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L Kruger

Publications and source records attributed to L Kruger.

At least 73 records · Page 4Linked to original sources
PubMed1980

An axonal transport study of the ascending projection of medial lemniscal neurons in the rat.

The pattern of projection of the rat medial lemniscus was studied by axonal transport labeling following injections of tritiated leucine, proline and/or adenosine, or of horseradish peroxidase for retrograde identification of the neurons of origin. The vast majority of neurons in the gracile, cuneate, and principal trigeminal nuclei contribute to an almost totally crossed projection primarily to the thalamic ventrobasal complex. Additional thalamic components were traced to specific sites within the "posterior group," including a medial component largely traversed by lemniscal axons and a caudolateral component lying between the principal nucleus of the medial geniculate and ventral nucleus of the lateral geniculate. We have designated this latter zone "intermediate geniculate," distinguishing a somatosensory portion of the geniculate group on the basis of its myelo- and cytoarchitecture, as well as its connections. Other projections replicated in several animals included the zona incerta and nearby sectors of the substantia nigra; three distinct mesencephalic arrangements within the deep layers of the superior colliculus, the external nucleus of the inferior colliculus, and the intercollicular nucleus; the anterior pretectal nucleus; dorsal sectors of the inferior olivary complex and the ipsilateral cerebellar cortex. The results are compared with findings in other species (with emphasis on the caudal thalamic region) in an attempt to resolve some of the apparent inconsistencies in nomenclature.

Afferent Pathways↗
PubMed1979

The organization of projections to selected points of somatosensory cortex from the cat ventrobasal complex.

The organization of neurons in the cat ventrobasal complex (VB) which project to somatosensory cortex (SI) was investigated by the use of the retrograde transport of the enzyme horseradish peroxidase (HRP). Two histochemical procedures were used to visualize retrogradely transported HRP. Injections of HRP in electrophysiologically characterized points of SI cortex labeled distinctive zones of neurons in VB ipsilateral to the injections. Injections placed in the forelimb or hindlimb cortical areas labeled laminar-like aggregates of neurons have long axis corresponded to the long axis of VB. Injections of the SI trigeminal representation resulted in very compact aggregates of HRP positive neurons which were less clearly laminar. The density of projection from VB to various portions of SI paralleled the general innervation density of the peripheral skin. Injections of the cortical vibrissal, face and forepaw representations labeled a greater number of neurons in VB per unit area of cortex injected than did injections of the hindpaw or trunk representations. For a given somatotopic area, the number of labeled neurons in VB increased linearly as the area of the cortical HRP injection increased. Differences in the sensitivity of each histochemical procedure and the relationship of differing sensitivities to the observed results are also discussed.

Animals↗
PubMed1979

Tactile neurons of the superior colliculus of the cat: input and physiological properties.

Neurons in the strata intermediale and profundum of the cat superior colliculus (SC) previously have been shown to be organized somatotopically and to respond to tactile stimuli. The stimulus properties required for neuronal activation suggest that these neurons are excited by inputs from selected classes of high-velocity, sensitive cutaneous mechanoreceptors, and that stimulus-response relationships indicate only a narrow range of information concerning stimulus magnitude. The properties of these neurons have been interpreted as serving a role in stimulus detection that recovers slowly and may be best suited for directed attention and orientation behavior. The input to the SC was studied by injection of horseradish peroxidase (HRP) for retrograde labeling of neurons projecting to this region. The main inputs subserving the tactile pathway are the principal trigeminal nucleus and the rostral portion of the spinal V subnucleus oralis and the main cuneate nucleus. Sparser labeling was found in other somatic relays, including the gracile and lateral cervical nuclei and posterior portion of the spinal trigeminal complex. Several other projections relating to visual mechanisms are also described.

Animals↗
PubMed1979

Membrane specializations and cytoplasmic channels of Schwann cells in mammalian peripheral nerve as seen in freeze-fracture replicas.

Mammalian Schwann cells in rat, rabbit and human fetal nerves were studied using several cryoprotective agents for electron microscopic study of freeze-fracture replicas. The findings in fixed and unfixed tissue reveal surface plasmalemma caveolar specializations and the outer layer membrane junctional complexes found in non-mammalian species. The plasmalemma also reveals a complex arrangement of contours outlining cytoplasmic channel networks distinct from the long-recognized Schmidt-Lanterman incisures and paranodal cytoplasmic loops. A specialized interconnected channel system in the outer "loose" myelin layer displays relatively uniform dimensions comparable in diameter to nodal microvilli, paranodal loops and some incisures. An adaxonal tubular channel system constituting the "axon-Schwann network" is found in the internodal region in addition to other variants of the adaxonal Schwann plasmalemma. The several forms of sequestration of Schwann cell cytoplasm presumably underlie the specialized needs of cytoplasmic continuity in a dynamic functional entity in which large domains of cytoplasm have been displaced by the formation of compact myelin.

Animals↗
PubMed1976

Relationship between visual and tactile representations in cat superior colliculus.

A stratified organization of visual, somatic and acoustic representations was observed in the cat SC. Cells of the superficial laminae were exclusively visual. Visual, somatic, and acoustic cells were observed in the intermediate laminae while the deeper laminae were predominantly nonvisual. A detailed examination of the tactile representation revealed a somatotopic plan which was in register with the overlying visuotopy. The magnified representation of central visual fields overlapped the magnified tactile representation of the face and, as visual RFS moved temporally, the underlying tactile RFS were displaced caudal and distal. This topographical overlap can be recognized if the visual field is depicted as a flexible sheet which is stretched over the body with the area centralis superimposed on the nose and the limbs radiating out at an acute angle. The overlapping topographies and similarities in stimulus specificity of somatic and visual cells, as well as the similar behavioral deficits previously described following SC lesions, suggests a functional parallel between modalities in the SC. The possibility that visual, somatic, and acoustic cells converge on a common delivery or distribution system, which is located in the intermediate-deeper SC strata and organizes orienting and following responses on the basis of multimodality cues, is discussed.

Acoustic Stimulation↗
PubMed1975

Superior colliculus: visuotopic-somatotopic overlap.

A laminar organization was present in the superior colliculus of the cat, with upper layer cells exclusively visual, lower layer cells primarily somatic (or acoustic), and intermediate layers showing significant modality overlap. The close topographic correspondence between the visual and somatic representations observed within this laminar pattern and the similarities in visual and somatic response specificity may be consistent with the hypothesis that the colliculus combines several sensory modalities to facilitate tracking of a given stimulus.

Animals↗