Biomedical subjects

M Iwakiri

Publications and source records attributed to M Iwakiri.

7 recordsLinked to original sources

PubMed2002

Alterations of ubiquitin immunoreactivity in the hippocampal formation after perforant pathway lesion.

Immunohistochemical techniques were employed to examine the changes in free ubiquitin within the hippocampus 1, 3, 7, 14, and 30 days after a unilateral perforant pathway lesion occurred in the rat brain. Immunoreactivity for ubiquitin was remarkably decreased in the cell body and proximal dendrites of neurons throughout the hippocampus ipsilateral to the lesion at 1 day post-lesion. At 3 days post-lesion, ubiquitin immunoreactivity was recovered in interneurons in the whole hippocampus as well as in mossy cells in the hilar region, although granule cells in the dentate gyrus and pyramidal cells in the CA1 subfield remained unlabeled, and pyramidal cells in the CA3 subfield demonstrated only weak immunoreactivity. In addition, we observed an increase in ubiquitin immunolabeling of the hilar neuropil ipsilateral to the lesion at 1 and 3 days post-lesion, and a decrease in immunolabeling in the inner portion of the molecular layer at 3 days post-lesion. All these alterations were transient, and by 7 days post-lesion, ubiquitin immunoreactivity was indistinguishable in the hippocampus ipsilateral to the lesion, compared to the controls. Immunoblot analysis also revealed a decrease in the amount of ubiquitin in the hippocampus ipsilateral to the lesion 1 and 3 days post-lesion. These data suggest that deafferentation of the perforant pathway results in transient reduction in free ubiquitin of the hippocampus, and that the ubiquitin system is involved in hippocampal plasticity following perforant lesions.

Animals↗

PubMed2000

Immunohistochemical localization of gamma-aminobutyric acid(B) receptor in the hippocampus of subjects with schizophrenia.

Recent studies have demonstrated the involvements of gamma-aminobutyric acid (GABA) neurotransmitter systems in the schizophrenic brain. In order to further elucidate the alterations of this system in schizophrenia, we employed immunohistochemical techniques and examined the expression and anatomical distribution of the GABA(B) receptor in the hippocampus of five subjects with schizophrenia and three age-matched controls. In the control hippocampus, the most intense immunoreactivity was observed in the soma and processes of multipolar interneurons throughout the hippocampus. Pyramidal cells too were intensely labeled in their soma and proximal portion of dendrites, although the labeling intensity was varied in each subregion. For example, in the CA1 subfield, the labeling intensity of pyramidal cells was much less intense than that in the CA3 and CA2 subfields. In the subjects with schizophrenia, GABA(B) immunoreactivity was markedly reduced in granule cells as well as in pyramidal cells throughout the CA fields. In interneurons, GABA(B) labeling was relatively preserved compared to that in pyramidal cells. Our findings suggest that in the hippocampus of schizophrenic patients the expression of the GABA(B) receptor is reduced, and raise the possibility that this reduction contributes to the pathophysiological process in the schizophrenic brain.

Dentate Gyrus↗

PubMed2000

Factors affecting the survival of frozen-thawed mouse spermatozoa.

Mouse epididymal spermatozoa were frozen in solutions containing various compounds with different molecular weights, and the factors affecting the postthawing survival were examined. Monosaccharides (glucose, galactose) had almost no protective effect regardless of the concentration and the temperature of exposure. On the other hand, disaccharides (sucrose, trehalose) and trisaccharides (raffinose, melezitose) resulted in higher survival rates, especially at a concentration of around 0.35 mol/kg H(2)O (0.381-0.412 Osm/kg). Macromolecules, such as PVP10, Ficoll 70, bovine serum albumin, and skim milk had almost no effect, but compounds with a molecular weight of about 800, such as metrizamide and Nycodenz, had some protective effect. When a raffinose solution was supplemented with 10% metrizamide, resulting in an osmolality of approximately 0.400 Osm/kg, a high survival rate was obtained. Solutions at about 0.400 Osm/kg containing trehalose alone, trehalose + metrizamide, raffinose alone, and raffinose + metrizamide, were all effective for sperm freezing; frozen-thawed sperm could fertilize oocytes, and the resultant embryos could develop to live young after transfer. For freezing mouse spermatozoa, aqueous solutions at approximately 0.400 Osm/kg containing a disaccharide or a trisaccharide seem to be effective.

Animals↗

PubMed1993

Postnatal development of NMDA receptor-mediated synaptic transmission in cat visual cortex.

Postnatal development of N-methyl-D-aspartate (NMDA) receptors in cat visual cortex (area 17) was studied by intracellular recording from cortical cells in slice preparations obtained from kittens aged 0-20 weeks after birth and adult cats. Cells were sampled from layer IV and the lower half of layer II-III, where it is known that most cells receive direct inputs from lateral geniculate nucleus. Excitatory postsynaptic potentials (EPSPs) evoked in cortical cells by white matter stimulation were mediated by both non-NMDA and NMDA receptors, because bath application of a non-NMDA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX), left slow depolarizing responses which were abolished by an NMDA receptor antagonist, 2-amino-5-phosphonovaleric acid. The contribution of NMDA receptors to the synaptic transmission was assessed by the ratio of the initial rising slope of EPSPs in the presence of DNQX to that in control solution. The NMDA receptor-mediated component of monosynaptic EPSPs was small at 0-2 weeks after birth, steeply increased to the peak value at 5-6 weeks and then declined gradually to the almost initial value by 20 weeks. This time-course agrees with the developmental changes in susceptibility of ocular dominance preference of visual cortical cells to monocular deprivation, suggesting that NMDA receptors play a role in plastic changes in geniculocortical synapses.

2-Amino-5-phosphonovalerate↗

PubMed1993

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.

2-Amino-5-phosphonovalerate↗

PubMed1992

Low-threshold Ca2+ channels mediate induction of long-term potentiation in kitten visual cortex.

1. The induction mechanism of long-term potentiation (LTP) in developing visual cortex was studied by recording intracellular responses from layer III-IV cells in slice preparations of kitten visual cortex at 30-40 days after birth. 2. Strong stimulation of white matter produced a late depolarizing response after an orthodromic action potential. This depolarizing response was abolished by membrane depolarization or hyperpolarization caused by current injection through the recording electrode. In addition, this response was reduced by bath application of a low concentration (100 microM) of Ni2+ without any changes in the rising slope of the excitatory postsynaptic potential (EPSP) or orthodromic action potential. This suggests that this response is mediated by low-threshold Ca2+ channels (LTCs). 3. The involvement of LTCs in the induction of LTP was tested. White matter was stimulated at 2 Hz for 15 min as a conditioning stimulus to induce LTP, and the resultant changes in EPSPs were tested by low-frequency (0.1 Hz) stimulation of white matter. Conditioning stimulation produced a large N-methyl-D-aspartate (NMDA) receptor-mediated depolarizing response in these cells, which obscured the presence of the late depoliarzation. Therefore the test was conducted in a solution containing an NMDA antagonist 2-amino-5-phosphonovalerate (APV). 4. Weak conditioning stimulation, which evoked no LTC responses, never induced LTP; whereas strong conditioning stimulation, which evoked LTC responses, always induced LTP. Strong conditioning stimulation failed to induce LTP when LTC responses were prevented either by membrane depolarization or hyperpolarization or by a bath application of 100 microM Ni2+. 5. In a solution without APV, the application of Ni2+ also prevented the induction of LTP. 6. When cells were impaled by an electrode containing a Ca2+ chelator 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), LTP was never induced, even though LTC responses were evoked by conditioning stimulation. These results indicate that Ca2+ influx into postsynaptic cells through LTCs induces the LTP. 7. The responses mediated by LTCs, which were evoked by the injection of current pulses into the cells, were maximum at the critical period of visual cortical plasticity, suggesting that LTCs in postsynaptic cells regulate the plastic changes in developing visual cortex.

2-Amino-5-phosphonovalerate↗

PubMed1991

Postnatal development of neuronal connections in cat visual cortex studied by intracellular recording in slice preparation.

Postnatal development of neuronal connections in cat visual cortex (area 17) was studied in slice preparations obtained from kittens aged 1-18 weeks after birth and adult cats by recording intracellularly excitatory (EPSP) and inhibitory postsynaptic potentials (IPSP) evoked in cortical cells by stimulation of white matter. The EPSPs were already present in all cells at 1 week of age. Their efficiency assessed by their maximum rate of rise was low initially and increased progressively with age. In contrast, the IPSPs were absent in half of the cells at 1 week and almost all of the cells came to demonstrate inhibition by 9 weeks except for a few layer II-III cells. At all ages about three-quarters of the IPSPs had GABAA-mediated early and GABAB-mediated late components with different time courses, reversal potential and sensitivity to GABA antagonists, while the remaining IPSPs had only the early component. The efficiency of both IPSPs assessed by the associated conductance increase showed an increase of more than twice from 1 to 5 weeks, reaching the same level as adults. The time course of the development of inhibition demonstrated in this study paralleled the time course of the development of selective visual responsiveness in cortical cells, suggesting that the postnatal maturation of inhibitory connections is a basis of maturation of visual responsiveness.

Aging↗