The dopamine from Substantia Nigra neurons acts on D1 (excitatory) and D2 (inhibitory) receptors on the neurons of the direct and indirect pathway (respectively). Which of the following outcomes is a possible effect of a drug that selectively reduced the activity of the neurons in the striatum (caudate and putamen) that expressed D2 receptors?
黑质神经元释放的多巴胺作用于直接通路和间接通路神经元上的 D1（兴奋性）和 D2（抑制性）受体。下列哪种结果可能是选择性药物的作用？降低了纹状体（尾状核和壳核）中表达 D2 受体的神经元的活性？

Question

The dopamine from Substantia Nigra neurons acts on D1 (excitatory) and D2 (inhibitory) receptors on the neurons of the direct and indirect pathway (respectively). Which of the following outcomes is a possible effect of a drug that selectively reduced the activity of the neurons in the striatum (caudate and putamen) that expressed D2 receptors?
黑质神经元释放的多巴胺作用于直接通路和间接通路神经元上的 D1（兴奋性）和 D2（抑制性）受体。下列哪种结果可能是选择性药物的作用？   降低了纹状体（尾状核和壳核）中表达 D2 受体的神经元的活性 ？

BlackTom AI · Accepted Answer

Reduction of activity in D2-expressing striatal neurons decreases the strength of the indirect pathway and therefore facilitates movement, producing spontaneous (involuntary) movements.

Relevant concepts:
- Two basal ganglia pathways control movement: the direct (D1-expressing striatal neurons) facilitates movement; the indirect (D2-expressing striatal neurons) inhibits movement.
- Normal dopamine from the substantia nigra excites D1 neurons and inhibits D2 neurons, netting an overall facilitation of movement.
- Circuit chain: striatum (D2) → inhibits external globus pallidus (GPe) → GPe inhibits subthalamic nucleus (STN) → STN excites internal globus pallidus/substantia nigra reticulata (GPi/SNr) → GPi/SNr inhibit thalamus → thalamus excites cortex (movement).

Step-by-step reasoning:
1. Drug selectively reduces activity of D2-expressing striatal neurons (the indirect pathway neurons).
2. With less activity in these striatal D2 neurons, they exert less inhibition on the GPe.
3. GPe becomes more active (disinhibited) and so exerts stronger inhibition on the STN.
4. STN activity falls, so it drives the GPi/SNr less strongly (less excitatory input).
5. GPi/SNr output decreases, producing less inhibition of the thalamus.
6. Thalamic drive to motor cortex increases, producing excessive, spontaneous motor output (hyperkinesia/involuntary movements).

Why the correct answer is correct:
This sequence shows that reducing D2 striatal activity effectively weakens the indirect “braking” pathway, leading to disinhibition of thalamocortical motor output and spontaneous movements. Clinically, reduced indirect pathway function causes hyperkinetic syndromes (e.g., chorea, hemiballism).

Why the other choices are incorrect:
- Inability to initiate movements: would result from decreased direct pathway activity or increased indirect activity (hypokinetic state), not from reducing D2 neurons.
- No effect unless D1 also activated: incorrect because altering the indirect pathway alone changes motor output through the basal ganglia circuit.
- Poor postural reflexes and tremors: these are typical of Parkinsonism from global dopamine loss (both D1 and D2 effects), not from isolated reduction of D2-striatal neuron activity.

Conclusion: The correct outcome is spontaneous movements, which matches the provided answer.

Similar Questions

According to the Radiolab episode "Unraveling Bolero," the basal ganglia, the part of the brain we move with, can also be known as our __________ brain. Notice: The questions and answer sets for this quiz are protected under copyright, and may not be reproduced without the author's consent.

(14.2) The ________________ is a collection of subcortical brain areas that inhibits the cortex and makes it less likely for a motor movement to be executed.

The basal ganglia are involved in all of the following processes except:

Dysfunction of the basal ganglia is known to be implicated in all of the following except:

Name the nuclear mass that the black arrow is pointing to in this image [input]

Name the nuclear mass that the black arrow is pointing to in this image [input]

The __________ are a group of nuclei that surround the thalamus and regulate body movements by processing sensory and motor information coming from the cerebral cortex.

Which deep brain structures work to initiate and terminate motor functions?

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