Dopamine, which is the primary neurotransmitter responsible for eliciting feelings of euphoria and pleasure, is the main component of the mechanism of dependence [15]. It works in conjunction with the opioid peptides and receptors to stimulate the dopaminergic pathway that is required for dopamine transmission [15]. The release of GABA, an inhibitory neurotransmitter also identified in this pathway, is decreased when opioid agonists bind to presynaptic mu-opioid receptors of (GABA)-ergic interneurons [17, 19]. The inhibition of GABA-ergic neurons via activation of the mu-opioid receptor allows dopaminergic neurons to release more dopamine into the reward pathway, creating a positive reinforcement of pleasurable feelings [15, 19].
