Molecular role of dopamine in anhedonia linked to reward deficiency syndrome (RDS) and anti-reward systems

Anhedonia is a condition that leads to the loss of feelings pleasure in response to natural reinforcers like food, sex, exercise, and social activities. This disorder occurs in addiction, and an array of related neuropsychiatric syndromes, including schizophrenia, depression, and Post Traumatic Stress Disorder (PTSD). Anhedonia may by due to derangements in mesolimbic dopaminergic pathways and their terminal fields (e.g., striatum, amygdala, and prefrontal cortex) that persist long after the traces of the causative drugs are eliminated (pharmacokinetically). Here we postulate that anhedonia is not a distinct entity but is rather an epiphenomenon of hypodopaminergic states and traits arising from the interaction of genetic traits and epigenetic neurobiological alterations in response to environmental influences. Moreover, dopaminergic activity is rather complex, and so it may give rise to differential pathophysiological processes such as incentive sensitization, aberrant learning and stress-like "anti-reward" phenomena. These processes may have additive, synergistic or antagonistic interactions with the concurrent reward deficiency states leading in some instances to more severe and long-lasting symptoms. Operant understanding of the neurogenetic antecedents to reward deficiency syndrome (RDS) and the elucidation of reward gene polymorphisms may provide a map for accessing an individual's genetic risk for developing Anhedonia. Prevention techniques that can restore homeostatic balance via physiological activation of dopaminergic receptors (D2/D3) may be instrumental for targeting not only anhedonia per se but also drug craving and relapse.