Neurochemistry and Signal Transduction

Neurochemistry: Neurotransmitter Systems & Signaling Pathways Overview

• MCAT Question Review: Enzymes in Dopaminergic and Adrenergic Neurons

  • Pathway: Tyrosine $\rightarrow$ DOPA $\rightarrow$ Dopamine $\rightarrow$ Norepinephrine (Adrenaline)

  • Enzymes involved:

    1. Tyrosine Hydroxylase (TH): Catalyzes Tyrosine $\rightarrow$ DOPA.

    2. Dopa Decarboxylase (DDC): Catalyzes DOPA $\rightarrow$ Dopamine.

    3. Dopamine Beta Hydroxylase (DBH): Catalyzes Dopamine $\rightarrow$ Norepinephrine.

  • Dopaminergic neurons: Synthesize dopamine, requiring TH and DDC.

  • Adrenergic neurons: Synthesize norepinephrine (typically in the brain), requiring TH, DDC, and DBH.

  • Answer: Both dopaminergic and adrenergic neurons contain Tyrosine Hydroxylase and Dopa Decarboxylase (Option D).

• Location of Neuron Cell Bodies

  • Dopamine neurons: Located in the Substantia Nigra and Ventral Tegmental Area (VTA).

  • Noradrenergic neurons: Cell bodies are typically found in the Locus Coeruleus.

• Key Questions for Neurotransmitter Systems

  • For major neurotransmitters (Acetylcholine, Glutamate, GABA, Dopamine, Norepinephrine, Serotonin), be prepared to answer:

    1. How is the transmitter synthesized? What enzymes are required?

    2. What are the postsynaptic receptors (e.g., ionotropic like AMPA, NMDA, Kainate for Glutamate; metabotropic like G-protein-coupled receptors)?

    3. How is the transmitter removed from the synaptic cleft (diffusion, uptake mechanisms, enzymes, or both)?

    4. Is the transmitter recycled and/or metabolized?

    5. Where are the cell bodies (of the neurons that produce this transmitter) located?

  • Example: Glutamate

    • Receptors: AMPA, NMDA, Kainate (all ionotropic); Metabotropic glutamate receptors (G-protein coupled).

    • Location: Glutamatergic neurons are found