Correlation of gp140trk expression and NGF-induced neuroblast chemotaxis in the embryonic rat spinal cord

Using biomaterials to modulate chemotactic signaling for central nervous system repair

Chemotaxis enables cellular communication and movement within the body. This review focuses on exploiting chemotaxis as a tool for repair of the central nervous system (CNS) damaged from injury and/or degenerative diseases. Chemokines and factors alone may initiate repair following CNS injury/disease, but exogenous administration may enhance repair and promote regeneration. This review will discuss critical chemotactic molecules and factors that may promote neural regeneration. Additionally, this review highlights how biomaterials can impact the presentation and delivery of chemokines and growth factors to alter the regenerative response.

Olfactory ensheathing cells: attractant of neural progenitor migration to olfactory bulb

Olfactory ensheathing cells (OECs) are the glial cells that derive from the olfactory placode, envelop olfactory axons in the course of migration from the olfactory epithelium to the olfactory bulb and reside primarily in the olfactory nerve layer. OECs transplantation as a promising experimental therapy for axonal injuries has been intensively studied; however, little is known about their roles in olfactory bulb development. In this study, we examined the effects of OECs on the migration of neural progenitors in rostral migratory stream (RMS). Initially, the neurosphere migration assay showed that OEC-conditioned medium promoted progenitors to migrate from RMS neurospheres in a concentration dependent manner. Moreover, co-culturing OECs nearby the RMS explants led to asymmetric migration of explants in different developing stages. However, OECs could influence the migration in a distance not further than 1.5 mm. Finally, slice assay that mimic the circumstance in vivo revealed that OECs had a chemoattractive activity on RMS neural progenitors. Together, these results demonstrate that OECs attract neural progenitors in RMS through the release of diffusible factors and it is likely that OECs mainly influence radial migration in the olfactory bulb but not tangential migration of the RMS invivo during development. This suggests a previously unknown function for OECs in olfactory development and a novel mechanism underlying the targeting of RMS cells.

Neurotrophin receptor immunostaining in the rat ventral cochlear nucleus

By virtue of its known segregated distribution of cell types, their known neurotransmitters and neurophysiologic properties, the cochlear nucleus is an excellent model and provides the opportunity to study the relation between neurotrophins and their receptors along with the functional properties of the adult cochlear nucleus. To investigate the potential role of neurotrophins in the mature cochlear nucleus, we determined the expression of the three major neurotrophin tyrosine kinase receptors (Trk) in the adult rat ventral cochlear nucleus, as revealed by antibodies against the full-Trk proteins. A qualitative and a cartographic analysis showed a widespread distribution of the three Trk receptors throughout the nucleus. Immunostaining was mainly restricted to neurons as shown by the lack of double immunostaining with specific markers for glial cells. However, we observed variability in immunostaining for given receptors. Three classes of cells were distinguished by their specificity for Trk receptors. The first one was a cell population that stained for TrkA or TrkB. This population characterizes the majority of small and small round neurons and fusiform cells. The second group consists of TrkC-immunolabeled cells and comprises the majority of spherical, globular, granule and small multipolar cells. The third group consists of cells that seem to be immunopositive for all three Trk receptors. This group includes in part multipolar, giant and octopus cells. A possible correlation between Trk expression and cell functional properties is suggested: TrkA- and TrkB-immunoreactive cells could include inhibitory neurons while cells stained for TrkC could include excitatory neurons. The abundant and widespread neuronal distribution of signal-transducing forms of TrkA, TrkB and TrkC predicts that their cognate ligands may exert significant effects on a large proportion of neurons within the mature ventral cochlear nucleus.

Dynamic distribution of chemoattractant receptors in living cells during chemotaxis and persistent stimulation

While the localization of chemoattractant receptors on randomly oriented cells has been previously studied by immunohistochemistry, the instantaneous distribution of receptors on living cells undergoing directed migration has not been determined. To do this, we replaced cAR1, the primary cAMP receptor of Dictyostelium, with a cAR1-green fluorescence protein fusion construct. We found that this chimeric protein is functionally indistinguishable from wild-type cAR1. By time-lapse imaging of single cells, we observed that the receptors remained evenly distributed on the cell surface and all of its projections during chemotaxis involving turns and reversals of polarity directed by repositioning of a chemoattractant-filled micropipet. Thus, cell polarization cannot result from a gradient-induced asymmetric distribution of chemoattractant receptors. Some newly extended pseudopods at migration fronts showed a transient drop in fluorescence signals, suggesting that the flow of receptors into these zones may slightly lag behind the protrusion process. Challenge with a uniform increase in chemoattractant, sufficient to cause a dramatic decrease in the affinity of surface binding sites and cell desensitization, also did not significantly alter the distribution profile. Hence, the induced reduction in binding activity and cellular sensitivity cannot be due to receptor relocalization. The chimeric receptors were able to "cap" rapidly during treatment with Con A, suggesting that they are mobile in the plane of the cell membrane. This capping was not influenced by pretreatment with chemoattractant.