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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