Receptors and Intracellular Signal Transduction
Receptor signaling beyond ion flux
Receptor classes
Neuronal receptors include ionotropic ligand-gated channels, GPCRs, receptor tyrosine kinases, cytokine receptors, and adhesion receptors. Each class couples extracellular signals to distinct temporal scales and downstream molecular architectures.
Temporal coding
Fast synaptic signaling is ideal for precise transmission, whereas metabotropic and kinase-based pathways encode context, history, and plasticity.
Second messenger pathways
GPCRs regulate cAMP, IP, diacylglycerol, and intracellular calcium, thereby controlling enzymes such as protein kinase A, protein kinase C, and Ca/calmodulin-dependent kinases. These pathways modulate channel conductance, gene transcription, and synaptic efficacy.
Which second messenger is directly produced by adenylyl cyclase?
Adenylyl cyclase converts ATP into cAMP.
Correct answer: cAMP
What is one major function of GPCR signaling in neurons?
GPCRs regulate ion channels, enzymes, and transcriptional programs.
Correct answer: Modulation of synaptic and intrinsic excitability
Signal transduction outputs
Membrane-proximal effects
- Alter channel opening probability
- Change transmitter release probability
Nuclear effects
- Alter transcription
- Support long-term plasticity
Common signaling nodes
Why are GPCR pathways especially important in neuromodulation?
GPCR pathways amplify signals and can reshape neuronal and circuit behavior.
Correct answer: They can amplify weak extracellular signals and alter circuit state
Mapping a signaling cascade
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Step 1: Identify receptor engagement and ligand dose.
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Step 2: Determine the immediate second messenger response.
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Step 3: Measure kinase activation and substrate phosphorylation.
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Step 4: Track downstream transcriptional or physiological effects.
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Step 5: Test causality with pathway-specific perturbations.