Central Neural Cardiorespiratory Areas in Exercise

114 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2002.Neural control of cardiorespiratory function in exercise is accomplished by two mechanisms: a reflex arising from contracting muscles termed "exercise pressor reflex", and a "central command" mechanism. The three experiments described in this thesis were concerned with fundamental issues regarding both mechanisms. In study one, because neurons in the lateral tegmental field (LTF) respond to muscular contraction and produce pressor responses when stimulated, it was hypothesized that spinal neurons project directly to LTF. Wheat-germ agglutin conjugated with horseradish peroxidase was injected into LTF of cats, with a transport time of 56--90 h. Neurons were located bilaterally in cervical and upper thoracic segments, the majority in C2, mostly in laminae V, VII, VIII and X. These results demonstrated that LTF receives direct projections from upper cervical segments. However, muscle afferent input is likely to project to LTF polysynaptically. In study two, plastic changes in neuronal structure and function have been associated with different conditions and stimuli. The effects of training on the activity of central cardiorespiratory control areas was studied in rats. C-fos immunocytochemistry was used to determine neural activity in response to a single bout of exercise in sedentary and trained rats. Trained rats showed fewer labeled neurons than sedentary in the posterior hypothalamus, periaqueductal grey, nucleus tractus solitarius and rostral ventrolateral medulla, all of which are known cardiorespiratory control areas. These results strongly suggest that regular physical activity changes the pattern and extent of activation in the brain. In study three, insular cortex has been associated with cardiovascular function during exercise. The response of insular cortex neurons to muscular contractions and their discharge characteristics were studied using spike-triggered averaging techniques. The extracellular single unit recording of insular cortex neurons revealed that most of those neurons showed depressed activity in response to isometric muscular contractions and their basal discharge was correlated with sympathetic and cardiac rhythms. We concluded that information from contracting muscles reaches neurons in the insular cortex, and therefore they likely participate in the control of cardiorespiratory function during exercise.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD