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At least 793 records · Page 44Linked to original sources
PubMed1991

Bicuculline-induced epileptogenesis in the human neocortex maintained in vitro.

Intracellular and extracellular recordings were made from human neocortical slices of the temporal lobe maintained in vitro. The slices were treated with bicuculline methiodide to reduce synaptic inhibition mediated by tha gamma-aminobutyric acid A (GABAA) receptor. Spontaneously occurring epileptiform activity was never observed in over 60 slices examined. All epileptiform discharges were elicited by single-shock stimuli delivered in the underlying white matter or within the cortical layers. Intracellularly, the stimulus-induced epileptiform discharge resembled the paroxysmal depolarization shift (PDS). This potential was observed in neurons located between 200 and 2200 microns from the pia. It was characterized by a 100-1800 ms long depolarization which triggered burst firing of action potentials, and was at times followed by an afterdischarge. Simultaneous intracellular and extracellular recordings showed that each PDS was reflected by the synchronous discharge of a neuronal aggregate. The voltage behaviour of the PDS and its preceding EPSP was analyzed in cells that were injected with the lidocaine derivative QX-314. The amplitudes of the PDS depolarizing envelope measured at its peak and during its falling phase both behaved as a monotonic function of the membrane potential by increasing in amplitude during hyperpolarization. In addition, the PDS peak amplitude showed a much greater rate of increase than the early EPSP peak amplitude, thus suggesting that the synaptic conductance underlying the PDS was much greater. Perfusion of the neocortical slices with the N-Methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-phosphonovaleric acid (APV) reduced both the duration and the amplitude of the paroxysmal field discharge in a dose related fashion. The effects of APV were reflected intracellularly by an attenuation of the PDS's late phase and a blockade of the afterdischarge. Similar findings were also obtained by using the NMDA receptor antagonist 3-((+-)-2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid. These data indicate that reduction or blockade of the GABAA receptor is sufficient to elicit epileptiform discharges in the human neocortex maintained in vitro. Mechanisms dependent upon the NMDA receptor contribute to this type of epileptiform response mainly by prolonging the stimulus-induced depolarizing potential and the associated burst of firing.

2-Amino-5-phosphonovalerate↗
PubMed1984

Nucleus basalis magnocellularis: optimal coordinates for selective reduction of choline acetyltransferase in frontal neocortex by ibotenic acid injections.

The present experiment was designed to determine the optimal placement of ibotenic acid in the nucleus basalis magnocellularis (NBM) in order to get a substantial destruction of cholinergic input to the frontolateral cortex, while sparing that to the hippocampus. Two different volumes of ibotenic acid were injected at four different placements in the basal forebrain. Choline acetyltransferase (ChAT) levels were measured in three regions of neocortex and two regions of hippocampus. Lesions in the NBM produced significant decreases in neocortical ChAT (up to 54%), with the greatest and most extensive effects being produced by lesions that were more lateral and caudal (0.9 mm posterior to Bremga; 2.6 mm lateral to the midline). All lesions that were placed 0.4 mm posterior to bregma, or placed 2.0 mm lateral to the midline, produced significant decreases in ChAT activity levels in the ventral hippocampus. The results show that the specific coordinates and volumes of ibotenic acid are critical to produce selective and substantial destruction of cells in the NBM. These findings have substantial implications for the interpretation of results of experiments examining the behavioral changes that occur following injections of ibotenic acid into the NBM.

Animals↗
PubMed1978

Brain stem neurons projecting to neocortex: a HRP study in the cat.

The cortical projections of the brain stem were investigated in detail in the cat by means of the horseradish peroxidase (HRP) retrograde axonal transport. Most of the cells providing ascending fibers to the neocortex were located in the pons (locus coerulus and related structures, central gray substance, dorsal tegmental nucleus, raphe nuclei, reticular nuclei); labeled neurons were also identified in the mesencephalon, mainly in the periaqueductal gray and in the nucleus linearis rostralis. These projections, and particularly the pontine fibers, were diffusely distributed throughout the cerebral cortex.

Animals↗
PubMed1989

Anaesthetic depression of excitatory synaptic transmission in neocortex.

A decrease in synaptic excitation as well as an enhancement of neuronal inhibition in the central nervous system have been suggested as possible mechanisms of anaesthesia which we have investigated with intraneuronal recording techniques in neocortex. The effects of a volatile agent--isoflurane and a steroid preparation--Althesin, on excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) evoked by epicortical electrical stimulation were investigated in in vitro slice preparations of anterior cingulate and sensorimotor cortices of guinea pig. Applications of isoflurane (0.5-2.5 minimum alveolar concentration or MAC) and Althesin (10-200 microM) induced a dose-dependent, reversible depression of EPSPs with EC50's of 1 MAC and approximately 50 microM respectively. In order to eliminate the possibilities of a shunting effect on EPSPs by the conductances involved in the concomitant IPSPs, a GABAA-antagonist (bicuculline) was applied together with the anaesthetics. With this IPSP blockade, both anaesthetics depressed the EPSPs and were effective in reducing the epileptiform activities evoked by bicuculline during the subpial stimulation. The IPSPs also were evoked during the blockade of K-conductances by internal Cs-applications in order that the effects of anaesthetics could be studied exclusively on the Cl-mediated GABAergic IPSPs. Both isoflurane (0.5-2.5 MAC) and Althesin (10-100 microM) depressed the IPSPs in a dose dependent manner. These investigations demonstrate that applications of isoflurane and Althesin depressed the excitabilities of neocortical neurons by interfering with synaptic excitation, possibly at pre- and postsynaptic sites, rather than by potentiating neuronal inhibition.

Action Potentials↗
PubMed1981

The marginal layer in the neocortex of a 7 week-old human embryo. A light and electron microscopic study.

Ultrastructural study of the molecular layer of the neocortex of a 7 week-old human embryo confirms recent observations on various laboratory animals that call for revision of some classical concepts of corticogenesis. 1. At 7 weeks, the subpial, marginal or molecular layer is the first layer to differentiate from the ventricular layer and represents almost half the thickness of the telencephalic vesicle. 2. The first cells that have already migrated from the ventricular zone, even before any cortical plate is visible, are to be found in this marginal layer. These large cells are well differentiated and most probably represent the so called Cajal Retzius cells. 3. The earliest synapses ever seen in human embryo are found in the marginal or plexiform layer; this indicates the presence of a precocious set-up for an elaborate neuronal circuitry at this level.

Cell Differentiation↗
PubMed1984

Neuronal types in the neocortex-dependent lateral territory of the human thalamus. A Golgi-pigment study.

Nerve cell types of the neocortex-dependent nuclei of the human thalamus were investigated with the use of a transparent Golgi technique, that allows one to study not only the peculiarities of the cell processes, but also the marking characteristics of the intraneuronal lipofuscin pigment deposits. Three principal types of neurons have been distinguished: Type I is a medium-sized to large neuron with a profusely radiating dendrite system. Numerous large vacuolated lipofuscin granules are contained in one pole of the cell body. Type II is a small to medium-sized neuron with a few sparsely branching dendrites. Small and intensely stained pigment granules are dispersed within the cell body. Type III is a medium-sized to large neuron with only a few thick and almost unbranched dendrites devoid of spiny appendages. The dendrites extend over long distances. The cell body is devoid of lipofuscin granules.

Aged↗
PubMed1979

Acetylcholinesterase-containing neurons of layer VIb in immature neocortex: possible component of an early formed intrinsic cortical circuit.

In this ontogenetic study the neurons of layer VIb of rodent somatosensory cortex have been characterized using acetylcholinesterase (AchE) histochemistry, Golgi, and electron microscopic techniques. Already, at birth, the neurons were found to be AchE-rich. They contain presumed AchE reaction product within their granular endoplasmic reticulum. These cells send fine axons upwards towards the subpial layer where they terminate in a dense, AchE-rich, fiber plexus. In chronically undercut cortex, AchE staining persists in layer VIb neurons and in the subpial fiber plexus. These observations continue to support the view that there is an intrinsic neuronal circuit connecting layer VI with I in immature neocortex. The findings also raise the possibility that the putative circuit is cholinergic.

Acetylcholinesterase↗
PubMed1987

Fetuin as a marker of cortical plate cells in the fetal cow neocortex: a comparison of the distribution of fetuin, alpha 2HS-glycoprotein, alpha-fetoprotein and albumin during early development.

Fetuin, alpha 2HS-glycoprotein (alpha 2HS), alpha-fetoprotein (AFP) and albumin have been shown to be present in some regions of the neocortex in two early stages of development of the cow brain using PAP immunocytochemistry. In the pre-cortical plate stage fibres of the primordial plexiform layer stained positively for fetuin. No staining was seen for albumin but plasma and cerebrospinal fluid (CSF) were positive for alpha 2HS and AFP. In the early cortical plate stage the strongest fetuin positive staining was seen in the earliest formed cells of the plate. alpha 2HS staining was much less intense but similar in distribution. The possible role of fetuin, or related glycoproteins, in cortical plate differentiation is discussed. Staining for AFP and for albumin was seen mainly in the ventricular zone and marginal zone fibres, and had a similar distribution and intensity for both proteins. Plasma and CSF stained for all four proteins. Tests showed some cross-reactivity between fetuin and anti-alpha 2HS and, to a much lesser extent, between antisera to AFP and albumin and antigens denatured by fixation.

Animals↗
PubMed1983

Tangential preferential orientations of neuron processes in the rat neocortex.

The orientations in the tangential plane, i.e., parallel to the pial surface, of dendrites and axons in several functionally different areas of the rat neocortex were investigated. Using a large data base of over 30,000 measurements and the t-test and chi 2 test for significance, we found an overall preference of both dendrites and axons for the anteroposterior and adjacent orientations. The degree of preference varied from area to area and among different cortical laminae. Other variations were correlated with neuron type and dendritic rank (in a tree). The pyramidal cell dendritic fields show little orientation in the tangential plane, whereas a large fraction of the stellate cells are oriented. The overall preferential orientations are apparently related to brain axes and growth lines, whereas the variability is probably due to the influence of the functional topography.

Animals↗
PubMed1977

Generality of the functional structure of the neocortex.

The fundamental similarities between various neocortical areas are elaborated by pointing out the common principles of its afferent, intrinsic, and efferent organization, with special emphasis on the generality of thalamocortical circuits. Interareal differences in morphology and function can be considered as accidental, i.e., depending on the circuit in which a given cortical area is involved. The neocortex is a link in the chain of afferent-efferent signal processing, and can be understood as a cooperative network that acts as a nonlinear spatiotemporal filter with adaptive properties (memory) and that transforms afferent signal flow. It is assumed that these filter properties are identical for all neocortical areas. The functional role of a circumscribed cortical area depends exclusively on its position uithin a certain functional circuit and is defined by it.

Afferent Pathways↗
PubMed1989

Tau, paired helical filaments and amyloid in the neocortex: a morphometric study of 15 cases with graded intellectual status in aging and senile dementia of Alzheimer type.

Tau immunoreactivity was studied in temporal neocortex, area 22, in 15 cases with graded intellectual status and compared with the immunoreactivity observed with an antiserum against paired helical filaments (PHF) and with the density of amyloid revealed by thioflavin S. Samples came from women over 75 years either intellectually normal or affected by senile dementia of the Alzheimer type at various degrees of severity. Mental status had been prospectively assessed by the Blessed's test score. Anti-tau labelled a neuropil meshwork, the density of which increased with the severity of the disease. This meshwork was denser in layers II, III and V in the most affected cases. The number and the size of the tau-positive fibers within the senile plaques increased with the intellectual deficit. Senile plaques were more numerous in layers II and III and neurofibrillary tangles in layers III and V whatever the staining technique: tau or PHF immunocytochemistry, and thioflavin S. The densities of senile plaques and of neurofibrillary tangles (NFT) were correlated with the severity of the disease whatever the staining method. The three methods revealed a systematically different number of changes. This systematic difference could greatly influence the neuropathological diagnosis. It could be the consequence of various factors: different sensitivities of the staining methods or changes in the antigenic and amyloid composition of the lesion according to the stage of the disease. In line with the last hypothesis, a higher proportion of amyloid-rich plaques was noted in the less affected cases, suggesting that tau and PHF epitopes appeared secondarily.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1987

The modulation of excitatory amino acid responses by serotonin in the cat neocortex in vitro.

1. The electrophysiological actions of excitatory amino acids and serotonin were investigated in slices from cat neocortex in vitro. Intracellular recordings were obtained from neurons (mainly in layer V) and the drugs applied extracellularly to the same neurons by microiontophoresis. 2. Serotonin, and to some extent noradrenaline, facilitated the excitatory actions of N-methyl-D-aspartate (NMDA), glutamate, and quisqualate but caused no changes in the passive neuronal membrane properties when presented alone. Serotonin had no effect on evoked excitatory postsynaptic potentials (EPSPs) or spike afterhyperpolarizations. 3. The facilitatory effect of serotonin on the responses to NMDA was observed with both somatic and dendritic applications. It persisted during Mg2+ depletion and in the presence of tetrodotoxin and tetraethylammonium. The effect was attenuated by the serotonin antagonist cinanserin but not by methysergide. A possible underlying receptor modulation is discussed.

Animals↗
PubMed1992

BC200 RNA in normal human neocortex, non-Alzheimer dementia (NAD), and senile dementia of the Alzheimer type (AD).

BC200 RNA is a polyadenylated 200 nucleotide primate brain-specific transcript with 80% homology to the left monomer of the human Alu family of repetitive elements. Whether this transcription product contributes anything to normal brain gene function or is a residue of post transcriptional processing of brain heterogeneous nuclear RNA (hnRNA) is uncertain. However, the high abundance, tissue-specific expression and nucleotide sequence characteristics of BC200 RNA suggests that the generation of this small RNA is associated with some brain cell function. Sustained levels of the BC200 RNA transcript may be indicative of a genetically competent and normally functioning cerebral neocortex. In this investigation, we have measured the abundance of the BC200 RNA transcript in total RNA isolated from 18 temporal neocortices (Brodman area 22) of brains with no pathology and those affected with neurodegenerative disease. Neocortices were examined from 3 neurologically normal brains, 5 non-Alzheimer demented [NAD; 3 Huntington's chorea (HC), 1 amyotrophic lateral sclerosis (ALS) and 1 dementia unclassified] and 10 Alzheimer disease (AD) affected brains. Our results indicate a strong BC200 presence in both the normal brains and NAD affected neocortices, but a 70 per cent reduction in BC200 signal strength in AD afflicted brains. These results may be related to the observation that Alzheimer brains exhibit marked deficits in the abundance of neuron-specific DNA transcripts; these deficits are consistent with the idea that AD is characterized by an impairment in the primary generation of brain gene transcription products.

Alzheimer Disease↗
PubMedDate not supplied

Neuronal activity in suspension transplants of the neocortex.

The characteristics of suspension (ST) and tissue (TT) transplants of the embryonal neocortex, transplanted into adult rats into the neocortical region of the representation of the vibrissae, were compared. The degree of taking of the ST and the TT did not differ significantly (89.5 and 95%, respectively). Transplants completely isolated from the brain were not found in the ST on the basis of histological and electrophysiological indices. The reactivity of ST neurons during electrical stimulation of the brain structures of the recipient and sensory stimulation, like the latent periods of the on-responses, did not differ significantly in the ST and the TT; however, the per cent of neurons responding with on-responses, was nearly twice as low in the ST as in the TT. At the same time, there were substantially more neurons in the ST responding to tactile stimulation with inhibition of discharges. It is hypothesized that the disruption in the primary cytoarchitectonics of the ST which takes place inevitably in the preparation of the suspensions is a cause of the differences indicated between the ST and the TT.

Animals↗
PubMed1995

Synaptogenesis and distribution of presynaptic axonal varicosities in low density primary cultures of neocortex: an immunocytochemical study utilizing synaptic vesicle-specific antibodies, and an electrophysiological examination utilizing whole cell recording.

Low-density primary cultures of neocortical neurons were utilized to examine: (i) early interactions of growing neurites with morphological characteristics of axons with other neuronal elements, and (ii) the distribution of presynaptic axonal varicosities closely apposed to MAP-2 immunoreactive, putatively postsynaptic, dendrites. At the light microscopical level axonal varicosities, presumably presynaptic terminals, were identified using immunocytochemistry incorporating antibodies specific for the synaptic vesicle antigens synaptophysin and synapsin. The presence of synaptophysin- and synapsin-immunoreactive swellings along axonal processes was first detected at 5 days post-plating and was also apparent in axons growing in isolation. At 5-7 days in vitro, immunolabelled axonal varicosities in close apposition to putative postsynaptic dendrites (MAP-2 immunoreactive) dendrites were detected. Electrophysiologically active synaptic contacts can also readily be detected at this stage. After 3 weeks in vitro presynaptic contacts do appear to be distributed heterogeneously along postsynaptic dendrites of many neurons in culture. As the culture matures a higher number of presynaptic profiles can be seen along dendrites, with a centrifugal distribution, e.g. a higher density of presynaptic axonal terminals in close apposition to more distal regions of larger dendrites, putatively considered to be apical dendrites of pyramidal-like neurons. In our cultures, the overall increase in the density and the pattern of distribution of presynaptic axon terminals immunoreactive for synaptic vesicle antigens closely apposed to putative post-synaptic structures mimics the general postnatal increase of synaptic density in the neocortex in vivo. Thus, low density primary cultures of neocortical neurons offer a valuable system to explore and manipulate (i) the molecular and cellular basis of neocortical synaptogenesis, and (ii) the pharmacology of neocortical synaptic transmission.

Animals↗
PubMedDate not supplied

The influence of high-frequency stimulation of the midbrain reticular formation on the interaction of neurons of the neocortex.

The influence of the stimulation of the midbrain reticular formation (NRT) at a frequency of 75-100 Hz, current strength 33-400 microA, on the interaction of neurons of the visual and sensorimotor areas of the neocortex of rabbits was investigated. Cross- and autocorrelation histograms of the impulse sequences were plotted. Stimulation of the NRT led to an increase in the number of pairs of neurons functioning in correlation and an increase in the probability of discharges of neurons one after the other with delays from 100 to 400 msec as compared with resting wakefulness. The mechanisms of the interaction of the cells were not altered in the process. Comparison with previously obtained data made it possible to conclude that activation of the NRT may lead to specific changes in the interaction of neurons which are observable during pseudoconditioning and at the beginning of the development of a conditioned reflex.

Animals↗
PubMedDate not supplied

Influence of local injection of 5,7-DHT and 6-OH-DA into the neocortex on learning and exploratory behavior of rats in the open field.

The features of the exploratory behavior in the open field, of the learning of a conditioned-reflex food-procuring reaction, and of the shift in the level of biogenic amines of the brain was studied in Wistar rats with local injections of the specific neurotoxins 6-hydroxydopamine (6-OH-DA) and 5,7-dihydroxytryptamine (5,7-DHT). It was shown that damage to the structure of the serotoninergic or catecholaminergic systems of the frontal cortex and hippocampus caused by local injection of 6-OH-DA and 5,7-DHT into the neocortex is accompanied by multidirectional changes in the exploratory behavior and learning of the animals.

5,7-Dihydroxytryptamine↗