Assessment of two glycated hemoglobin immunoassays.

INTRODUCTION: Glycated hemoglobin (HbA1c) level reflects chronic glycemic status if reliable tests are used, however, in some regions worldwide high performing assays might not be readily available. This study aimed to asses two HbA1c immunoassays, comparing them with high-performance liquid chromatography (HPLC) assay, three methods available in Ecuador. MATERIAL AND METHODS: HbA1c were measured in 114 fresh whole blood-samples by DCA-Vantage point-of-care analyzer, I-Chroma portable fluorescent scanner immunoassay and BioRad Variant II Turbo HPLC. Normal and pathological HbA1c ranges were included. Blood samples with variants of hemoglobin were excluded. HbA1c values were expressed in National Glycohemoglobin Standardization Program percentages and mmol/mol, as mean±standard deviation. RESULTS: HbA1c results by HPLC and DCA-Vantage were similar: 6.3±1.7% (45±18.6mmol/mol) vs. 6.3±1.8% (45±19.7mmol/mol), respectively, P=0.057; while HbA1c values by I-Chroma were lower than HPLC, 5.8±1.9% (40±20.8mmol/mol), P<0.001. The coefficient of variation was below 2% for high and low HbA1c levels, in all methods studied. HbA1c values by HPLC and DCA-Vantage were highly correlated (Spearman's Rank Correlation [SRC]: 0.916), while the correlation among HPLC and I-Chroma was weak (SRC: 0.368). The mean bias between DCA-Vantage and HPLC was -0.02±0.29% (-0.2±3.2mmol/mol), while for I-Chroma and HPLC mean bias was -0.50±1.62% (-5.5±17.7mmol/mol). CONCLUSION: HbA1c immunoassays DCA-Vantage was comparable to HPLC assay, showing good correlation, appropriate precision and low bias, whereas I-Chroma assay was precise but inaccurate. Therefore, DCA-Vantage has better performance than I-Chroma. These findings suggest that is convenient to assess the HbA1c immunoassays commercially available in our country, Ecuador.

Organization of cytochrome oxidase staining in the visual cortex of nocturnal primates (Galago crassicaudatus and Galago senegalensis): I. Adult patterns.

The distribution and differential staining patterns of cytochrome oxidase (CO) activity in visual cortical areas have provided useful anatomical markers for the modular organization of area 17 (striate cortex) and area 18 in primates. In macaque and squirrel monkeys, previous studies have shown that the majority of cells that lie in areas of high CO activity are color selective, are nonoriented, and project to adjacent zones of high CO activity in area 17 and to stripes of high CO activity in area 18. By contrast, most cells in zones with weak CO activity in area 17 have relatively narrow orientation tuning and are not color selective (Livingstone and Hubel: J. Neurosci. 4:309-356, 2830-2835, '84; 7:3371-3377, '87). The periodic organization of CO activity in area 17, the "blobs," and the stripe-like organization in area 18 thus seem to define visual cortical processing modules and/or channels in primates. We have investigated the organization of CO activity in areas 17 and 18 in two species of nocturnal prosimian primates [Galago crassicaudatus (GCC) and Galago senegalensis (GSS)] in order to evaluate CO staining patterns in primates that have been reported to possess almost exclusively rod retinae and no color vision. In area 17 of both species, our results show that, as in diurnal and nocturnal simian primates, the darkest CO staining occurs in layers III and IV, with clear periodicity in layer III (i.e., CO blobs) and homogeneous staining in layer IV beta, the cortical recipient sublayer of the geniculate parvocellular layers. In GCC, individual blobs in layer III appear to be larger and less frequent than has been reported for the macaque monkey. Unlike simian primates, both galago species exhibit clear CO periodicities within layer IV alpha, the cortical recipient sublayer of the magnocellular geniculate layers. In addition, faint CO periodicities are apparent in layer VI and scattered large darkly CO stained pyramidal cells are visible throughout layer V. Quantitative analysis suggests that CO periodicities are more frequent in GSS than in GCC, suggesting that there may be evolutionary pressure to maintain the same number of CO modules within the smaller striate cortex of the lesser galago, although this is not the trend found across distantly related species. CO activity in area 18 is less well-developed than reported in other primates. In fact, we could not reliably identify discontinuities in CO staining in area 18 of GSS.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological organization of thalamocortical relay cells in the dorsal lateral geniculate nucleus of the North American opossum.

The morphology of relay cells in the dorsal lateral geniculate nucleus of the North American opossum was studied by using both Golgi-Cox material and cells stained from retrograde transport of horseradish peroxidase. In general, soma sizes were largest in the part of the nucleus representing the central retina and decreased from the middle third of the nucleus to the anterior to posterior poles. Relay cells labeled with horseradish peroxidase were found to constitute approximately 90% of the dorsal lateral geniculate nucleus cells and have larger soma diameters than most unlabeled cells. From morphometric analysis of several structural characteristics, three classes of relay cells were identified in both Golgi-Cox and horseradish peroxidase material. Type 1 cells, the predominant class, exhibited radially arranged primary dendritic fields, symmetrically organized relative to projection lines. Type 2 cells had relatively few primary dendrites, and complex dendritic fields that were oriented parallel to projection lines. Least numerous were Type 3 cells, which were characterized by relatively sparse dendritic fields oriented perpendicular to projection lines. An additional class of neuron, Type 4 cells, with small somata and sparse dendritic branching, was found only in Golgi-Cox material. Cells with Type 4 dendritic morphology were not found with retrograde horseradish peroxidase labeling and may represent interneurons. The classification of morphologically characterized cells in the opossum dorsal lateral geniculate nucleus was evaluated quantitatively with multivariate discriminant analysis. The classes are compared to physiologically identified Y-, X-, and W-like relay cells in the opossum and to relay cell classes in other species.

beta-like ganglion cells in the retina of the North American opossum.

Injection of horseradish peroxidase into the severed optic tract or nerve of the opossum retrogradely filled retinal ganglion cells. An abundance of well-labeled ganglion cells had dendritic morphology closely resembling that of beta-type ganglion cells in the cat retina. This finding suggests that an X-like functional class of ganglion cells is prominent in the retina of the opossum.

Postnatal development of geniculocortical projections in the tree shrew.

We examined the postnatal development of retrogradely labeled cells in the tree shrew lateral geniculate nucleus (LGN) following cortical injections of horseradish peroxidase. Results show that at birth (P0) when the LGN is still unlaminated: (1) the mature proportion of relay cells and interneurons already exists, (2) relay cells present are larger than interneurons, and (3) relay cells are topographically connected with the cortex. Aside from changes in absolute LGN soma size, the primary postnatal change noted (from P0 to P7) was an apparent decline in the relative width of the labeled LGN projection column, suggesting a refinement in topography.

The development of neurons in the cat perigeniculate nucleus and reticular nucleus of the thalamus.

The postnatal development of soma size and cytochrome oxidase activity was examined in the perigeniculate nucleus (PGN) and reticular nucleus of the thalamus (RNT). Neurons in the PGN and RNT exhibited a rapid increase in soma size between 2 and 4 weeks of age. During this period of cell growth there is an increase in the intensity of cytochrome oxidase staining within the cell body. Cells in both the PGN and RNT decrease in size after 4 weeks of age, and become very fusiform in shape. During this postnatal period, there is also a shift in cytochrome oxidase staining from the cell body to the dendrites.

Development of cytochrome oxidase staining in the retina and lateral geniculate nucleus: a possible correlate of ON- and OFF-center channel maturation.

A histochemical stain for cytochrome oxidase (CO) activity was used to examine the maturation of a neurochemical correlate of ON and OFF channels in the retina and dorsal lateral geniculate nucleus (LGN) of the tree shrew. In the adult tree shrew, the CO staining pattern can be used as a histochemical marker of segregated ON- and OFF-center channels in the retina, LGN, and striate cortex. Our previous studies have shown that the retina is immature and the LGN unlaminated at birth. In the present study, we show that the laminar development of CO reactivity emerges during the first postnatal week in the LGN, while the maturation of CO staining in the presumed ON and OFF sublaminae of the retinal inner plexiform layer develops slowly, well after the appearance of differential laminar CO staining in the LGN.

The effect of altered neuronal activity on the development of layers in the lateral geniculate nucleus.

The main objective of this study was to examine the role of neural activity in the development of cell layers in the dorsal lateral geniculate nucleus (LGN). We studied this relationship in postnatal tree shrews either by completely blocking retinal ganglion cell activity with TTX or by selectively blocking activity to the developing ON-center LGN layers (1 and 2) with 2-amino-4-phosphonobutyric acid (APB), using unilateral and bilateral eye injections. All manipulations were carried out from birth (P0), when no LGN cell layers are evident, to or past the point when layers are recognizable (i.e., 1-2 weeks). Nissl-stained and cytochrome oxidase (CO)-reacted material was examined for all cases. Our results show that in the absence of activity produced by bilateral TTX injections, interlaminar spaces between cell layers do begin to develop. Retinal afferents, which are segregated at birth, remain segregated, and differential CO staining between matched sets of LGN layers is evident. The normal pace of LGN development, however, is slowed significantly: LGN cells are smaller and interlaminar spaces are narrower than are seen in age-matched controls. Unilateral TTX injections produce similar, but more dramatic and asymmetric, effects on LGN cells, perhaps because cells are at a competitive disadvantage relative to their normally innervated counterparts in cortex. Combining unilateral eye enucleation at P0 with subsequent TTX treatment of the other eye clearly demonstrates that axons from the remaining eye are capable of producing their normal complement of LGN layers. The development of the LGN ON-center layers, 1 and 2, and the interlaminar space between them are more affected by TTX treatment than are the other layers. By contrast, APB eye injections do not selectively affect the development of the ON-center layers, but do result in some slowing of overall LGN development. Taken together, these results suggest that activity of retinal afferents is not essential for initiating interlaminar space formation, but is important for the normal pace of maturation of LGN cell layers.

Is binocular competition essential for layer formation in the lateral geniculate nucleus?

In this paper we examine mechanisms that could explain how layers form within the lateral geniculate nucleus (LGN). Analysis of normal LGN development and development following experimental or genetic perturbation, together, suggest that binocular competitive interactions alone cannot account for either the segregation of retinogeniculate axons or subsequent formation of cell layers. Instead, it appears more likely that initial sorting of axons results from an activity-dependent interaction between populations of axons with different identities and differential affinities for postsynaptic LGN targets. Competitive interactions, however, may aid in sorting axons of like type or in refining topography. We also propose that the subsequent steps in LGN layer formation, such as the formation of interlaminar spaces, depend upon a sequence of interactions between retinal axons, extraretinal axons and outgrowth of developing dendrites of LGN cells.