Chapter 6 - Neurotransmitter Systems (Slide Notes)

Introduction to Neuroscience - Neurotransmitters & Receptors

Cell to Cell Communication

  • Overview of how neurons communicate with each other.
  • Key concepts include:
  • Resting Membrane Potential: The electrical potential across the cell membrane of a resting neuron.
  • Action Potential (AP): A rapid change in the membrane potential that propagates along the neuron.
  • Conduction of AP: How AP travels along axons.
  • Anesthetics: How local/general anesthetics disrupt AP conduction.
  • Synaptic Transmission: The process by which neurons communicate at the synapse.
  • Post-synaptic Receptors: How receptors on the receiving end of the synapse interpret neurotransmitter signals.

Small Molecule Neurotransmitters

Amino Acids

  • Glutamic Acid (Glutamate): Main excitatory neurotransmitter in the brain.
  • Role in synaptic plasticity, learning, and memory.
  • Gamma-Aminobutyric Acid (GABA): Main inhibitory neurotransmitter.
  • Decreased levels lead to conditions like Huntington's disease.
  • Glycine: Inhibitory neurotransmitter in the spinal cord.
  • Important for processing motor and sensory information.

Monoamines

  • Catecholamines: Subgroup that includes dopamine and norepinephrine.
  • Dopamine (DA): Important for movement and reward.
    • Loss leads to Parkinson’s disease.
  • Norepinephrine (NE): Involved in alertness and arousal, released by the sympathetic nervous system.
  • Indolamines: Another subgroup including serotonin.
  • Serotonin (5-HT): Affects mood, sleep, and sexual function.
    • Associated with several psychiatric disorders when imbalanced.
  • Important for various functions in both gut and brain.

Peptides

  • Neuropeptides: Large molecule neurotransmitters made in the soma.
  • Require repeated action potentials for release.
  • Examples include endorphins, which play a role in pain relief and reward.

Other Atypical Neurotransmitters

  • Soluble Gases (e.g. Nitric Oxide): Can act as neuro-modulators, released on demand and affect adjacent neurons.
  • Endocannabinoids: Lipid-based neurotransmitters that act on cannabinoid receptors, involved in regulating mood and perception.

Neurotransmitter Effects

  • The effect of a neurotransmitter is determined by the post-synaptic receptor.
  • Example: Acetylcholine (ACh) can either excite skeletal muscle or inhibit cardiac muscle depending on the receptor type (ionotropic vs metabotropic).
  • Glutamate can act through different receptors inducing diverse responses (e.g., NMDA and AMPA receptors).

Receptor Types and Actions

  • Autoreceptors: Located on the presynaptic membrane, sensing the neurotransmitter's release and modulating further release.
  • Drug Actions: Drugs can mimic or enhance neurotransmitter actions:
  1. Precursor: E.g., L-DOPA increases dopamine production.
  2. Enhance Synaptic Release: E.g., Black Widow venom induces neurotransmitter release.
  3. Agonists: Such as morphine and nicotine that activate receptors.
  4. Inhibit Degradative Enzymes: Prevent breakdown of neurotransmitters.
  5. Block Reuptake: Drugs like cocaine prolong neurotransmitter action by blocking reuptake pumps.

Example - Parkinson’s Disease

  • Treatment involves L-DOPA to enhance dopamine levels, counteracting the loss of dopamine neurons in the substantia nigra.

Recent Research Insights

  • MDMA's Effect: Interaction with serotonin transporter influencing social behavior in octopuses highlights genetic evolutionary links in neurotransmitter functionality across species.