Trophic Signals Research Articles

Hotdogs and Beer: Dietary Nitrosamine Exposure Exacerbates Neurodevelopmental Effects of Ethanol in Fetal Alcohol Spectrum Disorder

In the immature brain, ethanol impairs insulin, insulin-like growth factor (IGF) and other trophic factor signaling, increases cellular stress, and impairs neuronal and glial functions. However, given the phenotypic heterogeneity of fetal alcohol spectrum disorder (FASD), which is not always ethanol dose-dependent, we hypothesized that cofactors modulate spectrum and severity of disease. Herein, we determined if N-nitrosodiethylamine (NDEA) exposures could mimic or exacerbate ethanol's effects on cerebellar development; NDEA is present in processed foods, inhibits insulin signaling, and promotes oxidative injury. Rat pups were binge ethanol (2 g/kg) or vehicle exposed on postnatal day 3 (P3), P5, P7, and P9; and treated with vehicle or NDEA (2 mg/kg) on P7. Ethanol and NDEA disrupted cerebellar foliation and white matter integrity, inhibited expression of oligodendrocyte and astrocyte proteins, and increased expression of ER stress genes. Combined exposures had qualitatively additive effects. Therefore, cofactor exposures can either mimic or influence the phenotypic features of FASD.

Pre-TCRα supports CD3-dependent reactivation and expansion of TCRα-deficient primary human T-cells

Chimeric antigen receptor technology offers a highly effective means for increasing the anti-tumor effects of autologous adoptive T-cell immunotherapy, and could be made widely available if adapted to the use of allogeneic T-cells. Although gene-editing technology can be used to remove the alloreactive potential of third party T-cells through destruction of either the α or β T-cell receptor (TCR) subunit genes, this approach results in the associated loss of surface expression of the CD3 complex. This is nonetheless problematic as it results in the lack of an important trophic signal normally mediated by the CD3 complex at the cell surface, potentially compromising T-cell survival in vivo, and eliminating the potential to expand TCR-knockout cells using stimulatory anti-CD3 antibodies. Here, we show that pre-TCRα, a TCRα surrogate that pairs with TCRβ chains to signal proper TCRβ folding during T-cell development, can be expressed in TCRα knockout mature T-cells to support CD3 expression at the cell surface. Cells expressing pre-TCR/CD3 complexes can be activated and expanded using standard CD3/CD28 T-cell activation protocols. Thus, heterologous expression of pre-TCRα represents a promising technology for use in the manufacturing of TCR-deficient T-cells for adoptive immunotherapy applications.

The Regenerative Role of the Fetal and Adult Stem Cell Secretome.

For a long time, the stem cell regenerative paradigm has been based on the assumption that progenitor cells play a critical role in tissue repair by means of their plasticity and differentiation potential. However, recent works suggest that the mechanism underlying the benefits of stem cell transplantation might relate to a paracrine modulatory effect rather than the replacement of affected cells at the site of injury. Therefore, mounting evidence that stem cells may act as a reservoir of trophic signals released to modulate the surrounding tissue has led to a paradigm shift in regenerative medicine. Attention has been shifted from analysis of the stem cell genome to understanding the stem cell “secretome”, which is represented by the growth factors, cytokines and chemokines produced through paracrine secretion. Insights into paracrine-mediated repair support a new approach in regenerative medicine and the isolation and administration of specific stem cell-derived paracrine factors may represent an extremely promising strategy, introducing paracrine-based therapy as a novel and feasible clinical application. In this review, we will discuss the regenerative potential of fetal and adult stem cells, with particular attention to their secretome.

Purinergic signalling in the reproductive system in health and disease.

There are multiple roles for purinergic signalling in both male and female reproductive organs. ATP, released as a cotransmitter with noradrenaline from sympathetic nerves, contracts smooth muscle via P2X1 receptors in vas deferens, seminal vesicles, prostate and uterus, as well as in blood vessels. Male infertility occurs in P2X1 receptor knockout mice. Both short- and long-term trophic purinergic signalling occurs in reproductive organs. Purinergic signalling is involved in hormone secretion, penile erection, sperm motility and capacitation, and mucous production. Changes in purinoceptor expression occur in pathophysiological conditions, including pre-eclampsia, cancer and pain.

Microenvironment Assessment, Disease Characteristics and Prognosis In HIV-Associated (HIV-cHL) and HIV-Negative Classical Hodgkin Lymphoma: The Influence Of Epstein Barr Virus (EBV)

IntroductionStudies of EBV positive (+) and negative (-) classical Hodgkin lymphoma (cHL) have shown the importance of the immune microenvironment in affecting Reed-Sternberg (hRS) cell survival, proliferation, and biologic behavior. For example, macrophage infiltrates may correlate with inferior disease outcome and survival and proliferation of the hRS cells depends on trophic signals from various inflammatory cells, including CD4+ T cells. The latter finding may explain why HIV-cHL patients (pts) usually present with higher circulating CD4+ T-cell counts (cCD4) compared to HIV-related non-Hodgkin lymphoma. Pathobiologically, HIV-cHL differs from HIV negative cHL (cHL) in that it is nearly always EBV+, has higher numbers of hRS cells, presents with more advanced median stage, exhibits more commonly the mixed cellularity (MC) pattern, and some studies suggest it is more clinically aggressive. To investigate the microenvironment of HIV-cHL and its influence on cHL biology, we assessed the immune cell composition and clinical characteristics of HIV-cHL and compared the findings to those of EBV+ and EBV- cHLs. Methods31 HIV-cHL and 40 cHL (8 EBV+/32 EBV-) cases were identified and corresponding tissue microarrays (TMAs) created. TMAs were evaluated for EBV (EBER), CD30, and microenvironment-associated antigens: PAX5, CD3, CD4, CD8, CD68, CD163 (% positive), TIA1, FOXP3 (relative number 0-4+); the hRS-macrophage microenvironment was evaluated by assessing the number of hRS where >50% of the circumference of the neoplastic cell was associated with CD68+ cells. Results were compared based on HIV status, EBV status (in HIV negative pts), demographics, cCD4 and histology; each was correlated with overall survival. Analyses were performed using non-parametric Fisher's exact test, Kaplan-Meier method and Cox Proportional Hazards model. ResultsM F ratio was 9:1 in the HIV group vs. 1.3:1 in the HIV negative pts (p <0.001). The median cCD4 in the HIV+ pts at HIV-cHL diagnosis was 248 cells/mm3. No differences in age, stage, B symptoms, bulky disease, IPS score, and hRS concentration were found between HIV+ and HIV negative cHLs pts. 7% of cHLs and 33% of HIV-cHLs were classified as MC (p<0.01). 90% of HIV-cHLs were EBV+ compared to 20% of the cHL cases. Statistically significant differences were seen in the number of CD4+ and CD8+ cells between the EBV+ and EBV- cHLs irrespective of HIV status. The only difference among all the immune microenvironment markers observed between EBV+ HIV-cHL and EBV+ cHL cases was that of peri-hRS CD68 cells, which were more abundant in the EBV+ HIV-cHL (Table 1; 51% vs. 30% p<0.005). Similar differences in peri-hRS CD68 staining were observed between the HIV-cHL and all cHL pts. The only deaths in HIV-cHL pts occurred when CD68 was >15% (p<0.05). No statistical differences were noted for OS with respect to cCD4, histologic subtype, race, gender, or HIV status. ConclusionsNo significant differences were observed between HIV-cHL and cHL pts with respect to stage, B symptoms, bulky disease, IPS score, or overall survival, but there were more MC cases in the HIV-cHL cohort. The microenvironment of HIV-cHL and EBV+ cHL is similar, but different from EBV- cHL with respect to percentages of CD163+, PAX5+, CD4+ and CD8+ cells. The location of CD68+ macrophages was the only discordant result between the EBV+ HIV-cHL and EBV+ cHL cohorts. The differences in location of the CD68+ cells, which may be dependent on HIV status, suggests greater influence of these cells on the biologic behavior of the neoplastic process, correlating with poor survival. However, the similarity in the microenvironments in HIV-cHL and EBV+ cHL with respect to CD4, CD8, and CD163 staining implies an important role for EBV on disease biology, as well. Thus, these data suggest that EBV as well as HIV, play prominent roles in determining the immune response and disease behavior in HIV-cHL, warranting further study Disclosures:No relevant conflicts of interest to declare.

A Novel Platform For The Identification Of Stromal-Derived Factors That Enhance Acute Lymphoblastic Leukemia Cell Survival In The Context Of Maintenance Chemotherapy

IntroductionChildhood B-lineage acute lymphoblastic leukemia (ALL) is the most common form of malignancy in children. ALL is highly responsive to intensive, multi-agent chemotherapy, and most children enter remission; 25% of children relapse. Furthermore, cure requires an additional two years of low intensity maintenance chemotherapy with 6-mercaptopurine (6-MP) and methotrexate. It is known that serum levels of maintenance chemotherapy drugs are not highly cytotoxic for ALL cells, and it is thought that bone marrow stromal cells (BM-SC) provide trophic signals to leukemia cells that result in increased resistance to standard therapy. If anti-apoptotic signals from stromal cells to leukemia cells were known, new molecular targets for leukemia therapy could be developed. We are developing a conceptually simple screening system that will identify stromal cell-derived molecules that support ALL cell survival in the setting of 6MP and methotrexate. Our hypothesis is based on the observation that in serum-free conditions, BMSC prevent apoptosis of primary ALL cells. We reason that if we interfere with the production of key BMSC-derived trophic factors, an increase in ALL cell apoptosis in vitro will be seen. MethodsThe system has 3 components: (1) human marrow stromal cells; (2) primary ALL cells (not established cell lines); and (3) siRNAs to knockdown candidate stromal genes. We employ a human mesenchymal stromal cell (MSC) line immortalized with a human TERT gene that has been shown to be representative of primary human stroma. 20,000 BMSC are placed in wells of a 96-well plate and treated with siRNA. 48 hours later, 30,000 primary human ALL cells are added in serum-free media. After 5 days, viable ALL cells are measured by flow cytometry. Results(1) The addition of pharmacological concentrations of 6-MP to BMSC/ALL co-cultures does not significantly increase primary ALL apoptosis. Co-cultures were established as above and 6-MP was added at 1 micromolar. ALL survival was measured at 5 days. No increase in ALL survival was seen in the 6-MP containing cultures. On unmanipulated stroma cultured without 6-MP, 1948.8 (± 397.0) viable ALL cells were recovered; on manipulated stroma in the presence of 6-MP, 1698.5 (±299.3) (p value = 0.12). (2) Interference with stromal cell protein synthesis significantly increases ALL cell apoptosis. We hypothesize that interference with new protein synthesis might reduce stromal support of ALL cells. To test this we treated BMSC for 6 hours with 25 micrograms of G418 which irreversibly blocks polypeptide synthesis. Wells were then washed with serum-free medium. Stromal cells remained viable for up to 1 week. However, ALL cells apoptosis was much higher on such treated stromal cells (32.7±18.5 viable ALL cells on G418-treated stroma versus 1948.8 ± 397.0 on unmanipulated stroma, p value< 0.001)(Figure 1). (3) Interference with global stromal cell RNA transcription significantly increased ALL cell apoptosis. Triptolide is a molecule that irreversibly inhibits RNA transcription. BMSC were treated for 6 hr with 1 microgram triptolide and washed with serum-free medium. Stromal cells remain viable for up to 1 week. ALL cell apoptosis was significantly reduced by triptolide treatment of stroma (not shown in Figure 1). The number of viable ALL cells recovered from triptolide-treated stroma was 252.3±113.2, compared to 996.6±239.2 on unmanipulated stroma (p< 0.001). (4) Knockdown of CXCL12 gene expression in stromal cells signficantly increase ALL cell apoptosis. For proof of principle, we have started with CXCL12, a gene shown in CLL to contribute to leukemia cell survival. BMSC were treated with 0.3 picomolar anti-CXCL12 siRNA for 24 hr. As measured by quantitative RT-PCR, CXCL12 gene transcription was reduced by 80%. Moreover, there was a 53.5% reduction in ALL cell viability in ALL cells co-cultured with CXCL12 siRNA-treated stroma compared to ALL cells co-cultured with untreated stroma (p value< 0.001) (Figure 1). [Display omitted] ConclusionsThis BMSC cell/primary ALL cell system can be used to identify stromal cell genes that prevent apoptosis of primary ALL cells. The simple system can be scaled up to allow high throughput screening of candidate genes that have antagonistic or additive effects to maintenance chemotherapy drugs. Disclosures:No relevant conflicts of interest to declare.

Shake, rattle and roll: bringing a little rock to the IVF laboratory to improve embryo development

Shake, rattle and roll: bringing a little rock to the IVF laboratory to improve embryo development

The Pathobiology of Vascular Dementia

Vascular cognitive impairment defines alterations in cognition, ranging from subtle deficits to full-blown dementia, attributable to cerebrovascular causes. Often coexisting with Alzheimer's disease, mixed vascular and neurodegenerative dementia has emerged as the leading cause of age-related cognitive impairment. Central to the disease mechanism is the crucial role that cerebral blood vessels play in brain health, not only for the delivery of oxygen and nutrients, but also for the trophic signaling that inextricably links the well-being of neurons and glia to that of cerebrovascular cells. This review will examine how vascular damage disrupts these vital homeostatic interactions, focusing on the hemispheric white matter, a region at heightened risk for vascular damage, and on the interplay between vascular factors and Alzheimer's disease. Finally, preventative and therapeutic prospects will be examined, highlighting the importance of midlife vascular risk factor control in the prevention of late-life dementia.

SORLA-Mediated Trafficking of TrkB Enhances the Response of Neurons to BDNF

Stimulation of neurons with brain-derived neurotrophic factor (BDNF) results in robust induction of SORLA, an intracellular sorting receptor of the VPS10P domain receptor gene family. However, the relevance of SORLA for BDNF-induced neuronal responses has not previously been investigated. We now demonstrate that SORLA is a sorting factor for the tropomyosin-related kinase receptor B (TrkB) that facilitates trafficking of this BDNF receptor between synaptic plasma membranes, post-synaptic densities, and cell soma, a step critical for neuronal signal transduction. Loss of SORLA expression results in impaired neuritic transport of TrkB and in blunted response to BDNF in primary neurons; and it aggravates neuromotoric deficits caused by low BDNF activity in a mouse model of Huntington’s disease. Thus, our studies revealed a key role for SORLA in mediating BDNF trophic signaling by regulating the intracellular location of TrkB.

Mesenchymal stromal-cell transplants induce oligodendrocyte progenitor migration and remyelination in a chronic demyelination model

Demyelinating disorders such as leukodystrophies and multiple sclerosis are neurodegenerative diseases characterized by the progressive loss of myelin that may lead toward a chronic demyelination of the brain's white matter, impairing normal axonal conduction velocity and ultimately causing neurodegeneration. Current treatments modifying the pathological mechanisms are capable of ameliorating the disease; however, frequently, these therapies are not sufficient to repress the progressive demyelination into a chronic condition and permanent loss of function. To this end, we analyzed the effect that bone marrow-derived mesenchymal stromal cell (BM-MSC) grafts exert in a chronically demyelinated mouse brain. As a result, oligodendrocyte progenitors were recruited surrounding the graft due to the expression of various trophic signals by the grafted MSCs. Although there was no significant reaction in the non-grafted side, in the grafted regions oligodendrocyte progenitors were detected. These progenitors were derived from the nearby tissue as well as from the neurogenic niches, including the subependymal zone and dentate gyrus. Once near the graft site, the cells matured to myelinating oligodendrocytes. Finally, electrophysiological studies demonstrated that axonal conduction velocity was significantly increased in the grafted side of the fimbria. In conclusion, we demonstrate here that in chronic demyelinated white matter, BM-MSC transplantation activates oligodendrocyte progenitors and induces remyelination in the tissue surrounding the stem cell graft.

Proteomic techniques for characterisation of mesenchymal stem cell secretome

Mesenchymal stem cells (MSCs) are multipotent cells with a substantial potential in human regenerative medicine due to their ability to migrate to sites of injury, capability to suppress immune response and accessibility in large amount from patient's own bone marrow or fat tissue. It has been increasingly observed that the transplanted MSCs did not necessarily engraft and differentiate at the site of injury but might exert their therapeutic effects through secreted trophic signals. The MSCs secrete a variety of autocrine/paracrine factors, called secretome, that support regenerative processes in the damaged tissue, induce angiogenesis, protect cells from apoptotic cell death and modulate immune system. The cell culture medium conditioned by MSCs or osteogenic, chondrogenic as well as adipogenic precursors derived from MSCs has become a subject of intensive proteomic profiling in the search for and identification of released factors and microvesicles that might be applicable in regenerative medicine. Jointly with the methods for MSC isolation, expansion and differentiation, proteomic analysis of MSC secretome was enabled recently mainly due to the extensive development in protein separation techniques, mass spectrometry, immunological methods and bioinformatics. This review describes proteomic techniques currently applied or prospectively applicable in MSC secretomics, with a particular focus on preparation of the secretome sample, protein/peptide separation, mass spectrometry and protein quantification techniques, analysis of posttranslational modifications, immunological techniques, isolation and characterisation of secreted vesicles and exosomes, analysis of cytokine-encoding mRNAs and bioinformatics.

Cholinergic dysregulation in prodromal Alzheimer’s disease

The cholinergic hypothesis of geriatric memory dysfunction led to the development of FDA-approved anticholinesterase drugs to maintain this system in AD patients. The importance of defining the status of the cholinergic basal forebrain cortical projection system in subjects with prodromal AD who are at risk for developing AD continues to be of great clinical and translational interest. The findings presented are derived from molecular and cellular neuropathologic investigations of people who died with a premortem clinical diagnosis of no cognitive impairment (NCI), mild cognitive impairment (MCI) and Alzheimer's disease (AD) as well as from AD transgenic animal studies. Clinical pathologic investigations revealed that CBF neurons maintain their cholinergic neuronal phenotype despite exhibiting pretangles, which correlate with cognitive impairment and an altered ratio of 3 repeat to 4 repeat tau in the MCI brain. Interestingly, the cortical cholinergic system displays an upregulation of choline acetyltransferease (ChAT) activity in the frontal cortex and hippocampus suggesting early reparative mechanisms during prodromal AD. Moreover, despite the early accumulation of amyloid burden in the precuneus component of the default memory network, cholinergic enzyme activity remains stable in MCI and only declines in clinical AD, when PiB binding and soluble beta-amyloid 42 levels are substantially elevated compared to MCI. Moreover, amyloid deposition failed to induce cholinergic cortical neuronal degeneration in APP and triple transgenic mouse models of AD. Increased cortical levels of proNGF and a decrease in TrkA suggest a shift away from cell survival to apoptotic proNGF signaling. Interestingly, this switch to cell death mechanisms did not occur in the hippocampus during prodromal AD. Together these data suggest that CBF system dysregulation is not uniform, the system is neuroplastic, pretangle pathology plays a key role in cognitive impairment, amyloid deposition may not be toxic early on and there is a shift from cell survival to cell death trophic factor signaling in MCI.

Complexity of trophic factor signaling in experimental autoimmune encephalomyelitis: Differential expression of neurotrophic and gliotrophic factors

Soluble factors that promote survival and differentiation of glia and neurons during development are likely to play key roles in neurodegeneration and demyelinating diseases such as multiple sclerosis (MS) and have the potential to be important therapeutic targets. We examined the effect of TrkB signaling and the expression patterns of neurotrophic and gliotrophic factors in the mouse brain in MOG-induced experimental allergic encephalomyelitis (EAE). With induction of mild disease, TrkB heterozygous mice were more severely affected compared to their wild type littermates. However, with more potent disease induction, TrkB heterozygotes fared similar to their wild type littermates, suggesting complex modulatory roles for TrkB signaling. One possible explanation for this difference is that the expression patterns of neurotrophic factors correlate with disease severity in individual mice with mild disease, but not in more severe disease. With the less potent induction in C57BL/6 mice, we found that BDNF was consistently increased at EAE onset, while the soluble gliotrophic factor neuregulin (NRG1) was increased only in the chronic phase of the disease. Treatment of these animals with glatiramer acetate (GA) to decrease disease severity resulted in lower levels of both BDNF and NRG1 expression in some mice at 35days after immunization compared to those in untreated EAE mice, but had no direct effect on these factors in the absence of EAE. Our results suggest a complex interplay between neurotrophic and gliotrophic factors in EAE that is dependent on disease stage and severity. While signaling by BDNF through TrkB is protective in mild disease, this effect was not seen in more severe disease. The late induction of NRG1 in the chronic stage of disease could also worsen disease severity through its known ability to activate microglial, inflammatory pathways. While complex, these studies begin to define underlying axoglial trophic activities that are likely involved in both disease pathogenesis and repair.

Defective Axonal Transport of Rab7 GTPase Results in Dysregulated Trophic Signaling

Retrograde trophic signaling of nerve growth factor (NGF) supports neuronal survival and differentiation. Dysregulated trophic signaling could lead to various neurological disorders. Charcot-Marie-Tooth type 2B (CMT2B) is one of the most common inherited peripheral neuropathies characterized by severe terminal axonal loss. Genetic analysis of human CMT2B patients has revealed four missense point mutations in Rab7, a small GTPase that regulates late endosomal/lysosomal pathways, but the exact pathological mechanism remains poorly understood. Here, we show that these Rab7 mutants dysregulated axonal transport and diminished the retrograde signaling of NGF and its TrkA receptor. We found that all CMT2B Rab7 mutants were transported significantly faster than Rab7(wt) in the anterograde direction, accompanied with an increased percentile of anterograde Rab7-vesicles within axons of rat E15.5 dorsal root ganglion (DRG) neurons. In PC12M cells, the CMT2B Rab7 mutants drastically reduced the level of surface TrkA and NGF binding, presumably by premature degradation of TrkA. On the other hand, siRNA knock-down of endogenous Rab7 led to the appearance of large TrkA puncta in enlarged Rab5-early endosomes within the cytoplasm, suggesting delayed TrkA degradation. We also show that CMT2B Rab7 mutants markedly impaired NGF-induced Erk1/2 activation and differentiation in PC12M cells. Further analysis revealed that CMT2B Rab7 mutants caused axonal degeneration in rat E15.5 DRG neurons. We propose that Rab7 mutants induce premature degradation of retrograde NGF-TrkA trophic signaling, which may potentially contribute to the CMT2B disease.

Calmodulin Kinase IV–dependent CREB activation is required for neuroprotection via NMDA receptor‐PSD95 disruption

NMDA-type glutamate receptors mediate both trophic and excitotoxic signalling in CNS neurons. We have previously shown that blocking NMDAR- post-synaptic density-95 (PSD95) interactions provides significant protection from excitotoxicity and in vivo ischaemia; however, the mechanism of neuroprotection is unclear. Here, we report that blocking PSD-95 interactions with the Tat-NR2B9c peptide enhances a Ca²⁺-dependent protective pathway converging on cAMP Response Element binding protein (CREB) activation. We provide evidence that Tat-NR2B9c neuroprotection from oxygen glucose deprivation and NMDA toxicity occurs in parallel with the activation of calmodulin kinase signalling and is dependent on a sustained phosphorylation of the CREB transcription factor and its activator CaMKIV. Tat-NR2B9c-dependent neuroprotection and CREB phosphorylation are blocked by coapplication of CaM kinase (KN93 and STO-609) or CREB (KG-501) inhibitors, and by siRNA knockdown of CaMKIV. These results are mirrored in vivo in a rat model of permanent focal ischaemia. Tat-NR2B9c application significantly reduces infarct size and causes a selective and sustained elevation in CaMKIV phosphorylation; effects which are blocked by coadministration of KN93. Thus, calcium-dependent nuclear signalling via CaMKIV and CREB is critical for neuroprotection via NMDAR-PSD95 blockade, both in vitro and in vivo. This study highlights the importance of maintaining neuronal function following ischaemic injury. Future stroke research should target neurotrophic and pro-survival signal pathways in the development of novel neuroprotective strategies.

Axonal transport deficits and neurodegenerative diseases

The intracellular transport of organelles along an axon is crucial for the maintenance and function of a neuron. Anterograde axonal transport has a role in supplying proteins and lipids to the distal synapse and mitochondria for local energy requirements, whereas retrograde transport is involved in the clearance of misfolded and aggregated proteins from the axon and the intracellular transport of distal trophic signals to the soma. Axonal transport can be affected by alterations to various components of the transport machinery. Here, we review the current state of knowledge about axonal transport defects that might contribute to the pathogenesis of particular neurodegenerative diseases.

Midbrain Raphe Stimulation Improves Behavioral and Anatomical Recovery from Fluid-Percussion Brain Injury

The midbrain median raphe (MR) and dorsal raphe (DR) nuclei were tested for their capacity to regulate recovery from traumatic brain injury (TBI). An implanted, wireless self-powered stimulator delivered intermittent 8-Hz pulse trains for 7 days to the rat's MR or DR, beginning 4-6 h after a moderate parasagittal (right) fluid-percussion injury. MR stimulation was also examined with a higher frequency (24 Hz) or a delayed start (7 days after injury). Controls had sham injuries, inactive stimulators, or both. The stimulation caused no apparent acute responses or adverse long-term changes. In water-maze trials conducted 5 weeks post-injury, early 8-Hz MR and DR stimulation restored the rate of acquisition of reference memory for a hidden platform of fixed location. Short-term spatial working memory, for a variably located hidden platform, was restored only by early 8-Hz MR stimulation. All stimulation protocols reversed injury-induced asymmetry of spontaneous forelimb reaching movements tested 6 weeks post-injury. Post-mortem histological measurement at 8 weeks post-injury revealed volume losses in parietal-occipital cortex and decussating white matter (corpus callosum plus external capsule), but not hippocampus. The cortical losses were significantly reversed by early 8-Hz MR and DR stimulation, the white matter losses by all forms of MR stimulation. The generally most effective protocol, 8-Hz MR stimulation, was tested 3 days post-injury for its acute effect on forebrain cyclic adenosine monophosphate (cAMP), a key trophic signaling molecule. This procedure reversed injury-induced declines of cAMP levels in both cortex and hippocampus. In conclusion, midbrain raphe nuclei can enduringly enhance recovery from early disseminated TBI, possibly in part through increased signaling by cAMP in efferent targets. A neurosurgical treatment for TBI using interim electrical stimulation in raphe repair centers is suggested.

Anterograde trafficking of neurotrophin-3 in the adult olfactory system in vivo

The olfactory system continuously incorporates new neurons into functional circuits throughout life. Axons from olfactory sensory neurons (OSNs) in the nasal cavity synapse on mitral, tufted and periglomerular (PG) cells in the main olfactory bulb, and low levels of turnover within the OSN population results in ingrowth of new axons under normal physiological conditions. Subpopulations of bulb interneurons are continually eliminated by apoptosis, and are replaced by new neurons derived from progenitors in the adult forebrain subventricular zone. Integration of new neurons, including PG cells that are contacted by sensory axons, leads to ongoing reorganization of adult olfactory bulb circuits. The mechanisms regulating this adaptive structural plasticity are not all known, but the process is reminiscent of early nervous system development. Neurotrophic factors have well-established roles in controlling neuronal survival and connectivity during development, leading to speculation that trophic interactions between OSNs and their target bulb neurons may mediate some of these same processes in adults. A number of different trophic factors and their cognate receptors are expressed in the adult olfactory pathway. Neurotrophin-3 (NT3) is among these, as reflected by beta-galactosidase expression in transgenic reporter mice expressing lacZ under the NT3 promoter. Using a combination of approaches, including immunocytochemistry, real-time PCR of laser-captured RNA, and adenovirus-mediated gene transfer of NT3 fusion peptides in vivo, we demonstrate that OSNs express and anterogradely transport NT3 to the olfactory bulb. We additionally observe that in mice treated with adenovirus encoding NT3 tagged with hemagglutinin (HA), a subset of bulb neurons expressing the TrkC neurotrophin receptor are immunoreactive for HA, suggesting their acquisition of the fusion peptide from infected sensory neurons. Our results therefore provide evidence that OSNs may serve as an afferent source of trophic signals for the adult mouse olfactory bulb.

Diminished trkA receptor signaling reveals cholinergic-attentional vulnerability of aging.

The cellular mechanisms underlying the exceptional vulnerability of the basal forebrain (BF) cholinergic neurons during pathological aging have remained elusive. Here we employed an adeno-associated viral vector-based RNA interference (AAV-RNAi) strategy to suppress the expression of tropomyosin-related kinase A (trkA) receptors by cholinergic neurons in the nucleus basalis of Meynert/substantia innominata (nMB/SI) of adult and aged rats. Suppression of trkA receptor expression impaired attentional performance selectively in aged rats. Performance correlated with trkA levels in the nMB/SI. trkA knockdown neither affected nMB/SI cholinergic cell counts nor the decrease in cholinergic cell size observed in aged rats. However, trkA suppression augmented an age-related decrease in the density of cortical cholinergic processes and attenuated the capacity of cholinergic neurons to release acetylcholine (ACh). The capacity of cortical synapses to release ACh in vivo was also lower in aged/trkA-AAV-infused rats than in aged or young controls, and it correlated with their attentional performance. Furthermore, age-related increases in cortical proNGF and p75 receptor levels interacted with the vector-induced loss of trkA receptors to shift NGF signaling toward p75-mediated suppression of the cholinergic phenotype, thereby attenuating cholinergic function and impairing attentional performance. These effects model the abnormal trophic regulation of cholinergic neurons and cognitive impairments in patients with early Alzheimer's disease. This rat model is useful for identifying the mechanisms rendering aging cholinergic neurons vulnerable as well as for studying the neuropathological mechanisms that are triggered by disrupted trophic signaling.

Intrinsically determined cell death of developing cortical interneurons

Cortical inhibitory circuits are formed by GABAergic interneurons, a cell population that originates far from the cerebral cortex in the embryonic ventral forebrain. Given their distant developmental origins, it is intriguing how the number of cortical interneurons is ultimately determined. One possibility, suggested by the neurotrophic hypothesis1-5, is that cortical interneurons are overproduced, and then following their migration into cortex, excess interneurons are eliminated through a competition for extrinsically derived trophic signals. Here we have characterized the developmental cell death of mouse cortical interneurons in vivo, in vitro, and following transplantation. We found that 40% of developing cortical interneurons were eliminated through Bax- (Bcl-2 associated X-) dependent apoptosis during postnatal life. When cultured in vitro or transplanted into the cortex, interneuron precursors died at a cellular age similar to that at which endogenous interneurons died during normal development. Remarkably, over transplant sizes that varied 200-fold, a constant fraction of the transplanted population underwent cell death. The death of transplanted neurons was not affected by the cell-autonomous disruption of TrkB (tropomyosin kinase receptor B), the main neurotrophin receptor expressed by central nervous system (CNS) neurons6-8. Transplantation expanded the cortical interneuron population by up to 35%, but the frequency of inhibitory synaptic events did not scale with the number of transplanted interneurons. Together, our findings indicate that interneuron cell death is intrinsically determined, either cell-autonomously, or through a population-autonomous competition for survival signals derived from other interneurons.