Overlooking: a Sign of Bilateral Central Scotomata in Children

Four children are reported who always looked above objects of visual interest (overlooking). All had bilateral central scotomata (loss of central visual field). Three had optic nerve disease selectively affecting the papillomacular fibers; the fourth had ocular colobomata affecting the maculae. Overlooking is an important sign of bilateral central scotomata in children: it is an adaptation to loss of central vision.     

Antibody-independent complement activation by myelin via the classical complement pathway

Murine or rabbit whole brain homogenates were shown to activate human complement via the classical pathway by an antibody-independent reaction. This activity required Ca++ ions. Anticomplementary activity in fractionated murine brain was found to reside in the myelin fraction and in purified myelin. It was absent, however, both from highly purified myelin basic protein (MBP) and from the MBP-free residue. Because purified MBP is a monomer and this protein exists in brain tissue largely as a dimer, the ability of the cross-linked form of MBP to activate complement was investigated. MBP, dimerized with difluorodinitrobenzene, was highly anticomplementary. The murine brain, inactive when taken from the newborn mouse, was shown to first acquire the capacity to activate complement at 7 d after birth. This finding is consistent with the report that the synthesis of myelin protein has been shown to be initiated in murine brain 8 d after birth. Complement activation by MBP could play an important role in the pathological changes observed in neurological disorders.     

Enhanced DRL and impaired forced-choice alternation performance following hippocampal lesions in the pigeon

In four experiments, pigeons with bilateral lesions of the hippocampus were compared to unoperated control birds and operated control subjects that received bilateral lesions of the neostriatum on tasks sensitive to hippocampal damage in mammals. Consistent with the mammalian literature, hippocampal birds were impaired on forced-choice alternation in the T-maze, although they were unimpaired on spatial alternation and reversal learning in an operant chamber. Furthermore, in contrast to hippocampal mammals, hippocampal pigeons showed enhanced performance on a differential reinforcement of low-rates of responding schedule of reinforcement. The results are discussed with respect to a behavioural homology between the avian and mammalian hippocampal formations.     

Childhood giant axonal neuropathy. Case report and review of the literature

Giant axonal neuropathy (GAN) is a rare autosomal recessive childhood disorder characterized by a peripheral neuropathy and features of central nervous system involvement. Typically seen are distal axonal swellings filled with 8-10 nm in diameter neurofilaments in central and peripheral axons, and intermediate filament collections in several other cell types. Many neurotoxins produce a morphologically similar neuropathy in humans and experimental animals. Defective nerve fiber energy metabolism has been postulated as a cause in these toxic neuropathies. It is possible that GAN represents an inborn error of metabolism of enzyme-linked sulfhydryl containing proteins, resulting in impaired production of energy necessary for the normal organization of intermediate filaments.     

Regulation of acid-base transport in the rat thick ascending limb

The thick ascending limb of the rat influences urinary net acid excretion by reabsorbing both bicarbonate and ammonium. The bicarbonate absorption is mediated predominantly by apical membrane Na+-H+ exchange and occurs at rates that are comparable to or greater than rates measured in cortical and medullary collecting ducts. The ammonium absorption is mediated predominantly by apical membrane Na+-NH4+-2Cl- cotransport and enhances urinary ammonium excretion by promoting countercurrent multiplication of ammonium, which facilitates ammonium secretion into medullary collecting ducts. Studies with medullary thick ascending limbs (MTAL) in vitro have shown that the regulation of these transport processes involves both acute responses to changes in the luminal and peritubular environment and adaptive changes in tubule transport capacity in response to chronic systemic acid-base perturbations. In particular, an increase in potassium concentration inhibits ammonium absorption with no effect on net bicarbonate absorption whereas vasopressin inhibits bicarbonate absorption with no effect on net ammonium absorption. Chronic metabolic acidosis causes an adaptive increase in the ability of the MTAL to reabsorb both bicarbonate and ammonium. These results demonstrate that the MTAL is a site of regulation of renal acid-base transport and that ammonium and bicarbonate transport rates can vary independently in this nephron segment.     

Isolation and partial chemical characterization of the IgG Fc receptor of human T lymphocytes and production of an antiserum.

We report here the isolation of an IgG Fc receptor from normal human T lymphocytes. The purified receptor has a nonreduced and a reduced component of molecular weights 120,000 and 60,000, respectively, and it was functionally active in the in vitro blocking of rosette formation between T lymphocytes and IgG-coated ox erythrocytes. An antiserum raised to the Fc receptor and an isolated F(ab')2 fragment of this antiserum, also blocked rosette formation between T cells and IgG-coated ox erythrocytes. In contrast, rosette formation between T lymphocytes and IgM-coated ox or sheep erythrocytes was not blocked by the F(ab')2 fragment, demonstrating the marked specificity of this antiserum for the IgG Fc receptor. In addition, this antiserum did not block the Fc receptors of non-T cells, indicating that the T-cell IgG Fc receptor has unique antigenic determinants not shared with B cells.     

Dietary protein antigenemia in humoral immunodeficiency: Correlation with splenomegaly

Enhanced gastrointestinal absorption of dietary substances is an important feature of normal neonatal life that also exists in particular disease states such as selective IgA deficiency and atopic allergy. In these studies, it is shown that patients with hypogammaglobulinemia have increased absorption of dietary bovine antigens and that most patients have large amounts of these proteins present in the serum even after an overnight fast. The amounts of such proteins were found to be correlated with spleen size and/or peripheral lymphoid hypertrophy. Interestingly, three patients with X-linked agammaglobulinemia did not have detectable amounts of these proteins in the serum nor did they have splenomegaly or lymphadenopathy. It is speculated that hypogammaglobulinemic patients have a specific gastrointestinal mucosal lesion that permits the chronic excessive absorption of dietary antigens and may result in lymphoid hypertrophy.