Neurotransmitter Pathways

• Pathways in the brain


  • Activity follows specific pathways, symmetrically arranged on both sides of the midline
• Schizophrenia


  Associated with overactivity in the mesolimbic cortical (MLC) pathway, overabundance of dopamine and/or over-sensitive dopamine receptors
• Parkinson's Disease


  Associated with underactivity in the nigrostriatal (NS) pathway, caused by degeneration of the substantia nigra and lack of dopamine
• Neurotransmitters (NTs)


  The nervous system uses over 100 different NTs, classified by chemical structure (amines, amino acids, peptides, gases) and function (excitatory, inhibitory, information modulation)
• Neurotransmitter synthesis


  Produce tyrosine in the liver, transport to brain, convert to L-DOPA, convert to dopamine, store in neuron's vesicles
• Psychoactive drugs


  Substances that affect the central nervous system and alter alertness, perception, cognition, and/or emotion
• Functional categories of psychoactive drugs


  • Stimulants
  • Depressants
  • Analgesics
  • Hallucinogens
• Agonist


  Mimics the action of a neurotransmitter by binding to the receptor site and opening the channel
• Antagonist


  Prevents the action of a neurotransmitter by blocking the receptor site but not opening the channel
• Neurons are not distributed randomly in the nervous system, but cluster together and travel in parallel pathways
• Anatomical pathway


  Pathway identified by the structures it connects, e.g. retino-geniculo-cortical (visual) pathway
• Chemical pathway


  Pathway identified by the neurotransmitter used throughout, e.g. dopaminergic pathway
• Different receptors for the same neurotransmitter can have completely different functions, e.g. D1 receptor activates second messengers while D2 receptor inhibits them
• Brain structures have different distributions of neurotransmitter receptor subtypes, making it difficult to design selective drugs