Substance P acts on the GPRC known as the neurokinin-1 receptors (NK1R). Activation of NK1R results in decrease in potassium conductance.

Injection of Substance P into Pre-Bötzinger Complex:

Question

Substance P acts on the GPRC known as the neurokinin-1 receptors (NK1R). Activation of NK1R results in decrease in potassium conductance.

Injection of Substance P into Pre-Bötzinger Complex:

BlackTom AI · Accepted Answer

Decreased K+ conductance from NK1R activation depolarizes Pre-Bötzinger neurons, increasing their excitability and hence respiratory rhythm frequency.

1) Relevant concepts:
- Substance P is a tachykinin neuropeptide that activates the neurokinin-1 receptor (NK1R), a G-protein–coupled receptor expressed on neurons in the Pre-Bötzinger Complex (PreBötC), the brainstem’s key respiratory rhythm generator.
- NK1R signaling reduces potassium conductance (blocks K+ channels or suppresses leak/GIRK currents), which reduces outward K+ current responsible for maintaining the resting membrane potential.
- Reduction of K+ efflux leads to membrane depolarization, increased action potential firing, and increased excitability of pacemaker neurons controlling inspiratory rhythm.

2) Step-by-step reasoning:
- Step 1: Substance P binds NK1R on PreBötC neurons.
- Step 2: NK1R activation (via G-protein signaling pathways) leads to decreased potassium channel conductance.
- Step 3: With less K+ leaving the cell, the membrane potential moves closer to threshold (depolarization).
- Step 4: Depolarized pacemaker neurons fire more frequently or generate bursts more often.
- Step 5: Increased burst frequency in PreBötC neurons translates into an increased respiratory (breathing) frequency.

3) Intermediate physiological steps shown above (binding → decreased K+ conductance → depolarization → increased firing → increased respiratory rate).

4) Why the correct answer is correct:
Because the PreBötC contains rhythmogenic neurons whose firing rate sets inspiratory frequency, any agent that reduces K+ conductance and thereby depolarizes these neurons will increase their firing and thus respiratory frequency. Substance P acting on NK1R does exactly that.

5) Why other choices would be incorrect:
- A decrease in respiratory frequency would require hyperpolarization or increased K+ conductance, opposite to NK1R’s effect.  
- No change would imply Substance P has no effect on PreBötC excitability, which contradicts established physiological and experimental data showing NK1R modulation alters rhythm.

Conclusion: Injection of Substance P into the Pre-Bötzinger Complex will increase respiratory frequency, matching the provided correct answer.

Substance P acts on the GPRC known as the neurokinin-1 receptors (NK1R). Activation of NK1R results in decrease in potassium conductance. Injection of Substance P into Pre-Bötzinger Complex:单项选择题

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