Browsing by Subject "muovautuvuus"

Tissue plasminogen activator (tPA) is a serine protease that cleaves the inactive plasminogen to a broad-spectrum protease plasmin. Plasmin is involved in the degradation of blood clots by breaking down the fibrin network. In addition to it's role in the fibrinolytic system, tPA participates in the functions of the central nervous system. tPA is expressed in several brain areas and has been shown to be involved in neuronal plasticity. tPA's effects on brain plasticity are mediated in part via degradation of extracellular matrix proteins, but mainly via processing of brain-derived neurotrophic factor (BDNF). Plasmin cleaves pro-BDNF into BDNF that serves as primary endogenous ligand for TrkB neurotrophin receptor. TrkB signalling is strongly associated with the regulation of neuronal plasticity such as neurogenesis, synaptogenesis and long-term potentiation (LTP). On the contrary, pro-BDNF binds and activates p75 neurotrophin receptor that regulates many distinct, even opposite, effects on neuronal plasticity such as long-term depression and synapse refraction. Enhancement of brain plasticity is considered to be important for the therapeutic effects of antidepressant drugs and this is at least partially mediated via BDNF. Antidepressants activate TrkB receptors and increase BDNF protein levels in the rodent brain but the mechanism behind this remains obscure. Given that tPA is an important factor in the processing of BDNF, it is a possible mediator for antidepressants' neurotrophic effects. The effects of antidepressants on tPA activity have been previously studied only in the blood circulatory system. The aim of the experimental part of this Master's thesis was to examine the effects of antidepressant fluoxetine on tPA activity and protein levels in mouse hippocampus. Also the effects of fluoxetine on BDNF-TrkB signalling were studied. Fluoxetine was administered to mice acutely (30 mg/kg, i.p., 1 h) and chronically (0,08 mg/ml in drinking water, 3 weeks). tPA activity was studied using SDS-PAGE - and in situzymographies. TrkB activation, tPA and BDNF protein levels were measured using western blot. BDNF protein levels were also examined with ELISA method. No changes in tPA activity were found after acute fluoxetine treatment. In line with this result is the observation that also the BDNF levels remained unchanged. However, TrkB receptor activity was increased in fluoxetine treated mice. It seems possible that BDNF is not involved in the TrkB activation caused by acute fluoxetine treatment. Chronic fluoxetine treatment caused a significant increase in the BDNF protein levels compared to water-drinking control mice. This was not, however, associated with significant changes in TrkB activity. No changes in tPA activity were observed, which suggests that tPA is not involved in the increase of BDNF levels after chronic fluoxetine treatment. Interestingly, tPA antibody detected three distinct proteins in western blot of whose levels acute fluoxetine treatment regulated. However, more studies are needed to identify these proteins and to reveal the significance of such an effect of fluoxetine. According to this study, neither acute nor chronic fluoxetine treatment affects tPA activity in mouse hippocampus. However, environmental enrichment has been shown to enhance tPA activity and produce similar neurotrophic effects as chronic fluoxetine treatment. Therefore the result of this study concerning effect of chronic antidepressant treatment on tPA activity should be verified.