Single unit oscillations in rat trigeminal nuclei and their control by the sensorimotor cortex.

Oscillatory activity at both the single and multiunit levels has been reported in most central nervous system structures, and is postulated as a key factor in information processing and coding. Rats provide an excellent model for oscillation-based information processing, since tactile perception of the environment is achieved by rhythmic movements of their whiskers and information-related rhythmic activity has been identified in the thalamus and cortex. However, rhythmic activity related to information processing has never been reported in the sensory trigeminal complex (STC), the first brain stem relay station for whisker-related tactile information. In the present work, we demonstrate the existence of neural oscillations in the vibrissae-related neurons of the nuclei principalis (Pr5), oralis (Sp5o), interpolaris (Sp5i) and caudalis (Sp5c). Rhythmic activity was associated with the main task of each nucleus, prominent in nuclei responsible for tactile vibrissae information processing (up to 17% oscillating neurons in Pr5 and 26% in Sp5i) and less conspicuous in those concerned with pain (8% oscillating neurons in Sp5o and in Sp5c). The higher percentage of oscillating neurons and higher frequencies in Sp5i than in Pr5 suggests an active role for rhythmic activity in integrating multivibrissa inputs. Oscillations are generated within the brainstem; data obtained from decorticated animals suggest the existence of a differential cortical control of the rhythmic processes in STC nuclei. Corticofugal activity modifies oscillation frequency and synchronization strength of the rhythmic activity mainly during tactile stimulation of the vibrissae.

Early frequency-dependent information processing and cortical control in the whisker pathway of the rat: electrophysiological study of brainstem nuclei principalis and interpolaris.

The rat facial whiskers form a high-resolution sensory apparatus for tactile information coding and are used by these animals for the exploration and perception of their environment. Previous work on the rat vibrissae system obtained evidence for vibration-based feature extraction by the whiskers, texture classification by the cortical neurons, and "low-pass", "high-pass", and "band-pass" filtering properties in both thalamic and cortical neurons. However, no data are available for frequency-dependent information processing in the brainstem sensory trigeminal complex (STC), the first relay station of the vibrissae pathway. In the present paper, we studied the frequency-dependent processing characteristics of the STC nuclei that mainly project to the thalamus, nuclei principalis, and interpolaris. This is the first time that STC nuclei have been studied together via a wide range of stimulation frequencies (1-40 Hz), four different and complementary metrics, and the same experimental protocol. Moreover, the role of corticofugal projection to these nuclei as well as the influence of input from the whiskers has been analyzed. We show that both nuclei perform frequency-dependent coding of tactile information: low pass and band-pass filtering occurs for the spiking rate in short post-stimuli time intervals, high-pass and band-pass filtering occurs for the spiking rate in long trains of stimuli, and an increase of response latencies and low pass filtering occurs for phase-locked stimuli. These information-processing characteristics are neither imposed by the sensorimotor cortex nor introduced by the afferent fibres. The sensorimotor cortex exerts a distinct modulatory effect on each nucleus.

Determinación del patrón de conectividad cerebral a partir de EEG en presencia de artefactos / Determining brain-connectivity patterns in presence of artefacts using EEG

Los diferentes estados del cerebro provocan la formacióntemporal de circuitos corticales cuya discriminación experimentalabre el camino al estudio y caracterización de respuestasde comportamiento. En este trabajo recogemos eilustramos en ejemplos los pasos necesarios para la determinaciónde patrones de conectividad funcional entre zonascorticales a partir de los registros EEG. El primer paso, lasupresión de artefactos de diferentes tipos, se realizamediante el análisis de componentes independientes quepermite reconstruir la actividad neuronal subyacente alartefacto e indica en qué grado está presente el artefactosobre cada electrodo. En el segundo paso determinamos laconectividad funcional a partir de registros preprocesados.Empleamos métodos estadísticos: la Coherencia EspectralParcial y dDTF (direct Directed Transfer Function) que proporcionanun patrón de conectividad teniendo en cuenta elnivel de sincronización entre señales de los electrodos.Demostramos y cuantificamos las diferencias el la topologíade la red cortical utilizando como ejemplo dos estados del sujeto: ojos abiertos y cerrados. Para no cerrarnos a la ideade que dos estructuras interactúan solo cuando están sincronizadas,también consideramos las señales registradasen un contexto determinista. Demostramos que la dinámicalocal en el estado de ojos abiertos es más compleja, debidoa que el patrón de conectividad es más denso

The different brain states incite in the generation of temporalcortical circuits, whose experimental discriminationallows the study and characterization of behavioral responses.In this work, we summarize and illustrate in examplesthe needed steps for the determination of functional connectivitypatterns among cortical areas from EEG recordings.The firts step, different types of artifacts removal, istreated by means of independent component analysis thatallows the recovering of neural activity under the artifactand show the presence degree of the artifact over eachelectrode position. In the second steps we determine thefunctional connectivity from the preprocessed recordings.We employ statistical methods: Partial Spectral Coherenceand dDTF (direct Directed Transfer Function), that providethe connectivity patterns taking into account the synchronizationlevel among the signal. We demostrate and quantifythe differences in the cortical network topology usingas an example two subject states: open and close eyes. Tobe opened to the idea that two structures interact only when they are synchronized, we also consider the signal ina deterministic framework. We demostrate that the localdynamic in open eye state is more complex, due to theconnectivity pattern is more dense

Information coding by ensembles of resonant neurons.

In the present paper, we propose a novel neural procedure for signal processing and coding based on the subthreshold oscillations and resonance of the neural membrane potential that could be used by real neurons to perform frequency spectra analysis and information coding of incoming signals. Taking into account the biophysical properties of the neural membranes, we note that the subthreshold resonant behaviour they exhibit can be used to analyse incoming signals and represent them in the frequency domain. We study the reliability of the representation of signals depending on the biophysical parameters of the neurons, the fault-tolerance of this coding scheme and its robustness against noise and in the presence of spikes. The principal characteristics of our system are the use of the physical phenomenon of neural resonance (rarely considered in the literature for signal coding); it fits well with the biophysical parameters of most neurons that exhibit subthreshold oscillations; it is compatible with experimental data; and it can be easily integrated in a more general model of information processing and coding that includes communication between neurons based on spikes.

Artificial stimulation of the peripheral nerves to generate natural-like activity in the central nervous system.

In the present work we study how sensory inputs conveyed by nerve fibers in the form of spatiotemporal patterns generate different responses in the central nervous system (CNS) depending on the physical characteristics of the stimulus applied and then we reproduce similar responses by means of electrical stimulation of the nervous fibers.

Rhythmic neuronal interactions and synchronization in the rat dorsal column nuclei.

Single-unit and multiunit activities were recorded from dorsal column nuclei of anesthetized rats in order to study the characteristics of the oscillatory activity expressed by these cells and their neuronal interactions. On the basis of their firing rate characteristics in spontaneous conditions, two types of dorsal column nuclei cell have been identified. Low-frequency cells (74%) were silent or displayed a low firing rate (1.9+/-0.48 spikes/s), and were identified as thalamic-projecting neurons because they were activated antidromically by medial lemniscus stimulation. High-frequency cells (26%) were characterized by higher discharge rates (27.2+/-5.1 spikes/s). None of them was antidromically activated by medial lemniscus stimulation. Low-frequency neurons showed a non-rhythmic discharge pattern spontaneously which became rhythmic under sensory stimulation of their receptive fields (48% of cases; 4.8+/-0.23Hz). All high-frequency neurons showed a rhythmic discharge pattern at 13.8+/- 0.68Hz either spontaneously or during sensory stimulation of their receptive fields. The shift predictor analysis indicated that oscillatory activity is not phase-locked to the stimulus onset in either type of cell, although the stimulus can reset the phase of the rhythmic activity of high-frequency cells. Cross-correlograms between pairs of low-frequency neurons typically revealed synchronized rhythmic activity when the overlapping receptive fields were stimulated. Rhythmic synchronization of high-frequency discharges was rarely observed spontaneously or under sensory stimulation. High-frequency neuronal firing could be correlated with the low-frequency neuronal activity or more often with the multiunit activity during sensory stimulation. Moreover, the presence of oscillatory activity modulated the sensory responses of dorsal column nuclei cells, favoring their responses. These findings indicate that thalamic-projecting and non-projecting neurons in dorsal column nuclei exhibited distinct oscillatory characteristics. However, both types of neuron may be entrained into an oscillatory rhythmic pattern when their overlapping receptive fields are stimulated, suggesting that in those conditions the dorsal column nuclei generate a populational oscillatory output to the somatosensory thalamus which could modulate and amplify the effectiveness of the somatosensory transmission.

Sensory information processing in the dorsal column nuclei by neuronal oscillators.

The dorsal column nuclei, a first relay station of the somatosensory system, express coherent oscillatory activity in the 4-22 Hz frequency range at single unit, multiunit and local field potential levels. This activity appears spontaneously (33% of the cases) or, more commonly (83%), during natural sensory stimulation of the receptive field. Such oscillations are not imposed upon the dorsal column nuclei by incoming sensory afferents nor cortico-nuclear projections, which indicates that they are generated within the dorsal column nuclei. We concluded that dorsal column nuclei transform a non-rhythmic input from the periphery to a populational oscillatory output to the somatosensory thalamus during sensory stimulation.

Electrophysiological effects of temporary deafferentation on two characterized cell types in the nucleus gracilis of the rat.

Single- and multiunit recordings were made in the nucleus gracilis of anaesthetized rats in order to study the characteristics of the responses to natural cutaneous stimulation before and during local anaesthetic-induced deafferentation. Two types of cells were found which exhibited different electrophysiological features at rest and in response to stimulation of their receptive fields (RFs). Low-frequency (LF) neurons (77%) had very low spontaneous activity, and most could be antidromically activated from the medial lemniscus. High-frequency (HF) cells (23%) had a much higher spontaneous discharge rate, with shorter spike duration, and did not project through the lemniscus. Both cell types generated phasic responses with similar latencies following cutaneous stimulation. Recordings of lemniscal axons had similar characteristics to those of LF neurons. Within minutes after anaesthetizing the functional centre of the RF, the LF and HF cells displayed new RFs, and enhanced responses to stimuli delivered at the periphery of the original fields. Firing rates increased during anaesthesia, but only in LF cells. Using a paired-stimulation paradigm, many LF neurons displayed during anaesthesia a decrease of the normal inhibition that the conditioning stimulus evoked on the responses to the test stimulus; the opposite effect was observed in all HF cells. These results suggest that (i) LF neurons correspond to thalamic projection cells, and HF neurons may be inhibitory interneurons; (ii) by disinhibiting LF (but not HF) cells, temporary deafferentation may increase neuronal responsiveness to peripheral stimulation, and thus contribute to reveal new RFs, and (iii) these changes in the nucleus gracilis may partly account for the reorganization of representational maps at higher levels of the somatosensory pathways.

Local anaesthesia induces immediate receptive field changes in nucleus gracilis and cortex.

The reorganization of receptive fields of nucleus gracilis neurones after local anaesthesia, and its relationship to the reorganization of cortical maps were studied in the rat. Cutaneous stimulation was performed using electronically gated air jets. Single unit recordings were obtained in gracilis nucleus and somatosensory cortex. Temporary anaesthesia was induced with lidocaine (2%, 5-15 microliters s.c.), which blocked the responses in < 2 min and provoked the simultaneous appearance of new overlapping receptive fields in gracilis and cortical neurones in 2-30 min. The present results suggest that the early reorganization of somatosensory cortical maps after temporary anaesthesia may be partly due to the emergence of new receptive fields in nucleus gracilis neurones.

Purification to homogeneity of an active opioid receptor from rat brain by affinity chromatography.

Active opioid binding proteins were solubilized from rat brain membranes in high yield with sodium deoxycholate in the presence of NaCl. Purification of opioid binding proteins was accomplished by opioid antagonist affinity chromatography. Chromatography using the delta-opioid antagonist N,N-diallyl-Tyr-D-Leu-Gly-Tyr-Leu attached to omega-aminododecyl-agarose (Affi-G) (procedure A) yielded a partially purified protein that binds selectively the delta-opioid agonist [3H]Tyr-D-Ser-Gly-Phe-Leu-Thr ([3H]DSLET), with a Kd of 19 +/- 3 nM and a Bmax of 5.1 +/- 0.4 nmol/mg of protein. Subsequently, Lens culinaris agglutinin-Sepharose 4B chromatography of the Affi-G eluate resulted in isolation of an electrophoretically homogeneous protein of 58 kDa that binds selectively [3H]DSLET with a Kd of 21 +/- 3 nM and a Bmax of 16.5 +/- 1.0 nmol/mg of protein. Chromatography using the nonselective antagonist 6-aminonaloxone coupled to 6-aminohexanoic acid-Sepharose 4B (Affi-NAL) (procedure B) resulted in isolation of a protein that binds selectively [3H]DSLET with a Kd of 32 +/- 2 nM and a Bmax of 12.4 +/- 0.5 nmol/mg of protein, and NaDodSO4/PAGE revealed a major band of apparent molecular mass 58 kDa. Polyclonal antibodies (Anti-R IgG) raised against the Affi-NAL protein inhibit the specific [3H]DSLET binding to the Affi-NAL eluate and to the solubilized membranes. Moreover, the Anti-R IgG inhibits the specific binding of radiolabeled Tyr-D-Ala-Gly-N-methyl-Phe-Gly-ol (DAMGO; mu-agonist), DSLET (delta-agonist), and naloxone to homogenates of rat brain membranes with equal potency. Furthermore, immunoaffinity chromatography of solubilized membranes resulted in the retention of a major protein of apparent molecular mass 58 kDa. In addition, immunoblotting of solubilized membranes and purified proteins from the Affi-G and Affi-NAL matrices revealed that the Anti-R IgG interacts with a protein of 58 kDa.