N-acetylaspartate (NAA) is the second most abundant metabolite in the brain. Its physiological roles have eluded researchers for sixty years and hypotheses on its functions are contentious. Clinical evidence suggests both absence and accumulation of NAA are poorly tolerated. Hypoacetylaspartia is caused by a null-mutation of the NAA-synthesizing enzyme NAT8L. It exhibits complete absence of NAA, causing developmental delay and psychomotor retardation. Conversely, Canavan disease (CD) is a fatal childhood leukodystrophy with abnormally high NAA due to the absence of its degrading enzyme ASPA. Recently published data on NAT8L/ASPA double-deficient mice indicate NAA toxicity may be the primary culprit in CD pathology rather than ASPA dysfunction. This thesis studied the genetic abolishment of NAA to assess the efficacy ceiling of NAA-knockdown in CD treatment; the effects of increased NAA on the brain to separately investigate this arm of the CD pathology; and the metabolic consequences of altered NAA levels. The Nat8l-deficient mouse is a model of hypoacetylaspartia and genetic knockdown for treatment of CD. Phenotyping of this model revealed previously unreported neurological deficit despite normal myelin. Experimental results indicated NAA deficiency affects unconscious defensive reactions that protect the body from harm. The constitutive elevation of the NAT8L protein causing excess NAA levels in the presence of normal ASPA was achieved in a novel CD mouse model. These transgenic ThyNAT8L mice presented with growth retardation characteristic of CD pathology, suggesting NAA toxicity is complicit in the aetiology of this disorder. However, supraphysiological NAA levels are uncoupled from neurotoxicity per se when oligodendroglial aspartoacylase is present. Metabolomic analysis of ThyNAT8L mice revealed profound differences in the levels of major energy substrates. NAA deficiency, somewhat unexpectedly, does not affect these levels. Neither mouse line abnormally utilizes the brain energy substrates glucose and acetate under normal conditions. Gene replacement therapies for CD should target reconstitution of oligodendroglial aspartoacylase. A combination therapy aiming to restore Aspa gene function should attenuate, not eliminate, NAA in the CNS. The Nat8l-deficient and novel ThyNAT8L mouse models will be invaluable tools to elicit the role of NAA in health, disease and neuroenergetics in future studies.