Biomedical subjects
Publications and source records attributed to R A Johnston.
Spinal cord tumours continue to be a challenging clinical problem. Early diagnosis, especially with widespread use of magnetic resonance imaging (MRI), and advances in surgical technique enable a more aggressive approach to the management of these lesions.
Amino acid sequences for the alpha-chains of the Moraceae lectins, jacalin and Maclura pomifera agglutinin, were determined by protein sequencing. Both are 133 residues long and contain several genetically variant positions; the overall homology is 85%. A possible site for the known glycopeptide of jacalin was located. The alpha-chains have a conserved tryptophan residue that may be part of the binding-site.
The amino acid sequence of peanut (Arachis hypogaea) agglutinin was determined from three major fragments obtained by mild acid cleavage at Asp-Pro peptide bonds. The sequence of 236 amino acids has residues identical to those that form the metal-binding site and the hydrophobic pocket in concanavalin A and other lectins, although the overall similarity is only 42%. In the segments of peanut agglutinin that correspond to the four loops that form the carbohydrate-binding site in concanavalin A and favin, several central residues are homologous, while others show changes to smaller side chains, such as Tyr----Gly. The carbohydrate-binding site of peanut agglutinin may therefore have a similar peptide-backbone architecture, but form a considerably more open cleft.
An implementation of Bruce and Young's (1986) functional model of face recognition is used to examine patterns of covert face recognition previously reported in a prosopagnosic patient, PH. Although PH is unable to recognize overly the faces of people known to him, he shows normal patterns of face processing when tested indirectly. A simple manipulation of one set of connections in the implemented model induces behaviour consistent with patterns of results from PH obtained in semantic priming and interference tasks. We compare this account with previous explanations of covert recognition and demonstrate that the implemented model provides the most natural and parsimonious account available. Two further patients are discussed who show deficits in person perception. The first (MS) is prosopagnosic but shows no covert recognition. The second (ME) is not prosopagnosic, but cannot access semantic information relating to familiar people. The model provides an account of recognition impairments which is sufficiently general also to be useful in describing these patients.
A retrospective study was carried out of the outcome of surgical decompression of cervical spondylotic myelopathy in 21 elderly patients. The presenting symptoms and signs were similar to those in younger patients. The indication for surgery was recent progressive neurological deficit. Assessment of pre-operative state was based on information from hospital records. Post-operative evaluation was made from a home visit in 17 cases (mean age 71) after a mean post-operative period of 19 months (3 patients had died in the interim and one had emigrated). Objective functional improvement was found in the upper limb in 58% and in the lower limb in 71%; the remainder were unchanged. Surgical decompression in cervical spondylotic myelopathy is a safe procedure, which benefits appropriately selected elderly.
One hundred and two patients with suspected cervical spondylotic myelopathy were prospectively investigated using MRI as the initial imaging technique. The aim was to discover if clinicians could manage patients with MRI alone, or if they would find a second investigation necessary. Eighty two patients were managed using MRI alone, 34 of whom were treated surgically. Twenty patients had a second investigation: a myelogram in 18 and a CT myelogram in two. This was performed in nine patients to exclude structural pathology in the thoracic or lumbar region (which was not examined with MRI), and in 11 to obtain more specific information about the cervical region. Only five of these 20 patients had surgical treatment. The diagnosis changed after the second investigation in four patients, but management was not influenced in any of these. MRI is a satisfactory alternative to myelography for most patients with suspected cervical spondylotic myelopathy.
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In this paper we describe how the microstructure of the Bruce & Young (1986) functional model of face recognition may be explored and extended using an interactive activation implementation. A simulation of the recognition of familiarity of individuals is developed which accounts for a range of published findings on the effects of semantic priming, repetition priming and distinctiveness. Finally, we offer some speculative predictions made by the model, and point to an empirical programme of research which it suggests.
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Single crystals of Maclura pomifera agglutinin, a seed lectin from the Moraceae family, complexed with the disaccharide Gal beta 1-3GalNAc have been obtained by the method of vapor diffusion with Li2SO4 as precipitant at pH 4.5. The crystals belong to the trigonal space group P3(1)21 or P3(2)21, with a = b = 67.4 A, c = 149.3 A. They contain two subunits per asymmetric unit and diffract beyond 2.7 A. This and other evidence indicate that both this lectin and the Artocarpus integrifolia lectin, jacalin, have dimeric structures rather than the tetrameric structures previously proposed.
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