The connections between the cortex and the striatum are critically involved in control and execution of voluntary movements. Here we focused on the expression of calcium binding protein parvalbumin (PV) in the corticostriatal pathway. Injections of Fluorogold into the striatum gave rise to retrograde labeling of PV-positive neurons in the retrosplenial cortex and somatosensory cortex. The PV-positive corticostriatal projection neurons were mainly found in layer V, but occasionally seen in layers II, III, and VI. The PV immunoreactivity of retrogradely labeled cells was weaker than that of nonlabeled cells. Although it was rather difficult to analyze the morphology of Fluorogold-labeled neurons that exhibited PV immunoreactivity, some of them showed distinct apical dendrites and were considered pyramidal cells. The main target of PV-positive cortical afferents was the caudal striatum on the ipsilateral side. Next, we tested whether PV-positive corticostriatal projection neurons were GABAergic or not, because previous studies emphasized that PV was an important marker for cortical GABAergic neurons. Unexpectedly, we found that the majority of PV-positive corticostriatal projection neurons were glutamic acid decarboxylase (GAD)-negative, while some of them were GAD-positive. Finally, an anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) injection into the somatosensory cortex resulted in many PV-positive corticostriatal terminals that were vesicular glutamate transporter 1-positive, whereas some of the PV-positive PHA-L-labeled terminals were GAD-positive. Our results provide anatomical evidence for expression of PV in glutamatergic and GABAergic corticostriatal pathway in mice and suggest that a subset of cortical afferents may exert some inhibitory influence on striatal activity.
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