Lecture Seven

• Neurotransmitters are chemicals used to relay, amplify, and modulate signals between a neuron and another cell are neurotransmitters
• To be a neurotransmitter, the chemical must:

  • Be present in the presynaptic terminal
  • Be released in an amount sufficient to elicit a response on the postsynaptic cell
  • Induce the same changes as the endogenous chemical when added to extracellular fluid
  • Have a mechanism for breakdown or removal
  • Have similar effects of drugs at the synapse for both endogenous and exogenous application
• Neurotransmitters are divided into two types based on size:

  • Small molecules: most identified, with most synapses in the CNS involving amino acids
  • Large molecules: more uncommon, usually co-transmitters, such as neuropeptides
• Neuropeptides are 3-55 amino acids long, synthesized as a propeptide in ribosomes in the cell body, packed into dense core vesicles, transported down the axon, not released at active zones, and have no reuptake
• Neurotransmitter receptors:

  • Multiple receptors for each neurotransmitter
  • Result in EPSP (excitatory postsynaptic potential) or IPSP (inhibitory postsynaptic potential)
  • Neurons can have multiple types of receptors
• Examples of neurotransmitters:

  • GABA (Gamma-Aminobutyric Acid): most common inhibitory neurotransmitter in the brain, related to anxiety, can be modulated
  • Acetylcholine: has nicotinic receptors at the neuromuscular junction, inhibitory action on the heart through muscarinic receptors, affected in Alzheimer's disease
  • Glutamate: most common neurotransmitter in the brain, important for learning and memory
  • Catecholamines: start with tyrosine, involved in arousal, aggression, motivation, pleasure, reward, movement (e.g., Parkinson's), and schizophrenia
• • Serotonin: metabotropic or ionotropic amine, involved in mood, sleep, appetite, sexual function, and targeted by SSRIs (selective serotonergic reuptake inhibitors)
  • Endorphin: peptide concentrated in brain regions involved in pain, stimulation leads to analgesia and "runner's high"
  • Substance P: involved in cell growth, vomiting, and pain