Spontaneous Basilar-Membrane Oscillation (SBMO) and Coherent Reflection

In a previous report (in JARO) we have described a relatively high-frequency (15 kHz) spontaneous oscillation of the basilar membrane (SBMO) in a guinea pig ear; this oscillation was accompanied by a spontaneous otoacoustic emission (SOAE) at the same frequency. During the spontaneous oscillation and after it had subsided, the mechanical frequency response of the basilar membrane was measured by way of a wide-band random-noise stimulus, and it showed a number of spectral peaks, one of which having the frequency of the original oscillation. This pattern of peaks cannot be explained by assuming a single place of reflection in the cochlea. In this paper the process of ‘coherent reflection’ is artificially evoked in a three-dimensional model of the cochlea by imposing random place-fixed irregularities to the basilar-membrane impedance. It is shown that in the model a series of peaks arises in the frequency spectrum of the basilar-membrane response which phenomenon resembles the one found in the experimental animal. It is also shown that these peaks are actually due to superposition of the primary wave and a wave resulting from ‘coherent reflection’ which is reflected at the stapes. When the intensity of the acoustic stimulus signal is increased, the relative sizes of these peaks in the simulation diminish in about the same way as in the experiment. It is concluded that coherent reflection most likely is the cause of the ‘extra peaks’, and that this concept can also explain the observed level dependence of these peaks. The findings of this study lead to a minor refinement regarding the actual requirements for coherent reflection to arise.     

Surveillance of invasive infection in children and adults admitted to QECH,Blantyre, 1996–2002

This is a report of blood CSF isolates from the adults medical and paediatric of wards QECH, Blantyre, cultured and identified at the Welcome Trust Research Laboratories during 1996–2002. The commonest causes of adults and children bacteraemia were non-typhoidal Salmonella (35% of all blood isolates for adults and children) and Streptococcus pneumoniae (14% and 13% respectively). Cryptococcus neoformans was the commonest isolates from CSF of adults with meningitis(67%) but was very rare in children. S.pneumoniae was the commonest cause of bacterial meningitis in children and adults (38% and 28% of all CSF isolates respectively). Haemophilus influenzae type b was also a common cause of meningitis in children (27%). Data of in vitro antibiotic sensitivity are also reported. A major concern is the recent marked rise of chloramphenicol resistance among Salmonella enteritidis and Salmonella typhimurium to over 80% resistance.     

A profile of cortical gray matter volume deficits characteristic of schizophrenia

Quantitative magnetic resonance imaging (MRI) studies from our laboratory have reported that patients with schizophrenia show a widespread cortical gray matter volume deficit, which is especially pronounced in the prefrontal and anterior superior temporal cortices. The present study compared two separate samples of schizophrenic patients -- 71 men from a Veterans Administration (VA) hospital and a sample of 57 severely ill men from a state hospital (SH) -- in an effort to test whether the pattern of brain volume abnormalities previously observed in VA schizophrenic patients can be generalized to other groups of schizophrenic patients. MRI-derived brain volumes of gray matter, white matter and sulcal cerebrospinal fluid (CSF) in six cortical regions, and CSF in the lateral and third ventricles were computed. All MRI volumes were adjusted for normal variation in head size and age and were expressed as standardized Z-scores, which also permitted structures of different sizes to be compared directly. The two schizophrenic groups displayed similar patterns of volume abnormalities: cortical gray matter but not white matter volume deficits that were widespread but especially notable in the prefrontal and temporal regions. The regional gray matter deficits in the SH group were generally greater than those in the VA group, particularly in the prefrontal and posterior superior temporal regions. Both schizophrenic groups had abnormally large volumes of the cortical sulci and lateral and third ventricles; however, the SH group showed greater enlargements, the most prominent occurring in the ventricles and temporal sulci. The overlapping patterns of cortical gray matter deficits in the two groups provide evidence for generality of this pattern of regional brain volume abnormalities in schizophrenia.      

X-linked glycerol kinase deficiency in the mouse leads to growth retardation, altered fat metabolism, autonomous glucocorticoid secretion and neonatal death

Glycerol kinase is an X chromosome-encoded enzyme involved in the metabolism of endogenous and dietary glycerolipids. The physiological significance of its activity in mammals is not well understood. Glycerol kinase deficiency in humans occurs as an isolated enzyme deficiency or as part of a contiguous gene deletion syndrome in variable association with Duchenne muscular dystrophy and adrenal hypoplasia congenita. Isolated glycerol kinase deficiency has an inconstant phenotype, ranging from asymptomatic hyperglycerolemia to a severe metabolic disorder with growth and psychomotor retardation. Although intragenic mutations were reported recently, the pathophysiological basis for the phenotypic variability remains unknown. To understand better the physiological significance of glycerol kinase and the pathophysiology of its deficiency, we generated glycerol kinase-deficient mice by gene targeting. Mutant male mice appear normal at birth, but exhibit postnatal growth retardation, altered fat metabolism with profound hyperglycerolemia and elevated free fatty acids, autonomous glucocorticoid synthesis and death by 3-4 days of age. Heterozygous females are healthy and biochemically normal. The biochemical features observed in glycerol kinase-deficient mice provide the basis for further investigations into the pathogenesis of the human disorder.