The spatial frequency sensitivity of bipolar cells

Retinal bipolar cells constitute the output stage of the outer layer of the retina. There are several constraints on the ability of the bipolar cell array to respond to the different spatial frequency components of the visual image, including (i) electrical coupling in the dendritic tree receiving receptor input; (iii) the "lateral inhibition" mediated by horizontal cells. Using simple mathematical models, we derive analytical expressions for the spatial frequency response of the bipolar cell array for the case in which horizontal cells are presynaptic to bipolar cells (feedforward model) and also for the case in which horizontal cells are presynaptic to receptors (feedback model). The results illustrate the importance of the three factors mentioned in determining the bipolar cells' properties. The optimal spatial frequency for stimulating the bipolar cell array, and the range of spatial frequencies transmitted onward to the inner plexiform layer, are thus related to the anatomical and electrical properties of the cells in the outer plexiform layer.     

Hyperparathyroidism in pregnancy: case report and review of the literature.

The apparent incidence of hyperparathyroidism (HPT) is low in pregnancy but will likely increase now that more asymptomatic HPT is being diagnosed. However, since the serum calcium levels are decreased in pregnant women, mild primary HPT may go unrecognized. In untreated cases of HPT, complications during pregnancy or during the neonatal period have included spontaneous abortion, stillbirth, neonatal death, neonatal tetany and hypercalcemia. A review of the literature indicates a substantial improvement in fetal outcome when parathyroidectomy is done during pregnancy, as in the case reported here. Therefore, parathyroidectomy is the treatment of choice when the diagnosis is made during pregnancy, although oral phosphate therapy may be an alternative if surgery is contraindicated.     

A cytological basis for the separation of Geropogon from Tragopogon (Compositae: Lactuceae)

The single species ofGeropogon, G. hybridus (L.) Schultz-Bip., is sometimes submerged in the morphologically similarTragopogon. A comparative study of the karyotypes ofGeropogon andTragopogon sensu stricto clarified their relationship. The karyotype ofG. hydridus (2n=14) was compared with that ofT. dubius Scop. (2n=12). The karyotypes are distinct, offering a compelling reason to recognizeGeropogon as a separate genus.     

The in vitro effect of indomethacin on basal bone resorption, on prostaglandin production and on the response to added prostaglandins

Mouse calvaria were maintained in organ culture without serum additives. Basal active resorption, as measured by ⁴⁵Ca and hydroxyproline release, was significantly inhibited to 74% control levels by indomethacin (1.4 × 10⁻⁷ M). Prostaglandin F and prostaglandin E₂ production, determined by radioimmunoassay, were both significantly lowered by this concentration of indomethacin. DNA, protein and hydroxyproline synthesis, as indices of cell toxicity, were unaffected by low concentrations of indomethacin, while concentrations of 1.4 × 10⁻⁶M inhibited protein synthesis (p<0.005). In the presence of indomethacin (1.4 × 10⁻⁷M) both PGE₂ and PGF_2α stimulated resorption in a dose-dependent manner, with PGE₂ being the more potent. Neither prostaglandin affected hydroxyproline synthesis at low concentrations, but PGE₂ had a marked inhibitory action at a higher concentration (10⁻⁶M). In combination, the effects of PGE₂ and PGF_2α showed no evidence of synergism or any antagonistic action. The study shows that in vitro calcium and hydroxyproline resorption in the unstimulated mouse calvaria are inhibited by indomethacin at concentrations measured in serum during human therapy. The decreased PGF and PGE₂ production associated with this decreased bone resorption in the presence of non-toxic concentrations of indomethacin would suggest a role for these prostaglandins in maintaining the basal resorption of cultured bone.     

An unusual phenotypic expression of Hb-Leiden

After a boy of Mexican-American descent became jaundiced during treatment of a serious urinary tract infection with an oxidant drug, an extensive hematological examination was made. The important finding was the presence of Hb-Leiden to the extent of less than 3% or about a tenth of the usual percentage. Although inclusion bodies are present in the erythrocytes at all times, his hematological parameters have remained normal. The genetic basis for the unusually small amount of Hb-Leiden in the propositus may be due to the Hb-Leiden gene in an anti-Lepore configuration, that is, and Hb-Leiden gene in cis to the normal β and δ genes.     

The gene for aromatase (P450arom) in the chicken is located on the long arm of chromosome 1

An 125I-labeled partial cDNA for the chicken aromatase P450 was used for in situ hybridization to chromosomes from primary chicken embryo fibroblast cultures. The results indicate that the gene that encodes aromatase is located on the long arm of chromosome 1 at approximately position 0.16.     

Inhibitors of sterol synthesis. Characterization of trimethylsilyl dienol ethers of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one. Applications in the analysis of mitochondrial metabolites of the 15-ketosterol by gas chromatography-mass spectrometry.

Derivatization of delta 8(14)-15-ketosterols as bis-TMS dienol ethers facilitates their analysis by gas chromatography-mass spectrometry (GC-MS). Conditions are presented for the preparation of each of the three possible bis-TMS dienol ethers of 3 beta-hydroxy-5 alpha-cholest-8(14)-en-15-one (1), a potent regulator of cholesterol metabolism. Treatment of 1 with N,O-bis(tri-methylsilyl)-trifluoroacetamide (BSTFA) and pyridine for 20 h at 100 degrees C produced primarily 3 beta,15-bis(trimethylsilyloxy)-5 alpha-cholesta-7,14-diene. Treatment of 1 with BSTFA-pyridine in the presence of 0.1% perchloric acid for 20 h at 22 degrees C gave mainly the delta 8(14)15, dienol ether. Heating this reaction mixture at 100 degrees C for 4 days gave mainly the delta 8,14 ether. The structures of the three dienol ethers were established by GC-MS and 1H and 13C nuclear magnetic resonance spectroscopy. The three TMS dienol ethers of 1 were resolved by capillary GC and gave very simple mass spectra upon electron impact with fragmentation limited almost exclusively to the elimination of trimethylsilanol, methyl, and the side chain. The TMS dienol ethers showed reduced artefact formation, improved chromatographic resolution, and increased sensitivity relative to the delta 8(14)-15-ketosterols, properties that improve the detection and identification of minor components in analyses of complex biological mixtures. The utility of this derivatization is illustrated for the delta 7,14 TMS dienol ethers of the 3-deoxy, 3-keto, 3 alpha-hydroxy, and 3 beta-methoxy analogs of 1 and for delta 8(14)-15-ketosterols in mixtures obtained from incubations of 1 with rat liver mitochondria in the presence of NADPH.     

Antigenic analysis of iron-regulated proteins in Pasteurella haemolytica A and T biotypes by immunoblotting reveals biotype-specific epitopes.

The antigenic relationships of the iron-regulated proteins (IRPs) in Pasteurella haemolytica A and T biotype strains were examined by SDS-PAGE and immunoblotting. P. haemolytica cells of the A biotype, grown under conditions of iron-limitation, expressed two IRPs, of 35 and 70 kDa. All T biotype strains expressed IRPs with slightly different molecular masses of 37 and 78 kDa. Immunoblotting of all 16 P. haemolytica serotypes was carried out using a panel of polyclonal and monoclonal antibodies raised against serotype A2 antigens. Polyclonal antibodies revealed inter-serotype cross-reactivity towards the 35 and 70 kDa IRPs within the A biotype but no cross-reactivity against a T biotype protein in the 78 kDa region. Monoclonal antibody against the 35 kDa antigen reacted only with the A biotype 35 kDa IRP. Identical profiles were obtained for 10 field isolates of serotype A2, further emphasizing the antigen conservation within the A biotype. These findings reinforce the view that the A and T biotypes of P. haemolytica should be considered as separate species and suggest that IRPs from single A and T biotype strains incorporated into a vaccine might provide cross-protection against all P. haemolytica serotypable strains. Similar studies on the IRPs of 10 untypable strains revealed some of these to have different antigenic reactivities from those observed within the A and T biotypes.