[Pharmacotherapy of solid tumors. New hopes and frustrations]. / Arzneitherapie solider Tumoren. Hoffnung und Frustration.

Recent years have seen dramatic changes in the biological understanding and treatment of solid tumors. Based on the tumor biology, targeting agents have been developed which directly affect the underlying genetic or immunological changes found in specific tumor entities. Significant increases in survival have delivered the functional proof of the concept of targeted and immunological tumor therapy. The management and adherence of the patient as well as optimized cooperation with clinicians are decisive for the results of therapy and disease control.Several solid tumors are currently under investigation in clinical studies evaluating the (sequential) therapy with targeting and immunologically active agents, e.g. tyrosine kinase and mTOR inhibitors, targeting antibodies, such as bevacizumab, specific antagonists, such as enzalutamide and immunological checkpoint inhibitors via PD(L)1 and/or CTLA 4 antibodies.Currently approved agents have dramatically changed the landscape of treatment options especially for prostate cancer. Such agents include hormone therapy with enzalutamide and abiraterone, radiotherapy with cabazitaxel and xofigo (radium 223), metastatic breast cancer (eribulin and everolimus), renal cell carcinoma (sunitinib, sorafenib, axitinib, everolimus and temsirolimus), non-small cell lung cancer (crizotinib and afatinib), colorectal cancer and gastrointestinal stromal tumor (regorafenib) and melanoma (ipilimumab and vemurafenib). The treatment of rarer tumors, such as pancreatic and hepatocellular cancer and soft tissue sarcoma has entered the stage of targeted therapy with the approval of nanoparticle albumin-bound (nab)-paclitaxel, sorafenib, and eribulin/pazopanib. Current clinical trials are focusing on the best time point and sequence of therapy and also improvement in the management of these promising agents.

Distinct expression and subcellular localization patterns of Na+/HCO3- cotransporter (SLC 4A4) variants NBCe1-A and NBCe1-B in mouse brain.

The electrogenic Na+/HCO3- cotransporter (NBCe1) has been identified as a key player for regulation of intracellular pH in several cell types. The present study was undertaken to determine expression and subcellular localization of the NH2-terminal solute carrier (SLC) 4A4 variants NBCe1-A and NBCe1-B in mouse brain using variant-specific antibodies by immunohistochemistry and immunoelectron microscopy. In addition, distribution of NBCe1 variants and activity-dependent regulation was investigated in mouse embryonic day 17.5 (E17.5) hippocampal primary cultures in vitro. The results showed NBCe1-A and NBCe1-B transcript expression in the mouse olfactory bulb, cerebral cortex, hippocampus and cerebellum. NBCe1-A was predominantly expressed in Purkinje cells, granule cells of the dentate gyrus, non-pyramidal cell bodies in cerebral cortex, and in periglomerular and mitral cells in the olfactory bulb. Pyramidal neurons in cerebral cortex and apical cell dendrites in the hippocampus were stained for both NBCe1-A and NBCe1-B. Moreover, NBCe1-B was present in Bergmann glia. At the ultrastructural level, NBCe1-B was preferentially expressed in perivascular astroglial lamellae, whereas both NBCe1 NH2-terminal variants were localized in pre- and postsynaptic compartments. Except for the olfactory bulb, NBCe1-A was always colocalized with calbindin. Treatment of E17.5 primary hippocampal cultures with KCl, showed dramatic downregulation of NBCe1-B mRNA and protein after 60 min, whereas NBCe1-A expression remained unchanged. These data demonstrate for the first time distinct cellular distribution of NBCe1 NH2-terminal variants in mouse brain. NBCe1 may be involved in neuronal modulation, and pH regulation during neuronal activity.

The cerebellum-specific Munc13 isoform Munc13-3 regulates cerebellar synaptic transmission and motor learning in mice.

Munc13 proteins form a family of three, primarily brain-specific phorbol ester receptors (Munc13-1/2/3) in mammals. Munc13-1 is a component of presynaptic active zones in which it acts as an essential synaptic vesicle priming protein. In contrast to Munc13-1, which is present in most neurons throughout the rat and mouse CNS, Munc13-3 is almost exclusively expressed in the cerebellum. Munc13-3 mRNA is present in granule and Purkinje cells but absent from glia cells. Munc13-3 protein is localized to the synaptic neuropil of the cerebellar molecular layer but is not found in Purkinje cell dendrites, suggesting that Munc13-3, like Munc13-1, is a presynaptic protein at parallel fiber-Purkinje cell synapses. To examine the role of Munc13-3 in cerebellar physiology, we generated Munc13-3-deficient mutant mice. Munc13-3 deletion mutants exhibit increased paired-pulse facilitation at parallel fiber-Purkinje cell synapses. In addition, mutant mice display normal spontaneous motor activity but have an impaired ability to learn complex motor tasks. Our data demonstrate that Munc13-3 regulates synaptic transmission at parallel fiber-Purkinje cell synapses. We propose that Munc13-3 acts at a similar step of the synaptic vesicle cycle as does Munc13-1, albeit with less efficiency. In view of the present data and the well established vesicle priming function of Munc13-1, it is likely that Munc13-3-loss leads to a reduction in release probability at parallel fiber-Purkinje cell synapses by interfering with vesicle priming. This, in turn, would lead to increases in paired-pulse facilitation and could contribute to the observed deficit in motor learning.

The onset of parvalbumin-expression in interneurons of the rat parietal cortex depends upon extrinsic factor(s).

Parvalbumin (PV) belongs to the large family of EF-hand calcium-binding proteins and is an excellent marker for a subpopulation of GABAergic neocortical interneurons. During cortical development, PV first appears on postnatal day (P)8, in the infragranular layers; after P14, it also becomes apparent within the supragranular layers. However, nothing is known about the factors controlling its expression, which could involve functional activity, neuronal connectivity and/or neurotrophic factors. It being difficult to manipulate these parameters in vivo, their role may be more readily assessed in organotypic cultures, which are deprived of their subcortical afferents and efferents, and hence of subcortically derived neurotrophic factors and extrinsic functional activity. We prepared slices of the rat brain on P3, P5, P7 and P9, maintained them in culture for 2-5 weeks, and compared the temporal and spatial distribution pattern of PV-immunoreactivity within these slices with the in vivo situation. We found, first, that during late postnatal in vivo development and ageing, the number of PV-immunoreactive neurons in the parietal cortex decreases significantly, and second, that the expression of PV-immunoreactivity in the parietal cortex was markedly influenced by the phase of postnatal development at which slice cultures were explanted. In those removed on P7 and P9, the number of PV-immunoreactive cells, as well as the temporal and spatial distribution pattern of PV-immunoreactivity corresponded to the in vivo situation, but in explants obtained on P3 or P5, PV-immunoreactivity remained confined to layer V of the cortex, reminiscent of the expression profile manifested at the end of the second postnatal week in vivo. Also, the number of PV-immunoreactive cells in these cultures was significantly lower than in explants at the later stages. Our results indicate that the onset of PV-expression in the parietal cortex depends upon extrinsic cortical factors subsisting prior to P7. Once the production of this protein has been initiated, such influences are no longer required.

Munc13-1 is a presynaptic phorbol ester receptor that enhances neurotransmitter release.

Munc13-1, a mammalian homolog of C. elegans unc-13p, is thought to be involved in the regulation of synaptic transmission. We now demonstrate that Munc13-1 is a presynaptic high-affinity phorbol ester and diacylglycerol receptor with ligand affinities similar to those of protein kinase C. Munc13-1 associates with the plasma membrane in response to phorbol ester binding and acts as a phorbol ester-dependent enhancer of transmitter release when overexpressed presynaptically in the Xenopus neuromuscular junction. These observations establish Munc13-1 as a novel presynaptic target of the diacylglycerol second messenger pathway that acts in parallel with protein kinase C to regulate neurotransmitter secretion.

S100 protein expression in subpopulations of neurons of rat brain.

Available data are conflicting as regards the occurrence of Ca2+ and Zn2+ binding S100 proteins in neurons of mammalian brain. Here the localization and expression of S100 was re-investigated using several different antibodies and in situ hybridization. A map is provided for the distribution of two classes of S100-positive neuron populations in the adult rat CNS. "Persistently S100-positive" neurons had large size, were strongly immunoreactive and were mainly distributed in the nuclei of the lower brainstem and cerebellum. "Variably S100-positive" neurons were preferentially found in the forebrain of rats older than 90 days and were especially numerous in limbic regions. The S100-immunoreactivity in these neurons was moderately intense, occurred with high interindividual variation and appeared related to function as suggested by variations due to anesthesia. The expression of S100 mRNA in neurons was re-investigated at high spatial resolution with non-radioactive in situ hybridization using an oligonucleotide specific for S100 beta-mRNA. Expression of S100 was demonstrated in astrocytes and in those neuron populations which were also strongly S100-immunoreactive. No expression of S100 beta message was seen in weakly immunoreactive neurons, b but this may be due to low sensitivity of the techniques used. The data suggest that the S100 proteins are synthesized in all astrocytes and in distinct subpopulations of neurons in rat brain. These neurons show a characteristic topography and vary in S100 expression probably due to their function and maturation.

Expression of S100 protein in the vestibular nuclei during compensation of unilateral labyrinthectomy symptoms.

In adult guinea pigs, unilateral labyrinthine lesions were inflicted by chloroform injections into the middle ear. Immunoreactivity for S100 protein (S100) in the vestibular nuclei was studied during compensation of lesion-induced postural asymmetry symptoms, i.e., nystagmus, asymmetrical head position. 1 h after unilateral labyrinthectomy, increased levels of astroglial S100 immunoreactivity were found in the superior vestibular nucleus and in the medial/lateral vestibular nucleus border region on the side contralateral to the deafferentation. Bilaterally, the astrocytic S100 immunoreaction increased in the lateral vestibular nuclei around Deiters neurons. Maximal expression of S100 was noted 3 h after the lesion. Subsequently, it diminished. Our data reveal that transsynaptically altered neuronal activity induces an astrocytic reaction which provides increased levels of S100 to the local neuropil. Calcium and zinc binding S100 proteins may play a functional role for the neuroplasticity during vestibular compensation.

Modifications of S100-protein immunoreactivity in rat brain induced by tissue preparation.

Immunocytochemistry using antibodies against various molecular forms of the Ca++ and Zn(++)-binding S100 proteins predominantly labelled astrocytes. However, especially in the neocortex the staining pattern is variable. Methods of tissue preparation have been evaluated with the aim to preserve as much S100 immunoreactivity as possible. Optimal results were obtained after perfusion fixation with 4-5% aldehydes, 0.1 M sodium cacodylate, 0.1% CaCl2, pH 7.3. In such preparations, astrocytes were completely labelled including their lamellar compartments in large parts of the central nervous system. Ca(++)-withdrawal had adverse affects on S100 immunoreactivity. Cryostat sections treated with EDTA-containing solutions before fixation showed that Ca(++)-free S100 can apparently not be fixed to the tissue. Perfusion fixatives containing EDTA resulted in inhomogeneous loss of S100 staining, indicating a differential susceptibility of astrocytic subpopulations. A different type of reduction in S100 immunoreactivity occurred around large neocortical blood vessels. Perivascular defects in immunostaining occasionally appeared even after optimal fixation, but could be regularly provoked by mildly acidic fixation (pH 6.6) or prolonged barbiturate anaesthesia. These defects might be based on S100 release into the cerebrospinal fluid. Presumably under none of the conditions studied can the immunoreactivity of all S100-forms and -fractions be completely preserved in the tissue. However, recommendations are presented for optimizing tissue preparation, to the extent that premortal modifications affecting the stainability of astrocytes may be detected by S100 immunohistochemistry in fixed brain tissue.

S100 immunoreactivity in a subpopulation of oligodendrocytes and Ranvier's nodes of adult rat brain.

The Ca(2+)- and Zn(2+)-binding S-100 proteins (S100) are predominantly localized in astrocytes of adult mammalian brain. In addition, light and electron microscopic immunocytochemistry revealed S100 in a small subpopulation of oligodendrocytes. By nuclear morphology and abundance of rough ER and Golgi fields, these cells resembled actively myelinating oligodendrocytes. S100 immunoreactivity was also found in paranodal loops and outer mesaxons of isolated of myelin sheaths. Data suggests that oligodendroglial content of S100 relates to cell turnover and/or myelin repair in the adult rat brain, and that S100 is present during myelin compaction.

Chloride is preferentially accumulated in a subpopulation of dendrites and periglomerular cells of the main olfactory bulb in adult rats.

GABA is predominantly an inhibitory transmitter. Mediated by GABAA receptors, GABA opens chloride channels, induces a passive flux of chloride ions, which is usually directed from extracellular to intracellular space, and hyperpolarizes postsynaptic neurons. Recent electrophysiological data suggested that GABA may also depolarize neurons and exert excitatory actions. However, it remained unclear whether excitatory GABA effects are based on reversed transmembrane chloride gradient due to modifications in extracellular or intracellular chloride concentrations. Here, the first histochemical evidence is provided for local redistribution of chloride in the CNS of healthy adult rats. Olfactory bulbs were examined using freeze substitution, silver trapping of chloride and intensification techniques at light and electron microscopic level. The chloride content of precipitates was evidenced by electron spectroscopic imaging using a CEM 902 (Zeiss) electron microscope. Chloride concentration was high in a subpopulation of some periglomerular cell bodies and isolated dendritic profiles, while it seemed to be very low in certain parts of the glomerular neuropil including intercellular clefts. Data suggest that reversed chloride gradients can be demonstrated by cytochemical methods, and may be responsible for excitatory GABA effects on selected periglomerular neurons and dendrites in the olfactory glomeruli. Conditions leading to chloride redistribution in the CNS of normal adult rats remain to be determined.

Distribution of Bergmann glial somata and processes: implications for function.

We have used immunocytochemistry for glial fibrillary adidic protein and glutamine synthetase to selectively label Bergmann glia in the adult rat cerebellum. From measurements of radial, tangential and en face sections we provide new data on the distribution and disposition of these glial cells. Specifically, Bergmann glia were found to have a mean areal packing density of 8,269 somata/mm2, their radial processes are packed at a mean density of 39,000/mm2, and their endfeet at the pial surface have a mean density of 19,973/mm2. Each Bergmann glial cell ist "responsible" for the equivalent of a column of cerebellar cortex having a base of 11 microns x 11 microns, a height of 170 microns, and a volume of 20,559 microns3. There are 8.1 Bergmann glia for each Purkinje cell, and each glial cell ensheaths between 2,142 and 6,358 Purkinje cell synapses. We use these data to offer insights on the roles of Bergmann glia during development and in the adult brain.

Perineuronal nets provide a polyanionic, glia-associated form of microenvironment around certain neurons in many parts of the rat brain.

The nature and function of previously described perineuronal nets are still obscure. In the present study their polyanionic components were demonstrated in the rat brain using colloidal iron hydroxide (CIH) staining. In subcortical regions, such as the red nucleus, cerebellar, and vestibular nuclei, most neurons were ensheathed by CIH-binding material. In the cerebral cortex perineuronal nets were seen around numerous nonpyramidal neurons. Biotinylated hyaluronectin revealed that hyaluronan occurs in perineuronal nets. Two plant lectins [Wisteria floribunda agglutinin (WFA) and Vicia villosa agglutinin (VVA)] with affinity for N-acetylgalactosamine visualized perineuronal nets similar to those rich in anionic components. Glutamic acid decarboxylase (GAD)-immunoreactive synaptic boutons were shown to occupy numerous meshes of perineuronal VVA-positive nets. Electron microscopically, VVA binding sites were scattered throughout perisynaptic profiles, but accumulated at membranes and in the extracellular space except not in synaptic clefts. To investigate the spatial relationship between glial cell processes and perineuronal nets, two astrocytic markers (S100-protein and glutamine synthetase) were visualized at the light and electron microscopic level. Two methods to detect microglia by the use of Griffonia simplicifolia agglutinin (GSA I-B4) and the monoclonal antibody, OX-42, were also applied. Labelled structures forming perineuronal nets were observed with both astrocytic, but not with microglial, markers. It is concluded that perineuronal nets are composed of a specialized type of glia-associated extracellular matrix rich in polyanionic groups and N-acetylgalactosamine. The net-like appearance is due to perisynaptic arrangement of the astrocytic processes and these extracellular components. Similar to the ensheathment of nodes of Ranvier, perineuronal nets may provide a special ion buffering capacity required around various, perhaps highly active, types of neurons.

x-y-recording in transmission electron microscopy. A versatile and inexpensive interface to personal computers with application to stereology.

An interface for IBM XT/AT-compatible computers is described which has been designed to read the actual specimen stage position of electron microscopes. The complete system consists of (i) optical incremental encoders attached to the x- and y-stage drivers of the microscope, (ii) two keypads for operator input, (iii) an interface card fitted to the bus of the personal computer, (iv) a standard configuration IBM XT (or compatible) personal computer optionally equipped with a (v) HP Graphic Language controllable colour plotter. The small size of the encoders and their connection to the stage drivers by simple ribbed belts allows an easy adaptation of the system to most electron microscopes. Operation of the interface card itself is supported by any high-level language available for personal computers. By the modular concept of these languages, the system can be customized to various applications, and no computer expertise is needed for actual operation. The present configuration offers an inexpensive attachment, which covers a wide range of applications from a simple notebook to high-resolution (200-nm) mapping of tissue. Since section coordinates can be processed in real-time, stereological estimations can be derived directly "on microscope". This is exemplified by an application in which particle numbers were determined by the disector method.

An unbiased estimation of the total number of synapses in the superior cervical ganglion of adult rats established by the disector method. Lack of change after long-lasting sodium bromide administration.

Previous physiological and morphological studies suggested that sodium bromide promotes synaptogenesis of implanted cholinergic nerves in the superior cervical ganglion of adult rats. To check whether sodium bromide also modifies synaptic numbers in the intact ganglion, quantitative electron microscopy was used to determine the total number of synaptic junctions in the superior cervical ganglion of adult rats. Untreated controls were compared with animals which drank water containing 280 mg ml-1 sodium bromide for 7 days. The disector method, an unbiased estimator of volume density of certain particles, has been adapted to this particular case. To accomplish the task, an on-line counting procedure was developed, which permitted the efficient adaptation of the disector method for the superior cervical ganglion, in which the synapses are known to be distributed sparsely. Three pairs of (control and treated) ganglia have been completely processed by three independent examiners. The estimated number of synapses in the ganglia ranged from 4 to 8 million while the volumes of the ganglia varied from 0.65 to 0.90 mm3. Evaluation of the results showed that variations in the total number of synapses were in each case proportional to differences in ganglionic volumes. This suggests that: (1) sodium bromide does not lead to changes in density of intrinsic synapses; and (2) the morphogenetic action of sodium bromide on principal ganglion cells previously described is essentially postsynaptic and requires additional presynaptic elements to increase the number of synapses.

The anatomical substrate for telencephalic function.

The basic thesis for this study was that the telencephalon is needed to make decisions in new situations. Subsidiary hypotheses were that the telencephalon consists of: (a) a sensorimotor system which generates motor activity from sensory input and (b) a selection system which makes choices from possible motor programs. It was postulated that the selection system should fulfil the following requirements: be accessible for past and present events, have the capacity to process this information in a nondetermined way with a possibility for ordering, and have access to motor-affecting systems (the sensorimotor system). The ability of the selection system to correlate information in a nonpredetermined way was considered most important. In short: The selection system should be able to associate any information in any combination, and have the capability for internal control of neuronal activity and external selection of motor programs (see Fig. 1A.) Xenopus laevis was chosen as a subject, since it has a relatively simple telencephalon, with characteristics that it shares with "primitive" species of different vertebrate classes, and because it is easy to maintain as a laboratory animal. The main method used was the determination of connections with HRP. The pallium was in the focus of attention, since it was considered to be the core of the selection system. Immunohistochemistry was used as an additional parameter to compare Xenopus laevis forebrain with those of other vertebrates. The results showed that the pallium can be subdivided into a rostral (third) and a caudal (two-thirds) entity. The rostral third is the main recipient for thalamic and olfactory input. The caudal two-thirds are linked up to the rostral third and have a refined microcircuitry. Efferents from the pallium remain restricted to the forebrain. The entire pallium consists of a network of intrinsic reciprocal connections and can be considered to be positioned between the medial pallium (hippocampus), septum, and amygdaloid complex (amygdala). As a whole this system targets the hypothalamus. The hypothalamus in turn projects into the striatum complex (striatum with anterior entopeduncular nucleus). The rostral dorsal pallium and the amygdaloid complex also project into the striatum complex. The striatum is positioned between the sensory input from the thalamus and olfactory bulbs, and the motor output to the medulla. It is concluded, on the basis of its straightforward input-output relations and uniform appearance, that the striatum complex fulfils the requirements for a sensorimotor system. The pallium together with the septum, amygdaloid complex, and hypothalamus fulfils the requirements for a selection system.(ABSTRACT TRUNCATED AT 400 WORDS)

Organization of radial glial cells during the development of the rat dentate gyrus.

The temporal and spatial patterns of development of radial glial processes in the rat dentate gyrus have been studied in immunohistochemical preparations stained for the presence of either the glial fibrillary acidic protein (GFAP) or the vimentin-associated antigen R4. Additional electron microscopic (EM) observations were made from material prepared either immunohistochemically or by the Golgi method. R4 immunoreactive radial fibers were observed in the incipient dentate gyrus as early as E13 and by E14 the density of stained fibers was clearly higher in the anlage of the dentate gyrus than in the adjacent hippocampus. By E15 it was possible to identify in the EM the endfeet of radial glial cells that contained numerous glycogen particles. GFAP-positive radial processes were first observed on E17; these processes tended to be of larger diameter than those stained with the R4 antibody, suggesting that they were among the more mature processes. The orientation of both the R4- and GFAP-positive glial processes changed throughout the last week of embryonic life and by the end of the first postnatal week they formed a complex meshwork of intertwined processes. The distribution of their cell bodies also changed with time; initially their perikarya were located in the neuroepithelium at the lateral margin of the hippocampal primordium; later they were found mainly beneath the granule cell layer. Dividing cells that contained GFAP were observed along the trajectory of the migrating granule cell precursors and in the hilus of the dentate gyrus; at later stages some GFAP-positive mitotic figures were seen within and immediately below the granule cell layer. On the basis of these observations, we have attempted to reconstruct the role that radial glial processes play in the morphogenesis of the dentate gyrus. First, radial processes extend from the neuroepithelium to the pial surface prior to the migration of neurons that will form the dentate gyrus. These early generated glia appear to form the boundaries of the developing dentate gyrus and provide an internal lattice that may guide the initial wave of migrating progenitor cells. As the dentate gyrus enlarges, these early formed processes maintain their contacts along the hippocampal fissure and along the pial surface of the dentate anlage. Thus, with time they become increasingly distorted and are ultimately compressed into two bundles; one lies deep to the hippocampal fissure parallel to the granule cell layer and the other is located at the fimbriodentate juncture.(ABSTRACT TRUNCATED AT 400 WORDS)

A light- and electron-microscopic study of mesencephalic neurons projecting to the ganglion of the nervus terminalis in the goldfish.

After application of various neuronal tracers (horseradish peroxidase, cobalt-chloride lysine, true blue) to the ganglion of the nervus terminalis a small number of neurons was retrogradely labeled in the mesencephalon. As revealed by combined horseradish peroxidase and catecholamine-fluorescence techniques these neurons are located in the isthmic area immediately rostral to, but not within the locus coeruleus. Cobalt-labeled axons of the mesencephalic neurons were traced individually in serial sections. Neurons projecting contralaterally cross in the horizontal commissure. Tracing of single fibers provided no evidence for axon collaterals within this pathway. Retrograde labeling reveals two different types of isthmic neurons afferent to the ganglion of the nervus terminalis: One smaller-sized type is located bilaterally and consists of four to six neurons; another type possessing many dendritic processes was consistently found as only one single cell located contralateral to the side of injection. The existence of two types of neurons was confirmed by their cytological differences: The small-sized type receives only sparse perisomatic input, while the large-sized type shows heavy somatic and dendritic, probably monoaminergic innervation.

The migration of neural crest cells and the growth of motor axons through the rostral half of the chick somite.

We have studied the pathway of migration of neural crest cells through the somites of the developing chick embryo, using the monoclonal antibodies NC-1 and HNK-1 to stain them. Crest cells, as they migrate ventrally from the dorsal aspect of the neural tube, pass through the lateral part of the sclerotome, but only through that part of the sclerotome which lies in the rostral half of each somite. This migration pathway is almost identical to the path which presumptive motor axons take when they grow out from the neural tube shortly after the onset of neural crest migration. In order to see whether the ventral root axons are guided along this pathway by neural crest cells, we surgically excised the neural crest from a series of embryos, and examined the pattern of axon outgrowth approximately 24 h later. In somites which contained no neural crest cells, ventral root axons were still found only in the rostral half of the somite, although axonal growth was slightly delayed. These axons were surrounded by sheath cells, which had presumably migrated out of the neural tube, to a point about 50 micron proximal to the growth cones. With appropriate antibodies we found that the extracellular matrix components fibronectin and laminin are evenly distributed between the rostral and caudal halves of the somite. Neither of these molecules therefore plays a critical role in determining the specific pathway of neural crest cells or motor axons through the rostral half of the somite.

Optic tract cells projecting to the retina in the teleost, Pantodon buchholzi.

Horseradish peroxidase was employed to trace retino-fugal and retino-petal connections in the teleost fish, Pantodon buchholzi. Most of the reciprocal connections found were within the range also observed in previously studied species of teleosts. Of particular interest is the discovery of cells located within the optic tract and projecting to the retina. These neurons were investigated electron microscopically.