Browsing by Subject "amygdala"

Chronic stress has been linked to the pathogenesis of various disorders, such as generalized anxiety disorder, depression, and post-traumatic stress disorder (PTSD). Stress-induced hyperexcitability of the basolateral amygdala (BLA) has implications in anxiety-like behavior. Promising evidence points to the direction of GluK1 subunit containing kainate receptors (KARs) having a role in the modulation of GABAergic transmission in the lateral amygdala (LA). The aim of the present study was to investigate whether dysfunction of KARs contribute to stress-induced amygdala hyperexcitability and anxiogenesis in mice. Chronic restraint stress (CRS) is an animal model simulating chronic psychological stress. An in situ hybridization experiment was performed to investigate how CRS affects expression levels of GluK1 in the different neuronal populations in the LA. These data show that CRS leads to downregulation of GluK1 expression in the parvalbumin-positive (PV+) interneurons specifically. Patch clamp recordings of spontaneous inhibitory postsynaptic currents showed that CRS did not affect synaptic GABAergic transmission to the principal neurons in the LA. Lastly, conditional knock-out (cKO) mice that have the Grik1 gene knocked out selectively in the PV-expressing interneurons showed no change in anxiety-like behavior after CRS while their wild-type counterparts demonstrated an increase in anxiety-like behavior observable in the elevated plus maze test. Thus, ablation of GluK1 in PV+ interneurons affects the stress-induced anxiogenesis. Due to low number of animals, it cannot be confirmed yet whether the deletion leads to stress resilience or a phenotype where even regular handling is an aversive experience comparable to physical restraint. GluK1 KAR modulation of PV+ interneuron excitability and its susceptibility to stress-related alterations is only a recently discovered phenomenon, and even though this study provides some insight into the underlying mechanism, further research is needed. Systematic characterization of the mechanism could provide a novel tool for understanding and treating stress-related pathological anxiety, possibly helping patients suffering from anxiety disorders resistant to current treatments available.

Appetite regulation is a complex process involving regulation of energy homeostasis and the rewarding nature of food. Abnormalities in appetite regulation lead to obesity and eating disorders which are challenging to treat with medicines. Especially obesity is an increasing public health problem and drug development against it is a current subject in research. Hypothalamus is the most important brain area related to appetite regulation. Also, the basal forebrain and the amygdala which are part of the reward system in the brain, contribute to the appetite regulation. There is cholinergic innervation from the basal forebrain to the amygdala and most of the cholinergic activity in the amygdala is originating from the basal forebrain. It is known that the cholinergic system inhibits appetite but there is still no research about impact of cholinergic projections between these two brain areas. Aim of this study was to find out if the cholinergic projections from the basal forebrain to the amygdala effect on appetite regulation. The study included two stereotactic surgery. In the first surgery the mice (n=14) received injections to the basal forebrain that contained genetic materials for DREADDs in AAV. DREADDs appeared in the cholinergic cells of the basal forebrain and emanated within their axons to the amygdala. In the second surgery cannulas were placed to the amygdala. CNO was injected through the cannulas to the amygdala to cause the DREADDs activate or inhibit the cholinergic cells. As a control, mice received vehicle. The feeding experiments were performed in normal conditions or after food restriction and there were either food or sugar pellets available. The pellet dispenser monitored how many pellets mice ate during the six hours after the CNO or vehicle treatment. The success of virus injections was checked after the feeding experiments by antibody dyeing. In any conditions there was no significant differences in the results due to DREADDs and treatment. Because of the small group sizes and dispersion of the results no final conclusions can be made but the additional research about this topic is needed.

The ability to regulate release of noradrenaline, dopamine and GABA is one of the most important roles of the nicotinic receptors. The release of neurotransmitters following stimulation of nicotinic receptors is addressed in the thesis, with focus on dopamine and noradrenaline. Release of neurotransmitters, mediated through nicotinic receptors, has been researched using various methods, including brain slices, microdialysis and synaptosomes. Research using synaptosomes have provided valuable information regarding nicotinic receptors and their ability to regulate neurotransmitter release. Research using receptor specific antagonists have provided information regarding the stoichiometry of nicotinic receptor in different regions of the brain. The primary focus in the thesis, was the characterization of [3H]dopamine release following stimulation of nicotinic receptors with varenicline and acetylcholine, using synaptosomes from mouse striatum. Using a-conotoxin-MII, the [3H]dopamine release was divided into a-conotoxin- MII-resistant and -sensitive release. [3H]Dopamine release was mediated through a6b2*- and a4b2*-receptors from striatal synaptosomes. The involvement of other receptors could not be ruled out, but based on these results and results from previous studies, the involvement of other nicotinic receptors is supposedly low.

MDMA is an illegal stimulant known for its empathy-enhancing effects. Its positive effects are mainly based on increasing the concentrations of monoamines such as serotonin (5-HT), dopamine (DA) and norepinephrine (NE). In addition to its positive effects, MDMA can cause adverse effects such as hyperthermia and neurotoxicity. Especially with long-term use, MDMA can cause serotonergic and dopaminergic neurotoxicity. In addition, there are also indications of MDMA-induced neurotoxicity in systems where gamma-aminobutyric acid (GABA) functions as the main neurotransmitter. Glutamate decarboxylase (GAD) 67 is an enzyme that synthesizes GABA from glutamate and is a specific marker for GABAergic cells. The amygdala is a nucleus in the brain that regulates anxiety and fear response. In addition to GABAergic interneurons, there are also glutamatergic cells in the basolateral nucleus (BLA) of the amygdala, however in the central nucleus (CeA) there are only GABAergic cells. Disturbances in the GABAergic system can predispose to psychiatric diseases such as anxiety. The aim of thisstudy was to investigate the effects of MDMA (20 mg/kg) on the number of GAD67-positive cells in two nuclei of the mouse amygdala, BLA and CeA. In addition, this study aimed to examine the importance of the dose (4 or 16 injections) for neurotoxicity and the duration of the effects (2, 7 or 30 days). Adolescent wild type mice were divided into 12 groups according to the treatment (MDMA or saline), dose and timepoint. After euthanasia, the brain sections at the level of the amygdala were collected and stained with an immunohistochemical method and imaged using a confocal microscope. This study showed that MDMA reduced the number of GAD67-positive cells in the BLA when mice were given a total of 4 injections. This effect lasted up to 30 days. In contrast, MDMA did not reduce the number of GAD67-positive cells in the BLA in mice that were given 16 injections. Also, MDMA did not decrease the number of GAD67-positive cells in the CeA, regardless of dose. Statistical significance could have been improved, for example, by using more mice or analysing more sections from each individual animal. It is important to continue studying the effects of MDMA to better treat and prevent its adverse effects. In addition, increased understanding would urge users to exercise caution when using MDMA.

Objective. Changes in work life pose challenges for employees to recover. Today’s work culture is flexible and limitless in nature. Work-related stress has increased significantly, as work is being done, although labor productivity has clearly increased. This phenomenon increases interest towards stress research and well-being at work. This literature review examines the neural effects of chronic stress and presents recovery theories in response to these challenges. Method. The articles in the review dealt with neural effects of stress and depression, as well as recovery theories. Articles were retrieved from Google Scholar and PubMed databases with keywords recovery from work, chronic stress, work related stress, neural effects from stress. The search criteria were limited to studies published in the 21th century. For recovery theories, original sources were searched. Results and conclusions. The review showed that chronic stress causes changes, especially in the amygdala, hippocampus, and prefrontal cortex. These changes impair individuals' cognitive abilities. Stress, for example, makes it difficult to regulate emotions and functioning, thus impairing memory activity. Chronic stress and lack of recovery create a cycle in which stress reactions become more intense and the individual’s ability to regulate stress reactions is harmed. While stress is a vital reaction and an important part of effective functioning, continued stress reactions and chronic stress are a threat to well-being. Failure to recover from stress results in an allostatic load that has been shown to be associated with mental health problems and illnesses. Because most of the recovery takes place outside working hours, it is conceivable that everyone is responsible for her own recovery process. On the other hand, the flexibility of work leads to more work becoming part of one’s leisure time. While continued availability is admired, organizations should understand the risks it poses to employee well-being and brain health. Therefore, organizations should focus on the recovery of their employees. Luckily, the development is heading towards an improved work environment.