ABSTRACT
The opioid system constitutes an important neuropeptidergic system in the central nervous system. There are many central and peripheral biological functions that are regulated by the opioid peptides. Among these functions, the opioid system is able to regulate the emotional status. There are a number of ˜ndings that prove that the opioid system is able to modulate mood in depression, a devastating illness that affects millions of individuals worldwide. In this chapter, we review the current knowledge about the implication of the opioid system in depression. Before we proceed, however, as a mode of introduction, we ˜rst review the main aspects of the biology of this system.
