Brain
After it was demonstrated that RA1c homologs—Olr59 in rat [13] and Olfr78 in mouse [14]—were expressed in areas of the brain and olfactory epithelium, much effort has been made to confirm the expression of ORs in the brain. MOL2.3, called Olfr78, was reported to be expressed in the ganglia of the autonomic nervous system [16]. Some mouse ORs—M71 (olfr151), C6 (Olfr49), and OR3—are detected in the cerebral cortex and might play a role in developmental processes, such as axon guidance and target recognition during the postnatal period [17]. OR expression (OR1E1, OR2J3, OR2L13, OR11H1, and OR52L1) in the frontal cortex is downregulated in Parkinson disease (PD) patients [18].
The expression of a mouse OR, Olfr110, was detected in the cerebral cortex of wild-type mice for 1 postnatal year, and its mRNA levels did not vary during that period [19]. It was observed that 8 ORs and 6 taste receptors (TASRs) are constitutively expressed in the frontal cortex, entorhinal cortex, and cerebellum in human control brains. These data imply that variable dysregulation of certain ORs and TASRs is common in several neurodegenerative diseases, including Alzheimer disease, Progressive Supranuclear Palsy, and Creutzfeldt–Jakob disease. The same research group also reported a decrease in olfactory and TASR expression in the dorsolateral prefrontal cortex in chronic schizophrenia [20]. There was a report that ORs are expressed in mouse mesencephalic dopaminergic (mDA) neurons. After screening ligands on Olfr287, carvone enantiomers were identified as agonists of Olfr287 and able to increase intracellular Ca2＋ in solitary mDA neurons. The ORs were found to be expressed in human Substantia Nigra and downregulated in PD postmortem brains [21].
Gong et al. [22] found that some ORs are differentially expressed in the sciatic nerve and dorsal root ganglia after sciatic nerve injury in rats. The expression and expression profile of several ORs in the sciatic nerve were verified, and they also observed that the expression of some ORs in primary cultures of Schwann cells was upregulated under H2O2 stimulation [22]. Recently, there has been a report that Olfr544 is expressed in mouse brain and heart, as well as nose, adipose tissue, and spleen [23].