II and lamina IX layers [11]. Rat brain endothelial cells also express PPARδ mRNA, suggesting a possible role in blood-brain barrier (BBB) maintenance [29]. PPARδ is also widely expressed in the mouse brain, with high levels in the entorhinal cortex, hypothalamus, hippocampus, and corpus callosum. Localization studies identified PPARδ mRNA and protein in mouse neurons and oligodendrocytes, but not in astrocytes [26]. However, in cell culture, PPARδ expression has been documented in mouse and rat cortical astrocytes as well as in rat cerebral astrocytes [30, 31]. Results from our own laboratory demonstrate that the receptor is also expressed in microglia. Taken together, PPARδ expression has been observed in all the major cell types within the CNS, including astrocytes, endothelial cells, microglia, neurons, and oligodendrocytes.
