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At least 487 records · Page 27Linked to original sources
PubMed2001

Effect of transplantation of embryonic nervous tissue on reorganization of interneuronal relationships after mechanical damage to sensorimotor cortex.

The effect of implanted embryonic nervous tissue on restoration of axonal connections in the cerebral cortex after mechanical injury was studied on albino rats using fluorescent lipophilic probe DiI (1,1'-dioctadecyl-3,3,3',3'-tetramethyl-indocarbocyanine perchlorate) and confocal laser scanning microscope. Implantation of embryonic tissue to damaged area promotes the growth of axons through the transplant to adjacent tissue. The damaged area is impenetrable for axons growing without implantation.

Animals↗
PubMed2002

The pyramidal cell of the sensorimotor cortex of the macaque monkey: phenotypic variation.

Recent studies have revealed striking differences in pyramidal cell structure among cortical regions involved in the processing of different functional modalities. For example, cells involved in visual processing show systematic variation, increasing in morphological complexity with rostral progression from V1 through extrastriate areas. Differences have also been identified between pyramidal cells in somatosensory, motor and prefrontal cortex, but the extent to which the pyramidal cell phenotype may vary between these functionally related cortical regions remains unknown. In the present study we investigated the structure of layer III pyramidal cells in somatosensory and motor areas 3b, 4, 5, 6 and 7b of the macaque monkey. Cells were intracellularly injected in fixed, flat-mounted cortical slices and analysed for morphometric parameters. The size of the basal dendritic arbours, the number of their branches and their spine density were found to vary systematically between areas. Namely, we found a trend for increasing complexity in dendritic arbour structure through areas 3b, 5 and 7b. A similar trend occurred through areas 4 and 6. The differences in arbour structure may determine the number of inputs received by neurons and may thus be an important factor in determining function at the cellular and systems level.

Animals↗
PubMed1997

Morphological Characterization of a Cortico-cortical relay in the cat sensorimotor cortex.

One feature of the cerebral cortex circuitry is the complex network of fibers which links its different functional regions. Our knowledge of the specific relationships between neurons which form these pathways is limited. The cortico-cortical connections between primary somatosensory cortex (SI) and primary motor cortext (MI) were the focus of the study. The aims were twofold: first, to identify characteristics of inter-areal cortico-cortical connections; and second, to determine if pathways exist which support the notion that peripheral signals are integrated in the somatosensory cortext before being relayed to the motor cortex. Neurons in area 2 of SI, which projected to the motor cortex were identified. The morphological characteristics of these neurons and the pattern of input that they received from the area 3a were determined. The fluorescent retrograde tracer, fast blue, was injected into the electrophysiologically defined forepaw representation of motor cortex and the anterograde tracer, dextran-tetramethylrhodamine (DR), was injected into the somatotopically matched region of area 3a. Labeled neurons in area 2 which were located in a field of labeled axons arising from area 3a were identified in fixed tissue sections. Some of these labeled cells were impaled with a Lucifer yellow (LY)-filled micropipette and were intracellulary labeled by iontophoretic injection of LY Cells in area 2 that projected to the motor cortex were located primarily in layers II-III. They were all classified as pyramidal neurons and were morphologically similar. Their apical dendrites for the most part did not extend beyond layer II. Their apical tufts exhibited 2-4 branches within layers II-III, while basal dendrites exhibited more numerous tertiary basal dendritic branches. Light microscopic (LM) examination revealed the presence of appositions between LY-filled profiles and DR-labeled axons. Appositions were observed between swellings along DR-labeled axons and dendritic shafts or spines of 1 degrees, 2 degrees and 3 degrees branches of apical and 1 degrees and 2 degrees branches of basal dendrites. The appositions were primarily on proximal segments of labeled dendritic shafts. Fewer appositions with distal dendrites were observed and some of these were with dendritic spines. No appositions with the somata were observed. Only one or two appositions were observed for individual cells. The pattern of cortico-cortical synaptic input arising from area 3a onto this population of cells was predicted from these LM findings. An ultrastructural analysis was performed to confirm the existence of contacts and the predicted pattern of connectivity. Neurons in area 2 which projected to the motor cortex, and area 3a axons which projected to area 2, were identified with electron dense retrograde and anterograde tracers respectively. Labeled neurons located in a field of labeled axons were examined throughout a sequential series of ultrathin sections. Electron microscopic analysis revealed a similar pattern, but with a slightly higher density of synaptic input (1-8 contacts per target cell) than that predicted from the LM studies. These results revealed a specific density and pattern of coritco-cortical input onto an identified population of cortico-cortical projection neurons. Individual target cells received only sparse input from a functionally different but somatotopically related region of the cortex. The pattern of input onto cells was unexpected in that most axons contacted the shafts of proximal dendrites. This aspect of the connection may exemplify a unique feature of the cortical circuit which helps to define its functional role. The significance of these results in defining cortical function is that the particular cortical circuit described may provide an anatomical substrate for the modulation of motor cortex activity by integrated signals from the sensory cortex. The synaptic relationships of neurons in this pathway may be characteristic of i

Animals↗
PubMed1996

Melatonin-dopamine interaction in the striatal projection area of sensorimotor cortex in the rat.

The excitatory response to motor cortex stimulation of 201 striatal neurones was recorded electrophysiologically to test the effects of melatonin (aMT) and/or D1 and D2 antagonists. Iontophoresis of aMT attenuated the excitatory response in 68.5% of neurones, with a latency of 2-4 min and enhanced the excitatory response in 11.9% of the neurones; 19.6% showed no change in response. Iontophoresis of sulpiride (D2 antagonist) produced an immediate increase in the excitatory response in 62.8% of neurones, an attenuation in 2.3% and no change in the response of 34.9%. The ejection of sulpiride counteracted the aMT-dependent inhibition of the excitatory response of striatal neurones. SCH-23390 (D1 antagonist) iontophoresis had no significant effect. The results show that the same striatal units may be driven by aMT and D2 receptors. However, the significant difference in the latency of the responses suggests that the effects of these two substances are mediated by different receptor/intracellular messengers.

Animals↗
PubMed2000

The representation of articulation in the primary sensorimotor cortex.

Bilabial, alveolar and velar sounds are produced at different locations around the oral cavity. fMRI was used to localize cortical representation of articulation in seven healthy subjects during repetitive lip and vertical tongue movements as well as repetitive articulation of /pa/ (bilabial), /ta/ (alveolar), /ka/ (velar consonants) and a combination of all three in /pataka/. Centers of gravity (COG) analysis of fMRI activation in the primary motor (M1) and sensory cortex (S1) revealed /pa/- adjacent to lip representation and /ta/- articulation to tongue representation. The articulation of /pataka/ showed an activation pattern with a combination of the two M1/S1-components and additional activation in the supplementary motor area.

Adult↗
PubMed2005

Functional somatotopy in sensorimotor cortex.

In an effort to understand the highly distributed somatotopy of primary motor cortex, this review draws on principles derived from studies of auditory, visual and somatosensory cortical areas. In each case, a behaviorally important feature or function is overlaid in multiple locations on an underlying topographic map of the peripheral sensory surface. Recent studies of hand muscle synergies suggest the types of two-dimensional functional axes that might reasonably be mapped to the two-dimensional surface of the primary motor cortex. However, other research emphasizes that even a functional somatotopy must be extremely flexible.

Animals↗
PubMed1989

Prelabeled red nucleus and sensorimotor cortex neurons of the rat survive 10 and 20 weeks after spinal cord transection.

To demonstrate definitively the fate of the somata of rubrospinal and corticospinal neurons axotomized by a complete spinal cord transection at T-9, in young adult rats we prelabeled the neurons by injection into the lumbar enlargement of a retrogradely transported fluorescent dye, Fluoro-Gold, and four days later transected the cord. We found no loss in cell number ten or 20 weeks after axotomy. The average size of the neurons in each case is slightly but significantly reduced. These findings unequivocally demonstrate that the somata of long tract neurons of the rubrospinal and corticospinal systems persist in an atrophic and presumably inactive state for at least 20 weeks, and raise the possibility that treatment of spinal cord injury may normalize cell activity and allow long tract regeneration.

Animals↗
PubMed1979

Electromagnetic muscle stretch strongly excites sensorimotor cortex neurons in behaving primates.

Responses of single units in primary motor and sensory cortex of behaving primates to electromagnetic stretch of the muscle flexor carpi ulnaris are comparable in latency and intensity to responses to wrist extension. Thus, muscle stretch appears to be a major factor in cortical response to limb displacement during performance and probably has an important role in motor control at the cortical level.

Animals↗
PubMed2005

Characteristic membrane potential trajectories in primate sensorimotor cortex neurons recorded in vivo.

We examined the membrane potentials and firing properties of motor cortical neurons recorded intracellularly in awake, behaving primates. Three classes of neuron were distinguished by 1) the width of their spikes, 2) the shape of the afterhyperpolarization (AHP), and 3) the distribution of interspike intervals. Type I neurons had wide spikes, exhibited scoop-shaped AHPs, and fired irregularly. Type II neurons had narrower spikes, showed brief postspike afterdepolarizations before the AHP, and sometimes fired high-frequency doublets. Type III neurons had the narrowest spikes, showed a distinct post-AHP depolarization, or "rebound AHP" (rAHP), lasting nearly 30 ms, and tended to fire at 25-35 Hz. The evidence suggests that an intrinsic rAHP may confer on these neurons a tendency to fire at a preferred frequency governed by the duration of the rAHP and may contribute to a "pacemaking" role in generating cortical oscillations.

Action Potentials↗
PubMed2006

Electrophysiological classification of somatostatin-positive interneurons in mouse sensorimotor cortex.

Classification of inhibitory interneurons is critical in determining their role in normal information processing and pathophysiological conditions such as epilepsy. Classification schemes have relied on morphological, physiological, biochemical, and molecular criteria; and clear correlations have been demonstrated between firing patterns and cellular markers such as neuropeptides and calcium-binding proteins. This molecular diversity has allowed generation of transgenic mouse strains in which GFP expression is linked to the expression of one of these markers and presumably a single subtype of neuron. In the GIN mouse (EGFP-expressing Inhibitory Neurons), a subpopulation of somatostatin-containing interneurons in the hippocampus and neocortex is labeled with enhanced green fluorescent protein (EGFP). To optimize the use of the GIN mouse, it is critical to know whether the population of somatostatin-EGFP-expressing interneurons is homogeneous. We performed unsupervised cluster analysis on 46 EGFP-expressing interneurons, based on data obtained from whole cell patch-clamp recordings. Cells were classified according to a number of electrophysiological variables related to spontaneous excitatory postsynaptic currents (sEPSCs), firing behavior, and intrinsic membrane properties. EGFP-expressing interneurons were heterogeneous and at least four subgroups could be distinguished. In addition, multiple discriminant analysis was applied to data collected during whole cell recordings to develop an algorithm for predicting the group membership of newly encountered EGFP-expressing interneurons. Our data are consistent with a heterogeneous population of neurons based on electrophysiological properties and indicate that EGFP expression in the GIN mouse is not restricted to a single class of somatostatin-positive interneuron.

Algorithms↗
PubMed1980

Correlations between task-related activity and responses to perturbation in primate sensorimotor cortex.

1. Monkeys were trained to maintain hand position against a range of constant forces. Short-latency responses to passive wrist extension or flexion, as well as short-latency responses to stretch of a single wrist muscle, were recorded from units in areas 4, 3, 1, and 2. These responses were compared to unit activity during active holding and during active movement. 2. Units related to active holding and to active movement were most common in areas 4 and 2. Three-quarters of these units displayed a specific correlation between their passive and active behaviors. Thus, a unit excited by passive extension was excited during active holding against extension force and excited during an active flexion movement. This behavior is similar to the expected concurrent behavior of muscle stretch receptors. By demonstrating that a significant number of task-related units give qualitatively similar responses to passive extension and passive flexion, the results appear to explain the disagreement among previous studies (5, 9, 36) in regard to area 4 behavior during active and passive movements. 3. Area 4 units responded similarly to passive wrist extension and electromagnetic stretch of a single flexor muscle occurring in the absence of wrist extension, indicating that muscle stretch was important in determining area 4 unit responses to passive movements. 4. The similarity of area 4 behavior to area 2 behavior in active and passive situations, along with the observation that area 2 responses to passive movements occurred several milliseconds earlier than those of area 4, emphasizes the importance of area 2 in motor performance and is consistent with significant area 2 mediation of area 4 responses. 5. Results support the hypothesis of an oligosynaptic transcortical pathway (22, 32, 34), beginning in large part with muscle stretch receptors. Furthermore, the correlation noted between short-latency responses to passive movement and task-related activity suggests that this transcortical pathway not only mediates responses to passive movement but may be responsible, to a significant degree, for task-related activity during undisturbed performance. Thus, active position maintenance and active movement were probably accomplished, at least in part, by increasing and decreasing the influence of this pathway on specific area 4 neurons and thereby producing the patterns of area 4 activity responsible for task performance.

Animals↗