2.3 Neurotransmitters

Roles of Major Neurotransmitters

Epinephrine (Adrenaline):
- Structure: Amine
- Receptor: Metabotropic
- Effect: Excitatory
- Modulated/Broken-down: Monoamine oxidase (MAO)
- Involved in:
  - Fight or flight response
Glutamate:
- Structure: Amino Acid
- Receptor: Ionotropic and Metabotropic
- Effect: Excitatory
- Modulated/Broken-down: Taken up by glia via Na+
- Involved in:
  - Memory

Acetylcholine ( $ACh$ ):
- Structure: Amine
- Receptor: Ionotropic and Metabotropic
- Effect: Excitatory or Inhibitory
- Modulated/Broken-down: Acetylcholinesterase (AChE)
- Involved in:
  - Regulation of muscle contractions
Serotonin:
- Structure: Amine
- Receptor: Ionotropic and Metabotropic
- Effect: Excitatory or Inhibitory
- Modulated/Broken-down: Monoamine oxidase (MAO)
- Involved in:
  - Mood
  - Appetite
Dopamine:
- Structure: Amine
- Receptor: Metabotropic
- Effect: Excitatory or Inhibitory
- Modulated/Broken-down: Monoamine oxidase (MAO)
- Involved in:
  - Pleasure
  - Fine motor behaviour
  - Arousal
  - Working memory
  - Compulsion
GABA ( $\text{gamma-aminobutyric acid}$ ):
- Structure: Amino Acid
- Receptor: Ionotropic and Metabotropic
- Effect: Inhibitory
- Modulated/Broken-down: Metabolised by GABA transaminase in glia
- Involved in:
  - Calming
  - Muscle relaxant
Substance P:
- Structure: Neuropeptide
- Receptor: Metabotropic
- Effect: Excitatory
- Modulated/Broken-down: Intracellular enzymatic breakdown in lysosomes
- Involved in:
  - Pain signalling
  - Nausea/inflammation
Endocannabinoids:
- Structure: Other
- Receptor: Metabotropic
- Effect: Excitatory or Inhibitory
- Modulated/Broken-down: Enzymatic breakdown in membrane diffusion
- Involved in:
All amino acids are modulated/broken-down by glia
With the exception of acetylcholine, all amines are broken down by monoamine oxidase (MAO)
Glutamate is taken up by Na+ via glia
GABA is modulated by transaminase in glia
Substance P is modulated by intracellular breakdown by lysosomes
Endocannabinoids are modulated by enzymatic breakdown via passive membrane diffusion

Compare and Contrast Ionotropic and Metabotropic Neurotransmitter Receptors

Categorisation of Major Neurotransmitters

Chemical Type:
- Amino Acids (Start with G): Glutamate, GABA, Glycine.
- Amines (End with IN, or INE): Acetylcholine, Dopamine, Norepinephrine, Epinephrine, Serotonin.
- Peptides: Substance P.
- Other Types: Neurotensin, Endorphins, Oxytocin, Vasopressin.
Receptor Target Type:
- Ionotropic: Speed: Fast response due to direct opening of ion channels. Mechanism: Neurotransmitter binding directly leads to ion flow; the receptor is the ion channel
- Metabotropic: Speed: Slower response as they activate G-proteins, leading to secondary messenger cascades. Mechanism: Neurotransmitter binding activates G-proteins, causing changes in cellular functions via secondary messengers,
Post-Synaptic Effect:
- Excitatory Neurotransmitters: Increasing action potential likelihood (EPSP).
- Inhibitory Neurotransmitters: Decreasing action potential likelihood (IPSP).