Legionella pneumophila occurrence in drinking water supplied by private wells.

Unregulated private wells are understudied potential sources of community-acquired Legionnaires' disease. Here we conducted a comprehensive survey of 44 homes supplied by private wells in Wake County, North Carolina, quantifying Legionella spp. DNA, Legionella pneumophila DNA, and total bacterial 16S rRNA genes via real-time polymerase chain reaction in hot and cold drinking water samples, along with culturable L. pneumophila via IDEXX Legiolert in cold drinking water samples. Legionella spp. DNA, L. pneumophila DNA and culturable L. pneumophila were detected in 100, 65·5 and 15·9% of the 44 homes, respectively, and culturable levels were comparable to some municipal surveys applying the same methods. Total coliforms and Escherichia coli were monitored as representative faecal indicators and were found in 20·4 and 0·0% of homes. Within certain sample types, Legionella spp. and L. pneumophila gene copy numbers were positively associated with total bacteria (i.e. total 16S rRNA genes) and water softener use, but were not associated with faecal indicator bacteria, inorganic water parameters or other well characteristics. These findings confirm that occurrence of Legionella and L. pneumophila is highly variable in private wells. SIGNIFICANCE AND IMPACT OF THE STUDY: Legionella is the leading identified cause of waterborne disease outbreaks associated with US municipal water systems. While Legionella is known to occur naturally in groundwater, prior efforts to characterize its occurrence in unregulated private wells are limited to sampling at the wellhead and not in the home plumbing where Legionella can thrive. This work documents much higher levels of Legionella in home plumbing versus water directly from private wells and examines factors associated with higher Legionella occurrence.

Nanoscale electrochemical kinetics & dynamics: the challenges and opportunities of single-entity measurements.

The development of nanoscale electrochemistry since the mid-1980s has been predominately coupled with steady-state voltammetric (i-E) methods. This research has been driven by the desire to understand the mechanisms of very fast electrochemical reactions, by electroanalytical measurements in small volumes and unusual media, including in vivo measurements, and by research on correlating electrocatalytic activity, e.g., O2 reduction reaction, with nanoparticle size and structure. Exploration of the behavior of nanoelectrochemical structures (nanoelectrodes, nanoparticles, nanogap cells, etc.) of a characteristic dimension λ using steady-state i-E methods generally relies on the well-known relationship, λ2 ∼ Dt, which relates diffusional lengths to time, t, through the coefficient, D. Decreasing λ, by performing measurements at a nanometric length scales, results in a decrease in the effective timescale of the measurement, and provides a direct means to probe the kinetics of steps associated with very rapid electrochemical reactions. For instance, steady-state voltammetry using a nanogap twin-electrode cell of characteristic width, λ ∼ 10 nm, allows investigations of events occurring at timescales on the order of ∼100 ns. Among many other advantages, decreasing λ also increases spatial resolution in electrochemical imaging, e.g., in scanning electrochemical microscopy, and allows probing of the electric double layer. This Introductory Lecture traces the evolution and driving forces behind the "λ2 ∼ Dt" steady-state approach to nanoscale electrochemistry, beginning in the late 1950s with the introduction of the rotating ring-disk electrode and twin-electrode thin-layer cells, and evolving to current-day investigations using nanoelectrodes, scanning nanocells for imaging, nanopores, and nanoparticles. The recent focus on so-called "single-entity" electrochemistry, in which individual and very short redox events are probed, is a significant departure from the steady-state approach, but provides new opportunities to probe reaction dynamics. The stochastic nature of very fast single-entity events challenges current electrochemical methods and modern electronics, as illustrated using recent experiments from the authors' laboratory.

Quantitative analysis of iontophoretic drug delivery from micropipettes.

Microiontophoresis is a drug delivery method in which an electric current is used to eject molecular species from a micropipette. It has been primarily utilized for neurochemical investigations, but is limited due to difficulty controlling and determining the ejected quantity. Consequently the concentration of an ejected species and the extent of the affected region are relegated to various methods of approximation. To address this, we investigated the principles underlying ejection rates and examined the concentration distribution in microiontophoresis using a combination of electrochemical, chromatographic, and fluorescence-based approaches. This involved a principal focus on how the iontophoretic barrel solution affects ejection characteristics. The ion ejection rate displayed a direct correspondence to the ionic mole fraction, regardless of the ejection current polarity. In contrast, neutral molecules are ejected by electroosmotic flow (EOF) at a rate proportional to the barrel solution concentration. Furthermore, the presence of EOF was observed from barrels containing high ionic strength solutions. In practice, use of a retaining current draws extracellular ions into the barrel and will alter the barrel solution composition. Even in the absence of a retaining current, diffusional exchange at the barrel tip will occur. Thus behavior of successive ejections may slightly differ. To account for this, electrochemical or fluorescence markers can be incorporated into the barrel solution in order to compare ejection quantities. These may also be used to provide an estimate of the ejected amount and distribution provided accurate use of calibration procedures.

Quantitative electrostatic force microscopy with sharp silicon tips.

Electrostatic force microscopy (EFM) probes are typically coated in either metal (radius ∼ 30 nm) or highly-doped diamond (radius ∼ 100 nm). Highly-doped silicon probes, which offer a sharpened and stable tip apex (radius ∼ 1-10 nm) and are usually used only in standard atomic force microscopy, have been recently shown to allow enhanced lateral resolution in quantitative EFM and its application for dielectric constant measurement. Here we present the theoretical modelling required to quantitatively interpret the electrostatic force between these sharpened tips and samples. In contrast to a sphere-capped cone geometry used to describe metal/diamond-coated tips, modelling a sharpened silicon tip requires a geometry comprised of a cone with two different angles. Theoretical results are supported by experimental measurements of metallic substrates and ∼10 nm radius dielectric nanoparticles. This work is equally applicable to EFM and other electrical scanned probe techniques, where it allows quantifying electrical properties of nanomaterials and 3D nano-objects with higher resolution.

Cervical spine clearance in the elderly: do elderly patients get a bad deal?

OBJECTIVE: To investigate whether elderly patients, presenting following trauma and requiring immobilisation and imaging of the cervical spine, require increased use of CT and spend longer immobilised when compared to the younger population. METHODS: A retrospective chart review was undertaken of 35 adults aged 18-65 years, and 32 adults over 65 years, requiring cervical spine imaging following trauma. RESULTS: 1 of the 35 younger patients, and 16 of the 32 elderly patients, underwent CT. Elderly patients spent 1:05 h longer immobilised (p<0.005). CONCLUSIONS: Half of the elderly patients underwent CT, and they were immobilised for significantly longer than younger patients. Measures should be adopted to facilitate early diagnosis and mitigate complications of prolonged immobilisation in elderly patients with neck trauma.

Nanoscale measurement of the dielectric constant of supported lipid bilayers in aqueous solutions with electrostatic force microscopy.

We present what is, to our knowledge, the first experimental demonstration of dielectric constant measurement and quantification of supported lipid bilayers in electrolyte solutions with nanoscale spatial resolution. The dielectric constant was quantitatively reconstructed with finite element calculations by combining thickness information and local polarization forces which were measured using an electrostatic force microscope adapted to work in a liquid environment. Measurements of submicrometric dipalmitoylphosphatidylcholine lipid bilayer patches gave dielectric constants of ε(r) ~ 3, which are higher than the values typically reported for the hydrophobic part of lipid membranes (ε(r) ~ 2) and suggest a large contribution of the polar headgroup region to the dielectric response of the lipid bilayer. This work opens apparently new possibilities in the study of biomembrane electrostatics and other bioelectric phenomena.

Theory of amplitude modulated electrostatic force microscopy for dielectric measurements in liquids at MHz frequencies.

A theoretical analysis of amplitude modulated electrostatic force microscopy (AM-EFM) in liquid media at MHz frequencies, based on a simple tip-sample parallel plate model, is presented. The model qualitatively explains the main features of AM-EFM in liquid media and provides a simple explanation of how the measured electric forces are affected by: the frequency of the applied voltage, the tip-sample distance, the ionic concentration, the relative dielectric constant of the solution, and the relative dielectric constant and thickness of the sample. These results provide a simple framework for the design of AM-EFM measurements for localized dielectric characterization in liquid media.

Efficacy of a therapeutic cocaine vaccine in rodent models.

Cocaine abuse is a major medical and public health concern in the United States, with approximately 2.1 million people dependent on cocaine. Pharmacological approaches to the treatment of cocaine addiction have thus far been disappointing, and new therapies are urgently needed. This paper describes an immunological approach to cocaine addiction. Antibody therapy for neutralization of abused drugs has been described previously, including a recent paper demonstrating the induction of anti-cocaine antibodies. However, both the rapidity of entry of cocaine into the brain and the high doses of cocaine frequently encountered have created challenges for an antibody-based therapy. Here we demonstrate that antibodies are efficacious in an animal model of addiction. Intravenous cocaine self-administration in rats was inhibited by passive transfer of an anti-cocaine monoclonal antibody. To actively induce anti-cocaine antibodies, a cocaine vaccine was developed that generated a high-titer, long-lasting antibody response in mice. Immunized mice displayed a significant change in cocaine pharmacokinetics, with decreased levels of cocaine measured in the brain of immunized mice only 30 seconds after intravenous (i.v.) administration of cocaine. These data establish the feasibility of a therapeutic cocaine vaccine for the treatment of cocaine addiction.

Benchmarking hospital outcomes for laparoscopic adjustable gastric banding.

BACKGROUND: Since the Food and Drug Administration (FDA) approval of laparoscopic adjustable gastric bands (LAGB) in June 2001, the number LAGB procedures performed in the United States has increased exponentially. This study aimed to benchmark the authors' initial hospital experience to FDA research trials and evidence-based literature. METHODS: Over a 2-year period, 87 consecutive patients with a mean age of 43 years (range, 21-64 years) and a body mass index of 45.6 kg/m2 (range, 35-69 kg/m2) underwent an LAGB procedure at the authors' institution. The authors conducted a retrospective review of the outcomes including conversion, reoperation, mortality, perforation, erosion, prolapse, port dysfunction, excess weight loss, and changes in comorbidities, then compared the data with published benchmarks. RESULTS: Gender, age, and body mass index were comparable with those of other series. Perioperative adverse events included acute stoma obstruction (n = 1) and respiratory complications (n = 2). Delayed complications included gastric prolapse (n = 4) and port reservoir malposition (n = 4). Five bands were explanted. The mean follow-up period was 14 months (n = 79). The mean percentage of excess weight loss was 30% (range, 4.7-69%) at 6 months, 41% (range, 9.6-82%) at 12 months, and 47% (range, 14-92%) at 24 months. Comorbidities resolved included diabetes (74%), hypertension (57%), gastroesophageal reflux disease (55%) and dyslipidemia (38%). CONCLUSIONS: The short-term outcomes for LAGB were comparable with published benchmarks. With adequate weight loss, most patients achieve significant improvement in obesity-related illnesses. With new bariatric accreditation standards and mandates required for financial reimbursement, hospitals will need to demonstrate that their clinical outcomes are consistent with best practices. The authors' early experience shows that LAGB achieves significant weight loss with low mortality and morbidity rates. Despite a more gradual weight loss, most patients achieve excellent weight loss with corresponding improvement of comorbidities within the first 2 years postoperatively.

FORAGES AND PASTURES SYMPOSIUM: Improving efficiency of production in pasture- and range-based beef and dairy systems.

Despite overall increased production in the last century, it is critical that grazing production systems focus on improving beef and dairy efficiency to meet current and future global food demands. For livestock producers, production efficiency is essential to maintain long-term profitability and sustainability. This continued viability of production systems using pasture- and range-based grazing systems requires more rapid adoption of innovative management practices and selection tools that increase profitability by optimizing grazing management and increasing reproductive performance. Understanding the genetic variation in cow herds will provide the ability to select cows that require less energy for maintenance, which can potentially reduce total energy utilization or energy required for production, consequently improving production efficiency and profitability. In the United States, pasture- and range-based grazing systems vary tremendously across various unique environments that differ in climate, topography, and forage production. This variation in environmental conditions contributes to the challenges of developing or targeting specific genetic components and grazing systems that lead to increased production efficiency. However, across these various environments and grazing management systems, grazable forage remains the least expensive nutrient source to maintain productivity of the cow herd. Beef and dairy cattle can capitalize on their ability to utilize these feed resources that are not usable for other production industries. Therefore, lower-cost alternatives to feeding harvested and stored feedstuffs have the opportunity to provide to livestock producers a sustainable and efficient forage production system. However, increasing production efficiency within a given production environment would vary according to genetic potential (i.e., growth and milk potential), how that genetic potential fits the respective production environment, and how the grazing management fits within those genetic parameters. Therefore, matching cow type or genetic potential to the production environment is and will be more important as cost of production increases.

Anatomical demonstration of ocular segregation in the retinogeniculocortical pathway of the New World capuchin monkey (Cebus apella).

We describe the architecture of the dorsal lateral geniculate nucleus and primary visual cortex (striate cortex; area 17) of the New World capuchin monkey (Cebus apella) on the basis of the distribution of cell bodies and cytochrome oxidase histochemistry. Changes in staining for cytochrome oxidase following unilateral enucleation served to indicate the organization of the representation of the two eyes in the retinogeniculocortical pathway. The number and disposition of eye-specific layers within the lateral geniculate nucleus of Cebus are consistent with the common plan of geniculate organization in anthropoid primates, and the radial organization of area 17 fits the pattern common to New World squirrel and Old World macaque monkeys, including the presence of cytochrome-oxidase-rich zones in supragranular and deeper cortical layers (Horton: Philos. Trans. R. Soc. Lond. [Biol.] 304:199-253, '84). Our principal finding is that cytochrome oxidase histochemistry following unilateral eye removal unequivocally reveals ocular dominance columns in the striate cortex of Cebus. As in the macaque (Hubel: Nature 292:762-764, '82), ocular dominance columns extend through the thickness of cortex and blobs are centered on columns, but the array of columns viewed tangentially is less orderly or more mosaic than in the macaque, and there is apparently significant overlap between columns. The presence of well-defined ocular dominance columns in Cebus, as in Ateles (Florence, Conley, and Casagrande: J. Comp. Neurol. 243:234-248, '86) but not in other New World monkeys examined previously, emphasizes the phylogenetic lability of binocular segregation in the primate visual cortex. In addition, the present results indicate significant differences with respect to the tangential organization of the ocular dominance domain between primate species in which ocular dominance columns are present.

A quantitative study of the reinnervation of the goldfish optic tectum following optic nerve crush.

Stereological and quantitative morphometric methods were used to study changes in the stratum fibrosum et griseum superficialis (SFGS), the major retinal target, in optic tectum of goldfish, during regeneration of the optic nerve. Orthograde transport of HRP by optic axons was used to characterize the retinal projection in SFGS. Profiles of HRP-labeled optic terminals contained rounded vesicles, contacted small dendrites, and were distributed uniformly throughout the area of SFGS sampled; labeling density estimates indicate that at least 37% of the total terminal population in SFGS is retinal in origin. Partial denervation of the tectum by optic nerve crush is accompanied by a loss of 40% of the total terminal population in SFGS and by a marked decrease of SFGS thickness. Entry of massive numbers of regenerating optic axons into SFGS begins about 3 weeks postoperatively, about the time that some visual function recovers and produces a marked increase in SFGS thickness which persists for several months postoperatively. The area occupied by regenerating axons and the number of terminals in the tectum only approach preoperative levels 3 months postoperatively. The recovery of normal synaptic number is therefore delayed several months beyond the time of entry of regenerative axonal sprouts. The results indicate that return of synaptic number to normal is temporally associated with the reduction of the excess number of regenerating optic axons and that both these processes are prolonged.

Selective retinal reinnervation of a surgically created tectal island in goldfish. II. Electron microscopic analysis.

In the preceding study (Edwards et al., '85), we showed that regenerating optic axons reestablish a topographically restricted projection to a caudal tectal island created by surgical removal of a 1-mm-wide strip of caudal tectum in goldfish. In the present ultrastructural study, we evaluated the dependence of this axonal outgrowth on the presence of tectal target tissue caudal to the gap. Axon counts in the lesion zone were compared between cases with complete caudal tectal ablation and cases with ablation sparing a caudal tectal island (with and without optic nerve crush). During the postoperative interval of 20-50 days (early period), up to about 1,000 unmyelinated axons with features characteristic of optic axons were present in numerous small subpial bundles in both preparations. In the subsequent interval of 50-110 days (middle period), less than 200 axons were counted caudal to simple half-tecta, whereas 4,000-14,000 myelinated and unmyelinated axons were present in a few large bundles which crossed the lesion zone of tectal island cases. In this period, optic terminals could be demonstrated in the tectal island using the anterograde horseradish peroxidase method. At 170-300 days after surgery (late period), bridging bundles contained between 2,000 and 6,000 largely myelinated axons. We conclude that caudal tectal tissue is not necessary for the initial outgrowth of a small number of axons beyond a rostral half-tectum. The target is essential, however, for the maintenance of these axon fascicles and for the subsequent massive outgrowth of axons to the island. The contributions of glial guidance, diffuse exploratory outgrowth, and target-produced trophic factors to the formation of an initially exuberant projection to the island are discussed. A process of selective axon collateral withdrawal is proposed to account for the decrease in axon numbers within bridging bundles in the late period and for the late restriction in the retinal origin of the island projection indicated by results in the preceding study (Edwards et al., '85).

Effects of permeability of midtectal barriers in goldfish on compression of the visuotectal projection rostrally and regenerative escape caudally.

Physiological mapping and anatomical methods were used to evaluate changes in the retinotectal projection of goldfish 16-200 days after insertion of permeable or impermeable barriers that bisected the tectum into rostral and caudal halves. The projection to rostral tectum was left intact. Barriers composed of Gelfilm or impermeable Nucleopore material induced within 2-3 months an orderly compression of the visual field representation in rostral tectum only slightly less complete than that observed in animals with caudal half-tectal ablation. In contrast, Nucleopore filter barriers with 0.1-micron or 8-micron holes did not cause significant compression. According to both mapping and autoradiographic tracing, reinnervation of tectum behind the barriers occurred among all groups within 1-2 months. Physiologically, the projection caudal to permeable barriers was typically complete and appropriate, whereas the caudal projection in fish with impermeable barriers eventually consisted of a greatly expanded representation of the extreme temporal visual field. Autoradiography, normal fiber impregnations, and the orthograde horseradish peroxidase method revealed that regeneration past the barriers involved the formation of large bundles passing vertically along the cut tectal margin and through the underlying valvula cerebelli or lateral tegmentum. The simultaneous rostral compression and caudal expansion in the visual representation formed when more impermeable barriers were used provides evidence that, in addition to the influence of position-dependent properties, axonal competition for target territory contributes to the control of the distribution of optic arbors. Further research is required to determine why reinnervation of tectum caudal to the more permeable barriers was more complete with respect to visual representation.

Immunocytochemical demonstration of early appearing astroglial structures that form boundaries and pathways along axon tracts in the fetal brain.

During normal development of the mammalian forebrain, the paired cerebral hemispheres are initially separated midsagittally by the connective tissue-filled longitudinal fissure. During subsequent stages, the hemispheres fuse as basal lamina is remodeled and fibroblasts are eliminated from the fissure to create new central nervous system (CNS) territory in the midline. Two axon pathways, the corpus callosum and dorsal callosal stria, eventually use this region as part of their pathway. In order to assess the possible role of glial cells in the fusion process and in the guidance of axons in this and several other areas of the forebrain, we have analyzed the developing brain in timed cat and mouse embryos with immunohistochemical and morphological techniques. With the use of astroglial-specific antibodies and electron microscopy, we have visualized two distinct, primitive astroglial structures associated with the cerebral midline, and seven more associated with other specific brain regions. The way in which one of these structures moves as a column along the hemispheric midline in synchrony with seam formation suggests the possibility that during morphogenesis of the telencephalon, astrocytes may aid in the fusion process. In addition, the compact assemblage, early appearance and location of this and the other glial structures in relation to well defined neuroanatomical landmarks or axon pathways suggest that they may transiently compartmentalize relatively large regions of the CNS and organize certain developing fiber systems by acting as guides or barriers at critical stages of ontogeny.

Target regulation of synaptic number in the compressed retinotectal projection of goldfish.

In order to determine the morphological consequences of the formation of a compressed retinotectal projection, the optic neuropil lamina (stratum fibrosum et griseum superficialis, SFGS) was examined in large goldfish 3 months to 4 years after ablation of the caudal half of the tectum both with crush of the optic nerve (HTX) without (HT). In semithin sections, the SFGS, as delineated with orthograde HRP labeling, shows a persistent hypertrophy of about 25% in HTX and HT groups. Comparison of ultrastructural stereological data with similar data on control and regenerated projections to intact tecta (Murray and Edwards, '82) indicated that this hypertrophy can be attributed largely to an increased number of axons and not to increases in terminal or dendritic compartments. A normal number of synaptic terminals per column through SFGS is conserved in HTX and HT groups. Planimetric analysis and observations using orthograde HRP labeling reveal no group differences in size and shape of terminal profiles. The same number of retinal ganglion cells project to a half-tectum as to an intact tectum, as indicated by estimates of ganglion cell number and of the minimum percentage of them which project to the tectum using retrograde HRP labeling. The results suggest that the regenerating and sprouting optic axons participating in the formation of a compressed retinotopic projection compete for a limited accommodation inthe SFGS and that this capacity to accept synaptic input becomes saturated at the control innervation density. The results are consistent with the formation of a smaller than normal number of terminals per optic axon, numerical estimates for which are given. If the percentage of terminals which are optic does not change, then the number of terminals per axon is reduced by about 40%.

Selective retinal reinnervation of a surgically created tectal island in goldfish. I. Light microscopic analysis.

Through anatomical and physiological studies of the regenerating retinotectal projection of goldfish, we sought to determine whether the establishment of a topographic projection is attained through a refinement of an initially less precise pattern of innervation. A 1-mm-wide mediolateral strip of caudal tectum was removed so that a small island of tectal tissue was spared at the caudal pole, and the contralateral nerve was either crushed (TIX) or left intact (TI). The presence of regenerated axons in the ablated zone and the reinnervation of the caudal island were assessed with anterograde and retrograde labeling methods in the following postoperative intervals: early, 20-50 days; middle, 50-110 days; and late, more than 170 days. The anterograde radioautographic method revealed that the appropriate layers of the tectal island became reinnervated by optic axons during the early period. During the middle and late periods, one to several large, discrete bundles bridging the lesion zone along the surface of exposed subtectal structures were readily identified both by radioautography and by anterograde or retrograde labeling following application of horseradish peroxidase to the transected optic nerve or tectal island, respectively. In contrast, the anterograde horseradish peroxidase method did not reveal axon bundles extending caudal to the half-tectum in the absence of a tectal island. Among TIX cases, retrograde horseradish peroxidase labeling of the contralateral nasal retina was more widespread in the middle period than in the late period, a result we interpret as reflecting an improvement in topographical precision with time. The area of retinal labeling among TIX cases in the late period was similar to that following caudal tectal injection in cases with simple nerve crush, although it was still elevated above normal control values. Physiological maps indicated a focal representation of the nasal retina in the tectal island in both periods and did not reveal a transient extreme convergence of retinal input. These findings are discussed in relation to Sperry's chemoaffinity theory.

Development of the crossed retinocollicular projection in the mouse.

Changes in the distribution of axons of the crossed retinal projection within the superior colliculus of the developing mouse were studied by means of normal fiber and Golgi impregnations and by anterograde horseradish peroxidase labelling. Retinal axons advance along the optic tract from gestational days E12 to E14 and first invade the superior colliculus on E15. Over the subsequent days until birth (E19), the retinal axons extend within rostrocaudally oriented fascicles that distribute through the full thickness of the uppermost collicular layer, the stratum superficiale (SS). A dramatic transformation of this fiber stratification pattern into the mature pattern occurs over the first postnatal week. The fiber bundles are progressively cleared from the upper half of SS, identified as the future stratum griseum superficiale (SGS). Concurrently, the fiber bundles in the deep SS, identified as the stratum opticum (SO), give rise to individual, nonfasciculated fibers, which arborize within SGS. The contralateral retinal origin of the transient population of axons in SGS as well as the majority of axons that persist in SO is evident from the observation that they degenerate following neonatal enucleation. The number of fiber bundles lost is estimated to be 40-50% of the total population present in the superficial layers at birth. The combined set of observations indicates that axon elimination plays a major role in shaping the laminar pattern of retinal innervation of the colliculus. Retinal ganglion cell death, and not axon pruning, is proposed as the most probable mechanism by which axon fascicles are eliminated from SGS.

Development of cell and fiber lamination in the mouse superior colliculus.

The emergence of laminar organization in the superior colliculus was investigated in the mouse with several anatomical methods, including tritiated-thymidine autoradiography, Golgi impregnation, and general stains for cell bodies and for fibers. The sequence of neurogenesis, cell migration, and early morphological differentiation of neurons was shown to exhibit a discontinuity between the lower and upper divisions (i.e., between the deep and intermediate "gray" and "white" layers and the superficial "gray" and "white" layers). These events proceed in an inside-out order within the lower division, but the same events within the upper division commence in advance of the completion of this progression. Thus, peak generation times for layers of the lower division proceed from (embryonic day) E11 to E13 and for the upper division from E12 to E13. Cell migration, as monitored with tritiated-thymidine labelling, reflects closely the pattern of cytogenesis. This is most clearly evident on E15 when a population of E11-labelled cells is divided into superficial and deep layers (the strata superficiale and profundum--SS and SP) by the interposition of E13-labelled cells at an intermediate level (stratum intermedium--SI). A contingent of the latter cells continue their migration and join their predecessors within the SS on E17, a time point when cell migrations are largely complete. Paralleling this sequence of arrival of neurons and the formation of three primary layers, both the time course of accumulation of fiber fascicles and the early morphological differentiation of neurons in the interval from E13 to E17 tends to proceed from SP to SS and from SS to SI. Thus, the transverse fiber system and large multipolar neurons of SP develop in advance of the longitudinal fiber system and vertically oriented neurons of SS, which in turn develop precociously with respect to the longitudinal fibers and medium-sized multipolar neurons of SI. In contrast, later events of differentiation that underly a major radial growth and an architectonic sublamination of the primary strata proceed in a simpler inside-out sequence from E17 to (postnatal day) P6. The major morphogenetic events underlying the establishment of statification in the colliculus appear to involve the operation of relatively independent programs of assembly for the two basic subdivisions. It is probable that selective cell-cell interactions contribute to the delivery of concurrently generated neurons to different laminae as well as to the deployment of axons in a manner that respects laminar boundaries.

Complications of therapeutic apheresis, including a fatal case with pulmonary vascular occlusion.

A high incidence of anaphylactic reactions has been observed in patients undergoing therapeutic plasma exchange. In three of 22 patients who underwent multiple exchanges, urticaria, bronchospasm, and hypotension developed during a course of plasma exchange that responded to treatment with steroids, antihistamines, and epinephrine. Fatal pulmonary microvascular occlusion with platelets and granulocytes developed in an additional patient eight hours following an apheresis procedure involving albumin replacement. The mechanism for the latter complication is not known but did not appear to invoke complement activation. This unexpectedly high risk of potentially fatal complications must be considered when a course of therapeutic apheresis, particularly involving treatment of a chronic disease, is planned.