Thesis (Ph. D.)--Georgia State University, 2006. / Marise B. Parent, committee chair; Timothy J. Bartness, Kim L. Huhman, Kyle J. Frantz, committee members. Electronic text (352 p. : ill.)) : digital, PDF file. Description based on contents viewed July 12, 2007. Includes bibliographical references (p. 307-352).

Nutrient sensing neurons are unique in coupling changes in the concentration of nutrients to changes in neuronal activity. These neurons typically exist in regions of the brain where the blood brain barrier is fenestrated, such as the arcuate nucleus of the hypothalamus. Glucose and leucine are nutrients known to be sensed by neurons in this brain region, but the mechanisms by which they are sensed, and cells that sense them require further study. Using calcium imaging of adult neuron cultures from the mouse mediobasal hypothalamus, I demonstrated that leucine bidirectionally regulates neuronal activity in a neurochemically heterogeneous population of neurons, including AgRP/NPY and POMC neurons. Using pharmacological tools, I demonstrated, unexpectedly, that this acute sensing is independent of mTOR and leucine metabolism, known pathways involved in leucine sensing in vivo. Leucine sensing is LAT1 independent. The response principally relies on calcium entry into the cell across the plasma membrane, but IP3 sensitive calcium stores play a role in neurons inhibited by leucine. Using phosphoTRAP and single cell RNA sequencing, I aimed to identify a molecular marker for leucine sensing cells to allow their manipulation in vivo. PhosphoTRAP, and subsequent pharmacological studies identified a T Type calcium channel may be a marker for leucine sensing cells. AgRP neurons are essential for feeding, and also play roles in controlling glucose homeostasis. Using chemogenetics to selectively activate these neurons, I demonstrated, in contrast to a similar, recently published study, that blood glucose concentrations did not rise upon activation of these neurons. A subpopulation of AgRP neurons express glucokinase, and some AgRP neurons are glucose inhibited, but the role of glucokinase in these neurons has not been characterised. Our lab generated an AgRP neuron specific glucokinase knock out mouse line. Preliminary results suggest 18 – 25 week old female AgRP glucokinase knock out mice may have altered glucose tolerance, but conclusions can only be drawn once further mice have been phenotyped, and the success of the glucokinase knock out from AgRP neurons has been confirmed.

Patients admitted in similar clinical condition after spontaneous SAH can develop very different clinical courses. This could depend on the severity of the initial global ischemic brain injury at ictus. In the present study, we explored relations between clinical and radiological parameters at admission that indicate a more severe initial impact, and the following days hormone levels and brain metabolism. Early global cerebral oedema (GCE) on computed tomography occurred in 57 % of SAH patients and was associated with a more severe clinical condition. The brain’s glucose metabolism, measured with intracerebral microdialysis (MD), changed the first days. MD-glucose was initially high and MD-pyruvate low. MD-glucose gradually decreased and MD-pyruvate and MD-lactate increased, suggesting a transition to a hyperglycolytic state. This was more pronounced in patients with GCE. Similar patterns were seen for interstitial non-transmitter amino acids. From initial low concentrations, they gradually increased in parallel with MD-pyruvate. The amino acid concentrations were higher for patients admitted in better clinical condition. Insulin lowered MD-glucose and MD-pyruvate even when plasma glucose values remained high. P-ACTH and S-cortisol were elevated early after SAH. GCE was associated with higher S-cortisol acutely. Urine cortisol excretion, indicating levels of free cortisol, were higher in patients in a better clinical condition. Suppressed P-ACTH occurred in periods of brain ischemia. We suggest that GCE on the first CT scan is a warning sign indicating increased vulnerability if the patient is exposed to compromised energy supply or increased energy demand. Reduction of blood glucose after SAH should be done with caution. The temporal change of the glucose metabolism and the amino acid concentrations probably reflect activated repair mechanisms. This should be considered in the intensive care treatment of SAH patients. Finally, our results support earlier observations that the response of the hypothalamic-pituitary-adrenal system is important in critical care.