TRPV1 and major depressive disorder: Since few references on the depression-related behavioral alterations caused by TRPV1 ligands are available, the TRPV1 ligands were selected from those which provided some behavioral effects upon intraperitoneal or intravenous injections: the prototypic agonist capsaicin (CP) [33], the potent and antidepressant agonist olvanil (OL) [29], the antagonist capsazepine (CZ) [29], the endogenous TRPV1-agonistic CB1 agonists anandamide (arachidonylethanolamide: AEA) [27] and N-arachidonyldopamine (NADA) [34], as well as the synthetic TRPV1 and CB1 agonist arvanil (AR) [35].