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At the cerebellar parallel fiber-Purkinje cell synapse, isolated presynaptic activity induces fast excitatory postsynaptic currents via ionotropic glutamate receptors while repetitive, high-frequency, presynaptic activity can also induce a slow excitatory postsynaptic current that is mediated by metabotropic glutamate receptors (mGluR1-EPSC). Here we investigated the involvement of glutamate uptake in the expression of the mGluR1-EPSC. Inhibitors of glutamate uptake led to a large increase of the mGluR1-EPSC. d-aspartate (0.4 mM) andl(−)-threo-3-hydroxyaspartate (0.4 mM) increased the mGluR1-EPSC ∼4.5 and ∼9-fold, respectively, while dihydrokainic acid (1 mM), had no significant effect on the mGluR1-EPSC.d-aspartate (0.4 mM) shifted the concentration-response curve of the depression of the mGluR1-EPSC by the low-affinity mGluR1 antagonist ( S)-a-Methyl-4-carboxyphenylglycine [( S)-MCPG] to higher concentrations and decreased the stimulus intensity and the number of necessary stimuli to evoke an mGluR1-EPSC. Depression of the mGluR1-EPSC by rapid pressure application of ( S)-MCPG at varying time intervals after tetanic stimulation of the parallel fibers indicated that the glutamate concentration in the peri- and extrasynaptic space decayed with time constants of 36 and 316 ms under control conditions and with inhibition of glutamate uptake, respectively. These results show that expression of the slow mGluR-mediated excitatory postsynaptic current is controlled by glutamate transporter activity. Thus in contrast to fast glutamatergic synaptic transmission, metabotropic glutamate receptor-mediated transmission is critically dependent on the activity and capacity of glutamate uptake.

We have investigated several mixed-valence vanadium oxides, single-crystals by X-ray photoelectron spectroscopy (XPS). Many studies have been performed on V 2 O 5 , VO 2 and V 2 O 3 . Less investigated are the mixed-valence compounds, as the V 3 O 5 , V 4 O 7 and V 6 O 13 systems, which are discussed here. They exhibit as a function of temperature metal–insulator transitions (MIT). A detailed analysis for these systems, above and below the MIT temperature is given. The core-level spectra for the mixed-valence compounds are compared with those of the related systems, V 2 O 5 , VO 2 and V 2 O 3 having V 5+ , V 4+ and V 3+ ions, respectively. The electronic structures for all investigated oxides are characterized by strong V 3d–O 2p hybridization and they are discussed in relation with similar studies.

This paper describes mathematical and software developments needed for the effective solution of differential algebraic equations of index 1 in the integrated computing environment MATLAB and the dynamic simulation package Simulink. The developments are applicable to other problem-solving environments and some are applicable to general scientific computation.

A VO2 single-crystal has been subject of a combined investigation by high resolution XPS, x-ray emission spectroscopy with electron and energy-selective x-ray excitation (V L-alpha, V K-beta-5- and O K-alpha emission) and x-ray absorption spectroscopy (O1s). We performed first principles tight-binding LMTO band structure calculations of VO2 in both monoclinic and tetragonal rutile structures and compare the densities of states with the experimental data. From this we conclude that the electronic structure of VO2 is more bandlike than correlated.

The phase diagram of the ternary system Sr/Mo/O has been determined at a temperature of 1000°C. Powder samples of the ternary compounds SrMoO4, Sr3MoO6, SrMoO3, Sr2MoO4 and SrMo5O8 were prepared by solid state reactions. The thermochemical data of all ternary compounds were determined. A new compound, Sr3Mo2O7, with a layered perovskite structure (a = 3.967(1), c = 20.588(5) Å, I4/mmm) was found. Rietveld analysis based on powder X-ray diffraction data confirms that the compound Sr2MoO4 has the K2NiF4 structure (I4/mmm) with a = 3.9176(1), c = 12.8545(4) Å.

The phase diagram of the ternary system Ca/Mo/O has been determined. Powder samples of the ternary compounds CaMoO4, CaMoO3, CaMo5O8, Ca16.5Mo13.5O40 and Ca5.45Mo18O32 were prepared by solid state reactions. Rietveld analysis based on powder X-ray diffraction data shows that the compound CaMo5O8 has monoclinic structure (P21/c) with a = 7.549, b = 9.064, c = 9.974 Å, β = 110.04°. CaMo5O8, Ca16.5Mo13.5O40 and Ca5.45Mo18O32 are semiconductors over the temperature range 75 to 300 K.

This paper describes mathematical and software developments for a suite of programs for solving ordinary differential equations in MATLAB.

In this paper we describe a novel generalized successive overrelaxation (SOR) algorithm for accelerating the convergence of the dynamic iteration method known as waveform relaxation. A new waveform convolution SOR algorithm is presented, along with a theorem for determining the optimal convolution SOR parameter. Both analytic and experimental results are given to demonstrate that the convergence of the waveform convolution SOR algorithm is substantially faster than that of the more obvious ordinary waveform SOR algorithm. Finally, to demonstrate the general applicability of this new method, it is used to solve the differential-algebraic system generated by spatial discretization of the time-dependent semiconductor device equations. Results from experiments on serial and parallel machines are presented to indicate a dramatic speedup over a more conventional method such as pointwise GMRES.

Fur das ternare System Mn/Mo/O wird uber die phasenreine Darstellung der Verbindungen MnMoO4 und Mn2Mo3O8 durch chemischen Transport berichtet. Die Abscheidung aus koexistierenden Dreiphasengemischen ermoglicht die Darstellung von Einkristallen unter definiertem Sauerstoffpartialdruck. Der Einflus der verschiedenen Bodenkorper und der Transportmittel Cl2, HCl, I2, HI, TeCl4 und SeCl4 auf das Transportverhalten wird beschrieben. Die bisherigen Untersuchungen an den erhaltenen Einkristallen lassen nur die Annahme eines sehr kleinen Homogenitatsgebietes fur beide Phasen zu. Chemical Transport Reactions in the System Mn/Mo/O For the ternary system Mn/Mo/O the phasepure preparation of the compounds MnMoO4 and Mn2Mo3O8 by chemical transport is reported. The deposition from a source of coexisting threephase mixtures give the possibility to prepare single crystals under defined oxygen partial pressure. The influence of different startmixtures and the agents Cl2, HCl, I2, HI, TeCl4 and SeCl4 on the transport behaviour are described. Results hitherto existing for the single crystals give hints of only very small homogeneity ranges for both phases.

Die IR-spektroskopische Untersuchung von getemperten Pulverproben (1273 K) fuhrte zum Nachweis von bisher in der Literatur nicht beschriebenen Verbindungen und deren Phasenkoexistenzen im ternaren System Ru/Sn/O. Die erhaltenen Resultate zeigen eine gute Ubereinstimmung mit den durch Rontgenbeugung gefundenen. Fur zwei der Phasen wurden die Zusammensetzungen RuSn3O4 und RuSn5O4 ermittelt. Daruber hinaus kann aus den Ergebnissen die Existenz einer weiteren Phase gefolgert werden. Deren Zusammensetzung liegt nahe RuSn9O8. Infrared Spectroscopic Investigations on Phase Equilibria in the System Ru/Sn/O Infrared spectroscopic investigations give evidence for the existence of new phases and their phase relations in the system Ru/Sn/O. The obtained results coincide well with X-ray diffraction investigation. The composition of two phases was found to correspond to the formula: RuSn3O4 and RuSn5O4. Evidence is given for the existence of a third phase, the composition should correspond to RuSn9O8.

The ternary compounds Ca 2 CuO 3 , Sr 2 CuO 3 , and their solid solution Sr 2− x Ca x CuO 3 have been prepared by the decomposition of coprecipitated oxalates and/or by conventional solid state reaction. Both reaction methods are compared. The obtained compounds crystallize in the orthorhombic system. The lattice constants were determined, and the formation of solid solution crystals over the whole range of composition was obtained. The compounds were characterized concerning their thermal stability and their decomposition in moist air. Thermogravimetric, X ray, and vapor pressure measurement show that the compounds are of a very slight variation in oxygen stoichiometry. First measurements of the specific heat and IR spectra are discussed.

The temperature dependencies of the heat capacity of MnMoO 4 and Mn 2 Mo 3 O 8 have been investigated from 5 K to 300 K with a vacuum-jacketed adiabatic calorimeter. The thermodynamic functions have been calculated on the basis of experimental results on C p,m ( T ). The standard values at the temperature 298.15 K for MnMoO 4 are: C p,m = 13.924 · R; S S o m = 17.992 · R ; H o m (T) − H o m (0) = 2556.7 · R · K; and Φ o m = 9.417 · R . For Mn 2 Mo 3 O 8 the same quantities are equal to 29.575 · R , 30.609 · R , 4797.7 · R · K and 14.517 · R , respectively. The λ-anomalies connected with the magnetic-ordering phase transitions were observed and studied in detail. The phase-transition temperatures for MnMoO 4 and Mn 2 Mo 3 O 8 correspond to 10.5 K and 39.44 K, respectively. A sharp increase of the thermal-relaxation time has been revealed in MnMoO 4 at T

Die Temperaturfunktionen des Sauerstoffzersetzungsdruckes der ternaren Phasen YCuO2 und Y2Cu2O5 wurden im Temperaturbereich von 1 050 bis 1 330 K unter Anwendung von Festelektrolytmeszellen bestimmt. Ausgehend von den gemessenen EMK-Werten wurden die Standardbildungsenthalpie sowie die Standardentropien der ternaren Phasen berechnet. Thermochemical Investigations on the Compounds YCuO2 and Y2Cu2O5 It has been investigated the oxygen partial pressure of the decomposition of the ternary compounds YCuO2 and Y2Cu2O5 in dependence from the temperature in the temperature range 1050–1330 K by using the e.m.f. method. The enthalpies of formation and the standard entropies of the two compounds have been derived basing on measured e.m.f. values.

In order to optimize the synthesis of BaCuO2, different modes were developed and estimated. Wet chemical powders produced by coprecipitation of oxalates or hydroxycarbonates were characterized and their reactivity is compared with the conventional ceramic process of firing a mixture of BaCO3 and CuO by DTA, XRD and IR-investigations. This becomes possible, because the decomposition of these chemical precursors to BaCO3 and CuO is finished up to 600 °C. Hence, the same reaction for the formation of BaCuO2 is monitored. Zur Optimierung der Synthese von BaCuO2 wurden verschiedene Methoden der Praparation entwickelt und getestet. Durch Mischfallung hergestellte Pulver (Oxalate und Hydroxycarbonate) werden charakterisiert und ihre Reaktivitat mit der einer Mischung aus Bariumcarbonat und Kupferoxid verglichen. Das ist moglich, da sich die genannten Mischfallprodukte in einer ersten Stufe bei Temperaturen bis 600 °C zu Bariumcarbonat und Kupferoxid zersetzen.

Etude du comportement magnetique des monocristaux de Mn 2 Mo 3 O 8 en presence de champs magnetiques faibles dans l'intervalle de temperatures allant de 4.3 a 180 K. Mesure de la variation de la susceptibilite magnetique statique χ avec la temperature. Dependance thermique du moment magnetique. Observation d'une transition de phase magnetique

We present resonant inelastic x-ray scattering (RIXS) results on insulating monoclinic $\mathrm{V}{\mathrm{O}}_{2}$ with excitation across the ${L}_{2,3}$ edges of vanadium. The spectra measured near threshold in the ${L}_{3}$ region and in the ${L}_{2}$ region show a Raman behavior with a clear peak around $0.9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ transferred energy. The analysis of the data allows the neutral excitation spectrum of the system up to about $2--2.5\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ to be determined. These excitations are due to $dd$ transitions, whose main contributions are discussed. The possibility of ${{d}^{1};{d}^{1}\ensuremath{\rightarrow}{d}^{2};{d}^{0}}$ charge fluctuations within a dimer in RIXS is also discussed. The results are compared with available information on optical constants and on electron energy loss spectroscopy. Due to the low symmetry of the system, there is a similarity between the Raman spectrum obtained with RIXS and the optical absorption spectrum.

We present a detailed study of the valence and conduction bands of VO2 across the metal-insulator transition using bulk-sensitive photoelectron and O K x-ray absorption spectroscopies. We observe a giant transfer of spectral weight with distinct features that require an explanation which goes beyond the Peierls transition model as well as the standard single-band Hubbard model. Analysis of the symmetry and energies of the bands reveals the decisive role of the V 3d orbital degrees of freedom. Comparison to recent realistic many body calculations shows that much of the k dependence of the self-energy correction can be cast within a dimer model.

Triosmium pentadecatin tetradecaoxide, Os 3 Sn 15 O 14 , is isostructural with Ru 3 Sn 15 O 14 . It is a metal-rich stannate and contains osmium-centred tin octahedra. These OsSn 6 octahedra form triple chains in which the Sn atoms which link the octahedra have the oxidation state +1.

We found direct experimental evidence for an orbital switching in the V $3d$ states across the metal-insulator transition in ${\mathrm{VO}}_{2}$. We have used soft-x-ray absorption spectroscopy at the V ${L}_{2,3}$ edges as a sensitive local probe and have determined quantitatively the orbital polarizations. These results strongly suggest that, in going from the metallic to the insulating state, the orbital occupation changes in a manner that charge fluctuations and effective bandwidths are reduced, that the system becomes more one dimensional and more susceptible to a Peierls-like transition, and that the required massive orbital switching can only be made if the system is close to a Mott insulating regime.

The traditional approach for computing the solution to large systems of ordinary differential or differential-algebraic equations typically includes discretization in time with an implicit integration formula. The primary opportunity for parallelization is therefore limited to the linear system solution that is performed at each timestep. Waveform techniques, on the other hand, decompose the problem at the equation level and solve for different components of the system independently, using previous iterates from other processors as inputs. This approach is particularly well-suited for message-passing computing environments, especially those with high communication latency because synchronization and communication take place infrequently and communication consists of large packets of information. We present an MPI-based implementation of a waveform relaxation-based semiconductor device simulation program and provide experimental results using this program to solve the time dependent semiconductor drift-diffusion equations on a cluster of workstations. >

Retinal detachment remains one of the most frequent causes of visual impairment in humans, even after ophthalmoscopically successful retinal reattachment. This study was aimed at monitoring (ultra-) structural alterations of retinae of rabbits after experimental detachment. A surgical procedure was used to produce local retinal detachments in rabbit eyes similar to the typical lesions in human patients. At various periods after detachment, the detached retinal area as well as neighbouring attached regions were studied by light and electron microscopy. In addition to the well-known degeneration of photoreceptor cells in the detached retina, the following progressive alterations were observed, (i) in both the detached and the attached regions, an incomplete but severe loss of ganglion cell axons occurs; (ii) there is considerable ganglion cell death, particularly in the detached area; (iii) even in the attached retina distant from the detachment, small adherent groups of photoreceptor cells degenerate; (iv) these photoreceptor cells degenerate in an atypical sequence, with severely destructed somata and inner segments but well-maintained outer segments; and (v) the severe loss of retinal neurons is not accompanied by any significant loss of Müller (glial) cells. It is noteworthy that the described progressive (and probably irreparable) retinal destructions occur also in the attached retina, and may account for visual impairment in strikingly large areas of the visual field, even after retinal reattachment.

CuMoO4 crystals reversibly change their color from green to brown upon heating, accompanied by a loss in transmittance. UV/VIS spectroscopic analysis revealed that these changes are due to particular electronic properties of the crystal instead of its chemical decomposition or structural change. Investigations were carried out in the temperature range 23-400 degrees C. The intensive green color of the crystal at room temperature is caused by a small transmission window between two absorption bands, the band gap of the crystal in the blue and the 3d9--4p absorption of the Cu2+ ions in the red. With increasing temperature the band gap shifts towards longer wavelengths, and the crystal changes both color and transmittance. Spectroscopic features of the crystal are discussed together with the temperature dependence of its electrical resistance. Resistance measurements were performed simultaneously to the optical measurements.

To determine the electrophysiological properties of Müller (glial) cells from experimentally detached rabbit retinas.A stable local retinal detachment was induced by subretinal injection of a sodium hyaluronate solution. Müller cells were acutely dissociated and studied by the whole-cell voltage-clamp technique.The cell membranes of Müller cells from normal retinas were dominated by a large inwardly rectifying potassium ion (K+) conductance that caused a low-input resistance (100 M(Omega)) and a high resting membrane potential (-82 +/- 6 mV). During the first week after detachment, the Müller cells became reactive as shown by glial fibrillary acidic protein (GFAP) immunoreactivity, and their inward currents were markedly reduced, accompanied by an increased input resistance (200 M(Omega)). After 3 weeks of detachment, the input resistance increased further (300 M(Omega)), and some cells displayed significantly depolarized membrane potentials (mean -69 +/- 18 mV). When PVR developed (in 20% of the cases) the inward K+ currents were virtually completely eliminated. The input resistance increased dramatically (1000 MOmega), and almost all cells displayed strongly depolarized membrane potentials (-44 +/- 16 mV).Reactive Müller cells are characterized by a severe reduction of their K+ inward conductance, accompanied by depolarized membrane potentials. These changes must impair physiological glial functions, such as neurotransmitter recycling and K+ ion clearance. Furthermore, the open probability of certain types of voltage-dependent ion channels (e.g., Ca2+-dependent K+ maxi channels) increases that may be a precondition for Müller cell proliferation, particularly in PVR when a dramatic downregulation of both inward current density and resting membrane potential occurs.

The electrophysiological properties of Müller cells, the principal glial cells of the retina, are determined by several types of K(+) conductances. Both the absolute and the relative activities of the individual types of K(+) channels undergo important changes in the course of ontogenetic development and during gliosis. Although immature Müller cells express inwardly rectifying K(+) (K(IR)) currents at a very low density, the membrane of normal mature Müller cells is predominated by the K(IR) conductance. The K(IR) channels mediate spatial buffering K(+) currents and maintain a stable hyperpolarized membrane potential necessary for various glial-neuronal interactions. During "conservative" (i.e., non-proliferative) reactive gliosis, the K(IR) conductance of Müller cells is moderately reduced and the cell membrane is slightly depolarized; however, when gliotic Müller cells become proliferative, their K(IR) conductances are dramatically down-regulated; this is accompanied by an increased activity of Ca(2+)-activated K(+) channels and by a conspicuous unstability of their membrane potential. The resultant variations of the membrane potential may increase the activity of depolarization-activated K(+), Na(+) and Ca(2+) channels. It is concluded that in respect to their K(+) current pattern, mature Müller cells pass through a process of dedifferentiation before proliferative activity is initiated.

To determine differences of K+ channel activity between Müller glial cells obtained from retinas of healthy human donors and of patients with retinal detachment and proliferative vitreoretinopathy.Müller cells were enzymatically isolated from retinas of healthy donors and from excised retinal pieces of patients. The whole-cell and the cell-attached configurations of the patch-clamp technique were used to characterize the current densities of different K+ channel types and the activity of single Ca2+ -activated K+ channels of big conductance (BK).Cells from patients displayed a less negative mean membrane potential (-52.8 mV) than cells from healthy donors (-80.6 mV). However, the membrane potentials in cells from patients scattered largely between -6 and -99 mV. The inwardly rectifying K+ permeability in cells from patients was strongly reduced (0.3 pA/pF) when compared with cells from healthy donors (6.0 pA/pF). At the resting membrane potential, single BK channels displayed a higher mean activity (open probability, Po, and channel current amplitude) in cells from patients (Po, 0.30) than in cells from healthy donors (Po: 0.03). The variations of BK current amplitudes were correlated with the variations of the membrane potential.The dominant expression of inwardly rectifying channels in cells from healthy donors is thought to support important glial cell functions such as the spatial buffering of extracellular K+. The downregulation of these channels and the less negative mean membrane potential in cells from patients should impair spatial buffering currents and neurotransmitter clearance. The increased activity of BK channels may support the proliferative activity of gliotic cells via feedback regulation of Ca2+ entry and membrane potential.

The distribution of mitochondria within retinal glial (Müller) cells and neurons was studied by electron microscopy, by confocal microscopy of a mitochondrial dye and by immunocytochemical demonstration of the mitochondrial enzyme GABA transaminase (GABA-T). We studied sections and enzymatically dissociated cells from adult vascularized (human, pig and rat) and avascular or pseudangiotic (guinea-pig and rabbit) mammalian retinae. The following main observations were made. (1) Müller cells in adult euangiotic (totally vascularized) retinae contain mitochondria throughout their length. (2) Müller cells from the periphery of avascular retinae display mitochondria only within the sclerad-most end of Müller cell processes. (3) Müller cells from the vascularized retinal rim around the optic nerve head in guinea-pigs contain mitochondria throughout their length. (4) Müller cells from the peripapillar myelinated region ('medullary rays') of the pseudangiotic rabbit retina contain mitochondria up to their soma. In living dissociated Müller cells from guinea-pig retina, there was no indication of low intracellular pH where the mitochondria were clustered. These data support the hypothesis that Müller cells display mitochondria only at locations of their cytoplasm where the local O2 pressure (pO2) exceeds a certain threshold. In contrast, retinal ganglion cells of guinea-pig and rabbit retinae display many mitochondria although the local pO2 in the inner (vitread) retinal layers has been reported to be extremely low. It is probable that the alignment of mitochondria and the expression of mitochondrial enzymes are regulated by different mechanisms in various types of retinal neurons and glial cells.

Selective antibodies were used to assess the cellular and subcellular localization of glutathione, and the glutathione precursors gamma-glutamylcysteine, glutamate, and cysteine, in neuronal (photoreceptors) and non-neuronal (pigment epithelial cells and Müller cells) cell types in the outer retina of the guinea pig. In each cell type the highest level of glutathione immunoreactivity occurred in the mitochondria. The labeling density in the cytoplasmic matrix was higher (and the mitochondrial-cytoplasmic gold particle ratio lower) in pigment epithelial cells than in Müller cells and photoreceptors. The latter two cell types showed a mitochondrial-cytoplasmic gold particle ratio of 15.5 and 21.7, respectively. In contrast to glutathione, gamma-glutamylcysteine seemed to be enriched in the cytoplasmic matrix relative to the mitochondria. The immunogold labeling for this dipeptide was stronger in the pigment epithelial cells than in Müller cells and photoreceptors. Glutamate immunoreactivity was high in photoreceptors, intermediate in pigment epithelial cells, and low in Müller cells, while the cysteine immunogold signal was low in each cell type and cell compartment. The present results suggest that glutathione is concentrated in mitochondria but to different degrees in different cells. The low mitochondrial content of gamma-glutamylcysteine (the direct precursor of glutathione) is consistent with biochemical data indicating that glutathione is synthesized extramitochondrially and transported into the mitochondrial matrix. Judged from the immunocytochemical data, cysteine may be a rate-limiting factor in glutathione synthesis in each cell type while glutamate can be rate limiting only in Müller cells.

The aim of this study was to define the neurologic risk of heart transplantation compared to coronary artery bypass grafting (CABG) and valve surgery.A retrospective study.A university hospital.8001 patients undergoing heart transplantation, CABG and valve surgery.The incidences of perioperative central nervous system (CNS) complications were compared between different procedures. Risk factors were analysed using univariate and multivariate methods.The overall incidence of CNS complications was 19.8% (78/393) in heart transplantation, 3.1% (176/5734) in elective CABG, 9.5% (161/1689) in elective valve surgery, 10.3% (15/146) in emergency CABG and 51.3% (20/39) in emergency valve surgery. Most powerful predictors of CNS complications were preoperative intra-aortic counterpulsation (IABP) in the heart transplantation group, age65 years in the CABG group and preoperative use of catecholamine in the valve group.CNS complications occur much more frequently after heart transplantation than elective CABG and valve surgery. The high incidence of CNS complications after emergency operations as well as preoperative catecholamine and IABP as powerful contributing factors suggest that preoperative cerebral hypoperfusion due to a compromised hemodynamic state facilitates postoperative CNS complications and this may partly explain the high incidence of CNS complications after heart transplantation.

Müller cells from 22 mammalian species were subjected to morphological and electrophysiological studies. In the 'midperiphery' of retinae immunocytochemically labeled for vimentin, estimates of Müller cell densities per unit retinal surface area, and of neuron-to-(Müller) glia indices were performed. Müller cell densities were strikingly similar among the species studied (around 8000-11,000 mm-2) with the extremes of the horse (or = 5000 mm-2) and the tree shrew (or = 20,000 mm-2). By contrast, the number of neurons per Müller cell varied widely, being clustered at 6-8 (in retinae with many cones), at about 16, and at up to more than 30 (in strongly rod-dominated retinae). Isolated Müller cell volumes were estimated morphometrically, and cell surface areas were calculated from membrane capacities. Müller cells isolated from thick vascularized retinae (carnivores, rats, mice, ungulates) were longer and thinner, and had smaller volumes but higher surface-to-volume ratios than cells from thin paurangiotic (i.e. with blood vessels only near the optic disc) or avascular retinae (rabbits, guinea pigs, horses, zebras). In whole-cell voltage-clamp studies, Müller cells from all mammals studied displayed two dominant K+ conductances, inwardly rectifying currents and delayed rectifier currents. TTX-sensitive Na+ currents were recorded only in some species. Based on these data, the following hypotheses are presented, (a) neuron-to-(Müller) glia indices are determined by precursor cell proliferation rather than by metabolic demands; (b) Müller cell volumes depend on available space rather than on the number of supported neurons; and (c) it follows that, the specific metabolic activities of Müller cells must differ greatly between species, a difference that may contribute to distinct patterns of retinal vascularization.