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  • 1
    ISSN: 1432-1106
    Keywords: β-galactosidase ; Striatal grafts ; Basal ganglia ; Gene expression ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A retrovirus which encodes β-galactosidase was used to infect embryonic rat striatal cells before grafting these cells into the lesioned adult rat striatum. Examination of the grafts after long term survival (8 months) revealed that a few small and large cells expressed large amounts of bacterial β-galactosidase activity. The larger diameter cells were identified as neurones by their size, shape and presence of neuronal processes. The identity of the small diameter cell types was not established.
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  • 2
    ISSN: 1432-1106
    Keywords: Striatal spiny neurons ; Nigro-striatal fibers ; Striatal PSP's corpus striatum ; Substantia nigra stimulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Responses of striatal neurons to stimulation in substantia nigra were recorded intracellularly in intact rats and after acute or chronic unilateral lesions of cerebral cortex or after combined cortical lesions and unilateral thalamic transections. Spiny striatal efferent neurons were identified by intracellular injection of horseradish peroxidase. In intact animals substantia nigra stimulation evoked a complex response with both excitatory and inhibitory phases. Acute unilateral decortication abolished the inhibitory phase of the response and reduced the amplitude of the initial EPSP. Thus, part of the excitatory phase and most or all of the inhibitory phase of the response result from polysynaptic routes to striatum involving cerebral cortex. The remaining EPSP observed in acute decorticate animals exhibited two components distinguished on the basis of their time courses. The latter of these was abolished by thalamic transections. The earlier component was shown to be a monosynaptic EPSP evoked by axon collaterals of cortical efferent neurons projecting to brainstem and was not observed in animals subjected to chronic decortication. After removal of all of these non-nigral response components a small long latency EPSP could be evoked by nigral stimulation. This EPSP is probably due to activation of dopaminergic nigro-striatal axons.
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  • 3
    ISSN: 1432-1106
    Keywords: Long-lasting neostriatal inhibition ; Neostriatal spiny neuron ; Basal ganglia ; Disfacilitation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Excitatory postsynaptic potentials evoked in rat neostriatal spiny projections neurons were followed by a long (100–300 ms) period of membrane hyperpolarization, followed in turn by a late depolarization. Concomitant with these changes in membrane potential were inhibition and subsequent excitation of spontaneous firing and excitatory activity evoked from substantia nigra and cerebral peduncle, but not from cortical stimulating sites. Thalamic-evoked excitatory activity was sometimes sensitive and sometimes insensitive to this inhibition, which has previously been believed to result from intrinsic inhibitory synaptic activity among neostriatal neurons. In intracellular recordings from neostriatal neurons in urethane anesthetized rats this longlasting inhibitory response (1) exhibited alterations with intracellularly applied steady currents comparable to those of the EPSP, (2) failed to respond to intracellular injection of chloride ions, (3) was associated with either a decrease or no detectable change in the input conductance of the neurons, and (4) was abolished after lesions that interrupted polysynaptic pathways to neostriatum through intracortical and intrathalamic synaptic circuits. These findings indicate that the long lasting inhibitory portion of the responses of neostriatal neurons arises from a phasic inhibition of tonically active corticostriatal and thalamostriatal neurons and a concurrent decrease in the excitability of polysynaptic pathways converging on neostriatal neurons.
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  • 4
    ISSN: 1432-1106
    Keywords: PT cells ; Pyramidal tract fibers ; Recurrent IPSPs ; SDPs ; Corticostriatal neurons
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Responses evoked in neurons of rat sensorimotor cortex upon stimulation of the pyramidal tract and ipsilateral cerebral peduncle were analysed using intracellular recording. Neurons responding antidromically to pyramidal tract stimulation (PT cells) and neurons failing to respond anti-dromically but exhibiting orthodromic responses were both stained by intracellular injection of horse-radish peroxidase (HRP). Layer V pyramidal neurons, including those responding antidromically, exhibited prominent long lasting membrane hyperpolarizations and inhibitions of action potentials following pyramidal tract or cerebral peduncle stimulation. Upon passage of polarizing intracellular current two components were identified within the hyperpolarizing potential. A short duration initial component readily reversed with hyperpolarizing current. Frequently this earlier component over-lapped a period of early excitation consisting of action potentials arising from recurrent EPSPs or large slow depolarizing potentials (SDPs). The second, much longer duration hyperpolarizing component did not reverse with passage of hyperpolarizing current and was often followed by a rebound period of depolarization and action potential generation. Both the excitatory and the inhibitory portions of these responses could be demonstrated in animals with acute thalamic transections severing the ascending lemniscal pathway to cortex. Following intracellular staining with HRP, two types of PT cells were identified by their different intracortical axonal arborizations. Most of the injected neurons had local axonal fields extending widely in layers V and VI, but with few or no collaterals extending radially toward the more superficial layers. A second type of PT cell had axon collaterals limited to a narrow zone around the dendritic field but extending radially as far as layer I. Cells of both types were observed to send axon collaterals into neostriatum. Both types of neurons exhibited morphological and physiological characteristics of slow PT cells, and we could find no cells comparable to the fast conducting PT cells observed in other species.
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  • 5
    ISSN: 1432-1106
    Keywords: Substantia nigra ; 5-OHDA ; Dendro-dendritic synapses ; Self-inhibition ; Monoamine storage sites
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Intraventricular administration of 1 or 2 mg of the osmiophilic “false transmitter” 5-hydroxydopamine (5-OHDA) was used to label monoamine storage and release sites in the rat substantia nigra. Vesicles containing unusually dense cores indicative of the presence of the marker were seen forming from the Golgi apparatus in the cell bodies of medium-sized neurons of the substantia nigra, pars compacta, and from smooth endoplasmic reticulum in the dendrites of those neurons and in small unmyelinated axons of unknown origin. In serial sections, both axons and dendrites containing synaptic vesicles marked with 5-OHDA were seen to form synapses “en passage” in pars compacta, and some presynaptic dendrites containing vesicles filled by the marker were also observed to form contacts with dendrites in pars reticulata. The only identified postsynaptic elements engaging in monoaminergic synapses in the substantia nigra were dendrites of medium-sized pars compacta neurons.
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  • 6
    ISSN: 1432-1106
    Keywords: Thalamostriatal pathway ; Neostriatum ; Basal ganglia ; Neostriatal spiny neuron ; Thalamostriatal EPSPs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Stimulation of thalamic intralaminar nuclei or structures along the intrathalamic trajectory of thalamostriatal axons evoked complex EPSPs and subsequent hyperpolarizations in rat neostriatal spiny neurons identified by intracellular injection of horseradish peroxidase and/or antidromic activation from substantia nigra. In intact urethane-anesthetized rats, the initial EPSP portion of the response consisted of several components and lasted up to 75 ms. Short (1–10 ms) latency components exhibiting latency variations suggestive of a polysynaptic origin were often observed, and sometimes were the earliest components of the response. However, individual components of the excitatory response could not be clearly distinguished in most neurons and the earliest excitatory component usually appeared to be monosynaptic. After large acute aspiration lesions of ipsilateral cerebral cortex, the early polysynaptic EPSP components of thalamic-evoked EPSPs were absent or greatly attenuated. This suggested that most or all of the short latency polysynaptic EPSP components arose via a thalamo-cortico-striatal route. A short latency (1.6–4.0 ms) monosynaptic EPSP and a second excitatory component with a longer and more variable latency (8–28 ms) remained intact after acute decortication. These were not dependent upon intact corticothalamic or corticostriatal axons, since they were both still present in experiments performed as long as 4 days following ipsilateral hemidecortication. The longer latency excitatory response was shown to be polysynaptic by its latency variation with changes in stimulus intensity and frequency. This component of the response was abolished after acute thalamic hemitransections separating thalamostriatal neurons from their axons. In these experiments, stimulation of thalamostriatal axons rostral to the transection continued to evoke monosynaptic EPSPs in neostriatal spiny neurons. These EPSPs ranged from 1.8 to 3.0 ms in latency, had peak amplitudes up to 11 mV and were 20–37 ms in duration.
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 385 (1997), S. 306-307 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Dade and Huppert1 present a model for emplacement of the Taupo ignimbrite (New Zealand) from a turbulent dilute pyroclastic current (0.3% solids by volume). This model contrasts sharply with that of a concentrated current (tens of per cent solids by volume) previously proposed by me2 to explain ...
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  • 8
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The central Taupo Volcanic Zone (TVZ; Fig. 1) is the most productive Quaternary rhyolitic volcanic system on Earth. At least 34 voluminous ignimbrites (30-1,000 km3 bulk volume) have been erupted from eight caldera volcanoes"'12 in central TVZ since 1.6Myr. Several of the New Zealand ignimbrites ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 286 (1980), S. 912-912 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] WALKER ET AL. REPLY-We accept without reservation the relationships described by Fisher and others from the Lesser Antilles. We have long believed in the concept that pyroclastic flows sensu stricto and pyroclastic surges have fundamentally different transport mechanisms. What is in question, ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 283 (1980), S. 286-287 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The young age of the Taupo and Rabaul ignimbrites, and their occurrence in humid areas where a luxuriant vegetation anchors and protects pyroclastic deposits very soon after they have formed, has resulted in their remarkably good structural preservation. These ignimbrites shown new features which ...
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