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At least 1,063 records · Page 59Linked to original sources
PubMed1994

Morphine insensitive allodynia is produced by intrathecal strychnine in the lightly anesthetized rat.

The acute blockade of spinal glycinergic inhibition with intrathecal strychnine (i.t. STR; a glycine antagonist) in rats induces a change in somatosensory processing which is very similar to the sensory dysesthesia of clinical neural injury pain. In the present study, the effects of i.t. STR were examined in urethane-anesthetized rats. Noxious paw pinch (PP) or tail immersion (TI) in 55 degree C water evoked a pronounced pressor response, increased heart rate (HR) and desynchronized the electroencephalogram; a non-noxious, hair deflection (HD) elicited only minor cardiovascular responses. After i.t. STR (40 micrograms), an identical HD stimulus evoked markedly enhanced cardiovascular responses, resembling those evoked by noxious stimuli, and a HD-evoked motor withdrawal was observed. Consistent STR-dependent responses were only observed if a light plane of anesthesia was maintained for the duration of the experiment. The effects of i.t. STR were dose-dependent and reversible, lasting 15-30 min. Spinal morphine (50 micrograms) completely abolished the cardiovascular responses to PP and TI, but the HD-evoked, STR-dependent cardiovascular and motor withdrawal responses remained unchanged. In contrast, the non-selective excitatory amino acid antagonist, gamma-D-glutamylglycine (DGG; 50 micrograms) was effective in suppressing both the STR-dependent cardiovascular and motor withdrawal responses. These data suggest that STR-dependent responses evoked by non-noxious stimuli are mediated by mechanisms distinct from those of conventional noxious stimuli and that i.t. STR may be useful for investigating the spinal pharmacology of somatosensory processing following the loss of spinal glycinergic inhibition.

Anesthesia↗
PubMed1985

Tonic desynchronisation of cortical electroencephalogram by electrical and chemical stimulation of superior colliculus and surrounding structures in urethane-anaesthetised rats.

Damage to the superior colliculus in rats impairs desynchronisation of the cortical electroencephalogram in response to light flashes. However, it is unclear which elements within the superior colliculus, and which efferent collicular pathways, might be involved in alerting cerebral cortex to visual stimuli. To investigate this problem, the superior colliculus and surrounding structures were stimulated either electrically (3 s trains of 0.2 ms 100 Hz cathodal pulses), or chemically (200 nl of 5 mM sodium L-glutamate), in rats anaesthetised with urethane. The cortical electroencephalogram was recorded bilaterally from frontal cortex. At each site tested with electrical stimulation the threshold current (up to 60 microA) required to produce tonic desynchronisation (outlasting stimulation-offset by at least 10 s) was determined. Comparison of the effects of electrical and chemical stimulation suggested the following: (1) stimulation of cells in the deep layers of the superior colliculus can desynchronise the cortical electroencephalogram. There may also be an additional effective area in the rostral part of the superficial layers, but this needs to be confirmed in unanaesthetised animals. (2) Stimulation of fibres in the deep white layers of caudal superior colliculus, and of cells in a wide area of caudal midbrain reticular formation, are also effective at desynchronising the cortical electroencephalogram. It is therefore possible that the ipsilateral descending pathway, that runs from the superior colliculus to terminate in the parabigeminal and cuneiform nuclei and surrounding reticular formation, is involved in mediating cortical desynchronisation initiated by the superior colliculus. Evidence from other studies indicates that some sites in this pathway may be part of a "defence arousal system". (3) Sites on the ascending pathways from the superior colliculus, to structures including dorsal thalamus, pretectum, zona incerta and rostral midbrain reticular formation, were relatively ineffective at tonically desynchronising the cortex. However, some of these pathways might mediate phasic, movement-related arousal of collicular origin.

Animals↗
PubMed1995

Impairment of blood-brain barrier function by serotonin induces desynchronization of spontaneous cerebral cortical activity: experimental observations in the anaesthetized rat.

The possibility that elevation of serotonin in the circulation, which is found in various pathological states, influences the spontaneous cerebral cortical activity was examined in a rat model. The electroencephalogram was recorded using bipolar epidural electrodes placed over the frontal and parietal cerebral cortex. Intravenous infusion of serotonin (10 micrograms/kg per min for 10 min) decreased the electroencephalogram amplitude in both frontal and parietal recordings within 4 min of infusion. This decrease in amplitude was reversible, Pretreatment with cyproheptadine (a potent serotonin2 receptor antagonist) prevented the serotonin-induced decrease of the electroencephalogram amplitude. The blood-brain barrier permeability to Evans Blue and [131I]sodium was increased in frontal and parietal cortex. This increase in blood-brain barrier permeability was absent in animals pretreated with cyproheptadine. These results provide direct evidence that an elevated level of serotonin in blood has the capacity to influence spontaneous cortical electrical activity. This effect of serotonin on electroencephalogram appears to be due to its ability to enter into the brain parenchyma by inducing a short-term breakdown of the blood-brain barrier, probably via serotonin2 receptors.

Anesthesia↗
PubMed1996

Differential effects of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid and N-methyl-D-aspartate receptor antagonists applied to the basal forebrain on cortical acetylcholine release and electroencephalogram desynchronization.

It is known that glutamatergic tracts activated from the pedunculopontine tegmentum represent a major input to the nucleus basalis magnocellularis. To establish the role of different ionotropic glutamate receptors in synaptic transmission in the basal forebrain, the pedunculopontine tegmentum was stimulated in urethane-anesthetized rats and the resulting increases in cortical acetylcholine release and desynchronization of the electroencephalogram were monitored. R(-)-3-(2-carboxypiperazine-4-yl)-propyl-I-phosphonic acid (CPP), an antagonist at N-methyl-D-aspartate-type glutamate receptors, and 6, 7-dinitroquinoxaline-2, 3-dione (DNQX), an antagonist at alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)-type glutamate receptors, were delivered through a microdialysis probe placed in the basal forebrain. The N-methyl-D-aspartate antagonist preferentially inhibited cortical acetylcholine release, while the AMPA antagonist was more powerful in reducing desynchronization. A combination of both N-methyl-D-aspartate and AMPA antagonists abolished the increase in cortical acetylcholine release without reducing desynchronization. The dissociation between increased cortical acetylcholine release and electroencephalogram desynchronization suggests that the activity of corticopetal basal forebrain cholinergic neurons is neither necessary nor sufficient to produce electroencephalogram desynchronization. Rather, the nucleus basalis can probably affect the electroencephalogram by its projections to the thalamus. The reversal of the inhibitory effect of DNQX on the electroencephalogram by CPP may be due to the blockade of N-methyl-D-aspartate receptors on the GABAergic projection from the basal forebrain to the thalamus.

Acetylcholine↗
PubMedDate not supplied

Neuromuscular blockade: the effects on two hippocampal RSA (theta) systems and neocortical desynchronization.

Neocortical and hippocampal electroencephalographic (EEG) activity were recorded from rats during: (a) spontaneous activities, (b) paralysis produced by curare or gallamine neuromuscular blockade, and (c) urethane anesthesia. All of the patterns of EEG recorded from normal rats were obtained from paralyzed rats including: (a) atropine resistant neocortical desynchronization and fast (6--12 Hz) hippocampal rhythmical slow activity (RSA) normally associated with overt Type I or voluntary movement, (b) atropine sensitive and urethane resistant slow (4--6 Hz) RSA which can be recorded from immobile animals during conditioning procedures, or during brain or sensory stimulation, and (c) large amplitude irregular neocortical and hippocampal EEG which can be recorded from immobile or sleeping animals. Depth profiles of RSA were taken from the hippocampal formation of urethanized and curarized rats during posterior hypthalamic stimulation. The results confirmed findngs of two RSA amplitude maxima with an approximate 180 degree phase difference, one location in stratum oriens of area CA-1, the other in stratum moleculare of the dentate gyrus, and suggest there are two generators of RSA. Atropine sensitive and atropine resistant types of RSA were found in each generator. The results suggest that RSA may be supported by both cholinergic and noncholinergic input to each generator and that neither RSA type could be only the result of proprioceptive feedback from joints or muscles.

Animals↗
PubMedDate not supplied

Strength-duration properties of single units driven by electrical stimulation of the lateral hypothalamus in rats.

Cathodal strength-duration functions were measured for 27 single units which were driven by electrical stimulation of the lateral hypothalamus. The distribution of chronaxies of these units showed four clusters at about 0.1, 0.25, 0.4 and 0.5 msec. These chronaxies are not fundamentally different from those previously reported for peripheral nerve. Two units fired repetitively during a long-duration stimulation pulse. Anodal strengitation. The data are discussed with reference to behaviorally determith duration properties were obtained from 14 units. Four units were not excited by anodal pulses of any strength or duration, four were excited during an anodal pulse (anode-make excitation) but not at the termination of the pulse (anode-break excitation), and six showed both anode-make and anode-break excitation. The data are discussed with reference to behaviorally determined strength-duration functions for brain stimulation reward.

Action Potentials↗
PubMedDate not supplied

Epileptogenic activity in the amygdala is not affected by the amidine steroid, R 5135.

The synthetic steroid amidine 3-alpha-hydroxy-16-imino-5-beta-17aza androstan-11-one (R 5135) is known to elicit long-lasting spiking in the cortex in the presence of neocortical damage. R 5135 administered to amygdaloid-kindled and naive rats resulted in regular, high-amplitude spiking in the cortex but only occasionally elicited small-amplitude spikes in the amygdala (AMY) and hippocampus (HPC). Interictal spikes from the AMY of kindled rats were not synchronized with cortical spikes induced by the steroid. Given that R 5135 is known to be a GABAA receptor antagonist, these findings suggest that GABAA receptors in AMY and HPC may have lower affinity for 3 alpha-hydroxysteroids.

Amygdala↗
PubMed1996

Sound-evoked electrocortical desynchronization is inhibited by N omega-nitro-L-arginine methyl ester microinfused into the inferior colliculi in rats.

In previous experiments we have shown that systemic or intracerebroventricular administration of N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, is able to significantly reduce sound-evoked electrocortical (ECoG) desynchronization in rats. The present experiments were aimed at identifying the site(s) of the brain through which these effects are mediated. L-NAME (200 and 300 nmol), oxyhaemoglobin (200 and 300 nmol), a NO-trapping agent, and methylene blue (100 and 150 nmol), an inhibitor of guanylate cyclase and NO synthase, given bilaterally into the inferior colliculi, but not in other relay stations of the acoustic pathway, prevented the reduction in ECoG amplitude induced by sound stimulation in rats. Significant reduction of sound-evoked ECoG desynchronization has also been observed in rats receiving injection of CGP37849 (125 and 500 pmol) and LY274614 (125 pmol), two competitive N-methyl-D-aspartate receptor antagonists into the inferior colliculi. The present results show that the inferior colliculus represents the main site where sound-evoked ECoG desynchronization is prevented by L-NAME and provide further support for the hypothesis that NO may play a role at this level in the control of the measured response.

Animals↗
PubMed2006

Dissociation of event-related potentials indexing arousal and semantic cohesion during emotional word encoding.

Event-related potential (ERP) studies have shown that emotional stimuli elicit greater amplitude late positive-polarity potentials (LPPs) than neutral stimuli. This effect has been attributed to arousal, but emotional stimuli are also more semantically coherent than uncategorized neutral stimuli. ERPs were recorded during encoding of positive, negative, uncategorized neutral, and categorized neutral words. Differences in LPP amplitude elicited by emotional versus uncategorized neutral stimuli were evident from 450 to 1000 ms. From 450 to 700 ms, LPP effects at midline and right hemisphere frontal electrodes indexed arousal, whereas LPP effects at left hemisphere centro-parietal electrodes indexed semantic cohesion. This dissociation helps specify the processes underlying emotional stimulus encoding, and suggests the need to control for semantic cohesion in emotional information processing studies.

Adult↗
PubMed2006

Benefits of interhemispheric collaboration can be eliminated by mixing stimulus formats that involve different cortical access routes.

Previous studies indicate that the benefits of dividing an information processing load across both cerebral hemispheres outweigh the costs of interhemispheric transfer as tasks become more difficult or cognitively complex. This is demonstrated as better performance when two stimuli to be compared are presented one to each visual field and hemisphere than when both stimuli are presented to the same single hemisphere (an across-hemisphere advantage). Two experiments indicate that this finding does not generalize to complex tasks that require matching numeric quantities represented by two very different visual formats whose processing involves somewhat different cortical areas: digits and dice-like dot patterns. In fact, mixing these stimulus formats consistently produces a within-hemisphere advantage. We propose that, when two simultaneously presented stimuli are presented in sufficiently different visual formats, identification of the two stimuli may take place in parallel, via different cortical access routes and with little or no interference, even when they are presented to the same cerebral hemisphere.

Adolescent↗
PubMed2004

Human cortical rhythms during visual delayed choice reaction time tasks. A high-resolution EEG study on normal aging.

Neuroimaging cognitive study of aging requires simple tasks ensuring a high rate of correct performances even in stressful neurophysiological settings. Here two simple delayed choice reaction time tasks were used to unveil event-related desynchronization (ERD) of theta (4-6 Hz) and alpha (6-12 Hz) electroencephalographic rhythms across normal aging. In the first condition, a cue stimulus (one bit) was memorized along a brief delay period (3.5-5.5 s). The explicit demand was visuo-spatial, but the retention could be also based on phonological and somatomotor coding. In the second condition, the cue stimulus remained available along the delay period. Correct performances were higher than 95% in both groups and tasks, although they were significantly better in young than elderly subjects (P < 0.03). During the delay period, theta and alpha ERD accompanying correct responses were recognized in the two groups, the alpha ERD being stronger and prolonged during the memory than non-memory task. On the other hand, the fronto-parietal theta and parietal alpha ERD were stronger in young than elderly subjects during both tasks. Notably, the frontal alpha ERD was negligible in elderly subjects. In conclusion, the present simple tasks unveiled in elderly compared to young subjects (i) a weaker involvement of (para)hippocampal-cortical circuits as revealed by theta ERD and (ii) a weaker involvement of "executive" thalamo-cortical circuits as revealed by frontal alpha ERD. These effects might worsen behavioral performances to the simple cognitive tasks with age. The present protocol is promising for the neuroimaging study of pathological aging.

Adult↗
PubMed2005

A capability model of individual differences in frontal EEG asymmetry.

Researchers interested in measuring individual differences in affective style via asymmetries in frontal brain activity have depended almost exclusively upon the resting state for EEG recording. This reflects an implicit conceptualization of affective style as a response predisposition that is manifest in frontal EEG asymmetry, with the goal to describe individuals in terms of their general approach or withdrawal tendencies. Alternatively, the response capability conceptualization seeks to identify individual capabilities for approach versus withdrawal responses during emotionally salient events. The capability approach confers a variety of advantages to the study of affective style and personality, and suggests new possibilities for the approach/withdrawal motivational model of frontal EEG asymmetry and emotion. Logical as well as empirical arguments supportive of this conclusion are presented.

Adolescent↗
PubMed2005

The NMDA receptor NR2B subunit contributes to epileptogenesis in human cortical dysplasia.

Cortical dysplasia (CD) is often associated with pharmacoresistant epilepsy. Previous studies showed increased expression of the NMDA receptor subunit NR2B in dysplastic and epileptic human neocortex. We tested the hypothesis that differential increase of NR2B constitutes an epileptogenic mechanism in humans. Dysplastic neocortex and lateral temporal lobe regions resected for treatment of pharmacoresistant seizures were processed for electrophysiological, histological, and immunocytochemical studies. Assignment to the "dysplastic" (n = 8) and "non-dysplastic" (n = 8) groups was based on histology. Neurons in "dysplastic" samples differentially stained for NR2B. Western blot (n = 6) showed an immunoreactive band for NR2B in three out of four "dysplastic" samples. Epileptiform field potentials (EFP) were elicited in vitro by omission of magnesium from the bath. EFP in "dysplastic" slices were characterized by multiple afterdischarges, occurring at a significantly higher repetition rate than EFP in non-dysplastic slices. The NR2B-specific NMDA receptor inhibitor ifenprodil (10muM) suppressed EFP in dysplastic slices. In non-dysplastic slices, burst repetition rate did not change with ifenprodil application. In both dysplastic and non-dysplastic slices, EFP were suppressed by a non-specific NMDAR antagonist (APV) or AMPA receptor antagonist (CNQX). These results provide additional evidence that the differential expression of NR2B in dysplastic human neocortex may play a role in the expression of in-situ epileptogenesis in human CD. NR2B may constitute a target for new diagnostic and pharmacotherapeutic approaches.

Adolescent↗
PubMed2005

Novelty-induced correlation between visual neurons and the hippocampal theta rhythm in sleep and wakefulness.

Various rhythms have been shown to affect sensory processing such as the waking-sleep cycle and the hippocampal theta waves. Changes in the firing of visual lateral geniculate nucleus neurons have been reported to be dependent on the animal's behavioral state. The lateral geniculate extracellular neuronal firing and hippocampal field activity were recorded in chronically implanted animals to analyze the relationship during quiet wakefulness and sleep associated with stimulation shifts that may introduce novelty. During wakefulness, a change in light flash stimulation pattern (stimuli frequency shift, stimuli on and off) caused an increment in the theta band power in 100% of the cases and a phase-locking of the spikes in 53% of the recorded neurons. During slow wave sleep, there were no consistent changes in the theta power notwithstanding 13% of the neurons exhibited phase-locking, i.e., novelty may induce changes in the temporal correlation of visual neuronal activity with the hippocampal theta rhythm in sleep. The present results suggest that visual processing in slow wave sleep exists, while auditory information and learning were reported during slow wave sleep in animals and newborn humans. The changes in the theta power as well as in the neuronal phase-locking amount indicate that in slow wave sleep, the ability of the hippocampus to detect/process novelty, although present, may be decreased. This is consistent with the noticeable decrease in awareness of the environment during sleep.

Animals↗
PubMed2006

Modality matters: the effects of stimulus modality on the 4- to 30-Hz brain electric oscillations during a lexical decision task.

The aim of the current study was to assess modality-specific brain oscillatory responses during cognitive processing. Brain oscillatory ERD/ERS responses of the 4- to 30-Hz EEG frequency bands were examined during lexical decision where the task is to identify whether the presented stimulus is a word or a pseudoword. Seven subjects performed the task with visual stimuli and twelve subjects with auditory stimuli. Visual stimuli elicited greater theta ERS responses as compared to the auditory stimuli. Both stimulus modalities elicited alpha and beta frequency ERD, these being greater for the auditory stimuli. Auditory stimuli elicited also later emerging beta ERS responses, absent for the visual stimuli. The lexicality effects (words vs. pseudowords) were greater for the auditory than for the visual stimuli. When studying brain oscillatory correlates of cognitive processing, the stimulus modality matters. Some effects may arise and some vanish depending on in which modality a cognitive experiment is being conducted.

Acoustic Stimulation↗
PubMed2006

Effects of memory load on cortical oscillatory activity during auditory pattern working memory.

The present magnetoencephalography study investigated memory load-dependent changes in cortical oscillatory activity during a modified auditory version of the Sternberg paradigm. Twelve subjects were presented with test stimulus sets of 1-3 syllables spoken in a natural female voice. After an 800-ms delay period, a probe syllable was presented and subjects had to judge whether the probe had been included in the preceding test set. Compared to a non-memory-control task, memory trials elicited an increase of beta activity over right temporal regions and an increase of alpha activity over right middle prefrontal cortex at the end of the delay phase. Monotonic increases in spectral amplitude as a function of memory load were revealed for the beta band over right temporal sensors and the alpha band over right frontal sensors during the delay period. The results demonstrate the relevance of both beta and alpha oscillations for the memorization of multiple stimuli. The former may be associated with the representation of task-relevant stimulus features, while the latter may reflect the top-down control of these representations.

Acoustic Stimulation↗
PubMed2003

The role of electrical signaling via gap junctions in the generation of fast network oscillations.

In recent years, several key studies have shed new light on the roles of electrical signaling via gap junctions between neurons in the adult brain. In particular, it is now clear that electrical signaling is important, if not essential, for the generation of a wide variety of different network interactions which may underlie rhythmic activity, of cognitive relevance, seen in EEG recordings. Two types of such rhythmic activity observed in the hippocampus both in vivo and in vitro are gamma frequency (30-80Hz) oscillations and ultrafast (>80Hz) "ripple" oscillations. Several lines of work, discussed here, show that gap junction-mediated signaling plays a central role in the generation of both these types of network activity. Recent work also now suggests that a number of different, anatomically discrete, gap junction-mediated networks may exist which could both function and be modulated independently.

Animals↗