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  • 1
    Electronic Resource
    Electronic Resource
    Induction of high frequency activity in the somatosensory thalamus of rats in vivo results in long-term potentiation of responses in SI cortex (1992)
    Springer
    Experimental brain research 90 (1992), S. 253-261 
    Details
    ISSN: 1432-1106
    Keywords: Long-term potentiation (LTP) ; Ventral posterior medial ; Thalamus ; Somatosensory cortex ; Bicuculline ; in vivo
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Extracellular single-unit techniques were employed to record unitary activity simultaneously from the thalamic ventral posterior medial (VPM) nucleus and the ipsilateral primary somatosensory cortex of adult rats. Cross-correlation analysis triggered by the spontaneous firing of thalamocortical relay neurons in VPM and the discharge of layer IV neurons in the corresponding ipsilateral cortical barrel indicated that the paired-units included in this study were strongly correlated in their activity. The baseline responses of highly correlated cortical/thalamic pairs to a 10 ms deflection of a vibrissa on the contralateral side were measured using poststimulus time histograms. After establishing the baseline response, high frequency activity in VPM was induced in one of two ways: i) direct electrical stimulation of thalamic neurons or ii) whisker stimulation in the presence of bicuculline methiodide (BIC) released near the thalamic neurons. Both methods resulted in a conditioning stimulus (CS) paradigm consisting of “bursts” of high-frequency activity (50–100 Hz) with an inter-burst interval of 150 ms (∼7 Hz). Almost immediately following the presentation of the CS, the response of layer IV cortical neurons to vibrissa stimulation increased by 37–62% over baseline values, which was maintained after the effects of BIC had worn off in VPM. This enhancement in the response of the cortical neurons was not accompanied by a concomitant increase in the thalamic responses. Thus, these results strongly suggest that the potentiation first occurred at the thalamocortical synapse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00227236
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  • 2
    Electronic Resource
    Electronic Resource
    Laminar organization of efferent cells in the parietal cortex of the Virginia opossum (1981)
    Springer
    Experimental brain research 43 (1981), S. 330-336 
    Details
    ISSN: 1432-1106
    Keywords: Axoplasmic transport ; Neocortex ; Opossum ; Parietal cortex
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The size, shape and laminar position of efferent neurons in the parietal cortex of the Virginia opossum were identified using the method of retrograde transport of horseradish peroxidase (HRP). Injection of HRP into the spinal cord, dorsal column nuclei or pontine nuclei leads to labeling of cells in layer V and occasionally in layer VI, while a large injection of HRP in the dorsal thalamus labels many cells in layer VI, with fewer cells in layer V. HRP injections in the SSM cortex label cells in layers II-VI of ipsilateral and contralateral cortical areas. However, the majority of these cortico-cortical cells are found in the supragranular layers. Examination of the size, shape and laminar position of retrogradely labeled layer V neurons after injections in each of these areas suggests that none of these features can be used to predict accurately the projection target of individual neurons. We conclude that the laminar organization of efferent cells of the opossum parietal cortex is very similar to that seen in the neocortex of other mammals, despite the complete coalescence of somatic sensory (SI) and motor (MI) areas in the opossum.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00238375
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of thiamine deficiency on the structure and physiology of the rat forebrain (1988)
    Springer
    Metabolic brain disease 3 (1988), S. 91-124 
    Details
    ISSN: 1573-7365
    Keywords: thiamine deficiency ; thalamic intralaminar nuclei ; neocortex ; synchronous burst spontaneous activity ; excitotoxic brain lesions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Dietary thiamine deficiency, enhanced by pyrithiamine administration in adult rats, produces overt lesions in the brain that are especially prominent in the thalamus. The present study was undertaken to determine whether the thalamic lesions could be correlated with alterations in the physiological properties of neurons in the thalamus and somatosensory cortex. The regimen for experimentally inducing thiamine deficiency produced large lesions in the thalamus of every case; the lesions included most, if not all, of the neurons in the intralaminar thalamic nuclei. The extent of the lesion in the intralaminar thalamus was highly correlated with the loss of bilaterally synchronous spontaneous activity in the cerebral cortex. This correlation was seen in animals analyzed as early as 1–18 hr after the appearance of opisthotonus, the crisis state of thiamine deficiency, and as late as 2–9 weeks of recovery following thiamine replacement therapy. The loss of bilateral synchronous bursting neuronal activity following intralaminar thalamic lesions is consistent with the proposed role of the intralaminar thalamus as a pacemaker for rhythmic cortical activity (Armstrong-Jameset al.,Exp. Brain Res., 1985; Fox and Armstrong-James,Exp. Brain Res. 63: 505–518, 1986). The location and size of the central lesions within the thalamus suggest that the observed neuronal loss could result from a nonhemorrhagic infarction in the ventromedial branches of the superior cerebellar arteries. Experimental thiamine deficiency also produced alterations in the receptive field properties of the somatosensory cortex neurons in all animals examined. Changes in cortical receptive field properties were correlated with the destruction of sensory relay neurons in the thalamic ventrobasal complex. The loss of the central lateral thalamic input to the cortex and the loss of somatosensory relay neurons in the ventrobasal thalamus in experimental thiamine deficiency produce alterations in cortical function which may contribute to deficits in memory and cognition analogous to those which characterize Korsakoff's psychosis in humans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01001012
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  • 4
    Electronic Resource
    Electronic Resource
    The synaptic architecture of neurons in opossum somatic sensory-motor cortex: A combined anatomical and physiological study (1978)
    Springer
    Journal of neurocytology 7 (1978), S. 39-60 
    Details
    ISSN: 1573-7381
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Neurons in opossum somatic sensory-motor (SSM) cortex were studied to define some features of their normal ultrastructure and to identify the morphology and location of cortical cells that can be activated at short latencies by peripheral stimulation. Pyramidal neurons are characterized by rather triangular perikarya containing a relatively low density of cytoplasmic organelles and receiving few synaptic contacts on their somata and proximal dendrites. Synaptic contacts in this location are always of the ‘flat-symmetrical’ variety. The dendrites of pyramidal cells are densely laden with spines, and most of these postsynaptic elements receive ‘round-asymmetrical’ contacts. Some non-pyramidal neurons with beaded dendrites contain a high density of cytoplasmic organelles and receive both types of synaptic contact on their cell bodies. The dendrites of these neurons rarely bear spines. Many cortical neurons have electron-opaque satellite cells in close apposition to their perikaryal plasmalemma. Thus, the constituent neurons follow the same general rules of synaptic organization as equivalent cells in other mammals. To study these neurons, a technique was developed for the intracellular injection of Procion brown and horseradish peroxidase, because these substances are visible in both the light and electron microscope. Procion brown injection into single cortical neurons produces a vigorous response from a small number of glial cells that leads to partial phagocytosis in only a few hours after the injection. This response was not seen following HRP injections, and HRP-filled neurons could be studied at both the light and EM levels. Serial reconstruction of the cell body region of four pyramidal neurons showed that they received an average of 48 flat-symmetrical contacts per cell. Cells responding with a short latency to peripheral stimulation were all located in layer III of SSM cortex. We conclude that the basal dendrites of layer III pyramidal cells form one target of thalamic fibres in this cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01213459
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