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Anti-CD18 monoclonal antibodies (MAb) have demonstrated variable protection against neutrophil (PMN)-mediated myocardial reperfusion injury. To identify factors contributing to this variability, open-chest dogs underwent coronary artery occlusion for 90 min followed by reperfusion for 3.5 h. Ten minutes before reperfusion the dogs received saline (n = 18) or one of three anti-CD18 MAb: MHM.23, R15.7, or PLM-2 (2, 1, and 1 mg/kg and n = 19, 8, and 4, respectively). Collateral flow was measured with radioactive microspheres, area at risk was assessed with monastral blue dye, and infarct size was measured postmortem by triphenyltetrazolium chloride. In vitro, all three MAb bound to canine PMNs, but only MHM.23 and R15.7 inhibited their adherence to keyhole limpet hemocyanin-coated plastic. In vivo, only MHM.23 and R15.7 significantly reduced infarct size after adjusting for the effect of collateral flow. MHM.23 afforded protection in dogs with moderate ischemia (epicardial collateral flow > 0.1 ml.min-1.g-1, infarct size reduced 46%) but not in dogs with more severe ischemia. Only R15.7 was effective in dogs with severe ischemia. Although MHM.23 and R15.7 produced similar inhibition of tissue PMN accumulation, as reflected by myeloperoxidase activity. R15.7 markedly inhibited H2O2 production by PMNs after exposure to platelet-activating factor, whereas MHM.23 had only a minimal effect. The effectiveness of different anti-CD18 MAb in preventing reperfusion injury appears to be 1) highly dependent on the specific anti-CD18 MAb employed, 2) predicted only partially by in vitro binding to PMNs, static in vitro tests of PMN adherence, or the extent of inhibition of PMN accumulation in vivo, 3) related more to their ability to inhibit oxidant release from activated PMNs, and 4) strongly influenced by the severity of myocardial ischemia before reperfusion.

The large glycoprotein tenascin is one of the extracellular matrix proteins that is abundant in the developing nervous system. To determine its distribution and possible role in the ontogenty of the avian retinotectal system, the distribution of the protein, the expression of its mRNA, and the effect of the protein on growing retinal neurites in vitro was investigated. Immunocytochemistry demonstrated that relatively little tenascin was present in the optic fiber layer of the retina, the optic nerve and tract. Tenascin, however, was abundant in the stratum opticum of the tectum, the target of retinal axons in the brain. Whereas tenascin protein is found only in discrete portions and layers of the brain, in situ hybridization studies showed that tenascin mRNA was expressed throughout development by radial glial cells at the ventricular surfaces of the brain, distant from the tissue localization of the protein. Injection of antitenascin antiserum into the tectal ventricle disturbed the distribution of the protein in the tectum by binding tenascin closer to its origin at the ventricular border. This suggests that the localization of tenascin in the brain is not restricted to its site of synthesis, but is mediated by tenascin-binding proteins that are expressed in defined areas and layers in the brain. In vitro studies showed that tenascin did not promote neurite outgrowth of retinal axons. On the contrary, the addition of tenascin to retinal explants growing on collagen or on L1 slowed the growth rate of optic axons by as much as 50%. The inhibitory function in vitro suggests that this protein has a modulatory role in axonal growth in vivo. The absence of tenascin from the optic fiber layer of retina, optic nerve, and optic tract and its abundance in the tectum suggest that tenascin may function to slow the rapidly growing optic nerve fibers once they arrive at the tectum. The slowing of optic fiber outgrowth may then facilitate terminal arborization and synapse formation within the tectum. The abundant tenascin in synaptic layers may also serve to stabilize synapses once they have formed.

DARPP-32 (dopamine- and adenosine 3',5'-monophosphate-regulated phosphoprotein of Mr = 32,000) mRNA distribution was examined in adult mouse central nervous system by in situ hybridization. In general, DARPP-32 mRNA was found in regions of brain where cells express the dopamine D1 subtype receptor. Cells of the olfactory tubercle, caudate-putamen, and nucleus accumbens had the highest levels of DARPP-32 mRNA, as did choroid plexus and Purkinje cells. Relatively high levels were found in medial habenula and lateral piriform cortex. Moderate levels were seen in cerebral cortex layer VI, medial piriform cortex, lateral entorhinal cortex, tenia tecta, anterior olfactory nucleus, and lateral bed nucleus of the stria terminalis. Low levels were observed in hippocampus, cerebral cortex layers II and III, olfactory bulb, and the nucleus of the lateral olfactory tract. DARPP-32 mRNA levels in the amygdaloid nuclei varied greatly.