Diss. (sammanfattning) Stockholm : Karol. inst. / Härtill 5 uppsatser.

Thesis (M.S.)--University of Wisconsin--Madison, 1969. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.L.S.)--University of Toledo, 2006. / Typescript. "A thesis [submitted] as partial fulfillment of the requirements of the Master of Liberal Studies degree." Bibliography: leaves 57-59.

The vagus nerve is the principal pathway by which autonomic sensory information is carried from the periphery to the CNS where it influences the activity of a numerous structures including the locus coeruleus. Electrical stimulation of the vagus nerve has been demonstrated to enhance performance in a variety of memory tasks in both rats and humans and is used clinically for the control of epilepsy in humans. Electrical stimulation of the vagus nerve has also been shown to improve functional recovery following experimental brain injury in rats. The central hypothesis in these experiments is that vagus nerve stimulation exerts its beneficial effects by mediating the release of norepinephrine in the CNS. The results from Experiment I indicate that VNS results in increased extracellular NE concentration in the hippocampus at both the 0.5 and 1.0 mA stimulus intensities, and in the cortex at the 1.0 mA intensity. Increased concentrations of extracellular NE induced by VNS, regardless of structure, were transient, dissipating before the subsequent baseline recording period. Further, VNS-induced alterations in extracellular NE concentrations were observed bilaterally. Insult to the CNS by means of FPI resulted in long lasting depression of extracellular NE concentrations in the cortex of the injured controls and 1.0 mA VNS group that was partially attenuated 1.0 mA VNS. In the 0.5 mA VNS group NE concentrations remained above pre-injury levels for the majority of the post-FPI measurement period. In the hippocampus, mean NE concentrations in the period immediately following FPI were decreased in comparison to pre-FPI concentrations. Concentrations of hippocampal NE remained depressed in the injured control group throughout the 48 hr sample period. Hippocampal NE concentrations in both the 0.5 mA VNS and 1.0 mA VNS group recovered to above pre-injury levels by 14-20 hrs post-FPI and were significantly higher than that of the injured controls in the 20-26 and 26-32 hr post-FPI sampling periods. Further, hippocampal NE concentrations remained significantly higher in 0.5 mA VNS group in comparison to injured controls in the 32-38 and 38-44 hr sampling periods.

No description available.

Thesis (Ph. D.)--Memorial University of Newfoundland, Faculty of Medicne, 2001. / Typescript. Includes bibliographical references (leaves 156-172).

Non-invasive transcutaneous auricular vagus nerve stimulation (taVNS) is a neuromodulatory technique used to activate vagal afferent fibers located in the concha of the outer ear. Vagal afferents project to the nucleus of the solitary tract (NTS) where information is processed and propagated to higher brain regions. Widespread NTS connections provide a mechanism through which taVNS can be used to influence multiple systems and be a potential treatment for many disorders including heart failure, gastric motility disorders, and migraines. Recent studies are now investigating taVNS as an alternative treatment option to invasive cervical vagus nerve stimulation (cVNS) which is FDA approved to treat drug-resistant epilepsy and depression but has limited patient availability due to the invasiveness of the procedure. Migraine and epilepsy clinical studies have shown therapeutic taVNS benefits and human fMRI studies have demonstrated comparable brain activation between cVNS and taVNS. However, questions remain regarding optimal taVNS parameters, and no study has compared the direct mechanisms responsible for cVNS and taVNS effects. In this study, a high-impedance tungsten electrode was stereotaxically placed into NTS in 10 chloralose-anesthetized rats, and 40-70 neurons were interrogated using electrophysiological methods. Firing rate changes during stimulation on-times were compared to activity levels during stimulation off-times. Neurons were classified as positive responders if they displayed consistent firing rate increases during stimulation, negative responders if they displayed consistent decreases, and non-responders if there was no consistency using a mathematical cosine similarity score. Six taVNS stimulation parameters were investigated using three frequencies (20, 100, 250Hz) at two intensities (0.5, 1.0mA) to identify parameter-specific effects on NTS neurons. Additionally, neuronal activity was evaluated following cVNS at 20 and 250Hz at the bradycardic intensity (lowest intensity to generate a transient 5% decrease in heart rate, BI) and compared to taVNS effects at the corresponding frequencies. Our data shows that taVNS at 20Hz, 1.0mA yields the greatest number of positive responders and 100Hz, 1.0mA yields the greatest number of negative responders (p<0.05) suggesting different taVNS parameters can differentially influence NTS activity. Comparisons between the number of responders generated with cVNS and taVNS revealed significantly fewer negative responders with cVNS at 20Hz compared to taVNS at 20Hz regardless of intensity (p<0.01) but yielded comparable positive responders between cVNS at 20Hz, BI and taVNS at 20Hz, 1.0mA. No significant differences were observed between the number of cVNS and taVNS responders at 250Hz. Interestingly, individual neuronal responses were different between both methods of stimulation, suggesting that they could work through different neuronal pathways.

No description available.

The effects of certain NSAIDs were determined on agonist-evoked responses recorded from rat neurones maintained in vitro using electrophysiological techniques. Initially, the rat isolated vagus and optic nerves were employed. Alphaxalone, pentobarbitone, propofol and the NSAID, mefenamic acid (MFA), potentiated GABA-evoked responses of the vagus nerve. Propofol (1-100µM) selectively potentiated GABA and glycine-evoked responses of the rat vagus and optic nerves, but had little effect on nicotinic acetylcholine-, a,β-methylene-ATP or 5-hydroxytryptamine-mediated responses. The interaction between MFA and ligand-gated receptors was investigated further using voltage-clamped rat hippocampal neurones maintained in culture. MFA (3-100µM) selectively, concentration-dependently and reversibly potentiated GABA-evoked responses, consistent with the observations made using the vagus nerve. MFA (3-100|aM) however had little or no effect on glycine, AMPA, kainate or NMDA-receptor mediated responses. A final series of experiments investigated the site and molecular mechanism of the interaction between MFA and the GABA-gated chloride ion channel. The potentiating effects of MFA (and other fenamates) were not the result of prostaglandin synthesis inhibition, since other NSAIDs did not modulate the GABA(_A) receptor (GR). The actions of MFA were not mediated via the benzodiazepine site of the GR, nor where they due to inhibition of GABA- uptake or membrane perturbation. The modulatory effects of MFA were not use-dependent, but the potentiating effects of MFA were voltage-dependent, where the potentiation was 3-fold greater at -100mV than at +40mV, with no change in the equilibrium potential for GABA. MFA activated a current, in the absence of GABA. Hippocampal neurones varied in sensitivity to modulation by MFA and the anticonvulsant, loreclezole, which may indicate a degree of sub- unit selectivity. These data are discussed in relation to the possible site and mechanism of action of fenamates at the GR, their similarities with other positive modulators of the GR and the neurophysiological implications of these findings.

No description available.