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PubMedDate not supplied

[The transmission of coded information over neuronal systems exemplified by the motor rhythmic dominant].

Functional organization of neurons in rabbit's sensorimotor cortex was studied before and within several days after formation of the rhythmical dominant focus. Functional reorganization of neurons in cortical microareas took place during actualization of the dominant. The number of functional interneuronal relations within neuronal pairs of a certain type could be increased in comparison with the control values and decreased within pairs of another type. As a result, the total percent of the interneuronal correlations in cortical microareas in the control animals and rabbits with the acting dominant was approximately equal. The total percent of correlations between neurons of the adjacent cortical areas during the actualization of the dominant was significantly higher than in the control due to increased number of correlations with participation of small and medium-sized neurons. A possibility of information circulation about the "stimulus image" in the closed chain of neurons was exemplified by the real micronetwork. The data suggest the reverberation of encoded information between adjacent microareas of the sensorimotor cortex within several days after application of the stimulus, which has formed the excitation focus.

Animals↗
PubMedDate not supplied

Correlation of behavior with brain damage after in utero exposure to toxic agents.

Early postnatal behaviors involving sensorimotor integration were measured along with thickness of the sensorimotor cortex in rats irradiated with 1.0 Gy on gestational day 11 or 17. Body weight and morphology of anterior pituitary cells were recorded. Irradiation on day 17 was more effective in reducing cortical thickness and body weight and performance on behavioral tests and less effective in altering pituitary cells than irradiation on day 11. Prediction of behavioral effects, using cortical layers, body weight and pituitary morphology as predictors in stepwise multiple regression, was measured in both irradiated and control rats. Cortical Layer V more than I more than IV and VI as significant predictors of behavior. The best predictions accounted for about half of the variance in the data. When behavioral data were used to predict brain damage, the best predictor was negative geotaxis. Significant association of behavior with Layers V and VI was found. These experiments show the difficulties in correlating complex behaviors with specific brain areas and, at the same time, implicate especially Layer V of the sensorimotor cortex in these behaviors.

Animals↗
PubMed2004

Facilitation of motor skill learning by callosal denervation or forced forelimb use in adult rats.

Unilateral forelimb sensorimotor cortex lesions in adult rats produce a compensatory hyper-reliance on the forelimb ipsilateral to the lesion and temporally related glial and neural plasticity in the contralateral homotopic cortex. Recently, we found that these lesions enhance acquisition of a motor skills task with the ipsilateral, non-impaired, forelimb in comparison to shams. This effect might be related to a denervation-induced facilitation of neuroplastic changes in the motor cortex opposite the lesion and/or to the lesion-induced hyper-reliance on the non-impaired forelimb. The present study assessed whether increased forelimb use, denervation of motor cortical callosal afferents, or a combination of the two influences acquisition of a skilled reaching task. Adult rats with partial corpus callosum transections or sham procedures were either forced to rely on one forelimb or permitted normal forelimb use for 8 days. Rats were then trained for 14 days with their previously non-preferred forelimb (and the forced-use limb) on a unilateral pellet retrieval task. Compared to shams, transections produced a greater acquisition rate and asymptotic performance level on the task. Forced-use improved reaching performance relative to controls, but this effect was less enduring than the improvements produced by transections alone. The addition of forced-use to transections did not further enhance performance. These findings suggest that denervation-induced changes are likely to be a major contributor to the enhanced learning observed after unilateral sensorimotor cortex lesions.

Animals↗
PubMed1986

Differences in function and structure of the capillary endothelium in gray matter, white matter and a circumventricular organ of rat brain.

Physiological and morphometric studies were conducted on the microvascular endothelium of four individual cerebral structures having different neural activities--the inferior colliculus, sensorimotor cortex (both gray matter regions), genu of the corpus callosum (white matter), and the subfornical organ (a circumventricular organ) of rats. The physiological data, obtained by quantitative autoradiography, produced new findings: the rate of blood-to-tissue flux across capillary endothelial cells of a neutral amino acid, 14C-alpha-aminoisobutyric acid, was 100-400 X more rapid in the subfornical organ than in gray and white matter regions, and the transit time of labeled albumin in the subfornical organ microcirculation was 7-12 X longer than in the blood-brain barrier regions. These quantitative studies suggest that circulating messengers, such as hormones, would have more prolonged receptor contact with capillary endothelial cells and greater rates of transendothelial passage in the subfornical organ than in gray or white matter. Capillary densities, volume fractions, and surface areas were similar for the inferior colliculus (which has the highest rates of tissue glucose metabolism and blood flow among blood-brain barrier regions) and the subfornical organ, but were significantly smaller for sensorimotor cortex and corpus callosum (about 35 and 70% lower, respectively). Electron microscopic morphometry of capillary endothelial cells in the inferior colliculus and corpus callosum indicated the ultrastructural basis of blood-brain barrier mechanisms in these regions--intercellular junctions that appeared tight, few cytoplasmic vesicular profiles, and no fenestrations. Analysis of endothelial cells in the subfornical organ demonstrated 7 X more vesicular profiles and 4 fenestrations per cross section of capillary. These findings represent structural evidence for high rates of solute flux across the capillary endothelium of circumventricular organs.

Animals↗
PubMed2003

The effect of diazepam on motor cortical oscillations and corticomuscular coherence studied in man.

EEG recordings from sensorimotor cortex show oscillations around 10 and 20 Hz. These modulate with task performance, and are strongest during periods of steady contraction. The 20 Hz oscillations are coherent with contralateral EMG. Computer modelling suggests that oscillations arising within the cortex may be especially dependent on inhibitory systems. The benzodiazepine diazepam enhances the size of GABA(A) IPSPs; its effects are reversed by the antagonist flumazenil. We tested the effect of these drugs on spectral measures of EEG and EMG, whilst eight healthy human subjects performed a precision grip task containing both holding and movement phases. Either an auxotonic or isometric load was used. EEG changes following electrical stimulation of the contralateral median nerve were also assessed. The EEG power showed similar changes in all task/stimulation protocols used. Power around 20 Hz doubled at the highest dose of diazepam used (5 mg), and returned to control levels following flumazenil. EEG power at 10 Hz was by contrast little altered. The peak frequency of EEG power in both bands was not changed by diazepam. Corticomuscular coherence at ca 20 Hz was reduced following diazepam injection, but the magnitude of this effect was small (mean coherence during steady holding in the auxotonic task was 0.062 in control recordings, 0.051 after 2.5 mg and 5 mg doses of diazepam). These results imply that 20 Hz oscillations in the sensorimotor cortex are at least partially produced by local cortical circuits reliant on GABA(A)-mediated intracortical inhibition, whereas 10 Hz rhythms arise by a different mechanism. Rhythms generated during different tasks, or following nerve stimulation, are likely to arise from similar mechanisms. By examining the formulae used to calculate coherence, we show that if cortical oscillations are simply transmitted to the periphery, corticomuscular coherence should increase in parallel with the ratio of EEG to EMG power. The relative constancy of coherence even when the amplitude of cortical oscillations is perturbed suggests that corticomuscular coherence itself may have a functional role in motor control.

Adult↗
PubMedDate not supplied

[The correlational characteristics of the electrical activity of the rabbit brain in a state of hunger].

Motivational state of hunger, created in rabbit by alimentary deprivation, leads to an increase of coherent connections between potentials of the neocortex. In the state of hunger a complex mosaic of changes of intercentral relations of the cortical and subcortical electrical processes arises, the character of spatial potential interrelations depends on the level of alimentary motivation, created by deprivation of different duration. At daily deprivation coherence values increase in the slow-frequency band between potentials of the lateral, ventromedial hypothalamus, the medial preoptic area, and potentials of the orbitofrontal cortex. Coherence decreases between potentials of the ventromedial hypothalamus, the medial preoptic area and potentials of the sensorimotor cortex. Synchronization of electrical processes of the lateral and ventromedial hypothalamus does not significantly change. At 2-day deprivation changes of the cortical coherence become less regular than at daily deprivation. Synchronization of the electrical processes of the lateral hypothalamus and the orbitofrontal, sensorimotor-2 cortices increases, and decreases with the potentials of the sensorimotor-1 cortex. Coherence between potentials of the ventromedial hypothalamus and the orbitofrontal cortex, on the contrary, decreases, and increases with the potentials of sensorimotor-1 cortex. Synchronization of electrical activity of the lateral and ventromedial hypothalamus attains the level of 100% manifestations. It the state of hunger interhemispheric asymmetry appears in the parameters of coherence due to more regular intensification of interrelations of electrical processes in the left hemisphere.

Animals↗
PubMed2003

Electrobehavioral characteristics of epileptic rats following photothrombotic brain infarction.

The goal of this study was to characterize the electroencephalographic (EEG) and behavioral properties of young adult rats during extended video-EEG monitoring following photothrombotic brain infarction. Two-month-old male Sprague-Dawley rats underwent photothrombotic brain infarction of the left sensorimotor cortex with the photosensitive dye rose bengal (n=10) or were used as controls (n=9). Qualitative and quantitative EEG analysis was performed on digital video-EEG records obtained during 6 months of recording. The main finding of this study was that 5/10 (50%) lesioned animals developed focal epileptic seizures ipsilateral to the cortical infarct characterized by rhythmic spike-wave discharges with or without behavioral change. Epileptic animals demonstrated increased delta, theta, and low beta-range power ipsilateral to the infarct that reliably distinguished them from lesioned nonepileptic and control animals. Lesioned animals (epileptic and nonepileptic) also demonstrated a distinct pattern of focal rhythmic theta activity before or after generalized high beta-range discharges. Electrical and behavioral characteristics common to both lesioned and control animals included: (1) focal rhythmic theta activity in either hemisphere; (2) focal low beta-range discharges in either hemisphere; (3) generalized high beta-range discharges; (4) absence seizures; (5) generalized pseudoperiodic spike discharges associated with mild multifocal body jerks; (6) tonic-clonic seizures (one nai;ve control; one lesioned animal). Cresyl violet staining of lesioned animals' brains showed consistent infarcts of the sensorimotor cortex extending to the subcortical white matter. These results provide an expanded electrobehavioral description of young adult rats following photothrombotic brain infarction and augment further investigation into the molecular, cellular, and network alterations that contribute to the establishment of post-stroke epilepsy.

Animals↗
PubMed1992

Subcortical deterioration after cortical damage: effects of diazepam and relation to recovery of function.

Agents which enhance the activity of gamma-aminobutyric acid (GABA) can severely disrupt behavioral recovery in rats following damage to the neocortex if delivered during a sensitive postoperative period. The mechanisms of this disruption have not been found. It has been suggested previously that the ipsilateral striatum and related structures may be transiently disabled after cortical lesions and that diazepam may interfere with restoration of function in these areas. In the present experiment, the subcortical anatomical effects of chronic (3 weeks) administration of diazepam, an indirect GABAergic agonist, were assessed following unilateral lesions of the anteromedial cortex (AMC) or the sensorimotor cortex (SMC) in rats. Atrophic and degenerative changes were examined in the striatum, substantia nigra and thalamus. Following either AMC or SMC lesions, there was a reduction in the size of the ipsilateral striatum and thalamus and a loss of neurons in the ipsilateral substantia nigra pars reticulata (SNr). After AMC lesions, striatal atrophy and neuron loss in the SNr were increased by the diazepam regimen relative to vehicle-treated controls. In addition, diazepam interfered with the behavioral recovery from somatic-sensorimotor asymmetries in AMC-lesioned rats. After SMC lesions, the sites of striatal and thalamic atrophy were different from that observed after AMC lesions, and the extent of atrophy and neuron loss was not exaggerated by diazepam treatment. Consistent with these data, diazepam did not significantly affect recovery from SMC lesions. These findings suggest that the long-term disruptive effects of diazepam on recovery of function after AMC lesions may be related to an augmentation of lesion-induced degeneration.

Animals↗
PubMedDate not supplied

Somatosensory evoked potentials during natural and learning rearrangements of posture accompanied by limb elevation in dogs.

Changes in the functional state of the sensorimotor cortex associated with reorganization of the natural pattern of postural rearrangement before limb elevation (the "diagonal" patten and of an artificial rearrangement (the "unilateral" pattern) were studied in dogs. The state of cortical structures on postural rearrangement was assessed in terms of the pattern of somatosensory evoked potentials produced in response to stimulation of the forelimb during postural preparation of the animal for elevating the hindlimb (acquired avoidance response to a sound signal). Evoked potentials during the natural postural preparation (the "diagonal" pattern) were compared with those during the altered pattern of postural preparation (the "unilateral" pattern), this preparation taking place prior to elevation of the limb. Controls consisted of evoked potentials in the resting state. Decreases were seen in the latencies and amplitudes of most components of evoked potentials during postural rearrangement. In general, changes in evoked potentials were less marked in the "unilateral" pattern than in the "diagonal" pattern, though the differences were significant only for the amplitude of the first negative component. Changes in evoked potentials were similar regardless of whether the supporting forces of the limb to which the test stimulus was applied increased or decreased during postural rearrangement. It is suggested that differences in evoked potentials may reflect changes in the interaction between neuronal populations within the sensorimotor cortex during reorganization of the pattern of postural rearrangement associated with learning.

Animals↗
PubMed2005

Induction of long-term potentiation leads to increased reliability of evoked neocortical spindles in vivo.

Large amplitude electroencephalographic spindle waves (7-14 Hz) occur spontaneously in the neocortex during both sleep and awake immobility, and it has been proposed that synchronous neuronal activation during spindles may contribute to learning-related synaptic plasticity. Spindles can also be evoked in the sensorimotor cortex by electrical stimulation of cortical or thalamic inputs in the rat. To determine if strengthening cortical synapses can affect the initiation and maintenance of electrically evoked spindles, stimulation pulses were delivered at a range of intensities to the corpus callosum or ventrolateral thalamus in the awake rat before and after the induction of long-term potentiation (LTP) by tetanization of the corpus callosum. The morphology of evoked spindles was similar to that of naturally occurring spindles. Spindles were evoked less reliably during slow-wave sleep than during waking, and this was correlated with smaller synaptic responses during slow-wave sleep. Similar to previous findings, daily tetanization of the corpus callosum for 15 days decreased the early component and increased the late component of synaptic responses evoked by corpus callosum stimulation, but did not significantly affect synaptic responses evoked by thalamic stimulation. Similarly, LTP induction increased the reliability with which low-intensity corpus callosum stimulation evoked spindles, but increases in spindles evoked by thalamic stimulation were not significant. Synaptic potentiation and the increased reliability of spindles developed with a similar time-course over the 15-day LTP induction period. These results reflect strong correlations between the strength of cortical layer V activation and the initiation of spindles in the sensorimotor cortex, and support the idea that monosynaptic and polysynaptic horizontal collaterals of layer V neurons can play a significant role in the initiation of spindles.

Animals↗
PubMed1994

Nitric oxide inhibition aggravates ischemic damage of hippocampal but not of NADPH neurons in gerbils.

BACKGROUND AND PURPOSE: Nitric oxide may influence pathophysiology of brain ischemia in a complex way depending on the sources of its production either from neurons or endothelial cells. We investigated whether inhibition of nitric oxide synthesis affects postischemic neuronal death in hippocampus. Moreover, we evaluated whether the presence of nitric oxide synthase activity in specific neurons protects these against ischemia in the hippocampus, striatum, and sensorimotor cortex. METHODS: To inhibit nitric oxide synthase, several dosing regimens of NG-nitro-L-arginine methyl ester (L-NAME) were used (5 or 50 mg/kg IP, twice a day for 4 days, or 30 mg/kg IV) in gerbils. Control animals received either the isomer NG-nitro-D-arginine methyl ester or the vehicle. The gerbils underwent 10-minute occlusion of carotid arteries under ether anesthesia and controlled body temperature while physiological parameters were monitored. Neuronal damage was assessed 5 days after ischemia using Nissl-stained sections of hippocampus. Nitric oxide synthase neurons were histochemically stained for reduced nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity. RESULTS: L-NAME treatments, but not the chronic one at 5 mg/kg, induced elevation of blood pressure (30% to 80% greater than the control level, P < .01), as observed shortly before and after bilateral carotid occlusion. Postischemic neuronal loss in the CA1 through CA4 sectors was worsened by chronic pretreatment with L-NAME at 50 mg/kg (eg, CA1 neuronal counts per 100-microns length: 3.2 +/- 2.74, mean +/- SD; n = 19; P < .01). After the acute (30 mg/kg) or chronic pretreatment at lower dosage (5 mg/kg) with L-NAME, neuronal loss was comparable to that of animals treated with the D-isomer or the vehicle (CA1 counts in vehicle-treated animals: 7.65 +/- 6.51, mean +/- SD; n = 14). None of the L-NAME treatments affected postischemic survival of NADPH diaphorase-positive neurons in hippocampus, striatum, and sensorimotor cortex. CONCLUSIONS: These observations demonstrate that inhibition of endothelial and neuronal nitric oxide synthase activity does not modify resistance of nitric oxide-producing neurons to transient ischemia. The severe inhibition of nitric oxide production aggravates postischemic neuronal death in the hippocampus, whereas the mild inhibition is ineffective.

Amino Acid Oxidoreductases↗
PubMed1998

Plasticity of primary somatosensory cortex paralleling sensorimotor skill recovery from stroke in adult monkeys.

Adult owl and squirrel monkeys were trained to master a small-object retrieval sensorimotor skill. Behavioral observations along with positive changes in the cortical area 3b representations of specific skin surfaces implicated specific glabrous finger inputs as important contributors to skill acquisition. The area 3b zones over which behaviorally important surfaces were represented were destroyed by microlesions, which resulted in a degradation of movements that had been developed in the earlier skill acquisition. Monkeys were then retrained at the same behavioral task. They could initially perform it reasonably well using the stereotyped movements that they had learned in prelesion training, although they acted as if key finger surfaces were insensate. However, monkeys soon initiated alternative strategies for small object retrieval that resulted in a performance drop. Over several- to many-week-long period, monkeys again used the fingers for object retrieval that had been used successfully before the lesion, and reacquired the sensorimotor skill. Detailed maps of the representations of the hands in SI somatosensory cortical fields 3b, 3a, and 1 were derived after postlesion functional recovery. Control maps were derived in the same hemispheres before lesions, and in opposite hemispheres. Among other findings, these studies revealed the following 1) there was a postlesion reemergence of the representation of the fingertips engaged in the behavior in novel locations in area 3b in two of five monkeys and a less substantial change in the representation of the hand in the intact parts of area 3b in three of five monkeys. 2) There was a striking emergence of a new representation of the cutaneous fingertips in area 3a in four of five monkeys, predominantly within zones that had formerly been excited only by proprioceptive inputs. This new cutaneous fingertip representation disproportionately represented behaviorally crucial fingertips. 3) There was an approximately two times enlargement of the representation of the fingers recorded in cortical area 1 in postlesion monkeys. The specific finger surfaces employed in small-object retrieval were differentially enlarged in representation. 4) Multiple-digit receptive fields were recorded at a majority of emergent, cutaneous area 3a sites in all monkeys and at a substantial number of area 1 sites in three of five postlesion monkeys. Such fields were uncommon in area 1 in control maps. 5) Single receptive fields and the component fields of multiple-digit fields in postlesion representations were within normal receptive field size ranges. 6) No significant changes were recorded in the SI hand representations in the opposite (untrained, intact) control hemisphere. These findings are consistent with "substitution" and "vicariation" (adaptive plasticity) models of recovery from brain damage and stroke.

Analysis of Variance↗
PubMed1984

Patterns of afferent projections to transitional zones in the somatic sensorimotor cerebral cortex of albino rats.

The organization of somatosensory projections to the dysgranular areas of somatic sensory cortex was mapped in albino rats. Receptive fields that activate layer IV granule cells in these dysgranular zones were: cutaneous and deep (including muscle), roughly somatotopic, larger, and required stronger stimulation (tap) than the cutaneous light touch RFs of the adjacent granule cell zones.

Afferent Pathways↗
PubMed1993

Neurons in rat cerebral cortex that synthesize nitric oxide: NADPH diaphorase histochemistry, NOS immunocytochemistry, and colocalization with GABA.

Neurons that stain for NADPH diaphorase, which colocalizes with nitric oxide synthase (NOS), are scattered uniformly across neocortex, and denser in entorhinal cortex. In the primary sensorimotor cortex, 0.5-2% of neurons contain NOS. These are most numerous in layers II-III, whereas NOS-positive fibers are concentrated in layers IV and VI. Most stained neurons are aspiny bipolar cells. Some in deep layers are multipolar; very few are pyramidal-shaped. In layer IV, NOS-positive neurons and their dendrites are confined to the septa between barrels. Retrograde tracing experiments demonstrate that NOS-positive cells are local circuit neurons. Double staining demonstrates that NOS-positive neurons also contain GABA.

Amino Acid Oxidoreductases↗
PubMed2003

Atrophy pattern in SCA2 determined by voxel-based morphometry.

We applied voxel-based morphometry, an indirect volumetric technique, to MRI volumes of patients carrying the spinocerebellar ataxia type 2 mutation to determine patterns of brain atrophy. Nine patients were compared to 27 controls matched for age, sex and handedness. An optimised voxel-based morphometry protocol was used for pre-processing to minimize systematic bias. We observed significant volume loss in the cerebellar hemispheres, vermis, pons, mesencephalon and thalamus. Also affected were several supratentorial areas such as the right orbito-frontal cortex, right temporo-mesial cortex and the primary sensorimotor cortex bilaterally. The volumetric changes of cerebellar hemispheres were inversely correlated to cerebellar symptoms rated by a cerebellar ataxia scale. Two mechanisms could contribute to the observed cortical atrophy. It could be either the result of primary supratentorial degeneration as part of the disease process and/or secondary atrophy due to cerebellar deafferentation.

Ataxins↗