A drug that blocks the uptake of dopamine and norepinephrine into presynaptic nerve terminals and also blocks sodium channels in the axonal membrane is :
**Core Concept**
The question is testing the pharmacological action of a drug that affects the neurotransmitter uptake and sodium channel blockade. This involves the neurotransmitter dopamine and norepinephrine, as well as the presynaptic nerve terminals and axonal membrane. The correct answer is a drug that modulates these mechanisms.
**Why the Correct Answer is Right**
The correct answer, tetracaine, is a local anesthetic that blocks sodium channels in the axonal membrane, preventing the depolarization of the neuron. Additionally, it blocks the uptake of dopamine and norepinephrine into presynaptic nerve terminals, increasing their concentration in the synaptic cleft. This action is due to the inhibition of the dopamine and norepinephrine transporters, specifically the dopamine transporter (DAT) and the norepinephrine transporter (NET).
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the drug mentioned in this option does not have a significant effect on dopamine and norepinephrine uptake or sodium channel blockade.
**Option B:** This option is incorrect because the drug mentioned in this option primarily affects the muscarinic receptors and does not have a significant effect on dopamine and norepinephrine uptake or sodium channel blockade.
**Option C:** This option is incorrect because the drug mentioned in this option primarily affects the GABA receptors and does not have a significant effect on dopamine and norepinephrine uptake or sodium channel blockade.
**Clinical Pearl / High-Yield Fact**
Local anesthetics like tetracaine can cause a rapid increase in the concentration of neurotransmitters in the synaptic cleft, leading to excitatory effects on the postsynaptic neuron.
**Correct Answer:** C. Tetracaine