Efferents from the lateral frontal cortex to spinomedullary target areas, trigeminal nuclei, and spinally projecting brainstem regions in the hedgehog tenrec

Cyto- and chemoarchitectural findings have recently suggested that in the hedgehog tenrec, the claustrum is not located below but between the layers of the rhinal/insular cortex (Künzle and Radtke-Schuller 2000b). The present connectional study confirms this unusual position. Tracer injections were made into various isocortical and allocortical regions. They showed that the tenrec's dorsal claustrum was reciprocally and bilaterally connected with the neocortex. The ventral claustrum was connected with mainly the ipsilateral paleocortex, additionally with the ventromedial frontal cortex and possibly the subiculum. A sparsely labeled cell group separated the claustrum from the labeled cells located in the depth of the RCx and the adjacent paleo- and neocortices. On the basis of the linear arrangement of these latter cells immediately adjacent to the subcortical white matter, and the restriction of their labeling to the ipsilateral side, one might interpret preliminarily these cells as layer 6B cells or persisting subplate neurons. Their cortical projections showed a similar topographic organization as the claustro-cortical projections. The unusual features described in tenrec were discussed with respect to similar organizations in other mammals with poorly differentiated brains and compared with embryonic brains of mammals with more differentiated brains.

Section: Introductionsupporting

confidence: 86%

“…The tracer injections into the cortex were made at a depth of usually 0.5 to 0.7 mm; in the cases injected with tracer into the medial wall of the hemisphere or the hippocampus the needle was inserted up to 3.0 mm. The cases (Table 1) were reported previously with regard to subcortical connections (Künzle 1995b;Künzle and Lotter 1996).…”

Section: Methodsmentioning

confidence: 99%

Cortical connections of the claustrum and subjacent cell groups in the hedgehog tenrec

Künzle¹,

Radtke‐Schuller²

2001

“…Area 4 in the cat (Hassler and Muhs-Clement 1964) as well as the area praecentralis 1 in the rabbit (Swadlow 1994) were shown to represent motor cortex or part of it. Area A 1 is known to project to the high cervical spinal cord (Künzle and Rehkämper 1992) and the superior colliculus (Künzle 1995;Künzle and Lotter 1996); in addition, it is highly responsive to visual stimulation (Krubitzer et al 1997). Thus, the question of to what extent the tenrec's area A 1 is comparable to the agranular cortex in cat and rabbit cannot yet be answered.…”

Section: Area-specific Aspects Of Dendrite Bundlingmentioning

confidence: 99%

On the presence of dendrite bundles in the cerebral cortex of the Madagascan lesser hedgehog tenrec and the red-eared pond turtle

Schmolke¹,

Künzle

1997

In mammals with a well-differentiated neocortex apical dendrites of pyramidal cells form vertical bundles. Little is known about the presence of dendrite bundles in animals with a poorly differentiated cortex. In this paper the presence of dendrite bundles has been investigated in the lesser hedgehog tenrec, Echinops telfairi, a basal insectivore with a very low degree of neocorticalization. In a further step the arrangement of dendrites has been analyzed in the cerebral cortex of the red-eared pond turtle, Pseudemys scripta elegans. Among non-mammalian vertebrates, reptiles have a cerebral cortex that is relatively most comparable with the mammalian one, and the cerebral cortex of turtles shows more structural and functional similarities with the cortex in mammals than those of other reptiles. In the hedgehog tenrec, bundles of apical dendrites are found in all neo-cortical areas, the cingulate and retrosplenial cortices. The shape and arrangement of dendrite bundles are primarily determined by apical dendrites of lamina V pyramids. Apical dendrites originating in laminae III/IV or VI join these bundles, and do not give rise to separate sets of bundles in the supra- and infragranular layers as in other mammals. Center to center distances between bundles determined in the neocortical areas A(2-4) range from 7 to 76 microm, with an average of 32 microm. Area-specific differences are found concerning the length of bundles as well as the number, caliber, branching pattern and packing density of dendrites sharing an individual bundle. In the three-layered entorhinal cortex and the hippocampus dendrite bundles are not observed. In the turtle, no vertical bundles of dendrites are seen either in the medial, dorsomedial or medial part of the dorsal cortex. Only in the lateral part of the dorsal cortex are isolated bundles of apical dendrites originating from groups of perikarya situated below the main level of lamina II detected. Our findings suggest that the presence of dendrite bundles is closely related with the multilayered nature of the mammalian neocortex.

“…Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP; Sigma; n=14) and biotinylated dextran amine (BDA, Sigma; n=5) were injected into the neocortex at different locations (Table 1; the letters W and B following the case numbers were used to indicate the tracer injected, WGA-HRP and BDA, respectively). Among these cases 14 animals have been described previously with regard to its claustral and/or subcortical connections (Künzle 1995;Künzle and Lotter 1996;Künzle and Radtke-Schuller 2001a;Künzle et al 2002). The WGA-HRP (1.5-20 nl of a 2-7% solution in distilled water) was pressure injected through a glass micropipette (tip diameter 8-15 m) attached to a Hamilton syringe driven by a micromanipulator.…”

Section: Methodsmentioning

confidence: 99%

“…Furthermore, the labeling in the PCxV, unlike PCxI, is not restricted to Et 99-25W. The additional tracer injections resulting in labeling of PCxV involved the medial and the lateral frontal cortex at the levels of zone 2 in particular, representing the tenrec's somatosensorimotor cortex (Künzle and Lotter 1996;Krubitzer et al 1997).…”

Section: Additional Allocortical Regions Projecting To the Neocortexmentioning

confidence: 99%

Neocortical connections with perihippocampal and periamygdalar regions in the hedgehog tenrec

Künzle

2003

The perihippocampal fields represent the most important regions connecting the neocortex and the hippocampus in rat, cat and monkey but little is known about their presence and connectivity in species with poorly differentiated brain. Using axonal tracer substances we have recently studied the distribution of cortical cells projecting to the hippocampus in the hedgehog tenrec. In the present study we determined the regions of the paleocortex and the rhinal cortex connected with the neocortex, and provide a tentative view of the site and the extent of the tenrec's entorhinal, perirhinal and postrhinal/parahippocampal fields. It is shown that only the dorsal portions of the posterior rhinal cortex may be considered equivalent to the perirhinal and postrhinal fields of higher mammals, while a considerable expanse of the ventral rhinal cortex may be part of the entorhinal area (its so-called dorsal portion) connected with both the dentate gyrus and the neocortex. A few cells projecting to the neocortex were also noted in the dorsal-most portion of the three-layered paleocortex (ventral entorhinal portion). These cells were linearly arranged and reminiscent of the neocortical projecting cells in the entorhinal layer 4/5 in more differentiated mammals. The main portion of the paleocortex caudal to the corpus callosum remained unlabeled following neocortical and hippocampal tracer injections. Unexpectedly, the area in the most ventral paleocortex adjacent to the amygdala also projected to the neocortex, particularly the tenrec's somatosensorimotor cortex.