On the roles of hypothalamic tanycytes in energy homeostasis

The hypothalamus is a key player in energy homeostasis. While hypothalamic neurons have been heavily focused on, tanycytes, glial cells that line the wall of the 3rd ventricle (3V) have gained recent attention. Tanycytes are privileged in their access to hypothalamic nuclei, circulating factors within the blood and cerebrospinal fluid. With knowledge of their ability to respond to nutrients in vitro, this work aimed to elucidate their functions in vivo. The role of tanycytes was scrutinized using WT and mutant mice lacking the Tas1r1 taste receptor (KO). This mutation increases tanycyte sensitivity to L-arginine (Arg) in male mice and decreases sensitivity in female mice. In response to Arg gavage, all groups except KO female mice exhibited reduced locomotor activity, linking tanycyte responses to physical activity for the first time. Glucose biosensors were implanted into the 3V and Arcuate nucleus (Arc) of mice to develop our understanding of nutrient access to these areas. Intraperitoneal injection, food intake and consumption of a glucose solution all rapidly increased glucose concentration within the 3V, while the concentration within the Arc remained stable. The observed glucose dynamics resembled the environment required to elicit strong Ca2+ responses in tanycytes. Miniature microscopes were used to visualise tanycyte signalling within awake, behaving mice for the first time. This thesis documents responses to glucose, amino acids and food intake. While further characterisation is required, tanycytes are shown to respond to low levels of glucose within 10 minutes. This thesis presents the novel findings that tanycytes may have influence over energy expenditure, respond to nutrients in vivo, and that glucose rapidly increases within the 3V but not the Arc. It strongly suggests that previous in vitro work is physiologically relevant and further solidifies the role of tanycytes in nutrient detection since they are unlikely to access the Arc directly.

An improved model of moderate sleep apnoea for investigating its effect as a comorbidity on neurodegenerative disease

Sleep apnoea is a highly prevalent disease that often goes undetected and is associated with poor clinical prognosis, especially as it exacerbates many different disease states. However, most animal models of sleep apnoea (e.g., intermittent hypoxia) have recently been dispelled as physiologically unrealistic and are often unduly severe. Owing to a lack of appropriate models, little is known about the causative link between sleep apnoea and its comorbidities. To overcome these problems, we have created a more realistic animal model of moderate sleep apnoea by reducing the excitability of the respiratory network. This has been achieved through controlled genetically mediated lesions of the preBötzinger complex (preBötC), the inspiratory oscillator. This novel model shows increases in sleep disordered breathing with alterations in breathing during wakefulness (decreased frequency and increased tidal volume) as observed clinically. The increase in dyspnoeic episodes leads to reduction in REM sleep, with all lost active sleep being spent in the awake state. The increase in hypoxic and hypercapnic insults induces both systemic and neural inflammation. Alterations in neurophysiology, an inhibition of hippocampal long-term potentiation (LTP), is reflected in deficits in both long- and short-term spatial memory. This improved model of moderate sleep apnoea may be the key to understanding why this disorder has such far-reaching and often fatal effects on end-organ function