The mesolimbic pathway, sometimes referred to as the reward pathway, is a dopaminergic pathway in the brain. The pathway begins in the ventral tegmental area of the midbrain and connects to the nucleus accumbens. It is the most significant neural pathway in the brain in which changes occur in all known forms of addiction.
The following structures are considered to be a part of the mesolimbic pathway:
- Ventral tegmental area
- The ventral tegmental area (VTA) is a part of the midbrain. It consists of dopaminergic, GABAergic, and glutamatergic neurons. The VTA communicates with the nucleus accumbens via the medial forebrain bundle.
- Nucleus accumbens
- The nucleus accumbens is found in the ventral striatum and is composed of medium spiny neurons. It is subdivided into limbic and motor subregions known as the shell and core. The medium spiny neurons receive input from both the dopaminergic neurons of the VTA and the glutamatergic neurons of the hippocampus, amygdala, and medial prefrontal cortex. When they are activated by these inputs, the medium spiny neurons' projections release GABA onto the ventral pallidum. The release of dopamine in this structure drives the mesolimbic system.
This pathway plays a central role in neurobiology of addiction; in particular, a drug addiction is defined as the compulsive use of a drug that is rewarding (i.e., activate this pathway), despite adverse consequences. It is also implicated in schizophrenia and depression. Addiction, schizophrenia, and depression all involve distinct structural changes with in this pathway.
Other dopamine pathways
The other dopamine pathways are:
- Dreyer JL (2010). "New insights into the roles of microRNAs in drug addiction and neuroplasticity". Genome Med 2 (12): 92. doi:10.1186/gm213. PMC 3025434. PMID 21205279.
- Robison AJ, Nestler EJ (November 2011). "Transcriptional and epigenetic mechanisms of addiction". Nat. Rev. Neurosci. 12 (11): 623–637. doi:10.1038/nrn3111. PMC 3272277. PMID 21989194.
ΔFosB has been linked directly to several addiction-related behaviors ... Importantly, genetic or viral overexpression of ΔJunD, a dominant negative mutant of JunD which antagonizes ΔFosB- and other AP-1-mediated transcriptional activity, in the NAc or OFC blocks these key effects of drug exposure14,22–24. This indicates that ΔFosB is both necessary and sufficient for many of the changes wrought in the brain by chronic drug exposure. ΔFosB is also induced in D1-type NAc MSNs by chronic consumption of several natural rewards, including sucrose, high fat food, sex, wheel running, where it promotes that consumption14,26–30. This implicates ΔFosB in the regulation of natural rewards under normal conditions and perhaps during pathological addictive-like states.
- Blum K, Werner T, Carnes S, Carnes P, Bowirrat A, Giordano J, Oscar-Berman M, Gold M (2012). "Sex, drugs, and rock 'n' roll: hypothesizing common mesolimbic activation as a function of reward gene polymorphisms". J. Psychoactive Drugs 44 (1): 38–55. doi:10.1080/02791072.2012.662112. PMC 4040958. PMID 22641964.
It has been found that deltaFosB gene in the NAc is critical for reinforcing effects of sexual reward. Pitchers and colleagues (2010) reported that sexual experience was shown to cause DeltaFosB accumulation in several limbic brain regions including the NAc, medial pre-frontal cortex, VTA, caudate, and putamen, but not the medial preoptic nucleus. Next, the induction of c-Fos, a downstream (repressed) target of DeltaFosB, was measured in sexually experienced and naive animals. The number of mating-induced c-Fos-IR cells was significantly decreased in sexually experienced animals compared to sexually naive controls. Finally, DeltaFosB levels and its activity in the NAc were manipulated using viral-mediated gene transfer to study its potential role in mediating sexual experience and experience-induced facilitation of sexual performance. Animals with DeltaFosB overexpression displayed enhanced facilitation of sexual performance with sexual experience relative to controls. In contrast, the expression of DeltaJunD, a dominant-negative binding partner of DeltaFosB, attenuated sexual experience-induced facilitation of sexual performance, and stunted long-term maintenance of facilitation compared to DeltaFosB overexpressing group. Together, these findings support a critical role for DeltaFosB expression in the NAc in the reinforcing effects of sexual behavior and sexual experience-induced facilitation of sexual performance. ... both drug addiction and sexual addiction represent pathological forms of neuroplasticity along with the emergence of aberrant behaviors involving a cascade of neurochemical changes mainly in the brain's rewarding circuitry.
- Olsen CM (December 2011). "Natural rewards, neuroplasticity, and non-drug addictions". Neuropharmacology 61 (7): 1109–22. doi:10.1016/j.neuropharm.2011.03.010. PMC 3139704. PMID 21459101.
- Pierce RC, Kumaresan V. 2006. The mesolimbic dopamine system: The final common pathway for the reinforcing effect of drugs of abuse? Neuroscience and Biobehavioral Reviews 30:215-38
- Zhang TA, Maldve RE, Morrisett RA. 2006. Coincident signaling in mesolimbic structures underlying alcohol reinforcement. Biochemical Pharmacology 72:919-27
- Purves D et al. 2008. Neuroscience. Sinauer 4ed. 754-56
- Janhunen S, Ahtee L. 2007. Differential nicotinic regulation of the nigrostriatal and mesolimbic dopaminergic pathways: Implications for drug development. Neuroscience and Biobehavioral Reviews 31:287–314
- Van den Heuval DMA, Pasterkamp RJ. 2008. Getting connected in the dopamine system. Progress in Neurobiology 85:75–93
- Laviolette SR. 2007. Dopamine modulation of emotional processing in cortical and subcortical neural circuits: evidence for a final common pathway in schizophrenia? Schizoprenia Bulletin 33:971–981
- Diaz J. 1996. How Drugs Influence Behavior: A Neurobehavorial Approach. Prentice Hall