Mosaics of neurons are usually quantified by methods based on nearest-neighbor distance (NND). The commonest indicator of regularity has been the ratio of the mean NND to the standard deviation, here termed the 'conformity ratio.' However, an accurate baseline value of this ratio for bounded random samples has never been determined; nor was its sampling distribution known, making it impossible to test its significance. Instead, significance was assessed from goodness-of-fit to a Rayleigh distribution, or from another ratio, that of the observed mean NND to an expected mean predicted by theory, termed the dispersion index. Neither approach allows for boundary effects that are common in experimental mosaics. Equally common are 'missing' neurons, whose effects on the statistics have not been studied. To address these deficiencies, random patterns and real neuronal mosaics were analyzed statistically. Ns independent random-point samples of size Np were generated for 13 Np values between 25 and 6400, where Ns x Np > or = 144,000. Samples were generated with rectangular boundaries of aspect ratio 1:1, 1:5, and 1:10 to examine the influence of sample geometry. NND distributions, conformity ratios, and dispersion indices were computed for the resulting 45,997 independent random patterns. From these, empirical sampling distributions and critical values were determined. NND distributions for small-to-medium, bounded, random populations were shown to differ significantly from Rayleigh distributions. Thus, goodness-of-fit tests are invalid for most experimental mosaics. Charts are presented from which the significance of conformity ratios or dispersion indices can be read directly. The conformity ratio reacts conservatively to extremes of sample geometry, and provides a useful and safe test. The dispersion index is nonconservative, making its use problematic. Tests based on the theoretical distribution of the dispersion index are unreliable for all but the largest samples. Random deletions were also made from 33 real retinal ganglion cell mosaics. The mean NND, conformity ratio, and dispersion index were determined for each original mosaic and 36 independent samples at each of nine sampling levels, retaining between 90% and 10% of the original population. An exclusion radius, based on a spatial autocorrelogram, was also calculated for each of these 10,725 mosaic samples. The mean NND was moderately insensitive to undersampling, rising smoothly. The exclusion radius was remarkably insensitive. The conformity ratio and dispersion index fell steeply, sometimes failing to reach significance while half of the cells still remained. For the same 33 original mosaics, linear regression showed the exclusion radius to be 62 +/- 3% of the mean NND.

Animals↗

PubMedDate not supplied

Biplexiform ganglion cells, characterized by dendrites in both outer and inner plexiform layers, are regular, mosaic-forming elements of teleost fish retinae.

Biplexiform ganglion cells were labelled by retrograde transport of HRP in five species of marine fish from the neoteleost acanthopterygian orders Perciformes and Scorpaeniformes. Their forms and spatial distributions were studied in retinal flatmounts and thick sections. Biplexiform ganglion cells possessed sparsely branched, often varicose, dendrites that ramified through the inner nuclear layer (INL) to reach the outer plexiform layer (OPL), as well as conventional arborizations in the most sclerad part of the inner plexiform layer (IPL). Their somata were of above-average size and were displaced into the vitread border of the INL. Mean soma areas ranged from 99 +/- 6 microns2 in Bathymaster derjugini (Perciformes) to 241 +/- 12 microns2 in Hexagrammos stelleri (Scorpaeniformes), but were similar in each species to those of the outer-stratified alpha-like ganglion cells, whose dendritic trees occupied the same IPL sublamina. In the best-labelled specimens, biplexiform cells formed clear mosaics with spacings and degrees of regularity much like those of other large ganglion cells, but spatially independent of them. Biplexiform mosaics were plotted in three species, and analyzed by nearest-neighbor distance and spatial correlogram methods. The exclusion radius, an estimate of minimum mosaic spacing, ranged from 113 microns in Hexagrammos stelleri, through 150 microns in Ernogrammus hexagrammus (Perciformes), to 240 microns in Myoxocephalus stelleri (Scorpaeniformes). A spatial cross-correlogram analysis of the distributions of biplexiform and outer-stratified alpha-like cells in Hexagrammos demonstrated the spatial independence of their mosaics. Similar cells were previously observed not only in the freshwater cichlid Oreochromis spilurus (Perciformes) but also in the goldfish Carassius auratus (Cypriniformes) which, being an ostariophysan teleost, is only distantly related. Thus, biplexiform ganglion cells may be regular elements of all teleost fish retinae. Their functional role remains unknown.

Animals↗

PubMedDate not supplied

Large retinal ganglion cells in the pipid frog Xenopus laevis form independent, regular mosaics resembling those of teleost fishes.

Population-based studies of retinal neurons have helped to reveal their natural types in mammals and teleost fishes. In this, the first such study in a frog, labeled ganglion cells of the mesobatrachian Xenopus laevis were examined in flatmounts. Cells with large somata and thick dendrites could be divided into three mosaic-forming types, each with its own characteristic stratification pattern. These are named alpha a, alpha ab, and alpha c, following a scheme recently used for teleosts. Cells of the alpha a mosaic (approximately 0.4% of all ganglion cells) had very large somata and trees, arborizing diffusely within sublamina a (the most sclerad). Their distal dendrites were sparsely branched but achieved consistent coverage by intersecting those of their neighbors. Displaced and orthotopic cells belonged to the same mosaic, as did cells with symmetric and asymmetric trees. Cells of the alpha ab mosaic (approximately 1.2%) had large somata, somewhat smaller trees that appeared bistratified at low magnification, and dendrites that branched extensively. Their distal dendrites arborized throughout sublamina b and the vitread part of a, tessellating with their neighbors. All were orthotopic; most were symmetric. Cells of the alpha c mosaic (approximately 0.5%) had large somata and very large, sparse, flat, overlapping trees, predominantly in sublamina c. All were orthotopic; some were asymmetric. Nearest-neighbor analyses and spatial correlograms confirmed that each mosaic was regular and independent, and that spacings were reduced in juvenile frogs. Densities, proportions, sizes, and mosaic statistics are tabulated for all three types, which are compared with types defined previously by size and symmetry in Xenopus and potentially homologous mosaic-forming types in teleosts. Our results reveal strong organizational similarities between the large ganglion cells of teleosts and frogs. They also demonstrate the value of introducing mosaic analysis at an early stage to help identify characters that are useful markers for natural types and that distinguish between within-type and between-type variation in neuronal populations.

Animals↗

PubMedDate not supplied

Large retinal ganglion cells that form independent, regular mosaics in the ranid frogs Rana esculenta and Rana pipiens.

Population-based studies of ganglion cells in retinal flatmounts have helped to reveal some of their natural types in mammals, teleost fish and, recently, the aquatic mesobatrachian frog Xenopus laevis. Here, ganglion cells of the semiterrestrial neobatrachian frogs Rana esculenta and Rana pipiens have been studied similarly. Ganglion cells with large somata and thick dendrites could again be divided into three mosaic-forming types with distinctive stratification patterns. Cell dimensions correlated inversely with density, being smallest in the visual streak. Cells of the alpha a mosaic (< 0.2% of all ganglion cells) had the largest somata at each location (often displaced) and their trees were confined to one shallow plane within sublamina a of the inner plexiform layer. In regions of high regularity, many trees were symmetric. Elsewhere, asymmetric, irregular trees predominated and their dendrites, although sparsely branched, achieved consistent coverage by intersecting in complex ways. Cells of the alpha ab mosaic were more numerous (approximately 0.7%) and had large somata, smaller (but still large) trees, and dendrites that branched extensively in two separate shallow planes in sublaminae a and b. The subtrees did not always match in symmetry, and each subtree tessellated independently with its neighbors. Cells of the alpha c mosaic (approximately 0.1%) had large, orthotopic somata and large, sparse trees (often asymmetric and irregular) close to the ganglion cell layer. Nearest-neighbor analyses and spatial correlograms confirmed that each mosaic was regular and independent. Densities, proportions, sizes, and mosaic statistics are tabulated for all three types, which are compared with types defined by size and symmetry in R. pipiens, by discriminant analysis in R. temporaria, by physiological response in both, and by mosaic analysis in Xenopus and several teleosts. The variable stratification of these otherwise similar types across species is consistent with other evidence that stratification may be determined, in part, by functional interactions.

Animals↗

PubMedDate not supplied

Evidence for spatial regularity among retinal ganglion cells that project to the accessory optic system in a frog, a reptile, a bird, and a mammal.

The vertebrate retina contains only five major neuronal classes but these embrace a great diversity of discrete types, many of them hard to define by classical methods. Consideration of their spatial distributions (mosaics) has allowed new types, including large ganglion cells, to be resolved across a wide range of vertebrates. However, one category of large ganglion cells has seemed refractory to mosaic analysis: those that project to the accessory optic system (AOS) and serve vestibulocerebellar mechanisms of motion detection and image stabilization. Whenever AOS-projecting cells have been analyzed by nearest-neighbor methods, their distribution has appeared almost random. This is puzzling, because most aspects of visual processing require the visual scene to be sampled regularly. Here, spatial correlogram methods are applied to distributions of large ganglion cells, labeled retrogradely from the AOS in frogs, turtles, and rats, and to the AOS-projecting displaced ganglion cells of chickens. These methods reveal hidden spatial order among AOS-projecting populations, of a form that can be simulated either by superimposing a single regular mosaic on a random population or, more interestingly, by overlapping three or more regular, similar but spatially independent mosaics. The rabbit is known to have direction-selective ganglion cells (not, however, AOS projecting) that can be subdivided into functionally distinct, regular mosaics by their tracer-coupling patterns even though they are morphologically homogeneous. The present results imply that the direction-selective AOS-projecting ganglion cells of all vertebrates may, likewise, be subdivided into regular, independent mosaics.

Accessory Nerve↗

PubMedDate not supplied

Large retinal ganglion cells that form independent, regular mosaics in the bufonoid frogs Bufo marinus and Litoria moorei.

Population-based methods were used to study labeled retinal ganglion cells from the cane toad Bufo marinus and the treefrog Litoria moorei, two visually competent bufonoid neobatrachians with contrasting habitats. In both, cells with large somata and thick dendrites formed distinct types with independent mosaics. The alpha(a), alpha(ab), and alpha(c) mosaics of Bufo in all major respects resembled those of ranids, studied previously, and could be provisionally matched to the same functional classes. As in other frogs, some alpha(a) cells were displaced and many alpha-cells of all types were asymmetric, but within each type all variants belonged to one mosaic. Nearest-neighbor analyses and spatial correlograms confirmed that all three mosaics were regular and independent. In Litoria, monostratified alpha(a) cells were not found. Instead, two bistratified types were present, distinguished individually by soma size and dendritic caliber and collectively by membership of independent mosaics: the larger (approximately 0.8% of all ganglion cells) was termed alpha1(ab) and the smaller (approximately 2.2%) alpha2ab. An alpha(c) cell type was also present, although too inconstantly labeled for mosaic analysis. Nearest-neighbor analyses and spatial correlograms confirmed that the two alpha(ab) mosaics were regular and independent. Densities, proportions, soma sizes, and mosaic statistics are tabulated for each species. The emergence of a consensus pattern of alpha-cell types in fishes and frogs, from which this treefrog partly diverges, offers new possibilities for studying correlations between function, phylogeny, ecology, and neuronal form.

Animals↗

PubMedDate not supplied

Three mutations and the karyotype of the prairie vole. White spotting, polydipsia, and muscular dystrophy in Microtus ochrogaster.

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Animals↗

PubMedDate not supplied

Intrapelvic urethral anastomosis. A comparison of three techniques.

Three intrapelvic urethral anastomosis techniques were performed on 12 mature male dogs to compare the degree of stricture. The intrapelvic urethra was transected 1 cm caudal to the prostate, and anastomosis was performed using either suturing of the urethra over an indwelling catheter, suturing of the urethra without an indwelling catheter, or apposition of the urethra without sutures over an indwelling catheter. Postoperatively, the dogs were evaluated using clinical urination patterns, biochemical tests, radiography, and pathology. Three of four suture-catheter dogs and one of four catheter-only dogs had normal urinary patterns. Stricture (25-84%) with urethral dilation or fistulas tracts was visible on retrograde, positive contrast urethrograms of 3 of 12 intact dogs 20 weeks after surgery, and on all 12 excised lower urinary tracts. Suture-catheter dogs subjectively had the least amount of stricture. All eight dogs (1 suture-catheter dog, 4 suture-only dogs, and 3 catheter-only dogs) with severe stricture (greater than 60% lumen diameter reduction) had histopathologic signs of chronic, inflammatory urinary tract disease, including four with chronic, ascending lymphocytic pyelonephritis. Hydroureter and hydronephrosis developed in two catheter-only dogs. Complete urethral transection resulted in some degree of stricture, regardless of technique used for anastomosis. Urethral anastomosis over an indwelling catheter appeared to result in a lesser degree of stricture and clinical and histopathologic derangement.

Anastomosis, Surgical↗