SIGMAR1 and neurodegenerative disease: Identifying the putative endogenous ligands excludes the Sig-1R as an orphan receptor, and the later discovery on the chaperoning function via the IP3R3 re-defines the pivotal role of the Sig-1R, nevertheless, the subtle and coordinated actions/balances between Sig-1R and its putative endogenous ligands remain to be clarified to elucidate potential roles in the neurodegenerative diseases or other psychiatric illnesses toward Sig-1Rs.