Rapid frozen section in pediatric pathology.

Frozen section examination in pediatrics differs from that in adult practice in two ways. First, there is a high proportion of undifferentiated small-cell cancers in which it it difficult to make a definitive diagnosis without additional information. Second, there are special categories of congenital disorders where one is seeking not neoplasia but the presence, absence, or size of normal structures. In 520 pediatric frozen sections, there was a comparatively high incidence of deferred (5.6%) or inaccurate diagnoses (3.5%). However, as there were 99 small-cell cancers, it is perhaps surprising that the number was not greater. In the nervous system (208 cases), it was sometimes difficult to distinguish between malignant ependymoma and medulloblastoma. In other neoplasms, e.g., soft tissues and bone, the most important requirement was adequate clinical and radiological information. In Hirschsprung's disease (132 cases), ganglion cell detection was 100% accurate. In measuring the diameter of bile ducts in the porta hepatis during surgery for biliary atresia (18 cases), it was sometimes difficult to recognize ducts that had lost their epithelial lining.

Three dimensional structure of erabutoxin b neurotoxic protein: inhibitor of acetylcholine receptor.

The three-dimensional structure of erabutoxin b, a neurotoxin in the venom of the sea snake Laticauda semifasciata, has been determined from a 2.75 A resolution electron density map. Erabutoxin b is one of a family of snake venom neurotoxins, all low-molecular-weight proteins, which block neuromuscular transmission at the postsynaptic membrane. They specifically inhibit the acetylcholine receptor. The molecular shape is that of a shallow elongated saucer with a footed stand formed by the six-membered ring at the COOH-terminal end. The central core of the molecule is an assembly of four disulfide bridges. Three long chain loops emerge as broad fronds from the core region. Approximately 40% of the main chain is organized into a twisted antiparallel beta-pleated sheet of five short strands. In 28 snake venom neurotoxins of established sequence which inhibit the acetylcholine receptor, the four disulfide bridges and seven other residues remain invariant. Three substitution positions conserve residue type. In one wing of the molecule, there is a broad shallow depression which may characterize the reactive site. It is populated by the sevent invariant residues and two of the three type conserved residues. This region is "anchored" on the undersurface of the molecule by the hydroxyl group of Ser-9, the remaining conservatively substituted residue.