Alterations of interneurons in the striatum and frontal cortex of mice during postnatal development.

We investigated the postnatal alterations of neuronal nuclei (NeuN)-positive neurons, parvalbumin (PV)-positive interneurons, neuronal nitric oxide synthase (nNOS)-positive interneurons, and neurotrophic factors in the mouse striatum and frontal cortex using immunohistochemistry. NeuN, PV, nNOS, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) immunoreactivity were measured in 1-, 2-, 4- and 8-week-old mice. Total number of NeuN-positive neurons was unchanged in the mouse striatum and frontal cortex from 1 up to 8 weeks of age. In contrast, a significant decrease in the number of PV-positive interneurons was observed in the striatum and frontal cortex of 1-, 2- and 4-week-old mice. Furthermore, a significant increase of nNOS-positive interneurons was found in the striatum and frontal cortex of 1- and/or 2-week-old mice. NGF-positive neurons were unchanged in the mouse striatum from 1 up to 8 weeks of age. In the frontal cortex, a significant increase in the number of NGF-positive neurons was observed only in 1-week-old mice. In contrast, a significant increase in the number of NGF-positive glia 1 cells was found in the striatum and frontal cortex of 4-week-old mice. Our double-labeled immunostaining showed that nNOS immunoreactivity was not found in PV-immunopositive interneurons. Furthermore, BDNF immunoreactivity was observed in both nNOS-positive and PV-positive interneurons in the striatum of 1- or 2-week-old mice. These results show that the maturation of nNOS-immunopositive interneurons precedes the maturation of PV-immunopositive interneurons in the striatum and frontal cortex during postnatal development. Furthermore, our results demonstrate that the expression of BDNF may play some role in the maturation of interneurons in the striatum and frontal cortex during postnatal development. Moreover, our findings suggest that the expression of NGF in glia cells may play some role in the maturation of glial cells and PV-positive interneurons in the striatum and frontal cortex during postnatal development.