Disseminated gonococcal infection in a homosexual man diagnosed by nucleic acid amplification testing from a skin lesion swab

Disseminated gonococcal infection (DGI) often presents a diagnostic challenge. Through the novel application of molecular technology, a case is presented that suggests how the diagnostic sensitivity for this systemic complication of gonococcal infection can be improved. In a typical case of DGI seen in a homosexual man in whom all mucosal and blood specimens were culture negative, nucleic acid amplification testing (NAAT) helped to confirm the diagnosis. Both throat and skin lesion specimens tested positive for gonococcal DNA and this was confirmed with a supplementary porA pseudogene NAAT. The use of adjuvant NAAT assessment is recommended as part of the diagnostic work-up for suspected DGI cases.

Development of theta rhythmicity in entorhinal stellate cells of the juvenile rat

Mature stellate cells of the rat medial entorhinal cortex (EC), layer II, exhibit subthreshold membrane potential oscillations (MPOs) at theta frequencies (4-12 Hz) in vitro. We find that MPOs appear between postnatal days 14 (P14) and 18 (P18) but show little further change by day 28+ (P28-P32). To identify the factors responsible, we examined the electrical responses of developing stellate cells, paying attention to two currents thought necessary for mature oscillation: the h current I(h), which provides the slow rectification required for resonance; and a persistent sodium current I(NaP), which provides amplification of resonance. Responses to injected current revealed that P14 cells were often nonresonant with a relatively high resistance. Densities of I(h) and I(NaP) both rose by about 50% from P14 to P18. However, I(h) levels fell to intermediate values by P28+. Given the nonrobust trend in I(h) expression and a previously demonstrated potency of even low levels of I(h) to sustain oscillation, we propose that resonance and MPOs are limited at P14 more by low levels of I(NaP) than of I(h). The relative importance of I(NaP) for the development of MPOs is supported by simulations of a conductance-based model, which also suggest that general shunt conductance may influence the precise age when MPOs appear. In addition to our physiological study, we analyzed spine densities at P14, P18, and P28+ and found a vigorous synaptogenesis across the whole period. Our data predict that functions that rely on theta rhythmicity in the hippocampal network are limited until at least P18.

Control of neuronal persistent activity by voltage-dependent dendritic properties

Neural integrators and working memory rely on persistent activity, a widespread neural phenomenon potentially involving persistent sodium conductances. Using a unique combination of voltage-clamp, dynamic-clamp, and frequency-domain techniques, we have investigated the role of voltage-dependent conductances on the dendritic electrotonic structure of neurons of the prepositus hypoglossi nucleus (PHN), which is known to be involved in oculomotor integration. The PHN contains two main neuronal populations: type B neurons with a double afterhyperpolarization and type D neurons, which not only are oscillatory but also have a greater electrotonic length than that of type B neurons. The persistent sodium conductance is present in all PHN neurons, although its effect on the dynamic electrotonic structure is shown to significantly differ in the two major cell types present in the nucleus. The electrotonic differences are such that the persistent sodium conductance can be almost perfectly manipulated in a type B neuron using an on-line dynamic clamp to add or subtract virtual sodium ion channels. The dynamic-clamp results are confirmed by data-fitted models, which suggest that the persistent sodium conductance has two different roles depending on its somatic versus dendritic location: perisomatic conductances could play a major role in maintaining action potential discharge and dendritic conductances would be more involved in other computational properties, such as those involving remote synaptic processing or bistable events.

Two-photon imaging of spatially extended neuronal network dynamics with high temporal resolution

We describe a simple two-photon fluorescence imaging strategy, called targeted path scanning (TPS), to monitor the dynamics of spatially extended neuronal networks with high spatiotemporal resolution. Our strategy combines the advantages of mirror-based scanning, minimized dead time, ease of implementation, and compatibility with high-resolution low-magnification objectives. To demonstrate the performance of TPS, we monitor the calcium dynamics distributed across an entire juvenile rat hippocampus (>1.5mm), at scan rates of 100 Hz, with single cell resolution and single action potential sensitivity. Our strategy for fast, efficient two-photon microscopy over spatially extended regions provides a particularly attractive solution for monitoring neuronal population activity in thick tissue, without sacrificing the signal-to-noise ratio or high spatial resolution associated with standard two-photon microscopy. Finally, we provide the code to make our technique generally available.

Effects of imperfect dynamic clamp: computational and experimental results

In the dynamic clamp technique, a typically nonlinear feedback system delivers electrical current to an excitable cell that represents the actions of "virtual" ion channels (e.g., channels that are gated by local membrane potential or by electrical activity in neighboring biological or virtual neurons). Since the conception of this technique, there have been a number of different implementations of dynamic clamp systems, each with differing levels of flexibility and performance. Embedded hardware-based systems typically offer feedback that is very fast and precisely timed, but these systems are often expensive and sometimes inflexible. PC-based systems, on the other hand, allow the user to write software that defines an arbitrarily complex feedback system, but real-time performance in PC-based systems can be deteriorated by imperfect real-time performance. Here, we systematically evaluate the performance requirements for artificial dynamic clamp knock-in of transient sodium and delayed rectifier potassium conductances. Specifically, we examine the effects of controller time step duration, differential equation integration method, jitter (variability in time step), and latency (the time lag from reading inputs to updating outputs). Each of these control system flaws is artificially introduced in both simulated and real dynamic clamp experiments. We demonstrate that each of these errors affect dynamic clamp accuracy in a way that depends on the time constants and stiffness of the differential equations being solved. In simulations, time steps above 0.2ms lead to catastrophic alteration of spike shape, but the frequency-current relationship is much more robust. Latency (the part of the time step that occurs between measuring membrane potential and injecting re-calculated membrane current) is a crucial factor as well. Experimental data are substantially more sensitive to inaccuracies than simulated data.

Contributions of Ih to feature selectivity in layer II stellate cells of the entorhinal cortex

Abstract Stellate cells (SCs) of the entorhinal cortex generate prominent subthreshold oscillations that are believed to be important contributors to the hippocampal theta rhythm. The slow inward rectifier Ih is expressed prominently in SCs and has been suggested to be a dominant factor in their integrative properties. We studied the input-output relationships in stellate cells (SCs) of the entorhinal cortex, both in control conditions and in the presence of the Ih antagonist ZD7288. Our results show that Ih is responsible for SCs' subthreshold resonance, and contributes to enhanced spiking reliability to theta-rich stimuli. However, SCs still exhibit other traits of rhythmicity, such as subthreshold oscillations, under Ih blockade. To clarify the effects of Ih on SC spiking, we used a generalized form of principal component analysis to show that SCs select particular features with relevant temporal signatures from stimuli. The spike-selected mix of those features varies with the frequency content of the stimulus, emphasizing the inherent nonlinearity of SC responses. A number of controls confirmed that this selectivity represents a stimulus-induced change in the cellular input-output relationship rather than an artifact of the analysis technique. Sensitivity to slow features remained statistically significant in ZD7288. However, with Ih blocked, slow stimulus features were less predictive of spikes and spikes conveyed less information about the stimulus over long time scales. Together, these results suggest that Ih is an important contributor to the input-output relationships expressed by SCs, but that other factors in SCs also contribute to subthreshold oscillations and nonlinear selectivity to slow features.

Disambiguation of overlapping experiences by neurons in the medial entorhinal cortex

Hippocampal neuronal activity distinguishes separate events that share common elements. Here, we examined whether the capacity to disambiguate overlapping experiences is an exclusive feature of hippocampal processing or whether information processing one stage earlier in the hippocampal system also disambiguates common elements of distinct experiences. We compared the spatial firing patterns of neurons in the dorsocaudal medial entorhinal cortex (dcMEC) and hippocampal CA1 neurons in animals continuously alternating left-turn and right-turn routes through a T-maze. Neurons in the dcMEC more strongly distinguished left-turn from right-turn trials compared with CA1 neurons, whereas CA1 neurons more selectivity encoded places traversed within each route. These results indicate that dcMEC spatial firing patterns are experience dependent and reflect the mnemonic demands of a spatial memory task. Furthermore, the results suggest that neuronal populations in the dcMEC and CA1 differentially emphasize complementary aspects of spatial memory representations.

Sniffing controls an adaptive filter of sensory input to the olfactory bulb

Most sensory stimuli are actively sampled, yet the role of sampling behavior in shaping sensory codes is poorly understood. Mammals sample odors by sniffing, a complex behavior that controls odorant access to receptor neurons. Whether sniffing shapes the neural code for odors remains unclear. We addressed this question by imaging receptor input to the olfactory bulb of awake rats performing odor discriminations that elicited different sniffing behaviors. High-frequency sniffing of an odorant attenuated inputs encoding that odorant, whereas lower sniff frequencies caused little attenuation. Odorants encountered later in a sniff bout were encoded as the combination of that odorant and the background odorant during low-frequency sniffing, but were encoded as the difference between the two odorants during high-frequency sniffing. Thus, sniffing controls an adaptive filter for detecting changes in the odor landscape. These data suggest an unexpected functional role for sniffing and show that sensory codes can be transformed by sampling behavior alone.

Roles of IA and morphology in action potential propagation in CA1 pyramidal cell dendrites

Dendrites of CA1 pyramidal cells of the hippocampus, along with those of a wide range of other cell types, support active backpropagation of axonal action potentials. Consistent with previous work, recent experiments demonstrating that properties of synaptic plasticity are different for distal synapses, suggest an important functional role of bAPs, which are known to be prone to failure in distal locations. Using conductance-based models of CA1 pyramidal cells, we show that underlying "traveling wave attractors" control action potential propagation in the apical dendrites. By computing these attractors, we dissect and quantify the effects of I(A) channels and dendritic morphology on bAP amplitudes. We find that non-uniform activation properties of I(A) can lead to backpropagation failure similar to that observed experimentally in these cells. Amplitude of forward propagation of dendritic spikes also depends strongly on the activation dynamics of I(A). I(A) channel properties also influence transients at dendritic branch points and whether or not propagation failure results. The branching pattern in the distal apical dendrites, combined with I(A) channel properties in this region, ensure propagation failure in the apical tuft for a large range of I(A) conductance densities. At the same time, these same properties ensure failure of forward propagating dendritic spikes initiated in the distal tuft in the absence of some form of cooperativity of synaptic activation.

Chlamydia trachomatis load at matched anatomic sites: implications for screening strategies

Urethral and endocervical swabs and self-collected vaginal swabs (SCVSs) and urine specimens are all used as samples for diagnosis of urogenital infection with Chlamydia trachomatis. We have now determined chlamydial organism load in matched specimens from different anatomic sites and examined its relation to clinical signs and symptoms in men and women. Organism load was measured with assays based on the ligase chain reaction or real-time PCR analysis. The mean organism loads in 58 infected men were 1,200 and 821 elementary bodies (EBs) per 100 microl of sample for first-void urine (FVU) and urethral swabs, respectively (P>0.05). Organism load in FVU samples or urethral swabs was positively associated with symptoms (P<0.01) and clinical signs (P<0.01) in men. The mean organism loads in 73 infected women were 2,231, 773, 162, and 47 EBs/100 microl for endocervical swabs, SCVSs, urethral swabs, and FVU samples, respectively (P<0.001 for each comparison). Only the presence of multiple symptoms or clinical signs was associated with organism load in women. These results show that FVU is a suitable noninvasive sample type for men, given the fact that its chlamydial load did not differ significantly from that of urethral swabs. Given their higher organism load compared with FVU, SCVSs are the preferred noninvasive sample type for women.

Hybrid neuronal network studies under dynamic clamp

Even a complete understanding of the biophysical properties driving neuronal behavior would be insufficient to explain the interactions between neurons, neuronal assemblies, and brain regions. Exploring interactions between small numbers of synaptically coupled neurons in vitro can provide insight into the in vivo activity of neuronal assemblies. However, pairs of synaptically coupled neurons are notoriously difficult to find in vitro, and trying to study networks of more than two neurons is nearly impossible. The advent of the dynamic-clamp technique enables researchers to generate hybrid networks of neurons in which living neurons are synaptically coupled through computationally generated synapses. In this chapter, we provide an overview of the components of a dynamic-clamp system. We detail how to use dynamic clamp to construct simple neuronal networks from living neurons as well as hybrid networks including both living and in silico neurons.

Low-dimensional maps encoding dynamics in entorhinal cortex and hippocampus

Cells that produce intrinsic theta oscillations often contain the hyperpolarization-activated current I(h). In this article, we use models and dynamic clamp experiments to investigate the synchronization properties of two such cells (stellate cells of the entorhinal cortex and O-LM cells of the hippocampus) in networks with fast-spiking (FS) interneurons. The model we use for stellate cells and O-LM cells is the same, but the stellate cells are excitatory and the O-LM cells are inhibitory, with inhibitory postsynaptic potential considerably longer than those from FS interneurons. We use spike time response curve methods (STRC), expanding that technique to three-cell networks and giving two different ways in which the analysis of the three-cell network reduces to that of a two-cell network. We show that adding FS cells to a network of stellate cells can desynchronize the stellate cells, while adding them to a network of O-LM cells can synchronize the O-LM cells. These synchronization and desynchronization properties critically depend on I(h). The analysis of the deterministic system allows us to understand some effects of noise on the phase relationships in the stellate networks. The dynamic clamp experiments use biophysical stellate cells and in silico FS cells, with connections that mimic excitation or inhibition, the latter with decay times associated with FS cells or O-LM cells. The results obtained in the dynamic clamp experiments are in a good agreement with the analytical framework.

Simple models show the general advantages of dendrites in coincidence detection

Dendrites can influence and improve information processing in single neurons. Here, simple models are used to elucidate mechanisms underlying the dendritic enhancement of coincidence detection. We focus on coincidence-detecting cells in the auditory system, which have bipolar dendrites and show acute sensitivity to interaural time difference (ITD), a critical cue for spatial hearing. A three-compartment model consisting of a single-compartment soma and two single-compartment dendrites is primarily used, although multiple-compartment dendrites are also tested. Two varieties of somata, with and without active ion channels, are studied. Using constant conductance inputs, we show analytically that the somatic response to balanced bilateral inputs is largest, whereas the response monotonically decreases as the input distribution becomes increasingly monolateral. This enhancement is a consequence of the sublinear saturating dendritic voltage response to conductance input and occurs when dendrites are composed of a single compartment or either a finite number or an infinite number (i.e., a cable) of compartments. Longer, thinner dendrites or greater numbers of compartments increase the enhancement of the somatic response to bilateral input. The time-independent dendritic enhancement, moreover, underlies improved coincidence detection of time-varying input. Coincidence sensitivity to a pair of conductance pulses and rate-ITD modulation to low-frequency (400-Hz) periodic inputs increases with dendritic length. These findings are related to the length gradient in the avian system, where low characteristic frequency (CF) cells have long dendrites and high CF cells have short dendrites. We conclude that dendrites fundamentally improve coincidence detection, increasing the computational power of many neurons in the nervous system.

The dynamic structure underlying subthreshold oscillatory activity and the onset of spikes in a model of medial entorhinal cortex stellate cells

Medial entorhinal cortex layer II stellate cells display subthreshold oscillations (STOs). We study a single compartment biophysical model of such cells which qualitatively reproduces these STOs. We argue that in the subthreshold interval (STI) the seven-dimensional model can be reduced to a three-dimensional system of equations with well differentiated times scales. Using dynamical systems arguments we provide a mechanism for generations of STOs. This mechanism is based on the "canard structure," in which relevant trajectories stay close to repelling manifolds for a significant interval of time. We also show that the transition from subthreshold oscillatory activity to spiking ("canard explosion") is controlled in the STI by the same structure. A similar mechanism is invoked to explain why noise increases the robustness of the STO regime. Taking advantage of the reduction of the dimensionality of the full stellate cell system, we propose a nonlinear artificially spiking (NAS) model in which the STI reduced system is supplemented with a threshold for spiking and a reset voltage. We show that the synchronization properties in networks made up of the NAS cells are similar to those of networks using the full stellate cell models.

Density functional theory of fluids in nanopores: Analysis of the fundamental measures theory in extreme dimensional-crossover situations

Two density functional theories, the fundamental measures theory of Rosenfeld [Phys. Rev. Lett. 63, 980 (1989)] and a subsequent approximation by Tarazona [Phys. Rev. Lett. 84, 694 (2000)] are applied to the study of the hard-sphere fluid in two situations: the cylindrical pore and the spherical cavity. The results are compared with those obtained with grand canonical ensemble Monte Carlo simulations. The differences between both theories are evaluated and interpreted in the terms of the dimensional crossover from three to one and zero dimensions.

Synaptic input statistics tune the variability and reproducibility of neuronal responses

Synaptic waveforms, constructed from excitatory and inhibitory presynaptic Poisson trains, are presented to living and computational neurons. We review how the average output of a neuron (e.g., the firing rate) is set by the difference between excitatory and inhibitory event rates while neuronal variability is set by their sum. We distinguish neuronal variability from reproducibility. Variability quantifies how much an output measure is expected to vary; for example, the interspike interval coefficient of variation quantifies the typical range of interspike intervals. Reproducibility quantifies the similarity of neuronal outputs in response to repeated presentations of identical stimuli. Although variability and reproducibility are conceptually distinct, we show that, for ideal current source synapses, reproducibility is defined entirely by variability. For physiologically realistic conductance-based synapses, however, reproducibility is distinct from variability and average output, set by the Poisson rate and the degree of synchrony within the synaptic waveform.

Finite-size effects in the microscopic structure of a hard-sphere fluid in a narrow cylindrical pore

We examine the microscopic structure of a hard-sphere fluid confined to a small cylindrical pore by means of Monte Carlo simulation. In order to analyze finite-size effects, the simulations are carried out in the framework of different statistical mechanics ensembles. We find that the size effects are specially relevant in the canonical ensemble where noticeable differences are found with the results in the grand canonical ensemble (GCE) and the isothermal isobaric ensemble (IIE) which, in most situations, remain very close to the infinite system results. A customary series expansion in terms of fluctuations of either the number of particles (GCE) or the inverse volume (IIE) allows us to connect with the results of the canonical ensemble.

Plasma membrane voltage changes during nanosecond pulsed electric field exposure

The change in the membrane potential of Jurkat cells in response to nanosecond pulsed electric fields was studied for pulses with a duration of 60 ns and maximum field strengths of approximately 100 kV/cm (100 V/cell diameter). Membranes of Jurkat cells were stained with a fast voltage-sensitive dye, ANNINE-6, which has a subnanosecond voltage response time. A temporal resolution of 5 ns was achieved by the excitation of this dye with a tunable laser pulse. The laser pulse was synchronized with the applied electric field to record images at times before, during, and after exposure. When exposing the Jurkat cells to a pulse, the voltage across the membrane at the anodic pole of the cell reached values of 1.6 V after 15 ns, almost twice the voltage level generally required for electroporation. Voltages across the membrane on the side facing the cathode reached values of only 0.6 V in the same time period, indicating a strong asymmetry in conduction mechanisms in the membranes of the two opposite cell hemispheres. This small voltage drop of 0.6-1.6 V across the plasma membrane demonstrates that nearly the entire imposed electric field of 10 V/mum penetrates into the interior of the cell and every organelle.