Dopamine Neurons

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Midbrain Dopaminergic Neurons (MD) are found in found vertebrates and can be uniquely identified by their expression of homeodomain proteins Lmx1a and Msx1 [10]

MD neurons possess Dopamine, which is a neurotransmitter that is utilized in the brains of most animal species. Neurons that release dopamine have neuromodulatory functions

Fig. 1 A schematic of Dopamine Neurons in various locations in the brain at various stages of life in the rhesus monkey. Notice on the diagram the number of DA's as the age of the monkey progresses in the different regions of the brain.[1]

Basic information

Dopamine is a neurotransmitter found in the brain of most vertebrate and invertebrate species. Dopamine is involved in the reward system of the brain. Degeneration of these neurons is associated with conditions such as Parkinson's disease [6].

Fig. 2 This is a picture of Dopamine Neurons in cell culture that has been stained, using Tyrosine Hydroxylase immunocytochemistry. PNAS August 5, 1997 vol. 94 no. 16 8818-8823

Anatomy

The cell bodies are located in several areas of the brain including: the ventral tegmental area, substantia nigra pars compacta, and the hypothalamus, specifically, the arcuate nucleus. [6]

Fig. 3 A diagram of the vertebrate brain detailing the locations of the primary location of the cell bodies. This photo is from reference [2]

MD neurons project to other regions of the brain using the following pathways:Mesocortical pathway, the Mesolimbic pathway, the Nigrostriatal pathway, and the Tuberoinfundibular pathway.

Molecular profile

  • Neurotransmitter:

Dopamine is a important neurotransmitter in the brain due to its many functions and interactions with other systems. It is involved with motor functions, sleep, cognitive capabilities and several others.[3 and 8].

  • Unique molecular markers: Homeodomain proteins Lmx1a and Msx1. Lmx1a's primary role it to trigger dopamine cell differentiation and induce Msx1's expression. Msx1 is a co-inducer by activating Neuronal differentiation and the protein Ngn2 [10]

Physiology

Synaptic Connections

The three primary connections for Dopamine Neurons are dendritic spines, excitatory cortical terminals at the tip of dendritic spines, and dopamine varicosities contacting the same dendritic spines [2]

Spiking properties

Dopamine neurons can be recognized by their firing properties [1]

There are two modes of firing for Dopamine Neurons termed phasic and tonic. Tonic firing usually occurs when there is no salient stimuli in the region. Tonic firing typically affects afferent regions of the brain and can is affected by external stimuli that affect DA receptors. Phasic firing requires more energy and affects actual dopamine concentrations. This firing affects the efferent regions of the brain. [5]

Behavior

The behavior of Dopamine neurons can change in response to certain stimuli. Dopamine neurons seem to encode a certain reward probability prediction. Aversive stimuli have been found to inhibit the firing of dopamine neurons so the stimulus required to stimulate these neurons are more specific than orginally predicted. [3]

References

  1. Kanaan, N.M., et al. (2008) Age-Related changes in glial cells of dopamine midbrain subregions in rhesus monkeys, Neurobiology of Aging, 7415: pages 16. http://www.ncbi.nlm.nih.gov/pubmed/18715678?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum
  2. Schultz, Wolfram (1999). The Reward Signal of Midbrain Dopamine Neurons, News Physiological Science, vol 14: pages 249-255. http://physiologyonline.physiology.org/cgi/reprint/14/6/249]
  3. Ungless, M.A., et al. (2004) Uniform Inhibition of Dopamine Neurons in the Ventral Tegmental Area by Aversive Stimuli Science Magazine Vol #303 no. 5666, pgs. 2040-2042 http://www.sciencemag.org/cgi/content/full/303/5666/2040
  4. Humanillnesses.com http://www.humanillnesses.com/Behavioral-Health-Sel-Vi/Substance-Abuse.html
  5. Scholarpdia.org http://www.scholarpedia.org/article/Dopamine_neurons
  6. University of Texas Research http://www.utexas.edu/research/asrec/dopamine.html
  7. Wikipedia.org http://en.wikipedia.org/wiki/Neuromodulators#Dopamine_system
  8. Wikipedia.org http://en.wikipedia.org/wiki/Dopamine
  9. Wikipedia.org http://en.wikipedia.org/wiki/Neuron
  10. Andersson, Elisabet. et al. (2006) Identification of Intrinsic Determinants of Midbrain Dopamine Neurons Cell 124, 393–405, January 27, 2006. [2]