Dense arrays of micro-needles for recording and electrical stimulation of neural activity in acute brain slices

OBJECTIVE

This paper describes the design, microfabrication, electrical characterization and biological evaluation of a high-density micro-needle array. The array records from and electrically stimulates individual neurons simultaneously in acute slices of brain tissue.

APPROACH

Acute slices, arguably the closest in-vitro model of the brain, have a damaged surface layer. Since electrophysiological recording methods rely heavily on electrode-cell proximity, this layer significantly attenuates the signal amplitude making the use of traditional planar electrodes unsuitable. To penetrate into the tissue, bypassing the tissue surface, and to record and stimulate neural activity in the healthy interior volume of the slice, an array of 61 micro-needles was fabricated.

MAIN RESULTS

This device is shown to record extracellular action potentials from individual neurons in acute cortical slices with a signal to noise ratio of up to ∼15:1. Electrical stimulation of individual neurons is achieved with stimulation thresholds of 1.1-2.9 µA.

SIGNIFICANCE

The novelty of this system is the combination of close needle spacing (60 µm), needle heights of up to 250 µm and small (5-10 µm diameter) electrodes allowing the recording of single unit activity. The array is coupled to a custom-designed readout system forming a powerful electrophysiological tool that permits two-way electrode-cell communication with populations of neurons in acute brain slices.

Photovoltaic retinal prosthesis: implant fabrication and performance

The objective of this work is to develop and test a photovoltaic retinal prosthesis for restoring sight to patients blinded by degenerative retinal diseases. A silicon photodiode array for subretinal stimulation has been fabricated by a silicon-integrated-circuit/MEMS process. Each pixel in the two-dimensional array contains three series-connected photodiodes, which photovoltaically convert pulsed near-infrared light into bi-phasic current to stimulate nearby retinal neurons without wired power connections. The device thickness is chosen to be 30 µm to absorb a significant portion of light while still being thin enough for subretinal implantation. Active and return electrodes confine current near each pixel and are sputter coated with iridium oxide to enhance charge injection levels and provide a stable neural interface. Pixels are separated by 5 µm wide trenches to electrically isolate them and to allow nutrient diffusion through the device. Three sizes of pixels (280, 140 and 70 µm) with active electrodes of 80, 40 and 20 µm diameter were fabricated. The turn-on voltages of the one-diode, two-series-connected diode and three-series-connected diode structures are approximately 0.6, 1.2 and 1.8 V, respectively. The measured photo-responsivity per diode at 880 nm wavelength is ∼0.36 A W(-1), at zero voltage bias and scales with the exposed silicon area. For all three pixel sizes, the reverse-bias dark current is sufficiently low (<100 pA) for our application. Pixels of all three sizes reliably elicit retinal responses at safe near-infrared light irradiances, with good acceptance of the photodiode array in the subretinal space. The fabricated device delivers efficient retinal stimulation at safe near-infrared light irradiances without any wired power connections, which greatly simplifies the implantation procedure. Presence of the return electrodes in each pixel helps to localize the current, and thereby improves resolution.

Photodiode circuits for retinal prostheses

Photodiode circuits show promise for the development of high-resolution retinal prostheses. While several of these systems have been constructed and some even implanted in humans, existing descriptions of the complex optoelectronic interaction between light, photodiode, and the electrode/electrolyte load are limited. This study examines this interaction in depth with theoretical calculations and experimental measurements. Actively biased photoconductive and passive photovoltaic circuits are investigated, with the photovoltaic circuits consisting of one or more diodes connected in series, and the photoconductive circuits consisting of a single diode in series with a pulsed bias voltage. Circuit behavior and charge injection levels were markedly different for platinum and sputtered iridium-oxide film (SIROF) electrodes. Photovoltaic circuits were able to deliver 0.038 mC/cm(2) (0.75 nC/phase) per photodiode with 50- μm platinum electrodes, and 0.54-mC/cm(2) (11 nC/phase) per photodiode with 50-μ m SIROF electrodes driven with 0.5-ms pulses of light at 25 Hz. The same pulses applied to photoconductive circuits with the same electrodes were able to deliver charge injections as high as 0.38 and 7.6 mC/cm(2) (7.5 and 150 nC/phase), respectively. We demonstrate photovoltaic stimulation of rabbit retina in-vitro, with 0.5-ms pulses of 905-nm light using peak irradiance of 1 mW/mm(2). Based on the experimental data, we derive electrochemical and optical safety limits for pixel density and charge injection in various circuits. While photoconductive circuits offer smaller pixels, photovoltaic systems do not require an external bias voltage. Both classes of circuits show promise for the development of high-resolution optoelectronic retinal prostheses.

Host and parasite factors influencing the expression of cutaneous leishmaniasis

Host and parasite factors influencing the expression of cutaneous leishmaniasis were investigated in two murine models of different leishmanial diseases. The role of B lymphocytes in the uncontrolled disease manifested by BALB/c mice infected with cutaneous leishmaniasis was investigated in animals of this inbred strain depleted of B cells by neonatal administration of anti-mouse mu-chain antisera. Whereas non-depleted control mice developed chronic metastatic infections with both Leishmania tropica and Leishmania mexicana and showed depressed delayed-type hypersensitivity when skin-tested with leishmanial antigens, the mu-suppressed mice controlled their initial lesions while displaying strong antigen-specific delayed-type hypersensitivity. These findings reveal an inverse relationship between humoral and cell-mediated immunity in the expression of chronic leishmaniasis and suggest that B lymphocytes or their products regulate the delayed-type hypersensitivity response to leishmanial infection. In a separate study, healing and chronic strains of Leishmania were compared for their susceptibility to killing by lymphokine-activated mouse peritoneal macrophages. Whereas amastigotes of the healing strains were readily destroyed by these macrophages, amastigotes of two Leishmania strains, previously shown to produce chronic infections in mice, were resistant to killing by the same cells. These findings suggest that the ability of certain leishmanial strains to induce chronic disease may result from their capacity to evade intracellular destruction by activated macrophages.

Induction and regulation of host cell-mediated immunity by Toxoplasma gondii

Toxoplasma gondii is a highly infectious intracellular parasite which, if left unchecked by the immune system, rapidly overwhelms its intermediate hosts, as illustrated by the pathogenesis of toxoplasmic encephalitis in patients with AIDS. In order to insure both its host's and consequently its own survival simultaneously, T. gondii induces a potent gamma-interferon (IFN-gamma)-dependent cell-mediated immunity early in infection that controls the replication of the protozoan and facilitates transformation into the dormant cyst stage. The protective IFN-gamma is derived from three sources: natural killer cells; and CD4+ and CD8+ T lymphocytes, which can partially compensate for each other in knockout mice lacking the appropriate major histocompatibility complex-restricting elements. At least two properties of the parasite appear to be responsible for the early induction of these effector cells. The first is a hydrophobic molecule (or group of related molecules) that triggers interleukin 12 (IL-12), tumour necrosis factor alpha and IL-1beta synthesis in macrophages. This response can also promote HIV replication in the same cells. The second is a superantigen activity that drives IFN-gamma-producing Vbeta5+ CD8+ T cells. These potentially lethal responses are later regulated through the triggering of IL-10 and by the induction of anergy in the superantigen-stimulated Vbeta5+ T cell population.

Sepsis-induced organ failure is mediated by different pathways in the kidney and liver: acute renal failure is dependent on MyD88 but not renal cell apoptosis

Toll-like receptors (TLRs) are important in sepsis. Myeloid differentiation factor 88 (MyD88) is a key molecule involved in signal transduction by multiple TLRs. The objective of this study was to investigate the contribution of TLR4 and MyD88 to acute renal failure (ARF) induced by polymicrobial sepsis. Liver dysfunction and apoptosis in the spleen contribute to sepsis severity after cecal ligation and puncture (CLP). Therefore, we also investigated liver injury and splenic apoptosis. We used a mouse model of sepsis-induced ARF using CLP to generate polymicrobial sepsis. Despite fluid and antibiotic resuscitation the mice developed multi-organ failure, including ARF, which resembles human sepsis. We investigated the role of the TLR4 receptor by comparing C3H/HeJ mice (which lack TLR4) with C3H/He0UJ normal controls. The role of MyD88 was investigated by comparing MyD88 knockout mice (MyD88(-/-)) with wild-type controls. Following CLP, mice lacking TLR4 and wild-type mice both developed comparable ARF. However, MyD88(-/-) mice did not develop ARF compared to wild-type controls. In contrast, MyD88(-/-) mice developed liver injury comparable to wild type. After CLP, MyD88(-/-) mice had significantly reduced apoptosis in the spleen compared with wild type. Apoptosis was not detected in the kidney of wild-type or MyD88(-/-) mice after CLP. In summary, ARF induced by polymicrobial sepsis is dependent on MyD88, but not TLR4. The absence of MyD88 dissociates ARF from liver injury; liver injury is MyD88-independent. There was MyD88-dependent apoptosis in the spleen, but no apoptosis in the kidney. MyD88 may be a good drug target for some, but not all, organ dysfunctions following sepsis.

Fidelity of the ensemble code for visual motion in primate retina

Sensory experience typically depends on the ensemble activity of hundreds or thousands of neurons, but little is known about how populations of neurons faithfully encode behaviorally important sensory information. We examined how precisely speed of movement is encoded in the population activity of magnocellular-projecting parasol retinal ganglion cells (RGCs) in macaque monkey retina. Multi-electrode recordings were used to measure the activity of approximately 100 parasol RGCs simultaneously in isolated retinas stimulated with moving bars. To examine how faithfully the retina signals motion, stimulus speed was estimated directly from recorded RGC responses using an optimized algorithm that resembles models of motion sensing in the brain. RGC population activity encoded speed with a precision of approximately 1%. The elementary motion signal was conveyed in approximately 10 ms, comparable to the interspike interval. Temporal structure in spike trains provided more precise speed estimates than time-varying firing rates. Correlated activity between RGCs had little effect on speed estimates. The spatial dispersion of RGC receptive fields along the axis of motion influenced speed estimates more strongly than along the orthogonal direction, as predicted by a simple model based on RGC response time variability and optimal pooling. on and off cells encoded speed with similar and statistically independent variability. Simulation of downstream speed estimation using populations of speed-tuned units showed that peak (winner take all) readout provided more precise speed estimates than centroid (vector average) readout. These findings reveal how faithfully the retinal population code conveys information about stimulus speed and the consequences for motion sensing in the brain.

High statistics measurement of the K+-->pi0e+nu (K+e3) branching ratio

E865 at the Brookhaven National Laboratory AGS collected about 70 000 K(+)(e3) events to measure the K(+)(e3) branching ratio relative to the observed K+-->pi(+)pi(0), K+-->pi(0)micro(+)nu, and K+-->pi(+)pi(0)pi(0) decays. The pi(0) in all the decays was detected using the e(+)e(-) pair from pi(0)-->e(+)e(-)gamma decay and no photons were required. Using the 2002 Particle Data Group branching ratios for the normalization decays, we obtain BR(K(+)(e3(gamma)))=(5.13+/-0.02(stat)+/-0.09(syst)+/-0.04(norm))%, where K(+)(e3(gamma)) includes the effect of virtual and real photons. This result is approximately 2.3sigma higher than the current Particle Data Group value. Implications for the V(us) element of the CKM matrix, and the matrix's unitarity are discussed.

Modified Giemsa staining for rapid diagnosis of malaria infection

OBJECTIVES

To develop and evaluate a rapid method for the diagnosis of malaria infection by microscopy of stained blood films.

SUBJECTS AND METHODS

Blood specimens were collected from randomly selected confirmed malaria cases (n = 75) and suspected malaria cases (n = 175). The microscopy was done on each set of blood films stained by modified and the standard Giemsa staining methods.

RESULTS

All the 75 previously diagnosed malaria cases were confirmed by the microscopy of blood films stained by both methods. Forty-nine (28%) of the 175 cases suspected for malaria infection showed malarial parasites on microscopy of blood films stained by both methods. However, due to homogeneous staining and clearer background of the blood films it was possible to determine the parasite species in 65% of the cases on microscopy of the thick films stained with the modified method compared to only 20% with the standard method. Further, the turnaround time for reporting the microscopy test result was 15-20 and 45-50 min with modified and standard staining methods, respectively.

CONCLUSION

Our data showed that performance of the modified staining method in detecting malarial parasites was comparable to that of the standard staining method. Moreover, the modified staining method was rapid, easy to use, and reliable.

Drug-resistant Plasmodium falciparum infection in immigrants and non-immune travellers

OBJECTIVE

To detect the incidence of drug-resistant Plasmodium falciparum malaria infection in immigrants and travellers in non-endemic Kuwait.

METHODS

Over a period of 3 years, July 1995 to September 1998, 1352 malaria patients were enrolled in the study. Of these, 1293 were immigrants from countries where malaria is endemic and 59 were non-immune travellers with a recent history of travel to these countries. The in vitro drug sensitivity was determined in 892 patients.

RESULTS

In all, 892 of 1352 (66.0%) P. falciparum isolates were successfully cultured in vitro for drug sensitivity and 419 (47.0%) isolates showed in vitro resistance to chloroquine or mefloquine. Fifty-six (13.4%) isolates were resistant to both drugs. Chloroquine resistance was observed in > 70% of the isolates from Africa and India followed by Pakistan (39.9%) and Bangladesh (35.9%). The resistance to mefloquine ranged from 26.2% in isolates from Sri Lanka to 47.5% in isolates from African countries.

CONCLUSION

The study highlights the important trend in drug resistance in P. falciparum malaria in immigrants from south-east Asian and African countries.

Experimental study of the radiative decays K+-->mu(+)nue(+)e(-) and K+-->e(+)nue(+)e(-)

Experiment 865 at the Brookhaven Alternating Gradient Synchrotron obtained 410 K+-->e(+)nue(+)e(-) and 2679 K+-->mu(+)nue(+)e(-) events including 10% and 19% background. The branching ratios were measured to be [2.48+/-0.14(stat)+/-0.14(syst)]x10(-8) (m(ee)>150 MeV) and (7.06+/-0.16+/-0.26)x10(-8) (m(ee)>145 MeV), respectively. Results for the decay form factors are presented.

Positive and negative regulation of pathogen induced dendritic cell function by G-protein coupled receptors

The induction of IL-12 from dendritic cells (DC) is a major initiating step in host resistance to intracellular pathogens. We have studied the regulation of this response using an in vivo model in which IL-12 production by splenic CD8alpha+ DC is followed after injection of a soluble extract (STAg) of the protozoan parasite Toxoplasma gondii. Our findings indicate that the potent IL-12 response observed is highly dependent on both the chemokine receptor CCR5 and G(i)-protein coupled signaling. In addition, we have examined the basis of the unresponsiveness of DC to secondary STAg injection which occurs following primary exposure to this parasite stimulus. Our results demonstrate that this refractory state correlates with the down-regulation of CCR5 expression on DC which, in turn, appears to depend on the induction of endogenous lipoxin A(4) (LXA(4)), a product of arachidonic acid metabolism. Since LXA(4) is known to also signal through a G-protein coupled receptor pathway, these findings taken together support a major role for G-protein signaling in the regulation of microbial-induced DC function.

Lipoxin-mediated inhibition of IL-12 production by DCs: a mechanism for regulation of microbial immunity

Lipoxins are eicosanoid mediators that show potent inhibitory effects on the acute inflammatory process. We show here that the induction of lipoxin A(4) (LXA(4)) accompanied the in vivo suppression of interleukin 12 (IL-12) responsiveness of murine splenic dendritic cells (DCs) after microbial stimulation with an extract of Toxoplasma gondii. This paralysis of DC function could not be triggered in mice that were deficient in a key lipoxygenase involved in LXA(4) biosynthesis. In addition, DCs pre-treated with LXA(4) became refractory to microbial stimulation for IL-12 production in vitro and mice injected with a stable LXA(4) analog showed reduced splenic DC mobilization and IL-12 responses in vivo. Together, these findings indicate that the induction of lipoxins in response to microbial stimulation can provide a potent mechanism for regulating DC function during the innate response to pathogens.

T-bet is rapidly induced by interferon-gamma in lymphoid and myeloid cells

Differentiation of naive CD4(+) T cells into IFN-gamma-producing T helper 1 (T(H)1) cells is pivotal for protective immune responses against intracellular pathogens. T-bet, a recently discovered member of the T-box transcription factor family, has been reported to play a critical role in this process, promoting IFN-gamma production. Although terminal T(H)1 differentiation occurs over days, we now show that challenge of mice with a prototypical T(H)1-inducing stimulus, Toxoplasma gondii soluble extract, rapidly induced IFN-gamma and T-bet; T-bet induction was substantially lower in IFN-gamma-deficient mice. Naive T cells expressed little T-bet, but this transcription factor was induced markedly by the combination of IFN-gamma and cognate antigen. Human myeloid antigen-presenting cells showed T-bet induction after IFN-gamma stimulation alone, and this induction was antagonized by IL-4 and granulocyte/macrophage colony-stimulating factor. Although T-bet was induced rapidly and directly by IFN-gamma, it was not induced by IFN-alpha, lipopolysaccharide, or IL-1, indicating that this action of IFN-gamma was specific. Moreover, T-bet induction was dependent on Stat1 but not Stat4. These data argue for a model in which IFN-gamma gene regulation involves an autocrine loop, whereby the cytokine regulates a transcription factor that promotes its own production. These findings substantially alter the current view of T-bet in IFN-gamma regulation and promotion of cell-mediated immune responses.

Mutation of Tec family kinases alters T helper cell differentiation

The Tec kinases Rlk and Itk are critical for full T cell receptor (TCR)-induced activation of phospholipase C-gamma and mitogen-activated protein kinase. We show here that the mutation of Rlk and Itk impaired activation of the transcription factors NFAT and AP-1 and production of both T helper type 1 (TH1) and TH2 cytokines. Consistent with these biochemical defects, Itk-/- mice did not generate effective TH2 responses when challenged with Schistosoma mansoni eggs. Paradoxically, the more severely impaired Rlk-/-Itk-/- mice were able to mount a TH2 response and produced TH2 cytokines in response to this challenge. In addition, Rlk-/-Itk-/- cells showed impaired TCR-induced repression of the TH2-inducing transcription factor GATA-3, suggesting a potential mechanism for TH2 development in these hyporesponsive cells. Thus, mutations that affect Tec kinases lead to complex alterations in CD4+ TH cell differentiation.

New measurement of K(+)(e4) decay and the s-pave pi pi-scattering length a(0)(0)

A sample of 4 x 10(5) events from the decay K(+)-->pi(+)pi(-)e(+)nu(e) (K(e4)) has been collected in experiment E865 at the Brookhaven Alternating Gradient Synchrotron. The analysis of these data yields new measurements of the K(e4) branching ratio [(4.11+/-0.01+/-0.11) x 10(-5)], the s-wave pi pi scattering length [a(0)(0) = 0.216+/-0.013(stat)+/-0.004(syst)+/-0.005(theor)], and the form factors F, G, and H of the hadronic current and their dependence on the invariant pi pi mass.

Mice infected with Schistosoma mansoni develop a novel non-T-lymphocyte suppressor population which inhibits virus-specific CTL induction via a soluble factor

We previously observed that Schistosoma mansoni-infected mice were deficient in their ability to mount a CTL response to unrelated viral antigens and to clear a vaccinia viral infection. Here, we explore the mechanism of that deficiency. Mixing experiments showed that splenocytes from S. mansoni-infected mice actively suppress stimulation in vitro of both viral-peptide specific CTL in spleen cells from virus-infected mice, and allospecific CTL. The mechanism of suppression involves at least in part a soluble factor, in that it can occur across a 0.4-microm membrane which prohibits direct cell contact. However, the inhibition is not alleviated by blocking with antibodies to IL-4, IL-10 or TGF-beta. Fractionation of the splenocyte population from S. mansoni-infected mice shows that the suppression is mediated by a non-B, non-T cell that expresses CD16 and Mac-1, but not FcepsilonR or NK1.1. This represents a novel suppressor population that is distinct from the FcepsilonRI(+) populations of non-B, non-T cells in the spleens of S. mansoni-infected mice that provide a major source of IL-4 in these animals. Similar cells in schistosome-infected humans could affect susceptibility to other infections or responsiveness to vaccines.

A multi-institutional study of radiofrequency volumetric tissue reduction for OSAS

OBJECTIVES

Radiofrequency volume reduction (RFTVR) is a minor procedure directed at reducing the tongue base volume to treat obstructive sleep apnea. Subjective and objective treatment effectiveness was evaluated.

STUDY DESIGN AND SETTING

Two separate prospective, matched, nonrandomized, open enrollment treatment groups (RFTVR, n = 73 and nasal continuous positive airway pressure (CPAP, n = 99) were concurrently enrolled in a multicenter study.

RESULTS

Fifty-six (76.7%) RFTVR completed PSG with a mean 5.4 +/- 1.8 treatments (13,394 +/- 5459 joules). Perioperatively, acute pain was mild to moderate; edema, mucosal erosion, paresthesia, tinnitus were infrequent; and speech, swallowing taste, or throat irritation were unchanged. Self-reported outcomes did not differ between RFTVR and CPAP groups. Mean apnea/hypopnea index decreased (40.5 +/- 21.5 to 32.8 +/- 22.6 events/hr, P < 0.01). Electrolyte solution injected predicted results (r = 0.43, P < 0.001). The most severe complication was abscess (1.1%).

CONCLUSION

RFTVR improves apnea/hypopnea index. Improvement may be related to solution injected with treatment. RFTVR and CPAP clinical outcomes improvement were similar.

CLINICAL SIGNIFICANCE

In mild obstructive sleep apnea, treatment of symptomatic outcomes with RFTVR may be an alternative to CPAP.