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At least 883 records · Page 49Linked to original sources
PubMed1991

Adaptation of the Reitboeck method of multiple microelectrode recording to the neocortex of the waking monkey.

We adapted to the neocortex of waking monkeys a method for multiple microelectrode recording devised by Reitboeck. A sliding platform allows micropositioning of 7 electrodes independently, in 2 microns steps. Microelectrodes are quartz glass filaments (80 microns o.d.) with central metal cores (30 microns) of tungsten-platinum alloy. Filaments are drawn in a high temperature chamber, and ground to the desired form and tip size. The microdrive is held over the region to be explored, and the microelectrodes passed through 300 microns o.d. guide tubes fixed in implant thimbles of chosen size an and x - y arrangement of tubes, sealed by an O-ring into a small craniotomy opening. A microprocessor controlled recording system provides gain, noise and wave-shape filtering, impedance testing, and differential amplitude discrimination for each channel. Electrode movement is obtained via the microprocessor which displays and updates on the console terminal the electrode depth, impedance, and the channel assignment of each electrode. A second microprocessor based system is used to collect, buffer, and encode in real time all event data, which are transferred whenever convenient to a minicomputer that controls the experiment. Exploratory recordings were made in the posterior parietal, somatic sensory, and motor cortical areas. The system has now been used successfully in a number of investigations.

Action Potentials↗
PubMed1982

Obstructed neuronal migration along radial glial fibers in the neocortex of the reeler mouse: a Golgi-EM analysis.

The interrelationship of radial glial fibers (RGF) and young neurons migrating to the neocortex of normal and reeler mutant mice at 17 days of gestation are reconstructed from serial and from closely spaced thin sections. The glial fibers are identified unequivocally by correlated light and electron microscopy by means of the Golgi-gold toning method of Fairén and associates. The migrating cell in the normal animal is closely apposed to and coiled about the RGF throughout most of its ascent. In the terminal few microns of its movement, however, it begins rapidly to differentiate and at the same time surrenders its close attachment to the RGF. In the reeler, by contrast, the migrating cell maintains normal apposition to the RGF only until it enters the cortex. There its leading process is unable to pass between the surfaces of the RGF and those of postmigratory elements. Abnormally extensive contact between the glial fiber and the somata of postmigratory cells appears to be sustained in the mutant. The upward migration of the young neuron is terminated in the depths of the cortex and the cell soma gives rise to a profusion of small processes. This study affirms the critical role served by RGF as guides to neuronal migration and provides evidence that abnormal adhesions between postmigratory cells and the RGF obstruct neuronal migration in the reeler mouse.

Animals↗
PubMed1983

The postnatal development of post-activation potentiation in the rat neocortex.

The postnatal development of short-term potentiation (STP) and long-term potentiation (LTP) of the transcallosal response (TCR) was examined in anesthetized rats, aged 7 days (PN7) to adult (greater than or equal to PN180). Stimulation of callosal fibers produced a biphasic, positive-negative TCR recorded at the surface of the anterior neocortex in all age groups. The TCR showed a decrease in threshold, latency and halfwidth, and an increase in peak amplitude with age. High frequency callosal stimulation produced marked STP and LTP of the mature TCR. STP in young animals, however, could not be reliably detected until after PN16. LTP was not detected until PN18. STP and LTP approached adult levels rapidly after their initial appearance. The correlations between STP/LTP onset and development and known structural developments such as initial synaptogenesis, spine formation and myelinogenesis were not particularly strong. The implications of these results for specific hypotheses of STP/LTP mechanisms were discussed.

Animals↗
PubMed1985

Transient expression of tyrosine hydroxylase immunoreactivity in some neurons of the rat neocortex during postnatal development.

Tyrosine hydroxylase-like immunoreactive neurons were observed in the dorsolateral and medial neocortex of the rat during postnatal development. They occurred from 8 up to 24 days of age and lacked other catecholamine synthetizing enzymes. They appeared to be insensitive to the suppression of cortical noradrenergic innervation induced by neonatal subcutaneous injections of 6-hydroxydopamine.

Animals↗
PubMed1986

Immunocytological localization of cell adhesion molecules L1 and N-CAM and the shared carbohydrate epitope L2 during development of the mouse neocortex.

The expression of the two adhesion molecules L1 and N-CAM and their shared carbohydrate epitope recognized by monoclonal antibody L2, was studied during development of the embryonic mouse neocortex by immunohistology at light- and electron-microscopic levels between embryonic days 9 and 18. Throughout this time period N-CAM is expressed in all layers of the telencephalic anlage. L1 antigen shows a more restricted expression than N-CAM. It is not detectable at day 9. From day 10 onward it is expressed on young neurons in the marginal zone, but not in the ventricular layer. At embryonic day 13 L1 antigen appears also in the intermediate zone on afferent fibers from subcortical structures and on migrating neurons. Neuronal cell bodies in the cortical plate and subplate express L1 antigen only transiently on embryonic days 13-16. These observations suggest that L1 antigen does not play a prominent role in the initiation of neuronal migration in the ventricular zone, but could be functional during later stages of migration and in the aggregation of neuronal cell bodies at their final position in the cortical plate. The L2 epitope also shows a more restricted expression than N-CAM during the time period studied. Similar to L1 antigen, it first appears at embryonic day 10 in the marginal zone and remains undetectable in the ventricular layer also at later stages. In the marginal zone the L2 epitope is strongly expressed on neuroepithelial endfeet at the basal lamina. The basal lamina itself is L2 epitope-negative. From embryonic day 10 onward the L2 epitope is most strongly expressed in the marginal zone and subplate and more weakly in the cortical plate and intermediate zone. In the subplate it is not only associated with the surface membrane, but also with the extracellular matrix. These observations support previous biochemical data which show that the L2 epitope is not present on all N-CAM molecules of the embryonic or adult forms and suggest that the independent regulation or L2 epitope expression may have functional implications during development.

Animals↗
PubMed1987

Extracellular K+ and Ca2+ changes during epileptiform discharges in the immature rat neocortex.

Picrotoxin-induced epileptiform activity was examined in neocortical slices prepared from 8- to 15-day-old rats. This activity consisted of spontaneous bursts of 3-5 discharges that resembled interictal spikes and were interspersed with ictal-like paroxysms lasting 10-30 s. Measurements of extracellular potassium ([K+]o) and calcium ([Ca2+]o) were made during these spontaneous epileptiform events, using ion-sensitive electrodes. Individual interictal spikes were associated with [Ca2+]o decreases of 0.1-0.2 mM, whereas sustained ictal-like discharges were accompanied by decreases of 0.3-0.4 mM. Measurement of [K+]o showed that individual interictal spikes were associated with increases in [K+]o up to 12 mM, whereas increases to more than 20 mM accompanied long-lasting ictal-like discharges. Maximum increases in [K+]o were observed ca. 600 microns below the pial surface. [K+]o increases were followed by undershoots of the resting [K+]o level. The unusually high [K+]o levels associated with epileptiform discharges in the immature neocortex suggest that disturbances in [K+]o regulation may contribute to the generation of the picrotoxin-induced, spontaneous, prolonged ictal-like discharges observed in the 8- to 15-day age group.

Animals↗
PubMed1988

Control of cell number in the developing neocortex. II. Effects of corpus callosum section.

To determine if cell death participates in the regulation of cell number between interconnecting populations of the neocortex, we sectioned the corpus callosum of neonatal hamsters, thus depriving callosally projecting cells of their normal targets and callosally-recipient cells of their normal afference. The numbers of neurons per unit column in two areas of the cortex which have heavy callosal projections (the 17-18a border and area 6) and one area that is relatively acallosal (area 3) were compared in animals with early corpus callosum sections and controls. No differences were found, either for a 'unit cortical column,' or for the callosally-projecting layers (II-III and V). Mean soma sizes in layers II-III and V of all three areas were likewise unchanged. In area 6 and part of area 3, however, the distribution of soma sizes in callosally projecting and recipient laminae was significantly altered. The change in size distribution without change in mean soma area suggests that the cortex responds to the elimination of the callosal pathway in more than one way. Since no role for cell death in removal of diffuse connectivity or in target regulation of neuron number has yet been found, a new hypothesis for the function of cell death in local cytoarchitectural differentiation of the cortex is proposed.

Aging↗
PubMed1988

Transient postnatal elevation of serotonin levels in mouse neocortex.

Serotonin (5-HT), norepinephrine (NE) and 5-hydroxyindoleacetic acid (HIAA) levels were measured during ontogeny of frontoparietal cortex in Balb/C mice by high-pressure liquid chromatography (HPLC) with electrochemical detection. Unlike NE, the concentration of 5-HT was transiently elevated to more than twice the adult level during the first postnatal week; this was accompanied by increased HIAA content comparable to the adult, indicating elevated levels of 5-HT release. Since a transient hyperplasia of 5-HT-immunoreactive fibers and uptake sites has been observed previously in the same cortical areas, the transient elevation of 5-HT levels may play an important role in shaping early postnatal morphogenetic events in neocortex.

Aging↗
PubMed1989

A comparative study of prenatal development in the olfactory bulb, neocortex and hippocampal region of the precocial mouse Acomys cahirinus and rat.

Unlike the remainder of the rodent subfamily Muridae, Acomys cahirinus (the 'spiny' mouse) is born in a precocial state after a long (39 day) gestation. In this paper, the development of the olfactory bulb, neocortex and hippocampal formation of Acomys from prenatal days 14-34 was examined and the rate of maturation compared with that of its cousin, the laboratory rat (Rattus norvegicus). At the earliest stages examined, Acomys was approximately 2 days less mature than the same post-conception aged rat. The difference between the two species increased: Acomys at 28 days postconception resembled the 22-day rat. By the end of gestation, Acomys and the rat were in a relatively similar developmental state. Therefore, Acomys exhibits a quite different timetable of early maturation which includes a protracted period of relatively slow growth during mid-gestation. As such, it offers many benefits as a subject for studies of both early ontogenesis and the mechanisms which result in species differences.

Animals↗
PubMed1989

Quantitative assessment of dendritic branching and spine densities of neurons of hippocampal embryonic tissue transplanted into juvenile neocortex.

Embryonic 18-day-old hippocampal tissue was transplanted into a fresh cavity in frontal neocortex in 18-day-old (juvenile) Wistar rats. The transplant was examined after 2-5 months. The rapid Golgi procedure was used to assess quantitatively the dendritic branching (intersections and branching orders) and spine numbers per neuronal region, and spine densities (per 20 microns segment) on the pyramidal neurons, granule neurons and other types. The results revealed that the graft neurons generally have significant deviations from those of normal native hippocampal neurons. The aberrations were present in both pyramidal and granule cells. There were also many neurons which could not be classified into the known types. The pyramidal neurons showed a significant deficiency in dendritic branching, more often in basal dendrites than in apical dendrites. Apical dendrites of the graft pyramidal neurons also developed spine densities relatively better than basal dendrites, and sometimes significantly higher than even normal neurons. The significant deficiency in spine numbers of basal dendrites was primarily due to deficiency in dendritic branching rather than to spine density. On the contrary, the granule cells developed significantly less of both dendritic branching and spine densities (hence spines per neuron) than normal hippocampal granule neurons. The unclassifiable neuronal types had generally high dendritic branching and spine densities relative to the other neurons of the graft. The study discusses the importance and necessity of making quantitative assessments of neurons to understand whether the apparently normal neurons of transplants are really normal, and how far they are deviant. So far, quantitative assessments have been seldom reported in this important area of research, hence, this study is the first of its kind to highlight it.

Animals↗
PubMed1989

Alterations in the microenvironment during spreading depression associated with epileptiform activity in the immature neocortex.

Local changes in extracellular ion concentrations were measured with ion-sensitive microelectrodes in slices of mature (greater than 40 days of age) or immature (16-30 days of age) rat neocortex maintained in vitro. Repetitive stimulation resulted in increases in extracellular potassium ([K+]o) to levels of 8.85 +/- 2.1 mM in slices from adult animals and 12.77 +/- 1.8 mM in slices from immature animals. During exposure to picrotoxin, maximum levels were 11.3 +/- 2.6 and 14.8 +/- 2.5 mM in the mature and immature groups, respectively. Picrotoxin (50 microM) induced spontaneous bursts of repetitive spiking, followed by a slow, negative field potential, associated with spreading depression (SD), in slices from immature animals. [K+]o levels increased to 10.2 +/- 3.9 mM during repetitive spike discharges and reached 30.3 +/- 18.5 mM during SDs. Variations in the size of the extracellular space (ES) were examined during SD. The ES was found to reversibly decrease by 39 +/- 4.5%. Clusters of repetitive spikes were associated with 0.1-0.2 mM decreases in [Ca2+]o, whereas 1.12 +/- 0.06 mM decreases were observed during SDs. Decreases in [Na+]o and [Cl-]o of 56 +/- 10 mM and 41 +/- 9 mM, respectively, were observed during SDs suggesting that a net transmembrane movement of water occurred during SDs. These results indicate that changes in [K+]o associated with epileptiform activity in the immature nervous system are quantitatively different from those observed in the mature brain. These large increases in [K+]o may contribute to the prolonged nature of epileptiform discharges in the developing nervous system.

Aging↗
PubMed1990

Control of NMDA receptor-mediated activity by GABAergic mechanisms in mature and developing rat neocortex.

The effects of diazepam and low concentrations of bicuculline methiodide (BMI) on the expression of long-latency N-methyl-D-aspartate (NMDA) receptor-mediated activity was studied in supragranular layers of juvenile (14-18 days old) and adult rat (greater than or equal to 28 days) primary somatosensory cortex. In juvenile slices, orthodromic stimulation of layer VI/white matter evoked a long-lasting oscillatory field potential response which could be blocked by the NMDA receptor antagonist D(-)-2-amino-5-phosphonovaleric acid (D-APV) and by diazepam. Similar D-APV-sensitive responses could be observed in adult slices when the GABAergic system was slightly suppressed by adding low doses of BMI to the bathing solution. Our findings indicate that a small decrease in the efficacy of the inhibitory system, whether caused by developmental events or by processes that modulate inhibitory electrogenesis, can lead to NMDA receptor-mediated synchronized afterdischarges, which might play an important role in the functional maturation of the neocortex and in susceptibility to epileptogenesis.

2-Amino-5-phosphonovalerate↗
PubMed1992

Spontaneous firing as an epigenetic factor in brain development--physiological consequences of chronic tetrodotoxin and picrotoxin exposure on cultured rat neocortex neurons.

Functional consequences of either suppressing or intensifying spontaneous neuronal firing have been studied in developing rat cerebral cortex cultures using, respectively, tetrodotoxin (TTX) and picrotoxin (PTX) added chronically to the growth medium. Simple measures derived from the interspike interval histogram were able to powerfully discriminate between age and treatment groups. After return to control medium, most TTX-treated neurons spontaneously displayed stereotyped clustering of action potentials ('phasic' firing) which closely resembled the characteristic firing patterns seen acutely in the presence of PTX. The 'TTX-syndrome' thus suggests that GABAergic synaptic inhibition is ineffective in cortical networks grown under conditions which prevent the expression of bioelectric activity. In contrast, after return to control medium, neurons which had been partially disinhibited throughout development (by continuous exposure to PTX) had even less phasic firing than was measured in age-matched controls. Based upon these and previous findings, a two (main) factor model is put forth which can economically account for the major effects. The working hypothesis embodied in this model is that phasic neuronal discharges not only accelerate the maturation of excitatory connections within the neocortex but, even more important, are crucial for the development of adequate inhibitory synaptic transmission.

Animals↗
PubMed1994

Radial glia in the neocortex of adult rats: effects of neonatal brain injury.

Microgyria can be induced in otherwise normal rat neocortex by a freezing injury to the cortical plate before the completion of neuronal migration. We had previously reported radial glial like-immunoreactive fibers in the area of the microgyria in 32-day-old rats. Here we demonstrate that these glial fibers, which are immunoreactive to Rat-401, vimentin, and glial fibrillary acidic protein (GFAP) antibodies, are seen in adult rats. The appearance of these fibers is hypothesized to result from the release of a trophic factor during the recovery from neonatal injury which acts to either (1) halt the transformation of radial glia to astrocytes and/or dedifferentiate already committed astrocytes, (2) create a hybrid cell, or (3) induce increased proliferation of glia.

Aging↗
PubMed1996

Elevated GM2 ganglioside is associated with dendritic proliferation in normal developing neocortex.

Mature pyramidal neurons of cerebral cortex in several neuronal storage diseases elaborate ectopic dendrites. These dendrites appear specifically on pyramidal neurons containing elevated GM2 ganglioside and a variety of studies support the hypothesis that this ganglioside is responsible for inducing the new dendrite growth. To determine whether a similar association between GM2 ganglioside and dendrite growth occurs in normal neurons, we used an antibody to localize GM2 in developing cat neocortex. Our results show that GM2 ganglioside is elevated in normal cortical neurons during the period when dendritogenesis is occurring, but is greatly diminished in these cells after dendritic differentiation is complete. Elevations of GM2 occur in deep neurons earlier than in superficial ones, a sequence that corresponds closely to the inside-first, outside-last progression of cortical neuron differentiation. Ultrastructurally, GM2 immunoreactivity is found sequestered in vesicles with a distribution that coincides with sites of ganglioside synthesis and transport. The close association between elevated GM2 ganglioside and dendrite growth in cortical pyramidal neurons during normal development, coupled with a similar correlation between GM2 and ectopic dendritogenesis in neuronal storage diseases, support the view that this specific ganglioside plays a pivotal role in regulating dendritogenesis.

Age Factors↗
PubMed1990

Cross-modal plasticity in cortical development: differentiation and specification of sensory neocortex.

Early developmental manipulations can induce sensory afferents of one modality to project to central targets of a different sensory modality. We and other investigators have used such cross-modal plasticity to examine the role of afferent inputs and their patterns of activity in the development of sensory neocortex. We suggest that the afferent rewiring can significantly influence the internal connectivity or microcircuitry of sensory cortex, aspects of which appear to be determined or specified relatively late in development, but that they cannot influence, or influence only to a minor extent, the laminar characteristics and external connectivity patterns of cortex, which appear to be specified earlier.

Animals↗
PubMed1994

Temporal and spatial properties of local circuits in neocortex.

A large body of anatomical data has detailed many complexities of neocortical circuitry, and physiological studies have indicated some roles for this circuitry in the complex functions of the cortex. Until recently, however, we have little precise information about the spatio-temporal properties of synaptic connections between individual neocortical neurones. Studies of synaptic responses elicited in one neocortical neurone by action potentials in another, and parallel morphological studies that have identified these neurones and the synaptic connections between them, have now described these parameters for certain types of local circuit connection in the neocortex. Some of these studies confirmed previous observations and inferences, but others provided major surprises. Evidence indicates that the class of both the presynaptic and postsynaptic neurone together determine a wide range of synaptic properties, such as the type of postsynaptic receptors involved and the temporal pattern of transmitter release, so that each type of synapse displays unique properties. A role for retrograde diffusable messages in determining the temporal properties of these circuits is postulated.

Animals↗
PubMed1994

Cellular and synaptic localization of NMDA and non-NMDA receptor subunits in neocortex: organizational features related to cortical circuitry, function and disease.

Excitatory amino acid (EAA) receptors are an important component of neocortical circuitry as a result of their role as the principal mediators of excitatory synaptic activity, as well as their involvement in use-dependent modifications of synaptic efficacy, excitoxicity and cell death. The diversity in the effects generated by EAA-receptor activation can be attributed to multiple receptor subtypes, each of which is composed of multimeric assemblies of functionally distinct receptor subunits. The use of subunit-specific antibodies and molecular probes now makes it feasible to localize individual receptor subunits anatomically with a high level of cellular and synaptic resolution. Initial studies of the distribution of immunocytochemically localized EAA-receptor subunits suggest that particular subunit combinations exhibit a differential cellular, laminar and regional distribution in the neocortex. While such patterns might indicate that the functional heterogeneity of EAA-receptor-linked circuits, and the cell types in which they operate, are based partly on differential subunit parcellation, a definitive integration of these anatomical details into current schemes of cortical circuitry and organization awaits many further studies. Ideally, such studies should link a high level of molecular precision regarding subunit localization with synaptic details of identified connections and neurochemical features of neocortical cells.

Animals↗