Biomedical subjects

Yoshikazu Isomura

Publications and source records attributed to Yoshikazu Isomura.

10 recordsLinked to original sources

PubMed2006

Integration and segregation of activity in entorhinal-hippocampal subregions by neocortical slow oscillations.

Brain systems communicate by means of neuronal oscillations at multiple temporal and spatial scales. In anesthetized rats, we find that neocortical "slow" oscillation engages neurons in prefrontal, somatosensory, entorhinal, and subicular cortices into synchronous transitions between UP and DOWN states, with a corresponding bimodal distribution of their membrane potential. The membrane potential of hippocampal granule cells and CA3 and CA1 pyramidal cells lacked bimodality, yet it was influenced by the slow oscillation in a region-specific manner. Furthermore, in both anesthetized and naturally sleeping rats, the cortical UP states resulted in increased activity of dentate and most CA1 neurons, as well as the highest probability of ripple events. Yet, the CA3-CA1 network could self-organize into gamma bursts and occasional ripples during the DOWN state. Thus, neo/paleocortical and hippocampal networks periodically reset, self-organize, and temporally coordinate their cell assemblies via the slow oscillation.

Anesthesia↗

PubMed2006

Direct recording of theta oscillations in primate prefrontal and anterior cingulate cortices.

Recent evidence has suggested that theta-frequency (4-7 Hz) oscillations around the human anterior cingulate cortex (ACC) and frontal cortex--that is, frontal midline theta (Fm theta) oscillations--may be involved in attentional processes in the brain. However, little is known about the physiological basis of Fm theta oscillations because invasive study in the human is allowed in only limited cases. In the present study, we developed a monkey model for Fm theta oscillations and located the generators of theta waves using electrodes implanted in various cortical areas. Monkeys were engaged in a self-initiated hand-movement task with a waiting period. The theta power in area 9 (the medial prefrontal cortex) and area 32 (the rostral ACC) was gradually increased from a few seconds before the movement and reached a peak immediately after the movement. When the movement was rewarded, the theta power attained a second peak, whereas it swiftly decreased in the unrewarded trials. Theta oscillations in areas 9 and 32 were coherent and phase locked together. This theta activity may be associated with "executive attention" including self-control, internal timing, and assessment of reward. It is probably a homologue of human Fm theta oscillations, as judged from the similar localization, corresponding frequency, and dependency on attentional processes. The monkey model would be useful for studying executive functions in the frontal cortex.

Animals↗

PubMed2005

Comparable GABAergic mechanisms of hippocampal seizurelike activity in posttetanic and low-Mg2+ conditions.

It is known that GABA is a major inhibitory neurotransmitter in mature mammalian brains, but the effect of this substance is sometimes converted into depolarizing or even excitatory when the postsynaptic Cl- concentration becomes high. Recently we have shown that seizurelike afterdischarge induced by tetanic stimulation in normal extracellular fluid (posttetanic afterdischarge) is mediated through GABAergic excitation in mature hippocampal CA1 pyramidal cells. In this study, we examined the possible contribution of similar depolarizing/excitatory GABAergic input to the CA1 pyramidal cells to the seizurelike afterdischarge induced in a low extracellular Mg2+ condition, another experimental model of epileptic seizure activity (low-Mg2+ afterdischarge). Perfusion of the GABAA antagonist bicuculline abolished the low-Mg2+ afterdischarge, but not the interictal-like activity, in most cases. Each oscillatory response during the low-Mg2+ afterdischarge was dependent on Cl- conductance and contained an F- -insensitive depolarizing component in the pyramidal cells, thus indicating that the afterdischarge response may be mediated through both GABAergic and nonGABAergic transmissions. In addition, local GABA application to the recorded cells revealed that GABA responses were indeed depolarizing during the low-Mg2+ afterdischarge. Furthermore, the GABAergic interneurons located in the strata pyramidale and oriens fired in oscillatory cycles more actively than those in other layers of the CA1 region. These results suggest that the depolarizing GABAergic input may facilitate oscillatory synchronization among the hippocampal CA1 pyramidal cells during the low-Mg2+ afterdischarge in a manner similar to the expression of the posttetanic afterdischarge.

Action Potentials↗

PubMed2005

Region-specific modulation of electrically induced synchronous oscillations in the rat hippocampus and cerebral cortex.

Strong tetanization induces synchronous membrane potential oscillations (seizure-like afterdischarge) in mature pyramidal cells of the hippocampal CA1 region. To investigate whether local networks in other brain regions can generate such an afterdischarge independently, we studied the inducibility of afterdischarge in individual 'isolated slices' of the rat hippocampal CA1 and CA3 regions, dentate gyrus (DG), entorhinal cortex (EC), and temporal cortex (TC) using intracellular and extracellular recordings. The strong tetanization constantly induced afterdischarges in the CA1 and CA3 pyramidal cells as well as in the EC and TC superficial principal cells. However, parameters of the afterdischarges, such as the frequency and duration of afterdischarges, varied among the regions. A mixture of N-methyl-D-aspartate (NMDA) and non-NMDA receptor antagonists or a GABA(A) receptor antagonist completely blocked the afterdischarges. Local GABA application during the afterdischarge elicited depolarization, rather than hyperpolarization. Moreover, reversal potentials of the afterdischarge were around -40 mV. In contrast, the tetanization resulted in occasional afterdischarge-like activities in DG slices, which were blocked by the non-NMDA or GABA(A) receptor antagonist. These findings suggest that the afterdischarges mediated through the excitatory GABAergic and glutamatergic transmissions might be common to, but be modulated differently by individual local networks in the hippocampus and cortex.

Animals↗

PubMed2004

Synaptic interactions between pyramidal cells and interneurone subtypes during seizure-like activity in the rat hippocampus.

We have recently reported that excitatory GABAergic and glutamatergic mechanisms may be involved in the generation of seizure-like (ictal) rhythmic synchronization (afterdischarge), induced by a strong synaptic stimulation of the CA1 pyramidal cells in the mature rat hippocampus in vitro. To clarify the network mechanism of this neuronal synchronization, dual whole-cell patch-clamp recordings of the afterdischarge responses were performed simultaneously from a variety of interneurones and their neighbouring pyramidal cells in hippocampal CA1-isolated slice preparations. According to morphological and electrophysiological criteria, the recorded interneurones were then classified into distinct subtypes. The non-fast-spiking interneurones located in the strata lacunosum-moleculare and radiatum hardly discharged during the afterdischarge, whereas most of the fast-spiking and non-fast-spiking interneurones in the strata oriens and pyramidale, including the basket, chandelier and bistratified cells, exhibited prominent firings that were precisely synchronous with oscillatory responses in the pyramidal cells. Field potential recordings showed that excitatory synaptic transmissions might take place primarily in the strata oriens and pyramidale during the afterdischarge. Restricted lesions in the strata oriens and pyramidale, but not in the other layers, resulted in the complete desynchronization of afterdischarge activity, and also, local application of glutamate receptor antagonists to these layers blocked the expression of afterdischarge. The present findings indicate that the neuronal synchronization of epileptic afterdischarge may be accomplished in a 'positive feedback circuit' formed by the excitatory GABAergic interneurones and the glutamatergic pyramidal cells within the strata oriens and/or pyramidale of the hippocampal CA1 region.

2-Amino-5-phosphonovalerate↗

PubMed2004

Neural mechanisms of versatile functions in primate anterior cingulate cortex.

The anterior cingulate cortex (ACC) is located on the medial wall of the cerebral hemisphere in humans and non-human primates, and has well developed intracortical and subcortical connections. Recent brain-imaging studies have suggested the possible involvement of the ACC in a variety of cognitive and motor-related functions. To clarify the cellular mechanisms underlying such higher-order functions in the ACC, neuronal activity in distinct areas of the ACC and its adjacent cingulate areas has been examined, through single unit recordings, in monkeys performing specific tasks. Each of the rostral (CMAr), dorsal (CMAd), and ventral (CMAv) cingulate motor areas basically participates in motor-related functions such as preparation and execution of movements. In particular, the CMAr appears to be involved in selection of appropriate motor responses as well as in planning of sequential movements. Furthermore, the CMAr and area 32 may participate in attentional functions which are necessary to select correct actions. These areas have also been implicated in detection of error actions and/or monitoring of action performance. Finally, a number of neurons in the ACC exhibit specific or modulated activity relevant to reward expectation. The primate ACC may play critical roles in performing appropriate actions with attention and in checking the performance to acquire rewards efficiently.

Animals↗

PubMed2003

Prefrontal theta oscillations associated with hand movements triggered by warning and imperative stimuli in the monkey.

In order to investigate the functional significance of theta oscillations in the brain, we recorded the cortical field potential in monkeys engaged in a visually-initiated hand movement task. In each trial a warning signal (S1) was followed 3 s later by an imperative signal (S2) to which the monkey had to respond to get a reward. The theta power in the prefrontal area 9 and the prelimbic area 32 was higher in the S1-S2 interval than in the pre-S1 period. This theta activity may be related to attentional processes and is probably a homologue of the human frontal midline theta (Fm theta) rhythms.

Action Potentials↗

PubMed2003

Neural coding of "attention for action" and "response selection" in primate anterior cingulate cortex.

Noninvasive imaging techniques showed that the anterior cingulate cortex is related to higher-order cognitive and motor-related functions in humans. To elucidate the cellular mechanism of such cingulate functions, single-unit activity was recorded from three cingulate motor areas of macaque monkeys performing delayed conditional Go/No-go discrimination tasks using spatial (location) and nonspatial (color) visual cues. Unlike prefrontal neurons, only a few neurons coded the visual information on individual features (e.g., "left" or "red") in all of the rostral (CMAr), dorsal (CMAd), and ventral (CMAv) cingulate motor areas. Instead, many neurons in the CMAr exhibited the attention-like activity anticipating the second (conditioned) visual cues, with the specificity to visual category ("location" or "color"). In addition, there were a number of CMAr neurons specific to motor response (Go or No-go) in relation to the second visual cues. Some of the visual category-specific neurons in the CMAr further displayed the motor response-specific activity. On the other hand, many of the task-related CMAd and CMAv neurons seemed to be implicated directly in motor functions, such as preparation and execution of movements in Go trials. The present results suggest that the CMAr neurons may participate in cognitive and motor functions of "attention for action" and "response selection" for an appropriate action according to an intention, whereas the CMAd and CMAv neurons may be involved in "motor preparation and execution".

Animals↗

PubMed2003

Glutamatergic propagation of GABAergic seizure-like afterdischarge in the hippocampus in vitro.

Previous investigations have suggested that GABA may act actively as an excitatory mediator in the generation of seizure-like (ictal) or interictal epileptiform activity in several experimental models of temporal lobe epilepsy. However, it remains to be known whether or not such GABAergic excitation may participate in seizure propagation into neighboring cortical regions. In our in vitro study using mature rat hippocampal slices, we examined the cellular mechanism underlying synchronous propagation of seizure-like afterdischarge in the CA1 region, which is driven by depolarizing GABAergic transmission, into the adjacent subiculum region. Tetanically induced seizure-like afterdischarge was always preceded by a GABAergic, slow posttetanic depolarization in the pyramidal cells of the original seizure-generating region. In contrast, the slow posttetanic depolarization was no longer observed in the subicular pyramidal cells when the afterdischarge was induced in the CA1 region. Surgical cutting of axonal pathways through the stratum oriens and the alveus between the CA1 and the subiculum region abolished the CA1-generated afterdischarge in the subicular pyramidal cells. Intracellular loading of fluoride ions, a GABAA receptor blocker, into single subicular pyramidal cells had no inhibitory effect on the CA1-generated afterdischarge in the pyramidal cells. Furthermore, the CA1-generated afterdischarge in the subicular pyramidal cells was largely depressed by local application of glutamate receptor antagonists to the subiculum region during afterdischarge generation. The present results indicate that the excitatory GABAergic generation of seizure-like activity seems to be restricted to epileptogenic foci of origin in the seizure-like epilepsy model in vitro.

Animals↗

PubMed2002

Distance-dependent Ni(2+)-sensitivity of synaptic plasticity in apical dendrites of hippocampal CA1 pyramidal cells.

Low concentration of Ni(2+), a T- and R-type voltage-dependent calcium channel (VDCC) blocker, is known to inhibit the induction of long-term potentiation (LTP) in the hippocampal CA1 pyramidal cells. These VDCCs are distributed more abundantly at the distal area of the apical dendrite than at the proximal dendritic area or soma. Therefore we investigated the relationship between the Ni(2+)-sensitivity of LTP induction and the synaptic location along the apical dendrite. Field potential recordings revealed that 25 microM Ni(2+) hardly influenced LTP at the proximal dendritic area (50 microM distant from the somata). In contrast, the same concentration of Ni(2+) inhibited the LTP induction mildly at the middle dendritic area (150 microM) and strongly at the distal dendritic area (250 microM). Ni(2+) did not significantly affect either the synaptic transmission at the distal dendrite or the burst-firing ability at the soma. However, synaptically evoked population spikes recorded near the somata were slightly reduced by Ni(2+) application, probably owing to occlusion of dendritic excitatory postsynaptic potential (EPSP) amplification. Even when the stimulating intensity was strengthened sufficiently to overcome such a reduction in spike generation during LTP induction, the magnitude of distal LTP was not significantly recovered from the Ni(2+)-dependent inhibition. These results suggest that Ni(2+) may inhibit the induction of distal LTP directly by blocking calcium influx through T- and/or R-type VDCCs. The differentially distributed calcium channels may play a critical role in the induction of LTP at dendritic synapses of the hippocampal pyramidal cells.

Animals↗