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.

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.

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.

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.

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.

Seismic and aseismic weakening effects in transtension: field and microstructural observations on the mechanics and architecture of a large fault zone in SE Tibet

Fault-zone surveying and microstructural analyses focus on a transtensionally strained section of a >100 km-long, 5–15 km-wide, active, sinistral strike-slip W-E fault — the Damxung-Jiali Shear Zone (DJSZ). Deformation fabric superposition, palaeostress and neotectonic measurements reveal a progressive dominance of the transtension coaxial component. Vertical flattening and broadening of the DJSZ results in a 10–20 km-wide pull-apart depression with reciprocal emergence of flanking highlands that expose abandoned fault-zone domains that are hundreds of metres by tens of km in size. Polylithological fault rocks preserve a suite of frictional and viscous deformation to c. 350 °C. Amongst the fault strands, intensity and distribution of grain size reduction from comminution, widespread solution transfer, intragranular plasticity and recrystallization is heterogeneous. A regular pattern of pseudotachylite-coated surfaces short-cutting strong volcanic mylonite domains between weak creeping calcite domains indicates seismic with aseismic strain, and is interpreted as velocity-weakening evidence. Re-brecciation of solution-transfer accommodation-assisted S-C-cataclasite domains document switches from frictional to viscous strain and back again. The co-location of brittle and plastic constituent behaviour for varied fault lithologies plus our interpretations on deformation temperatures suggests major overlap for the frictional and viscous depth ranges. This indicates a very broad and strongly velocity- and fluid-dependent ‘brittle-ductile’ transition.

Effects of nitric oxide synthase inhibitors on the discriminative stimulus effects of cocaine in rats

RATIONALE

Nitric oxide synthase (NOS) inhibitors may modulate the discriminative stimulus effects of cocaine because they alter dopamine (DA) release.

OBJECTIVES

The effects of the NOS inhibitors NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitro-indazole (7-NI) were examined in experiments designed to better understand the mechanisms that may underlie the interactions between NOS inhibitors and cocaine.

METHODS

Rats were trained to discriminate 10 mg/kg cocaine from saline, and then substitution and pretreatment tests with L-NAME and 7-NI were conducted. To determine if the combined effects of NOS inhibitors and cocaine might be related to DA mechanisms and/or to N-methyl-D-aspartate (NMDA) receptor mechanisms, substitution tests with other indirect DA agonists and NMDA antagonists were carried out in the presence and absence of L-NAME. In addition, the roles of the D1 and D2 families of DA receptors in mediating the cocaine-altering effects of L-NAME and 7-NI were examined in antagonism tests using SCH 23390 and haloperidol, respectively.

RESULTS

The results demonstrated that neither NOS inhibitor alone substituted for the 10 mg/kg cocaine training dose, but when given as a pretreatment, 100 mg/kg L-NAME as well as 10 mg/kg 7-NI enhanced the discriminative stimulus and rate-decreasing effects of cocaine. L-NAME pretreatment also enhanced the potency of (+)-amphetamine and GBR 12909, but not MK-801, phencyclidine, or NPC 17742, for producing discriminative stimulus and rate-decreasing effects in substitution tests. Further testing showed that the cocaine-enhancing effects of L-NAME and 7-NI were attenuated by doses of haloperidol and SCH 23390 that minimally altered the effects of cocaine alone.

CONCLUSIONS

These findings suggest that L-NAME and 7-NI may increase the potency of cocaine and other indirect DA agonists through a central mechanism whereby DA neurotransmission is directly enhanced by NOS inhibition.

Southern Tibet Detachment System at Khula Kangri, Eastern Himalaya: A Large-Area, Shallow Detachment Stretching into Bhutan?

A new map and cross sections of the Khula Kangri and Kankar Pünzum-Monlakarchung High Himalayan ranges in the Tibet-Bhutan frontier area are presented from integration of unpublished mapping from the summit section of Khula Kangri and new remote sensing together with previous mapping. The ranges define an orographic bifurcation of the High Himalaya that results in a north-south repetition of the main geological section and coincides with the morphological repetition. The Southern Tibet Detachment System that juxtaposes the Tethyan sedimentary rocks against the gneisses and granites of the High Himalayan Crystalline can be continuously traced around both ranges and is not imbricated. Postdetachment kilometer-scale flexure and faulting account for the features of the observed bifurcation. The true map extent of the Khula Kangri and Monlakarchung-Passalum granite batholiths is now apparent. We propose that the two plutons are part of the same originally continuous body.

Modulation of the discriminative stimulus and rate-altering effects of cocaine by competitive and noncompetitive N-methyl-D-aspartate antagonists

The purpose of this study was to determine the extent to which N-methyl-D-aspartic acid (NMDA) antagonists modified the discriminative stimulus effects of cocaine in rats trained to discriminate 5 mg/kg cocaine from vehicle on a fixed-ratio schedule of food presentation as well as the rate-altering effects of cocaine in rats maintained on a fixed-interval schedule of food presentation. NMDA-associated ion channel blockers (dizocilpine, phencyclidine, and magnesium chloride) and competitive NMDA antagonists (NPC 17742 and CGP 37849) displayed similar behavioral effects when administered alone: each drug engendered intermediate levels of cocaine-appropriate responses and rate-dependent effects on food-reinforced operant responding. Selected doses of dizocilpine, magnesium chloride, and phencyclidine given in combination with 1 mg/kg cocaine produced more cocaine-appropriate responses than this dose of cocaine alone. In addition, dizocilpine and magnesium chloride each attenuated the discriminative stimulus effects of higher doses of cocaine. The competitive NMDA antagonists did not appreciably modify the discriminative stimulus effects of any dose of cocaine. Under the fixed-interval schedule, each NMDA antagonist attenuated the effects of 3 mg/kg cocaine, which normally produced maximal increases in response rate. Attenuation of the rate-decreasing effects of the highest dose of cocaine (30 mg/kg) also were observed after pretreatment with dizocilpine and magnesium chloride. These findings demonstrated differences in the way that NMDA-associated ion channel blockers and competitive NMDA antagonists interact with cocaine, and suggest that some NMDA-associated ion channel blockers may either enhance or antagonize the effects of cocaine, depending on the dose and type of behavioral procedure.

Discriminative stimulus effects of magnesium chloride: substitution studies with monoamine uptake inhibitors and N-methyl-D-aspartate antagonists

Previous studies suggest that magnesium chloride may have discriminative stimulus effects that partially overlap with those of noncompetitive N-methyl-D-aspartate antagonists as well as certain monoamine uptake inhibitors. In our study, rats were trained to discriminate 100 mg/kg magnesium chloride from saline and its discriminative stimulus effects were characterized with respect to N-methyl-D-aspartate receptor and monoamine transporter functions in substitution tests. The discriminative stimulus effects of magnesium chloride were acquired within a moderate number of training sessions and showed dose-related substitution after either subcutaneous (3-300 mg/kg) or intracerebroventricular (0.3-300 microg) administration. The intracerebroventricular administration of magnesium chloride was over 4000 times more potent than its s.c. administration. The monoamine uptake inhibitors cocaine, GBR 12909, talsupram and citalopram fully substituted (> or =90% magnesium-appropriate responses) for magnesium chloride in the majority of subjects tested and the group averages reached a maximum of 72 to 82% responses on the magnesium-appropriate lever. Based on relative potency analysis, the rank order of potency of these four drugs for producing magnesium-appropriate responses was talsupram = cocaine > citalopram = GBR 12909. The N-methyl-D-aspartate receptor antagonists dizocilpine, phencyclidine and NPC 17742 engendered maximum group averages of 49 to 65% responses on the magnesium-appropriate lever. The results suggest that the centrally mediated discriminative stimulus effects of magnesium chloride may be more directly related to interactions with monoamine neurotransmitter functions than to N-methyl-D-aspartate receptor blockade.

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.

Effects of N-methyl-D-aspartate antagonists in rats discriminating different doses of cocaine: comparison with direct and indirect dopamine agonists

Dose-response functions for selected N-methyl-D-aspartate (NMDA) antagonists and direct and indirect dopamine agonists were compared in rats trained to discriminate either a low (2 mg/kg) or a high (10 mg/kg) dose of cocaine from vehicle. The NMDA-associated ion channel blockers, dizocilpine, phencyclidine and MgCl2, substituted fully for cocaine (> or = 90% cocaine-appropriate responses) in the majority of subjects under the low-dose training condition, but showed little or no substitution for cocaine under the high-dose training condition. The competitive NMDA antagonist [2R,4R,5S-(2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid)] did not substitute for cocaine under either training condition. Cocaine, 1-(2-[bis(4-fluorophenyl)methoxyl)-4-(3-phenylpropyl)piperazine, (+)-amphetamine and the D1 receptor agonist SKF 77434 engendered full substitution for cocaine under both training conditions. Dose-response functions for all four drugs were displaced to the left and average ED50 values were reduced by 3-fold or more under the low-dose compared to the high-dose training condition. The nonselective DA receptor agonist (-)-apomorphine substituted substantially for cocaine only under the low-dose training condition, whereas the D2 receptor agonist (+)-4-propyl-9-hydroxynapthoxazine substituted similarly for cocaine under both training conditions. The results show that change in the training dose of cocaine can affect both the shape and position of the dose-response functions for representative NMDA-associated ion channel blockers and direct and indirect dopamine agonists. The findings further show that under low-dose training conditions, NMDA-associated ion channel blockers can engender cocaine-like stimulus effects comparable to those of direct and indirect dopamine agonists.

Purkinje cell compartments in the reeler mutant mouse as revealed by Zebrin II and 90-acetylated glycolipid antigen expression

The cerebellum is organized into a series of parasagittally aligned bands that may be revealed histologically in the adult mouse by largely complementary immunostaining of Purkinje cells sets with the monoclonal antibodies Zebrin II (ZII; antigen:aldolase C) and P-path (PP; antigen:90-acetyl glycolipids). We compared the normal staining pattern using these markers and an antibody to calbindin with that found in the reeler mutants (rl/rl), in which most Purkinje cell migration is halted beneath the cerebellar white matter. The results revealed that Purkinje cells in reeler mutants, despite their ectopic location in large subcortical masses, show a clear tendency to distribute into alternating zones that either stain for Zebrin II or for P-path, with variable transition zones of mixed labeling. However, the estimated number of zones was fewer than in the normal adult cortex: roughly 7-9 zones are revealed per side in the mutant compared with 14 major divisions in wild type mice. These results raise the possibility that neurons destined to express these markers are segregated during their migration and that the final phase of migration into the cortex might involve further splitting or interdigitation between cell sets expressing the two antigens.

Effects of nervous mutation on Purkinje cell compartments defined by Zebrin II and 9-O-acetylated gangliosides expression

The cerebellum is organized into a series of parasagittally aligned bands which are well delineated in the adult mouse by the largely complementary immunostaining of Purkinje cell groups with the monoclonal antibodies Zebrin II (ZII; antigen: aldolase C) and P-path (antigen: 9-O-acetyl gangliosides). We examined the effect of nervous mutation on compartmental organization using these markers and an antibody to calbindin. In nervous mutant, up to 90% of Purkinje cells die in late postnatal development. The size of the cerebellum is about half that of normal, and caudal lobules appear to decrease in size more than anterior ones. Surviving Purkinje cells corresponded to P-path positive ones that were concentrated in two bilateral bands in the vermis and in medial portions of the hemispheres. Only small numbers of ZII positive cells remained, confirming the report by Wassef et al. with Zebrin I antibody. They were primarily located in caudal lobules IX, X and a portion of lobule IV, paraflocculus and flocculus, and their immunoreactivity was weak compared to that of normal. ZII positive cells are dominant in these caudal lobules, while P-path positive cells dominate in rostral lobules in normal mice, and the similar tendency remains in mutant. Thus, the nervous gene action respects not only sagittal compartments delineated by two antibodies, but also rostro-caudal gradient. The cause of the dominant survival of P-path positive cells awaits future study.

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.

Initial stages of retinofugal axon development in the hamster: evidence for two distinct modes of growth

In order to characterize differences in growth patterns of axons as they elongate toward their targets and during the initial stages of terminal arbor formation within the targets, we examined the primary visual system of fetal and newborn hamsters using three morphological methods: the Cajal-deCastro reduced silver method, the rapid Golgi technique, and anterograde transport of HRP. Axons emerge from the retina between the 10th and 11th embryonic days (E10-E11). The front of retinal axons crosses the chiasm, extends over the primitive dorsal nucleus of the lateral geniculate body (LGBd) by E13, and advances to the back of the superior colliculus (SC) by E13.5-E14. The rate of axon growth during this advance is nearly 2 mm/day. Collateral sprouts appear on axons around E15.5. In the LGBd and SC, these sprouts arise from multiple sites along the parent axons. Only one or a few of the sprouts continue to grow and branch, while others are eliminated. The net rate of axon collateral advance in this second phase is an order of magnitude slower than during the stage of axon elongation. Thus, formation of CNS projections may involve two qualitatively distinct modes of axon growth. The arborization mode contrasts with the elongation mode by the presence of branching, a lack of fasciculation and a slower average rate of extension. The stereotypic direct advance of axons during elongation also differs from the remodelling which occurs during arborization. The delay between axon arrival at targets and onset of arborization could be a reflection of axons "waiting" for a maturational change to occur in the retina or in targets. Arborization in the LGBd and SC is initiated around the same time, implicating the former possibility. However, a slower differentiation of retinal arbors in the SC, in addition to morphological differences of arbors in the two structures, suggests that alterations in substrate factors also play a critical role in triggering the early stages of arbor formation.

Organization of radial glia and related cells in the developing murine CNS. An analysis based upon a new monoclonal antibody marker

A monoclonal antibody, RC1, has been generated which provides a selective and sensitive immunohistochemical marker of radial glial cells and related cell forms during development of the mouse CNS. Beginning on embryonic day E10, immunocytochemistry performed on cryostat sections stains throughout the CNS a subpopulation of cells in the ventricular zone with radial processes that terminate with endfeet at the pial surface. These processes become fasciculated and attain maximal densities by E12-14 in the spinal cord and lower brainstem and by E14-16 in the midbrain, cerebellum and forebrain. Fasciculation is especially prominent for a subclass of these cells at the midline of the brainstem and spinal cord. As nuclear and cortical structures develop, the trajectories of the radial fiber fascicles undergo systematic and region-specific distortions in their initially simple linear configuration, in the process maintaining a consistent spatial registration of germinal ventricular zones with distal sites of assembly of post-migratory neurons. In the late fetal period, radial glial progressively disappear and scattered immature astrocytes bearing multiple fine processes appear in most regions of the CNS. In the spinal cord, a transitional unipolar radial form is identified in the emerging ventral and lateral funiculi between E13 and E17. In the cerebellum, precursors to the unipolar Bergmann glial cell are identified by E15, and in the retina, precursors of the bipolar Müller cell are identified by E16. Postnatally, RC1-stained radial glia become sparse, and after one week, immunoreactive cells include only ependymal cells, hypothalamic tanycytes, Bergmann glia, Müller cells, a unipolar radial form in the dentate gyrus, and a subpopulation of white matter astrocytes. These results suggest that radial cells of astroglial lineage comprise a diverse set of cell classes which subserve multiple functions in the developing and adult brain.

Early axonal differentiation in mouse CNS delineated by an antibody recognizing extracted neurofilaments

A monoclonal antibody, C2, raised against chick embryo spinal cord, is shown by a solid phase immunoabsorbent assay to recognize a molecular species associated with neurofilaments extracted from adult mouse and rat brain. As immunoreactivity is lost following pre-treatment with alkaline phosphatase, the antibody probably recognizes a phosphorylated protein. Immunocytochemical staining in fetal mouse indicates that this antigen is expressed selectively in axons from the earliest stages of their development. Neuronal somata tend to show only weak immunoreactivity. The C2 antibody allowed visualization of the spatiotemporal pattern of axonal growth in the retina, neocortex and cerebellum with greater resolution than in previous light microscopic descriptions. The concept that the leading process of some classes of migratory neurons becomes transformed into an axon is supported by the expression of C2 immunoreactivity in radially ascending processes from principle neuron classes in the fetal retina and cerebellum.

Identification of radial glial cells within the developing murine central nervous system: studies based upon a new immunohistochemical marker

The monoclonal antibody RC2 was generated in mouse by conventional hybridoma methodology. The antigen recognized by RC2 is robust, allowing aldehyde fixation appropriate to high resolution light and electron microscopic analyses. From the neural tube stage of fetal development the antibody delineates throughout the central nervous system a subpopulation of neuroepithelial cells which have a radial bipolar morphology. A descending process extends to the ventricular margin, and an ascending process contacts the glial limiting membrane by one or more endfeet varicosities. The persistence of these cells through the neurogenetic period allows their identification as radial glial. From as early as E9-10 the fibers appear to be organized in simple straight fascicles. Later in fetal development these fascicles show marked region-specific transformations in density and trajectory, particularly in association with cerebral corticogenesis and with cerebellar and basal ganglia development. The bipolar forms continue to stain with RC2 until they disappear in the postnatal period. Concurrently with a progressive perinatal loss of stained bipolar radial glia, RC2 identifies multipolar cell forms at various levels of the brain wall, as consistent with the transformation of radial glia into astrocytes. RC2 also recognizes monopolar cell forms in the spinal cord and the cerebellum as early as E15, and in the dentate gyrus of the hippocampal formation from the day of birth. Monopolar forms in the cerebellum are inferred to be progenitors of Bergmann glia. Although Bergmann glia are known to persist in adult life, these cells do not stain with RC2 beyond the 2nd postnatal week. The robustness of the antigen recognized by RC2 makes this probe a valuable tool to study the morphological transformations of the bipolar radial glia during their mitotic turnover. It also provides a sensitive stain for the study of the organization and the histogenetic role of the overall radial fiber system.

A practical approach to the investigation of amino acid disorders

We have, in this paper, highlighted some of the common problems in amino acid analysis in our experience and listed the possible causes for increases in specific amino acids in urine--together with guidance on appropriate follow-up investigations.

Mitotic cycling of radial glial cells of the fetal murine cerebral wall: a combined autoradiographic and immunohistochemical study

Radial glial cells of the embryonic murine cerebral wall are selectively labeled by staining with antibody RC1. In order to study the mitotic cycling of these cells, we combined RC1 immunohistochemistry and autoradiographic analysis following [3H]thymidine injection at 1, 2, 6, 48 h prior to sacrifice. Many radial glial cells, i.e. RC1-positive cells, incorporate the DNA tracer and hence must be mitotically active. Other proliferative cells of the ventricular zone do not stain with RC1. With the transition from S to M phase, the nuclei of the radial glial cells participate in the interkinetic 'to-and-fro' nuclear translocation characteristic of the non-radial glial cells of the ventricular zone. The density of radioactive grains over nuclei of both RC1-positive and negative cells of the ventricular zone becomes similarly reduced in the 48 h following the [3H]thymidine incorporation. Thus, the subpopulation of radial glia with nuclei within the ventricular zone which have incorporated the DNA tracer does not appear to become arrested in a prolonged G1 phase. The results suggest that the ventricular zone includes at least two subpopulations of stem cells, neuronal and radial glial. Radial glial cells, i.e. RC1-positive cells, are inferred to serve initially as a progenitor population for new radial glial cells. Later in development, they probably become a source of other cells of astroglial lineage.

Increased excretion of propan-1,3-diol and 3-hydroxypropionic acid apparently caused by abnormal bacterial metabolism in the gut

Three patients who died in infancy showed an unusual urinary organic acid pattern with excessive excretion of 3-hydroxypropionic acid but none of the other metabolites normally associated with propionyl-CoA carboxylase deficiency. Propan-1,3-diol was present in the urine in all three cases. In the two patients examined propionyl-CoA carboxylase activity was not deficient in cultured skin fibroblasts. A fourth patient, also severely ill, showed similar urinary abnormalities. Feeding a medium-chain triglyceride-rich diet to this patient increased the ratio of 3-hydroxypropionic acid to propan-1,3-diol and resulted also in the appearance of malonic acid in the urine. These abnormal metabolites disappeared on the administration of neomycin and presumably were produced by gut bacteria.

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.

Retinotectal projection in reeler mutant mice: relationships among axon trajectories, arborization patterns and cytoarchitecture

The distribution of axons in the midbrain and thalamus of homozygous reeler mutant mice is anomalous. The cytoarchitecture of these regions is normal. In the normal mouse SC there is a distinct SO in which fascicles of retinotectal axons pass caudally before terminating in the overlying SGS. In reeler, by contrast, fascicles of retinotectal axons are distributed through the entire thickness of SGS as well as through SO. There are also abnormalities of fiber pattern in the thalamus, most notably in the region of the dorsal nucleus of the LGd. Retinotectal axon trajectory and patterns of terminal arborization in reeler and normal animals were compared by single-fiber HRP axonography. In normal mice, two distinct morphological classes of retinotectal axons form focal terminal arborizations at different radial levels in the superficial layers of the SC. Class U axons are of relatively small diameter and terminate in upper portions of SGS. Class L1 axons are of larger diameter and form terminal arbors which are confined to SO and deeper regions of SGS. Axons of both classes ascend to their terminal zones from parent axons which course through SO. Similarly, in reeler mice axons of both large and small diameter can be distinguished. However, many axons of both classes pass caudally in anomalous fascicles distributed through the full thickness of SGS and descend to terminate. Other axons pass in normal fashion in SO and ascend to terminate in SGS. Regardless of their trajectories, the small axons terminate superficially in SGS while the thick axons terminate deeper in SGS and/or SO, as in normal mice. These findings suggest that the ingrowth of afferents and the formation of terminal arbors are regulated by different mechanisms and that fiber architecture and cytoarchitecture are regulated by different mechanisms. It is not known if the anomalous fiber pattern in reeler adults arises in development through a defect in initial patterns of axon fasciculation or from a failure of axon elimination.

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.

Diurnal change in refraction, corneal curvature, visual acuity, and intraocular pressure after radial keratotomy in the PERK Study

Selected patients who complained of fluctuating visual acuity in the Prospective Evaluation of Radial Keratotomy (PERK) Study were examined before 8:00 a.m. and after 7:00 p.m. on the same day to determine diurnal change in uncorrected visual acuity, best corrected visual acuity, manifest refractive error, average central keratometric power, and intraocular pressure. Sixty-three operated eyes were examined at three months, while 46 operated and 40 unoperated contralateral eyes were examined at one year after radial keratotomy. One year after surgery, 42% of the operated eyes had an increase in minus power of the manifest refraction of 0.50 to 1.25 diopters, 26% of the eyes changed their uncorrected visual acuity by 2 to 4 Snellen lines, and 35% of the operated eyes showed central steepening of the cornea by 0.50 to 1.25 diopters. These changes in the operated eyes at one year were similar to the changes at three months. Minimal diurnal changes occurred in the unoperated eyes at one year. Only 11% of the unoperated eyes changed their manifest refraction by 0.50 to 1.00 diopters, none changed their uncorrected visual acuity by 2 to 4 Snellen lines, and only one of the unoperated eyes changed its central keratometric power by 0.50 diopters. This study documents that many patients who experience diurnal fluctuation of vision have steepening of the cornea and an increase in the minus power of their refraction during the day.

Glutaric aciduria type I misdiagnosed as Leigh's encephalopathy and cerebral palsy

Two cases are reported of boys who suffer epileptic seizures only after playing video games. It is suggested that the amount of time the patient spends in front of the screen before the seizure is important, and also that video games trigger electrocortical activity far more efficiently than either television or intermittent photic stimulation.

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.

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.

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.

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%.

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.

Cobalt staining of Actinia equina nematocysts

Nematocysts of Actinia equina are stained black by incubation in 2% CoCl2 followed by an aqueous wash and H2S treatment. They are also stained positively by morin. Nematocysts isolated from the acrorhage were found to have a high concentration of calcium of which only 30% was "free." It is suggested that the high concentration of calcium in the nematocysts accounts for their staining by cobalt and morin. Cobalt staining offers a simple and effective technique for investigation of nemotocysts.

Mechanical properties of semipermeable microcapsules

A study has been made of the mechanical properties of the membrane of semipermeable nylon microcapsules containing erythrocyte hemolysate. The use of a "cell elastimeter" and the application of Laplace's Law have shown that the nylon membrane has very high resistance to stretching, but only negligible resistance to bending. The membrane tension in undeformed microcapsules has been determined to be 1840 dynes/cm and observed to increase with deformation, indicating elastic properties in the membrane. At a tension of 2520 dynes/cm, resistance to stretching is sharply reduced. The results indicate that the internal pressure varies directly as the reciprocal of microcapsule radius, and an extrapolation of these results, assuming that the relation holds for very small capsules, yields an internal pressure of 4.3 × 106 dynes/cm2 for a microcapsule of erythrocyte diameter. Any stretch in the nylon membrane has been shown to be almost irreversible. The diameter of the smallest pipette through which a spherical microcapsule can pass without suffering irreversible change has been found to be no smaller than 90% of the microcapsule diameter, and the pressure required is of the order of 105 dynes/cm2.

The role of arteriovenous anastomoses in cold-induced vasodilation, rewarming, and reactive hyperemia as determined by 24Na clearance

The rate of removal of24Na from a deposit in the rabbit's foot was used to determine the degree of involvement of arteriovenous anastomoses in the blood flow of cold-induced vasodilation, in the rewarming following intense vasoconstriction, and in reactive hyperemia. The results indicate that in the first two cases the total flow is through the arteriovenous anastomoses. In reactive hyperemia an initial flow which is partly capillary and partly through the anastomoses gives way to a flow which is entirely through the anastomoses.