Representation of spatial frequency and orientation in the visual cortex

Knowledge of the response of the primary visual cortex to the various spatial frequencies and orientations in the visual scene should help us understand the principles by which the brain recognizes patterns. Current information about the cortical layout of spatial frequency response is still incomplete because of difficulties in recording and interpreting adequate data. Here, we report results from a study of the cat primary visual cortex in which we employed a new image-analysis method that allows improved separation of signal from noise and that we used to examine the neurooptical response of the primary visual cortex to drifting sine gratings over a range of orientations and spatial frequencies. We found that (i) the optical responses to all orientations and spatial frequencies were well approximated by weighted sums of only two pairs of basis pictures, one pair for orientation and a different pair for spatial frequency; (ii) the weightings of the two pictures in each pair were approximately in quadrature (1/4 cycle apart); and (iii) our spatial frequency data revealed a cortical map that continuously assigns different optimal spatial frequency responses to different cortical locations over the entire spatial frequency range.     

Book reviews

JGIM solicits reviews of new books from its readers. If you wish to review a book, please submit a letter of intent that identifies the book in question (title, author, and publisher) to Robert Aronowitz, MD, Book Review Editor,JGIM, Department of Medicine, Cooper Hospital, 3 Cooper Plaza—Suite 220, Camden, NJ 08103, telephone (609)342-2489.     

Relationship of HLA to schizophrenia not supported in multiplex families.

The role of the human histocompatibility complex (HLA) in the pathogenesis of schizophrenia has been suggested in previous reports. We conducted a genetic study in 33 new families. Our linkage analysis, which used the affected sib-pair method, did not provide evidence for nonrandom assortment. Moreover, the results of an association study using the "haplotype relative risk" method failed to confirm the positive association between HLA A9 and schizophrenia. Taken together, our data did not support any relationship of HLA type to schizophrenia.     

The reconstitution of cell-mediated immunity in the cutaneous lesions of lepromatous leprosy by recombinant interleukin 2

Human rIL-2 (10-30 micrograms) was injected intradermally into the skin of patients with lepromatous leprosy with high bacillary loads. All patients responded to the lymphokine with local areas of induration that peaked at 24 h and persisted for 4-7 d irrespective of whether the site was "normal skin" or a nodular lesion. Within 24 h there was an extensive emigration of T cells and monocytes into the site. The percentage of the dermis infiltrated by mononuclear cells increased by more than sevenfold, peaking at 4 d and persisting for greater than 15 d. Both CD4+ and CD8+ T cells entered the site. T cells of CD4+ phenotype predominated at 2-7 d but by 11 d, CD8+ cells were predominant. Considerable numbers of T6+ Langerhans' cells appeared in the dermis by 72 h and persisted for 3 wk. By 4 d the thickness of the overlying epidermis had increased twofold, and keratinocytes were expressing MHC class II antigen and the IFN-gamma-induced peptide IP-10. Starting at 48 h, there was an extensive destruction of mononuclear phagocytes that contained structurally intact or fragmented M. leprae observed at the electron microscope level. The organisms, either free or contained within endocytic vacuoles, were discharged into the extracellular space and then reingested by blood-borne monocytes. This was followed by marked reductions in the number of acid-fast organisms in the injected site, evident as early as 4-7 d and more marked at 2-3 wk after injection. 13 of 15 patients exhibited a disposal of acid-fast bacilli ranging from 5- to 1,000-fold with a mean value of approximately 100-fold. The administration of IL-2 leads to the generation of an effective cell-mediated immune response, recapitulating an antigen-driven event and leading to striking local reductions in M. leprae. In comparison with the purified protein derivative of tuberculin reaction, bacilli are cleared more promptly, although emigratory cells persist for a shorter time.     

Osteogenic differentiation of human bone marrow stromal cells on partially demineralized bone scaffolds in vitro

Tissue engineering has been used to enhance the utility of biomaterials for clinical bone repair by the incorporation of an osteogenic cell source into a scaffold followed by the in vitro promotion of osteogenic differentiation before host implantation. In this study, three-dimensional, partially demineralized bone scaffolds were investigated for their ability to support osteogenic differentiation of human bone marrow stromal cells (BMSCs) in vitro. Dynamic cell seeding resulted in homogeneous cell attachment and infiltration within the matrix and produced significantly higher seeding efficiencies when compared with a conventional static seeding method. Dynamically seeded scaffolds were cultured for 7 and 14 days in the presence of dexamethasone and evaluated on biochemical, molecular, and morphological levels for osteogenic differentiation. Significant elevation in alkaline phosphatase activity was observed versus controls over the 14-day culture, with a transient peak indicative of early mineralization on day 7. On the basis of RT-PCR, dexamethasone-treated samples showed elevations in alkaline phosphatase and osteocalcin expression levels at 7 and 14 days over nontreated controls, while bone sialoprotein was produced only in the presence of dexamethasone at 14 days. Scanning electron microscopy evaluation of dexamethasone-treated samples at 14 days revealed primarily cuboidal cells indicative of mature osteoblasts, in contrast to nontreated controls displaying a majority of cells with a fibroblastic cell morphology. These results demonstrate that partially demineralized bone can be successfully used with human BMSCs to support osteogenic differentiation in vitro. This osseous biomaterial may offer new potential benefits as a tool for clinical bone replacement.     

An action of disodium cromoglycate: inhibition of cyclic 3',5'-AMP phosphodiesterase.

Disodium cromoglycate (DSCG) prevents allergic asthma by inhibiting the release of chemical mediators of immediate-type allergic reactions. The mechanism of this action is unclear and prompted us to examine the effect of DSCG on cyclic adenosine 3',5'-monophosphate (cAMP), the implicated regulator of IgE-mediated reactions. We used the peripheral blood lymphocyte as a model to mirror the biochemical events occurring in the allergic shock organs. Isolated peripheral blood lymphocytes from perennial allergic asthmatic children receiving only DSCG had significantly (p less than 0.005) lower phosphodiesterase (PDE) activity (mean 1.05 +/- 0.17 SE per 10(6) cells) than normal individuals (2.93 +/- 0.14) and allergic children receiving methylxanthines (4.08 +/- 0.28) or no medications (3.58 +/- 0.2). DSCG (10 mug/ml) significantly lowered PDE activity in normal lymphocytes (p less than 0.005) in a beef heart extract (p less than 0.001), and 100 mug/ml lowered PDE activity in fetal rabbit lung homogenates (p less than 0.001). DSCG (10 mug/ml) significantly elevated (p less than 0.01) cAMP concentration in normal human lymphocytes (118 +/- 38 vs 30 +/- 10 picomoles cAMP/10(6) lymphocytes). Thus, DSCG appears to inhibit chemical mediator release by increasing intracellular cAMP through the inhibition of cAMP PDE.     

Mutations in the retinal guanylate cyclase (RETGC-1) gene in dominant cone-rod dystrophy

The dominant cone-rod dystrophy gene CORD6 has previously been mapped to within an 8 cM interval on chromosome 17p12-p13. The retinal- specific guanylate cyclase gene (RETGC-1), which maps to within this genetic interval and previously was implicated in Leber's congenital amaurosis, was screened for mutations within this family and in a panel of small families and individuals with various cone and cone- rod dystrophy phenotypes. A missense mutation (E837D) was identified in affected members of the CORD6 family, as well as a second missense mutation (R838C) in three other families with dominant cone-rod dystrophy. RETGC-1 is only the fourth gene to be implicated in cone-rod dystrophy and this is the first report of dominant mutations in this gene.