Depressed nNOS expression during spine transition in the developing hippocampus of FMR1 KO mice

Nitric oxide (NO), synthesized as needed by NO synthase (NOS), is involved in spinogenesis and synaptogenesis. Immature spine morphology is characteristic of fragile X syndrome (FXS). The objective of this research was to investigate and compare changes of postnatal neuronal NOS (nNOS) expression in the hippocampus of male fragile X mental retardation 1 gene knockout mice (FMR1 KO mice, the animal model of FXS) and male wild-type mice (WT) at postnatal day 7 (P7), P14, P21, and P28. nNOS mRNA levels were analyzed by real-time quantitative PCR (N = 4-7) and nNOS protein was estimated by Western blot (N = 3) and immunohistochemistry (N = 1). In the PCR assessment, primers 5'-GTGGCCATCGTGTCCTACCATAC-3' and 5'-GTTTCGAGGCAGGTGGAAGCTA-3' were used for the detection of nNOS and primers 5'-CCGTTTCTCCTGGCTCAGTTTA-3' and 5'-CCCCAATACCACATCATCCAT-3' were used for the detection of β-actin. Compared to the WT group, nNOS mRNA expression was significantly decreased in FMR1 KO mice at P21 (KO: 0.2857 ± 0.0150, WT: 0.5646 ± 0.0657; P < 0.05). Consistently, nNOS immunoreactivity also revealed reduced staining intensity at P21 in the FMR1 KO group. Western blot analysis validated the immunostaining results by demonstrating a significant reduction in nNOS protein levels in the FMR1 KO group compared to the WT group at P21 (KO: 0.3015 ± 0.0897, WT: 1.7542 ± 0.5455; P < 0.05). These results suggest that nNOS was involved in the postnatal development of the hippocampus in FXS and impaired NO production may retard spine maturation in FXS.