advanced breast cancer

BACKGROUND: Induction chemotherapy has become the standard of care for patients with locally advanced breast cancer (LABC) and currently is being evaluated in prospective clinical trials in patients with earlier-stage disease. To better gauge the role of axillary lymph node dissection in patients with LABC this study was performed to assess initial axillary status on physical and ultrasound examination, axillary tumor downstaging following induction chemotherapy, and the accuracy of physical examination compared with axillary sonography in predicting which patients will have axillary lymph node metastases found on pathologic examination. METHODS: Between 1992 and 1996, 147 consecutive patients with LABC were registered in a prospective trial of induction chemotherapy using 5-fluorouracil, doxorubicin, and cyclophosphamide. Physical and ultrasound examinations of the axilla were performed at diagnosis and after induction chemotherapy. Segmental resection with axillary lymph node dissection or modified radical mastectomy was performed, followed by postoperative chemotherapy and irradiation of the breast or chest wall and regional lymphatics. RESULTS: Following induction chemotherapy, 43 (32%) of the 133 patients with clinically positive lymph nodes on initial examination had axillary tumor downstaging as assessed by physical and ultrasound examination. The sensitivity of axillary sonography in identifying axillary metastases was significantly higher than that of physical examination (62% vs. 45%, P=.012). The specificity of physical examination (84%) was higher than that of sonography (70%), but the difference did not reach statistical significance. Among the 55 patients in whom the findings of both physical and ultrasound examination of the axilla were negative following induction chemotherapy, 29 patients (53%) were found to have axillary lymph node metastases on pathologic examination of the axillary contents. However, 28 (97%) of these patients had either 1 to 3 positive lymph nodes or only micrometastases 2 to 5 mm in diameter. CONCLUSIONS: Preoperative clinical assessment of the axilla by physical examination combined with ultrasound examination is not completely accurate in predicting metastases in patients with LABC following tumor downstaging. However, patients with negative findings on both physical and ultrasound examinations of the axilla may be potential candidates for omission of axillary dissection if the axilla will be irradiated because minimal axillary disease remains. Patients who have positive findings on preoperative physical or ultrasound examinations should receive axillary dissection to ensure local control. A prospective randomized trial of axillary dissection versus axillary radiotherapy in patients with a clinically negative axilla following induction chemotherapy is currently underway.     

Clinical outcome in stage I to III breast carcinoma and eIF4E overexpression

OBJECTIVE: The objective of this study is to determine if high eukaryotic initiation factor 4E (eIF4E) overexpression (sevenfold elevation or more over benign breast tissue) is associated with a worse clinical outcome. SUMMARY BACKGROUND DATA: Dysregulation of cellular functions by selective overexpression of specific proteins can lead to malignant transformation. The overexpression of eIF4E preferentially increases translation of mRNAs with long, G-C rich 5'-untranslated regions. Selective gene products, such as tumor neoangiogenic factors, ornithine decarboxylase, and cyclin D1, are upregulated. METHODS: One hundred fourteen breast specimens were analyzed and eIF4E overexpression was quantified by Western blot analysis. Quantification for eIF4E protein level was accomplished using a rabbit anti-eIF4E antibody and colorimetric development of Western blots using nitro blue tetrazolium and 5-bromo-4-chloro-3-indolyl phosphate. The blots were scanned and analyzed by densitometry. Treatment, pathologic, and clinical outcome data variables were analyzed. Statistical analysis was performed to determine if eIF4E overexpression is associated with breast cancer clinical outcome. RESULTS: In the 55 benign specimens, the mean eIF4E expression was 1.1+/-0.4 fold (mean +/- standard deviation). All 59 malignant breast carcinoma specimens were noted to have eIF4E overexpression (range, 1.9-fold to 30.6-fold), with a mean overexpression of 10.8+/-6.3-fold. The mean level of eIF4E expression in malignant specimens was higher than benign specimens (p < 0.05, unpaired t test). The degree of eIF4E overexpression appears to be independent of T and N stage. In the 21 patients with eIF4E overexpression of less than sevenfold, there was one cancer recurrence but no cancer-related deaths. In the 38 patients with high eIF4E overexpression (sevenfold or more), 14 patients had breast cancer recurrences (p = 0.03, log rank test), of whom 11 have died from the disease (p = 0.04, log rank test). The average follow-up interval in this study was 40 months. CONCLUSIONS: Patients with stage I to III breast cancer and high eIF4E overexpression had a higher rate of cancer recurrence and a higher rate of cancer-related death when compared to similar-stage breast cancer patients with low eIF4E overexpression. Therefore, eIF4E protein overexpression may be of prognostic value in stage I to III breast carcinoma.     

Effects of milk and milk products on rectal mucosal cell proliferation in humans

The interferon (IFN)-induced protein kinase (PKR) functions as a gatekeeper of mRNA translation initiation and is, therefore, a key mediator of the host IFN-induced antiviral defense system. Many viruses have invested countermeasures against PKR. Some apparently use more than one mechanism. The influenza virus can repress PKR activity through the use of at least two factors, the cellular P58IPK protein and the viral NS1 protein. The exact mode of action of the latter has not been established. Here, using a coprecipitation assay, we found that PKR could form a complex with NS1 in crude cell extracts prepared from influenza virus-infected HeLa cells. The NS1-PKR interaction was verified by using the yeast two-hybrid system and an in vitro binding assay. Deletion analysis mapped the NS1 binding site to the N-terminal 98 residues of PKR regulatory region. Furthermore, an NS1 mutant, which lacks PKR inhibitory activity, did not bind PKR. Finally, the functional role of NS1 in PKR inhibition was substantiated using an in vivo assay for PKR activity. These results support the role of NS1 in PKR modulation during viral infection that is mediated through a complex formation between the two proteins.