Bidirectional Signaling of Neuregulin-2 Mediates Formation of GABAergic Synapses and Maturation of Glutamatergic Synapses in Newborn Granule Cells of Postnatal Hippocampus.

Expression of neuregulin-2 (NRG2) is intense in a few regions of the adult brain where neurogenesis persists; however, little is understood about its role in developments of newborn neurons. To study the role of NRG2 in synaptogenesis at different developmental stages, newborn granule cells in rat hippocampal slice cultures were labeled with retrovirus encoding tetracycline-inducible microRNA targeting NRG2 and treated with doxycycline (Dox) at the fourth or seventh postinfection day (dpi). The developmental increase of GABAergic postsynaptic currents (GPSCs) was suppressed by the early Dox treatment (4 dpi), but not by late treatment (7 dpi). The late Dox treatment was used to study the effect of NRG2 depletion specific to excitatory synaptogenesis. The Dox effect on EPSCs emerged 4 d after the impairment in dendritic outgrowth became evident (10 dpi). Notably, Dox treatment abolished the developmental increases of AMPA-receptor mediated EPSCs and the AMPA/NMDA ratio, indicating impaired maturation of glutamatergic synapses. In contrast to GPSCs, Dox effects on EPSCs and dendritic growth were independent of ErbB4 and rescued by concurrent overexpression of NRG2 intracellular domain. These results suggest that forward signaling of NRG2 mediates GABAergic synaptogenesis and its reverse signaling contributes to dendritic outgrowth and maturation of glutamatergic synapses. SIGNIFICANCE STATEMENT: The hippocampal dentate gyrus is one of special brain regions where neurogenesis persists throughout adulthood. Synaptogenesis is a critical step for newborn neurons to be integrated into preexisting neural network. Because neuregulin-2 (NRG2), a growth factor, is intensely expressed in these regions, we investigated whether it plays a role in synaptogenesis and dendritic growth. We found that NRG2 has dual roles in the development of newborn neurons. For GABAergic synaptogenesis, the extracellular domain of NRG2 acts as a ligand for a receptor on GABAergic neurons. In contrast, its intracellular domain was essential for dendritic outgrowth and glutamatergic synapse maturation. These results imply that NRG2 may play a critical role in network integration of newborn neurons.

Classification and prediction of free-radical scavenging activities of dangyuja (Citrus grandis Osbeck) fruit extracts using (1)H NMR spectroscopy and multivariate statistical analysis.

Different parts of dangyuja (Citrus grandis Osbeck) fruits at different maturation stages were classified using a (1)H NMR-based metabolomic technique. Principal components analysis allowed the clear separation of fractions extracted with 50% methanol of different parts of dangyuja fruits at different maturation stages by combining principal components PC1 and PC2, which together accounted for 80.4% of the variance. A loading-plot analysis revealed that sucrose, glucose, oxaloacetic acid and citric acid were dominant in mature flesh, while naringin, tyramine, proline and alanine were dominant in immature fruit samples. Projections to latent structures using a partial least squares (PLS) model were used to predict the free-radical scavenging activities (FRSA) of dangyuja fruit extracts based on their (1)H NMR spectra. The present study suggests the usefulness of combining (1)H NMR spectroscopy with multivariate statistical analysis for discriminating dangyuja fruit samples, and predicting the FRSA of different parts of dangyuja fruit samples at different stages of maturation.