Dopamine Pathways

Four Major Dopamine Pathways

Dopamine is a diverse and important neurotransmitter in the human body. Although it is typically thought of as our “reward and salience” neurotransmitter, it has different functions within its four major pathways. Dopamine pathways are neuronal connections in which dopamine travels to areas of the brain and body to convey important information such as executive thinking, cognition, feelings of reward and pleasure, and voluntary motor movements.

Mesolimbic Dopamine Pathways

The first major dopamine pathway is the mesolimbic pathway. This pathway is highly involved in dopamine’s most commonly thought of function: pleasure and reward. This pathway begins at the ventral tegmental area (VTA). The VTA is a dopamine-rich nucleus that covers part of the midbrain and projects dopaminergic action potentials to another area of the brain called the nucleus accumbens (NAc)¹. It is here in the NAc, where dopamine primarily mediates feelings of pleasure and reward. Thus, whenever a person encounters rewarding or pleasurable stimuli (such as food, sex, drugs, etc.), dopamine is released and sends signals from the VTA to the NAc, which creates positive feelings that reinforce the behavior.

Stimulation of the NAc is important for maintaining our day-to-day activity. However, over-stimulation can lead to cravings for the item that stimulated the NAc. These substances directly increase dopaminergic activity within the mesolimbic pathway, creating intense feelings of euphoria. Overcoming intense cravings that underlines dysfunction in the mesolimbic pathway can be difficult. However, therapy, certain medications, and even some dopamine-increasing supplements may help the struggling individual gain control over cravings ³.

Mesocortical Dopamine Pathways

The second pathway is called the mesocortical pathway. Like in the mesolimbic pathway, dopaminergic projections within the mesocortical pathway originate in the VTA. From the VTA, action potentials travel to areas in the prefrontal cortex (PFC). The PFC is highly involved in cognition, working memory, and decision making ². Thus, when dysfunction within this pathway occurs, individuals may experience poor concentration and the inability to make decisions.

Taking certain medications, such as amphetamines, can upregulate the release of dopamine in the mesocortical pathway, which in turn increases cognition and activity in the PFC. Although this increase in dopamine within the mesocortical pathway may aid in cognition, it may have unintended side effects in the mesolimbic pathway. Thus, one might consider other dopamine-increasing ingredients to potentially aid in cognition, while avoiding addiction ³.

Nigrostriatal Dopamine Pathways

The next dopamine pathway is the nigrostriatal pathway, which is involved in motor planning. As the name implies, the dopamine projections start in the substantia nigra and go to the caudate and putamen, parts of the basal ganglia. This pathway contains around 80% of dopamine in the brain.

Dopaminergic neurons in the nigrostriatal pathway stimulate purposeful movement. Reduced numbers of dopamine neurons in this pathway is a major aspect of motor control impairment. Additionally, D2 antagonists, such as first-generation antipsychotics, interfere with the nigrostriatal pathway and can cause extrapyramidal symptoms. These movement disorders may include spasms, contractions, tremors, motor restlessness, parkinsonism, and tardive dyskinesia (irregular/jerky movements).²

Tuberoinfundibular Dopamine Pathways

The final dopamine pathway is the tuberoinfundibular pathway. The dopamine neurons in this pathway begin in the arcuate and periventricular nuclei of the hypothalamus, and project to the infundibular region of the hypothalamus, specifically the median eminence. In this pathway, dopamine is released into the portal circulation that connects this region to the pituitary gland. Here, dopamine functions to inhibit prolactin release.

Prolactin is a protein secreted by the pituitary gland that enables milk production and has important functions in metabolism, sexual satisfaction (countering the arousal effect of dopamine), and the immune system. Blockage of the D2 receptors, common with antipsychotic medications, prevent dopamine’s inhibitory function, thus increasing prolactin levels in the blood. ² Increases in prolactin can affect menstrual cycles, libido, fertility, bone health, or galactorrhea.⁴

As we have seen, dopamine is far more than just a pleasure/reward neurotransmitter. Although it plays this role within the mesolimbic pathway, dopamine also plays important roles in hormone release, cognition, and movement. Since dopamine is such a diverse and important neurotransmitter, it may be beneficial to assess your overall level of dopamine.

Talk to your healthcare provider today about Sanesco’s neurotransmitter assessment, to check the status of your dopamine level or find a Sanesco provider near you. Clinicians can become a Sanesco provider and offer dopamine assessment as well as gain access to more neurotransmitter information.

References:

1. Adinoff, B. (2004). Neurobiologic Processes in Drug Reward and Addiction. Harvard Review of Psychiatry, 12(6), 305–320. http://doi.org/10.1080/10673220490910844
2. Guzmán, F. (n.d.). The Four Dopamine Pathways Relevant to Antipsychotics Pharmacology [Video blog post]. Retrieved November 15, 2016, from http://psychopharmacologyinstitute.com/antipsychotics-videos/dopamine-pathways-antipsychotics-pharmacology/
3. Yadav, S. K., Prakash, J., Chouhan, S., Westfall, S., Verma, M., Singh, T. D., & Singh, S. P. (2014). Comparison of the neuroprotective potential of Mucuna pruriens seed extract with estrogen in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced PD mice model [Abstract]. Neurochemistry International, 65, 1-13. doi:10.1016/j.neuint.2013.12.001
4. Majumdar, A., & Mangal, N. S. (2015). Hyperprolactinemia. In Principles and Practice of Controlled Ovarian Stimulation in ART(pp. 319-328). Springer India.