The molecular mechanisms of synaptic function and development have been studied extensively, but little is known about the energy requirements of synapses, or the mechanisms that coordinate their energy production with their metabolic demands. These are oversights, as synapses with high energy demands are more susceptible to degeneration and degrade in the early stages of diseases such as amyotrophic lateral sclerosis, spinal muscle atrophy and Parkinson’s disease. Here, in a structure-function study at Drosophila motor neuron terminals, a neurophysiological model was generated to investigate how power (ATP/s) supply is integrated to satisfy the power demand of presynaptic terminals. Power demands were estimated from six nerve terminals through direct measurements of neurotransmitter release and Ca2+ entry, as well as theoretical estimation of Na+ entry and power demands at rest (cost of housekeeping). The data was leveraged with a computational model that simulated the power demands of the terminals during their physiological activity, revealing high volatility in which power demands can increase 15-fold within milliseconds as neurons transition from rest to activity. Another computational model was generated that simulated ATP production scenarios regarding feedback to the power supply machinery (Oxphos and glycolysis) through changes in nucleotide concentrations, showing that feedback from nucleotides alone fail to stimulate power supply to match the power demands of each terminal. Failure of feedback models invokes the need for feed forward mechanisms (such as Ca2+) to stimulate power supply machinery to match power demands. We also quantified mitochondrial volume, density, number and size in each nerve terminal, revealing all four features positively correlate with the terminals power demands. This suggests the terminals enhance their oxidative capacity by increasing mitochondrial content to satisfy their power demands. And lastly, we demonstrate that abolishing an ATP buffering system (the phosphagen system) does not impair neurotransmission in the nerve terminals, suggesting motor nerve terminals are capable of satisfying their power demands without the ATP buffering system. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2019. / FAU Electronic Theses and Dissertations Collection

This thesis focused on the spatiotemporal patterning of classical excitatory and inhibitory synaptic contacts accounting for the majority of cerebral cortical connections, in relation to ageing and cognitive status. These investigations tested the hypothesis that higher CNS functions depend on the balance between excitatory and inhibitory synaptic connections. Glutamatergic and GABAergic presynaptic bouton densities were determined in aged animals segregated according to their cognitive status into aged and cognitively unimpaired (AU) and aged and cognitively impaired (AI), using the Morris water maze. These two groups were compared in terms of behaviour and the pattern of excitatory and inhibitory synapses. It was evident that an excitatory and inhibitory presynaptic decline is associated with age-related cognitive impairments; whereby both glutamatergic and GABAergic boutons gradually diminish from young to AU to AI. Nevertheless, the balance between excitatory and inhibitory presynaptic inputs was maintained. To determine whether postsynaptic sites differed with respect to ageing and cognitive impairments, excitatory and inhibitory postsynaptic scaffold proteins were investigated in the same cohort of segregated aged animals. There was an imbalance in density ratio between immunoreactive sites of excitatory versus inhibitory postsynaptic scaffold proteins in AI animals. This resulted from a marked decrease in the density of excitatory postsynaptic sites. To further investigate ultrastructural aspects of excitatory synapses I carried out electron microscopical studies of cerebral cortex to measure the abundance of NR2 receptor subunits of the NMDA receptor- a receptor site directly associated with excitatory postsynaptic scaffold proteins. This study revealed that NR2 immunoreactive sites were largely preserved during age-related cognitive decline with an uneven profile distribution. Finally, protein expression of specific receptor subunits and key proteins representative of excitatory and inhibitory postsynaptic sites was investigated by semi-quantitative Western blot analyses in selected cortical areas. It was clear that many of these postsynaptic proteins are affected by age and cognitive status. The most striking change was a marked up-regulation in neuroligin-1 in AI animals, which may affect the delicate balance between excitatory versus inhibitory synaptic inputs. Another notable finding was the down-regulated expression of GluR2 receptor subunits in AI animals, which should have implications for neuronal Ca2+ regulation. In conclusion, we have demonstrated the greater vulnerability of excitatory postsynaptic sites in aged and cognitively impaired animals.

No description available.