Microsporidia are obligate, intracellular, spore-forming protozoal parasites. Their host range is extensive and includes most invertebrates and all classes of vertebrates. Five microsporidial genera (Enterocytozoon, Encephalitozoon, Septata, Pleistophora, and Nosema) and unclassified microsporidia have been associated with human disease, which appears to manifest primarily in immunocompromised persons. The clinical manifestations of microsporidiosis are diverse and include intestinal, pulmonary, ocular, muscular, and renal disease. The majority of microsporidial infections in persons infected with human immunodeficiency virus (HIV) are attributed to Enterocytozoon bieneusi, an important cause of chronic diarrhea and wasting. Four cases of microsporidial infection among persons not infected with HIV who had documented or presumed cellular immunodeficiency and four cases of corneal stroma infection due to microsporidia in immunocompetent patients have been described. Furthermore, the first case of traveler's diarrhea due to E. bieneusi in an immunocompetent and otherwise healthy patient is reported in this issue. The sources of human microsporidial infections and modes of transmission are unknown.
Morbidity and mortality associated with bacterial meningitis remain high, although antibiotic therapy has improved during recent decades. The major intracranial complications of bacterial meningitis are cerebrovascular arterial and venous involvement, brain edema, and hydrocephalus with a subsequent increase of intracranial pressure. Experiments in animal models and cell culture systems have focused on the pathogenesis and pathophysiology of bacterial meningitis in an attempt to identify the bacterial and/or host factors responsible for brain injury during the course of infection. An international workshop entitled "Bacterial Meningitis: Mechanisms of Brain Injury" was organized by the Department of Neurology at the University of Munich and was held in Eibsee, Germany, in June 1993. This conference provided a forum for the exchange of current information on bacterial meningitis, including data on the clinical spectrum of complications, the associated morphological alterations, the role of soluble inflammatory mediators (in particular cytokines) and of leukocyte-endothelial cell interactions in tissue injury, and the molecular mechanisms of neuronal injury, with potential mediators such as reactive oxygen species, reactive nitrogen species, and excitatory amino acids. It is hoped that a better understanding of the pathophysiological events that take place during bacterial meningitis will lead to the development of new therapeutic regimens.
Practice of a novel task leads to improved performance. The brain mechanisms associated with practice-induced improvement in performance are largely unknown. To address this question we have examined the functional anatomy of the human brain with positron emission tomography (PET) during the naive and practiced performance of a simple verbal response selection task (saying an appropriate verb for a visually presented noun). As a control state, subjects were asked to repeat the visually presented nouns. Areas of the brain most active during naive performance (anterior cingulate, left prefrontal and left posterior temporal cortices, and the right cerebellar hemisphere), compared to repeating the visually presented nouns, were all significantly less active during practiced performance. These changes were accompanied by changes in the opposite direction in sylvian-insular cortex bilaterally and left medial extrastriate cortex. In effect, brief practice made the cortical circuitry used for verbal response selection indistinguishable from simple word repetition. Introduction of a novel list of words reversed the learning-related effects. These results indicate that two distinct circuits can he used for verbal response selection and normal subjects can change the brain circuits used during task performance following less than 15 min of practice. One critical factor in determining the circuitry used appears to be the degree to which a task is learned or automatic.
Oxidation of lipoproteins is hypothesized to promote atherosclerosis and, thus, a high intake of antioxidant nutrients may protect against coronary heart disease. The relation between the intakes of dietary carotene, vitamin C, and vitamin E and the subsequent coronary mortality was studied in a cohort of 5,133 Finnish men and women aged 30-69 years and initially free from heart disease. Food consumption was estimated by the dietary history method covering the total habitual diet during the previous year. Altogether, 244 new fatal coronary heart disease cases occurred during a mean follow-up of 14 years beginning in 1966-1972. An inverse association was observed between dietary vitamin E intake and coronary mortality in both men and women with relative risks of 0.68 (p for trend = 0.01) and 0.35 (p for trend < 0.01), respectively, between the highest and lowest tertiles of the intake. Similar associations were observed for the dietary intake of vitamin C and carotenoids among women and for the intake of important food sources of these micronutrients, i.e., of vegetables and fruits, among both men and women. The associations were not attributable to confounding by major nondietary risk factors of coronary heart disease, i.e., age, smoking, serum cholesterol, hypertension, or relative weight. The results support the hypothesis that antioxidant vitamins protect against coronary heart disease, but it cannot be excluded that foods rich in these micronutrients also contain other constituents that provide the protection.
Morphometric analysis was performed on three-dimensional MRI scans of 10 male and 10 female young adults with four principal objectives: (1) to characterize in vivo volumes of whole brain and substructures, (2) to explore volumetric symmetry in bilateral structures, (3) to consider the extent to which volumetric measures are dimorphic in the male and female brain, and (4) to provide a normal volumetric database for the young adult brain. Total brain volumes ranged between 1173 and 1626 cm(3). All bilateral structures were symmetric or nearly symmetric in volume, with the exception of a slightly larger right neocortex and amygdala, and larger left lateral ventricle. Male brains were larger in volume than female brains, a difference that reached significance for cerebellar but not for cerebral hemisphere volume. In females, there was less cerebral white matter while caudate volume was larger than in the male brains. The proportions of caudate and hippocampus relative to total cerebral volumes were larger in females than in males. These four measures accurately predicted gender in 85% of the subjects by discriminant analysis. No gender differences were noted in the structural symmetry analysis. These results represent the first step in establishing a comprehensive database of morphometric parameters, with unexpected findings relative to brain symmetry and sexual dimorphism.
Inferior temporal cortex is perhaps the highest visual processing area and much anatomical work has focused on its connections with other visual areas in temporal and occipital cortex. Here we report connections of inferior temporal cortex with regions in the frontal and parietal lobes. Inferior temporal areas TEO and TE were injected with WGA-HRP and H-3-AA, respectively, or vice versa, in 1-week-old infant and 3-4-year-old adult monkeys ((Macaca mulatta). The results indicated that whereas TEO has more extensive connections with parietal areas, TE has more extensive connections with prefrontal areas. Thus, in the intraparietal sulcus, area TEO is connected with areas LIPd, LIPv, and V3A, and with the as yet undefined region between LIPv and V3A, whereas the connections of TE are predominantly with LIPd, and to a lesser extent with LIPv. In the prefrontal cortex, area TE is connected with areas 8 and 45 in the inferior limb of the anterior bank of the arcuate sulcus, with area 12 on the inferior prefrontal convexity, and with areas 11 and 13 on the orbital surface. By contrast, the connections of area TEO are limited to areas 8, 45, and 12. Furthermore, within prefrontal cortex, the projections from areas TEO and TE terminate in different layers in areas 8 and 45, such that those from TEO terminate in all layers, whereas those from TE terminate in layers I and V/VI only. In contrast to the connections of areas TEO and TE with various medial temporal-lobe and subcortical structures, which are immature in infant monkeys (Webster et al., 1991, 1993b), the connections with parietal and prefrontal areas appear adult-like as early as 1 week of age.
Electrophysiological correlates of the processing of visual information were studied in epileptic patients with electrodes chronically implanted on the surface of striate and extrastriate cortex. In separate experiments patients viewed faces, letter strings (words and nonwords), numbers, and control stimuli. A negative potential, N200, was evoked by faces, letter strings, and numbers, but not by the control stimuli. N200 was recorded bilaterally from discrete regions of the fusiform and inferior temporal gyri. These category-specific face, letter-string, and number ''modules'' vary in location. In most cases there was no overlap in the location of face and letter-string modules, suggesting a mosaic of functionally discrete regions. In some cases letter-string and number N200s were recorded from the same location, suggesting that these modules may be less spatially and functionally discrete. Face N200-like potentials can be recorded from temporal scalp, allowing the possibility of studying early face processing in normal subjects. Longer-latency face-specific potentials were recorded from the inferior surface of the anterior temporal lobe. Potentials evoked by colored checkerboards were recorded from a region of the fusiform gyrus posterior to the fusiform region from which category-specific N200s were recorded. These results suggest that there are several processing streams in inferior extrastriate cortex. In addition to object recognition systems previously proposed for faces and words, our preliminary results suggest a separate system dealing with numbers. Postulated systems dealing with larger manipulable objects and animals have not been detected.
Since the turn of the century, the prefrontal association areas of the cerebral cortex have been thought to be among the last regions of the cortical mantle to develop, We have examined the course of synaptogenesis in the macaque prefrontal cortex by quantitative electron microscopic analysis in 25 rhesus monkeys ranging in age from embryonic day 47 (E47) to 20 years of age. A series of overlapping electron micrographs spanning the whole cortical thickness in each animal provided data on the number, the proportion, and the density of synapses per unit area (N-A) and per unit volume (N-V) of neuropil. The tempo and kinetics of synapse formation in prefrontal cortex closely resemble those described for sensory and motor areas, particularly during the stages of synapse acquisition and overproduction (Rakic et al., 1986). In young embryos, we describe a precortical phase (E47-E78), when synapses are found only above and below, but not within, the cortical plate. Following that, there is an early cortical phase, from E78 to E104, during which synapses accumulate within the cortical plate, initially exclusively on dendritic shafts. The next rapid phase of synaptogenesis begins at 2 months before birth and ends approximately at 2 months after birth, culminating with a mean density of 750 million synapses per cubic micrometer. This accumulation is largely accounted for by a selective increase in axospine synapses in the supragranular layers. The period of explosive synaptic density is followed by a protracted plateau stage that lasts from 2 months to 3 years of age when synaptic density remains relatively constant. The final period of decline, from 3 years through over 20 years of age, is marked by a slight but statistically significant decline in synaptic density. Concurrent recruitment of synapses with that of sensory and motor areas supports the concept that the initial establishment of cortical circuitry is governed by general mechanisms common to al areas, independent of their specific functional domain. The finding that synaptic density is relatively stable from early adolescence through puberty (the plateau period) is indicative of the importance, in primates, of a consistent and high synaptic density during the formative years when learning experiences are most intense.