Brain-derived neurotrophic factor (BDNF) has been implicated in regulating adult neurogenesis in the subgranular zone (SGZ) of the dentate gyrus; however, the mechanism underlying this regulation remains unclear. In this study, we found that Bdnf mRNA localized to distal dendrites of dentate gyrus granule cells isolated from wild-type mice, but not from Bdnfklox/klox mice where the long 3′ untranslated region (UTR) of Bdnf mRNA is truncated. KCl-induced membrane depolarization stimulated release of dendritic BDNF translated from long 3′ UTR Bdnf mRNA in cultured hippocampal neurons, but not from short 3′ UTR Bdnf mRNA. Bdnfklox/klox mice exhibited reduced expression of glutamic acid decarboxylase 65 (a GABA synthase), increased proliferation of progenitor cells, and impaired differentiation and maturation of newborn neurons in the SGZ. These deficits in adult neurogenesis were rescued with administration of phenobarbital, an enhancer of GABAA receptor activity. Furthermore, we observed similar neurogenesis deficits in mice where the receptor for BDNF, TrkB, was selectively abolished in parvalbumin-expressing GABAergic interneurons. Thus, our data suggest that locally synthesized BDNF in dendrites of granule cells promotes differentiation and maturation of progenitor cells in the SGZ by enhancing GABA release, at least in part, from parvalbumin-expressing GABAergic interneurons.

The neuropeptide galanin mediates its effects through the receptor subtypes Gal 1 , Gal 2 , and Gal 3 and has been implicated in anxiety- and depression-related behaviors. Nevertheless, the receptor subtypes relevant to these behaviors are not known because of the lack of available galanin-selective ligands. In this article, we use behavioral, neurochemical, and electrophysiological approaches to investigate the anxiolytic- and antidepressant-like effects of two potent small-molecule, Gal 3 -selective antagonists, SNAP 37889 and the more soluble analog SNAP 398299. Acute administration of SNAP 37889 or SNAP 398299 enhanced rat social interaction. Furthermore, acute SNAP 37889 was also shown to reduce guinea pig vocalizations after maternal separation, to attenuate stress-induced hyperthermia in mice, to increase punished drinking in rats, and to decrease immobility and increase swimming time during forced swim tests with rats. Moreover, SNAP 37889 increased the social interaction time after 14 days of treatment and maintained its antidepressant effects during forced swim tests with rats after 21 days of treatment. In microdialysis studies, SNAP 37889 partially antagonized the galanin-evoked reduction in hippocampal serotonin (5-hydroxytryptamine, 5-HT), as did the 5-HT 1A receptor antagonist WAY100635. Their combination produced a complete reversal of the effect of galanin. SNAP 398299 partially reversed the galanin-evoked inhibition of dorsal raphe cell firing and galanin-evoked hyperpolarizing currents. These results indicate that Gal 3 -selective antagonists produce anxiolytic- and antidepressant-like effects, possibly by attenuating the inhibitory influence of galanin on 5-HT transmission at the level of the dorsal raphe nucleus.

In the central nervous system (CNS), oligodendrocyte maturation and axonal myelination occur on a predictable schedule, but the underlying timing mechanisms are largely unknown. In the present study, we demonstrate that Nkx2.2 homeodomain transcription factor is a key regulator for the timing of oligodendrocyte differentiation during development. Whereas induced expression of Nkx2.2 in early oligodendrocyte precursor cells (OPCs) causes precocious differentiation of oligodendrocytes, conditional ablation of Nkx2.2 temporally delays oligodendrocyte maturation. Moreover, Nkx2.2 can directly bind to the promoter of platelet-derived growth factor receptor alpha (Pdgfra) and repress its gene expression. Genetic ablation of Pdgfra mimics the effect of Nkx2.2 overexpression in accelerating OPC differentiation in the developing spinal cord. Together, our findings strongly suggest that Nkx2.2 functions as a major 'switch' to turn off Pdgfra signaling in OPCs and initiate the intrinsic program for oligodendrocyte differentiation. KEY WORDS: Spinal cord, Tet-on, Transcription factor, Mouse INTRODUCTIONA requisite component of nervous system development is the achievement of proper axonal myelination for rapid and accurate transmission of electric activities. In the central nervous system (CNS), myelin sheaths are elaborated by oligodendrocytes (OLs), and the myelination process is preceded by molecular and morphological differentiation of oligodendrocyte precursor cells (OPCs). It was observed that OPCs differentiate on a predictable schedule both in vivo and in vitro, but the molecular pathways that control the timing of OPC differentiation have not been clearly defined.It has been recently shown that multiple classes of transcription factors are involved in the regulation of the OL differentiation process. They include the negative differentiation regulators Id2, Id4 and Hes5 (Kondo and Raff, 2000; Liu et al., 2006;Wang et al., 2001), and positive regulators such as Olig1 (Lu et al., 2002), Mrf (Myrf -Mouse Genome Informatics) (Emery, 2010), Mash-1 (Ascl1 -Mouse Genome Informatics) (Sugimori et al., 2008), Sip1 (Gemin2 -Mouse Genome Informatics) (Weng et al., 2012), Nkx2.2 (Qi et al., 2001 and Sox10 (Soula et al., 2001). Among these transcription factors, Nkx2.2 (Nkx2-2 -Mouse Genome Informatics) is uniquely positioned as a candidate regulator for the timing of OL differentiation. In the developing mouse spinal cord, Nkx2.2 expression is upregulated in OPCs immediately before their differentiation but rapidly downregulated after OPC differentiation (Fu et al., 2002;Soula et al., 2001;Xu et al., 2000;Zhou et al., 2001). Thus, Nkx2.2 expression in differentiating OPCs correlates seamlessly with the onset of OL differentiation. Functional analyses revealed that Nkx2.2 plays an essential role in the terminal differentiation of OLs (Qi et al., 2001;Zhou et al., 2001). However, because of the neonatal lethality of Nkx2.2 mutants, it has remained unknown whether Nkx2.2 is absolutely required for OPC maturation or simp...

Recent studies have suggested that Nkx6.2/Gtx and Nkx2.2 homeodomain transcription factors are involved in the regulation of oligodendrocyte maturation and/or myelination which occur predominantly in postnatal stages. However, their cellular specificity in postnatal central nervous system has not been characterized and their dynamic expressional relationship during oligodendrocyte lineage progression has not been determined. Here we report that both Nkx2.2 and Nkx6.2 are selectively expressed in Olig2+ cells of oligodendrocyte lineage in postnatal spinal cords. While Nkx6.2 is specifically expressed in the APC+ mature oligodendrocytes, Nkx2.2 is initially expressed in differentiating oligodendrocyte precursor cells (OPCs) but quickly down-regulated as OPCs undergo terminal differentiation. Intriguingly, Nkx2.2 expression is up-regulated in mature myelinating oligodendrocytes at later stages. The co-expression of Nkx2.2 and Nkx6.2 transcription factors in myelinating oligodendrocytes suggests their functional interactions in the regulation of myelin sheath formation and/or maintenance.

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Although brain-derived neurotrophic factor (BDNF) is known to regulate circuit development and synaptic plasticity, its exact role in neuronal network activity remains elusive. Using mutant mice (TrkB-PV −/− ) in which the gene for the BDNF receptor, tyrosine kinase B receptor (trkB), has been specifically deleted in parvalbuminexpressing, fast-spiking GABAergic (PV+) interneurons, we show that TrkB is structurally and functionally important for the integrity of the hippocampal network. The amplitude of glutamatergic inputs to PV+ interneurons and the frequency of GABAergic inputs to excitatory pyramidal cells were reduced in the TrkB-PV −/− mice. Functionally, rhythmic network activity in the gamma-frequency band (30-80 Hz) was significantly decreased in hippocampal area CA1. This decrease was caused by a desynchronization and overall reduction in frequency of action potentials generated in PV+ interneurons of TrkB-PV −/− mice. Our results show that the integration of PV+ interneurons into the hippocampal microcircuit is impaired in TrkB-PV −/− mice, resulting in decreased rhythmic network activity in the gamma-frequency band.gamma oscillations | synaptic transmission | Cre recombinase | dendrite | slice T yrosine kinase B receptor (TrkB), the cognate receptor for brain-derived neurotrophic factor (BDNF) and neurotrophin-4, mediates key signaling events that control many aspects of neuronal development and function (1-4), including the maturation of parvalbumin-positive (PV+) interneurons in the hippocampal microcircuit. BDNF is preferentially synthesized in, and secreted from glutamatergic neurons, whereas trkB is expressed in both glutamatergic and γ-aminobutyric acid (GABA)-ergic neurons in hippocampus (5). Among cortical interneurons, PV+ interneurons express trkB abundantly (6). This anatomical organization of the BDNF signaling components and the known importance of feedback and feedforward communication between principal cells and interneurons (7-11) suggest a potential role for TrkB signaling in modulating neuronal network function.Rhythmic activity in cortical networks is important for the formation of neuronal assemblies (12)(13)(14). Of particular interest is rhythmic network activity in the gamma-frequency band (30-80 Hz, gamma oscillations) (15-17). Gamma oscillations are a result of the synchronized electrical activity of the neurons within a network and are thought to be important for temporal encoding, binding of sensory features, and memory storage and retrieval (18)(19)(20)(21)(22). Moreover, gamma oscillations are altered in several brain disorders, such as Alzheimer's disease (23-25), schizophrenia (24, 26-31), and epilepsy (24,32,33). Gamma oscillations are exquisitely susceptible to modulation of the cellular and synaptic mechanisms underlying the rhythmic activity. Fast-spiking PV+ interneurons are the main recipient of recurrent glutamatergic innervations in the hippocampal circuitry, and their role in gamma-frequency synchronization in cortical and hippocampal networks is well-establish...

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Trafficking of the galanin R2 receptor (GALR2) fused with enhanced GFP (EGFP) was studied by using confocal fluorescence microscopy. The fusion protein was predominantly localized on the plasma membrane with some intracellular fluorescent structures (vesicles), mainly in the perinuclear region. Incubation with galanin resulted in a concentration-dependent increase in intracellular Ca 2؉ concentration levels, suggesting that the GALR2-EGFP conjugate is functional. After blocking endocytosis with methyl-␤-cyclodextrin GALR2-EGFP expression was increased on the surface and decreased in the cytoplasm. Blocking endocytic recycling with monensin caused an increase of intracellular GALR2-EGFP accumulation and a decrease of fluorescence on the plasma membrane. GALR2-EGFP on the plasma membrane was internalized within 5-10 min after treatment with galanin or AR-M1896, a selective GALR2 agonist, with a dramatic reduction in plasma membrane localization and appearance in intracellular vesicles. Neither M35 nor M40, two galanin analogues with putative antagonistic action, prevented GALR2 agonist-induced internalization of GALR2-EGFP, suggesting that they are not antagonists at this receptor under the present circumstances. Galanin stimulation at low temperature caused GALR2-EGFP aggregation and clustering on the surface but no translocation to cytoplasm. After coincubation with galanin the GALR2-EGFP was colocalized with internalized Texas red-transferrin, a marker of the clathrin endocytic pathway. Hyperosmotic sucrose inhibited internalization of GALR2-EGFP. Taken together these findings indicate that GALR2 undergoes constitutive endocytosis and recycling and that both ligand-independent and liganddependent internalization use the clathrin-dependent endocytic recycling pathway.