In vivo temporal property of GABAergic neural transmission in collateral feed-forward inhibition system of hippocampal-prefrontal pathway.

Anatomical evidence suggests that rat CA1 hippocampal afferents collaterally innervate excitatory projecting pyramidal neurons and inhibitory interneurons, creating a disynaptic, feed-forward inhibition microcircuit in the medial prefrontal cortex (mPFC). We investigated the temporal relationship between the frequency of paired synaptic transmission and gamma-aminobutyric acid (GABA)ergic receptor-mediated modulation of the microcircuit in vivo under urethane anesthesia. Local perfusions of a GABAa antagonist (-)-bicuculline into the mPFC via microdialysis resulted in a statistically significant disinhibitory effect on intrinsic GABA action, increasing the first and second mPFC responses following hippocampal paired stimulation at interstimulus intervals of 100-200 ms, but not those at 25-50 ms. This (-)-bicuculline-induced disinhibition was compensated by the GABAa agonist muscimol, which itself did not attenuate the intrinsic oscillation of the local field potentials. The perfusion of a sub-minimal concentration of GABAb agonist (R)-baclofen slightly enhanced the synaptic transmission, regardless of the interstimulus interval. In addition to the tonic control by spontaneous fast-spiking GABAergic neurons, it is clear the sequential transmission of the hippocampal-mPFC pathway can phasically drive the collateral feed-forward inhibition system through activation of a GABAa receptor, bringing an active signal filter to the various types of impulse trains that enter the mPFC from the hippocampus in vivo.

Dynamic change in expression of LECT2 during liver regeneration after partial hepatectomy in mice.

Leukocyte-cell-derived chemotaxin 2 (LECT2) was first isolated from the culture fluid of phytohemagglutinin-activated human T-cell leukemia SKW-3 cells and was found to be expressed in the human, bovine and murine livers. To further analyze the role of LECT2 in the liver, we investigated the expression of mouse LECT2 (mLECT2) during liver regeneration after partial hepatectomy (PHx) using immunohistochemical and in situ hybridization techniques. Mouse LECT2 protein and mRNA were detected in most hepatocytes in normal mouse; however, at 30 min after PHx, they were not detected in liver tissue. At 2 h after PHx, expression of mLECT2 protein was seen in hepatocytes surrounding the central vein, although mRNA expression levels were still low. At 6 h after PHx, a marked number of hepatocytes expressing mLECT2 protein and mRNA were seen throughout the liver, and at 12 h after PHx, hepatocytes expressing mLECT2 protein and mRNA further increased in number. However, expression levels of mLECT2 protein and mRNA at 24 h after PHx were significantly lower when compared with levels after 12 h. These results indicate that LECT2 triggers the early events of regeneration with concomitant suppression of hepatocyte proliferation.

Hybrid nanogels with physical and chemical cross-linking structures as nanocarriers.

Polymerizable nanogels were prepared by self-assembly of cholesteryl group-bearing pullulan (CHP) with methacryloyl groups (CHPMA). The CHPMA nanogel was polymerized with 2-methacryloyloxyethyl phosphorylcholine (MPC) by radical polymerization in dilute aqueous solution. The solution properties of the polymers in water were investigated by TEM, SEC-MALS, and fluorescence quenching technique. Monodispersed hybrid nanogels of CHPMA-MPC (CM nanogels) (25-30 nm in radius of gyration) were obtained by using CHPMA nanogel as a seed-nanogel. CM nanogels have a dual cross-linking structure that is physically cross-linked with the cholesteryl groups and chemically cross-linked with the MPC polymer chains. CM nanogels trap heat-denatured carbonic anhydrase B (CAB) and prevent their aggregations. The nanogels maintained the ability of trapping and releasing enzymes by host-guest interaction of cholesteryl group and cyclodextrin.

Identification of addicsin/GTRAP3-18 as a chronic morphine-augmented gene in amygdala.

Using subtractive cloning, we identified a 1.4 kb mRNA that was ubiquitously expressed in various tissues; this mRNA was highly up-regulated in amygdala nuclei in mice when morphine was repeatedly administered but not when an opiate-receptor antagonist was co-administered. The mRNA encodes a 23 kDa protein, designated 'addicsin'. This contains two putative PKC-phosphorylation motifs and several hydrophobic regions, and was recovered in a soluble protein fraction of brain lysate. Its primary structure showed 98% identity with that of rat glutamate-transporter-associated protein 3-18 (GTRAP3-18), a putative modulator of neural glutamate-transporter EAAC1. Up-regulation of addicsin expression by morphine may affect glutamate uptake in the amygdala, causing mice to develop morphine tolerance and dependence.

Regulation of neurite extension by expression of LECT2 and neurotrophins based on findings in LECT2-knockout mice.

Leukocyte cell-derived chemotaxin 2 (LECT2) was first isolated as a chemotactic factor from phytohemagglutinin-activated human T-cell leukemia SKW-3 cells. LECT2 is expressed in various tissues, including in the brain, stomach and liver, but the functions of LECT2 in the brain remains unclear. To elucidate these functions, we investigated the influence of a deficiency of LECT2 on the morphology of cultured hippocampal neurons during neuronal development, and examined the expression of neurotrophins (NGF, BDNF, and NT-3) and their receptors (TrkA, TrkB, TrkC, and p75NTR) in these neurons. The extension of axons and dendrites in neurons from LECT2-knockout (LECT2-KO) mice was shorter than that in neurons from wild-type mice during culture and significantly less than that in wild-type mice after 4 days in culture. Moreover, neurons from LECT2-KO mice showed different expression of NGF, BDNF and NT-3 during culture compared to wild-type mice. Our results show that LECT2 regulates the extension of axons and dendrites and the expressions of NGF, BDNF and NT-3 during neuronal development.

Regulation of katanin-P60 levels by LECT2 adjusts microtubular morphology.

Leukocyte cell-derived chemotaxin 2 (LECT2) facilitates neuritic extension in cultured hippocampal neurons during initial development. However, the functions of LECT2 in neuritic extension are poorly understood. To elucidate these functions, we examined microtubular morphology and levels of katanin-P60, a microtubule-severing enzyme, in cultured hippocampal neurons from wild-type mice and LECT2 knockout (KO) mice. Microtubules in LECT2-KO mice exhibited fragmentation and were shorter than those of wild-type mice. Furthermore, the expression of katanin-P60 in LECT2-KO mice was significantly elevated when compared with wild-type mice at 1 day in vitro (DIV1) and 4. Our results suggest that LECT2 regulates neuritic extension through microtubular morphallaxis through the control of katanin-P60 levels.

Synaptic plasticity dynamics in the hippocampal-prefrontal pathway in vivo.

We examined the effect of long-term potentiation (LTP) on paired-pulse responses across varied stimulus intensities and interstimulus intervals (ISIs), at ascending synapses from the intermediate and ventral hippocampus to the medial prefrontal cortex in urethane-anesthetized rats. LTP significantly shifted the median effective stimulus towards lower intensities in the intermediate route, and increased at 25-ms ISI the paired-pulse response, which was inversely proportional to the stimulus intensity. In the ventral route, the paired-pulse response varied with ISI rather than intensity, and increased at 50-ms and 100-ms ISI after LTP. The intermediate synaptic plasticity significantly exhibited total amplifier dynamics with wide ranges of frequency at lower intensity and intensity at 100-ms ISI in contrast to the ventral one.

Novel biodegradable polyphosphate cross-linker for making biocompatible hydrogel.

To obtain a novel biodegradable cross-linker, polymerizable polyphosphate (PIOP) was synthesized by ring-opening polymerization of 2-i-propyl-2-oxo-1,3,2-dioxaphospholane with 2-(2-oxo-1,3,2-dioxaphosphoroyloxyethyl methacrylate) (OPEMA). The number averaged molecular weight of the PIOP was 1.2 x 10(4), and the number of OPEMA units in one PIOP molecule was 2.2. Nonenzymatic degradation of the PIOP was evaluated in various pH aqueous media. The degree of hydrolysis was dependent on the pH; that is, it increased with an increase in the pH of the medium. At pH 11.0, the PIOP completely degraded in only 6 days. The poly[2-methacryloyloxyethyl phosphorylcholine (MPC)] cross-linked with the PIOP was prepared by radical polymerization. This polymer could form hydrogel, and the free water fraction in the hydrogel was high. The enzymatic activity of trypsin in contact with the hydrogel was similar to that in buffer solution. There is no adverse effect caused by the hydrogel to reduce the function of the trypsin. The cytotoxicity of poly(MPC) and degraded PIOP was evaluated using v79 cells, and it was not observed in either case. In conclusion, PIOP is a hydrolyzable polymer, which can be used as a cross-linker, and novel hydrogels having biodegradability and biocompatibility were prepared from poly(MPC) cross-linked with the PIOP.