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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 63 (1986), S. 650-654 
    ISSN: 1432-1106
    Keywords: Mouse somatosensory system ; Barrel ; Mystacial vibrissae ; Sensory innervation density ; Brain evolution ; Cortical magnification factor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The whisker-to-barrel pathway of mice (an important component of the animal's somatosensory system) was studied in two experiments. In one, the cortical representation of a row of whiskers was caused to be larger by lesioning a neighbouring row of follicles, while the innervation density remained unchanged. In the second experiment mice, selectively bred for particular whisker and barrel patterns, showed for their supernumerary vibrissal follicles a relatively large cortical representation. On the basis of the second experiment we formulate a possible role of the sensory periphery in brain evolution.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1106
    Keywords: Barrel ; Barreloid ; Thalamus ; Somatosensory system ; Mouse ; Phaseolus vulgaris ; HRP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to elucidate the geometric organization of projections from the barrel cortex to the thalamus, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were made. The injections were confined to one barrel column (i.e. barrel in layer IV + cortical tissue above and below it). Axonal terminations could be demonstrated in three thalamic nuclei: reticularis (RT), ventrobasalis (VB) and posterior (PO). Anterograde terminal labelling was obtained in RT + VB; in PO only; or in RT + VB + PO. The terminals labelled in PO were much larger than those in RT and VB. The termination areas in RT, VB and PO were shaped like rods which have a rostro-caudal orientation. These cortico-thalamic projections are discretely and topographically organized. The clearest such arrangement was found in VB. Here, projections from the A row of barrels in BF terminate dorsally, whereas those from the C row end ventrally. Barrel A1 projects to the lateral part of VB, whereas A4, to more medial parts; other rows are arranged similarly. These results were compared with the distribution of thalamo-cortical projection neurons that were labelled after iontophoretic HRP injections in individual barrels. We concluded that the corticothalamic projections originating from one barrel column contact an arc of barreloids in VB.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Experimental brain research 73 (1988), S. 411-435 
    ISSN: 1432-1106
    Keywords: Barrel ; Mouse somatosensory system ; Phaseolus vulgaris-leucoagglutinin ; Cortical efferents ; Trigeminal nuclei
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In order to analyze the organization of the efferent projections of single barrel columns (BC, i.e. a barrel in layer IV of parietal cortex plus the cortical tissue above and below it), we made small iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin in the barrel cortex of 20 adult mice. On the basis of reconstructions of the sites of terminal labelling, the brain regions receiving projections from the barrel cortex could be identified and classified in five groups. Each group is characterized by the topography of the distribution of efferents arising from a single BC. The projections to the trigeminal sensory complex are point to point: i.e. one BC projects only to the site of termination of the primary sensory neurons innervating the corresponding whisker follicle. In the ventrobasal thalamic nucleus BC projections are not restricted to the corresponding barreloid; instead they contact parts of barreloids belonging to one arc. In the reticular and posterior thalamic nuclei the projections from a row of BC's converge to a collective termination site, whereas in the superior colliculus the projections from an arc of BC's converge to a common termination site. There is a complete overlap of BC projections in restricted zones within SII, motor cortex, perirhinal cortex, contralateral barrelfield, caudoputamen and pons. The organization of the efferents from the barrel cortex demonstrates a contrast between feedback and feedforward projections from this important area of neocortex.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-1106
    Keywords: Corticothalamic projection ; Somatosensory system ; Barrel ; Phaseolus vulgaris ; leucoagglutinin ; Electron microscopy ; Mouse ; Synaptic glomerulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary By means of tracing with the lectin Phaseolusvulgaris leucoagglutinin (PHA-L), we examined in the thalamus of the mouse, the axon terminals of fibers originating in the barrel cortex. Vibratome sections of the brain were subjected to PHA-L immunocytochemistry and processed for light and electron microscopy. We observed small (0.5–0.8 μm in diameter) varicosities of labeled fibers in the nucleus ventrobasalis (VB) and the nucleus posterior (PO) as well as labeled giant terminals (3–5 μm in diameter) in PO. The analysis involved examination of serial sections and computer-aided reconstruction of several terminals. The small varicosities in VB appear to be small axon terminals forming distinct asymmetric synapses with small dendritic profiles. Some labeled terminals are apposed to, but not synaptically related with, the cell bodies of neurons in VB that are retrogradely labeled with PHA-L. The small varicosities seen with the light microscope in PO are terminals forming asymmetric synapses with dendritic shafts. The giant terminals in PO appear as large, vesicle-filled profiles forming part of synaptic glomeruli, i.e. complexes of one corticothalamic terminal engulfing several excrescences of a single dendrite. A giant terminal forms several asymmetric synapses (about 8) with these excrescences, as well as numerous (up to 15) puncta adhaerentia. The glomeruli are enveloped in glial lamellae, and they are often found at the bifurcations of primary dendritic segments. We suggest that the small terminals in VB are in the service of feedback signalling from the barrel cortex to its principal thalamic relay nucleus; the functional importance of this projection may reside in increased spatio-temporal discrimination. We interpret the giant terminals in PO as elements serving feed-forward processing, allowing the barrel cortex to influence, via PO, parts of the motor pathway modulating the animal's ongoing behavior.
    Type of Medium: Electronic Resource
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