Biomedical subjects

Katsunori Kobayashi

Publications and source records attributed to Katsunori Kobayashi.

6 recordsLinked to original sources

PubMed2006

Locomotor activity correlates with modifications of hippocampal mossy fibre synaptic transmission.

The hippocampus has long been implicated in memory formation. Although accumulating evidence suggests involvement of the hippocampus in other brain functions including locomotor regulation and emotional processes, cellular and synaptic bases underlying these functions remain largely unknown. We here report that environmental manipulations in mice unveiled the association of locomotor activity with the hippocampal mossy fibre (MF) synaptic transmission. Electrophysiological recordings of synaptic responses were made using hippocampal slices prepared from mice whose behaviour had been analysed. Environmental enrichment induced parallel decreases in open-field locomotor activity and MF synaptic facilitation. Facilitation induced by paired-pulse stimulation at relatively long intervals (>or=200 ms) was selectively reduced while the basal synaptic efficacy and high-frequency transmission were unaffected. Social isolation caused a change in behaviour in an elevated plus-maze, but neither the open-field activity nor the MF synaptic transmission was significantly altered. Effects of dopamine, a neurotransmitter essential for locomotor regulation, on the MF synapse were also examined using these mice. Environmental manipulations did not cause significant changes in potentiation of the MF synaptic transmission induced by dopamine. However, analysis of behavioural and electrophysiological results in individual subjects revealed that locomotor activity negatively correlates with magnitude of the dopamine-induced potentiation. These results suggest that the MF synapse plays important roles in the regulation of locomotor activity. We propose that the MF synapse can serve as the synaptic model for certain forms of locomotor regulation, with potential importance for investigation of the pathophysiology of psychiatric diseases using animal models.

Animals↗

PubMed2006

Dopamine selectively potentiates hippocampal mossy fiber to CA3 synaptic transmission.

Dopamine has been implicated in various brain functions and the pathology of neurological diseases. In the hippocampus, dopamine has been shown to induce acute depression of synaptic transmission in the CA1 region, but it remains largely unknown how it works in the CA3 region. We here report that dopamine induces acute synaptic potentiation at the synapse formed by mossy fibers (MFs) on mouse hippocampal CA3 pyramidal cells, but not at converging associational/commissural synapses. Dopamine potentiated both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) components of MF synaptic responses similarly in respect of the magnitude and time course. The dopamine-induced potentiation was intact in the presence of picrotoxin, required activation of D(1)-like receptors and was apparently occluded by an activator of adenylate cyclase. The potentiation was accompanied by a decrease in magnitude of synaptic facilitation, suggesting the presynaptic site for the expression of the potentiation. The present study is the first demonstration of acute potentiation of hippocampal excitatory synaptic transmission by dopamine, which is most probably mediated by presynaptic D(1)-like receptor-cAMP cascades.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2006

Serotonin derivatives, major safflower (Carthamus tinctorius L.) seed antioxidants, inhibit low-density lipoprotein (LDL) oxidation and atherosclerosis in apolipoprotein E-deficient mice.

The effects of defatted safflower seed extract and its phenolic constituents, serotonin derivatives, on atherosclerosis were studied. Ethanol-ethyl acetate extract of safflower seeds (SSE) inhibited low-density lipoprotein (LDL) oxidation induced in vitro by an azo-containing free-radical initiator V70 or copper ions. Two serotonin derivatives [N-(p-coumaroyl)serotonin, CS; N-feruloylserotonin, FS] and their glucosides were identified as the major phenolic constituents of the extract. The study with chemically synthesized materials revealed that a majority of the antioxidative activity of SSE was attributable to the aglycones of these two serotonin derivatives. Orally administered CS and FS suppressed CuSO(4)-induced plasma oxidation ex vivo. Long-term (15 week) dietary supplementation of SSE (1.0 wt %/wt) and synthetic serotonin derivatives (0.2-0.4%) significantly reduced the atherosclerotic lesion area in the aortic sinus of apolipoprotein E-deficient mice (29.2-79.7% reduction). The plasma level of both lipid peroxides and anti-oxidized LDL autoantibody titers decreased concomitantly with the reduction of lesion formation. Serotonin derivatives were detected as both intact and conjugated metabolites in the plasma of C57BL/6J mice fed on 1.0% SSE diet. These findings demonstrate that serotonin derivatives of SSE are absorbed into circulation and attenuate atherosclerotic lesion development possibly because of the inhibition of oxidized LDL formation through their strong antioxidative activity.

Animals↗

PubMed2004

Spike train timing-dependent associative modification of hippocampal CA3 recurrent synapses by mossy fibers.

In the CA3 region of the hippocampus, extensive recurrent associational/commissural (A/C) connections made by pyramidal cells may function as a network for associative memory storage and recall. We here report that long-term potentiation (LTP) at the A/C synapses can be induced by association of brief spike trains in mossy fibers (MFs) from the dentate gyrus and A/C fibers. This LTP not only required substantial overlap between spike trains in MFs and A/C fibers, but also depended on the temporal order of these spike trains in a manner not predicted by the well-known rule of spike timing-dependent plasticity and requiring activation of type 1 metabotropic glutamate receptors. Importantly, spike trains in a putative single MF input provided effective postsynaptic activity for the induction of LTP at A/C synapses. Thus, the timing of spike trains in individual MFs may code information that is crucial for the associative modification of CA3 recurrent synapses.

2-Amino-5-phosphonovalerate↗

PubMed2003

Developmental decrease in synaptic facilitation at the mouse hippocampal mossy fibre synapse.

Transmission at the hippocampal mossy fibre (MF)-CA3 pyramidal cell synapse is characterized by prominent activity-dependent facilitation, which is thought to provide a wide dynamic range in hippocampal informational flow. At this synapse in mice the magnitude of paired-pulse facilitation and frequency-dependent facilitation markedly decreased with postnatal development from 3 weeks (3W) to 9 weeks (9W). Throughout this period the mean amplitude and variance of unitary EPSCs stayed constant. By altering extracellular Ca2+/Mg2+ concentrations the paired-pulse ratio could be changed to a similar extent as observed during development. However, this was accompanied by an over 30-fold change in EPSC amplitude, suggesting that the developmental change in facilitation ratio cannot simply be explained by a change in release probability. With paired-pulse stimulation the Ca2+ transients at MF terminals, monitored using mag-fura-5, showed a small facilitation, but its magnitude remained similar between 3W and 9W mice. Pharmacological tests using CNQX, adenosine, LY341495, H-7 or KN-62 suggested that neither presynaptic receptors (kainate, adenosine and metabotropic glutamate) nor protein kinases are responsible for the developmental change in facilitation. Nevertheless, loading the membrane-permeable form of BAPTA attenuated the paired-pulse facilitation in 3W mice to a much greater extent than in 9W mice, resulting in a marked reduction in age difference. These results suggest that the developmental decrease in the MF synaptic facilitation arises from a change associated with residual Ca2+, a decrease in residual Ca2+ itself or a change in Ca2+-binding sites involved in the facilitation. A developmental decline in facilitation ratio reduces the dynamic range of MF transmission, possibly contributing to the stabilization of hippocampal circuitry.

Aging↗

PubMed1998

Transglutaminase in sporulating cells of Bacillus subtilis.

We screened various Bacillus species producing transglutaminase (TGase), measured as labeled putrescine incorporated into N,N-dimethylcasein. As a result, we detected TGase activity in sporulating cells of B. subtilis, B. cereus, B. alvei and B. aneurinolyticus, and found TGase activity related to sporulation. TGase activity of Bacillus subtilis was detected in lysozyme-treated sporulating cells during late sporulation, but not in cells without lysozyme treatment or the supernatant of the culture broth. TGase was found to be localized on spores. TGase was preliminarily purified by gel filtration chromatography for characterization. Its activity was eluted in the fractions indicating a molecular weight of approximately 23 kDa. TGase could cross-link and polymerize a certain protein. The enzyme was strongly suggested to form epsilon-(gamma-glutamyl)lysine bonds, which were detected in the spore coat proteins of B. subtilis. The activity was Ca(2+)-independent like the TGases derived from Streptoverticillium or some plants. It is suggested that TGase is expressed during sporulation and plays a role in the assembly of the spore coat proteins of the genus Bacillus.

Journal Article↗