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At least 55 records · Page 3Linked to original sources
PubMed1984

Mechanisms of epileptogenesis in cortical structures.

Studies of the mechanisms of epileptogenesis in brain-slice model systems have emphasized the role of three interacting processes in the development of interictal discharge. These processes are intrinsic burst activity, disinhibition, and excitatory synaptic coupling. Intrinsic membrane excitability may be altered by neuromodulators, injury, genetic mutations, and other factors. Disinhibition releases intrinsic burst-generating capacities in subpopulations of neurons and may become an important factor following cortical injury or repetitive activation of inhibitory circuits. Excitatory synaptic coupling is required in order to synchronize populations of neurons. Synaptic currents also serve as a major generator of slow depolarization shifts in individual neurons. The contribution of each of these factors to epileptogenesis may vary with the type of pathological process and the properties of the specific neuronal population.

Animals↗
PubMed1992

Composition, cortical structure and mechanical properties of chicken tibiotarsi: effect of growth rate.

1. Comparisons of tibial growth in slowly (X) and rapidly (F) growing chicks were carried out weekly until the birds weighed 500 g. 2. Bone volume and percentage of ash per dry weight increased with age and were similar at equal body weights between crossbreeds. In birds of the same age, the ratio of tibial dry weight to hydrated weight was greater in crossbreed X as compared with crossbreed F. Consequently, the tibial density and the mineral content per volume were higher, at equal body weights, in crossbreed X. 3. Cortical cross-sectional area was greater in crossbreed F at the different ages, but was similar in both crossbreeds at equal body weights. A peripheral active zone of greater porosity was predominantly characterised by radial fibrolamellar tissue in fast growing birds and covered a larger area in crossbreed F than in crossbreed X. 4. Biomechanical properties of the tibiotarsi were evaluated in a three-point flexure test. The area moment of inertia was equal at similar body weights in both crossbreeds, but the yield or maximal forces and stiffness of tibiotarsi were lower in the rapidly growing crossbreed F compared with crossbreed X. 5. It is concluded that an increased rate of growth is associated with a lower mineral density and higher porosity of the tibial cortices resulting in reduced bending resistance.

Animals↗
PubMed1987

Changes of intracellular calcium homeostasis in brain cortical structures during anoxia in vivo and in vitro.

This work characterizes the anoxia-evoked changes in the content of bound calcium (Cab) in brain cortex membraneous structures, studied in vivo, on living brain cortex preparation and in vitro, on subcellular fractions (synaptosomes, microsomes and mitochondria) in anoxic conditions. The chlorotetracycline (CTC) fluorescent chelate probe was used to monitor changes of Cab content in hydrophobic domains of intracellular membranes. In in vivo experiments the bioelectric activity of single neurons was recorded simultaneously with measurements of Ca-CTC fluorescence. In vitro experiments were supplemented with determinations of synaptosomal 45Ca-uptake. It was found that the response of cortical neurons to anoxia is manifested in a decrease of a portion of Ca2+ bound with membrane hydrophobic domains. These in vivo changes preceded the noticeable disturbances of neuronal electric activity. An anoxia-evoked drop in Cab was also clearly demonstrated in vitro, irrespective of K+ (for synaptosomes) or Na+ (for mitochondria) concentrations in incubation media, although the additional effect of Cab displacement was noted when Na+/K+ concentrations were modified in order to simulate their changes occurring in anoxic conditions. It was found that the membranes of different neuronal compartments are not uniformly vulnerable to anoxia in vitro as the anoxic decrease in Cab content occurred in synaptosomes and microsomes much sooner than in mitochondria. Therefore, in vivo and in vitro experiments visualized high sensitivity of Ca2+-binding mechanisms in different neuronal membranes to anoxia. The anoxia-evoked displacement of a portion of Cab to the free ionic form may trigger a complex intracellular response determining anoxic reactions and post-anoxic recovery.

Animals↗
PubMed2005

Protective effects of cisternal irrigation on leptomeningeal and cortical structures in meningitis: an experimental study.

BACKGROUND: Meningitis, termed as foreign material collection in the subarachnoid space, leads to various meningeal, cerebral and spinal cord pathologies. Meningitis still remains a problematic disease with severe complications in spite of advanced medical technology. AIMS: In this study, we aimed to investigate the role of cisternal irrigation in the prevention of meningitis complications. SETTING AND STUDY DESIGN: Experimental study was done in the Social Security Hospital of Erzurum. Histopathological specimens were evaluated in the Pathology Department in the Ataturk University Research Hospital, Erzurum, Turkey. MATERIALS AND METHODS: This study was conducted on twelve lambs. Experimental meningitis was achieved with streptococcus pneumonia. Two animals were not treated. Ten animals were given Cefotaxime (4 x 1g/day) for 20 days, and additionally half of these animals underwent cisternal irrigation. Then, all animals were sacrificed and brains were observed histopathologically. RESULTS: Massive purulent CSF formation, hemorrhagic cortical lesions, vascular congestion, leptomeningeal and cortical adhesions and brain edema were observed in the non-irrigated group, but these findings were observed slightly or absent in the irrigated group. CONCLUSION: Meningitis can affect all central neural tissues, consequently serious central nervous system lesions may develop. The irrigation procedure may decrease the percentage and severity of meningitis complications by way of the excretion of inflamed purulent collection from the subarachnoid spaces.

Animals↗
PubMed1995

[Synchronization processes in the mechanisms of short-term memory in monkeys: the participation of cholinergic and glutaminergic cortical structures].

Administration of amysil blocking M-cholinoreceptors, and APV the duration of short-term storing of information was decreased whereas the motor response time increased. This was followed by a considerable desynchronisation of the unit activity. The NMDA and APB improved the characteristics of the short-term memory. The role of synchronisation of the information processes in the short-term memory mechanisms and participation of cholinergic and glutamatergic systems in them, are discussed.

Acoustic Stimulation↗
PubMedDate not supplied

[The cross-correlation relations of the electrical activity of the cortical structures at different levels of the activation of the midbrain reticular formation in the rabbit].

Changes of correlation coefficients and coherence of the delta-, theta- and alpha-rhythms were studied between the somatosensory, motor and visual neocortex areas, dorsal hippocampus and dentate fascia at stimulation frequencies of the midbrain reticular formation from 60 to 1000 imp/s. It was shown that correlation coefficient between the structures studied increased at 60-200 imp/s and decreased at the further increase of stimulation frequency. In pairs with the visual area the correlation coefficient changed but little. The delta-rhythms coherence tended to decrease with the increase of stimulation frequency. Coherence of the theta-rhythms between the neocortical areas and the hippocampus increased with the increase of stimulation frequency up to 200 imp/s and decreased at higher frequency stimulation while in pairs of these areas with the dentate fascia it continued to rise with the increase of stimulation frequency up to 1000 imp/s. The coherence of the alpha-rhythms was almost unchanged at 60-200 imp/s and mostly had an increase at higher frequency stimulation.

Alpha Rhythm↗
PubMed1998

Altered expression of microtubule-associated protein 1B in cerebral cortical structures of pentylenetetrazole-treated rats.

Using Northern blot, immunoblotting, immunocytochemistry, and in situ hybridization, we show that a single administration of the convulsant pentylenetetrazole leads to robust, long-term changes in microtubule-associated protein 1B and its mRNA, in the adult rat brain. The first increases in MAP1B mRNA were detected at 15 hr following pentylenetetrazole administration in the temporal (Te2) and perirhinal cortex followed by increases in microtubule-associated protein 1B immunoreactivity at 72 hr postseizure. In contrast, the levels of microtubule-associated protein 1B mRNA and protein in layers I-II of the retrosplenial and parietal cortex (Par2) declined visibly by 24 hr and 72 h, respectively, post-seizure. The changes included loss of staining in layers I-II and development of structures resembling "strings-of-beads" along the fibers of projection neurons of layer V. The levels of microtubule-associated protein 1B mRNA in the entorhinal cortex peaked at later times (72 h), especially in layers II-III, and returned to control levels by 10 days. Whereas the levels of microtubule-associated protein 1B immunoreactivity in the retrosplenial and parietal cortex recovered by 5-10 days, it persisted at high levels through day 35 in layer V of the temporal cortex (Te2), layers II-III of the perirhinal cortex and layers I-II of the lateral entorhinal cortex. These results indicate that seizure activity leads to long-term upregulation of genes coding for structural elements that are characteristic of the immature brain such as microtubule-associated protein 1B.

Animals↗
PubMed1991

Acute effect of neodymium yttrium aluminium garment laser on the cerebral cortical structure, blood-brain barrier, and pial vessel behaviour in the cat.

Experimental brain lesions were created by Nd:YAG laser (wave length 1.06 microns) irradiation on the cerebral cortex of anaesthesized adult cats with 20 Watts impacts of 0.5, 1.0, 2.5, and 5.0 seconds exposure time through cranial windows. Histological changes, disruption of the blood-brain barrier (Evans blue extravasation) and pial vessel reaction (large vessels more than 100 microns and vessels smaller than 100 microns) were studied under constant PaCO2, blood pH, and mean arterial pressure. Histological changes of the lesions consisted of a zone of dense coagulation, a pale zone of homogeneous coagulation and an oedematous zone. Evans blue extravasation was uniformly seen extending from the histologically changed area into the surrounding tissue in all experiments. Pial arteries in the area with morphological changes showed pronounced dilatation (100.0 +/- 7.2%) and one third of these arteries were closed by thrombi. Pial arteries in the area of Evans blue extravasation but outside of histological changes also dilated (large arteries 60 +/- 4.1%, small arteries 77 +/- 5.9%). Pial arteries outside of the Evans blue extravasation were affected transiently and only in a very small zone: Within a distance of 200 microns from the Evans blue extravasation, large arteries initially dilated by 41 +/- 8.3%; small arteries dilated within 400 microns (42 +/- 3.7%). Within 4 minutes after irradiation arterial dilatation was again significantly reduced (p less than 0.01). It is concluded that no important vascular changes occur beyond the zones of histologically altered brain tissue.

Animals↗
PubMedDate not supplied

Phase relationships between the rhythmic activity of cortical structures of the rabbit at different midbrain reticular formation stimulation frequencies.

An investigation of the phase shifts between rhythmic constituents of the electrical activity of the hippocampus, somatosensory, motor, and visual areas of the neocortex of the rabbit during an increase in the frequency of stimulation of the reticular formation from 60 to 1000 imp/sec revealed the fluctuating character of the decrease in the phase shift in the theta range in pairings involving the visual area and of its increase in the remaining pairings. In the delta range, at the same time, an increase was observed in the phase angle in pairings between the hippocampus, somatosensory, and motor areas at a stimulation frequency above 200 imp/sec, while in the alpha range the changes in the phase shift were variously directed in character.

Alpha Rhythm↗
PubMedDate not supplied

Synchronization processes in the mechanisms of short-term memory in monkeys: the involvement of cholinergic and glutaminergic cortical structures.

Behavioral experiments were carried out in which monkeys had to solve a task involving delayed visual discrimination, and activity was simultaneously recorded from several neurons of the visual, prefrontal, and lower temporal regions of the cortex before and after modification of cholinergic (by systemic infusion of the M-cholinoceptor blocker amizil) and glutaminergic (by intracortical perfusion with glutaminergic agonists and antagonists, i.e., NMDA, aminophosphonovalerianic acid (APV) and aminophosphonobutyric acid (APB)) systems. Amizil and APV reduced the duration of short-term information retention and increased the delay before the motor response was made. Worsening of these parameters was accompanied by a significant level of desynchronization of activity in the groups of neurons studied. NMDA and APB improved short-term memory and increased neuron synchronization. The role of synchronization of information processes in the mechanisms of short-term memory and the involvement of the cholinergic and glutaminergic systems are discussed.

Aminobutyrates↗
PubMed1997

Cocaine administration in pregnant rabbits alters cortical structure and function in their progeny in the absence of maternal seizures.

Previous studies have reported that cocaine exposure in utero results in structural and functional alterations in the development of the anterior cingulate cortex (ACC). In the present study, the effects of maternal cocaine dosage and of cocaine-elicited maternal seizures on the progeny were studied. The incidence of maternal generalized tonic clonic seizures (GTCSs) elicited by cocaine was recorded. No GTCSs were elicited in pregnant rabbits by doses of 2 or 3 mg/kg of cocaine, but GTCSs were sometimes elicited by the highest dose (4 mg/kg per injection). We analyzed the offspring of cocaine-exposed and control animals using three assays of ACC development: (i) the structure of apical dendrites of pyramidal neurons, (ii) the distribution of a calcium binding protein (parvalbumin) in the dendrites of GABAergic neurons, and (iii) coupling of D1-like receptors and their G proteins. In all progeny of rabbits exposed to 3 or 4 mg/kg of cocaine during pregnancy, there was a significant change in the structure of apical dendrites, a significant increase in the number of dendrites of GABAergic neurons which were parvalbumin immunoreactive, and a significant reduction in D1/G protein coupling. In assays of apical dendrites, the effects on offspring of rabbits given 2 mg/kg cocaine were as pronounced as in offspring of rabbits given 3 or 4 mg/kg, but the effects on parvalbumin immunoreactivity and D1/G protein coupling were reduced at this low dose. Thus, previous findings of ACC developmental abnormalities in offspring of rabbits given a dose of 4 mg/kg were replicated, the effects were shown to be dose-related and to be independent of maternal seizures. A mechanism by which dysfunction of the D1 receptor system could mediate cocaine-associated changes in all three parameters of ACC structure and function is discussed.

Animals↗