Morphological characteristics of the striatal neural pathway by biotinylated dextran amine tracing in rats

Using neural pathway tracing and immunohistochemical technique, the striato-direct pathway （BDA3 kDa injected into the rat lateral globus pallidus） and striato-indirect pathway （BDA3 kDa injected into the substantia nigra pars reticulata） neurons were specifically labeled, and then subjected to double-labeled immunohistochemistry for mu-OPIOID Receptor （specifically-labeled striatal patch compartment）, D1, and D2, respectively. The experimental findings showed that there are no statistically significant differences in the soma diameter and the number of primary dendrites between the striato-direct （substantia nigra pars reticularis） and indirect （globus pallidum externum） neurons labeled retrograde by BDA3 kDa. In addition, these two kinds of projection neurons revealed no obvious coexistence. This evidence indicates that as a highly sensitive neural pathway tracer, BDA could yield reliably and exquisitely detailed labeling of target neurons and synaptic structures. The variance of the morphologic structures and the localization of neurons were not statistically significant between the striato-substantia nigra pars reticularis and the globus pallidum externum projection neurons. Mesencephalic and thalamic neurons correlated with striatal neurons in morphology. Especially the latter which make typical excitatory synaptic contacts with striato-direct and -indirect neurons. Thus, this evidence suggests that thalamic neurons may extensively excite striatal neurons.

The Secondary Motor Cortex-striatum Circuit Contributes to Suppressing Inappropriate Responses in Perceptual Decision Behavior

The secondary motor cortex(M2)encodes choice-related information and plays an important role in cue-guided actions.M2 neurons innervate the dorsal striatum(DS),which also contributes to decision-making behavior,yet how M2 modulates signals in the DS to influence perceptual decision-making is unclear.Using mice performing a visual Go/No-Go task,we showed that inactivating M2 projections to the DS impaired performance by increasing the false alarm(FA)rate to the reward-irrelevant No-Go stimulus.The choice signal of M2 neurons correlated with behavioral performance,and the inactivation of M2 neurons projecting to the DS reduced the choice signal in the DS.By measuring and manipulating the responses of direct or indirect pathway striatal neurons defined by M2 inputs,we found that the indirect pathway neurons exhibited a shorter response latency to the No-Go stimulus,and inactivating their early responses increased the FA rate.These results demonstrate that the M2-to-DS pathway is crucial for suppressing inappropriate responses in perceptual decision behavior.