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  • 1
    Electronic Resource
    Electronic Resource
    The emergence of long-lasting transients of activity in simple neural networks (1992)
    Springer
    Biological cybernetics 67 (1992), S. 269-277 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The question was investigated whether longlasting transients of activity, observed to occur in the intact cerebral cortex (EEG slow (δ) waves and ‘K’ complexes) as well as in isolated tissues cultured in vitro, can also emerge in a model network of excitatory and inhibitory cells. We show that such transients can indeed occur even if the cells do not have built-in slow kinetics. For certain parameter settings, the network is in a bistable state in which periods of increased activity (long-lasting transients) alternate with minimal activity. Transients are triggered by spontaneously firing cells (‘noise’), which, rather than via a build-up of recurrent synaptic inhibition, also initiate their termination. During a transient, the network continually makes transitions from one equilibrium to another as a result of spontaneous firing until it is switched back to the quiescent state, i.e., after a variable period of time of noise-induced transitions the transient is terminated. If the network is small, activity can terminate even without inhibition. In large networks, inhibition keeps the network sensitive to spontaneously firing cells by holding it in the neighbourhood of a critical point between active and quiescent state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00204400
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  • 2
    Electronic Resource
    Electronic Resource
    Model of brain rhythmic activity (1974)
    Springer
    Biological cybernetics 15 (1974), S. 27-37 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract 1. A model of a neuronal network has been set up in a digital computer based on histological and biophysical data experimentally obtained from the thalamus; the model includes two populations of neurons interconnected by means of negative feedback; in the model allowance is also made for other sort of interactions. 2. To test the hypothesis that the alpha-rhythm (8–13 Hz rhythmic activity characteristic of the EEG) is a filtered noise signal the simulated neuronal network was stimulated by random trains of pulses with a Poisson distribution. The density of pulses fired by the simulated neurons was computed as well as the oscillations of the mean membrane potential of the population of simulated neurons. The latter was found to be equivalent to the experimentally obtained alpha rhythms. 3. In order to test the hypothesis that several noise sources are responsible for thalamo-cortical coherences three simulated neuronal networks were coupled together using several noise sources as secondary inputs. It was shown that although all the networks produced simulated alpha signals with identical spectra they could have significantly different values of coherence depending on the relation between correlated and uncorrelated input signals. 4. The model was analysed by means of linear systems analysis after introducing the necessary simplifications and approximations. In this way it was possible to evaluate the influence of different physiological or histological parameters upon the statistical properties of the resulting rhythmic activity in an analytical form. 5. By changing the model parameters it was shown that a family of spectral curves could be obtained which simulated the development of the EEG as function of age from a predominantly low frequency to a clearly rhythmic type of signal. This was shown to depend mainly on the feedback coupling parameters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00270757
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  • 3
    Electronic Resource
    Electronic Resource
    Differential effects of enkephalin within hippocampal areas (1981)
    Springer
    Experimental brain research 44 (1981), S. 343-346 
    Details
    ISSN: 1432-1106
    Keywords: Hippocampus ; Dentate gyrus ; Enkephalins ; Neuropeptides
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The synthetic opiate D-Alaninemethionine enkephalin (D-Ala) affects neuronal activity of the fascia dentata (FD). D-Ala causes a depression of the population spike evoked by stimulation of the perforant path, which is antagonized by naloxone. In so called “Tandem” experiments it was shown that D-Ala had opposite effects on the CA1 pyramidal and FD granule cells. It is likely that in the FD the site of action of D-Ala is at the afferent synapses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236574
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  • 4
    Electronic Resource
    Electronic Resource
    Autoradiography of the olfactory-hippocampal pathway in the cat with special reference to the perforant path (1980)
    Springer
    Experimental brain research 38 (1980), S. 257-265 
    Details
    ISSN: 1432-1106
    Keywords: Hippocampus ; Perforant path ; Central olfactory projections ; Limbic system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The anatomical pathway from the prepyriform cortex to the hippocampus in the cat was traced autoradiographically by means of anterograde transport of [3H] leucine. A direct projection from the prepyriform cortex to the lateral entorhinal area was confirmed in the cat: the termination of these fibers was largely confined to the outer part of the molecular layer. From the lateral entorhinal area, the perforant path fibres terminate on the most distal parts of the dendrites of the hippocampal granule and pyramidal cells. However, differences between cat and rat were found with respect to the terminations in the CA1 area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236644
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  • 5
    Electronic Resource
    Electronic Resource
    The localization of leucine-enkephalin immunoreactivity within the guinea pig hippocampus (1982)
    Springer
    Experimental brain research 48 (1982), S. 288-295 
    Details
    ISSN: 1432-1106
    Keywords: Enkephalin ; Immunocytochemistry ; Hippocampus ; Fascia dentata ; Guinea pig
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The distribution of enkephalin immunoreactive fibres has been studied in the hippocampus, subiculum and entorhinal cortex of the guinea pig. Two immunoreactive enkephalin fibre systems were found. One system corresponds to the mossy fibre system from the fascia dentata to CA3 and courses at the level of the mossy fibre end bulb in a longitudinal direction along the main axis of the hippocampus. Another system originates in the medial and lateral entorhinal cortex, traverses the subiculum, and then courses in the stratum molecu-lare/lacunosum to CA1 and CA3; part of these fibres crosses the hippocampal fissure and reaches the stratum moleculare of the fascia dentata. In the fascia dentata intense immunoreactivity was observed in the distal and middle one-third of the stratum moleculare at the side of the terminations of the lateral and medial perforant path fibres. Various types of immunoreactive cell bodies were found in the fascia dentata, CA3, CA1, subiculum and in the entorhinal cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00237225
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  • 6
    Electronic Resource
    Electronic Resource
    Differential conduction velocities in perforant path fibres in guinea pig (1981)
    Springer
    Experimental brain research 42 (1981), S. 231-233 
    Details
    ISSN: 1432-1106
    Keywords: Hippocampus ; Perforant path ; Limbic system ; Conduction velocities ; Dentate gyrus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Conduction velocities (c.vs) of different hippocampal fibre groups have been measured in slices in vitro. In the mossy fibres, Schaffer collaterals and Str. oriens fibres the c.v. varied from 0.36–0.38 m/s; in the alveus c.v. was 1.20 m/s. In the perforant path (p.p.) two groups of c.vs were found: in the medial p.p. the mean (± s.e) c.v. was 0.32 ± 0.02 m/s, whereas in the lateral p.p. it was 1.36 ± 0.14 m/s.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236913
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  • 7
    Electronic Resource
    Electronic Resource
    On the principles underlying the diagnosis of brain tumours — A survey article (1995)
    Springer
    Acta neurochirurgica 135 (1995), S. 1-11 
    Details
    ISSN: 0942-0940
    Keywords: Brain tumour ; brain oedema ; blood brain barrier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A survey is given of the principles underlying the diagnosis of brain tumours. Traditionally diagnosis and localization of brain tumours have been based upon morphological criteria. Currently unsurpassed levels in imaging of anatomical details and topographical relations by the techniques of computed tomography (CT) and magnetic resonance imaging (MRI) have been achieved. The techniques of positron emission tomography (PET) and of magnetic resonance spectroscopy (MRS), which depict also metabolic and blood flow aspects, provide a refinement of our knowledge on the metabolism, structure and pathophysiological relations of a tumour to the surrounding parenchyma. Recent advances in the recording of function-related changes of the cerebral electro-magnetic field allow a better definition of critical functional areas.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02307407
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  • 8
    Electronic Resource
    Electronic Resource
    Changes in local cerebral blood flow, local EEG, and flow in the distal stump of the middle cerebral artery in cats with occlusion of the middle cerebral artery (1982)
    Springer
    Acta neurochirurgica 61 (1982), S. 227-240 
    Details
    ISSN: 0942-0940
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The local EEG, the local cerebral blood flow (1CBF), and the flow in the distal stump of the occluded middle cerebral artery were simultaneously recorded in 28 acute experiments in cats. Nembutal anaesthesia was used eleven times, and Halothane anaesthesia 17 times. The recordings were made via platinum electrodes: 12 in the ischaemic hemisphere, and 2–3 in the opposite non-ischaemic hemisphere. The flow in the occluded middle cerebral artery was recorded via a platinum electrode introduced into this artery via the transorbital approach. The changes in 1EEG, 1CBF, and middle cerebral artery flow were studied during normotension, hypertension, and hypotension. A beneficial effect of hypertension was noted in the acute phase of brain ischaemia. Hypertension counteracted also the “diaschisis” in the non-ischaemic part of the ischaemic hemisphere and in the opposite non-ischaemic hemisphere. A correlation between 1EEG changes and 1CBF changes was noted. In addition an interesting discrepancy was observed between the rapid H2 clearance in the middle cerebral artery stump and the much slower H2 clearance in the ischaemic brain area. Significant differences between experiments under Halothane and experiments under Nembutal anaesthesia were noted. In the acute phase those changes are probably the result of the different levels of blood pressure in those two groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01740087
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  • 9
    Electronic Resource
    Electronic Resource
    Opposite Changes in GABAA Receptor Function in the CA1-3 Area and Fascia Dentata of Kindled Rat Hippocampus (1995)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 64 (1995), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Muscimol-stimulated radiotracer 36Cl− uptake in synaptoneurosomes was used to investigate the function of the GABAA receptor complex in the CA1-3 area and fascia dentata (granular and molecular layers and hilus) of rats kindled by stimulation, twice a day, of the Schaffer collateral fibers. Two kindled groups were studied: (a) 24 h after the last generalized tonic-clonic seizure [fully kindled (FK) stage] and (b) 28 days after the last generalized seizure (long-term stage). Synaptoneurosomes were prepared in parallel from subslices of the CA1-3 area and fascia dentata. In FK animals, the muscimol-stimulated 36Cl− uptake was significantly reduced by 21% in the CA1-3 area in comparison with nonstimulated controls, whereas a significant increase of 29% was found in the fascia dentata. Significant changes were no longer present at 4 weeks after the last generalized seizure. The observed changes in muscimol-stimulated 36Cl− uptake at the FK stage closely parallel the recently observed changes in [3H]muscimol binding in the CA1 area and fascia dentata. These results indicate that kindling causes a transiently decreased GABAA receptor-mediated function in the CA1-3, in contrast to an increased GABAA receptor-mediated function in the fascia dentata.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1995.64062615.x
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  • 10
    Electronic Resource
    Electronic Resource
    Presynaptic Mechanism of Action of 4-Aminopyridine: Changes in Intracellular Free Ca2+ Concentration and Its Relationship to B-50 (GAP-43) Phosphorylation (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 56 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Recently we have shown that 4-aminopyridine (4-AP), a drug known to enhance transmitter release, stimulates the phosphorylation of the protein kinase C substrate B-50 (GAP-43) in rat brain synaptosomes and that this effect is dependent on the presence of extracellular Ca2+. Hence, we were interested in the relationship between changes induced by 4-AP in the intracellular free Ca2+ concentration ([Ca2+]i) and B-50 phosphorylation in synaptosomes. 4-AP (100 μM) elevates the [Ca2+]i (as determined with fura-2) to approximately the same extent as depolarization with 30 mM K+ (from an initial resting level of 240 nM to ∼480 nM after treatment). However, the underlying mechanisms appear to be different: In the presence of 4-AP, depolarization with K+ still evoked an increase in [Ca2+]i, which was additive to the elevation caused by 4-AP. Several Ca2+ channel antagonists (CdCl2, LaCl3, and diphenylhydantoin) inhibited the increase in B-50 phosphorylation by 4-AP. It is interesting that the increase in [Ca2+]i and the increase in B-50 phosphorylation by 4-AP were attenuated by tetrodotoxin, a finding pointing to a possible involvement of Na+ channels in this action. These results suggest that 4-AP (indirectly) stimulates both Ca2+ influx and B-50 phosphorylation through voltage-dependent channels by a mechanism dependent on Na+ channel activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb03437.x
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