Browsing by Subject "neurotransmission"

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  • Montonen, Heidi (Helsingfors universitet, 2013)
    Literature review: The plasma membrane DA transporter (DAT) belongs to the family of Na+/ClÙÄÉ≠ dependent neurotransmitter transporters. DAT is the primary mechanism for clearance of dopamine from the extracellular space and transporting it back to the presynaptic nerve terminals. There's a great interest in the DAT and its regulation as its substrate, dopamine, mediates a wide array of physiological functions e.g. locomotor activity, cognition and the control of motivated behaviors. With selective transport DAT limits the intensity and the duration of dopaminergic signal. Its function is regulated by several kinases, phosphatase and protein-protein interactions. The altered expression of DAT may be related to several neurological diseases such as Parkinson's disease, addiction and ADHD. To study DAT's function, several genetically modified mouse lines including DAT knockout mice, DAT knockdown mice and DAT knock in mice with elevated DAT levels have been generated. Experimental part: Glial cell line-derived neurotrophic factor (GDNF) plays important role in the survival and function of dopaminergic neurons, learning, memory and synaptic plasticity. More recently, several studies have shown that GDNF can also negatively regulate the actions of abused drugs. The aim of this study was to investigate GDNF's role and mechanism of action in plasticity and function of the dopaminergic neurons projecting to striatum. For that purpose, we used in vivo microdialysis in freely moving mice. We chose two different mouse lines: MEN2B mice with constitutive active Ret-signaling and elevated striatal dopamine concentrations, and GDND-cKO mice that lack GDND in the central nervous system. Microdialysis guide cannula was implanted in the dorsal striatum in the stereotaxic surgery and the mice were allowed to recover for 5-7 days. The concentrations of dopamine and its metabolites DOPAC and HVA and also 5-HIAA were determined from the samples by highperformance liquid chromatography. Microdialysis was performed twice for every mouse on days 1 and 4. Between microdialysis days, the mice were given amphetamine 1 mg/kg i.p. on days 2 and 3. In the microdialysis experiment, the mice received amphetamine stimulation (100 µM/60 min) via microdialysis probe. The placements of microdialysis probes were verified from fixed brain sections after the experiments. Amphetamine increased the dopamine output in both mouse lines, but there were no statistically significant differences in striatal dopamine concentrations between genotypes neither after acute nor chronic administration. However, there was a difference between the dopamine outputs in days 1 and 4 in both MEN2B and GDNF-cKO mice: The striatal dopamine concentrations were significantly lower on the second microdialysis day. This may be a sing from tolerance to the drug. However, without more research, it is not possible, by this experiment, to draw direct conclusions of GDNF's role in addiction and in plasticity in striatum. It is possible that the differences between genotypes are too small to be seen with microdialysis. Development of compensatory mechanisms in mice cannot be ruled out either. Effects may also vary between different brain areas.
  • Renko, Juho-Matti (Helsingfors universitet, 2012)
    Review of the literature: The purpose of the review is to go through what is known about mechanisms of actions of different neurotrophic factors (GDNF, neurturin, CDNF and MANF) and how they are transported within the brain. Neurotrophic factors are endogenous and secreted proteins which have a pivotal role in the development and maintenance of neurons. They support the survival of neurons and they can help them to recover from different injuries. Due to these functions neurotrophic factors might be beneficial for the treatment of neurodegenerative disorders like Parkinson's disease. There are a great deal of studies that clearly show the neuroprotective and neurorestrorative function of GDNF and neurturin on dopaminergic neurons. They are also studied in clinical studies with Parkinson's patients but the results have been partly contradictory. The signalling route of GDNF and neurturin via RET tyrosinekinasereceptor is fairly well known but the other mechanisms of action of these factors needs to be studied further. CDNF and MANF constitute a novel, evolutionarily conserved family of neurotrophic factors. They are shown to have neuroprotective and neurorestrorative actions on dopaminergic neurons both in vitro and in vivo in a rodent model of Parkinson's disease. The mechanisms of action of CDNF and MANF are not quite clear at the moment. There are two different domains in their structure both of which are likely to carry different functions. The N-terminal domains of these proteins are close to saposins, lipid and membrane binding proteins, some of which are shown to have neurotrophic and anti-apoptotic effects. The C-terminal domain of MANF, in turn, is structurally close to the SAP-domain of Ku70-protein which binds Bax in the cytoplasm and thus inhibits apoptosis mediated by Bax. CDNF and MANF might protect neurons both via intracellular mechanisms and extracellularly acting like a secreted neurotrophic factor. CDNF and GDNF are transported retrogradially from striatum to substantia nigra. MANF, unlike the others, is transported from striatum to the frontal cortex. MANF and CDNF are shown to have better diffusion properties in the brain parenchyma than GDNF. Experimental part: We studied, by means of microdialysis, the effects of CDNF, MANF and GDNF on the dopaminergic neurotransmission of naive rats within the striatum. Neurotrophic factors (10 µg) and PBS as a negative control were injected into the left striatum in stereotaxic surgery. After this rats recovered one week before the first mircodialysis. The second mircodialysis was performed three weeks after the surgery. The samples were collected from the left striatum of freely moving rats. During the microdialysis neurotransmission was stimulated by replacing the perfusion solution with hypertonic potassium solution and with amphetamine solution. The concentration of dopamine, DOPAC, HVA and 5-HIAA was measured from the dialysate samples. In vivo TH-activity experiment was carried out for three rats in each group. NSD1015 was injected i.p.after which rats were decapitated and their striatums were dissected. The concentration of L-DOPA, dopamine and metabolites on the treated and untreated hemisphere were analyzed from the tissue samples. The amount of L-DOPA in the striatum after NSD1015-treatment indicates how active TH-enzyme is. There were no significant differences in the concentrations of dopamine and metabolites during the baseline. MANF and CDNF increased the release of dopamine from the nerve terminals compared to GDNF and PBS one week after the surgery. Three weeks after the surgery there was still significant increase in the release of dopamine in MANF group compared to GDNF group. Also the dopamine-DOPAC-turnover was increased significantly in MANF group compared to GDNF and PBS groups one week after the surgery. DOPAC/HVA -ratio was significantly smaller in GDNF group than in other groups one week after the surgery. These findings suggest that MANF potentiates dopaminergic neurotransmission most drasticly. The effects of MANF seem to last longer time than the effects of other neurotrophic factors. CDNF seems to increase the release of dopamine from the nerve terminals as well. The potentiation of dopaminergic neurotransmission could be due to increased biosynthesis of dopamine or due to the potentiation of the function of nerve terminals. In the results of the TH-activity experiment there was a trend according to which L-DOPA is synthesized less after the neurotrophic factor treatment that after the PBS treatment. This suggests that neurotrophic factors might decrease the activity of TH-enzyme.
  • Vanaveski, Taavi; Molchanova, Svetlana; Dan Duc Pham; Schäfer, Annika; Pajanoja, Ceren; Narvik, Jane; Srinivasan, Vignesh; Urb, Mari; Koivisto, Maria; Vasar, Eero; Timmusk, Tonis; Minkeviciene, Rimante; Eriksson, Ove; Lalowski, Maciej; Taira, Tomi; Korhonen, Laura; Voikar, Vootele; Lindholm, Dan (2021)
    Peroxisome proliferator-activated receptor-gamma coactivator-1 alpha (PGC-1 alpha) is a master regulator of mitochondria biogenesis and cell stress playing a role in metabolic and degenerative diseases. In the brain PGC-1 alpha expression has been localized mainly to GABAergic interneurons but its overall role is not fully understood. We observed here that the protein levels of gamma-aminobutyric acid (GABA) type A receptor-alpha 2 subunit (GABAR alpha 2) were increased in hippocampus and brain cortex in transgenic (Tg) mice overexpressing PGC-1 alpha in neurons. Along with this, GABAR alpha 2 expression was enhanced in the hippocampus of the PGC-1 alpha Tg mice, as shown by quantitative PCR. Double immunostaining revealed that GABAR alpha 2 co-localized with the synaptic protein gephyrin in higher amounts in the striatum radiatum layer of the hippocampal CA1 region in the Tg compared with Wt mice. Electrophysiology revealed that the frequency of spontaneous and miniature inhibitory postsynaptic currents (mIPSCs) was increased in the CA1 region in the Tg mice, indicative of an augmented GABAergic transmission. Behavioral tests revealed an increase for anxiety-like behavior in the PGC-1 alpha Tg mice compared with controls. To study whether drugs acting on PPAR gamma can affect GABAR alpha 2, we employed pioglitazone that elevated GABAR alpha 2 expression in primary cultured neurons. Similar results were obtained using the specific PPAR gamma agonist, N-(2-benzoylphenyl)-O-[2-(methyl-2-pyridinylamino) ethyl]-L-tyrosine hydrate (GW1929). These results demonstrate that PGC-1 alpha regulates GABAR alpha 2 subunits and GABAergic neurotransmission in the hippocampus with behavioral consequences. This indicates further that drugs like pioglitazone, widely used in the treatment of type 2 diabetes, can influence GABAR alpha 2 expression via the PPAR gamma/PGC-1 alpha system.
  • Sun, Lihua; Tang, Jing; Liljenbäck, Heidi; Honkaniemi, Aake; Virta, Jenni; Isojärvi, Janne; Karjalainen, Tomi; Kantonen, Tatu; Nuutila, Pirjo; Hietala, Jarmo; Kaasinen, Valtteri; Kalliokoski, Kari; Hirvonen, Jussi; Scheinin, Harry; Helin, Semi; Eerola, Kim; Savontaus, Eriika; Yatkin, Emrah; Rinne, Juha O.; Roivainen, Anne; Nummenmaa, Lauri (2021)
    Seasonal rhythms influence emotion and sociability. The brain μ-opioid receptor (MOR) system modulates a multitude of seasonally varying socioemotional functions, but its seasonal variation remains elusive with no previously reported in vivo evidence. Here, we first conducted a cross-sectional study with previously acquired human [11C]carfentanil PET imaging data (132 male and 72 female healthy subjects) to test whether there was seasonal difference in MOR availability. We then investigated experimentally whether seasonal variation in daylength causally influences brain MOR availability in rats. Rats (six male and three female rats) underwent daylength cycle simulating seasonal changes; control animals (two male and one female rats) were kept under constant daylength. Animals were scanned repeatedly with [11C]carfentanil PET imaging. Seasonally varying daylength had an inverted U-shaped functional relationship with brain MOR availability in humans. Brain regions sensitive to daylength spanned the socio-emotional brain circuits, where MOR availability formed a spring-like peak. In rats, MOR availabilities in the brain neocortex, thalamus and striatum peaked at intermediate daylength. Varying daylength also affected the weight gain and stress hormone. We conclude that the in vivo brain MOR availability in humans and rats shows significant seasonal variation, which is predominately associated with seasonal photoperiodic variation. Given the intimate links between MOR signaling and socioemotional behavior, these results suggest that the MOR system might underlie seasonal variation in human mood and social behavior.SIGNIFICANCE STATEMENTSeasonal rhythms influence emotion and sociability. The brain’s μ-opioid receptor (MOR) system modulates numerous seasonally varying socioemotional functions, but its seasonal variation remains elusive. Here we used positron emission tomography to show that MOR levels in both human and rat brains show daylength-dependent seasonal variation. The highest MOR availability was observed at intermediate daylengths. Given the intimate links between MOR signaling and socioemotional behavior, these results suggest that the MOR system might underlie seasonal variation in human mood and social behavior.