Les horloges circadiennes, permettant l´anticipation des changements environnementaux cycliques, sont synchronisés par la lumière du jour via un signal lumineux à la rétine. Outre les cônes et les bâtonnets, la rétine contient des cellules ganglionnaires intrinsèquement photosensibles (ipRGCs), subdivisées en sous-types distincts exprimant le pigment mélanopsine et impliquées dans l´entrainement de l´horloge biologique à la lumière. Le système circadien est très similaire chez les animaux nocturnes et diurnes. L'objectif de cette thèse était d'étudier les propriétés morphologiques, moléculaires etphysiologiques des ipRGCs de rongeurs nocturnes (souris) et diurnes (Arvicanthis ansorgei). Ce travail révèle des morphologies comparables des différents types d´ipRGCs pour les deux espèces, mais la proportion du type M1 était plus élevée chez Arvicanthis. Des immunomarquages spécifiques des cellules ganglionnaires de la rétine ont révélé que les ipRGCs constituent une population hétérogène. Chez les deux espèces, l'expression de neurofilaments et de Brn3 différait selon le type d´ipRGC. Les propriétés physiologiques des ipRGCs étaient principalement similaires pour les deux espèces. Chez Arvicanthis, les ipRGCs de type I étaient plus sensibles à de courts éclairs lumineux. En conclusion , les ipRGCs des rongeurs nocturnes et diurnes partagent des caractéristiques communes. Cette étude est la première à décrire la sensibilité des ipRGCs a des éclairs de courte durée. De plus, ce travail étend les connaissances sur l'hétérogénéité moléculaire des différents types d´ipRGCs. / Circadian clocks permit anticipation of cyclic environmental changes and are synchronized to solar day through photic input from the retina. Besides rods and cones, the retina contains intrinsically photosensitive retinal ganglion cells (ipRGCs), consisting of distinct sub-types. IpRGCs express the photopigment melanopsin and are implicated in photoentrainment of the biological clock. Light information shapes the animal’s temporal behavior, but the circadian systems of nocturnal and diurnal animals appear to be very similar. The aim of this thesis was to investigate the morphological, molecular and physiologicalproperties of ipRGCs in nocturnal (C57BL/6 mouse) compared to diurnal (Arvicanthis ansorgei) rodents. The morphological analysis revealed comparable characteristics of the different ipRGC types in both species; however the proportion of M1 cells was higher in Arvicanthis than in mouse. Immunostaining patterns using RGC markers revealed that ipRGCs are a heterogeneous population. In both species, Brn3 and neurofilaments expression were partly distinct between the ipRGC types.The physiological properties of ipRGC types were mostly similar between the two species, but type I ipRGCs were more sensitive to short light flashes in Arvicanthis than in mouse. In conclusion, the melanopsin system of nocturnal and diurnal rodents shares many common features. Importantly, this study is the first describing responses of ipRGCs to short light flashes and the observed molecular heterogeneity extends the characterization of individual ipRGC types.

Pour élucider les effets récompensants de la lumière, deux approches expérimentales ont été adoptées. Une étude chez le rongeur diurne Arvicanthis ansorgei indique que le raccourcissement de la longueur du jour avec la diminution de l'intensité lumineuse induit des changements du rythme de l’activité locomotrice, de la quantité de dopamine dans le système de la récompense et sur l'expression du gène Per2 dans le noyau suprachiasmatique. Ces altérations ont été améliorées par l'exposition journalière à des créneaux d’une heure de lumière à la fin du jour. Dans une étude humaine, le bien-être subjectif mesuré par d'échantillonnage de ressentis, a été corrélée avec des mesures de fluctuations lumineuses environnementales chez des participants en bonne santé et des insomniaques. Les résultats ont montré que le bien-être subjectif augmente proportionnellement à l'intensité de la lumière chez de jeunes en bonne santé contrairement à un déficit global en matière d'évaluation hédonique chez les insomniaques. De plus amples études devraient être menées afin d'élucider l'effet des signaux lumineux environnementaux sur les circuits de récompense. / To elucidate the reward effects of light, two experimental approaches have been adopted. An experiment for the study of the effects of exposure to a winter-like photoperiod on the diurnal rodent Arvicanthis ansorgei indicated that shortened day length with reduced light intensity induces a phase change in locomotor activity, alterations in the dopamine content in reward system structures, and alterations in the Per2 clock gene expression in the suprachiasmatic nucleus. These measures were improved by daily exposure to a one-hour pulse of light at late in the day. In a human model, subjective wellbeing, measured by experience sampling, was correlated with ambient luminosity measurements in participants with insomnia and healthy controls. Results indicated that subjective wellbeing increases with increasing light intensity in healthy young volunteers, in contrast to an overall deficit in reward evaluation in insomniacs. Light exposure should be taken into account as an important factor in determining the quality of life of insomniacs and in depression. Further studies should be conducted to elucidate the effect of ambient light signals on reward circuits.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Within southern Africa, the widely distributed four-striped mouse Rhabdomys is parasitized by, amongst others, the host-specific ectoparasitic sucking louse, Polyplax arvicanthis. The present study investigated this parasite-host association from a phylogenetic and phylogeographic perspective utilizing mitochondrial and nuclear DNA markers. The findings support the existence of four species within Rhabdomys (three distinct lineages within the previously recognized arid-adapted R. pumilio and the mesic-adapted R. dilectus). These species have distinct geographic distributions across vegetational biomes with two documented areas of sympatry at biome boundaries. Ecological niche modelling supports a strong correlation between regional biomes and the distribution of distinct evolutionary lineages of Rhabdomys. A Bayesian relaxed molecular clock suggests that cladogenesis within the genus coincides with paleoclimatic changes (and the establishment of the biomes) at the Miocene-Pliocene boundary. Strong evidence was also found that the sucking louse P. arvicanthis consists of two genetically divergent lineages, which probably represent distinct species. The two lineages have sympatric distributions throughout most of the sampled range across the various host species and also occasionally occur sympatrically on the same host individual. Further, the absence of clear morphological differences among these parasitic lineages suggests cryptic speciation. Limited phylogeographic congruence was observed among the two P. arvicanthis lineages and the various Rhabdomys species and co-phylogenetic analyses indicated limited co-divergence with several episodes of host-switching, despite the documented host-specificity and several other traits predicted to favour congruence and co-divergence. Also, despite the comparatively smaller effective population sizes and elevated mutational rates found for P. arvicanthis, spatial genetic structure was not more pronounced in the parasite lineages compared to the hosts. These findings may be partly attributed to high vagility and social behaviour of Rhabdomys, which probably promoted parasite dispersal among hosts through frequent inter-host contact. Further, the complex biogeographic history of Rhabdomys, which involved cyclic range contractions and expansions, may have facilitated parasite divergence during periods of host allopatry, and host-switching during periods of host sympatry. Intermittent contact among Rhabdomys lineages could also have prevented adaptation of P. arvicanthis to specific host lineages, thus explaining the lack of host-specificity observed in areas of host sympatry. It is thus evident that the association between Polyplax arvicanthis and Rhabdomys has been shaped by the synergistic effects of parasite traits, biogeography, and host-related factors over evolutionary time. / AFRIKAANSE OPSOMMING: Binne suidelike-Afrika word die wyd-verspreide gestreepte veldmuis, Rhabdomys, onder andere deur die gasheer-spesifieke ektoparasitiese luis, Polyplax arvicanthis, geparasitiseer. Die huidige studie het hierdie parasiet-gasheer interaksie vanuit ‘n filogenetiese en filogeografiese oogpunt ondersoek deur van beide mitokondriale en nukluêre merkers gebruik te maak. Die bevindinge dui op die bestaan van vier spesies binne Rhabdomys, waaronder drie nuwe genetiese groepe binne die voorheen erkende R. pumilio asook R. dilectus. Hierdie spesies het nie-oorvleulende geografiese verspreidings binne spesefieke plantegroei biome met twee geidentifiseerde areas van simpatriese voorkoms by bioom grense. Ekologiese nis modellering ondersteun ‘n sterk korrelasie tussen biome en die verspreiding van die evolusionêre groepe binne Rhabdomys. ‘n Bayesiaanse verslapte molekulêre klok dui daarop dat kladoginese binne die genus gedurende paleoklimatiese veranderinge, wat tot die totstandkoming van die huidige biome gelei het, by die Mioseen-Plioseen grens plaasgevind het. Sterk bewyse is ook gevind dat die parasitiese luis P. arvicanthis uit twee geneties verskillende groepe, wat heel moontlik afsonderlike spesies verteenwoordig, bestaan. Hierdie genetiese groepe het simpatriese verspreidings oor meeste van die gebestudeerde geografiese area op die verskeie gasheer spesies en mag ook soms simpatries op dieselfde gasheer individu voorkom. Verder dui die afwesigheid van duidelike morfologiese verskille tusssen die parasiet genetiese groepe op moontlike kriptiese spesiasie. Beperkte filogeografiese ooreenstemming is tussen die P. arvicanthis genetiese groepe en die Rhabdomys spesies waargeneem en die vergelykende-filogenetiese analises het aangedui dat daar beperkte gesementlike-divergensie plaasgevind het met verskeie episodes van gasheer-wisseling, ten spyte van die gasheer-spesifieke aard van die parasiete asook verskeie ander kenmerke wat veronderstel is om filogeografiese ooreenstemming en gesementlike-divergensie te bevorder. Ten spyte van die vergelykbaar kleiner effektiewe bevolking groottes en verhoogde mutasie tempo wat vir P. arvicanthis gevind is, is die geografiese genetiese struktuur nie meer gedifferensieёrd in die parasiet groepe as in die gasheer nie. Hierdie bevindinge mag deels verklaar word deur die hoё beweeglikheid asook die sosiale gedrag van Rhabdomys, wat waarskynlik parasiet beweging tussen gashere bevorder deur gereelde tussen-gasheer kontak. Die komplekse biogeografiese geskiedenis van Rhabdomys, wat sikliese inkrimping en uitsetting van die geografiese verspreiding behels het, het heel moontlik parasiet divergensie tydens tydperke van gasheer allopatrie asook gasheer-wisseling tydens tydperke van gasheer simpatrie, gefasiliteer. Tussentydse kontak tussen Rhabdomys genetiese groepe kon aanpassing van P. arvicanthis tot sekere gasheer genetiese groepe verhoed het en verklaar dus die afwesigheid van waargenome gasheer-spesifisiteit in areas van gasheer simpatrie. Dit is dus duidelik dat die assosiasie tussen P. arvicanthis en Rhabdomys deur die sinergistiese uitwerking van parasiet kenmerke, biogeografie, asook gasheer-verwante faktore oor evolusionêre tyd gevorm is. / National Research Foundation (NRF)

A cutaneous leishmaniasis is the most common clinical form of human disease caused by parasite of the genus Leishmania. They are transmitted between the hosts by haematophagous females of dipteran sand flies of the genus Phlebotomus in the Old World and Lutzomyia in the New World. One of the major agents of cutaneous leishmaniasis in the Old World is Leishmania major. The disease caused by this species is a zoonosis where rodents act as reservoir host. The parasite long time circulates between reservoir rodents and sand flies, while humans are infected only accidentaly in the focus of infection. Rodents of the genus Arvicanthis belongs to the most abundant in the African continent. The genus has evolved in Ethiopia from where it expanded to a major part of Sub - Saharan Africa and the delta of the river Nile. These rodents are very abundant in endemic locations of cutaneous and visceral leishmanias and fulfil many reservoir host criterias including repeated field findings of individuals infected by L. major and another Leishmania species in nature. However, their role in the disease cycle remains to be confirmed. A. neumanni used in this study is an East African species spread from Ethiopia and Somalia to Kenya and Tanzania. Animals were experimentally infected with three different L. major...

La lumière influence fortement la physiologie et le comportement en exerçant des effets non-visuels de deux types : i) indirects, via la resynchronisation de l’horloge centrale qui est située dans les noyaux suprachiasmatiques (NSC), ii) directs, indépendants du processus circadien, via des mécanismes encore mal compris. Nos travaux chez la souris ont montré que l’influence directe de la lumière constitue un mécanisme majeur de régulation du sommeil, de l’éveil et de l’humeur, au même titre que le processus circadien. Ces effets sont majoritairement médiés par la mélanopsine, un photopigment exprimé dans la rétine, et relayés au niveau cérébral par différentes structures comme les NSCs et le VLPO. Ainsi, le rôle des NSCs ne doit pas être interprété qu’au travers de leur fonction d’horloge. Ensuite, dans une perspective de recherche translationnelle de l’animal à l’homme, nous avons validé Arvicanthis ansorgei, comme modèle d’étude du sommeil afin de pouvoir interpréter nos résultats chez un rongeur diurne. Enfin, de nombreuses données suggérant que les effets directs de la lumière modulent l’activité du système dopaminergique, nous avons évalué l’intérêt de la luminothérapie dans des pathologies dopaminergiques (maladie de Parkinson, syndrome des jambes sans repos, troubles de l’humeur). Ces avancées ouvrent de nombreuses perspectives pour une meilleure utilisation de la lumière dans notre société ainsi qu’en pathologie. / Light influences physiology and behavior through both types of non-image-forming effects: i) indirect, synchronizing the circadian master clock located in the suprachiasmatic nucleus (SCN), ii) direct effects, independent from the circadian process though mechanisms poorly understood. Our studies in mice demonstrate that the direct influence of light constitutes a key mechanism of regulation for sleep, alertness and mood and is as important as the circadian process. The direct effects of light are mainly mediated through melanopsin, a retinal photopigment that projects to the different structures of the brain such as the SCN and the VLPO. The SCN, beyond their role as circadian clock are also a relay system for the direct effects of light. Further, we validated Arvicanthis ansorgei as a diurnal model for the study of sleep regulatory mechanisms. This is an important step in the translational approach from animal research to applications in humans. Various data suggest that the direct effects of light interact with the dopaminergic system. In the last part of this thesis, we evaluated the indication of bright light therapy in dopaminergic pathologies (Parkinson disease, restless legs syndrome, mood disorders). These advances open up new perspectives for possible applications of light therapy and may help improving societal lightening conditions.

Leishmaniasis is a human and animal disease caused by digenetic parasites of the genus Leishmania, which is now divided into 4 subgenera - L. (Leishmania), L. (Viannia), L. (Sauroleishmania) and L. (Mundinia). Subgenus Mundinia was established in 2016 and consists of 5 species - L. enriettii and L. macropodum are parasites of wild mammals and L. martiniquensis, L. orientalis and unnamed L. sp. from Ghana are infectious to humans. Mundinia are geographically widely dispersed, their distribution covers all continents, except of Antarctica. Despite phlebotomine sand flies (Diptera: Psychodidae) also biting midges (Diptera: Ceratopogonidae) are supposed to be involved in transmission of these species, which is a unique feature for this subgenus. But there is little to no current information on natural reservoir hosts and vector species for any Mundinia species. In this thesis we tested possible vectors and potential model organisms (Guinea-pigs) and reservoir hosts of Mundinia species by experimental infections. We used 3 sand fly species sharing geographical distribution with respective Mundinia species and available in our laboratory for experimental infections. Sand flies from Australia had never been colonised so we used the permissive vector Lu. migonei for testing development of L. macropodum....