Amylin, or islet amyloid polypeptide is a 37-amino acid member of the calcitonin peptide family. Amylin role in the brainstem and its function in regulating heart rates is unknown. The diving reflex is a powerful autonomic reflex, however no neuropeptides have been described to modulate its function. In this thesis study, amylin expression in the brainstem involving pathways between the trigeminal ganglion and the nucleus ambiguus was visualized and characterized using immunohistochemistry. Its functional role in slowing heart rate and also its involvement in the diving reflex were elucidated using stereotaxic microinjection, whole-cel patch-clamp, and a rat diving model. Immunohistochemical and tract tracing studies in rats revealed amylin expression in trigeminal ganglion cells, which also contained vesicular glutamate transporter 2 positive. With respect to the brainstem, amylin containing fibers were discovered in spinal trigeminal tracts. These fibers curved dorsally toward choline acetyltransferase immunoreactive neurons of the nucleus ambiguus, suggesting that amylin may synapse to parasympathetic preganglionic neurons in the nucleus ambiguus. Microinjection of fluorogold to the nucleus ambiguus retrogradely labeled a population of trigeminal ganglion neurons; some of which also contained amylin. In urethane-anesthetized rats, stereotaxic microinjections of amylin to the nucleus ambiguus caused a dose-dependent bradycardia that was reversibly attenuated by microinjections of the selective amylin receptor antagonist, salmon calcitonin (8-32) (sCT (8-32)) or AC187, and abolished by bilateral vagotomy. In an anesthetized rat diving model, diving bradycardia was attenuated by glutamate receptor antagonists CNQX and AP5, and was further suppressed by AC187. Whole-cel patch-clamp recordings from cardiac preganglionic vagal neurons revealed that amylin depolarizes neurons while decreasing conductance. Amylin also resulted in a reduction in whole cell currents, consistent with the decrease in conductance. Amylin is also found to increase excitability of neurons. In the presence of TTX, spontaneous currents in cardiac preganglionic vagal neurons were observed to decrease in frequency in response to amylin while amplitude remained constant, signifying that amylin reduces presynaptic activity at cardiac preganglionic vagal neurons. Finally, evoked synaptic currents revealed that amylin decreases evoked currents, further demonstrating that amylin depolarization and increase in excitability of cardiac preganglionic vagal neurons is also associated with simultaneous inhibition of presynaptic transmission. Our study has demonstrated for the first time that the bradycardia elicited by the diving reflex is mediated by amylin from trigeminal ganglion cells projecting to cardiac preganglionic neurons in the nucleus ambiguus. Additionally, amylin results in the depolarization and increased excitability of cardiac preganglionic vagal neurons while inhibiting presynaptic transmission. / Pharmacology

Bakgrund: Dykreflexen är en reflex som aktiveras när däggdjur håller andan och när receptorer i ansiktet utsätts för kyla. Det är en evolutionär adaption som har utvecklats för att spara på syre i situationer då ny syretillförsel inte finns att tillgå. Den syresparande funktionen aktiveras även vid endast kylstimulering av ansiktet. Denna studie har undersökt vilken effekt dykreflexen har på återhämtningen efter aerob submaximal fysisk aktivitet. Syfte: Syftet med studien var att undersöka om dykreflexen påverkar återhämtningen efter aerob submaximal fysisk aktivitet med avseende på puls och självskattad ansträngning.  Metod: Studiedesignen var en randomiserad cross-over design. Studiedeltagarna var sina egna kontroller. Interventionen var applicering av kyla mot ansiktet (5–10 ºC) mot pannan och ögonen efter avslutad submaximal aerob fysisk aktivitet. Ett kontrolltest utfördes med hudtempererat vatten (27–33 ºC). Insamlade data var pulsåterhämtning och skattad ansträngning 60sek och 180sek efter avslutad submaximal aerob fysisk aktivitet. Resultat: Mediandifferensen mellan HRR60s med och utan kyla visade 0,5 pulsslag större återhämtning med interventionen. Mediandifferensen för HRR180s med och utan kyla visade 2 pulsslag större återhämtning med interventionen. Resultatet av självskattningen enligt Borgs RPE60s samt Borgs RPE180s visar 0,5 skalsteg större mediandifferens med interventionen. Signifikansnivå var satt till P = 0,05. Resultatet från de olika testerna visade P = 0,286 för HRR60s, P = 0,212 för HRR180s, P = 0,374 för Borgs RPE60s samt P = 1,000 för Borgs RPE180s. Konklusion: Resultaten visade inte någon statistiskt signifikant skillnad sett till pulsåterhämtning och självskattad ansträngning mellan interventionen med kyla i ansiktet och kontrolltestet med hudtempererat vatten i ansiktet. / Background: The diving reflex is a response triggered when mammals hold their breath and receptors in the face are exposed to cold. It's an evolutionary adaptation developed to conserve oxygen in situations where fresh oxygen isn't readily available. The oxygen-conserving function activates even with just facial cold stimulation. This study explored the impact of the diving reflex on recovery after aerobic submaximal physical activity. Objective: The purpose of the study was to investigate if the diving reflex affects recovery following aerobic submaximal physical activity in terms of heart rate and perceived exertion. Method: The study design was a randomized crossover design. Participants acted as their own controls. The intervention was cold stimulus (5–10°C) to the forehead and eyes after completing submaximal aerobic physical activity. The same procedure was conducted in the control test, but with skin-tempered water (27–33°C). Collected data included pulse recovery and perceived exertion at 60 seconds and 180 seconds after completing submaximal aerobic physical activity. Results: The median difference between HRR60s with and without cold showed a 0.5 bpm greater recovery with the intervention. The median difference for HRR180s with and without cold showed a 2 bpm greater recovery with the intervention. The self-assessed results using Borgs RPE60s and Borgs RPE180s displayed a 0.5 scale higher median difference with the intervention. The significance level was set at P = 0.05. The test results showed P = 0.286 for HRR60s, P = 0.212 for HRR180s, P = 0.374 for Borgs RPE60s, and P = 1.000 for Borgs RPE180s. Conclusion: The results do not show any statistically significant difference in terms of pulse recovery and self-perceived exertion between the intervention using facial cold application and the control test with application of skin-temperature water on the face.

<p>Sudden unexpected death in epilepsy (SUDEP) is a fatal complication of epilepsy that kills 1̃2 of every 10,000 epileptic patients every year. SUDEP has proven difficult to study because it frequently occurs unobserved and cannot be predicted. What limited clinical data exists suggests that SUDEP occurs as a cardiorespiratory collapse immediately following a seizure. In this work, I explore how a group of autonomic reflexes termed collectively as “oxygen‐conserving reflexes (OCRs)” lead to sudden death when activated during seizures. I also demonstrate multiple physiological parallels between the OCR‐mediated deaths that I report and the clinical data on cases of human SUDEP. Additionally, I explore the neural pathway underlying OCRs, identify the carotid body as a potential target for intervention, and demonstrate the efficacy of electroceutical intervention in reducing the mortality risk of OCR activation during seizures. This work seeks to both offer a neural explanation for SUDEP as well as present a promising target and means for potential intervention.</p>