Lesson 11

Biogenic Amine Neurotransmitters

  • Biogenic amines: Include dopamine (DA), norepinephrine (NE), epinephrine (Epi), serotonin (5-HT), and histamine.
  • Reuptake: Biogenic amine neurotransmitters are removed from the synaptic cleft primarily by reuptake or uptake into non-neuronal cells.
  • Receptors: Mostly metabotropic G protein-coupled, except for the ionotropic 5-HT3 receptor.

Adrenergic Receptors

  • Classes: Divided into alpha-1 (a1), alpha-2 (a2), and beta (ß) receptors, each with three subtypes.
  • Functions: Involved in numerous functions including arousal, attention, and cardiovascular regulation.

Serotonergic Function

  • Role: Critical for sleep, emotion, cognition, and various bodily functions.
  • Disorders: Abnormalities in serotonergic pathways are linked to mood disorders such as anxiety and depression.
  • 5-HT3 Target: Antagonists used to treat nausea and vomiting caused by chemotherapy or surgery.

Dopamine Synthesis & Function

  • Dopamine Pathway: Synthesized from L-tyrosine, which undergoes conversion by specific enzymes.
  • Associated Disorder: Degeneration in the substantia nigra leads to Parkinson's disease.
  • Dopamine Receptors: Classified into D1-like (increase activity) and D2-like (decrease activity) groups.

Norepinephrine & Epinephrine Synthesis

  • Synthesis Process: Begins with L-tyrosine, leading to the formation of norepinephrine (NE) and then epinephrine (Epi) in adrenal medulla.
  • Reuptake: NE and Epi in the synaptic cleft are primarily reabsorbed by neurons through reuptake.

Serotonin Synthesis & Removal

  • Synthesis: Derived from tryptophan and processed by specific enzymes to form serotonin (5-HT).
  • Removal Mechanism: 5-HT is removed from the synaptic cleft by active reuptake through serotonin transporter proteins (SERT).

Histamine as a Neurotransmitter

  • Origin: Synthesized from L-histidine by brain cells as it cannot cross the blood-brain barrier.
  • Receptors: Three metabotropic subtypes (H1, H2, H3).
  • Functions: Involved in arousal, attention, memory, and learning; antihistamines can cause drowsiness.