Obesity causes various physiological disorders between the central nervous system and peripheral tissues. Ketone bodies have a neuro-protective role and are strongly affected by obesity-related metabolic disorders. To clarify the effects of obesity on ketone body utilization in brain, we examined the mRNA localization of acetoacetyl-CoA synthetase (AACS), which activates ketone bodies for the synthesis of fatty acid and cholesterol, in various brain regions of Zucker fatty rats by in situ hybridization. The AACS mRNA level was increased in the paraventricular thalamic nucleus (PVT) but not affected in the cerebrum and hippocampus in Zucker fatty rats. In contrast, the AACS mRNA level was reduced in the arcuate hypothalamic nucleus (Arc) and ventromedial hypothalamic nucleus (VMH) in the hypothalamus. Succinyl-CoA:3-oxoacid CoA-transferase (SCOT) mRNA level was decreased only in the PVT but not affected in the Arc and VMH. These data raise the possibility that AACS is regulated by the leptin signaling pathway in the hypothalamus but not in the PVT. As AACS was expressed in neural-like cells, ketone bodies are assumed to be utilized for the synthesis of lipidic substances and to cause metabolic disorders in the nervous system.