The expression of PPARδ has been examined in many rodent tissues, including the CNS. The receptor is thought to be ubiquitously expressed in the adult rodent brain and spinal cord [11, 24–26]. In rats, PPARδ begins to be expressed at midgestation, reaching peak expression in all neural tissues in the late stage embryonic brain, suggesting that it may play a role in cell differentiation in the CNS [27]. In situ hybridization and immunolocalization studies have demonstrated that high levels of PPARδ are found in the hippocampus, telencephalic cortex, and the cerebellar cortex of rats [11, 27, 28]. Other studies in the rat brain indicate that PPARδ mRNA is highly expressed in the thalamic nuclei [25]. In the rat spinal cord, PPARδ is the most abundant PPAR subtype; it is expressed in every cell layer and highly expressed in the lamina 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,
