Shiushi Matsuura

Developmental Study of Hippocampal Kindling

Summary: The critical susceptibility to seizure in immature hippocampus of rat brain was investigated using the kindling model of epilepsy. Hourly electrical low‐intensity stimulations applied to the left dorsal hippocampus of suckling rats induced longer initial AD duration (p < 0.01) with faster development of kindling seizure than in that of adult rats. In contrast to the marked reduction of wet dog shakes (WDS) in adult rats, in suckling rats persistent and prolonged WDS were observed as kindling progressed. The faster development of hippocampal kindling in suckling rats than in adult rats was explained by the different excitability of the stimulated brain site and the different extent of neural connections in many brain structures, which participate in generalization of seizures arising from a stimulated site.

Potentiation of excitatory postsynaptic potentials by a metabotropic glutamate receptor agonist (1S,3R-ACPD) in frog spinal motoneurons

We conducted intracellular recordings of lumbar motoneurons in the arterially-perfused frog spinal cord and investigated the effects of a metabotropic glutamate receptor agonist, (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD), on excitatory postsynaptic potentials evoked by stimulation of the descending lateral column fibers (LC-EPSPs). In the absence of Mg2+, ACPD reversibly potentiated the amplitude of monosynaptic LC-EPSPs by more than 15% in 15 of 19 cells with 5 microM ACPD and in 7 of 12 cells with 0.5 microM ACPD. The EPSP amplitudes with 5 and 0.5 microM ACPD were 142 +/- 10% (mean +/- S.E.M., n = 19) and 130 +/- 13% (n = 12) of the controls. The potentiation was seen without a decrease in the input conductance. Glutamate-induced depolarizations in the absence and the presence of 0.5 microM ACPD were not significantly different in cells perfused with the low Ca(2+)-high Mg2+ solution which eliminated chemical transmission. Paired pulse facilitation of LC-EPSPs was reversibly decreased in association with the potentiation. ACPD-induced potentiation of monosynaptic LC-EPSPs was seen in 5 of 6 cells in the presence of D-(-)-2-amino-5-phosphonopentanoic acid (D-AP5), an NMDA receptor antagonist. ACPD occasionally activated polysynaptic components of LC-EPSPs which were mediated mainly via NMDA receptors. On the other hand, ACPD-induced potentiation of EPSPs was inhibited by extracellular Mg2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Amygdala kindling and associated changes of entorhinal responses in suckling rats

Entorhinal field potential with amygdala stimulation in suckling (16-18 days old) and adult rats was recorded with a tungsten wire electrode (tip diameter 2-5 microns) to study the developmental changes in behavioral seizures and long-term potentiation (LTP) in the responses to amygdala kindling stimulations. Stimulating (twisted enamel-coated wires) and recording electrodes were implanted in anesthetized rats 2-3 days before kindling. The mean amplitude of the responses to test pulses (600 microA, 0.3 Hz) in the sucklings (0.58 mV) was smaller than in the adults (1.32 mV), and latency was about 3.3 ms longer. Kindling stimulations consisted of 0.5-ms monophasic rectangular pulses of 10 Hz with a 10-s train duration; the intensity was the afterdischarge (AD) threshold. Kindling stimulation in the sucklings usually increased the amplitude of the test responses evoked 10 min or 1 h after the kindling stimulation. The increased amplitude persisted for at least 24 h, showing LTP in the synaptic transmission. The LTP was especially prominent in the first kindling stimulation, and the LTP gradually increased with successive stimulations, with gradual progression of AD and the behavioral seizure stage as well. The mean number of kindling stimulations to cause generalized seizures in the suckling rats (10.5) was less than that for adults (12.5), and the continued evolution of LTP over the course of kindling was more or less easier in the sucklings than in the adults.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of electrical stimulation on intracranial pressure and systemic arterial blood pressure in cats. Part II: Stimulation of cerebral cortex and hypothalamus.

This experimental work was carried out to examine whether activation of autonomic cortical and hypothalamic areas by electrical stimulation is related to changes in the intracranial pressure (ICP) in cats anaesthetized lightly with sodium pentobarbital. Electrical stimulation was performed using a concentric electrode with a train of electrical pulses (pulse duration, 0.4 ms; frequency, 40 Hz; intensity, 50-400 microA). Stimulation of sites in the anterior cingulate gyrus produced a rise in ICP associated with a fall in systemic arterial blood pressure (BP) or with no change in BP. Stimulation of sites in the anterior hypothalamus produced a fall in BP with an increase in ICP. Stimulation of sites in the area extending from the anterior hypothalamus to the posterior hypothalamus produced rises in BP and ICP. These observations suggest that activation of autonomic cortical and hypothalamic areas is involved in changes in ICP.

Effects of hypoglycemia on kindling seizures in suckling rats

The effects of insulin-induced hypoglycemia on epileptic disorders of suckling rats were examined using an amygdala kindling model. Kindling stimulations were conducted at 16 and 17 days of age with electrodes implanted in the amygdala 2 days earlier. In 18-day-old kindled rats, which acquired generalized behavioral seizures (stages 4 and 5; Moshés score) by kindling stimulations, the duration of afterdischarge and behavioral seizures evoked by the stimulation at a threshold intensity to produce a generalized seizure was significantly prolonged after an injection of insulin (25 U/kg, i.p.). The prolongation was not observed in kindled rats that exhibited normal blood glucose concentrations after the application of saline or insulin together with glucose. There were no apparent changes in the amplitude of the afterdischarge, the score of behavioral seizure stages, or the generalized seizure threshold. A similar, marked prolongation of afterdischarge and behavioral seizures following the application of insulin, as in the kindled rats, was also observed during the course of the kindling acquisition without accelerating the development of kindling seizure scores. These results indicate that insulin-induced hypoglycemia easily increases the risk of prolonged seizures in immature brain without precipitating the secondarily generalizing mechanism.

EFFECTS OF AN N-METHYL-D-ASPARTATE ANTAGONIST AND A GABAERGIC ANTAGONIST ON ENTORHINAL TETANIC RESPONSES DURING THE EARLY STAGES OF AMYGDALA KINDLING IN RATS

Changes in synaptic potentials during each train stimulation (tetanic responses) have been suggested to intimately relate to the development of kindling. We examined the effects of an NMDA antagonist, carboxypiperazinephosphonate (CPP), and a GABAergic antagonist, picrotoxin, on entorhinal tetanic responses evoked by train stimuli (10 Hz, 100 pulses) at the developmental stage (seizure stage; 0-2) of amygdala kindling in conscious rats, to clarify the significance of facilitation in tetanic responses and the roles of NMDA and GABA receptors in the development of kindling. Facilitation of tetanic responses was noted as a progressive increase in both amplitude and duration of negative potentials in the tetanic responses, especially during the later half of train pulses (51-100). The negative potential area (mV x ms) of the averaged tetanic responses was used as an estimate of the magnitudes of excitatory synaptic activity in the tetanic responses, and correlated significantly (P < 0.001) with the duration of afterdischarges (AD). CPP (10 mg/kg) reversibly blocked AD in association with a significant decrease (P < 0.05) in the negative potential area. The CPP-sensitive component consisted of a slow negative potential with a duration longer than 60 ms and was greater in the later tetanic responses (51-100) than the earlier ones (1-50). Picrotoxin (2-3 mg/kg), which did not produce convulsions, significantly (P < 0.005) increased the negative potential area in the tetanic responses in association with a reversible decrease in the AD threshold. Although positive potentials ascribable to inhibitory synaptic activity were often negligible in the tetanic responses in controls, picrotoxin further decreased the positive potentials of tetanic responses, if any.(ABSTRACT TRUNCATED AT 250 WORDS)

Glutamate-induced inhibition of paired pulse facilitation of monosynaptic excitatory post-synaptic potentials in frog spinal motoneurons

To evaluate actions of glutamate on excitatory synaptic transmission in the central nervous system, we examined glutamate-induced changes in the paired pulse facilitation of monosynaptic excitatory post-synaptic potentials evoked by stimulation of the lateral column fibers (LC-EPSPs) on lumbar motoneurons in the frog spinal cord. Glutamate (1 mM) depolarized motoneurons both in the presence and absence of Mg2+. In most cells perfused with Mg(2+)-free or high Ca(2+)-Mg2+ solutions, the glutamate potential was accompanied by a reduction in peak amplitude of EPSPs, although the degree of change varied with the cells. Glutamate enhanced the EPSP amplitude in a few cells with Mg(2+)-free and high Ca(2+)-Mg2+ solutions, and in most cells with high Mg2+ medium. In 3/5 cells tested, the paired pulse facilitation of EPSPs was reduced by glutamate when the EPSP amplitude either increased or decreased. NMDA (50 microM), kainate (50-100 microM), quisqualate (5-50 microM) and L-2-amino-4-phosphonobutyrate (L-AP4, 1 mM) also decreased the facilitation in about half of the cells tested. The glutamate-induced decrease in the facilitation was observed in both the presence and absence of Mg2+ and was not affected by the concomitant application of glutamate and antagonists for non-NMDA or NMDA receptors, such as 6-cyano-7-nitro-quinoxalinediones (CNQX, 60 microM) or 2-amino-5-phosphonovalerate (APV, 250 microM). Glutamate reduced the facilitation of excitatory post-synaptic currents (EPSCs) recorded at a constant membrane potential under voltage clamp, when the EPSC amplitude either increased or decreased and when the input conductance either increased or decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-cultured development of basic electrophysiological properties of spinal neurons obtained from rat embryo.

Basic electrical profiles of cultured neurons are modified by multiple factors, such as cell growth, differentiation and cell damage from the isolation procedure. In the present study, we assessed development of electrophysiological properties of rat spinal neurons over the late embryonic and early postnatal period in a neuron-enriched culture. After recovery from acute damage within 2 days after plating, the input conductance and amplitudes of voltage-gated Na(+) and K(+) currents increased parallel to the increase in the cell capacitance. Whether this depended on the period or the growth of the cell area was estimated by normalizing the parameters with the cell capacitance. The input conductance per unit area, the membrane time constant and the Na(+) current density remained constant for two weeks. However, densities of two types of outward K(+) currents, an A-current and a delayed rectifier, required 3--5 days to reach the maximum, although neither thresholds for activation nor sensitivities to blockers (TEA and 4AP) altered. The hyperpolarizing shift of the resting membrane potential became stabilized within 6--8 days, suggesting that the development of the K(+) currents underlay the shift. These results show that passive electrical properties and voltage-gated currents of rat spinal neurons in the neuron-rich culture differ in temporal patterns of development but stabilize at the latest within a week, corresponding to the day of birth.

Excitatory postsynaptic currents in response to different synaptic inputs of frog spinal motoneurons

Excitatory postsynaptic currents (EPSCs) evoked by the primary afferents (dorsal root; DR) and the descending lateral column (LC) fibers were studied in frog spinal motoneurons under voltage clamp with two separate electrodes. The average rise time and half-width of the EPSCs were shorter for LC-EPSCs than for DR-EPSCs, though the values of the parameters for LC- and DR-EPSCs were distributed within a similar range. The relation between the amplitudes of the EPSP and EPSC was almost linear. The amount of current required to generate a 1 mV increment in the EPSP was 5.0 +/- 2.3 nA for the DR-EPSC and 3.8 +/- 1.2 nA for the LC-EPSC. The decay time was shortened by hyperpolarization and prolonged by depolarization in DR- and LC-EPSCs and spontaneous EPSCs. The reversal potential ranged from -30 to -5 mV and was almost identical for DR- and LC-EPSCs and spontaneous EPSCs in individual motoneurons. The current-voltage relation was linear from -100 to +50 mV for these EPSCs. Spontaneous EPSCs became more prominent and frequent during a large hyperpolarization or a large depolarization. These results suggest that the ionic mechanisms underlying EPSC are similar for the functionally different excitatory synapses located on motoneurons.

RELATION OF THE ENHANCEMENT OF ENTORHINAL TETANIC RESPONSES BY 50-HZ AMYGDALA STIMULATION TO THE PROGRESSION OF KINDLING IN THE RAT

We recorded entorhinal tetanic responses to 50-Hz kindling stimulations applied at the amygdala in conscious rats, which produced facilitation and depression during the train pulses, in order to analyze the relationship of the changes in the tetanic responses to the development of both after-discharges (ADs) and behavioral seizures. Facilitation was always produced in the earlier tetanic responses and was followed by depression which reached a quasi-steady level in the later tetanic responses during each kindling stimulation. To estimate the changes in magnitude of the excitatory synaptic activation in the tetanic responses, with reference to the development of seizure stages, tetanic responses which produced the same behavioral seizure stage in each rat were averaged and the area between the negative (excitatory) potentials and the baseline of the averaged tetanic response was measured in terms of mV x ms. Magnitudes of the averaged negative components were significantly enhanced with an increase in the order of seizure stages in eight rats (P < 0.01). In addition, the mean magnitude of the averaged negative components had a linear correlation (r = 0.95, P < 0.05) with the mean AD duration with reference to the order of seizure stages in the eight rats. The magnitude of the positive (inhibitory) component in the averaged tetanic responses was also measured and found to decrease with an increase in the seizure stages (P < 0.01). The magnitude of the negative component in the test responses to single (0.3 Hz) stimuli just before kindling stimulations also increased with an increase in the order of seizure stages, indicating long term potentiation of the responses by kindling stimulations. We concluded from the results that the enhancement of facilitation of the excitatory synaptic activation and the reduction of the inhibitory synaptic activation in entorhinal tetanic responses by 50-Hz amygdala kindling stimulation is involved in the electrophysiological source of the progression of kindling epilepsy.