Neural Communication and Receptor Types

Introduction to Neural Communication Between Cells

• Neurons communicate via synapses.
• Axon terminals contain vesicles filled with neurotransmitters.
• Action potentials trigger neurotransmitter release into the synapse.
• Dendrites contain receptors that bind to neurotransmitters.

Receptor Types

• Ionotropic receptors are ligand-gated ion channels that open when neurotransmitters bind.
  • They produce fast, transient effects.
  • They can be excitatory (depolarizing) or inhibitory (hyperpolarizing).
• Metabotropic receptors are G-protein-coupled receptors that modulate cell signalling.
  • They have slower, longer-lasting effects.
  • They activate signal cascades.

Receptor Locations

• Postsynaptic receptors are located on the postsynaptic cell.
• Presynaptic receptors are located on the presynaptic cell.
  • Autoreceptors regulate the release of the same neurotransmitter.
  • Heteroreceptors regulate the release of a different neurotransmitter.

Neurotransmitter Clean-up

• Diffusion: Neurotransmitters diffuse away from the synapse.
• Enzymatic degradation: Enzymes break down neurotransmitters.
• Re-uptake: Neurotransmitters are transported back into the presynaptic cell or glial cells (e.g., astrocytes).

Drug Action

• Agonists mimic the effects of neurotransmitters by binding to receptors.
• Antagonists block the effects of neurotransmitters by binding to receptors.
• Other drug actions include:
  • Transporter blockers prevent reuptake of neurotransmitters.
  • Reuptake inhibitors block the reuptake of neurotransmitters.
  • Enzyme inhibitors block the breakdown of neurotransmitters.

Amino Acid Neurotransmitters

• Glutamate: The primary excitatory neurotransmitter.
  • Involved in learning, memory, and synaptic plasticity.
  • Receptors include AMPAR, NMDAR, Kainate receptors, and mGluR 1–8.
• GABA: The primary inhibitory neurotransmitter.
  • Involved in anxiety reduction, sleep, and motor control.
  • Receptors include both ionotropic and metabotropic types.

Monoamine Neurotransmitters

• Dopamine (DA):
  • Originates in the substantia nigra pars compacta and ventral tegmental area.
  • Involved in movement, motivation, reward, and attention.
  • Five receptor subtypes (D1R-D5R / D1-D5) are all metabotropic.
  • NOT the “pleasure molecule.”
• Norepinephrine (NE):
  • Also known as noradrenaline.
  • Originates in the locus coeruleus.
  • Involved in arousal, attention, and memory.
  • Plays a role in stress responses.
  • Two main receptor types (⍺1-2, β1-3) with subtypes and sub-subtypes are all metabotropic (GPCRs).
• Serotonin (5-HT):
  • Originates in the raphe nuclei.
  • Involved in mood, sleep, appetite, and cognition.
  • Fifteen receptor subtypes, almost all metabotropic.
  • NOT simply the “mood molecule.”

Other Small Neurotransmitters

• Acetylcholine:
  • The first discovered neurotransmitter.
  • Involved in muscle contraction, learning, and memory.
• Endocannabinoids:
  • Two neurotransmitters (anandamide and 2-arachidonoylglycerol).
  • Involved in pain perception, appetite, and mood.
  • Two receptors (CB1 and CB2) are both GPCRs.
• Adenosine:
  • A byproduct of ATP.
  • Involved in sleep, wakefulness, and energy metabolism.
• Endogenous Opioids:
  • Also known as endorphins.
  • Giant peptide neurotransmitters involved in pain perception, reward, and mood.
  • Receptors are all GPCRs.

Drugs Affecting Neurotransmitter Systems

• Glutamate antagonists:
  • Barbiturates
  • Nitrous oxide
  • Ketamine
  • Ethanol
• GABA agonists:
  • Benzodiazepines
  • Ethanol
  • Chloroform
  • Ether
• Dopamine drugs:
  • Addictive drugs increase dopamine transmission.
• Norepinephrine antagonists:
  • Propranolol (beta blocker) is used in PTSD treatment.
• Serotonin agonists:
  • Hallucinogens (LSD, DMT, psilocybin) affect perception and thoughts.
  • SSRIs (e.g., Prozac) are used for depression by blocking serotonin reuptake.
• Acetylcholine agonists:
  • Nicotine
• Endocannabinoid agonists:
  • THC (cannabis)
• Endogenous opioid agonists:
  • Heroin
  • Fentanyl
  • Naloxone (antagonist)

Explore the fascinating world of neural communication between cells. This quiz covers key concepts such as neurotransmitter release, types of receptors, and their functions in synaptic transmission. Test your knowledge on ionotropic and metabotropic receptors as well as their locations.