Yukio Komatsu

Neuroprotective role of phosphodiesterase inhibitor ibudilast on neuronal cell death induced by activated microglia

The phosphodiesterase inhibitor, ibudilast, has many effects on lymphocytes, endothelial cells, and glial cells. We examined the neuroprotective role of ibudilast in neuron and microglia co-cultures. Ibudilast significantly suppressed neuronal cell death induced by the activation of microglia with lipopolysaccharide (LPS) and interferon (IFN)-gamma. To examine the mechanisms by which ibudilast exerts a neuroprotective role against the activation of microglia, we examined the production of inflammatory and anti-inflammatory mediators and trophic factors following ibudilast treatment. In a dose-dependent manner, ibudilast suppressed the production of nitric oxide (NO), reactive oxygen species, interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha and enhanced the production of the inhibitory cytokine, IL-10, and additional neurotrophic factors, including nerve growth factor (NGF), glia-derived neurotrophic factor (GDNF), and neurotrophin (NT)-4 in activated microglia. Thus, ibudilast-mediated neuroprotection was primarily due to the inhibition of inflammatory mediators and the upregulation of neurotrophic factor. In the CA1 region of hippocampal slices, long-term potentiation (LTP) induced by high frequency stimulation (HFS) could be inhibited with LPS and interferon-gamma stimulation. Ibudilast returned this LTP inhibition to the levels observed in controls. These results suggest that ibudilast may be a useful neuroprotective and anti-dementia agent counteracting neurotoxicity in activated microglia.

Long-term potentiation investigated in a slice preparation of striate cortex of young kittens

In slice preparations from kitten striate cortex, long-term potentiation (up to 15 h) of field potentials was demonstrated after conditioning stimulation of white matter. Current source-density analysis and measurement of response latencies of cortical units indicated that the potentiation represented enhancement of both geniculo-cortical transmission in layer IV and intracortical transmission in layer II--III.

Long-term modification of inhibitory synaptic transmission in developing visual cortex.

The long-term modification of inhibitory postsynaptic potentials (IPSPs) was studied in visual cortex slices taken from developing rats. IPSPs evoked by layer IV stimulation were intracellularly recorded from layer V cells while excitatory synaptic transmission was blocked by NMDA and non-NMDA receptor antagonists. High-frequency conditioning stimulation of layer IV induced long-term potentiation of IPSPs. By contrast, long-term depression (LTD) of IPSPs was induced by the same conditioning stimulation applied while NMDA receptor-mediated synaptic transmission was unmasked by removing the NMDA antagonist from and adding a GABAA receptor antagonist to the medium. The LTD of IPSPs was also induced by NMDA application to the cells. The plasticity of IPSPs might explain the postnatal development of selective responsiveness of visual cortical cells.

Interferon-γ directly induces neurotoxicity through a neuron specific, calcium-permeable complex of IFN-γ receptor and AMPA GluR1 receptor

Interferon‐γ (IFN‐γ) is a proinflamma tory cytokine that plays a pivotal role in pathology of diseases in the central nervous system (CNS), such as multiple sclerosis. However, the direct effect of IFN‐γ on neuronal cells has yet to be elucidated. We show here that IFN‐γ directly induces neuronal dysfunction, which appears as dendritic bead formation in mouse cortical neurons and enhances glutamate neurotoxicity mediated via alpha‐amino‐3‐hydroxy‐5‐methyl‐4‐isox‐ azolepropionic (AMPA) receptors but not N‐methyl‐D‐ aspartate receptors. In the CNS, IFN‐γ receptor forms a unique, neuron‐specific, calcium‐permeable receptor complex with AMPA receptor subunit GluRl. Through this receptor complex, IFN‐γ phosphorylates GluRl at serine 845 position by JAKT2/STAT1 pathway, in creases Ca2+ influx and following nitric oxide production, and subsequently decreases ATP production, leading to the dendritic bead formation. These findings provide novel mechanisms of neuronal excitotoxicity, which may occur in both inflammatory and neurodegen erative diseases in the CNS.— Mizuno, T., Zhang, G., Takeuchi, H., Kawanokuchi, J., Wang, J., Sonobe, Y., Jin, S., Takada, N., Komatsu, Y., Suzumura, A. Inter feron‐γ directly induces neurotoxicity through a neu ron specific, calcium‐ permeable complex of IFN‐γ receptor and AMPA GluRl receptor. FASEB J. 22, 1797–1806 (2008)

Intracortical connectivity revealed by spike-triggered averaging in slice preparations of cat visual cortex

Intracortical connectivity was studied in slice preparations of cats visual cortex by spike-triggered averaging. The experiments documented the unitary postsynaptic potentials underlying the inhibitory and excitatory connections from layer III-IV border cells to supragranular cells, as demonstrated previously by cross-correlation studies. In addition the analysis demonstrated the existence of two excitatory connections, between supragranular and layer V cells, that were not detectable in previous cross-correlation studies.

Responsiveness of Clare-Bishop neurons to visual cues associated with motion of a visual stimulus in three-dimensional space

Photic responsiveness of cells in the medial bank of the lateral suprasylvian cortex (Clare-Bishop area) was studied using a three-dimensional visual stimulator that reproduced two visual cues (motion disparity and change in size) for perception of three-dimensional motion of a visual stimulus. About one third of them (48/148) were selectively responsive to motion disparity corresponding to approaching (AP cells, n = 30) or recessive motion (RC cells, N = 18), another half to motion of retinal images in the same direction between the two eyes corresponding to fronto-parallel motion (FP cells, n = 75), and the remaining cells were rather equally responsive to these types of stimuli (NS cells, n = 25). More than a half of the AP (19/30) or RC (11/18) cells were also responsive to increase or decrease in stimulus size, respectively, and they were optimally activated by a combination of the motion and size stimuli while relatively few FP and NS cells were sensitive to change in stimulus size. These findings indicate that the Clare-Bishop cells encode three-dimensional motion on the basis of photic responsiveness to the motion and size cues.

State-Dependent Bidirectional Modification of Somatic Inhibition in Neocortical Pyramidal Cells

Cortical pyramidal neurons alter their responses to input signals depending on behavioral state. We investigated whether changes in somatic inhibition contribute to these alterations. In layer 5 pyramidal neurons of rat visual cortex, repetitive firing from a depolarized membrane potential, which typically occurs during arousal, produced long-lasting depression of somatic inhibition. In contrast, slow membrane oscillations with firing in the depolarized phase, which typically occurs during slow-wave sleep, produced long-lasting potentiation. The depression is mediated by L-type Ca2+ channels and GABA(A) receptor endocytosis, whereas potentiation is mediated by R-type Ca2+ channels and receptor exocytosis. It is likely that the direction of modification is mainly dependent on the ratio of R- and L-type Ca2+ channel activation. Furthermore, somatic inhibition was stronger in slices prepared from rats during slow-wave sleep than arousal. This bidirectional modification of somatic inhibition may alter pyramidal neuron responsiveness in accordance with behavioral state.

Development of cortical inhibition in kitten striate cortex investigated by a slice preparation

Abstract The development of cortical inhibition was studied by intracellular and extracellular recordings from cortical cells using slice preparations of the striate cortex of infant kittens (1–60 days old). The cortical inhibition in newborn kittens was practically null in all cortical layers except for layer V. The inhibition developed to the adult level by the end of the ‘critical period’ for modification of photic responsiveness.

Age-dependent changes in projections from locus coeruleus to hippocampus dentate gyrus and frontal cortex

Age‐dependent changes in noradrenergic innervations of the hippocampal dentate gyrus (DG) and the frontal cortex (FC) have been studied in male F344 rats. The projections from the nucleus locus coeruleus (LC) to DG or FC with advancing age (from 7 to 27u2003months) in rats have been quantified by electrophysiological and immunohistochemical methods. In the electrophysiological study, we observed that the percentage of LC neurons activated antidromically by electrical stimulation (P‐index) of DG or FC decreased with age. We found that the percentage of LC neurons showing multiple antidromic latencies (M‐index), which suggests axonal branching of individual LC neurons, increased markedly between 15 and 17u2003months in DG or FC. In DG, the M‐index increased steadily between 15 and 24u2003months. In contrast, the increased M‐index in FC was maintained until 24u2003months. The increased M‐index in both targets declined at 27u2003months. These results suggest that LC neurons give rise to axonal branching following the loss of projections to DG or FC with age. In the immunohistochemical study, the density of dopamine‐β‐hydroxylase‐positive axonal varicosities was measured in molecular, granule cell and polymorphic layers of DG. The density in the polymorphic layer significantly decreased in the earlier stage of ageing (7–19u2003months), whilst the density in the molecular and granule cell layers decreased in the later stage (27u2003months). These findings suggested that a layer‐specific decline occurred with age in the noradrenergic axon terminals in DG.

Brain-derived neurotrophic factor-mediated retrograde signaling required for the induction of long-term potentiation at inhibitory synapses of visual cortical pyramidal neurons

High-frequency stimulation (HFS) induces long-term potentiation (LTP) at inhibitory synapses of layer 5 pyramidal neurons in developing rat visual cortex. This LTP requires postsynaptic Ca2+ rise for induction, while the maintenance mechanism is present at the presynaptic site, suggesting presynaptic LTP expression and the necessity of retrograde signaling. We investigated whether the supposed signal is mediated by brain-derived neurotrophic factor (BDNF), which is expressed in pyramidal neurons but not inhibitory interneurons. LTP did not occur when HFS was applied in the presence of the Trk receptor tyrosine kinase inhibitor K252a in the perfusion medium. HFS produced LTP when bath application of K252a was started after HFS or when K252a was loaded into postsynaptic cells. LTP did not occur in the presence of TrkB-IgG scavenging BDNF or function-blocking anti-BDNF antibody in the medium. In cells loaded with the Ca2+ chelator BAPTA, the addition of BDNF to the medium enabled HFS to induce LTP without affecting baseline synaptic transmission. These results suggest that BDNF released from postsynaptic cells activates presynaptic TrkB, leading to LTP. Because BDNF, expressed activity dependently, regulates the maturation of cortical inhibition, inhibitory LTP may contribute to this developmental process, and hence experience-dependent functional maturation of visual cortex.