Dopamine is an excitatory neurotransmitter in the catecholamine family responsible for modulating reward and pleasure. It plays a key role in regulating emotional responses, the reward seeking processes and movement.
Dopamine and Evolution
Dopamine is an evolutionarily ancient neurotransmitter that is found in both vertebrates and invertebrates. Comparative phylogeny studies show us that there are several links between dopamine and behavioral responses subjected to reward (Barron, et. al, 2010). Many studies have suggested that the reward pathway has evolved from modulation of motor circuits in order to respond to environmental stimuli, eventually developing more specialized functions to avoid adverse stimuli or react to rewarding stimuli. There are several examples of genes that indicate conserved functions among vertebrates and invertebrates. For example, cyclic AMP-dependent protein kinase-related proteins affect learning and memory. However, it is still unclear if the role of dopamine is a conserved pathway or a product of convergent evolution.
Function of Dopamine in Different Phyla:
- Cnidaria: affects mouth opening with food stimuli
- Nematodes: modulates motor neurons in response to food stimuli
- Mollusks: modulates motor neurons, affects reinforcement and reward learning
- Insects: affects reinforcement and reward learning in conjunction with octopamine
- Birds: development of learning and memory (ex. song/ vocalization in songbirds); working memory plasticity
- Rodents: fear conditioning, positive/ negative reinforcement
- Primates: reinforcement learning (error-reward feedback system)
- Humans: reward, cognition, working memory, motor coordination, lactation
Dopamine is a neurotransmitter that is synthesized in the brain itself. This is because Dopamine cannot pass through the blood brain barrier. Instead, a precursor to Dopamine, L-DOPA passes into the brain from he blood and is synthesized into Dopamine and other catecholamines. This step by step process is described below:
Dopaminergic Pathways in the Brain and Associated Disorders:
Dopamine Pathway Evolution
Evidence shows that dopamine first evolved as a neurotransmitter for movement, implicating the nigrostriatal pathway as the most ancestral of the four dopaminergic pathways. However, the evolutionary history of the other pathways and their functions is not as clear. We examine the evolutionary history and importance of two of these pathways, the mesolimbic and mesocortical pathways as they pertain to addiction and working memory respectively. Which of these pathways has the more rich evolutionary history? How did the behaviors associated with these pathways evolve throughout millions of years of selective pressures? Answer these questions for yourself on the following pages!
Barron, A., Søvik, E., & Cornish, J. (2010, October 12). The Roles of Dopamine and Related Compounds in Reward-Seeking Behavior Across Animal Phyla. Retrieved November 11, 2015, from http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2967375
August 2015 Newsletter – Clayton Behavioral. (2015, August 17). Retrieved November 20, 2015, from http://claytonbehavioral.com/august-2015-newsletter/
Other transmitters and modulators. In: Pharmacology, 4th edition. Rang HP, Dale MM and Ritter JM. Edinburgh, UK: Harcourt Publishers Ltd, 2001:483–499. https://www.cnsforum.com/educationalresources/imagebank/dopaminergic/da_rcpt_subtypes
(n.d.). Retrieved November 20, 2015, from https://en.wikipedia.org/wiki/Dopamine