Untersuchung des Effektes der Leukotrienbiosynthesehemmung nach experimentellem Schädel-Hirn-Trauma

Gegenstand der Dissertationsschrift ist die Untersuchung des Effektes einer Hemmung der Leukotrienbiosynthese auf die Entwicklung des Schädel-Hirn-Traumas (SHT) nach experimenteller fokaler Kontusionsverletzung im Rattenmodell. Die Ergebnisse der Arbeit wurden im Jahre 2011 in einer Publikation veröffentlicht. Das SHT ist eine schwerwiegende globale Erkrankung mit hoher Inzidenz und Mortalität. Diese führt zu hohen Kosten für das Gesundheitssystem, zum einen durch die akute Behandlung im Krankenhaus, zum anderen durch die sich daran anschließenden rehabilitativen Maßnahmen. Nach der primär biomechanischen Verletzung des Hirns, die nicht beeinflussbar ist, bietet die anschließende sekundäre Hirnschädigung aufgrund verschiedener Stoffwechselprozesse Angriffspunkte für eine (medikamentöse) Therapie des SHT. Die sekundären Hirnschäden werden maßgeblich durch die Entwicklung eines perikontusionellen Hirnödems und dem daraus resultierenden Anstieg des intrakraniellen Druckes beeinflusst. Wie in vorangegangenen Untersuchungen gezeigt werden konnte, kam es nach experimentellem SHT zu einem signifikanten Anstieg der Leukotrienwerte im Liquor von Ratten. Dies warf die Frage nach der Rolle der Leukotriene (LT) im posttraumatischen Hirnstoffwechsel bezüglich der Ödementwicklung auf. Ziel dieser Arbeit war der Nachweis einer direkten Beteiligung von Leukotrienen an der sekundären Hirnschädigung und das Aufzeigen eines möglichen therapeutischen Zuganges durch Substitution von Leukotrienbiosynthesehemmern. Dafür wurde bei adulten Ratten ein fokales SHT induziert. Anschließend wurden in zwei Therapiegruppen zwei unterschiedlich wirkende Leukotrieninhibitoren mehrmalig oral verabreicht und die Ausprägung des SHTs nach 24 bzw. 72 Stunden mittels Magnetresonanztomographie (MRT) und immunhistochemischen Aufarbeitung der Hirne mit einer nicht therapierten Kontrollgruppe verglichen. Bei einem dieser LT-Inhibitoren handelte es sich um ein Weihrauchpräparat, das als Nahrungsergänzungsmittel bereits zu erhalten ist und somit auch potentiell am Menschen zur Anwendung kommen kann. Die Ergebnisse waren vielversprechend und zeigten in beiden Therapiegruppen ein verringertes Kontusionsvolumen im MRT und immunhistochemisch einen geringeren Verlust von Neuronen im perikontusionellen Bereich. Somit scheinen Leukotriene einen Anteil an den sekundären Schädigungsprozessen nach SHT zu tragen. Weitere Untersuchungen, vor allem bezüglich eines eventuell verbesserten klinischen Outcome durch Leukotrienbiosynthesehemmung, erscheinen sinnvoll um den potentiellen Einsatz von LT-Synthesehemmstoffen in der Therapie des SHT in Erwägung ziehen zu können.:1. Abkürzungsverzeichnis 2. Bibliographische Beschreibung 3. Einleitung: Schädel-Hirn-Trauma 3.1. Einteilung 3.2. Epidemiologie 3.3 Klinik und Therapie 3.4 Posttraumatisches Hirnödem 3.5 Experimentelles Schädel-Hirn-Trauma 3.6 Leukotriene, MK886 und Boscari 4. Originalpublikation 5. Zusammenfassung der Arbeit 6. Referenzen 7. Anlagen 7.1 Erklärung über die eigenständige Abfassung der Arbeit 7.3 Danksagun

An example of burrow system architecture of dispersing Damaraland mole-rats

The Damaraland mole-rat (Fukomys damarensis) is a social, subterranean rodent that occurs in the red Kalahari sands. This species exhibits extreme reproductive skew with a single breeding female whereas reproduction in subordinate group members is completely blocked. Rainfall, as it greatly facilitates burrowing, provides the opportunity for individuals to disperse from their natal colony and hence, to overcome reproductive suppression. However, because rainfall is scarce, optimal conditions for burrow system construction are restricted to very short periods of the year. In order to observe the construction of a new burrow system of dispersing individuals, I released a small group (two females, one male) following heavy rains, and monitored their burrowing activity in the form of mound production during the following weeks. Recapture revealed that a new male had joined the group. Over a period of one month the four individuals extruded 127 mole hills and constructed a tunnel system with a total length of approximately 100 metres. Mound production ceased after 30 days due to the lack of subsequent rain. The study provides an example of dispersal in Damaraland mole-rats and gives new insights into the method of burrow system construction of this species. It further highlights the high costs associated with dispersal.http://africanzoology.journals.ac.za/am2014ab201

Gnrh mRNA expression in the brain of cooperatively breeding female Damaraland mole-rats

The Damaraland mole-rat (Fukomys damarensis) is a eusocial, subterranean rodent, in which breeding is limited to a single reproductive pair within each colony. Non-reproductive females, while in the confines of the colony, exhibit socially-induced infertility. Anovulation is thought to be caused by a disruption in the normal gonadotropin-releasing hormone (GnRH) secretion from the hypothalamus. In order to assess whether social suppression is associated with altered GnRH mRNA expression in the brain we investigated the distribution and gene expression levels by means of in situ hybridization in female breeders and nonbreeders from field captured colonies of the Damaraland mole-rat. We found expression of GnRH mRNA as a loose network in several forebrain areas of female Damaraland mole-rats with the majority of labelling in the preoptic and anterior hypothalamus. The distribution matched previous findings using immunocytochemistry in this and other social mole-rat species. Quantification of the hybridisation signal revealed no difference between breeding and non-breeding females in the average optical density of the hybridization signal and the size of the total area covered by GnRH mRNA. However, analysis along the rostro-caudal axis revealed significantly elevated GnRH mRNA expression in the rostral preoptic region of breeders compared to non-breeders, while the latter had increased GnRH mRNA expression at the caudal level of the anterior hypothalamus. This study indicates that social suppression affects the expression of GnRH mRNA in female Damaraland mole-rats. Furthermore, differential regulation occurs within different neuron subpopulations.This work was supported by a fellowship from the University of Pretoria to CV. We are grateful to the DST-NRF for funding to NB.http://www.reproduction-online.org2018-04-30hb2017Zoology and Entomolog

Reproductive status-dependent dynorphin and neurokinin B gene expression in female Damaraland mole-rats

Damaraland mole rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals, which exhibit high reproductive skew. Reproduction is monopolized by the dominant female of the group, while subordinates are physiologically suppressed. The blockade of reproduction results from an inhibition of ovulation, which is caused by inadequate secretion of luteinizing hormone (LH) from the pituitary, which in turn might be brought about by a disruption of the normal GnRH secretion from the hypothalamus. The neuropeptides dynorphin and neurokinin B are expressed together with kisspeptin in a subpopulation of neurons in the arcuate nucleus (ARC). This neuron population is termed KNDy neurons and is considered to constitute the GnRH pulse generator. To assess whether dynorphin (encoded by the Pdyn gene) and neurokinin B (NKB, encoded by the Tac3 gene) are involved in the mechanism of reproductive suppression we investigated the distribution and gene expression of Pdyn and Tac3 by means of in situ hybridisation in wild-caught female Damaraland mole-rats with different reproductive status. In both reproductive phenotypes, substantial Pdyn expression was found in several brain regions of the telencephalon including the cerebral cortex, the striatum, the hippocampus, the amygdala and the olfactory tubercle. Within the hypothalamus Pdyn expression occurred in the paraventricular nucleus, the dorsomedial nucleus, the supraoptic nucleus, the ventromedial nucleus and the ARC. Prominent Tac3 expression was found in the habenula, the bed nucleus of the stria terminalis, the cerebral cortex, the striatum, the hippocampus, the amygdala, the dorsomedial nucleus, the ARC and the lateral mammillary nucleus. Quantification of the gene expression levels in the ARC revealed decreased Pdyn and increased Tac3 expression in breeding compared to nonbreeding females. This suggests that both neuropeptides play a role in the regulation of reproduction in Damaraland mole-rats. Their exact role in mediating the inhibition of GnRH release in nonbreeding females remains to be determined.The University of Pretoria to CV and funding from the DST-NRF to NB.http://www.elsevier.com/locate/jchemneu2020-12-01hj2020Zoology and Entomolog

Reproductive status affects the expression of prolactin receptor mRNA in the brain of female Damaraland mole-rats

The eusocial Damaraland mole-rat (Fukomys damarensis) represents an extreme example of reproductive skew, in that reproduction is completely blocked in female subordinate group members. It is thought that in these animals normal GnRH secretion from the hypothalamus is disrupted. Prolactin, a peptide hormone secreted from the anterior pituitary gland, has been implicated in a wide variety of functions. Well documented in rodents is its role in mediating lactational infertility. Elevated circulating prolactin levels, such as during lactation, are associated with reduced GnRH release into the portal blood and with a reduction in the frequency and amplitude of LH pulses. The present study aimed at investigating whether such a mechanism could act in reproductively suppressed female Damaraland mole-rats. By means of in situ hybridisation we studied the distribution and gene expression of the prolactin receptor (Prlr) in wild-caught female Damaraland mole-rats with different reproductive status. Substantial Prlr expression was found in several brain regions, with highest levels in the choroid plexus and moderate expression in the preoptic and tuberal hypothalamus. While in reproductive and non-reproductive females plasma prolactin levels were very low and not significantly different, quantification of the Prlr hybridisation signal revealed significant differences in relation to reproductive status. Reproductively suppressed females had increased expression of Prlr in the choroid plexus and in the arcuate nucleus (ARC) when compared to reproductive females. This suggests higher local prolactin levels in the brain of suppressed females. Together with previous findings, it could indicate that prolactin inhibits ARC kisspeptin neurons, which then would lead to reduced activation of GnRH neurons in such females.A fellowship from the University of Pretoria to CV and funding from the DST-NRF to NB.http://www.elsevier.com/locate/jchemneu2019-12-01hj2018Zoology and Entomolog

Reproductive status‐dependent kisspeptin and RFamide‐related peptide (Rfrp) gene expression in female Damaraland mole‐rats

Damaraland mole rats (Fukomys damarensis) are cooperatively breeding, subterranean mammals that exhibit a high reproductive skew. Reproduction is monopolised by the dominant female of the group, whereas subordinates are physiologically suppressed to the extent that they are anovulatory. In these latter animals, it is assumed that normal gonadotropin‐releasing hormone secretion from the hypothalamus is disrupted. The RFamide peptides kisspeptin (Kiss1) and RFamide‐related peptide‐3 (RFRP‐3) are considered as potent regulators of gonadotropin release. To assess whether these neuropeptides are involved in the mechanism of reproductive suppression, we investigated the distribution and gene expression of Kiss1 and Rfrp by means of in situ hybridisation in wild‐caught female Damaraland mole‐rats with different reproductive status. In both reproductive phenotypes, substantial Kiss1 expression was found in the arcuate nucleus and only few Kiss1‐expressing cells were detected in the anteroventral periventricular nucleus (AVPV), potentially as a result of low circulating oestradiol concentrations in breeding and nonbreeding females. Rfrp gene expression occurred in the dorsomedial nucleus, the paraventricular nucleus and the periventricular nucleus. While in female breeders and nonbreeders, plasma oestradiol levels were low and not significantly different, quantification of the hybridisation signal for both genes revealed significant differences in relation to reproductive status. Reproductively active females had more Kiss1‐expressing cells and a higher number of silver grains per cell in the arcuate nucleus compared to nonreproductive females. This difference was most pronounced in the caudal part of the nucleus. No such differences were found in the AVPV. Furthermore, breeding status was associated with a reduced number of Rfrp‐expressing cells in the anterior hypothalamus. This reproductive status‐dependent expression pattern of Kiss1 and Rfrp suggests that both neuropeptides play a role in the regulation of reproduction in Damaraland mole‐rats. Enhanced long‐term negative feedback effects of oestradiol could be responsible for the lower Kiss1 expression in the arcuate nucleus of reproductively suppressed females.A fellowship from the University of Pretoria to CV and the DST-NRF for funding to NB.http://wileyonlinelibrary.com/journal/jne2019-03-18hj2018Zoology and Entomolog

Breeding status affects the expression of androgen and progesterone receptor mRNA in the brain of male Damaraland mole-rats

The eusocial Damaraland mole-rat (Fukomys damarensis) represents an extreme example of reproductive skew, in that reproduction is completely blocked in female subordinate group members. Similarly, male subordinates within the colony show no sexual behaviour. In contrast to females, however, non-reproductive males have functional gonads and do not differ in circulating levels of pituitary hormones and testosterone from reproductive males. Nevertheless, they have reduced numbers of follicle-stimulating hormone receptors in their testes and they produce fewer spermatozoa with a large proportion of immature spermatozoa and precursors. To understand the mechanism of reproductive suppression operational in subordinate males we studied the expression of androgen and progesterone receptor genes in forebrain regions involved in the control of reproductive behaviour in male breeders and nonbreeders from intact colonies. While it is well documented that testosterone activates maletypical behaviour, the role of progesterone in this process is less clear as previous studies have produced contradictory results. We found expression of androgen receptor (AR) and progesterone receptor (PGR) genes in several forebrain regions of male Damaraland molerats. The distribution of AR in males matches our previous findings in females. This is the first report showing the distribution of PGR in mole-rats. We found PGR in all areas which were also sensitive to androgens and estrogens. Analysis of the optical densities of the AR and PGR hybridisation signal revealed that breeding males had increased expression of AR and PGR compared to non-breeders in most brain regions examined, which include the medial preoptic area, the bed nucleus of the stria terminalis, the ventromedial nucleus of the hypothalamus, the arcuate nucleus and the medial amygdala. These status-related differences were more pronounced for PGR than for AR. This study shows that breeding position affects the neuroendocrine phenotype of male Damaraland mole-rats. Further, it suggests that androgens and progesterone might act synergistically in activating sexual behaviour in males.A fellowship from the University of Pretoria to CV and funding from the DST-NRF to NB.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-79982017-03-31hb2016Mammal Research InstituteZoology and Entomolog

Hatching late in the season requires flexibility in the timing of song learning

Most songbirds learn their songs from adult tutors, who can be their father or other male conspecifics. However, the variables that control song learning in a natural social context are largely unknown. We investigated whether the time of hatching of male domesticated canaries has an impact on their song development and on the neuroendocrine parameters of the song control system. Average age difference between early- and late-hatched males was 50 days with a maximum of 90 days. Song activity of adult tutor males decreased significantly during the breeding season. While early-hatched males were exposed to tutor songs for on average the first 99 days, late-hatched peers heard adult song only during the first 48 days of life. Remarkably, although hatching late in the season negatively affected body condition, no differences between both groups of males were found in song characteristics either in autumn or in the following spring. Similarly, hatching date had no effect on song nucleus size and circulating testosterone levels. Our data suggest that late-hatched males must have undergone accelerated song development. Furthermore, the limited tutor song exposure did not affect adult song organization and song performance.http://rsbl.royalsocietypublishing2016-08-30hb2016Zoology and Entomolog