Identify the ONE correct statement about synaptic transmission.
找出关于突触传递的唯一正确说法。

Question

BlackTom AI · Accepted Answer

Glutamate is the principal excitatory neurotransmitter in the neocortex and acts at synapses on dendritic spines via multiple receptor types (AMPA, NMDA and metabotropic glutamate receptors).

1) Relevant knowledge points and concepts
- Glutamate: major excitatory transmitter in the central nervous system, especially at cortical synapses on dendritic spines; it activates ionotropic receptors (AMPA, NMDA, kainate) and metabotropic glutamate receptors (mGluRs).
- GABA: the main inhibitory neurotransmitter in the mature brain, acting via ionotropic GABA_A (Cl− channels) and metabotropic GABA_B (G-protein coupled) receptors, but can be depolarizing/excitatory under immature or altered chloride-gradient conditions.
- Dopamine receptors: canonical dopamine receptors (D1–D5) are G-protein-coupled (metabotropic), not ionotropic; basal ganglia motor dysfunction in Parkinson’s is due to dopamine loss in the substantia nigra with complex receptor regulation.
  
2) Step-by-step reasoning
- Examine each choice against neurophysiology facts.
- Choice asserting glutamate is the major excitatory transmitter on spine synapses: matches established anatomy and receptor pharmacology (cortical excitatory synapses are glutamatergic and commonly located on dendritic spines).
- Other choices conflict with known receptor types and developmental physiology.

3) Calculations/intermediate steps
- No numerical calculations are required; logical verification of receptor types and developmental exceptions suffices.

4) Why the correct answer is correct
- Electrophysiology, anatomy and pharmacology show that excitatory cortical synapses on spines release glutamate, which activates AMPA/NMDA receptors to mediate fast excitatory postsynaptic currents and mGluRs for modulatory signaling.

5) Why the other options are incorrect
- “GABA is always inhibitory”: false — in immature neurons or when intracellular Cl− is high (e.g., altered NKCC1/KCC2 expression) GABA_A activation can be depolarizing/excitatory.
- “Ionotropic dopamine receptors…down-regulated in Parkinson Disease”: false — canonical dopamine receptors in striatum are metabotropic (GPCRs); ionotropic dopamine receptors are not the primary mediators of basal ganglia motor function, and receptor regulation in Parkinson’s is complex rather than a simple down-regulation statement.
- “Glutamate is the only transmitter that acts solely on ionotropic receptors”: false — glutamate also activates metabotropic glutamate receptors (mGluRs).

6) Conclusion
- Therefore the correct statement is: “Glutamate is the major excitatory neurotransmitter at synapses on synaptic spines in the neocortex,” which matches the provided answer.

Identify the ONE correct statement about synaptic transmission. 找出关于突触传递的唯一正确说法。单项选择题

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