Biomedical subjects

A Siniscalchi

Publications and source records attributed to A Siniscalchi.

At least 19 recordsLinked to original sources

PubMed2001

Effects of two-carbon bridge region methoxylation of benztropine: discovery of novel chiral ligands for the dopamine transporter.

6-Methoxylated and 8-oxygenated benztropines were prepared and evaluated for their DAT and SERT activity (binding and uptake inhibition). Methoxylation at the two-carbon bridge of benztropine produced a novel class of potent and selective DAT ligands. An interesting enantioselectivity was also observed for this new class of chiral benztropines. The inactivity of the 8-oxygenated analogues seems to point out that, unlike cocaine and its analogues, interactions of benztropine ligands with DAT may be strongly governed by the nitrogen atom.

Benztropine↗

PubMed2001

GABA-mediated synchronization in the human neocortex: elevations in extracellular potassium and presynaptic mechanisms.

Field potential and extracellular [K(+)] ([K(+)](o)) recordings were made in the human neocortex in an in vitro slice preparation to study the synchronous activity that occurs in the presence of 4-aminopyridine (50 microM) and ionotropic excitatory amino acid receptor antagonists. Under these experimental conditions, negative or negative-positive field potentials accompanied by rises in [K(+)](o) (up to 4.1 mM from a baseline of 3.25 mM) occurred spontaneously at intervals of 3-27 s. Both field potentials and [K(+)](o) elevations were largest at approximately 1000 microm from the pia. Similar events were induced by neocortical electrical stimuli. Application of medium containing low [Ca(2+)]/high [Mg(2+)] (n=3 slices), antagonism of the GABA(A) receptor (n=7) or mu-opioid receptor activation (n=4) abolished these events. Hence, they represented network, GABA-mediated potentials mainly reflecting the activation of type A receptors following GABA release from interneurons. The GABA(B) receptor agonist baclofen (10-100 microM, n=11) reduced and abolished the GABA-mediated potentials (ID(50)=18 microM). Baclofen effects were antagonized by the GABA(B) receptor antagonist CGP 35348 (0.1-1 mM, n=6; ID(50)=0.19 mM). CGP 38345 application to control medium increased the amplitude of the GABA-mediated potentials and the concomitant [K(+)](o) rises without modifying their rate of occurrence. The GABA-mediated potentials were not influenced by the broad-spectrum metabotropic glutamate agonist (+/-)-1-aminocyclopentane-trans-1,3-dicarboxylic acid (100 microM, n=10), but decreased in rate with the group I receptor agonist (S)-3,5-dihydroxyphenylglycine (10-100 microM, n=9). Our data indicate that human neocortical networks challenged with 4-aminopyridine generate glutamatergic-independent, GABA-mediated potentials that are modulated by mu-opioid and GABA(B) receptors presumably located on interneuron terminals. These events are associated with [K(+)](o) elevations that may contribute to interneuron synchronization in the absence of ionotropic excitatory synaptic transmission.

4-Aminopyridine↗

PubMed2000

NMDA and AMPA/kainate receptors are involved in the anticonvulsant activity of riluzole in DBA/2 mice.

The anticonvulsant activity of riluzole against sound-induced seizures was studied in the DBA/2 mouse model. Riluzole (0.1-4 mg kg(-1), intraperitoneal (i.p.)) produced dose-dependent effects with ED(50) values for the suppression of tonic, clonic and wild running phases of 0.72, 1.38 and 2.71 mg kg(-1), respectively. Riluzole also protected DBA/2 mice from seizures induced by an intracerebroventricular (i.c.v.) injection of N-methyl-D-aspartate (NMDA) with ED(50) values of 3.03 and 5.0 mg kg(-1) for tonus and clonus, respectively. Pretreatment with glycine, an agonist to the glycine/NMDA receptors, shifted the dose-response effect of riluzole to the right (ED(50)=6.53 against tonus and 9.34 mg kg(-1) vs. clonus). Similarly, D-serine, an agonist at the glycine site, shifted the ED(50) of riluzole against the tonic component of audiogenic seizures from 0.72 to 1.97, and that against clonus from 1.38 to 2.77 mg kg(-1). Riluzole was also potent to prevent seizures induced by administration of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), an AMPA/kainate receptor agonist (ED(50)=1.80 and 3.35 mg kg(-1), against tonus and clonus, respectively). Pretreatment with aniracetam, a positive allosteric modulator of AMPA/kainate receptors, shifted the dose-response curve of riluzole to the right (ED(50)=1.78 against tonus and 2.58 mg kg(-1) vs. clonus). The data indicate that riluzole is an effective anticonvulsant drug in the genetic model of seizure-prone DBA/2 mice. Our findings suggest that the anticonvulsant properties of riluzole depend upon its interaction with neurotransmission mediated by both the glycine/NMDA and the AMPA/kainate receptor complex.

Acoustic Stimulation↗

PubMed2000

Neurotensin increases endogenous glutamate release in rat cortical slices.

In the present study, the effects of the tridecapeptide neurotensin [NT(1-13)] and its fragments, NT(1-7) and NT(8-13), on endogenous glutamate release from rat cortical slices, were evaluated. NT(1-13) (100-1000 nM) slightly increased spontaneous glutamate release, while it was ineffective at 1 and 10 nM concentrations. Neither the biologically active NT fragment NT(8-13) nor the inactive one NT(1-7) affected basal glutamate release. NT(1-13) (1-1000 nM) enhanced potassium (35 mM)-evoked glutamate release displaying a bell-shaped concentration response curve. In addition NT(8-13) (10 nM) increased K+-evoked-glutamate release similarly to the parent peptide (10 nM), while the biologically inactive fragment NT(1-7) (10-100 nM) was ineffective. The effects of NT(1-13) and NT(8-13) were fully counteracted by the selective neurotensin receptor antagonist SR48692 (100 nM). These findings suggest that NT plays a role in regulating cortical glutamate transmission.

Animals↗

PubMed2000

[Cardiac rupture in thoracic trauma].

Thoracic trauma frequently involve damage to the cardiac structures and in the worst cases, the progressive degeneration and necrosis of the damaged tissue lead to cardiac rupture. The high mortality resulting from cardiac tamponade requires the prompt execution of diagnostic tests to provide as much useful information as rapidly as possible in order to start immediate therapy. A case of cardiac rupture manifested by the onset of atrial fibrillation in a patient admitted to Intensive Care after a car accident is described. The scarce significance of objective examination, the aspecific nature of chest X-ray and ECG alterations prompted the execution of a more thorough diagnosis. Transthoracic and transesophageal ultrasonography are both minimally invasive and highly specific: in a short time, not only did they confirm cardiac rupture, but they also focalised the site of the lesion, thus allowing a more targeted and rapid surgical approach. The relative frequency of cardiac lesions following closed thoracic trauma, the lack of incontrovertible signs and symptoms of late cardiac rupture, and the extreme severity of its clinical consequences argue in favour of using specific and sensitive diagnostic tests that can not only exclude or ascertain the presence of these lesions, but also allow subsequent serial controls aimed at diagnosing late cardiac ruptures.

Accidents, Traffic↗

PubMed1999

Neuroprotective effects of riluzole: an electrophysiological and histological analysis in an in vitro model of ischemia.

The protective effects of riluzole against the neuronal damage caused by O2 and glucose deprivation (ischemia) was investigated in rat cortical slices by recording electrophysiologically the cortico-cortical field potential and by evaluating histologically the severity of neuronal death. Five minutes of ischemia determined an irreversible depression of the amplitude of the field potential. In addition, this insult caused a clear enhancement of the number of death cells that were specifically colored with trypan blue (a vital colorant which stains altered cells). We found that riluzole, which by itself depressed the synaptic transmission, neuroprotected when perfused 15-20 min before and during ischemia. In fact, due to the treatment with riluzole, the ischemia-induced irreversible depression of the field potential recovered and less cells were stained with trypan blue. These findings demonstrate that riluzole prevents neuronal death in an in vitro model of ischemia and suggest a therapeutic use of this drug in order to reduce the pathophysiological outcomes of stroke.

Animals↗

PubMed1999

5-HT4 receptor modulation of acetylcholine outflow in guinea pig brain slices.

The effect of the 5-HT4 agonist, BIMU-8 was studied on [3H]choline outflow in guinea pig brain slices and synaptosomes. BIMU-8 did not modify [3H]choline efflux in slices kept at rest, but increased [3H]choline outflow in electrically stimulated slices of cerebral cortex (CC), hippocampus (hip) and nucleus basalis magnocellularis (nbm). This effect was prevented by the selective 5-HT4 antagonist, GR 125487. Conversely, BIMU-8 did not affect [3H]choline efflux in hippocampal synaptosomes depolarized with KCl 20 mM. These results provide evidence that BIMU-8 increases the electrically triggered [3H]choline efflux in CC, hip and nbm slices. A possible role of 5-HT4 agonists in memory and learning diseases is suggested.

Acetylcholine↗

PubMed1999

Early changes in adenosine A1 receptors in cerebral cortex slices submitted to in vitro ischemia.

The effects of brain ischemia on the maximum binding capacity (Bmax) and affinity (Kd) of A1 receptors were studied in the rat cerebral cortex, with an in vitro approach. The results were correlated with changes in 3H-adenosine release, studied under identical experimental conditions. Fifteen minutes of in vitro 'ischemia' (hypoxic, glucose-free medium) induced a significant increase in both Bmax (2398+/-132 fmol/mg protein, 151% of the control, P < 0.05) and in Kd (2.43+/-0.12 nM, 161% of the control, P < 0.01). At the same time, an increase in tritium efflux from [3H]-adenosine labeled cerebral cortex slices to 324% of the control was observed. A trend toward normalization was evident 5-15 min after 'reoxygenation' (restoring normal medium), but the binding parameters were still altered after 60 min (Bmax 2110+/-82 fmol/mg protein, Kd 2.26+/-0.14 nM, P < 0.01 vs the corresponding control) as was adenosine release (196% of the control). These findings suggest that the increased availability of adenosine and its receptors may be a defense mechanism against ischemic injury, while the reduced affinity of A1 receptors, possibly due to desensitization, may be a sign of ischemia-induced cellular damage.

Adenosine↗

PubMed1999

Inhibitory effect of nociceptin on [3H]-5-HT release from rat cerebral cortex slices.

1. The effect of nociceptin (NC) on 5-hydroxytryptamine (5-HT) release was studied in rat cerebral cortex slices preincubated with [3H]-5-HT and electrically stimulated (3 Hz, for 2 min) at the 45th (St1) and the 75th (St2) min of superfusion. 2. NC (0.1 - 3 microM), present in the medium from the 70th min onward, concentration-dependently reduced electrically evoked [3H]-5-HT efflux (pEC50=6.54, Emax -54%). The inhibition was not antagonized by naloxone (1 microM) ruling out the involvement of opioid receptors. 3. Phe1psi(CH2-NH2)Gly2]NC(1-13)NH2, which acts as an opioid-like receptor (ORL1) antagonist at the peripheral level, behaved as a partial agonist in cerebral cortex slices i.e. it inhibited [3H]-5-HT efflux when added before St2, however, when present in the medium throughout the whole experiment, [Phe1psi(CH2-NH2)Gly2]NC(1-13)NH2 prevented the action of NC added at the 70th min. 4. The non-selective ORL1 receptor antagonist, naloxone benzoylhydrazone (3 microM), in the presence of 10 microM naloxone, did not modify the St2/St1 ratio but completely abolished the NC effect. 5. These findings demonstrate that NC inhibits 5-HT release from rat cerebral cortex slices via ORL1 receptors, suggesting its involvement in central processes mediated by 5-HT.

Animals↗

PubMed1999

New insights on flow-independent mechanisms of 99mTc-HMPAO retention in nervous tissue: in vitro study.

UNLABELLED: SPECT using 99mTc-hexamethyl propyleneamine oxime (HMPAO) mainly reflects regional cerebral blood flow, however metabolic abnormalities also affect the retention of 99mTc-HMPAO. METHODS: To rule out any flow factor, a test-tube model was used to evaluate the effects of metabolic alterations both on intracellular trapping of 99mTc-HMPAO and on extracellular glutamate and lactate dehydrogenase (LDH) outflow from rat brain slices. RESULTS: Under control conditions, slices took up 7.0%+/-1.4% of 99mTc-HMPAO contained in the medium, whereas prelabeled slices released 10.8%+/-2.6% of their radioactive content; glutamate and LDH outflow were 49.1+/-21.6 pmol/mg protein/ min and 4.8+/-0.9 U/L/mg protein/min, respectively. The control medium was altered by adding a metabolic poison (5 mmol/L azide), removing glucose and replacing O2 with N2 to mimic ischemia (in vitro ischemia) and replacing Krebs solution with hypotonic medium to evoke cell lysis. Both azide and in vitro ischemia induced a significant increase in 99mTc-HMPAO release (15.8%+/-3.3% and 18.3%+/-6.2%, respectively), without any modification in LDH efflux. However, only azide reduced the uptake of the tracer. Conversely, glutamate outflow was massive during in vitro ischemia and was far lower during azide treatment. Under hypotonic medium conditions, the release of 99mTc-HMPAO, glutamate and LDH were dramatically increased. Surprisingly, a two-fold increase of 99mTc-HMPAO uptake was also found. When 1 mmol/L glutathione was added to the medium, to convert native lipophilic 99mTc-HMPAO into hydrophilic derivatives, tracer uptake was inhibited both under control and hypotonic medium conditions. CONCLUSION: This study provides evidence that not only poisoning of the tissue but also in vitro ischemia induced a reduction of 99mTc-HMPAO retention. Moreover, we demonstrated that injuries causing cell membrane disruption led to hyperfixation of 99mTc-HMPAO.

Animals↗

PubMed1998

An electrophysiological analysis of the protective effects of felbamate, lamotrigine, and lidocaine on the functional recovery from in vitro ischemia in rat neocortical slices.

We used field potential recording techniques to examine whether felbamate (FBM), lamotrigine (LTG), and lidocaine (LID) protect against the irreversible functional damage induced by transient ischemia. Five minutes of ischemia caused a depression of the field potential in rat cortical slices, which did not recover even after more than 1 h of washout. The N-methyl-D-aspartate (NMDA) antagonist ketamine (50 microM) protected against depression of the field caused by ischemia. On the other hand, the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2.3-dione (CNQX) (10 microM) had protective effects only if co-applied with ketamine. We found that either FBM (30-300 microM), which did not modify the amplitude of the field EPSP, or LTG (10-300 microM), which reversibly depressed the excitatory synaptic transmission, had a marked protective effect when superfused before and during the ischemic insult. After FBM (100 microM) and LTG (100 microM), the field EPSP recovered by 84 +/- 1% and 73 +/- 2.7% of control, respectively. Furthermore, LID (30-300 microM) was less effective than FBM and LTG in inducing a functional recovery from the damage caused by ischemia (58 +/- 1.8%). The rank order of potency, based on the maximal protection caused by the three drugs, was FBM > LTG > LID. Our results suggest that a noticeable neuroprotection can be obtained during glucose and O2 deprivation by preventive therapeutic regimens which use the two recently marketed anticonvulsant drugs, FBM and LTG.

Action Potentials↗

PubMed1998

Modification of levodopa responses by deprenyl (selegiline): an electrophysiological and behavioral study in the rat relevant to Parkinson's disease.

From using in vitro intracellular recordings from mesencephalic neurons and monoamine-depleted rats, we report that the functions of levodopa in the brain are greatly enhanced and prolonged by high doses of the monoamine oxidase (MAO) inhibitor deprenyl. Dopaminergic neurons were hyperpolarized and inhibited by levodopa application. These effects of levodopa were largely potentiated by pretreatment with nonselective doses of deprenyl. Furthermore, when locomotor activity induced by levodopa was examined on a rodent model of Parkinson's disease, pretreatment of the animals with nonselective doses of deprenyl caused an enhancement of the antiparkinsonian action of levodopa. The great increase in levodopa responses by deprenyl suggests a likely therapeutic use of this dopamine precursor with a higher dosage of the MAO inhibitor, to reduce effectively the daily levodopa requirements in Parkinson's disease patients.

Animals↗

PubMed1998

Riluzole interacts with voltage-activated sodium and potassium currents in cultured rat cortical neurons.

The actions of the neuroprotective and anticonvulsant agent riluzole on voltage-activated currents were studied in primary cultures of rat cortical neurons by using whole-cell patch-clamp recording techniques. Isolated Na+, Ca2+ and K+ currents were generated in these cells by depolarizing commands from a holding potential of - 80 mV. Riluzole (10-300 microM) reversibly reduced in a dose-dependent manner the inward Na+ currents with an IC50 of 51 microM in all the tested neurons (n=29). This drug also shifted the steady-state inactivation curve of the sodium current towards more negative values (about 20mV, n=15) while it did not change significantly the decay phase of the Na+ current. Furthermore, riluzole (100 and 300 microM; n=5 and n=3, respectively) did not modulate the inward Ca2+ currents evoked by depolarizing steps on cortical cells. An additional concentration-dependent effect of riluzole was observed on the outward potassium currents. In fact, while the amplitude of the peak of the outward current (IA) was not changed significantly, the amplitude of the late component of the outward K+ current (Iss) was markedly decreased during the perfusion of riluzole (IC50=88 microM; n=16). It is concluded that riluzole modulates the Na+- and the late K+-dependent currents in cortical neurons. Both phenomena may explain, at least in part, the anticonvulsant and neuroprotective properties of this compound.

4-Aminopyridine↗

PubMed1998

Experimental protocol for studying delayed effects of in vitro ischemia on neurotransmitter release from brain slices.

The mechanisms by which ischemic injury leads to delayed neuronal death are not completely understood. Notably, no data are so far available on the modifications in neurosecretory responses evoked by a period of ischemia. Superfused brain slices represent a useful preparation in studying the effects of in vitro ischemia on neurotransmitter release. Using this experimental model we describe a protocol which allows to study not only the immediate effects of an ischemic insult, but also, more interestingly, its delayed (1 h) effects on the release of different neurotransmitters. A first pulse (S1) of 50 mM KCl was applied at the 60th min of perfusion and a second one was applied at the 210th min (S2). In vitro ischemia was performed from the 120th to the 150th min, during the inclusive period between the two depolarizing stimuli. The delayed effects of the ischemic treatment on slice response to KCl were calculated as S2/S1 ratio. This protocol allows to study neurotransmitter release mechanisms associated with postischemic neuronal death. Moreover it will be useful in the evaluation of the neuroprotective potential of new drugs.

Animals↗

PubMed1998

Whole cell patch-clamp recordings of rat midbrain dopaminergic neurons isolate a sulphonylurea- and ATP-sensitive component of potassium currents activated by hypoxia.

The effects of brief (2-4 min) hypoxia on presumed dopaminergic "principal" neurons of the rat ventral mesencephalon were investigated by using either intracellular or whole cell patch-clamp recordings in in vitro conditions. Under single-electrode voltage clamp, with sharp microelectrode (Vh -60 mV), a brief hypoxia caused an outward current (hypoOUT) of 110.2 +/- 15.2 (SE) pA (n = 18), which was followed by a posthypoxic outward current (posthypoOUT) of 149.6 +/- 10.6 pA (n = 18). Although the hypoOUT reversed at -83.7 +/- 3.8 mV (n = 18), the posthypoOUT did not reverse. The K+ATP-blocking sulphonylureas tolbutamide (100 microM) and glibenclamide (30 microM), significantly reduced the peak of the hypoOUT by 47.6 +/- 7.7% (n = 16) and 54.18 +/- 7.5% (n = 3), respectively. In contrast, they did not affect the posthypoOUT. Extracellular barium (300 microM to 1 mM) almost abolished the hypoOUT, leaving the posthypoOUT unchanged. The large K+ channel blocker charybdotoxin (10-50 nM), depressed the hypoOUT after tolbutamide treatment. To investigate whether or not cytosolic factors might control the development of the hypoOUT, we dialyzed the principal neurons by patch-clamp recordings (Vh -60 mV). Under whole cell recordings hypoxia evoked an hypoOUT of 70.2 +/- 14.5 pA that reversed polarity at -87.9 +/- 5.1 mV (n = 8). A small posthypoxic response was detected upon reoxygenation in a few neurons (4 out of 14). Three different sulphonylureas, tolbutamide (100 microM), glibenclamide (10-30 microM), and glipizide (100 nM) completely blocked the hypoOUT in patch-clamped neurons. The hypoOUT was also abolished by extracellular BaCl2 (300 microM). When the content of ATP in the dialyzate was raised from 2 to 10 mM no outward current/hyperpolarization was evoked by hypoxia. These data suggest that the hypoOUT, in principal neurons, is a complex response sustained by at least two barium-sensitive components: 1) an ATP-dependent, sulphonylurea-sensitive K+ conductance which could be isolated by the patch-clamp techniques and 2) a K+ conductance remaining after tolbutamide in intracellularly recorded neurons, which is sensitive to charybdotoxin and dependent on dialyzable cytosolic factors.

Adenosine Triphosphate↗

PubMed1997

Monoamine oxidase inhibition causes a long-term prolongation of the dopamine-induced responses in rat midbrain dopaminergic cells.

The way monoamine oxidase (MAO) modulates the depression of the firing rate and the hyperpolarization of the membrane caused by dopamine (DA) on rat midbrain dopaminergic cells was investigated by means of intracellular recordings in vitro. The cellular responses to DA, attributable to the activation of somatodendritic D2/3 autoreceptors, were prolonged and did not completely wash out after pharmacological blockade of both types (A and B) of MAO. On the contrary, depression of the firing rate and membrane hyperpolarization induced by quinpirole (a direct D2 receptor agonist) were not affected by MAO inhibition. Furthermore, although the inhibition of DA reuptake by cocaine and nomifensine caused a short-term prolongation of DA responses, the combined inhibition of MAO A and B enzymes caused a long-term prolongation of DA effects. Moreover, the effects of DA were not largely prolonged during the simultaneous inhibition of MAO and the DA reuptake system. Interestingly, the actions of amphetamine were not clearly augmented by MAO inhibition. From the present data it is concluded that the termination of DA action in the brain is controlled mainly by MAO enzymes. This long-term prolongation of the dopaminergic responses suggests a substitutive therapeutic approach that uses MAO inhibitors and DA precursors in DA-deficient disorders in which continuous stimulation of the dopaminergic receptors is preferable.

Amphetamine↗

PubMed1997

Post-ischemic recovery of acetylcholine release in vitro: influence of different excitatory amino acid receptor subtype antagonists.

The release of endogenous acetylcholine was measured in electrically (5-20 Hz) stimulated guinea pig cerebral cortex and caudate nucleus slices under ischemic (hypoxic and glucose-free) conditions. Ischemia reduced acetylcholine release by 40-90%; the inhibition depended on the duration of ischemia (10-30 min) while the extent of post-ischemic recovery was inversely related to it. Caudate nucleus slices displayed a higher sensitivity to ischemia than did cortical slices. To test the effects of excitatory amino acid receptor antagonists on the ischemia-induced reduction of acetylcoline release and on its post-ischemic recovery, the following drugs were used: 5-methyl-10,11-dihydro-5-H-dibenzo-[a,b]-cyclohepten-5,10-imine (MK-801,-a blocker of the N-methyl-D-aspartate [NMDA] receptor-linked channel), 7-chloro-kynurenic acid (7-Cl-KYN) and (E)-3-[2(phenylcarbamoyl)ethenyl]-4,6-dichloroindole-2-carboxylic acid sodium salt (GV150526A, blockers of the glycine site of the NMDA receptor), eliprodil, (an antagonist at the polyamine site of the NMDA receptor), and 6-cyano- 7-nitro-quinoxalin-2,3-dione (CNQX, a D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid [AMPA] receptor antagonist). These did not modify the time-course and the extent of ischemia-induced inhibition but improved post-ischemic recovery in a concentration dependent manner. GV 150526A and CNQX appeared to be more effective in the cerebral cortex. Only eliprodil was devoid of any effect in both areas. The evaluation of acetylcholine release from brain slices represents a suitable in vitro model to quantify the effectiveness of drugs in favouring recovery from the cholinergic presynaptic failure induced by ischemic conditions. The different effects of the excitatory amino acid receptor antagonists cited above, depending on the brain areas considered and the receptor subtypes involved, may be of interest in view of their therapeutic potential.

Acetylcholine↗

PubMed1997

Epileptiform discharge induced by 4-aminopyridine in magnesium-free medium in neocortical neurons: physiological and pharmacological characterization.

An in vitro model of epileptiform activity was developed to study the role of excitatory and inhibitory neurotransmitters in the epileptogenesis. Intracellular recordings were obtained from rat neocortical slices exposed to 4-aminopyridine in a magnesium-free solution. Spontaneous epileptiform activity consisting of paroxysmal depolarization shifts with associated spontaneous depolarizing postsynaptic potentials were observed. The paroxysmal depolarization shifts were blocked either by D,L-2-amino-5-phosphonovalerate (50 microM), an N-methyl-D-aspartate receptor antagonist, or by 6-cyano-7-nitroquinoxaline-2.3-dione (10 microM), a non-N-methyl-D-aspartate receptor antagonist. These glutamate receptor antagonists also reduced the occurrence of spontaneous depolarizing postsynaptic potentials. Bicuculline methiodide, an antagonist of GABAA receptors, suppressed spontaneous depolarizing postsynaptic potentials, while it reduced the frequency of paroxysmal depolarization shifts and increased their duration. Hyperpolarization of the membrane potential by continuous current injection increased the frequency of paroxysmal depolarization shifts and reduced their duration, but it reduced the occurrence of spontaneous postsynaptic potentials. Paroxysmal depolarization shifts were blocked by tetrodotoxin (1 microM). The duration and the frequency of paroxysmal depolarization shift were reduced by dopamine (30-300 microM) in a dose-dependent manner. Our model suggests a different involvement of excitatory and inhibitory processes in the generation of epileptiform activity.

2-Amino-5-phosphonovalerate↗