The feasibility of well-logging measurements of arsenic levels using neutron-activation analysis.

Arsenic is an extremely toxic metal, which poses a significant problem in many mining environments. Arsenic contamination is also a major problem in ground and surface waters. A feasibility study was conducted to determine if neutron-activation analysis is a practical method of measuring in situ arsenic levels. The response of hypothetical well-logging tools to arsenic was simulated using a readily available Monte Carlo simulation code (MCNP). Simulations were made for probes with both hyperpure germanium (HPGe) and bismuth germanate (BGO) detectors using accelerator and isotopic neutron sources. Both sources produce similar results; however, the BGO detector is much more susceptible to spectral interference than the HPGe detector. Spectral interference from copper can preclude low-level arsenic measurements when using the BGO detector. Results show that a borehole probe could be built that would measure arsenic concentrations of 100 ppm by weight to an uncertainty of 50 ppm in about 15 min.

Potassium-dependent prolonged field bursts in the dentate gyrus: effects of extracellular calcium and amino acid receptor antagonists.

The dentate gyrus in rat hippocampal slices produces spontaneous, prolonged bursts of population spikes (i.e. prolonged field bursts) when [Ca2+]0 is lowered (0-0.5 mM) and [K+]0 is concurrently elevated (9-11 mM). In this investigation we examined whether the dentate gyrus could also generate spontaneous field bursts in relatively "normal" (i.e. nominal 1.3 mM) or only moderately decreased [Ca2+]0 (i.e. nominal 0.9 mM). In 1.3 mM [Ca2+]0, no prolonged field bursts occurred spontaneously in the dentate gyrus when [K+]0 was raised as high as 12 mM. Prolonged field bursts were generated, however, when [K+]0 was further increased to 13-15 mM. Similar bursts could be generated at [K+]0 within the "physiological ceiling level" observed in vivo during seizure activity (i.e. 11-12 mM) if: (i) the bath [Ca2+] was reduced to 0.9 mM; or (ii) the GABA type A-receptor antagonist bicuculline was added in the presence of "normal" (1.3 mM) [Ca2+]0. Adding both the N-methyl-D-aspartate and non-N-methyl-D-aspartate receptor antagonists, (+/-)-2-amino-5-phosphonopentanoic acid (50-100 microM) and 6,7-dinitroquinoxaline-2,3-dione (50-100 microM), respectively, did not block the occurrence of the field bursts. The bursts generated in 1.3 mM [Ca2+]0, 12 mM [K+]0, bicuculline, (+/-)-2-amino-5-phosphonopentanoic acid and 6,7-dinitroquinoxaline-2,3-dione could, however, be reversibly depressed or blocked if [Ca2+]0a was raised to 2.0 mM.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple-unit recordings during slow field-potential shifts in low-[Ca2+]0 solutions in rat hippocampal and cortical slices.

Multiple-unit and field-potential recordings in low-[Ca2+]0 solutions were used to study epileptiform bursts generated in hippocampal region CA1 and medial entorhinal cortex, a cortical region that is not as densely packed or highly laminated as the hippocampus. As expected in CA1, multiple-unit activity appeared as large spikes that corresponded one-to-one with population spikes in the field-potential recordings. During the negative field-potential shifts that lacked large population spikes, the multiple-unit recordings showed an increase in baseline activity. Initiation of the negative field-potential shift always coincided with increased multiple-unit activity. Slices displaying a post-burst positive overshoot showed a corresponding decrease in multiple-unit activity. In addition to the large ictal-like events in CA1, small-amplitude field-potential shifts were also observed, these events were associated with increases in baseline spike activity in the multiple-unit recording. These small-amplitude field-potential shifts appeared to precede the occurrence of the ictal-like events, but they decreased in frequency during low-[Ca2+]0 exposure. Recordings in normal artificial cerebrospinal fluid (nominally 1.3 mM [Ca2+]0) showed rhythmic, multiple-unit bursts of action potentials and corresponding negative small-amplitude field-potential shifts in the medial entorhinal cortex of immature rats (two-to three-weeks old), but not of adult rats. Rhythmic, spontaneous bursts of activity in low-[Ca2+]0 solution were found in both immature and adult medial entorhinal cortex, and were similar in amplitude to the small field-potential events generated in CA1. The probability of burst generation was higher in the immature than the adult medial entorhinal cortex, and the bursts in the immature cortex had more robust multiple-unit activity and an increased burst frequency compared with adult. These results indicate that the medial entorhinal cortex can also generate spontaneous synchronous bursts of activity in low-[Ca2+]0 solutions, and they suggest that the increased susceptibility of medial entorhinal cortex from immature versus adult rats to generate intense bursts of electrical activity does not require active chemical synaptic transmission. The various forms of epileptiform activity in low-[Ca2+]0 solutions probably arise from different contributions of electrical and ionic mechanisms of synchronization in these neuronal populations. The data suggest the hypothesis that ionic mechanisms (i.e. changes in [K+]0) may synchronize neurons in cortical regions (e.g. entorhinal cortex) that are not as densely packed and highly laminated as the hippocampus and dentate gyrus. The data also support the hypothesis that these mechanisms contribute significantly to the increased seizure susceptibility of the immature brain.

Effects of norepinephrine on rat neocortical neurons in dissociated cell culture.

Intracellular recordings were made from neurons in dissociated cell culture of neocortex during application of norepinephrine (NE) or other adrenergic agonists. In the population of neurons generally studied, greater than 18 micron in diameter, adrenergic agonists from 1 nM to 50 microM produced no change in membrane potential or input resistance 120 cells). Adrenergic agonists increased synaptic activity impinging on the impaled cell in 25/120 neurons (21%). In neurons in cocultures of locus coeruleus and cerebral cortex, again the same synaptic response to perfusion with NE was noted in 13/93 neurons (14%). In addition, direct effects of NE were noted on 6/93 neurons recorded from in cocultures, all close to the explant. In these cells, NE hyperpolarized the membrane in association with a small decrease in input resistance (11%). These responsive cells may have originated within the explant. A paradigm was used for testing the possibility of a responsive element in the cultures distinct from the impaled soma. 'Hot spots' were found using concentrations of isoproterenol as low as 10 nM.

Immunoreactive thymopoietin in the mouse central nervous system.

A thymopoietin-immunoreactive substance (TP-IRS) has been detected in homogenates of mouse spinal cord and brain using a radioimmunoassay; levels were maximal at birth. TP-IRS was also detected in supernatants of mouse neuroblastoma (NIE-115) and primary spinal cord cultures but not human astrocytic and meningeal tumors or mouse primary astrocyte cultures. With affinity purified rabbit anti-TP globulin, immunofluorescent staining was seen in mouse spinal cord cultures in association with nuclear membranes of neurons and, to a lesser degree, flat background cells. From supernatants of NIE-115 cells grown in tritiated leucine and lysine, proteins of approximately 8000 and 4500 Da were isolated by TP affinity chromatography (compared with 5562 Da for thymic thymopoietin). When injected into mice, these neural proteins partially blocked neuromuscular transmission in a manner similar to thymic thymopoietin.

Ependymoma of the cauda equina region: diagnosis, treatment, and outcome in 15 patients.

New diagnostic imaging techniques make possible a reappraisal of current diagnostic, therapeutic, and management strategies for certain rare lesions of the central nervous system. With this in mind, we have reviewed our experience with ependymoma of the filum terminale and cauda equina region. Fifteen patients with this tumor have been treated since 1955. Typical presentations included pain, lower extremity weakness, and, occasionally, bladder dysfunction. Delays in arriving at the proper diagnosis have been the rule; however, we have noted a substantial increase in the number of these tumors referred to us since the advent of magnetic resonance imaging. Treatment includes surgical resection to the extent consistent with preservation of neurological function; postoperative irradiation appears to be of benefit in controlling recurrence except in those patients whose well-circumscribed tumors have been removed completely. Presence of urinary difficulties at the time of diagnosis is a relatively poor prognostic sign, and a more liberal use of magnetic resonance imaging in cases of persistent or recurrent low back and radicular pain unresponsive to conservative therapy may help to achieve earlier diagnosis. Because of the possibility of late recurrence, prolonged follow-up is mandatory for all patients, and magnetic resonance imaging is the diagnostic tool of choice.

Abnormal responses to perforant path stimulation in the dentate gyrus of slices from rats with kainate-induced epilepsy and mossy fiber reorganization.

Previous electrophysiological studies have demonstrated that in a subset of hippocampal slices from tissue resected from patients with mesial temporal lobe epilepsy, perforant path stimulation can elicit prolonged negative field-potential shifts in the dentate granule cell layer (Masukawa et al., 1989. Brain Res. 493, 168-174; Isokawa and Fried, 1996. Neuroscience 72, 31-37). In this investigation, hippocampal slices were prepared from rats: (1) 2-4 days following kainate treatment, when little or no reorganization of the mossy fibers would be present and (2) 3-13 months after kainate treatment, when mossy fiber reorganization would have occurred. In saline-treated controls, perforant path stimulation typically evoked a single population spike. In contrast, perforant path stimulation could evoke 3-12 population spikes in nearly all slices from kainate-injected rats 2-4 days and 3-13 months after treatment. The majority of slices from kainate-injected rats 3-13 months after treatment had qualitatively similar responses to perforant path stimulation as that observed in slices from kainate-injected rats 2-4 days after treatment. However, in 17% of the slices from kainate-treated rats 3-13 months after treatment (29% of rats), the multiple population spikes were followed by a prolonged negative field-potential shift (duration: 140 ms-1.5 s) with variable superimposed population spike activity. This type of epileptiform activity was only observed in slices with robust Timm's staining in the inner molecular layer and similar responses could also be evoked in these slices with hilar stimulation. Furthermore, pharmacological depression of inhibition by adding the GABA(A) receptor antagonist bicuculline unmasked hilar-evoked prolonged negative field-potential shifts in most slices from kainate-treated rats 3-13 months following treatment, and these slices had robust Timm's staining in the inner molecular layer. Such events were not observed in slices from saline-treated controls or kainate-injected rats 2-4 days after treatment. In conclusion, the prolonged negative field-potential shifts evoked to perforant path stimulation in normal ACSF were associated with mossy fiber reorganization, but the relative contribution of altered inhibition, increased synaptic excitation, or even non-synaptic mechanisms is unknown.

Treatment of progressive cervical spinal instability secondary to hydatid disease. A case report.

STUDY DESIGN: A case report of a patient with progressive cervical spinal instability secondary to hydatid disease and the operative therapy. OBJECTIVE: To document how the combination of contemporary imaging, medical, and operative methods has obviated severe neurologic sequelae in a patient's cervical spine ravaged by hydatidosis. SUMMARY OF BACKGROUND DATA: The incidence of hydatid disease in the vertebral column is unusual and rare in the cervical spine. Until recently, patients with spinal hydatid disease have had guarded prognoses, because the various medical and surgical therapies could not effect curative or even palliative results. METHODS: The use of contemporary imaging methods, including computed tomography and magnetic resonance imaging, is described, in conjunction with current anthelminthic therapy and operative spinal instrumentation in this patient with recurrent quadriparesis from progressive hydatid spinal erosion. RESULTS: With the operative and medical therapies described in this case report, the patient has had six successful operative results in 6 years for cervical spinal hydatidosis and remains neurologically normal, with a stable cervical spine. CONCLUSIONS: It is hoped that this case presentation will justify a spirit of guarded optimism in the patient whose spine has been rendered unstable by hydatid disease and that, though a cure is still not likely, at least the past inexorable prognosis of paralysis and death is ameliorated.

Heavy ion beam measurement of the hydration of cementitious materials.

The setting and development of strength of Portland cement concrete depends upon the reaction of water with various phases in the Portland cement. Nuclear resonance reaction analysis (NRRA) involving the (1)H((15)N,alpha,gamma)(12)C reaction has been applied to measure the hydrogen depth profile in the few 100 nm thick surface layer that controls the early stage of the reaction. Specific topics that have been investigated include the reactivity of individual cementitious phases and the effects of accelerators and retarders.

Relationship between synaptic activity and prolonged field bursts in the dentate gyrus of the rat hippocampal slice.

1. Previous studies in the dentate granule cell layer of the rat hippocampal slice have demonstrated that nonsynaptic, seizurelike prolonged field bursts occur in conditions of low extracellular Ca2+ concentration ([Ca2+]o) and elevated [K+]o. We hypothesize that the extracellular ion concentration changes induced by synaptic activation of dentate granule cells would be sufficient to initiate these nonsynaptic bursts. 2. Using ion-selective electrode recording, we observed large changes in [Ca2+]o (from 1.3 mM baseline to approximately 0.7 mM) and [K+]o (from 3.5 to approximately 12 mM) in the dentate granule cell layer during repetitive electrical stimulation of the perforant path in rat hippocampal slices. Concomitant with these changes, bursts of population spikes similar to those seen during spontaneous prolonged field bursts appeared between the individual stimulus-evoked responses in the dentate gyrus in many of the slices studied (19 of 27). 3. Blockade of N-methyl-D-aspartate (NMDA), non-NMDA, and gamma-aminobutyric acid-A (GABAA)-mediated synaptic transmission during perforant path stimulation resulted in a marked reduction of the ion concentration changes and a loss of both stimulus-evoked and stimulus-independent population spikes in the dentate gyrus. 4. When slices were perfused with solutions containing [Ca2+]o and [K+]o equivalent to those measured during perforant path stimulation (i.e., 0.7 and 12 mM, respectively), spontaneous prolonged field bursts appeared in the dentate gyrus. Addition of NMDA, non-NMDA, and GABAA receptor antagonists did not prevent the occurrence of these spontaneous bursts. 5. We conclude that changes in [Ca2+]o and [K+]o sufficient to produce prolonged field bursts may be created in the dentate granule cell layer by perforant path stimulation. These effects are dependent on synaptic transmission. Once these ionic conditions occur, they are sufficient to trigger prolonged field bursts independent of fast amino-acid-mediated synaptic transmission. A similar mechanism could be important during the interictal-ictal transition in vivo.

Prolonged field bursts in the dentate gyrus: dependence on low calcium, high potassium, and nonsynaptic mechanisms.

1. The dentate gyrus has been proposed to be a gate for entry of neuronal activity into the hippocampus. This function would give it a critical role in the propagation of seizure activity in that region. The hallmark of epileptiform activity in the dentate itself, often referred to as "maximal dentate activation" (MDA), has not been reproduced previously in vitro. 2. With the use of rat hippocampal slices, bath [Ca2+] was decreased, and [K+] was increased concurrently to simulate conditions found during intense neuronal activity in vivo. Both evoked and spontaneous field bursts were observed in the dentate granule cell layer under these conditions. These bursts were similar to MDA, consisting of a prolonged negative shift in extracellular potential with large-amplitude population spikes. 3. In 0.5 mM bath [Ca2+], single stimuli applied to the perforant path could evoke prolonged field bursts in the dentate only when bath [K+] was > or = 9 mM. However, repetitive stimulation (10 Hz) of the perforant path could elicit similar dentate responses when bath [K+] was as low as 5 mM. 4. In 0.5 mM bath [Ca2+], interictal-type bursts appeared spontaneously in CA1 and CA3 when bath [K+] was > or = 5 mM but were lost when [K+] was > 9 mM. Spontaneous seizurelike activity in the dentate required a higher minimum bath [K+] (9 mM) and persisted at [K+] of 11 mM. 5. Stimulation-evoked field bursts in the dentate altered epileptiform activity in CA3. At bath [K+] insufficient to cause spontaneous CA3 bursts, CA3 was activated transiently when prolonged field bursts occurred in the dentate. At higher bath [K+] in which spontaneous CA3 bursts did occur, they were depressed during the dentate bursts. 6. Deletion of Ca2+ from the bath; the addition of 30 microM each of bicuculline methiodide, D,L-2-amino-5-phosphonopentanoate (AP-5), and 6,7-dinitroquinoxaline-2,3-dione (DNQX); or the combination of both manipulations did not block antidromically evoked or spontaneous prolonged field bursts in the dentate. Thus the mechanisms maintaining and propagating these events did not require fast amino acid-mediated synaptic transmission. 7. The concurrent alteration of [K+] and [Ca2+] required to produce prolonged field bursts in the dentate underscores the positive feedback relationship between neuronal excitation and extracellular ionic concentrations, whereas the ability of synaptic stimulation to trigger nonsynaptic seizurelike events such as these prolonged field bursts may be relevant to the transition from interictal to ictal activity in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)

Fibroblasts modulate expression of Thy-1 on the surface of skeletal myoblasts.

Thy-1 antigen is a well-characterized cell-surface glycoprotein known to be variably expressed in many different tissues, including lymphocytes, brain, and muscle. Its function remains unknown. In skeletal muscle, both in vivo and in vitro, the antigen has been reported on immature but not on adult tissue, and its disappearance corresponds roughly to the time of myoblast fusion. Using monoclonal H36 antibody to identify myoblasts unambiguously, we demonstrate here that Thy-1 is expressed only on a small (less than 1%) fraction of rat skeletal muscle myoblasts in heterogeneous primary cultures, but the number of myoblasts that express Thy-1 rises to a steady level of about 70% when fibroblasts are removed from secondary cultures. Restitution of fibroblasts or growth of purified myoblasts in medium conditioned by fibroblasts greatly suppresses this increase in myoblast Thy-1 expression. Thus an interaction between fibroblasts and myoblasts, mediated by a soluble nondialyzable molecule, modulates expression of Thy-1 on the myoblast outer membrane.

Differential expression and modulation of Thy-1 on myoblast clones.

In the preceding paper [J. S. Schweitzer, M. A. Dichter, and S. J. Kaufman, 1987, Exp. Cell Res. 172, 1] we demonstrated that expression of Thy-1 antigen by rat skeletal muscle myoblasts in culture is modulated by fibroblasts. Growth of myoblasts with myofibroblasts, or in medium in which fibroblasts have been grown, causes a sharp reduction in the percentage of myoblasts that express Thy-1 antigen on their membrane. In this paper we demonstrate that there are two populations of myoblasts that can be distinguished by their capacity to respond to the Thy-1-modulating factor (TMF). The majority of Thy-1-positive or -negative myoblasts grown at clonal densities are responsive to TMF. A second myoblast clonal type is Thy-1 positive and fuses to form contractile myotubes, but is insensitive to TMF and has a more fibroblast-like morphology. These clonal phenotypes are stable upon passage in vitro and may represent distinct subsets of the myogenic lineage.

pH Sensitivity of non-synaptic field bursts in the dentate gyrus.

Under conditions of low [Ca(2+)](o) and high [K(+)](o), the rat dentate granule cell layer in vitro develops recurrent spontaneous prolonged field bursts that resemble an in vivo phenomenon called maximal dentate activation. To understand how pH changes in vivo might affect this phenomenon, the slices were exposed to different extracellular pH environments in vitro. The field bursts were highly sensitive to extracellular pH over the range 7.0-7.6 and were suppressed at low pH and enhanced at high pH. Granule cell resting membrane potential, action potentials, and postsynaptic potentials were not significantly altered by pH changes within the range that suppressed the bursts. The pH sensitivity of the bursts was not altered by pharmacologic blockade of N-methyl-D-aspartate (NMDA), non-NMDA, and GABA(A) receptors at concentrations of these agents sufficient to eliminate both spontaneous and evoked synaptic potentials. Gap junction patency is known to be sensitive to pH, and agents that block gap junctions, including octanol, oleamide, and carbenoxolone, blocked the prolonged field bursts in a manner similar to low pH. Perfusion with gap junction blockers or acidic pH suppressed field bursts but did not block spontaneous firing of single and multiple units, including burst firing. These data suggest that the pH sensitivity of seizures and epileptiform phenomena in vivo may be mediated in large part through mechanisms other than suppression of NMDA-mediated or other excitatory synaptic transmission. Alterations in electrotonic coupling via gap junctions, affecting field synchronization, may be one such process.

The pathology of arteriovenous malformations of the brain treated by embolotherapy. II. Results of embolization with multiple agents.

Light microscopic and immunohistochemical examination was undertaken of intracranial arteriovenous malformations (AVMs) surgically resected from 18 patients, each of whom had undergone preoperative angiographic embolization with multiple agents. Distinct patterns of tissue reaction to these agents were noted, even when more than one substance was present in a vascular lumen. Avitene produced the mildest tissue response but resulted in relatively early endothelialization and recanalization. Cyanoacrylates were longer-lasting but associated with more acute and chronic (including granulomatous) inflammation and vessel wall changes. Polyvinyl alcohol foam/ethanol mixture had intermediate properties. Endothelial proliferation over embolization material was confirmed using immunohistochemical application of an antibody to cell proliferation-specific proteins. The significance of these findings for combined endovascular and surgical treatment of cerebral vascular malformations is discussed.