Polarized tip-enhanced Raman spectroscopy at liquid He temperature in ultrahigh vacuum using an off-axis parabolic mirror.

Tip-enhanced Raman spectroscopy (TERS) combines inelastic light scattering well below the diffraction limit down to the nanometer range and scanning probe microscopy and, possibly, spectroscopy. In this way, topographic and spectroscopic as well as single- and two-particle information may simultaneously be collected. While single molecules can now be studied successfully, bulk solids are still not meaningfully accessible. It is the purpose of the work presented here to outline approaches toward this objective. We describe a home-built, liquid helium cooled, ultrahigh vacuum TERS. The setup is based on a scanning tunneling microscope and, as an innovation, an off-axis parabolic mirror having a high numerical aperture of ∼0.85 and a large working distance. The system is equipped with a fast load-lock chamber, a chamber for the in situ preparation of tips, substrates, and samples, and a TERS chamber. Base pressure and temperature in the TERS chamber were ∼3 × 10-11 mbar and 15 K, respectively. Polarization dependent tip-enhanced Raman spectra of the vibration modes of carbon nanotubes were successfully acquired at cryogenic temperature. The new features described here including very low pressure and temperature and the external access to the light polarizations, thus the selection rules, may pave the way toward the investigation of bulk and surface materials.

Accessory muscle in the hypothenar region: a functional approach.

An accessory muscle was found in the hypothenar region on both hands during routine cadaver dissection. This muscle originated from the tendon of the flexor carpi radialis, crossed the palma manus region superficially and inserted together with the abductor digiti minimi muscle into the ulnar aspect of the basis of the fifth proximal phalanx. The muscle was supplied by one branch arising from the main trunk of the ulnar nerve. Abnormalities of the hypothenar muscles have been described by many authors with a focus on their structural aspects, but there is not enough data about the possible functions they could induce. In our study, we try to elucidate the functions of this accessory muscle. We did not name the variant muscle as it has various functions, each similar to that of individual hypothenar muscles.

Expression of axonin-1 in developing amacrine cells in the chick retina.

This study focused on the temporal and spatial pattern of expression of the cell adhesion molecule axonin-1 in amacrine cells and the identification of these cells in the developing chick retina. We analyzed 5-20-day-old chick embryos. The antigen was localized and visualized by the indirect immunogold and the immunofluorescence technique. Colocalization studies with antibodies against tyrosine hydroxylase, acetylcholinesterase, choline acetyltransferase, parvalbumin, calbindin, and calretinin served to characterize these cells further and to explore whether they have other properties in common. Axonin-1 was expressed in amacrine cells from E8 onward in the inner nuclear, in the inner plexiform, and in the ganglion cell layer. Their maturation showed a gradient similar to that found for amacrinogenesis. Expression was closely correlated with the period when the cells develop and shape their processes. The interneurons were classified with reference to Cajal, and most of the morphological types described by him were found. In addition, some cells were considered as axon-bearing amacrine cells. However, the total number of labeled cells was rather small. At least two morphologically different types terminated in each of the inner plexiform sublayers. Narrow- and wide-field arbors indicated the existence of a diversified network. The colocalization studies revealed that the neurotransmitters and neuropeptides overlapped partially with axonin-1 expression. This indicated that axonin-1-immunoreactive amacrine cells were also functionally diverse.

Gross anatomy in the surgical curriculum in Switzerland: improved cadaver preservation, anatomical models, and course development.

The invention of new techniques for surgery and interventional radiology demand improved training for ongoing specialists. The Anatomical Institutes in Switzerland support these requirements by establishing hands-on practical training courses by using new procedures for cadaver embalming and model construction. Improvements allow courses to provide students with more realistic simulations of both established and experimental surgical methods. Through these changes, the value of in-depth gross anatomy is enhanced as a topic of fundamental importance for the postgraduate medical and surgical curriculum. The web site http://www.unifr.ch/sgahe/snga.html contains information on courses using the Thiel embalming solution. Details about training courses in Switzerland using anatomical models are available at http://www.heartlab.org, http://www.vascular-international.org, and http://www.elastrat.com.

The course of later generated axons in the developing optic nerve of the chick embryo. A morphometric electron microscopic study.

The topographic position of growth cones (GCs) shows the course of ingrowing axons within the optic nerve and allows to draw conclusions with respect to the fiber order in this pathway. Therefore, the topographic distribution and frequency of GCs as well as the proximal and distal axon shaft segments were studied within cross-sections of the distal, middle, and prechiasmatic part of the nerve of 3-8-day-old embryos using electron microscopy. The ingrowth of GCs was not confined to a particular region. Initially, GCs were found near the ventral periphery. With increasing age, simultaneous ingrowth occurred within an area that expanded dorsally. In parallel, GCs also occurred in dorsal regions and eventually in the dorsal periphery. GCs intermingled everywhere with more mature axon profiles. However, youngest profiles predominated ventrally, oldest dorsally. Hence, maturity increased from ventral to dorsal. This indicated that the time of arrival of axons and the topographic position in the cross-section correlated significantly. It is concluded that axons are chronotopically organized, but in a probabilistic sense. The predominant ingrowth of axons in the ventral part may be associated largely with the first wave of neurogenesis of retinal ganglion cells. The ingrowth in dorsal regions of the cross section may be related to later generated axons that enter the nerve following older axons of the same retinal sector as well as axons of neighboring ganglion cells which continue to leave the mitotic cycle while the front of neurogenesis has spread into the periphery.

Developmental expression of amphiphysin in the retinotectal system of the chick: from mRNA to protein.

The role of amphiphysin in clathrin-mediated endocytosis of synaptic vesicles is well established. However, it is still uncertain if the protein is also involved in developmental mechanisms, e.g. axon outgrowth and synapse formation. To investigate the developmental changes in the expression of amphiphysin we used the retinotectal system of the chick, a highly ordered and easily accessible primary neuronal pathway. Reverse transcription polymerase chain reaction (RT-PCR) of total RNA from chick retina and tectum revealed first transcripts for amphiphysin, dynamin and synaptotagmin at embryonic day 5 (E5) for both regions. Surprisingly, Western blots of the retina revealed an increase of protein expression for amphiphysin only after E11 in the retina and the tectum. Immunofluorescence for amphiphysin was not detectable before E10 in the developing chick retina, while other presynaptic proteins like synaptotagmin showed already intense signals in the inner and outer plexiform layers. Subsequently, amphiphysin immunoreactivity follows the expression of synaptotagmin and synaptic vesicle protein 2 (SV2) as seen in the retina and the tectum, and exhibits the same staining as the other proteins in the mature chick brain. Ultrastructural data revealed for the first time that amphiphysin is not only limited to conventional synapses but is also abundant in retinal ribbon terminals. Taken together our data reveal that: (i) there is a developmental delay between mRNA transcription and protein expression for key proteins involved in endocytosis; (ii) amphiphysin gets upregulated after synapse formation; and (iii) amphiphysin is present in the synaptic vesicle cycle in retinal ribbon synapses.

Expression of presynaptic proteins is closely correlated with the chronotopic pattern of axons in the retinotectal system of the chick.

Newly synthesized presynaptic integral membrane proteins in neurons are transported in precursor vesicles from the site of protein biosynthesis in the cell body by fast axonal flow to the presynaptic terminal. We followed the path that presynaptic proteins travel on the way to their central targets of the highly ordered primary visual pathway of the chick and analyzed the developmental changes in the expression of synaptic vesicle protein 2 (SV2), synaptotagmin, and syntaxin. Immunofluorescences revealed that: (1) the onset of protein expression in the retinal ganglion cells occurs in a central to peripheral developmental pattern from embryonic day 4 (E4) onward; (2) the proteins were found first in the inner and later in the outer plexiform layer of the retina; and (3) they were redistributed from the photoreceptor inner segments and cell bodies to the terminals in the outer plexiform layer. From E4 onward, immunopositive axons for SV2, synaptotagmin, and syntaxin were found in the optic nerve, disappearing after E9 for SV2 and synaptotagmin. The optic tract was stained for SV2 and synaptotagmin between E7 and E12, for syntaxin until the posthatching period. Finally, immunoreactivities for the investigated proteins were present at the surface of the tectum from E8 onward, when first retinal axons arrived there. The present study revealed that SV2 and synaptotagmin, but not syntaxin, are, expressed in a transient wave that follows the advancement of optic axons and the proteins towards the optic tectum.

Developmental expression of dynamin in the chick retinotectal system.

Dynamin I, a GTPase involved in the endocytic cycle of synaptic vesicle membranes, is believed to support axonal outgrowth and/or synaptogenesis. To explore the temporal and spatial patterns of dynamin I distribution in neuronal morphogenesis, we compared the developmental expression of dynamin with the expression of presynaptic membrane proteins such as SV2, synaptotagmin, and syntaxin in the chick primary visual pathway. Western blots of retina and tectum revealed a steady increase of synaptotagmin and syntaxin from embryonic Day 7 (E7) to E11, whereas for the same time frame no detectable increase of dynamin was found. Later stages showed increasing amounts of all tested proteins until the first postnatal week. Immunofluorescence revealed that SV2, synaptotagmin, and syntaxin are present in retinal ganglion cell axons from E4 on. In later stages, the staining pattern in the retina and along the visual pathway paralleled the formation and maturation of axons. In contrast, dynamin is not detectable by immunofluorescence in the developing retina and optic tectum before synapse formation. Our data indicate that, in contrast to the early expression of synaptotagmin, SV2, and syntaxin during axonal growth, dynamin is upregulated after synapse formation, suggesting its function predominantly during and after synaptogenesis but not in axonogenesis.(J Histochem Cytochem 47:1297-1306, 1999)

Extracellular matrix and development of lamination in the dorsal lateral geniculate nucleus in the tree shrew (Tupaia belangeri).

In the tree shrew (Tupaia belangeri), the cytoarchitectonic lamination of the lateral geniculate nucleus cannot be detected at birth; it only appears during the early postnatal period. However, a laminated pattern was revealed with rapid Golgi staining and retinal afferents were segregated into the appropriate laminae well before cytoarchitectonic lamination could be seen. Both observations indicate that the extracellular matrix may play a role in the separation of lateral geniculate nucleus cells into laminae. In the present study, the organization of the extracellular matrix was investigated during development using immunohistochemical and in situ hybridization techniques. For immunohistochemistry, peanut agglutinin (PNA) lectin and antibodies against tenascin (TN) were chosen, while for in situ hybridization, mTN riboprobes were used, simultaneously, with antibodies against Vimentin (Vim) and microtubule associated protein (MAP-2). The results showed that the pattern of PNA-binding glycoproteins and that of tenascin were relatively similar, although tenascin appeared later and disappeared earlier. The first interlaminar spaces to be detected were those between layers innervated by opposite eyes. The TN specific mRNA was detected in the lateral geniculate nucleus at P0, but was no longer visible at P7. By comparing TN mRNA and Vim or MAP-2 stainings a correspondence could be observed. The extracellular matrix lamination therefore seems to precede cytoarchitectonic lamination, suggesting that the extracellular matrix may play a role in the development of laminated structures. The TN-producing cells seem to be developing astrocytes and neurons.

The response of cat visual cortex to flicker stimuli of variable frequency.

We examined the possibility that neurons or groups of neurons along the retino-cortical transmission chain have properties of tuned oscillators: To this end, we studied the resonance properties of the retino-thalamo-cortical system of anaesthetized cats by entraining responses with flicker stimuli of variable frequency (2-50 Hz). Responses were assessed from multi-unit activity (MUA) and local field potentials (LFPs) with up to four spatially segregated electrodes placed in areas 17 and 18. MUA and LFP responses were closely related, units discharging with high preference during LFP negativity. About 300 ms after flicker onset, responses stabilized and exhibited a highly regular oscillatory patterning that was surprisingly similar at different recording sites due to precise stimulus locking. Fourier transforms of these steady state oscillations showed maximal power at the inducing frequency and consistently revealed additional peaks at harmonic frequencies. The frequency-dependent amplitude changes of the fundamental and harmonic response components suggest that the retino-cortical system is entrainable into steady state oscillations over a broad frequency range and exhibits preferences for distinct frequencies in the theta- or slow alpha-range, and in the beta- and gamma-band. Concomitant activation of the mesencephalic reticular formation increased the ability of cortical cells to follow high frequency stimulation, and enhanced dramatically the amplitude of first- and second-order harmonics in the gamma-frequency range between 30 and 50 Hz. Cross-correlations computed between responses recorded simultaneously from different sites revealed pronounced synchronicity due to precise stimulus locking. These results suggest that the retino-cortical system contains broadly tuned, strongly damped oscillators which altogether exhibit at least three ranges of preferred frequencies, the relative expression of the preferences depending on the central state. These properties agree with the characteristics of oscillatory responses evoked by non-temporally modulated stimuli, and they indicate that neuronal responses along the retino-cortical transmission chain can become synchronized with precision in the millisecond range not only by intrinsic interactions, but also by temporally structured stimuli.

[Infrapopliteal angioplasty: a forgotten region?]. / Infrapopliteale Angioplastie--die vergessene Region?

Although percutaneous transluminal angioplasty (PTA) has become established as an endovascular technique--in the more strict sense as a balloon dilatation but being increasingly supplemented by stent implantations--for many vascular regions, reports on infrapopliteal angioplasties are rather scarce. With the development of hydrophilically coated guide wires, improved catheter materials, and dedicated balloon catheters for infrapopliteal use, dilatation treatments distal of the popliteal artery are now standard procedures. Major advances in peri-interventional drug management have also made their contribution. The initial technical and clinical results obtained are excellent. For the majority of the patients, the main concern is for limb salvage. In this context, infrapopliteal PTA also achieves satisfactory results. However, the long-term results must still be considered as unsatisfactory since recurrences are frequent and require repeat interventions. Therefore new therapeutic strategies are required that can reduce re-stenoses especially in this peripheral vascular segment.

Classes of axons and their distribution in the optic nerve of the tree shrew (Tupaia belangeri).

BACKGROUND: It has been suggested that retinal ganglion cells (RGCs) of Tupaia can be subdivided into three classes that correspond to the X, Y, and W classes in the cat. Estimates of these classes as determined by electrophysiological experiments and by histological studies of the retina are at variance. Because the RGC classes differ in axon diameter, this parameter could serve as a reliable criterion for the evaluation of RGC classes and their proportions. METHODS: An electronmicroscopic analysis of four optic nerves was carried out. The density of axons and their diameters was recorded from cross sections in the middle of the nerves. Based on a theoretical model, axons were classified according to the three known RGC classes. In addition, we investigated how axons of different size are distributed within the nerve. RESULTS: On average, the total number of axons is 570,000. More than 99% of axons are myelinated. Axon diameters can be 0.2-3.6 microns, and fiber diameters can be 0.3-4.6 microns. The frequency distributions of axon and fiber diameter are positively skewed and multimodal. Our analysis revealed three distinct axon diameter groups with the following mean axon diameters and proportions: the small or S group: 0.55 micron, 70%; the medium-sized or M group: 0.88 micron, 20%; the large of L group: 1.39 microns, 10%. Density and axon diameter plots produced consistent patterns, according to which axons of different sizes were distributed in the optic nerve. Thick axons are located dorsotemporally and centrally in the nerve. The average diameter value decreases toward the periphery. The smallest values are found at the ventronasal border of the nerve. CONCLUSIONS: The observed axon diameter groups probably arise from functionally distinct RGC types. There is evidence that these groups correspond to functional W, X, and Y RGC classes. Our study also provides the first evidence of the existence of a topographic order of fibers within the nerve of the tree shrew.

[Combined intraoperative retrograde stent implantation and thrombendarterectomy of the carotid artery]. / Kombinierte intraoperative retrograde Stent-Implantation und Thrombendarteriektomie der Arteria carotis.

HISTORY AND CLINICAL FINDINGS: A 63-year-old man developed recurrent transitory ischaemic episodes of vertigo and weakness in the legs 6 weeks before admission. 3 weeks later he had a left amaurosis fugax. A stenotic murmur was heard over the left carotid artery. INVESTIGATION: Intraarterial digital subtraction angiography of the arteries to the head revealed occlusion of the right internal carotid artery (RICA) and marked narrowing at the origin of the left common carotid artery (LCCA), which could not be passed by catheter. TREATMENT AND COURSE: As a catheter could not be passed into the LCCA, a stent was at operation placed retrogradely into it. Intraoperative angiography showed subtotal stenosis of the left ICA, which was treated by thrombendarterectomy and dacron patch-plasty. The postoperative course was without complication and the patient was free of symptoms. Follow-up angiography was unremarkable. CONCLUSION: If a stenosis of the carotid artery cannot be passed by catheter, intraoperative retrograde placement of a stent is an alternative to percutaneous antegrade transluminal angioplasty or surgical bypass.

Differential expression of the mRNAs of the axonal glycoproteins axonin-1 and NgCAM in the developing chick retina.

Cell adhesion molecules expressed on the axonal membrane have been thought to be involved in the guidance of axons to their target area. In the chick, axonin-1 and NgCAM have been shown to promote, through reciprocal interactions, neurite outgrowth in vitro. We have recently shown that chick retinal ganglion cells (RGC) express both proteins as early as the axonal elongation begins. Their expression continues throughout the development of the retinotectal system synchronously with the chronotopic spread of axons. To further investigate the spatiotemporal distribution of axonin-1 and NgCAM in the retina, we have analysed the expression of their mRNAs in the present study. From stage 36 (E10) until hatching photoreceptors express axonin-1 but not NgCAM. In the inner nuclear layer groups of amacrine cells were strongly labelled with both probes but they seemed to belong to different subgroups. These patterns of expression might indicate a differential influence of the two proteins on the development of the local neural circuits of the retina.

Expression of the axonal cell adhesion molecules axonin-1 and Ng-CAM during the development of the chick retinotectal system.

Cell surface glycoproteins expressed on growth cones and axons during brain development have been postulated to be involved in the cell-cell interactions that guide axons into their target area. Nevertheless, an unequivocal description of the mechanism by which such molecules exert control over the pathway of a growing axon has not been done. As a crucial requirement in support of a relevant involvement of an axonal surface molecule in growth cone guidance, this molecule should be expressed in the growth cone. The developing retinotectal system provides an excellent opportunity to test whether a particular neuronal surface molecule fulfills the requirement of the spatiotemporal coincidence between its appearance and the emergence of growth cones because its setup follows the rule of chronotopy, i.e., the position of axons in a certain site is determined by the time of their arrival. We have analyzed axonin-1 and the neuron-glia cell adhesion molecule (Ng-CAM), two axonal surface molecules that promote neurite growth in vitro, for their expression in the retina and in the retinotectal system of the chick throughout its development. At stage 18, both axonin-like (A-LI) and Ng-CAM-like immunoreactivity (Ng-CAM-LI) are clearly present in the area where first retinal ganglion cells (RGCs) are generated. The immunoreactivity spreads synchronously with the formation of RGCs over the developing retina. From stage 32 on, the inner plexiform layer is also stained according to its temporospatial gradient of maturation. In later stages, the outer plexiform layer and the inner segments of photoreceptors also show immunoreactivity. The development of A-LI and Ng-CAM-LI along the optic nerve, chiasm, optic tract, and in the superficial layers of the optic tectum follows the chronotopic pattern of axons, as was found by earlier morphological investigations. Older axons loose their A-LI. This allows to localize the position of newly formed axons. The fact that A-LI and Ng-CAM-LI parallel the formation and maturation of axons suggests that axonin-1 and Ng-CAM may play an important role in the organization of the retinotectal system.

Formation of alternating tiers in the optic chiasm of the chick embryo.

BACKGROUND: When the fibers of the two optic nerves of the chick cross to the contralateral side at the prospective chiasmatic region, they segregate into clearly defined bundles. These bundles form horizontally oriented tiers which alternate between the right and the left optic nerve. METHODS: We have analyzed the development of these tiers qualitatively and quantitatively using light and electron microscopy between embryonic days (E) 4 and E19. RESULTS: The formation of the chiasm begins on E4. In the course of E4, tiers become visible for the first time. Their number increases rapidly until E7. Then the increase is slowed down and the final value (32 +/- 1) is approximated by E18/19. Growing axons allow one to distinguish three different segments: the growth cone, the distal, and the proximal segment. The latter originates in the perikaryon. Growth cones and distal segments are found predominantly in the ventralmost tiers. Their frequency decreases from ventral to dorsal. Proximal segments which indicate the presence of older axons appear first in the dorsal tiers and later also in more ventrally located tiers. CONCLUSION: Based on these criteria it is concluded that newly formed axons contribute primarily but not exclusively to the ventral tiers. There is a gradient of maturity of axons from ventral to dorsal whose slope becomes steeper with age until the last growth cones have arrived by E18. Thus, the formation of the chiasm corresponds to the spatiotemporal pattern of ganglion cell formation in the retina. The process of cell death of retinal ganglion cells is also seen in the chiasm but probably does not lead to a transitory diminution in the number of tiers.

Central retinal area is not the site where ganglion cells are generated first.

The development of retinal ganglion cells (RGC) was studied in the chick from stage 18 to adulthood. Our main objectives were to identify the retinal site where the first RGCs differentiate, to locate this site relative to the optically defined central retinal area, and to map the spatial arrangement of the RGC field at different stages in development. The eyes of the experimental animals were fixed and serially sectioned. The borders of RGC fields were determined from the presence of either ganglion cell perikarya or ganglion cell axons. In seven cases between stages 21 and 26, the borders of the RGC fields were confirmed electron microscopically. The serial sections together with the RGC fields were then reconstructed in three dimensions. The reconstructed retinae were projected onto a plane by using the radially equidistant polar azimuthal projection. First, RGCs appear dorsal to the apex of the optic fissure. Ganglion cell development then initially spreads out symmetrically with respect to the optic fissure. However, from stage 29 on, the nasal half of the retina expands much more than the temporal half. This asymmetrical growth entails that the optic fissure is eventually located in the temporal half of the retina in the mature animal. The RGC fields of the embryonic stages were superimposed on the retina of a visually active animal according to their real size and position. It turned out that the central retinal area was at least 2 mm away from the site where the first RGCs were generated. It is not before stage 28 that the prospective central retinal area is included into the expanding ganglion cell field. The fact that RGCs at the central retinal area are generated 2.5 days later than first RGCs near the apex of the optic fissure has important implications for the formation of the retinotectal projection.

Gastric argyrophil (enterochromaffin-like), gastrin, and somatostatin cells after proximal selective vagotomy in man.

The number, size, and volume density of endocrine cells was determined in biopsies obtained endoscopically in patients after proximal selective vagotomy (PSV; N = 31), antrectomy (N = 9), untreated duodenal ulcer (DU) disease (N = 11), and in controls (N = 15). Serum gastrin was significantly elevated after PSV (mean 60 pg/ml) compared to DU patients (29 pg/ml), controls (26 pg/ml), and after antrectomy (11 pg/ml). Volume density of fundic argyrophil (largely enterochromaffin-like) cells after PSV (0.74%) and in DU disease (0.63%) were significantly (P < 0.001) higher when compared with controls (0.37%) but lower after antrectomy (0.24%; P < 0.02). The density of argyrophil cells was not influenced by the interval following PSV or the magnitude of hypergastrinemia. Antral gastrin cells were increased after vagotomy, whereas the antral and fundic somatostatin cell numbers were reduced after PSV. It is concluded that: (1) a major role of the vagal nerve as a trophic factor for enterochromaffin-like cells could not be demonstrated after PSV, and (2) moderate hypergastrinemia after PSV did not induce proliferation of ECL cells.

Postnatal development of area 17 callosal connections in Tupaia.

The goal of the present study was to investigate the pattern of maturation of callosal projecting neurons in a well-studied mammalian visual system with unique structural and functional properties. Studies of the distribution pattern of interhemispheric connections in the adult tree shrew primary visual cortex reveal not only a high concentration of labeled neurons along the area 17/18 border, as in standard experimental animals such as the cat and monkey, but also numerous callosal projecting neurons in the adjacent dorsal part of area 17, which largely corresponds to the binocular visual field (Kretz and Rager, Exp. Brain Res. 82:271, '90). Callosal projections were anatomically traced in 11 tree shrews (Tupaia belangeri) at various ages between postnatal day 7 (7, 9, 10, 13, 15, 17, 19, and 26 days old) and adulthood (107 days old). In each animal, four injections of wheat germ agglutinin conjugated to horseradish peroxidase were made in a standard configuration into the striate cortex of one hemisphere. In young tree shrews only 7 and 9 days old, heavily labeled terminal axon structures could be seen in the white matter and in layer VI of the opposite hemisphere. Only a few labeled neurons, however, were detected in layer III. The small number of labeled neurons indicated that early in postnatal development, only a few callosal axons had invaded the upper cortical layers. By 10 days of age, the number of supragranular neurons was increasing and the maximal value was counted in a 13-day-old tree shrew. A sharp decline in the number of labeled supragranular neurons was noticed--about 94% in our case--between days 13 and 15. In animals more than 15 days old, the distribution pattern and the density of the neurons looked like the pattern seen in the adult Tupaia brain. The labeled cells were mostly concentrated in layers II and III. The majority of neurons resembled typical pyramidal cells. However, some of the neurons in sublayer IIIc had elongated cell bodies oriented parallel to the laminar boundaries. In contrast to the supragranular cells found in all stages investigated, small populations of labeled cells in layer VI were observed in 9- to 17-day-old tree shrews only. In young postnatal animals 7 to 13 days old, a peculiar cell type was labeled on the ipsilateral side. In coronal sections these cell bodies formed a continuous band that extended from the ventricular wall to the subcortical white matter. These cells might belong to a population of cells still in migration.