D1 is excitatory(direct pathway)and D2 is inhibitory (indirect pathway) so as you taught D2 causes inhibition of indirect pathway how is that possible sir?
Let’s clarify the roles of the direct (D1) and indirect (D2) pathways in the basal ganglia, which are involved in the regulation of movement.
- Direct Pathway (D1):
- In the direct pathway, activation of D1 receptors leads to excitation of the thalamus.
- This excitation facilitates movement by promoting the initiation and execution of desired motor actions.
- In simplified terms, the direct pathway “goes” and promotes movement.
- Indirect Pathway (D2):
- In contrast, the indirect pathway, involving D2 receptors, has an inhibitory effect on movement.
- Activation of D2 receptors inhibits the thalamus, which leads to suppression of movement.
- This pathway is involved in selecting and inhibiting unwanted or inappropriate movements.
- In simplified terms, the indirect pathway “stops” or inhibits movement.
Now, let’s address your question about inhibition of the indirect pathway:
- Activation of the D2 receptors indeed leads to inhibition of the indirect pathway. However, this inhibition of the indirect pathway ultimately results in disinhibition of the thalamus, leading to facilitation of movement. So, while the D2 pathway itself is inhibitory, its net effect on movement is facilitatory due to its indirect influence on the thalamus.
In summary, while the direct (D1) pathway directly promotes movement, the indirect (D2) pathway indirectly facilitates movement by inhibiting unwanted movements through disinhibition of the thalamus. Thus, although D2 is inhibitory in its own pathway, its overall effect on movement is facilitatory.