Understanding bladder pain syndrome: characterization of chronic pelvic pain animal models

• Main Author: Pereira, Mariana Santos
• Publication Date: 2022
• Format: Master thesis
• Language: eng
• Source: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Download full: http://hdl.handle.net/10773/36526
• topic: Bladder Pain Syndrome; Chronic pain; Systemic syndrome; Phenotypes; Central nervous system; Pain behaviour; Animal modeling

Bladder Pain Syndrome is a debilitating chronic pain condition that is currently difficult to diagnose and treat due to the lack of consensus on the aetiology, definition, and management. In the past, the Bladder Pain Syndrome was recognized as a bladder-centred disease. However, several evidence have been indicating that this disease might be a systemic syndrome involving centrally mediated mechanisms and that it can manifest itself in different phenotypes. These different phenotypes might explain why the existent treatments are not universally effective. There is no single animal model capable of reproducing all these phenotypes. Thus, a better approach to improve the study of the Bladder Pain Syndrome and find more successful treatments to this disease involves to understand the pathophysiological mechanisms underlying each phenotype by using the animal models that show a phenotype more similar to each subgroup of patients. In this sense, in the current work we performed the cellular and molecular characterization of two brain structures known to be involved in chronic pain development, the insula and the hippocampus, in two systemic models of this disease, the Water Avoidance Stress Model and the Maternal Deprivation Model. In addition, we aimed to understand how the changes in these brain regions might be associated with animals pain behaviour. To establish a rat model of Water Avoidance stress, adult female Wistar rats were daily placed, during 10 consecutive days, for a period of 1 hour, on pedestals in the centre of cages filled with water. To establish the rat model of Maternal Deprivation, female Wistar pups were daily separated from their mother and their littermates for a period of 1 hour, during 14 consecutive days. Changes in microglia cells density, morphology and phagocytic activity were assessed in the granular and dysgranular areas of the insula and on the CA1 region of the hippocampus of the animals by immunofluorescence staining using the markers Iba1 and CD68. Changes in the mRNA expression levels of the markers Iba1, CD68, Olig2, Sst, GFAP, CCR2, c-fos, Pdyn and TNF-α were assessed in animals insula by quantitative real-time PCR using TaqMan probes. Thermal hyperalgesia and mechanical allodynia were also evaluated in the animals, by the Hargreaves test and the Von Frey test, respectively. Animals submitted to Water Avoidance Stress exhibited decreased mRNA expression levels of the markers Pdyn, Olig2 and GFAP and increased mRNA expression levels of CCR2 in the insula. They also exhibited an increased number of microglia cells in regions of the insula in study compared to the sham-sham animals, but these displayed a decreased ramification. As regard to the CA1 region of the hippocampus, these animals exhibited microglia cells with an increased ramification and phagocytic activity. These changes concurred with the development of mechanical allodynia in the animals. Animals submitted to maternal deprivation showed decreased mRNA expression levels of c-fos and a decreased number of microglia cells in the regions of the insula studied. Also, they exhibited microglia cells with an increased phagocytic activity comparatively with the sham-sham animals. Also, microglia cells from these animals displayed a different branch arrangement when compared to the sham-sham microglia cells. As regards to the CA1 region of the hippocampus, animals submitted to maternal deprivation exhibited a decreased number of microglia cells with a decreased territorial volume. Additionally, although these animals did not show microglia cells with a different number of branches, they exhibited a different branch arrangement, in a sense that the brunching points are more proximal to the cells soma. These changes concurred with mechanical allodynia and thermal hyperalgesia. Altogether, our data indicate that the changes induced in the insula and on the hippocampus of the female rats depend on the type of stress induced. More precisely, our results suggest that Water Avoidance Stress induced neuroinflammation and changes in neuronal and glial cells activity in the insula and that these changes might be associated with the mechanical allodynia observed in the animals in the present study and with the transient bladder hyperactivity observed in this model in other studies. The changes induced by this paradigm in microglia status in the hippocampus might also be involved in the development of the mechanical allodynia observed in the animals. However, more studies are required to clarify this hypothesis. As regards to the maternal deprivation model, together, our findings suggest that this stress paradigm seems to induce long last changes in the insula by decreasing the neuronal activity and increasing microglia phagocytic activity and that these changes might be associated with the mechanical allodynia and thermal hyperalgesia observed in the animals. If the changes induced by this paradigm in microglia in the CA1 region of the hippocampus are also associated with animals mechanical allodynia and thermal hyperalgesia, it is not yet clear. Further studies are needed to better study this correlation.