Local Field Responses Research Articles

Cholinergic modulation of interhemispheric inhibition in the mouse motor cortex.

Interhemispheric inhibition of the homotopic motor cortex is believed to be effective for accurate unilateral motor function. However, the cellular mechanisms underlying interhemispheric inhibition during unilateral motor behavior remain unclear. Furthermore, the impact of the neuromodulator acetylcholine on interhemispheric inhibition and the associated cellular mechanisms are not well understood. To address this knowledge gap, we conducted recordings of neuronal activity from the bilateral motor cortex of mice during the paw-reaching task. Subsequently, we analyzed interhemispheric spike correlation at the cell-pair level, classifying putative cell types to explore the underlying cellular circuitry mechanisms of interhemispheric inhibition. We found a cell-type pair-specific enhancement of the interhemispheric spike correlation when the mice were engaged in the reaching task. We also found that the interhemispheric spike correlation was modulated by pharmacological acetylcholine manipulation. The local field responses to contralateral excitation differed along the cortical depths, and muscarinic receptor antagonism enhanced the inhibitory component of the field response in deep layers. The muscarinic subtype M2 receptor is predominantly expressed in deep cortical neurons, including GABAergic interneurons. These results suggest that GABAergic interneurons expressing muscarinic receptors in deep layers mediate the neuromodulation of interhemispheric inhibition in the homotopic motor cortex.

Controlling Plasmonic Field Enhancement via the Interference of Orthogonal Plasmonic Modes

AbstractOptical nanoantennas concentrate light into their local fields. The field concentration property is governed by the plasmonic resonances and their interference. Here, we present a method for controllable local-field interferences in the hot spot of nanorods and experimentally demonstrate that the field enhancement can be tuned in a wide range. For this, we design nanoparticles with given phase relations between their plasmonic eigenmodes and at the same time tune the phase between the components of the external field by changing its polarization state to achieve in-phase excitation of the plasmon modes. Strong-field photoemission is applied to probe the field enhancement property of the nanorods employing femtosecond pulses of different polarization states. Our findings provide a new degree of freedom in plasmonic resonance tuning and may inspire diverse designs of local-field responses and expand the applications in nanoscale sensing, spectroscopy, and dynamically tunable devices.

In vivo spontaneous activity and coital-evoked inhibition of mouse accessory olfactory bulb output neurons

Little is known about estrous effects on brain microcircuits. We examined the accessory olfactory bulb (AOB) invivo, in anesthetized naturally cycling females, as model microcircuit receiving coital somatosensory information. Whole-cell recordings demonstrate that output neurons are relatively hyperpolarized in estrus and unexpectedly fire high frequency bursts of action potentials. To mimic coitus, a calibrated artificial vagino-cervical stimulation (aVCS) protocol was devised. aVCS evoked stimulus-locked local field responses in the interneuron layer independent of estrous stage. The response is sensitive to α1-adrenergic receptor blockade, as expected since aVCS increases norepinephrine release in AOB. Intriguingly, only in estrus does aVCS inhibit AOB spike output. Estrus-specific output reduction coincides with prolonged aVCS activation of inhibitory interneurons. Accordingly, in estrus the AOB microcircuit sets the stage for coital stimulation to inhibit the output neurons, possibly via high frequency bursting-dependent enhancement of reciprocal synapse efficacy between inter- and output neurons.

Turning a hot spot into a cold spot: polarization-controlled Fano-shaped local-field responses probed by a quantum dot

Optical nanoantennas can convert propagating light to local fields. The local-field responses can be engineered to exhibit nontrivial features in spatial, spectral and temporal domains, where local-field interferences play a key role. Here, we design nearly fully controllable local-field interferences in the nanogap of a nanoantenna, and experimentally demonstrate that in the nanogap, the spectral dispersion of the local-field response can exhibit tuneable Fano lineshapes with nearly vanishing Fano dips. A single quantum dot is precisely positioned in the nanogap to probe the spectral dispersions of the local-field responses. By controlling the excitation polarization, the asymmetry parameter q of the probed Fano lineshapes can be tuned from negative to positive values, and correspondingly, the Fano dips can be tuned across a broad spectral range. Notably, at the Fano dips, the local-field intensity is strongly suppressed by up to ~50-fold, implying that the hot spot in the nanogap can be turned into a cold spot. The results may inspire diverse designs of local-field responses with novel spatial distributions, spectral dispersions and temporal dynamics, and expand the available toolbox for nanoscopy, spectroscopy, nano-optical quantum control and nanolithography.

Evidence for the origin of the binaural interaction component of the auditory brainstem response.

The binaural interaction component (BIC) represents the mismatch between auditory brainstem responses (ABR) obtained with binaural stimulation and the sum of ABRs obtained with monaural left and right stimulation. It is generally assumed that the BIC reflects binaural integration. Its potential use as a diagnostic tool, however, is hampered by the lack of direct evidence about its origin. While an origin at the initial site of binaural integration seems likely, there is no general agreement on the contribution of the two primary candidate nuclei, the lateral and medial superior olives (LSO and MSO, respectively). Here, we recorded local field potentials (LFP) and responses of units in the LSO and MSO of Mongolian gerbils (Meriones unguiculatus), presenting clicks with an interaural time or level difference (ITD and ILD, respectively), while simultaneously recording ABR. We determined the BIC from the ABR and, importantly, from LFP and responses of units in the LSO and MSO. If stimulus-induced changes in the ABR-derived BIC have their source in the LSO and/or MSO, we expect coherent changes in the unit-derived and the ABR-derived BIC. We find that BIC obtained from LSO units exhibits the same ITD and ILD dependence as the ABR-derived BIC. Neither BIC obtained from MSO units nor LFP-derived BIC recorded in either LSO or MSO did. The data thus strongly suggest that it is the activity of LSO units in the gerbil that is decisive for the generation of the ABR-derived BIC, determining its properties.

Bonding and charge transfer plasmons of conductively bridged nanoparticles: The effects of junction conductance and nanoparticle morphology

A detailed study of charge transfer plasmon properties of conductively bridged nanoparticles is essential for designing artificial molecules and developing plasmonic sensors. In this report, we demonstrate spectral tuning and control of local field responses of conductively bridged and compositionally homogeneous plasmonic nanoparticles of various shapes and sizes. The scattering spectral peaks of connected nanoparticles are tuned by controlling inter-particle feed-gap, junction conductance, and nanoparticle morphology. The far-field spectral responses are further tuned by increasing the number of nanoparticles from dimer to trimer, and a generalized expression for charge transfer plasmon peak shift with junction geometry is developed for various shapes of nanotrimers. The corresponding near-field distributions of the linked nanoparticles also exhibit remarkable features. Specifically, the local field profiles of dimer nanoparticles calculated at the charge transfer wavelengths show strong interaction between the nanoparticles. On the other hand, in the bridged symmetrical nanotrimers, the central nanoparticles act as a bridge and only the rest two of the nanoparticles show bright modes. These findings suggest that using conductively bridged nanoaggregates could play a significant role in tuning far-field spectral responses of plasmonic nanostructures for practical applications in molecular sensing.

Expression of ionotropic receptors in terrestrial hermit crab's olfactory sensory neurons.

Coenobitidae are one out of at least five crustacean lineages which independently succeeded in the transition from water to land. This change in lifestyle required adaptation of the peripheral olfactory organs, the antennules, in order to sense chemical cues in the new terrestrial habitat. Hermit crab olfactory aesthetascs are arranged in a field on the distal segment of the antennular flagellum. Aesthetascs house approximately 300 dendrites with their cell bodies arranged in spindle-like complexes of ca. 150 cell bodies each. While the aesthetascs of aquatic crustaceans have been shown to be the place of odor uptake and previous studies identified ionotropic receptors (IRs) as the putative chemosensory receptors expressed in decapod antennules, the expression of IRs besides the IR co-receptors IR25a and IR93a in olfactory sensory neurons (OSNs) has not been documented yet. Our goal was to reveal the expression and distribution pattern of non-co-receptor IRs in OSNs of Coenobita clypeatus, a terrestrial hermit crab, with RNA in situ hybridization. We expanded our previously published RNAseq dataset, and revealed 22 novel IR candidates in the Coenobita antennules. We then used RNA probes directed against three different IRs to visualize their expression within the OSN cell body complexes. Furthermore we aimed to characterize ligand spectra of single aesthetascs by recording local field potentials and responses from individual dendrites. This also allowed comparison to functional data from insect OSNs expressing antennal IRs. We show that this orphan receptor subgroup with presumably non-olfactory function in insects is likely the basis of olfaction in terrestrial hermit crabs.

Origin and Properties of Striatal Local Field Potential Responses to Cortical Stimulation: Temporal Regulation by Fast Inhibitory Connections

Evoked striatal field potentials are seldom used to study corticostriatal communication in vivo because little is known about their origin and significance. Here we show that striatal field responses evoked by stimulating the prelimbic cortex in mice are reduced by more than 90% after infusing the AMPA receptor antagonist CNQX close to the recording electrode. Moreover, the amplitude of local field responses and dPSPs recorded in striatal medium spiny neurons increase in parallel with increasing stimulating current intensity. Finally, the evoked striatal fields show several of the basic known properties of corticostriatal transmission, including paired pulse facilitation and topographical organization. As a case study, we characterized the effect of local GABAA receptor blockade on striatal field and multiunitary action potential responses to prelimbic cortex stimulation. Striatal activity was recorded through a 24 channel silicon probe at about 600 µm from a microdialysis probe. Intrastriatal administration of the GABAA receptor antagonist bicuculline increased by 65±7% the duration of the evoked field responses. Moreover, the associated action potential responses were markedly enhanced during bicuculline infusion. Bicuculline enhancement took place at all the striatal sites that showed a response to cortical stimulation before drug infusion, but sites showing no field response before bicuculline remained unresponsive during GABAA receptor blockade. Thus, the data demonstrate that fast inhibitory connections exert a marked temporal regulation of input-output transformations within spatially delimited striatal networks responding to a cortical input. Overall, we propose that evoked striatal fields may be a useful tool to study corticostriatal synaptic connectivity in relation to behavior.

The role of cannabinoids in the neurobiology of sensory gating: A firing rate model study

Gating of sensory (e.g. auditory) information has been demonstrated as a reduction in the auditory-evoked potential responses recorded in the brain of both normal animals and human subjects. Auditory gating is perturbed in schizophrenic patients and pharmacologically by drugs such as amphetamine, phencyclidine or ketamine, which precipitate schizophrenic-like symptoms in normal subjects. The neurobiological basis underlying this sensory gating can be investigated using local field potential recordings from single electrodes. In this paper we use such technology to investigate the role of cannabinoids in sensory gating. Cannabinoids represent a fundamentally new class of retrograde messengers which are released postsynaptically and bind to presynaptic receptors. In this way they allow fine-tuning of neuronal response, and in particular can lead to so-called depolarisation-induced suppression of inhibition (DSI). Our experimental results show that application of the exogenous cannabinoid WIN55, 212-2 can abolish sensory gating as measured by the amplitude of local field responses in rat hippocampal region CA3. Importantly we develop a simple firing rate population model of CA3 and show that gating is heavily dependent upon the presence of a slow inhibitory ( GABA B ) pathway. Moreover, a simple phenomenological model of cannabinoid dynamics underlying DSI is shown to abolish gating in a manner consistent with our experimental findings.

Propagation of Neuronal Activity along the Neocortical–Perirhinal–Entorhinal Pathway in the Guinea Pig

The study of synaptic interactions within the parahippocampal region is crucial to understand the integrative functions performed by this region during memory information processing. Despite the extensive anatomical studies, the intrinsic physiology of the parahippocampal area has been poorly investigated. We describe here the organization pattern of the synaptic network formed by the temporal neocortex, areas 36 and 35 of the perirhinal cortex (PRC) and the entorhinal cortex (EC), in the in vitro isolated guinea-pig brain. Current source density analysis of laminar field potential profiles was performed with multichannel silicon probes positioned in different parahippocampal subfields. Stimulation of the temporal neocortex induced monosynaptic and polysynaptic potentials in areas 35 and 36, respectively. Area 36 stimulation evoked monosynaptic responses within areas 36 and 35. Stimuli in area 35 induced responses that propagated longitudinally along area 35 itself. No local field responses were observed in the EC after stimulation of both neocortex and areas 35/36. Despite the absence of a local extracellular response, intracellular recordings demonstrated that subpopulations of superficial layer neurons in medial and lateral EC showed polysynaptic EPSPs after stimulation of area 35 and area 36. The results demonstrate that the propagation of neuronal activity across the rhinal sulcus in the direction from the PRC to the EC is finely and diffusely distributed. In agreement with previous reports, these findings suggest that the PRC-EC pathway is highly regulated by inhibitory network interactions.

Olfactory inputs activate the medial entorhinal cortex via the hippocampus.

The lateral and medial regions of the entorhinal cortex differ substantially in terms of connectivity and pattern of activation. With regard to olfactory input, a detailed and extensive physiological map of the olfactory projection to the entorhinal cortex is missing, even if anatomic studies suggest that the olfactory afferents are confined to the lateral and rostral entorhinal region. We studied the contribution of the medial and lateral entorhinal areas to olfactory processing by analyzing the responses induced by lateral olfactory tract stimulation in different entorhinal subfields of the in vitro isolated guinea pig brain. The pattern of synaptic activation of the medial and lateral entorhinal regions was reconstructed either by performing simultaneous multisite recordings or by applying current source density analysis on field potential laminar profiles obtained with 16-channel silicon probes. Current source density analysis demonstrated the existence of a direct monosynaptic olfactory input into the superficial 300 microm of the most rostral part of the lateral entorhinal cortex exclusively, whereas disynaptic sinks mediated by associative fibers arising from the piriform cortex were observed at 100-350 microm depth in the entire lateral aspect of the cortex. No local field responses were recorded in the medial entorhinal region unless a large population spike was generated in the hippocampus (dentate gyrus and CA1 region) by a stimulus 3-5x the intensity necessary to obtain a maximal monosynaptic response in the piriform cortex. In these conditions, a late sink was recorded at a depth of 600-1000 microm in the medial entorhinal area (layers III-V) 10.6 +/- 0.9 (SD) msec after a population spike was simultaneously recorded in CA1. Diffuse activation of the medial entorhinal region was also obtained by repetitive low-intensity stimulation of the lateral olfactory tract at 2-8 Hz. Higher or lower stimulation frequencies did not induce hippocampal-medial entorhinal cortex activation. These results suggest that the medial and the lateral entorhinal regions have substantially different roles in processing olfactory sensory inputs.

Cylindrical Indentation of Orthotropic Laminates on Elastic Foundations

Problems of cylindrical indentation of orthotropic laminated beams on an elastic foundation are studied. Exact solution methods are developed to assess the displacement field for both the simply supported and clamped-ended cases. A numerical iteration algorithm is established to detect the contact length and the associated contact stresses for a prescribed contact load. The induced interlaminar shear stresses through the thickness and the amount of indentation are evaluated subsequently. The objective is to investigate the effects of span, indentor size, end support conditions, and foundation stiffness on the local field responses and load-indentation relationships. The results show that the effects of indentor size and foundation stiffness are significant. A sharp indentor or stiff foundation tends to localize the contact phenomenon, regardless of the span and the end support conditions. On the other hand, the effects of both the boundary condition and span may be prominent if a blunt indentor and a relatively soft foundation are employed.