[Possible involvement of FFAR1 signaling in mouse emotional behaviors through the regulation of brain monoamine releases].

The free fatty acid receptor 1 (FFAR1) is suggested to function as a G protein-coupled receptor for medium- to long-chain free fatty acids. We have previously shown that FFAR1 signaling pathway plays an important suppressive role in spinal nociceptive processing after peripheral inflammation and nerve injury, and that FFAR1 agonists might serve as a new class of analgesics for treating inflammatory and neuropathic pain. To further pursue the functional significance of central FFAR1 signaling, we investigated the possible involvement of FFAR1 in endogenous pain modulation, depressive-like behavior, and aberrant behavior induced by addictive drugs using FFAR1 agonist (GW9508), FFAR1 antagonist (GW1100), and FFAR1 gene-deficient mice. As a result, FFAR1-deficient mice were found to exhibit stronger inflammatory and peripheral neuropathic pain-like behavior as well as depressive-like behavior. In particular, we noticed that peripheral nerve injury-induced depressive-like behavior was insensitive to imipramine. Next, we employed in vivo microdialysis to investigate whether FFAR1 is actually involved in the regulation of brain monoamines (dopamine and serotonin) releases. Our findings suggest that FFAR1 indirectly regulates dopamine release by promoting serotonin release. Thus, we are currently investigating how FFAR1 is involved in behavioral changes induced by addictive drugs such as cocaine and morphine. In this review, we briefly discuss about the possible involvement of FFAR1 in cocaine-induced locomotor hyperactivity.