Nervous system

About: Nervous system is a research topic. Over the lifetime, 16729 publications have been published within this topic receiving 847181 citations.

Zebrafish primary neurons initiate expression of the LIM homeodomain protein Isl-1 at the end of gastrulation.

Abstract: Isl-1 has previously been established as the earliest marker of developing chicken spinal motor neurons where it is regulated by inductive signals from the floorplate and notochord. We now report that, in zebrafish, the expression of Isl-1 is initiated in Rohon-Beard cells, primary motor neurons, interneurons and cranial ganglia, hours before the neural tube itself is formed. The expression is initiated simultaneously in the Rohon-Beard cells and the primary motor neurons, at the axial level of the presumptive first somite. The Isl-1-expressing motor neurons appear on either side of the ventral midline whereas the interneurons and Rohon-Beard cells initiate expression while located at the edge of the germinal shield. Isl-1 expression is initiated in these cells before the formation of a differentiated notochord. Isl-1 is expressed in the various functional classes of primary neurons at 24 hours postfertilization. This selective expression of a homeodomain protein in the primary neurons implies that these neurons share a common program of early development and that they have evolved and been selected for as a coordinated system. One of the functions of the primary neurons is to send long axons which pioneer the major axon tracts in the zebrafish embryo. An evolutionary conserved functional role for Isl-1 in the expression of the pioneering phenotype of the primary neurons is suggested.

Effects of mouse tumor transplantation on the nervous system

Abstract: Mammalian tumors were first grown successfully on the chorio-allantoic membrane of the chick embryo by M ~ r p h y . ~ The recent development of this technique has been surveyed by Karnofsky, et a1.7 The first intraembryonic transplants of normal mouse tissue were performed by Rawles.lo Bueker2 has combined both techniques: he implanted mouse tumor in the body wall of three-day embryos. This experiment was performed in connection with certain neuro-embryological problems. Previous experiments had shown that the differentiation of primary sensory and motor systems in amphibia and in chick embryos is to a large extent under the control of extrinsic factors: The effect exerted by the periphery is not a speciesspecific; transplantations in Amphibia (Harrison,6 Detwiler3) had proved the capacity of nerve fibers to invade heteroplastic structures. The same compatibility was demonstrated by Buekerl to exist between nerve fibers of the chick embryo and the peripheral field provided by the guinea hen embryo. By transplanting mouse tumors intra-embryonically, Bueker wanted to test the capacity of nerve fibers to invade tissue of a different class. In addition, it was his intention to confront the nerve fibers with a homogeneous tissue, rather than with a set of heterogeneous and complex structures, as represented by a limb. He performed transplantations of three different tumors: mouse adeno-carcinoma which completely failed to grow, fowl Rous sarcoma which caused extensive hemorrhage and had no effect on the nerve structures, and mouse sarcoma 180, which grew vigorously and was invaded by nerve fibers of the host. The attention was then focused on sarcoma 180. The characteristics of tumor growth and the response of the spinal nerve centers were investigated in embryos between six and nine days of incubation, that is, between three and six days after the implantation of the tumor. In this short lapse of time, the tumor had infiltrated the somatopleure of the body wall of the embryo and bulged as a conspicuous mass in the coelomic cavity. The mesonephros was partly invaded and destroyed. In eightto nine-day embryos, nerve bundles were found inside the tumor. The sensory ganglia on the side and at the level of the tumor were considerably enlarged in comparison with the contralateral ganglia. The size increase was 33 per cent on the average. The motor column at the same level was, on the contrary, hypoplastic. The increase in size of the sensory ganglia and the coincident reduction of the motor column were taken as evidence for the sensory nature of the nerve fibers in the tumor. The author concluded that histochemical properties of the tumor favored the branching of sensory nerve fibers, whereas somatic motor fibers were refractory to these agents. Three important facts were thus established: (1) the sensory ganglia are responsive not only to tissues of the same class, but also to structures of a

Evidence that endogenous beta nerve growth factor is responsible for the collateral sprouting, but not the regeneration, of nociceptive axons in adult rats.

Abstract: A key role has not yet been identified for beta nerve growth factor (NGF) in the growth responses that continue to be expressed in the sensory neurons of adult animals. We have now examined the effects of daily administration to adult rats (and in a few experiments, mice) of antiserum to NGF on (i) the collateral sprouting of undamaged nociceptive nerves that occurs into denervated adjacent skin and (ii) the regeneration of cutaneous sensory axons that occurs after they are damaged. The results were unexpected. All collateral sprouting was prevented and that already in progress was halted; sprouting resumed when treatment was discontinued. In contrast, the reestablishment, and even enlargement, of cutaneous nerve fields by regenerating axons was unaffected by anti-NGF treatment, even after dorsal rhizotomy was done to eliminate any central trophic support. In denervated skin, regenerating and collaterally sprouting axons utilized the same cellular pathways to establish functionally identical fields, thus displaying apparently identical growth behaviors, yet anti-NGF treatment clearly distinguished between them. We suggest that endogenous NGF is responsible for the collateral sprouting of nociceptive axons, probably reflecting an ongoing function of NGF in the regulation of their fields. This demonstration in the adult sensory system of a defined role for NGF in nerve growth could apply to nerve growth factors generally in the adult nervous system. The regeneration, however, of nociceptive axons (and nonnociceptive one) is not dependent on NGF.