Biomedical subjects

Akihito Okabe

Publications and source records attributed to Akihito Okabe.

13 recordsLinked to original sources

PubMed2005

Differential functional expression of cation-Cl- cotransporter mRNAs (KCC1, KCC2, and NKCC1) in rat trigeminal nervous system.

GABA is the main inhibitory neurotransmitter in the adult brain, which causes Cl- influx into the cell via GABAA receptors. The direction of Cl- inflow is dependent on the Cl- gradient across the membrane. Cation-Cl- cotransporters have been considered to play pivotal roles in controlling intracellular Cl- concentration ([Cl-]i) of neurons; hence, they modulate the GABAergic function. To elucidate how these cotransporters are distributed in the trigeminal nuclei, we investigated the expressions of K+-Cl- cotransporters (KCC1 and KCC2) and Na+-K+-2Cl- cotransporter (NKCC1) mRNAs by using in situ hybridization histochemistry. KCC2 mRNA was expressed in the motor trigeminal nucleus (Mo5), the principal trigeminal nucleus (Pr5), and the spinal trigeminal nucleus (Sp5), but not in the trigeminal ganglion (TG) and the mesencephalic trigeminal nucleus (Me5). On the other hand, KCC1 and NKCC1 mRNAs were expressed in all the trigeminal nuclei. The resting [Cl-]i of Me5 neurons was significantly higher than that of Mo5 neurons. Thus, in primary sensory neurons such as the TG and the Me5, [Cl-]i would be higher than those in the other trigeminal nuclei because of the lack of KCC2 mRNA expression. Since Me5 neurons, but not Mo5 neurons, responded to GABA by depolarization, GABA would have differential physiological functions among trigeminal nuclei and TG.

Animals↗

PubMed2004

Cl- uptake promoting depolarizing GABA actions in immature rat neocortical neurones is mediated by NKCC1.

GABA is the principal inhibitory neurotransmitter in the mature brain, but during early postnatal development the elevated [Cl(-)](i) in immature neocortical neurones causes GABA(A) receptor activation to be depolarizing. The molecular mechanisms underlying this intracellular Cl(-) accumulation remain controversial. Therefore, the GABA reversal potential (E(GABA)) or [Cl(-)](i) in early postnatal rat neocortical neurones was measured by the gramicidin-perforated patch-clamp method, and the relative expression levels of the cation-Cl(-) cotransporter mRNAs (in the same cells) were examined by semiquantitative single-cell multiplex RT-PCR to look for statistical correlations with [Cl(-)](i). The mRNA expression levels were positively (the Cl(-) accumulating Na(+),K(+)-2Cl(-) cotransporter NKCC1) or negatively (the Cl(-) extruding K(+)-Cl(-) cotransporter KCC2) correlated with [Cl(-)](i). NKCC1 mRNA expression was high in early postnatal days, but decreased during postnatal development, whereas KCC2 mRNA expression displayed the opposite pattern. [Cl(-)](i) and NKCC1 mRNA expression were each higher in cortical plate (CP) neurones than in the presumably older layer V/VI pyramidal neurones in a given slice. The pharmacological effects of bumetanide on E(GABA) were consistent with the different expression levels of NKCC1 mRNA. These data suggest that NKCC1 may play a pivotal role in the generation of GABA-mediated depolarization in immature CP cells, while KCC2 promotes the later maturation of GABAergic inhibition in the rat neocortex.

Animals↗

PubMed2004

Experience-dependent changes in intracellular Cl- regulation in developing auditory neurons.

A developmental change in GABA and glycine responses, from a depolarization to a hyperpolarization, have been reported for a range of CNS neurons, and has been demonstrated to be due to a developmental decrease in the intracellular Cl- concentration ([Cl-](i)). We examined [Cl-](i) in isolated rat lateral superior olive (LSO) neurons using patch-clamp recordings of glycine gated Cl- currents and by measuring intracellular Cl- -fluorescence. In neurons from 14-16-day-old rats (P14-P16), which had previously received unilateral or bilateral cochlear ablations before the onset of hearing, there was no developmental decrease in [Cl-](i). No significant differences in [Cl-](i) were observed amongst rats with either ipsi- and contralateral ablations. Implanted strychnine pellets also prevented the decrease in [Cl-](i) in most neurons. In some of these neurons in which [Cl-](i) remained high, there was a lack of expression of the K+-Cl- cotransporter 2 (KCC2) mRNA. These results demonstrate that the developmental decrease in [Cl-](i) in LSO neurons is dependent on neuronal activity and that both GABAergic/glycinergic and glutamatergic afferent activity contribute to this maturation of the Cl- regulatory mechanisms.

Acoustic Stimulation↗

PubMed2004

Neuroprotective effects of melatonin against anoxia/aglycemia stress, as assessed by synaptic potentials and superoxide production in rat hippocampal slices.

Melatonin, which plays an important role in circadian rhythm regulation, is highly potent endogenous free radical scavenger and antioxidant. To clarify the neuroprotective effects of melatonin as a free radical scavenger, we recorded changes in synaptic potentials and monitored the generation of superoxide (O)(2)(-) (using hydroethidine) in the CA1 pyramidal layers of rat hippocampal slices exposed to anoxia/aglycemia ('ischemic') stress. Synaptic responses evoked by stimulation of Schaffer collateral/commissural afferents were suppressed by ischemic stress. When the duration of the stress was 8 min, the suppression was reversible, irrespective of the presence or absence of melatonin treatment, while the amount of O(2)(-) generated was reduced by the presence of melatonin. When stress duration was 12 min, the suppression of synaptic responses lasted more than 90 min, but melatonin significantly improved the recovery. The amount of O(2)(-) generated in the 'recirculation' phase after a 12 min ischemic stress was less in the ischemic alone group than in the melatonin-treated group. This probably reflects that the number of viable cells with the ability to generate O(2)(-) had been reduced by the more severe ischemic stress. Other radical scavengers (ascorbic acid and alpha-tocopherol) had similar effects. These results show that melatonin has the potential to protect the functions of neurons against an ischemic insult by reducing O(2)(-) generation.

Animals↗

PubMed2003

Changes in chloride homeostasis-regulating gene expressions in the rat hippocampus following amygdala kindling.

In a rat kindling model, we examined expression patterns of NKCC1, KCC1, KCC2, and CLC-2. In the dentate granule cell layer, there was an activity-dependent increase in NKCC1 mRNA but significant decreases in KCC1 and CLC-2 mRNAs. In addition, CLC-2 mRNA expression was markedly decreased in CA1 pyramidal layer. These results suggest that an increase in [Cl-]i and a resultant reduction in GABAergic inhibition may occur in hippocampus of epileptic rats.

Amygdala↗

PubMed2003

Differential development of cation-chloride cotransporters and Cl- homeostasis contributes to differential GABAergic actions between developing rat visual cortex and dorsal lateral geniculate nucleus.

A recent study suggested that gamma-aminobutyric acid (GABA) plays differential roles in activity-dependent plasticity between the visual cortex (VC) and the dorsal lateral geniculate nucleus (dLGN). In the present study, to investigate differential GABAergic functions in postnatal visual system development, the development of [Cl(-)](i), cation-Cl(-) cotransporter expression, and the [Ca(2+)](i) responses evoked by GABA were compared between VC and dLGN during the early stages of development. Using rat brain slices from postnatal days (P) 0-17, GABA-evoked [Ca(2+)](i) responses and resting [Cl(-)](i) were measured by means of optical imaging of Ca(2+) and Cl(-), respectively. Changes in the expression of cation-Cl(-) cotransporters (viz. the outwardly-directed K(+)-Cl(-) cotransporter, KCC2, and the inwardly-directed Na(+),K(+)-2Cl(-) cotransporter, NKCC1) were examined in VC and dLGN by in situ hybridization. At birth, the excitatory actions of GABA were powerful in VC, but missing in dLGN (as indicated by neuronal [Ca(2+)](i) transients), and the resting [Cl(-)](i) was significantly higher in VC than in dLGN. Signals for KCC2 mRNA expression were significantly higher in dLGN than in VC at P0. This suggests that extrusion of Cl(-) from neurons is stronger in dLGN than in VC at P0, so that a GABAergic excitatory effect was not observed in dLGN because of more negative equilibrium potential for Cl(-). The present study indicates clear differences in the molecular and physiological bases of Cl(-) homeostasis and GABA actions between the developing VC and dLGN. Such differential GABAergic actions may underlie the distinct mechanisms involved in VC and dLGN development within the visual system.

Animals↗

PubMed2002

Layer-specific expression of Cl- transporters and differential [Cl-]i in newborn rat cortex.

GABA is the main inhibitory neurotransmitter in the adult brain. However, GABAergic transmission is depolarizing during early postnatal development, suggesting that changes in the expression of cation-Cl- co-transporters regulating neuronal Cl- homeostasis underlie the ontogeny of GABAergic functions. The developmental changes in the expressions of Cl- co-transporter mRNAs in the neocortex were in opposite directions for NKCC1 (Cl- uptake) and KCC2 (Cl- extrusion). In the newborn, NKCC1 mRNA expression was highest in ventricular zone followed by cortical plate, and then by Layer V/VI, while the reverse was true for KCC2 mRNA. The [Cl-]i levels were in the same rank order as for NKCC1 mRNA. Thus, the ontogeny of Cl- homeostasis in neocortical neurons could be regulated via the differential expression of NKCC1 and KCC2.

Animals↗

PubMed2002

Developmental changes in KCC1, KCC2, and NKCC1 mRNA expressions in the rat brain.

We investigated the expressions of KCC1, KCC2 and NKCC1 mRNAs in the developing rat brain. The neuroepithelium showed abundant KCC1 and NKCC1 mRNA expressions, while KCC2 mRNA was not detected there. In contrast, KCC2 mRNA was preferentially expressed in postmitotic mature neurons. These results suggest that the appearance of KCC2 expression mainly depends on the maturation of individual neurons.

Animals↗

PubMed2002

Induction of NMDA and GABAA receptor-mediated Ca2+ oscillations with KCC2 mRNA downregulation in injured facial motoneurons.

To clarify the changes that occur in gamma-aminobutyric acid type A (GABA(A)) receptor-mediated effects and contribute to alterations in the network activities after neuronal injury, we studied intracellular Ca(2+) concentration ([Ca(2+)](i)) dynamics in a rat facial-nerve-transection model. In facial motoneurons, an elevation of the resting [Ca(2+)](i), GABA-mediated [Ca(2+)](i) transients, enhancement of the glutamate-evoked [Ca(2+)](i) increases, and spontaneous [Ca(2+)](i) oscillations were induced by axotomy. All these axotomy-induced modifications were abolished by the GABA(A)-receptor antagonist bicuculline and N-methyl-d-aspartate (NMDA)-receptor antagonist d(-)-2-amino-5-phosphonopentanoic acid. A downregulation of K(+)-Cl(-) cotransporter (KCC2) mRNA, an increase in intracellular Cl(-) concentration ([Cl(-)](i)), and transformation of GABAergic hyperpolarization to depolarization were also induced by axotomy. We suggest that in axotomized neurons KCC2 downregulation impairs Cl(-) homeostasis and makes GABA act depolarizing, resulting in endogenous GABA inducing [Ca(2+)](i) oscillations via facilitation of NMDA-receptor activation. Such GABA(A)-receptor-mediated [Ca(2+)](i) oscillations may play a role in neural survival and regeneration.

Animals↗

PubMed2002

Extracellular serine protease neuropsin (KLK8) modulates neurite outgrowth and fasciculation of mouse hippocampal neurons in culture.

A serine protease neuropsin expressed in the hippocampus of adult brain has been implicated in synaptic plasticity. We report here that endogenous neuropsin was localized extracellularly in neuronal cell bodies and their neurites in mouse hippocampal cultures. Furthermore, we found that, in cultured mouse hippocampal neurons, recombinant neuropsin enhanced neurite projection from soma after 14 h of culture and neuronal aggregation with neurite fascicles at 48 h. This suggests that neuropsin is involved in neurite outgrowth and fasciculation during the development of the nervous system.

Aging↗

PubMed2002

Amygdala kindling induces upregulation of mRNA for NKCC1, a Na(+), K(+)-2Cl(-) cotransporter, in the rat piriform cortex.

GABA, the main inhibitory neurotransmitter in the brain, elicits a hyperpolarizing response by activation of the GABA(A)-receptor/chloride-channel complex under conditions of normal Cl(-) homeostasis. Thus the pathogenesis of epilepsy could involve an impairment of GABA(A)-receptor-mediated inhibition due to a collapse of the Cl(-) gradient. We examined the expression patterns of Cl(-) transporters and a Cl(-) channel in a rat amygdala-kindling model. Activity-dependent increases were observed in the mRNA for NKCC1, an inwardly-directed Cl(-) transporter, in the piriform cortex. This suggests that an increase in [Cl(-)](i) and a resultant reduction in GABAergic inhibition may occur in the kindled piriform cortex.

Amygdala↗

PubMed2002

A case of sleep choking syndrome improved by the Kampo extract of Hange-koboku-to.

A case of sleep choking syndrome with typical symptoms is presented. A 44-year-old Japanese male suffered from multiple episodes of choking, which suddenly appeared with fear of impending death about 30 min after falling asleep almost every night. Overnight polysomnography showed an apnea index of 0.92 events/h, an apnea-hypopnea index of 2.77 events/h, and normal respiration during sleep with the exception of the episodes of apnea and hypopnea. No choking episode occurred in the sleep laboratory. The administration of 500 mg of acetazolamide was ineffective, but the choking episode improved after the administration of Kampo extract of Hange-koboku-to (Ban-xia-hou-pu-tang). Hange-koboku-to may be effective in treating choking sensation during sleep as well as during wakefulness.

Adult↗

PubMed2001

Diversity of neuron-specific K+-Cl- cotransporter expression and inhibitory postsynaptic potential depression in rat motoneurons.

Motoneurons receive a robust recurrent synaptic inhibition by gamma-aminobutyric acid and glycine, which activate Cl(-) channels. Thus, Cl(-) homeostasis determines the efficacy of synaptic inhibition in the motoneurons. In situ hybridization reveals that the neuronal K(+)-Cl(-) cotransporter isoform 2 (KCC2), a major mechanism in maintaining a low Cl(-) concentration in neurons, is abundantly expressed in the facial, hypoglossal (XII), and spinal motoneurons innervating striated muscle, whereas the dorsal vagal motoneurons (DMVs) controlling smooth muscle exhibited little expression of KCC2. This raises a general interest in the correlation between KCC2 expression and inhibitory postsynaptic potential (IPSP) performance in the native circuits. Intracellular and whole-cell patch recordings revealed that an activity-dependent depression of IPSPs and positive shift of IPSP reversal potentials were more prominent in the DMV than in the XII. Cl(-) influx through Cl(-) channels was extruded more potently in the XII than in the DMV, suggesting that differences in Cl(-) extrusion account for these dynamic differences of IPSP. Cl(-) extrusion was inhibited by either furosemide or an increase in extracellular potassium concentrations. Thus, the rigid maintenance of IPSP and rapid Cl(-) extrusion in the XII reflects an intense expression of KCC2. KCC2 expression may strongly influence the IPSP depression and functional properties of the motoneurons innervating striated muscles.

Animals↗