Monoclonal antibody 3CB2 recognizes an antigen expressed in discrete cell types derived from ectoderm and mesoderm. Biochemical and immunohistochemical studies indicate that the antigen recognized by the antibody is a 55 kDa cytoplasmic protein that may be an intermediate filament associated protein (IFAP). Developmental studies show that 3CB2 antigen is intensely expressed very early in the chick embryo, in the neural tube, myotomes, and in mesenchymal cells of visceral arches and the presumptive facial area. As development proceeds, antigen expression becomes restricted to astrocytes and radial glia cells throughout the brain. A detailed immunohistochemical study of the developing chick retina shows that the expression of 3CB2 antigen at embryonic day 8 (E8) is restricted to Müller cells, with the pattern of expression closely related to their degree of differentiation. We show, by immunocytochemistry labeling of entire Müller cells dissociated from retinas of E16-E20, that 3CB2 monoclonal is labeling the whole cell. 3CB2 selectively labels Müller cells in the rat and chameleon, but not their retinal horizontal cell axons. 3CB2 monoclonal is a very sensitive marker for early differentiating Müller cells. Our results provide evidence that 3CB2 antigen is a cytoskeletal component which may be involved in the morphogenesis of these cells, and also perhaps in the outgrowth of some axons.

The validity of rating of perceived exertion (RPE) in predicting lactate threshold during an incremental test was analyzed in 15 men with type 2 diabetes (M age = 53.4 yr., SD = 12.9). Blood glucose, lactate, and minute ventilation (VE)/VO2 responses identified the lactate, ventilatory, and glucose thresholds. Workloads (W) corresponding to RPEs 12, 13, 14, and 15 were determined. Second-order polynomials fit to VE/W and [lac]/W ratios corresponding to RPEs of 9-10, 12-13, and 16-17 also identified workloads above which there was an overproportional increase in VE and [lac]. These workload breakpoints did not differ, although at RPE 12 underestimated and at RPE 15 overestimated lactate threshold. RPE 13 and 14 and the responses of VE/W and [lac]/W to submaximal exercise accurately predicted lactate threshold.

The sequence of morphological differentiation of Müller cells in the chick retina was investigated in relation to the differentiation of the retinal neurons using the Golgi method. From the beginning of differentiation, the Müller cell develops spurs and lateral processes. Some of these glial processes become transformed into accessory prolongations of the Müller cell. From the 17th or 18th day of incubation, the morphology of the Müller cells is similar to that of the adult retina. On the basis of their inner prolongation, two types of Müller cells were identified. The first type, with diffuse and abundant descending processes, is identical to that described classically. The second type is a cell characterized by sparse and scanty inner ramifications. This report also describes electron microscopic observations of Müller cells and their enwrapping relationship with the axons of the optic nerve fiber layer.

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Peripapillary glial cells of the chick are a special type of glia, not only because of their position, forming a boundary between the retina on one side and the optic nerve head (ONH) and the pecten on the other, but also because although they have the same orientation and similar shape as the retinal Müller cell (a type of radial glia) and express common markers for these cells and astrocytes, they do not express glutamine synthetase (GS) or carbonic anhydrase C (CA-C), enzymes intensely expressed by Müller cells and astrocytes. In this study, we present further molecular characterization of these cells, using immunohistochemistry techniques. We show that peripapillary glial cells express a novel neuron antigen, 3BA8, that in the adult retina is located only in one neuron type (the amacrine cell) and in the inner plexiform layer (IPL). They also express an antigen specific to myelin and oligodendrocytes, MOSP, and a glial antigen, 3CB2, expressed by radial glia and astrocytes throughout the CNS. The study of the developmental expression of these three antigens in the peripapillary glial cell territory shows different spatiotemporal labeling patterns: 3CB2 and 3BA8 are expressed much earlier (embryonic days E3 and E5, respectively) than MOSP (E12), and during a developmental window (E6-E10) 3BA8 labels the peripapillary glial cells intensely and does not label the ONH or the optic nerve (ON), which are labeled later. The expression of 3CB2 is much more intense in the peripapillary glial cells than in Müller cells from early stages of development up to E16, and the expression of MOSP starts earlier in the peripapillary glial cells than in the Müller cells and is maintained with much higher intensity in the peripapillary glial cells throughout development. These findings show that Müller and peripapillary glial cells follow independent courses of differentiation, which together with the fact that the peripapillary glial cells express molecules typical of neurons, oligodendrocytes, radial glia, and astrocytes are evidence that peripapillary glial cells are a unique type of glia in the CNS.

The profile of glutamine synthetase (GS) activity in the neural retina of chicken embryos and adults was studied alongside the in vivo spatio-temporal patterns of generation and morphogenesis of Müller cell and of retinal synaptogenesis. The rise of GS activity during development is not related to Müller cell differentiation but to synaptogenesis in the outer plexiform layer (opl). GS expression was investigated by immunoreaction with GS-specific antiserum. Three spatial gradients of decreasing labeling were observed between embryonic (E)15 and E18, from central to peripheral retina, dorsal to ventral, and temporal to nasal, which are in spatio-temporal relationship with synaptogenesis in the opl. GS is localized in Müller cells and apparently also in a population of astrocyte-like glial cells, located in the ganglion cell layer throughout the retina. Precocious induction by hydrocortisone, in ovo, at E10, does not show the spatial pattern of GS immunoreactivity observed in control retinas at the time of natural induction (E15). We also show that dissociated (non-cultured) Müller cells of E18-20 retinas, to which only photoreceptors or photoreceptors and neurons remain joined, maintain an immunodetectable level of GS, while those in isolated state lose GS immunoreactivity rapidly. Our results suggest that the induction of GS expression might be mediated by Müller cell-neuron interactions at the opl and also perhaps at the outer nuclear layer (onl). An analysis of our results and those of previous authors suggests that the level of GS in differentiated Müller cells could be determined by conjoint cell interactions at the onl, opl, and inner plexiform layer.