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Nociceptors in peripheral ganglia display a remarkable functional heterogeneity. They can be divided into the following two major classes: peptidergic and nonpeptidergic neurons. Although RUNX1 has been shown to play a pivotal role in the specification of nonpeptidergic neurons, the mechanisms driving peptidergic differentiation remain elusive. Here, we show that hepatocyte growth factor (HGF)-Met signaling acts synergistically with nerve growth factor-tyrosine kinase receptor A to promote peptidergic identity in a subset of prospective nociceptors. We provide in vivo evidence that a population of peptidergic neurons, derived from the RUNX1 lineage, require Met activity for the proper extinction of Runx1 and optimal activation of CGRP (calcitonin gene-related peptide). Moreover, we show that RUNX1 in turn represses Met expression in nonpeptidergic neurons, revealing a bidirectional cross talk between Met and RUNX1. Together, our novel findings support a model in which peptidergic versus nonpeptidergic specification depends on a balance between HGF-Met signaling and Runx1 extinction/maintenance.

Stem/progenitor cell-based therapies hold promises for repairing the damaged nervous system. However, the efficiency of these approaches for neuronal replacement remains very limited. A major challenge is to develop pretransplant cell manipulations that may promote the survival, engraftment, and differentiation of transplanted cells. Here, we investigated whether overexpression of fibroblast growth factor-2 (FGF-2) in grafted neural progenitors could improve their integration in the host tissue. We show that FGF-2-transduced progenitors grafted in the early postnatal rat cortex have the distinct tendency to associate with the vasculature and establish multiple proliferative clusters in the perivascular environment. The contact with vessels appears to be critical for maintaining progenitor cells in an undifferentiated and proliferative phenotype in the intact cortex. Strikingly, perivascular clusters of FGF-2 expressing cells seem to supply immature neurons in an ischemic environment. Our data provide evidence that engineering neural progenitors to overexpress FGF-2 may be a suitable strategy to improve the integration of grafted neural progenitor cells with the host vasculature thereby generating neurovascular clusters with a neurogenic potential for brain repair.

Background: An increasing number of clinical observations suggest adverse neurologic outcome after methylene blue (MB) infusion in the setting of parathyroid surgery. Hence, the aim of the current study was to investigate the potentially neurotoxic effects of MB using a combination of in vivo and in vitro experimental approaches., Methods: Isoflurane-anesthetized adult rats were used to evaluate the impact of a single bolus intravascular administration of MB on systemic hemodynamic responses and on the minimum alveolar concentration (MAC) of isoflurane using the tail clamp test. In vivo, MB-induced cell death was evaluated 24 h after MB administration using Fluoro-Jade B staining and activated caspase-3 immunohistochemistry. In vitro, neurotoxic effects of MB were examined in hippocampal slice cultures by measuring excitatory field potentials as well as propidium iodide incorporation after MB exposure. The impact of MB on dendritic arbor was evaluated in differentiated single cell neuronal cultures., Results: Bolus injections of MB significantly reduced isoflurane MAC and initiated widespread neuronal apoptosis. Electrophysiologic recordings in hippocampal slices revealed a rapid suppression of evoked excitatory field potentials by MB, and this was associated with a dose-dependent effect of this drug on cell death. Dose-response experiments in single cell neuronal cultures revealed that a 2-h-long exposure to MB at non-cell-death-inducing concentrations could still induce significant retraction of dendritic arbor., Conclusions: These results suggest that MB exerts neurotoxic effects on the central nervous system and raise questions regarding the safety of using this drug at high doses during parathyroid gland surgery.

Isoforms of the neuronal cell adhesion molecule (NCAM) carrying the linear homopolymer of alpha 2,8-linked sialic acid (polysialic acid, PSA) have emerged as particularly attractive candidates for promoting plasticity in the nervous system. The large negatively charged PSA chain of NCAM is postulated to be a spacer that reduces adhesion forces between cells allowing dynamic changes in membrane contacts. Accumulating evidence also suggests that PSA-NCAM-mediated interactions lead to activation of intracellular signaling cascades that are fundamental to the biological functions of the molecule. An important role of PSA-NCAM appears to be during development, when its expression level is high and where it contributes to the regulation of cell shape, growth or migration. However, PSA-NCAM does persist in adult brain structures such as the hippocampus that display a high degree of plasticity where it is involved in activity-induced synaptic plasticity. Recent advances in the field of PSA-NCAM research have not only consolidated the importance of this molecule in plasticity processes but also suggest a role for PSA-NCAM in the regulation of higher cognitive functions and psychiatric disorders. In this review, we discuss the role and mode of actions of PSA-NCAM in structural plasticity as well as its potential link to cognitive processes.

Strategies to enhance the capacity of grafted stem/progenitors cells to generate multipotential, proliferative and migrating pools of cells in the postnatal brain could be crucial for structural repair after brain damage. We investigated whether the over-expression of basic fibroblast growth factor 2 (FGF-2) in neural progenitor cells (NPCs) could provide a robust source of migrating NPCs for tissue repair in the rat cerebral cortex. Using live imaging we provide direct evidence that FGF-2 over-expression significantly enhances the migratory capacity of grafted NPCs in complex 3D structures, such as cortical slices. Furthermore, we show that the migratory as well as proliferative properties of FGF-2 over-expressing NPCs are maintained after in vivo transplantation. Importantly, after transplantation into a neonatal ischaemic cortex, FGF-2 over-expressing NPCs efficiently invade the injured cortex and generate an increased pool of immature neurons available for brain repair. Differentiation of progenitor cells into immature neurons was correlated with a gradual down-regulation of the FGF-2 transgene. These results reveal an important role for FGF-2 in regulating NPCs functions when interacting with the host tissue and offer a potential strategy to generate a robust source of migrating and immature progenitors for repairing a neonatal ischaemic cortex.

Pigmented villonodular synovitis, a rare proliferative disease of unknown etiology, is rare in the foot (2% of these lesions). A retrospective review was undertaken of the case histories, radiographs, and imaging results of eight patients treated for pigmented villonodular synovitis of the foot. Pigmented villonodular synovitis was located in the rearfoot in five patients and in the forefoot in the other three. Radiographs in six patients showed bone involvement. Affected bones included the talus, first cuneiform, first and fifth metatarsals, and second phalanx. Treatment was surgical, and only one recurrence was recorded after 24 months. Pigmented villonodular synovitis should be considered in the differential diagnosis of foot tumors.

Administration of subanesthetic concentrations of ketamine, a noncompetitive antagonist of the N-methyl-d-aspartate (NMDA) type of glutamate receptors, is a widely accepted therapeutic modality in perioperative and chronic pain management. Although extensive clinical use has demonstrated its safety, recent human histopathological observations as well as laboratory data suggest that ketamine can exert adverse effects on central nervous system neurons. To further investigate this issue, the present study was designed to evaluate the effects of ketamine on the survival and dendritic arbor architecture of differentiated gamma-aminobutyric acidergic (GABAergic) interneurons in vitro. We show that short-term exposure of cultures to ketamine at concentrations of > or =20 microg/ml leads to a significant cell loss of differentiated cells and that non-cell death-inducing concentrations of ketamine (10 microg/ml) can still initiate long-term alterations of dendritic arbor in differentiated neurons, including dendritic retraction and branching point elimination. Most importantly, we also demonstrate that chronic (>24 h) administration of ketamine at concentrations as low as 0.01 microg/ml can interfere with the maintenance of dendritic arbor architecture. These results raise the possibility that chronic exposure to low, subanesthetic concentrations of ketamine, while not affecting cell survival, could still impair neuronal morphology and thus might lead to dysfunctions of neural networks.

Ketamine is a widely used drug in pediatric anesthesia practice, acting primarily through the blockade of the N-methyl-D-aspartate (NMDA) type of glutamate receptors. A growing body of laboratory evidence, accumulated during the past few years, suggests that this drug could have potential adverse effects on the developing central nervous system. The goal of this short review is to give a brief synopsis of experimental work indicating ketamine-induced developmental neurotoxicity as well as to discuss potential limitations concerning extrapolation of these studies to clinical practice.

In the mammalian brain, ongoing neurogenesis via the rostral migratory stream (RMS) maintains neuronal replacement in the olfactory bulb throughout life. Mechanisms that regulate the final number of new neurons in this system include proliferation, migration and apoptosis. Here we show that the polysialylated isoforms of the neural cell adhesion molecule (PSA-NCAM) act as a pro-survival molecule in immature newborn neurons. Confocal microscopic analysis revealed a threefold increase in TUNEL-positive cells in the subventricular zone (SVZ) and the RMS of transgenic animals lacking the gene encoding NCAM (NCAM(-/-)), as compared with wild types. The enhanced apoptotic cell death occurred specifically in the population of mCD24-positive newborn neurons, but not in GFAP-positive astrocytes. Using in vitro cultures of purified SVZ-derived neurons, we demonstrate that the loss or inactivation of PSA on NCAM, as well as the deletion of NCAM, lead to reduced survival in response to neurotrophins including BDNF and NGF. These changes in cell survival are accompanied by an upregulation of p75 neurotrophin receptor expression in vitro as well as in vivo. Furthermore, the negative effects of PSA-NCAM inactivation on cell survival could be prevented by the pharmacological blockade of the p75 receptor-signaling pathway. We propose that PSA-NCAM may promote survival by controlling the expression of the p75 receptor in developing neurons.

Ketamine, a noncompetitive antagonist of the N-methyl-D-aspartate type of glutamate receptors, was reported to induce neuronal cell death when administered to produce anesthesia in young rodents and monkeys. Subanesthetic doses of ketamine, as adjuvant to postoperative sedation and pain control, are also frequently administered to young children. However, the effects of these low concentrations of ketamine on neuronal development remain unknown. The present study was designed to evaluate the effects of increasing concentrations (0.01-40 microg/ml) and durations (1-96 h) of ketamine exposure on the differentiation and survival of immature gamma-aminobutyric acidergic (GABAergic) interneurons in culture. In line with previous studies (Scallet et al., 2004), we found that a 1-h-long exposure to ketamine at concentrations > or = 10 microg/ml was sufficient to trigger cell death. At lower concentrations of ketamine, cell loss was only observed when this drug was chronically (> 48 h) present in the culture medium. Most importantly, we found that a single episode of 4-h-long treatment with 5 microg/ml ketamine induced long-term alterations in dendritic growth, including a significant (p < 0.05) reduction in total dendritic length and in the number of branching points compared to control groups. Finally, long-term exposure (> 24 h) of neurons to ketamine at concentrations as low as 0.01 microg/ml also severely impaired dendritic arbor development. These results suggest that, in addition to its dose-dependent ability to induce cell death, even very low concentrations of ketamine could interfere with dendritic arbor development of immature GABAergic neurons and thus could potentially interfere with the development neural networks.

A characteristic feature of neurogenic sites in the postnatal brain is the expression of the polysialylated forms of the neural cell adhesion molecule (PSA-NCAM). To investigate the role of PSA-NCAM in generation of neuronal populations, we developed an in vitro model where neurogenesis occurs in primary cortical cultures following serum withdrawal. We show that removal or inactivation of the PSA tail of NCAM in these cultures leads to a significant decrease in the number of newly generated neurons. Similarly, cultures prepared from NCAM knock-out mice exhibit a significantly reduced neurogenesis. Pulse-chase experiments using the proliferation marker BrdU reveal that the lack of PSA does not affect the mitotic rate of neural progenitors but rather, it reduces the early survival of newly generated neurons. These results suggest that, in addition to its role in the migration of neuronal progenitors, PSA-NCAM is required for the adequate survival of these cells.

The involvement of matrix metalloproteinases (MMPs) in cerebral ischemia-induced apoptosis was investigated in a model of transient focal cerebral ischemia in rats treated intracerebroventricularly (i.c.v.) with 4-((3-(4-phenoxylphenoxy)propylsulfonyl)methyl)-tetrahydropyran-4-carboxylic acid N-hydroxy amide, a broad spectrum non-peptidic hydroxamic acid MMP inhibitor, and in MMP-9-deficient mice. Our results showed that MMP inhibition reduced DNA fragmentation by 51% (P < 0.001) and cerebral infarct by 60% (P < 0.05) after ischemia. This protection was concomitant with a 29% reduction of cytochrome c release into the cytosol (P < 0.005) and a 54% reduction of calpain-related alpha-spectrin degradation (P < 0.05), as well as with an 84% increase in the immunoreactive signal of the native form of poly(ADP) ribose polymerase (P < 0.01). By contrast, specific targeting of the mmp9 gene in mice did reduce cerebral damage by 34% (P < 0.05) but did not modify the apoptotic response after cerebral ischemia. However, i.c.v. injection of MMP-9-deficient mice with the same broad-spectrum inhibitor used in rats significantly reduced DNA degradation by 32% (P < 0.05) and contributed even further to the protection of the ischemic brain. Together, our pharmacological and genetic results indicate that MMPs other than MMP-9 are actively involved in cerebral ischemia-induced apoptosis.

Davis and Driver presented evidence suggesting that Kanizsa-type subjective contours could be detected in a visual search task in a time that is independent of the number of nonsubjective contour distractors. A linking connection was made between these psychophysical data and the physiological data of Peterhans and von der Heydt which showed that cells in primate area V2 respond to subjective contours in the same way that they respond to luminance-defined contours. Here in three experiments it is shown that there was sufficient information in the displays used by Davis and Driver to support parallel search independently of whether subjective contours were present or not. When confounding properties of the stimuli were eliminated search became slow whether or not subjective contours were present in the display. One of the slowest search conditions involved stimuli that were virtually identical to those used in the physiological studies of Peterhans and von der Heydt to which Davis and Driver wish to link their data. It is concluded that while subjective contours may be represented in the responses of very early visual mechanisms (eg in V2) access to these representations is impaired by high-contrast contours used to induce the subjective contours and nonsubjective figure distractors. This persistent control problem continues to confound attempts to show that Kanizsa-type subjective contours can be detected in parallel.