The role of the dopaminergic neurotrophin growth/differentiation factor-5 in the developing rat ventral midbrain

Growth differentiation factor-5 (GDF-5) is a member of the transforming growth factor-β superfamily, a family of proteins that play diverse roles in many aspects of cell growth, proliferation and differentiation. GDF-5 has also been shown to be a trophic factor for embryonic midbrain dopaminergic neurons in vitro (Krieglstein et al. 1995) and after transplantation to adult rats in vivo (Sullivan et al. 1998). GDF-5 has also been shown to have neuroprotective and neurorestorative effects on adult dopaminergic neurons in the substantia nigra in animal models of Parkinson’s disease (Sullivan et al. 1997, 1999; Hurley et al. 2004). This experimental evidence has lead to GDF-5 being proposed as a neurotrophic factor with potential for use in the treatment of Parkinson’s disease. However, it is not know if GDF-5 is expressed in the brain and whether it plays a role in dopaminergic neuron development. The experiments presented here aim to address these questions. To that end this thesis is divided into five separate studies each addressing a particular question associated with GDF-5 and its expression patterns and roles during the development of the rat midbrain. Expression of the GDF-5 in the developing rat ventral mesencephalon (VM) was found to begin at E12 and peak on E14, the day that dopaminergic neurons undergo terminal differentiation. In the adult rat, GDF-5 was found to be restricted to heart and brain, being expressed in many areas of the brain, including striatum and midbrain. This indicated a role for GDF-5 in the development and maintenance of dopaminergic neurons. The appropriate receptors for GDF-5 (BMPR-II and BMPR-Ib) were found to be expressed at high levels in the rat VM at E14 and BMPR-II expression was demonstrated on dopaminergic neurons in the E13 mouse VM. GDF-5 resulted in a three-fold increase in the numbers of dopaminergic neurons in cultures of E14 rat VM, without affecting the numbers of neurones or total cells. GDF-5 was found to increase the proportion of neurons that were dopaminergic. The numbers of Nurr1-positive cells were not affected by GDF-5 treatment, but GDF-5 did increase the numbers of Nurr1- positive cells that expressed tyrosine hydroxylase (TH). Taken together this data indicated that GDF-5 increases the conversion of Nurr1-positive, TH-negative cells to Nurr1-positive, TH-positive cells. In GDF-5 treated cultures, total neurite length, neurite arborisation and somal area of dopaminergic were all significantly increased compared to control cultures. Thus this study showed that GDF-5 increased the numbers and morphological differentiation of VM dopaminergic neurones in vitro. In order to examine if GDF-5 could induce a dopaminergic phenotype in neural progenitor cells, neurosphere cultures prepared from embryonic rat VM were established. The effect of the gestational age of the donor VM on the proportion of cell types generated from neurospheres from E12, E13 and E14 VM was examined. Dopaminergic neurons could only be generated from neurospheres which were prepared from E12 VM. Thus in subsequent studies the effect of GDF-5 on dopaminergic induction was examined in progentior cell cultures prepared from the E12 rat VM. In primary cultures of E12 rat VM, GDF-5 increased the numbers of TH-positive cells without affecting the proliferation or survival of these cells. In cultures of expanded neural progenitor cells from the E12 rat VM, GDF-5 increased the expression of Nurr1 and TH, an action that was dependent on signalling through the BMPR-Ib receptor. Taken together, these experiments provide evidence that GDF-5 is expressed in the developing rat VM, is involved in both the induction of a dopaminergic phenotype in cells of the VM and in the subsequent morphological development of these dopaminergic neurons

Expression and function of the neurotrophic factors GDF5 and GDNF in the nigrostriatal system during development and in rat models of Parkinson's disease

Growth/differentiation factor 5 (GDF5) and glial cell line-derived neurotrophic factor (GDNF) are neurotrophic factors that promote the survival of midbrain dopaminergic neurons in vitro and in vivo. Both factors have potent neurotrophic and neuroprotective effects in rat models of Parkinson's disease (PD), and may represent promising new therapies for PD. The aim of the present study was to investigate the endogenous expression and function of GDF5 and GDNF in the nigrostriatal dopaminergic system during development and in rat models of PD. Examination of the temporal expression patterns of endogenous GDF5, GDNF, and their respective receptors, in the developing and adult nigrostriatal dopaminergic system suggest that these factors play important roles in promoting the survival and maturation of midbrain dopaminergic neurons during the period of postnatal programmed cell death. The relative levels of GDF5 and GDNF mRNAs in the midbrain and striatum, and their individual temporal expression patterns during development, suggest that their modes of actions are quite distinct in vivo. Furthermore, the sustained expression of GDF5, GDNF, and their receptors into adulthood suggest roles for these factors in the continued support and maintenance of mature nigrostriatal dopaminergic neurons. The present study found that endogenous GDF5, GDNF, and their receptors are differentially expressed in two 6-hydroxydopamine-induced lesion adult rat models of PD. In both terminal and axonal lesion models of PD, GDF5 mRNA levels in the striatum increased at 10 days post-lesion, while GDNF mRNA levels in the nigrostriatal system decreased at 10 and 28 days post-lesion. Thus, despite the fact that exogenous GDF5 and GDNF have similar effects on midbrain dopaminergic neurons in vitro and in vivo, their endogenous responses to a neurotoxic injury are quite distinct. These results highlight the importance of studying the temporal dynamic changes in neurotrophic factor expression during development and in animal models of PD.

Exploring the relationship between social network sites and the consumption of cultural goods through the lens of affordances

This thesis presents research theorising the use of social network sites (SNS) for the consumption of cultural goods. SNS are Internet-based applications that enable people to connect, interact, discover, and share user-generated content. They have transformed communication practices and are facilitating users to present their identity online through the disclosure of information on a profile. SNS are especially effective for propagating content far and wide within a network of connections. Cultural goods constitute hedonic experiential goods with cultural, artistic, and entertainment value, such as music, books, films, and fashion. Their consumption is culturally dependant and they have unique characteristics that distinguish them from utilitarian products. The way in which users express their identity on SNS is through the sharing of cultural interests and tastes. This makes cultural good consumption vulnerable to the exchange of content and ideas that occurs across an expansive network of connections within these social systems. This study proposes the lens of affordances to theorise the use of social network sites for the consumption of cultural goods. Qualitative case study research using two phases of data collection is proposed in the application of affordances to the research topic. The interaction between task, technology, and user characteristics is investigated by examining each characteristic in detail, before investigating the actual interaction between the user and the artifact for a particular purpose. The study contributes to knowledge by (i) improving our understanding of the affordances of social network sites for the consumption of cultural goods, (ii) demonstrating the role of task, technology and user characteristics in mediating user behaviour for user-artifact interactions, (iii) explaining the technical features and user activities important to the process of consuming cultural goods using social network sites, and (iv) theorising the consumption of cultural goods using SNS by presenting a theoretical research model which identifies empirical indicators of model constructs and maps out affordance dependencies and hierarchies. The study also provides a systematic research process for applying the concept of affordances to the study of system use.

'Muchos Méxicos': widening the lens in Rulfo's cinematic texts

It is difficult to overstate the importance of Juan Rulfo’s two major pieces of fictional narrative work—his haunting, enigmatic novel Pedro Páramo (1955) and his unrelenting depictions of the failures of post-revolutionary Mexico in his short story collection El Llano en llamas (1953). In her foreword to the Margaret Sayers Peden English translation, Susan Sontag hails Pedro Páramo as ‘not only one of the masterpieces of 20th Century world literature, but one of the most influential of the century’s books’. García Márquez has compared the influence of Rulfo on 20th Century world literature to that of Sophocles: ‘No son más de 300 páginas, pero son casi tantas y creo tan perdurables como las que conocemos de Sófocles’ and, completing this oftrepeated triumvirate of recommendations, Jorge Luis Borges has referred to Pedro Páramo as: ‘una de las mejores novelas de las literaturas de lengua hispánica, y aun de la literatura.’ Despite the praise heaped upon Rulfo’s two most famous books, when his third book of fiction, El gallo de oro y otros textos para cine, was finally published in 1980, just six years before his death, it was greeted with almost critical silence. It is precisely this publication that provides the focus of this investigation. The collection contains three texts—El despojo, La fórmula secreta and El gallo de oro. Constituting a third of the fictional work he published in his lifetime, expanding upon themes present in El Llano en llamas and Pedro Páramo while, at the same time, examining new ground, no thematic discussion of Rulfo’s written output is complete without including these texts. Yet they are frequently dismissed. In this way this investigation attempts to go some way towards filling this critical gap in the work of one of the most influential writers of the twentieth century