Which change contributes to decreased neurotransmitter release during opioid receptor signaling?

Which change contributes to decreased neurotransmitter release during opioid receptor signaling?

• A. Increased cAMP
• B. Decreased potassium efflux
• C. Decreased calcium influx
• D. Activation of NMDA receptors

Answer: (C)

Opioid receptor activation engages Gi/o proteins that suppress calcium entry into the presynaptic terminal and promote potassium efflux, which hyperpolarizes the neuron. The release of neurotransmitter is driven by calcium entering the terminal and triggering vesicle fusion. Fewer calcium ions entering means fewer vesicles fuse and less transmitter is released, so decreased calcium influx directly leads to reduced neurotransmitter release. Other options don’t fit as well: lowering cAMP is a secondary effect and doesn’t acutely curb release as directly as calcium entry does; reducing potassium efflux would lessen hyperpolarization, not promote the decrease in release; activating NMDA receptors would increase calcium influx and enhance release rather than decrease it.

Opioid receptor activation engages Gi/o proteins that suppress calcium entry into the presynaptic terminal and promote potassium efflux, which hyperpolarizes the neuron. The release of neurotransmitter is driven by calcium entering the terminal and triggering vesicle fusion. Fewer calcium ions entering means fewer vesicles fuse and less transmitter is released, so decreased calcium influx directly leads to reduced neurotransmitter release.

Other options don’t fit as well: lowering cAMP is a secondary effect and doesn’t acutely curb release as directly as calcium entry does; reducing potassium efflux would lessen hyperpolarization, not promote the decrease in release; activating NMDA receptors would increase calcium influx and enhance release rather than decrease it.