CREB signalling regulates early survival, neuronal gene expression and morphological development in adult subventricular zone neurogenesis.

Neural stem cells in the subventricular zone (SVZ) of the lateral ventricles give rise to new interneurons of the olfactory bulb (OB) throughout life. SVZ/OB neurogenesis is influenced by olfactory network activity, which modulates the survival of new neurons during their integration into the OB network. Previous work suggested that such activity-dependent survival is regulated via the CREB signalling pathway. Curiously, CREB signalling is already active during the early developmental stages of adult SVZ/OB neurogenesis. To investigate the role of cell autonomous CREB signalling during early stages of adult SVZ/OB neurogenesis, we ablated CREB-pathway activity in the SVZ/OB neurogenic lineage using a retroviral strategy. Surprisingly, loss of CREB signalling resulted in increased cell death and loss of expression of the neurogenic transcription factor Pax 6, and of a subset of neuronal proteins in migrating neurons of the RMS. Moreover, post-migratory neurons in the OB displayed impaired dendritic development. These results demonstrate an essential role for CREB signalling in maturation of newborn neurons in the OB and uncover a novel role for CREB signalling in the survival and maintenance of neuronal gene expression during the early stages of SVZ/OB neurogenesis.

Epigenetic regulation of neurogenesis in the adult hippocampus.

The dentate gyrus of the hippocampus is an exception to a 'neurogenesis-unfriendly' environment of the adult brain. New functional neurons generated in this region contribute to learning and mood regulation, and thus represent a unique form of neural plasticity. The rate of hippocampal neurogenesis significantly changes on physiological or pathological influences, such as physical activity, environmental enrichment, stress, and aging. We suggest that epigenetic mechanisms could be sensors of environmental changes and fine modulators of adult hippocampal neurogenesis. Here, we examine the role of DNA methylation and methylation of core histones mediated by the Polycomb and Trithorax complexes in the regulation of adult neurogenesis. Given the recent surprising discovery of dynamic and reversible DNA methylation in the hippocampus, we speculate regarding its regulation and its role in adult neurogenesis.

Survival and differentiation of adult rat-derived neural progenitor cells transplanted to the striatum of hemiparkinsonian rats.

We investigated the survival, distribution and differentiation capabilities of adult rat hippocampus-derived progenitor cells (AHPs) by grafting them into either the intact or dopamine (DA)-denervated adult rat striatum (ST). Furthermore, we tested the effects of the in vivo administration of retinoic acid (RA) on the differentiation of the grafted cells. AHPs, prelabeled in vitro with bromodeoxyuridine (BrdU) and primed with RA, were transplanted bilaterally into the ST of hemiparkinsonian rats. Twenty animals were divided in four groups: three groups received i.p. injections of RA (1.5 mg/kg/day) for 1, 2 or 4 weeks and one group received vehicle injections for 4 weeks. Approximately 60% of the implanted BrdU-immunoreactive (BrdU+) cells were present in either intact or lesioned ST after 5 weeks of transplantation, with a striking widespread radial distribution from the implantation site. The cells became morphologically integrated with the surrounding host tissue, with no evidence of tumor formation. Approximately 18% of the BrdU+ cells were immunoreactive for the glial precursor marker NG2 and occasionally BrdU+ cells co-expressed the neuronal marker TuJ1. This differentiation pattern was similar in the intact and DA-denervated ST. Although further research is needed to find more adequate methods to drive the differentiation of these cells toward the desired phenotypes, the survival, differentiation potential and widespread distribution throughout the ST observed in this study suggest that AHPs may be useful in treatment of degenerative disorders affecting the nervous system.

Sonic hedgehog facilitates dopamine differentiation in the presence of a mesencephalic glial cell line.

The aim of this study was to establish a cellular system to investigate the requirement for cell surface and diffusible molecules in the differentiation of fetal mesencephalic cells toward the dopamine lineage. Toward this end, we immortalized rat embryonic day 14 (E14) mesencephalon with a regulatable retroviral vector encoding v-myc. The stably transduced cells were pooled and designated as VME14 cells. VME14 cells proliferated rapidly, stopped proliferating, extended processes, and expressed GFAP after suppression of the v-myc expression with tetracycline, suggesting that VME14 cells differentiated into glial cells. Dissociated cells derived from the E11 rat mesencephalon gave rise to only a small number of tyrosine hydroxylase (TH)-positive neurons. However, when grown on a monolayer of the differentiated VME14 cells, a significantly higher number of cells differentiated into TH-positive neurons. VME14 cells were transduced with the secreted N-terminal cleavage product of the Sonic hedgehog gene (SHH-N), an inducer of mesencephalic dopaminergic neurons. This monoclonal, SHH-N-overexpressing cell line further enhanced dopaminergic differentiation of E11 rat mesencephalon cells. Thus, SHH-N and signals derived from fetal mesencephalic glia act cooperatively to facilitate dopaminergic differentiation. These fetal mesencephalon-derived cell lines will provide tools for the study of signals involved in dopaminergic differentiation.

CNTF and its receptor subunits in human gliomas.

Ciliary neurotrophic factor (CNTF) promotes the survival of various neuronal cell populations. It is produced by astrocytes and influences the development and differentiation of glial cells. CNTF and related neuropoietic cytokines affect growth and differentiation of various neoplasms. Moreover, they induce the reactive transformation of astrocytes (gliosis) and influence growth and differentiation of neuroectodermal tumor cell lines in vitro. However, their role in gliomas is largely unknown. We studied the expression of CNTF and its receptor subunits in human astrocytomas and glioblastomas. In more than 95% of the tumors, CNTF transcripts were found by RNAase protection assay; in more than 80% of the cases, tumor cells were CNTF immunoreactive. CNTF receptor alpha (CNTFR alpha), the specific component of the tripartite CNTF receptor system, was detectable by Northern blot analysis in 80% of the cases. In situ hybridization revealed CNTFR alpha mRNA in the cytoplasm of neoplastic cells. Transcripts of the remaining two components of the CNTF receptor system, gp130 and LIFR beta, were found by Northern blotting in 83% and 70% of the tumors, respectively. Simultaneous expression of CNTF and all its receptor components was detected in approximately half of the tumors. These results indicate that CNTF and its receptor components are expressed by human glioma cells. The simultaneous expression of ligands and receptor subunits suggests that CNTF might act on human glioma cells via an auto- or paracrine mechanism.

Increased expression of CNTF receptor alpha in denervated human skeletal muscle.

The functional receptor for ciliary neurotrophic factor (CNTF) is comprised of a CNTF binding entity termed CNTF receptor alpha (CNTFRalpha), and 2 signaling molecules called LIF receptor beta and gp130. CNTFRalpha can be released from the cell surface; the soluble form can confer CNTF responsiveness to cells. CNTFRalpha has recently been localized to several nonneuronal cell types including rat skeletal muscle fibers. In this study we examined the expression pattern of CNTFRalpha in normal, denervated and dystrophic human muscle. In muscle biopsies from 12 normal subjects, 16 cases of neurogenic muscular atrophy, 4 cases of Duchenne muscular dystrophy, and 4 cases of limb girdle dystrophy, CNTFRalpha mRNA levels were determined by Northern blotting. Transcript levels were significantly increased in cases of neurogenic atrophy compared to normal controls and dystrophic muscle. By nonradioactive in situ hybridization, CNTFRalpha transcripts were detected in the sarcoplasm of both normal sized and atrophic muscle fibers. In addition, soluble CNTFRalpha was elevated 4.4-fold in the urine of ALS patients compared to normal adults. These results suggest that the expression of CNTFRalpha in human skeletal muscle fibers is regulated by innervation. This regulation appears to be selective, because CNTFRalpha mRNA was not increased in dystrophic human muscle. Increased CNTFRalpha could confer higher sensitivity to CNTF during neurodegeneration or nerve fiber regeneration.

GDNF expression is increased in denervated human skeletal muscle.

Glial cell line derived neurotrophic factor (GDNF) is a potent trophic factor for several subpopulations of neurons including motor neurons. Two different transcripts of the GDNF gene (GDNF633 and GDNF555) have been detected in various tissues, including skeletal muscle. Denervation leads to an upregulation of GDNF633 in rat skeletal muscle, indicating that GDNF is involved in the response of skeletal muscle to denervation and possibly in reinnervation. To determine the role of GDNF in human neuromuscular disease, we investigated the expression of both transcripts in normal and denervated muscle and in muscle biopsies from Duchenne muscular dystrophy patients. GDNF expression levels were analyzed by competitive RT-PCR in 38 muscle specimens. Levels of both transcripts were significantly elevated in denervated muscle compared to normal and dystrophic muscle. Morphometric analysis of muscle-fiber calibers and its correlation to GDNF expression revealed that higher levels of GDNF were expressed in rapidly-progressive neurogenic atrophy, including four amyotrophic lateral sclerosis (ALS) cases, compared to cases of chronic atrophy. In dystrophic muscle, transcript levels were not significantly altered compared to normal controls. These data indicate that denervation, but not dystrophy, enhances GDNF expression in human skeletal muscle. Thus, the increase of GDNF expression is part of the reaction of human skeletal muscle to denervation caused by motor nerve lesion. GDNF might act on regenerating nerve fibers during muscle fiber reinnervation.

Psychogeriatrics and general practice in Australia.

We describe the interface between general practice and psychogeriatrics in Australia. While aged care services are complex and there are serious deficiencies in the management of the elderly, several initiatives appear set to improve the level of care. Economic considerations, mutual education of general practitioners and psychogeriatricians, and social factors are strong determinants of good primary care of the mental health needs of older people.