A Review of Dopamine

 

Dopamine Pathways in the Brain

Dopamine Major Functions: mnemonic Drive DA-RAMP (reward, attention, movement/motivation, and pleasure) Dopamine’s capabilities depend primarily on its pathways, mnemonic MENT (mesocortical, mesolimbic “emotion”, nigrostriatal, and tuberoinfundibular). The 1st and 2nd pathways are the closest pathways related to human behavior.

4 Pathways of Dopamine

Brain stem -> midbrain -> substantia nigra (nigrostriatal pathway) OR ventral tegmental area (VTA) (prefrontal/mesocortical pathways) -> terminals

  1. Mesocortical: motivation, pleasure, socializing
  2. Mesolimbic: strong emotional responses, the grasp of reality or lack thereof
  3. Nigrostriatal: controls motor function and movement. Contains 80% of the brain’s DA
  4. Tuberoinfundibular: controls prolactin secretion via the pituitary gland

There was a recently discovered fifth pathway that innervates the hypothalamus but its function is not currently known.

Receptors of Dopamine

There are at least 5 subtypes of DA receptors

  • D1 and D5: mostly involved in postsynaptic inhibition, located in the brain & smooth muscle.
  • D2, D3, and D4: involved in both pre-and-post synapses, located in the brain and heart.
  • D2 is the predominant subtype in the brain: the functions of the D2 receptors are best understood because this is the primary binding site for virtually all antipsychotic agents as well as for dopamine agonists used to treat Parkinson’s disease.

Dopamine Pathways and Pathology

  1. Mesocortical: high DA causes negative symptoms of schizophrenia
  2. Mesolimbic: high DA causes positive symptoms of schizophrenia, hallucinations, confusion
  3. Nigro-striatal: low DA causes extrapyramidal symptoms (EPS)
  4. Tuber-infundibular: breast development, lactation. Elevated prolactin levels are associated with galactorrhea (breast secretions), amenorrhea (loss of ovulation and menstrual periods), and possibly other problems such as sexual dysfunction

Diseases and Conditions

  • Parkinson’s Disease: the core etiology is a decrease in DA
  • Schizophrenia: too much DA and with positive or negative symptoms depending on the pathways
  • Attention deficit hyperactivity disorder and obsessive-compulsive disorder, addiction: related to poor impulse control, reward dysfunctions
  • Restless legs syndrome (RLS): possibly related to the 5th pathway

-Source Doctor Lib

Drugs that Affect Dopamine

DA agonists

  • L-DOPA – increases the concentration of DA in the substantia nigra and alleviates symptoms of PD
  • Dihydrexidine – used to treat movement disorders
  • Bromocriptine – used to treat movement disorders
  • Cocaine – DA transporter blocker, increases attention and awareness
  • Methylphenidate – increases attention and awareness
  • Deprenyl – prevents the destruction of DA – used to treat pain

DA antagonists

  • AMPT – used to block the synthesis of DA – only used in experimental research on animals
  • Reserpine – keeps DA from entering synaptic vesicles –used in herbal medicine and used to be used to treat high blood pressure and stress (side effects)
  • Clozapine – blocks DA receptors – used to treat symptoms of schizophrenia
  • Chlorpromazine – blocks DA receptors – used to treat symptoms of schizophrenia

-Anti(P)/psychotics is also Anti(D)/dopamine

Related Media

Helpful Pictures about Neurotransmitters

DA Pathways: notice how the pathways start from the smallest and then move to bigger surface areas/terminals (DA can cause little or big problems, especially with addictions).

Dopamine Pathways

 

 

 

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