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The mystery of dopamine receptors: What are the differences between D1 and D2 neurons?
In the human basal ganglia structure, medium spiny neurons (MSNs) located in the striatum account for approximately 90% of the number of neurons. These neurons are mainly inhibitory GABAergic neurons and are divided into two main phenotypes: D1 type direct pathway and D2 type indirect pathway based on their functional characteristics. These neurons are not only different in structure, but also in their functions and effects.
"Neurons in the D1-type direct pathway promote behavior and activate the final basal ganglia output structure."
D1 type MSNs mainly express D1 type dopamine receptors, adenosine A1 receptors, arterial sinus peptide and substance P peptide, while D2 type MSNs express D2 type dopamine receptors, adenosine A2A receptors and endorphins. The network functions of these two types of neurons play an important role in the initiation and inhibition of actions.
Structure and location
The cell body of a medium-sized spiny neuron is typically 15-18 microns in diameter and possesses five major dendrites that form dense spines at their branching points. This makes their dendritic domains reach 200-300 microns. About 90% of striatal neurons are such medium-sized projection neurons, and only 10% are interneurons.
"Direct pathway neurons project directly to the medial globus pallidus (GPi) and substantia nigra pars compacta (SNpr)."
In the direct pathway, MSNs will immediately transmit signals to GPi and SNpr to control movement. In the indirect pathway, the final destination of these neurons is to connect to the globus pallidus lateralis (GPe) and ventral pallidum (VP) through intermediaries. Such network pathways demonstrate the critical role of MSNs in action control.
Function Overview
MSNs are inhibitory GABAergic neurons, and their direct MSNs (dMSNs) and indirect MSNs (iMSNs) have completely different effects on their final output structure in the basal ganglia: dMSNs can stimulate the basal ganglia, thereby promoting movement; iMSNs can inhibit the activity of the basal ganglia, thereby inhibiting the occurrence of specific behaviors.
"In the classic model of motor control, activation of the direct pathway is thought to cause movement, while the indirect pathway is responsible for the termination of movement."
For example, patients with Parkinson's disease (PD) suffer from the loss of dopamine neurons, resulting in inefficiency of the direct pathway and overactivation of the indirect pathway, which leads to motor dysfunction. Huntington's disease is caused by the degeneration of neurons in the indirect pathway, resulting in uncontrollable redundant movements. The balance of the two types of neurons is crucial during the initiation and selection of movements.
The difference between ventral and dorsal striatum
MNs in the ventral striatum play important roles in motivation, reward, reinforcement, and aversion. Among them, the direct pathway plays a key role in reward-based learning, while the indirect pathway is important in human responses to aversive stimuli. This suggests that these neurons are not limited to motor control but are also involved in emotional and cognitive processes.
"Although ventral and dorsal medium spiny neurons are phenotypically similar, their target structures and functions are different."
These studies reveal the intricate interactions between neurons, showing that they not only play an important role in motor function, but are also closely related to the regulation of emotion and behavior. The researchers are now further exploring how these neurons work together to support more complex behavioral patterns.
Finally, with an in-depth understanding of dopamine receptors and medium-sized spiny neurons, we may be able to better understand how these neural networks affect our behavior and emotions. So, behind these biological systems, are there Are there more mysteries and areas worth exploring?
