Structural and functional properties of homologous electrical synapses between retinal amacrine cells

Retinal amacrine cells regulate activities of retinal ganglion cells, the output neurons to higher visual centers, through cellular mechanism of lateral inhibition in the inner plexiform layer (IPL). Electrical properties of gap junction networks between amacrine cells in the IPL were investigated using combined techniques of intracellular recordings, Lucifer yellow and Neurobiotin injection, dual patch-clamp recordings and high voltage electron microscopy in isolated retinas of cyprinid fish. Six types of gap-junctionally connected amacrine cells were classified after their light-evoked responses to light flashes were recorded. Among them, gap junction networks of three types of amacrine cells were studied with structure-function correlation analysis. Cellular morphology of intercellular connections between three homologous cell classes was characterized. The interconnections between laterally extending dendrites in the IPL were localized at dendritic tip terminals. Three types of cells presented the dendrodendritic connections of tip-contact manner in the homologous cell population. High voltage as well as conventional electron microscopy revealed gap junctions between the dendritic tips of Neurobiotin-coupled cells. Receptive field properties of these amacrine cells were examined, displacing a slit of light along the distance from recording sites in the dorsal intermediate region of the retina. Receptive field size, space length constant, response latency and conduction velocity were measured. Spatial and temporal properties of receptive fields were symmetric along horizontally expanding dendrites in the dorsal retina. Simultaneous dual patch-clamp recordings revealed that the lateral gap junction connections between homologous amacrine cells expressed bidirectional electrical synapses passing Na(+) spikes. These results demonstrate that bidirectional electrical transmission in gap junction networks of these amacrine cells is symmetric along the lateral gap junction connections between horizontally extending dendrites. Lateral inhibition regulated by amacrine cells in the IPL appears to be associated with the directional extension of the dendrites and the orientation of dendrodendritic gap junctions.     

Effect of basic fibroblast growth factor on cultured rat neural stem cell in three-dimensional collagen gel

OBJECTIVES: The effect of growth factors on the three-dimensional culture of neural stem cells has not been reported. We studied the effect of basic fibroblast growth factor (bFGF) on cultured rat neural stem cells in a three-dimensional culture. METHODS: We cultured rat neural stem cells in collagen gel matrix for three-dimensional culture and examined the effect of bFGF under such culture conditions. RESULTS: After 4 days culture, the cell density in the bFGF treatment group was 12 times that of the non-treatment group, reaching a significantly high value. In the bFGF treatment group, microtubule associate protein (MAP)-2-positive cell aggregation occurred, although in the bFGF non-treatment group there was no MAP-2-positive cell aggregation and few of the cells were sparsely distributed. Also, in the bFGF treatment group, MAP-2-positive cell aggregation had a luminal structure similar to neural rosettes. There was elongation of MAP-2-positive neurites from the cell aggregation to the circumference in the bFGF treatment group. DISCUSSION: bFGF is known to induce the proliferation, but not the differentiation of neural stem cells in two-dimensional cultures. However, in the three-dimensional culture, bFGF induced both the proliferation and differentiation of neural stem cells. The three-dimensional culture is, therefore, considered a useful method for predicting the response of neural stem cells to cytokines or biologically active substances in vivo.     

Prediction of the origin of intracanalicular neoplasms with high-resolution MR imaging

Correct diagnosis of intracanalicular neoplasms is important to avoid unnecessary operations or an unsuitable surgical approach. We investigated the capability of high-resolution three-dimensional MR imaging in predicting the origin of intracanalicular neoplasms. Twenty cases underwent three-dimensional Fourier-transformation (3DFT) constructive interference in steady state and contrast-enhanced 3DFT-fast low angled shot MR imaging and surgery. Seventeen cases underwent caloric test. MR diagnosis on the origin of intracanalicular neoplasms was compared with surgical results. For MR diagnosis, the origin of intracanalicular neoplasms was predicted according to the location of the tumor in the internal auditory canal (IAC) in two ways, i.e., determining (1) a single specific nerve of origin and (2) whether the tumor originated from the superior or inferior aspect of the IAC. Surgery could determine the nerve of origin in 16 cases (14 inferior and 2 superior vestibular schwannomas), but it was indeterminate in 4. Comparison between MR prediction and surgical results on a single nerve origin revealed exact agreement in five, but inconsistent in three. Regarding whether the tumor was derived from superior or inferior aspect of the IAC, agreement was found in 10 of the 16 cases (62.5%). Caloric test was abnormal in all patients examined but one with superior vestibular schwannoma. 3DFT-MR imaging was not particularly useful in predicting a precise nerve of origin of intracanalicular neoplasms. The prediction on whether the tumor originated in the superior or inferior aspect of the IAC was superior to caloric test, which might have clinical significance in treatment planning especially for hearing preservation surgery.     

Evaluation of ischemic heart disease on a 1.5 Tesla scanner: combined first-pass perfusion and viability study

PURPOSE: We implemented a fast gradient echo (GRE) sequence with an echo-planar imaging (EPI) read-out (FGRE-ET) to conduct myocardial perfusion studies on a conventional scanner. The accuracy of combined perfusion and viability studies is evaluated in comparison with coronary angiography (CAG). MATERIALS AND METHODS: We enrolled 33 patients suspected of having coronary artery disease in this study. Short-axis perfusion images of the left ventricles were acquired following intravenous bolus injection of gadolinium-DTPA (0.05 mml/kg), both after myocardial loading by dipyridamole (0.56 mg/kg) and at rest. Viability studies were obtained using an inversion-recovery FGRE sequence. Radiologists performed blinded film readings. The findings with perfusion and the viability studies were compared with CAG on a segment-to-segment basis corresponding to the coronary arteries' territories. Stenosis equal to or greater than 75% in diameter was considered significant on CAG. The results were also compared with single photon emission computed tomography (SPECT) in 23 patients. RESULTS: The combination of perfusion and viability studies showed 85.7% sensitivity, 88.9% specificity, and 87.2% accuracy in comparison with CAG. SPECT revealed respective rates of 71.7%, 78.3%, and 73.9% in 23 patients of this group. CONCLUSION: Myocardial perfusion studies using FGRE-ET were feasible and accurate, even on a conventional scanner.     

Pharmacokinetic analysis of ductal carcinoma in situ of the breast using dynamic MR mammography

The purpose of this study was to assess the relationship between functional parameters derived from dynamic MR imaging and the histological findings of breast ductal carcinoma in situ (DCIS) and DCIS with invasive foci, and to evaluate whether these parameters might predict DCIS patient outcome. Two parameters, amplitude A and k₂₁, were determined from multicompartmental pharmacokinetic analyses of dynamic MR mammography in 39 patients with needle biopsy-proven primary DCIS. After surgery, the histological tumor characteristics, including microvessel density (MVD) (anti-CD-34), vascular permeability (anti-VEGF antigen) and histological grade, were evaluated. Histology revealed 27 pure DCIS and 12 DCIS with invasive foci. In pure DCIS, positive correlations between MVD and amplitude A (r=0.56, P<0.0025) and between MVD and k₂₁ (r=0.43, P=0.02) were found. As for histological grade, the differences in both functional parameters of grade 1 versus grade 2 and grade 1 versus grades 2 and 3 combined were significant (P<0.05). No significance was found in the analysis of DCIS with invasive foci. Our results indicated that functional MRI-based parameters might possess the potential to predict the outcome of patients with DCIS. Further study will be needed with larger series over longer periods.     

Determination in vivo of newly synthesized gene expression in hamsters during phases of the hibernation cycle

This study measured in vivo synthesis of total RNA and protein from cortex, cerebellum and midbrain/brainstem and 6 major organs from Syrian hamsters (Mesocricetus auratus) during (a) 33 h of torpor (body temperature 5-6 degrees C); (b) 90 min of the early arousal; (c) 90 min of the middle arousal; (d) 90 min in cold adapted cenothermic (CEN) hamsters of the same circannual period. Appropriate physiological parameters were used to confirm the phase of the hibernation cycle during infusion and incorporation of [3H]-uridine and [14C]-leucine. In torpor, RNA synthesis was 5-25% of CEN levels depending upon tissue. In brain and heart mRNA was not preferentially synthesized. Protein was synthesized at low, tissue specific levels during torpor. Initiation of arousal and the warming of anterior organs via non-shivering thermogenesis during the early arousal occurred without measurable synthesis of RNA or proteins. Tissue specific levels of RNA and protein synthesis occurred later after shivering thermogenesis had been recruited and was strongly influenced by thermal gradients in the body. In the middle arousal phase, protein synthesis is most active in the brain despite modest synthesis of RNA and mRNA. The majority of molecular processing required for the induction and maintenance of torpor and the arousal from torpor up until the onset of shivering thermogenesis occurs during the cenothermic period before the hamster initiates the hibernation cycle.     

Cytocompatibility and viscoelastic properties of phthalate ester-free tissue conditioners

We prepared prototype phthalate ester-free tissue conditioners (PFT) from a powder of poly(ethyl methacrylate) and a mixture of several liquids, including di-n-butyl sebacate, benzyl benzoate (BB), and ethanol. The estrogenic activities of the liquids in the PFT were measured by an E-screen assay. We also assessed the cytotoxicity of the prototype and commercial tissue conditioners against a living skin equivalent. Finally, the viscoelastic properties were determined by measuring the rubber hardness and initial flow, while the effect of the mixing liquid on the mechanical properties of a denture resin was assessed by three-point bending test. PFT did not show any estrogenic activity and displayed a low or a similar level of cytotoxicity as the conventional materials. The viscoelastic properties and the effect of the mixing liquid on mechanical properties were influenced by the quantity of BB present in the mixing liquid. The prototype is therefore a reasonable PFT candidate.     

Ethics roundtable debate: Child with severe brain damage and an underlying brain tumour

A young person presents with a highly malignant brain tumour with hemiparesis and limited prognosis after resection. She then suffers an iatrogenic cardiac and respiratory arrest that results in profound anoxic encephalopathy. A difference in opinion between the treatment team and the parent is based on a question of futile therapy. Opinions from five intensivists from around the world explore the differences in ethical and legal issues. A Physician-ethicist comments on the various approaches.