Role of orexin/hypocretin and CRF in the formation of drug-dependent synaptic plasticity in the mesolimbic system

Dopamine neurons in the ventral tegmental area (VTA) play a very important role in a variety of physiological as well as addictive behaviors. However, a clear understanding of the cellular mechanisms underlying these behaviors is still missing. Within the VTA, recent studies have shown that forms of synaptic plasticity such as long-term potentiation (LTP) and long-term depression (LTD) are produced by drugs of abuse. The main goal of this review is to discuss the relationship between plasticity at excitatory synapses in the VTA and addiction-associated behaviors such as behavioral sensitization and cocaine self-administration. Furthermore, recent studies have highlighted the role of orexin/hypocretin and corticotropin-releasing factor (CRF) as powerful modulators of excitatory synaptic transmission in the VTA. Here, we will discuss the potential correlation between the ability of these peptides in mediating excitatory synaptic transmission and the development of stress- and drug-dependent behaviors. Taken together, the results from the studies reviewed here shed new light on the mechanistic role of plasticity at glutamatergic synapses in the VTA in mediating addictive, as well as stress-dependent behaviors.