Current noise parameters derived from voltage noise and impedance in embryonic heart cell aggregates.

We have recorded membrane impedance and voltage noise in the pacemaker range of potentials (-70 to -59 mV) from spheroidal aggregates of 7-d embryonic chick ventricle cells made quiescent by exposure to tetrodotoxin in medium containing 4.5 mM K+. The input capacitance is proportional to aggregate volume and therefore to total membrane area. The specific membrane capacitance is 1.24 microF/cm2. The input resistance at constant potential is inversely proportional to aggregate volume and therefore to total membrane area. The specific membrane resistance in 18 k omega . cm2 at -70 mV and increases to 81 k omega . cm2 at -59 mV. The RC time constant is 22 ms at -70 mV and increases to 146 ms at -59 mV. The aggregate transmembrane small-signal impedance can be represented by a parallel RC circuit itself in parallel with an inductive branch consisting of a resistor (rL) and an inductor (L) in series. The time constant of the inductive branch (L/rL) is 340 ms, and is only weakly dependent on potential. Correlation functions of aggregate voltage noise and the impedance data were modeled by a population of channels with simple open-close kinetics. The time constant of a channel (tau s) derived from the noise analysis is 300 ms. The low frequency limit of the pacemaker current noise (SI[0]), derived from the voltage noise and impedance, increases from 10(-20) A2/Hz . cm2 at -67 mV to 10(-19) A2/Hz . cm2 at -61 mV.     

Respiratory impedance to ambient pressure changes at low frequencies

Respiratory impedance may be studied by measuring airway flow (Vaw) when pressure is varied at the mouth (input impedance) or around the chest (transfer impedance). A third possibility, which had not been investigated so far, is to apply pressure variations simultaneously at the two places, that is to vary ambient pressure (Pam). This provides respiratory impedance to ambient pressure changes (Zapc = Vaw/Pam). In that situation airway impedance (Zaw) and tissue impedance (Zt) are mechanically in parallel, and both are in series with alveolar gas impedance (Zg): Zapc = Zaw + Zg + Zaw.Zg/Zt. We assessed the frequency dependence of Zapc from 0.05 to 2 Hz in nine normal subjects submitted to sinusoidal Pam changes of 2-4 kPa peak to peak. The real part of Zapc (Rapc) was of 6.2 kPa.1(-1).s at 0.05 Hz and decreased to 1.9 kPa.1(-1).s at 2 Hz. Similarly the effective compliance (Capc), computed from the imaginary part of Zapc, decreased from 0.045 1.kPa-1 at 0.05 Hz to 0.027 1.kPa-1 at 2 Hz. Breathing against an added resistance of 0.46 kPa.1(-1).s exaggerated the negative frequency dependence of both Rapc and Capc. When values of airway resistance and inertance derived from transfer impedance data were introduced, Zapc was used to compute effective tissue resistance (Rt) and compliance (Ct). Rt was found to decrease from 0.32 to 0.15 kPa.1(-1).s and Ct from 1.11 to 0.64 1.kPa-1 between 0.25 and 2 Hz. Ct was slightly lower with the added resistance. These results are in good agreement with the data obtained by other approaches.     

Conductance transients onto dendritic spines in a segmental cable model of hippocampal neurons.

Dendritic shaft (Zd) and spine (Zsp) input impedances were computed numerically for sites on hippocampal neurons, using a segmental format of cable calculations. The Zsp values for a typical spine appended onto a dendritic shaft averaged less than 2% higher than the Zd values for the adjacent dendritic shaft. Spine synaptic inputs were simulated by a brief conductance transient, which possessed a time integral of 12 X 10(-10)S X ms. This input resulted in an average peak spine response of 20 mV for both dentate granule neurons and CA1 pyramidal cells. The average spine transient was attenuated less than 2% in conduction across the spine neck, considering peak voltage, waveform parameters, and charge transfer. The spine conductance transient resulted in an average somatic response of 100 microV in the dentate granule neurons, because of passive electrotonic propagation. The same input transient was also applied to proximal and distal sites on CA1 pyramidal cells. The predicted responses at the soma demonstrated a clear difference between the proximal and distal inputs, in terms of both peak voltage and waveform parameters. Thus, the main determinant of the passive propagation of transient electrical signals in these neurons appears to be dendritic branching rather than signal attenuation through the spine neck.     

Somatostatin immunohistochemistry of hippocampal slices with lucifer yellow-stained pyramidal neurons responding to somatostatin.

We have combined electrophysiology and immunohistochemistry to study the somatostatin (SS) innervation of neurons in the rat hippocampal slice. After recording the intracellular response of a pyramidal CA1 neuron in vitro to SS, Lucifer Yellow was injected into the cell and the slice fixed and processed for immunohistochemical localization of SS in the vicinity of the recorded neuron. Most pyramidal neurons (70%) responded to SS with a hyperpolarization associated with marked slowing of spontaneous discharge and reduced input resistance. SS-containing elements either crossed, ran parallel or seemingly terminated on the Lucifer Yellow-filled SS-responsive cell. These occurrences of close proximity of apparent pre- and postsynaptic elements were observed in all layers of the CA1 region and may represent synaptic terminations of SS elements on a pyramidal neuron that are likely to elicit membrane hyperpolarizations.     

Excitatory responses of trigeminal neurons to substance P suggest involvement in sensory transmission

Responses to substance P application were studied with intracellular recording techniques in in vitro preparations of trigeminal root ganglion neurons of guinea pigs. Perfusion of substance P in micromolar concentrations markedly depolarized neurons and reduced their input conductances. Also, the threshold for spikes evoked by injections of depolarizing current pulses was decreased. Single electrode voltage-clamp recordings showed that substance P increased inward, and decreased outward currents evoked by hyperpolarizing voltage steps from holding potentials near rest. Depolarizing responses to substance P were attenuated in Na+-deficient solutions. The excitatory actions of this endogenous peptide on the perikarya of primary sensory neurons give rise to the possibility of physiological actions of substance P at multiple sites in the trigeminal system.     

Phosphorylation of CRMP2 is involved in proper bifurcation of the apical dendrite of hippocampal CA1 pyramidal neurons

The neural circuit in the hippocampus is important for higher brain functions. Dendrites of CA1 pyramidal neurons mainly receive input from the axons of CA3 pyramidal neurons in this neural circuit. A CA1 pyramidal neuron has a single apical dendrite and multiple basal dendrites. In wild‐type mice, most of CA1 pyramidal neurons extend a single trunk, or alternatively, the apical dendrite bifurcates into two daughter trunks at the stratum radiatum layer. We previously reported the proximal bifurcation phenotype in Sema3A?/?, p35?/?, and CRMP4?/? mice. Cdk5/p35 phosphorylates CRMP2 at Ser522, and inhibition of this phosphorylation suppressed Sema3A‐induced growth cone collapse. In this study, we analyzed the bifurcation points of the apical dendrites of hippocampal CA1 pyramidal neurons in CRMP2KI/KI mice in which the Cdk5/p35‐phosphorylation site Ser522 was mutated into an Ala residue. The proximal bifurcation phenotype was not observed in CRMP2KI/KI mice; however, severe proximal bifurcation of apical dendrites was found in CRMP2KI/KI;CRMP4?/? mice. Cultured hippocampal neurons from CRMP2KI/KI and CRMP2KI/KI;CRMP4?/? embryos showed an increased number of dendritic branching points compared to those from wild‐type embryos. Sema3A increased the number of branching points and the total length of dendrites in wild‐type hippocampal neurons, but these effects of Sema3A for dendrites were notobserved in CRMP2KI/KI and CRMP2KI/KI;CRMP4?/?hippocampal neurons. Binding of CRMP2 to tubulin increased in both CRMP2KI/KI and CRMP2KI/KI:CRMP4?/? brain lysates. These results suggest that CRMP2 and CRMP4 synergistically regulate dendritic development, and CRMP2 phosphorylation is critical for proper bifurcation of apical dendrite of CA1 pyramidal neurons. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013     

Newly explored electrical properties of normal skin and special skin sites.

Skin impedance measurements at various skin sites yield different impedance loci for normal skin and special skin sites. The results of skin impedance measurements taken at such sites with a two-electrode measurement system are presented herein. Some of these sites can be identified as acupuncture points. Data from 4 volunteers were acquired by means of a data acquisition board and a measuring system consisting of the measurement circuit, including several electrode types, and a power supply. The Cole model is a model for an equivalent electrical circuit of the skin-electrode system. The system was used to derive skin-typical parameters from the Bode plot of the whole system. These parameters are the fractional power a, the pseudo-capacity K, the parallel resistance Rp, and the serial resistance Rs of the equivalent electrical circuit. The results show that the measured parameters differ between normal skin and special skin sites. These effects have not previously been discovered by other authors, since there has been no systematic investigation of many acupuncture points to date, and there has been no apparent need for such an investigation. A number of necessary criteria for acupuncture point detection can be derived from the results obtained.     

Sensitivity analysis of respiratory parameter uncertainties: impact of criterion function form and constraints

A sensitivity analysis based on weighted least-squares regression is presented to evaluate alternative methods for fitting lumped-parameter models to respiratory impedance data. The goal is to maintain parameter accuracy simultaneously with practical experiment design. The analysis focuses on predicting parameter uncertainties using a linearized approximation for joint confidence regions. Applications are with four-element parallel and viscoelastic models for 0.125- to 4-Hz data and a six-element model with separate tissue and airway properties for input and transfer impedance data from 2-64 Hz. The criterion function form was evaluated by comparing parameter uncertainties when data are fit as magnitude and phase, dynamic resistance and compliance, or real and imaginary parts of input impedance. The proper choice of weighting can make all three criterion variables comparable. For the six-element model, parameter uncertainties were predicted when both input impedance and transfer impedance are acquired and fit simultaneously. A fit to both data sets from 4 to 64 Hz could reduce parameter estimate uncertainties considerably from those achievable by fitting either alone. For the four-element models, use of an independent, but noisy, measure of static compliance was assessed as a constraint on model parameters. This may allow acceptable parameter uncertainties for a minimum frequency of 0.275-0.375 Hz rather than 0.125 Hz. This reduces data acquisition requirements from a 16- to a 5.33- to 8-s breath holding period. These results are approximations, and the impact of using the linearized approximation for the confidence regions is discussed.     

Central mechanisms of vascular headaches

The intracranial blood vessels supplying the dura and brain are innervated by sensory afferents from the trigeminal nerve. These fibers are believed to be responsible for conveying the pain associated with vascular head pain such as migraines. This paper reviews recently published data describing the existence of neurons within the cat trigeminal nucleus and thalamus that respond to electrical stimulation of the middle meningeal artery and superior sagittal sinus. Almost all of these neurons receive convergent input from the facial skin and most of the receptive fields include the periorbital region. On the basis of their cutaneous inputs, most of the neurons are classified as nociceptive. The characteristics of these cerebrovascular-activated neurons are consistent with their role in mediating vascular head pains and with the typical referral of such pains in man to the orbital region. This paper also presents preliminary results of recordings from rat trigeminal ganglion neurons activated by electrical stimulation of the middle meningeal artery and sagittal sinus. The latencies of activation of these neurons are indicative of conduction in slowly conducting myelinated axons and in unmyelinated axons. Some of the neurons could also be activated by mechanical stimuli applied to the vessels.     

Differences in activity of hippocampal and neocortical neurons in active and passive rabbits in negative emotional situations

Activities of individual hippocampal (CA1 area) and neocortical parietal-temporal neurons were compared in active and passive rabbits in negative emotional situations during emotionally significant stimuli by plotting histograms of autocorrelations. As compared to passive animals, in active rabbits, the mean firing rate of hippocampal neurons was higher, bursting and periodic oscillations of discharges occurred more frequently. Oscillation periods in the theta 1 band (6.0-9.0 Hz) appeared more frequently (in the baseline state and active exploratory or defensive reactions), whereas those in the theta 2 band (4.0-5.9 Nz), on the contrary, were infrequently observed (during freezing). The greatest changes in activity ofhippocampal neurons were observed during active locomotor responses of active rabbits. Intergroup differences in neocortical neuronal activities were less pronounced than in hippocampus. The results indicate that individual typological features in behaviour of animals appear in negative emotional situations and are reflected in activity of activity ofhippocampal (area CA1) and to lesser extent parietal-temporal neocortical neurons. The results suggest different activation levels of the septohippocampal system of active and passive rabbits and possible differences in the afferent input to the CA1 field.     

高频电刺激对大鼠海马脑片癫痫样放电特性影响的研究

本文采用电极阵列检测技术,在大鼠海马脑切片上诱导出稳定的癫痫样放电,分析、研究130 Hz的高频电刺激(high-frequency stimulation,HFS) CA3区时,海马切片在癫痫发作间期放电(inter-ictal discharges,IID)和发作期放电(ictal discharges,ID)的各项参数、癫痫样放电地起始位点、传播方向和传输速率以及各频段的功率谱密度.结果显示:高频电刺激可以有效地降低癫痫发作期的幅值、减少持续时间、增长潜伏时间、抑制癫痫样放电由IID向ID的转变等.提示高频电刺激抑制癫痫的作用机制是通过促进神经元之间的抑制性传输系统,并且抑制海马神经元之间的兴奋性连接,从而达到抑制效果.     

Electrical Impedance Analysis in Plant Tissues8

Electrical impedance spectra (100 Hz–800 kHz) were measuredin leaves of Peperomia obtusifolia L. (a succulent) and Brassicaoleracea L. (cabbage). By measuring impedances at three or moreinter-electrode distances in a single leaf, electrode impedanceand specific tissue impedance were separated. Analysis of impedance data from B. oleracea leaves in relationto an equivalent circuit model showed that leaf developmentwas accompanied by increases in extracellular resistance, cytoplasmicresistance and vacuole interior resistance, together with decreasesin plasma membrane capacitance and tonoplast capacitance. AfterB. oleracea leaves were subjected to a –6 °C freeze-thawstress, extracellular resistance, cytoplasmic resistance andvacuole interior resistance decreased, but plasma membrane capacitanceand tonoplast capacitance did not change. These results indicatethat useful measurements of leaf parameters can be obtainedby this technique. Examination of the electrode impedance spectrum showed thatelectrode insertion produced a damaged collar, 0·4–0·5mm wide, around the electrode. This was confirmed by visualobservation of the damage in P. obtusifolia leaf. Key words: Peperomia obtusifolia L., Brassica oleracea L. (cabbage), electrical impedance, equivalent circuit, electrode polarization     

Electrical stimulation of the trigeminal tract in chronic, intractable facial neuralgia

In this paper the treatment of patients with chronic, intractable trigeminal neuralgia by invasive electrical stimulation of the Gasserion ganglion is reviewed. Two different surgical techniques are employed in this treatment. Most frequently, a method similar to the traditional technique for percutaneous glycerol and radiofrequency trigeminal rhizolysis is used: a small percutaneous stimulation electrode is advanced under fluoroscopic control through a thin needle via the foramen ovale to the Gasserian cistern. Some neurosurgeons use an open surgical technique by which the Gasserian ganglion is approached subtemporally and extradurally, and the bipolar pad electrode is sutured to the dura. When percutaneous test stimulation is successful (at least 50% pain relief) the electrode is internalized and connected to a subcutaneous pulse generator or RF-receiver. Data from 8 clinical studies, including 267 patients have been reviewed. Of all 233 patients with medication-resistant atypical trigeminal neuralgia 48% had at least 50% long term pain relief. The result of test stimulation is a good predictor of the long term effect, because 83% of all patients with successful test stimulation had at least 50% long term relief, and 70% had at least 75% long term relief. Patients generally preferred this invasive method over TENS. The success rate in patients with postherpetic trigeminal neuralgia was very low (less than 10%). It is suggested that the likelihood of pain relief by electrical stimulation is inversely related to the degree of sensory loss. It is concluded that invasive stimulation of the Gasserian ganglion is a promising treatment modality for patients with chronic, intractable, atypical trigeminal neuralgia.     

Single Versus Repetitive Spiking to the Current Stimulus of A-β Mechanosensitive Neurons in the Crotaline Snake Trigeminal Ganglion

1. Intrasomal recordings of potentials produced by current stimulation in vivo were made from 24 (A-) touch and 19 vibrotactile neurons in the trigeminal ganglion of 29 crotaline snakes, Trimeresurus flavoviridis. 2. Usually touch neurons responded with a single action potential at the beginning of a prolonged depolarizing pulse, whereas all vibrotactile neurons responded with multiple spikes.3. The electrophysiological parameters examined were membrane potential, threshold current, input resistance and capacitance, time constant, rebound latency, and its threshold current. Touch neurons had higher input resistance (and lower input capacitance) than vibrotactile neurons.4. In conclusion, current injection, which elicits a single or multiple spiking, seems a useful way to separate touch neurons from vibrotactile neurons without confirming the receptor response, and some membrane properties are also specific to the sensory modality.     

Role of EGR1 in hippocampal synaptic enhancement induced by tetanic stimulation and amputation

Hippocampal neurons fire spikes when an animal is at a particular location or performs certain behaviors in a particular place, providing a cellular basis for hippocampal involvement in spatial learning and memory. In a natural environment, spatial memory is often associated with potentially dangerous sensory experiences such as noxious or painful stimuli. The central sites for such pain-associated memory or plasticity have not been identified. Here we present evidence that excitatory glutamatergic synapses within the CA1 region of the hippocampus may play a role in storing pain-related information. Peripheral noxious stimulation induced excitatory postsynaptic potentials (EPSPs) in CA1 pyramidal cells in anesthetized animals. Tissue/nerve injury caused a rapid increase in the level of the immediate-early gene product Egr1 (also called NGFI-A, Krox24, or zif/268) in hippocampal CA1 neurons. In parallel, synaptic potentiation induced by a single tetanic stimulation (100 Hz for 1 s) was enhanced after the injury. This enhancement of synaptic potentiation was absent in mice lacking Egr1. Our data suggest that Egr1 may act as an important regulator of pain-related synaptic plasticity within the hippocampus.     

Voltage clamping with a single microelectrode.

A technique is described which allows neurons to be voltage clamped with a single microelectrode, and the advantages of this circuit with respect to conventional bridge techniques are discussed. In this circuit, the single microelectrode is rapidly switched from a current passing to a recording mode. The circuitry consists of: (1) an electronic switch; (2) a high impedance, ultralow input capacity amplifier; (3) a sample-and-hold module; (4) conventional voltage clamping circuitry. The closed electronic switch allows current to flow through the electrode. The switch then opens, and the electrode is in a recording mode. The low input capacity of the preamplifier allows the artifact from the current pulse to rapidly abate, after which time the circuit samples the membrane potential. This cycle is repeated at rates up to 10 kHz. The voltage clamping amplifier senses the output of the sample-and-hold module and adjusts the current pulse amplitude to maintain the desired membrane potential. The system was evaluated in Aplysia neurons by inserting two microelectrodes into a cell. One electrode was used to clamp the cell and the other to independently monitor membrane potential at a remote location in the soma.     

Adaptation of trigeminal ganglion cells to periodic whisker deflections

Trigeminal ganglion neurons in adult rats adapt to periodic whisker deflections in the range of 1-40 Hz, manifested as a reduction in spike counts to progressively later stimuli in a train of pulsatile or sinusoidal deflections. For high velocity, pulsatile deflections, adaptation is time- and frequency-dependent; as in the case of thalamic and cortical neurons, adaptation is greater at higher stimulus frequencies. With slower velocity, sinusoidal movements, trigeminal ganglion cells differ from central neurons, however, by exhibiting strong adaptation even at low frequencies. For both types of stimuli, effects in trigeminal ganglion neurons were more pronounced in rats maintained during the recording session under neuromuscular blockade than in non-paralysed animals. Results are consistent with previous findings in other systems that frequency-dependent adaptation of cutaneous primary afferent neurons is affected by mechanical properties of the skin. Such effects are likely to vary depending on the nature of the whisker stimuli and physiological states that affect skin viscoelasticity.     

Noncanonical projections to the hippocampal CA3 regulate spatial learning and memory by modulating the feedforward hippocampal trisynaptic pathway

The hippocampal formation (HF) is well documented as having a feedforward, unidirectional circuit organization termed the trisynaptic pathway. This circuit organization exists along the septotemporal axis of the HF, but the circuit connectivity across septal to temporal regions is less well described. The emergence of viral genetic mapping techniques enhances our ability to determine the detailed complexity of HF circuitry. In earlier work, we mapped a subiculum (SUB) back projection to CA1 prompted by the discovery of theta wave back propagation from the SUB to CA1 and CA3. We reason that this circuitry may represent multiple extended noncanonical pathways involving the subicular complex and hippocampal subregions CA1 and CA3. In the present study, multiple retrograde viral tracing approaches produced robust mapping results, which supports this prediction. We find significant noncanonical synaptic inputs to dorsal hippocampal CA3 from ventral CA1 (vCA1), perirhinal cortex (Prh), and the subicular complex. Thus, CA1 inputs to CA3 run opposite the trisynaptic pathway and in a temporal to septal direction. Our retrograde viral tracing results are confirmed by anterograde-directed viral mapping of projections from input mapped regions to hippocampal dorsal CA3 (dCA3). We find that genetic inactivation of the projection of vCA1 to dCA3 impairs object-related spatial learning and memory but does not modulate anxiety-related behaviors. Our data provide a circuit foundation to explore novel functional roles contributed by these noncanonical hippocampal circuit connections to hippocampal circuit dynamics and learning and memory behaviors.

This study reveals extensive non-canonical synaptic inputs to dorsal hippocampal CA3 from ventral CA1, perirhinal cortex and subicular complex, and shows that genetic inactivation of projection from ventral CA1 to dorsal CA3 impairs object-related spatial learning and memory.     

Adaptation of trigeminal ganglion cells to periodic whisker deflections

Trigeminal ganglion neurons in adult rats adapt to periodic whisker deflections in the range of 1–40?Hz, manifested as a reduction in spike counts to progressively later stimuli in a train of pulsatile or sinusoidal deflections. For high velocity, pulsatile deflections, adaptation is time- and frequency-dependent; as in the case of thalamic and cortical neurons, adaptation is greater at higher stimulus frequencies. With slower velocity, sinusoidal movements, trigeminal ganglion cells differ from central neurons, however, by exhibiting strong adaptation even at low frequencies. For both types of stimuli, effects in trigeminal ganglion neurons were more pronounced in rats maintained during the recording session under neuromuscular blockade than in non-paralysed animals. Results are consistent with previous findings in other systems that frequency-dependent adaptation of cutaneous primary afferent neurons is affected by mechanical properties of the skin. Such effects are likely to vary depending on the nature of the whisker stimuli and physiological states that affect skin viscoelasticity.