In this paper we describe the dendritic morphology of ganglion cells that have been retrogradely stained with HRP taken up by the cut optic nerve. This technique produces an extensive Golgi-like filling of the cells. From their appearance in the retinal whole-mount, they were classified as four types, according to the sizes of the soma and dendritic field, the thickness of the primary dendrites, and the density of the arbors. Each type was subdivided according to the level(s) of stratification of the dendrites within the inner and outer plexiform layer(s) to yield a total of 15 subtypes (four for three types, three for the other). The retina of the goldfish grows by a balloon-like expansion, and by the addition of new neurons, in annuli, at the margin. Therefore, a similar cell type may be examined at a variety of stages of development in the same retina, as well as in the retinae from fish of various ages. We have used a computer-assisted microscope to do so, quantitatively, for one large and easily identified subtype. In small fish (ca. 4 cm long), the number of dendritic branch points, the total dendritic length, and the dendritic field sizes of these cells are constant inside a central zone extending to 70-80% of the retinal radius. The magnitudes of all three numeric descriptors decrease closer to the margin. In large fish (ca. 14 cm long), the central zone extends to more than 90% of the retinal radius, and the same pattern holds. The area of the dendritic fields and the total dendritic lengths are both greater in the central zone of the large fish than in the small, but the number of branches is the same in both. This suggests that once a cell has achieved the "mature" number of dendritic branches, further growth is interstitial. A comparison of dendritic morphologies across the retina shows that the pattern of dendritic outgrowth in peripheral retina is initially directed parallel to the margin, and, later, toward the margin. This suggests that dendritic growth is impeded by the dendrites present in more central retina and proceeds preferentially where they are absent. Cells of the same age are at different distances from the optic disk in the small and large retinae. In some cases, they have quite different dendritic morphologies. This implies that dendritic development depends not only on the age and subtype of the cell, but on extrinsic factors as well.(ABSTRACT TRUNCATED AT 400 WORDS)

The retina of the goldfish grows by a balloon-like expansion and by the addition of new neurons at the margin. It has been proposed that as a consequence of this expansion the dendritic arbors of ganglion cells in central retina grow in a uniform manner without the addition of new branches. In the present study, we have examined this proposal by comparing the geometries of individual dendritic arbors of large-field ganglion cells from the retinas of small/young and large/old fish. These comparisons were based on measurements of several parameters of dendritic morphology, including number of segments and branches, branch angles, changes in diameter at branch points, and proximal versus distal distribution of arbor length. In addition, we used passive, steady-state cable modeling as an independent method of estimating the functional architectures of small and large dendritic arbors. Our morphometric data indicate that, though they are very different in absolute size, dendritic arbors of small and large ganglion cells have remarkably similar architectures. Analysis with steady-state cable equations indicates that the arbors from small and large cells have equivalent electrotonic lengths and show comparable propagation of synaptic currents. These data are consistent with the hypothesis that dendritic arbors of small and large ganglion cells are scaled versions of one another. We conclude that the growth of these cells during the expansion of the retina is the result of the addition of dendritic mass to an arbor whose basic geometry remains unchanged.

No abstract

Tin(I1) is more readily handled coulometrically than volumetrically, and the electrode processes are critically evaluated. Zero-current tin(1V)tin(I1) potentials cannot be measured or derived from Lewartowicz plots, and chargetransfer kinetic parameters must therefore be referred to 0 V. Gold cathodes are deactivated towards reduction of hydrogen ion by specific adsorption of bromide ion, and give well separated waves for the reduction of tin(1V) to tin(I1) and to tin metal, with limiting currents proportional to the tin(1V) concentration in 3.0 M bromide @us 0.4 M perchloric or hydrobromic acid medium. Mass and charge transfer kinetic parameters are derived from the voltammograms. Platinum cathodes become filmed and theories of the nature of the film are reviewed in the light of new work, which shows that the film is difficult to remove and was not completely removed in earlier work. The generation of tin(I1) in bromide medium is superimposed on the filmsuppressed hydrogen-ion wave. Chloride media are unsuitable. Kinetic parameters must be derived from anodic voltammograms of tin(II), which are uncomplicated in the bromide medium. A t low bromide concentrations, the platinum anode is filmed with a species such as [SnBr,OHI2-, which blocks the reaction. The electrode mechanism is discussed. Charge-transfer parameters vary with potential or current, but synthesised computer-plotted voltammograms give a good fit with experimental curves. From the kinetic parameters the current efficiency for tin(I1) generation is computed, and for 0-2 M tin(1V) the efficiency is better than 99.98 per cent. over the current density range 100 to 300 mA cm-2 but decreases rapidly outside this range. Sample concentrations must be chosen so as to maintain the intermediate current within range throughout the determination, and platinum cathodes must be filmed quickly, but not aged for too long.

Endothelial cells emerge from the atrioventricular canal (AVC) to form nascent coronary blood vessels in the juvenile zebrafish heart. We found that pdgfrβ is first expressed in the epicardium around the AVC and later becomes localized mainly in the mural cells. pdgfrβ mutant fish display severe defects in mural cell recruitment and coronary vessel development. pdgfrβ+ mural cells are heterogeneous and those associated with coronary arteries also express cxcl12b. Mural cells positive for both pdgfrβ and cxcl12b transgenic reporters had elevated expression of smooth muscle cell genes. Interestingly, these mural cells were associated with coronary arteries even in the absence of Pdgfrβ, although smooth muscle gene expression was downregulated in these cells. We found that pdgfrβ expression dynamically changes in the epicardium derived cells, which we found to be a heterogeneous population. mdka was identified as a gene upregulated in subpopulations of pdgfrβ+ cells during heart regeneration. However, pdgfrβ but not mdka mutants showed defects in heart regeneration. Our results demonstrated that pdgfrβ+ cells and Pdgfrβ signaling are essential for coronary development and heart regeneration.SUMMARY STATEMENTHeterogeneous pdgfrβ positive cells are present in developing and regenerating zebrafish hearts and are required for development of mural cells and their association with the nascent coronary vessels during zebrafish heart development and regeneration.

It cannot be said that the problem of measuring the rate parameters for all the reactions , including the solvent molecule and ion reactions, in vigorously stirred solutions under the conditions of coulometry has been solved for fast reactions. However, the method of pattern

Titanium(II1) has found considerable use as a coulometric intermediate, and is the strongest reductant that can be generated with good efficiency in aqueous media.At such high concentrations, a surfactant impurity becomes adsorbed on the working electrode and very seriously reduces the speed of the charge-transfer process and therefore the current efficiency. A method of purification of the sulphuric acid by electrosorption is shown to give a charge-transfer rate constant in excess of 10-5 1 cm-2 s-l, but charcoal column purification is without effect. Both 7 and 10 M sulphuric acid media were examined, but because the mass-transfer rate is decreased by the higher viscosity of the 10 M acid there is little difference in current efficiency. Addition of iron(II1) or iron(I1) hinders the adsorption of the impurity and the deactivation of the electrode, but offers no special benefit. Electrode kinetic parameters are reported for various treated and untreated media, and current efficiencies for the generation of titanium(II1) are computed. The behaviour in perchloric acid is re-interpreted.

The following are summaries of the papers presented at an Ordinary Meeting of the Society held on May lst, 1968, and reported in the May issue of Proceedings (p. 75). The Titrimetric Determination of 2-Ethylanthraquinone and its TetrahydroDerivative BY T. E. FORSTER AND V. J. JENNINGS 2-ETHYLANTHRAQUINONE and its tetrahydro derivative are of importance in the industrial production of hydrogen peroxide by the process known as auto-oxidation.The simultaneous production of the t etrahydro-an t hrahydroquinone during the catalytic hydrogenation of ZEAQ is of importance.We have attempted to produce methods for the standardisation and determination of the purity of both quinones.Although considerable attention has been paid to the determination of the parent compound, anthraquinone, by gravimetry, sulphonation and polarography, no satisfactory titrimetric method has been reported. Further, no chemical method has been proposed for the determination of ZEAQ and its tetrahydro derivative.