PubMed Health⌕ Search

Biomedical subjects

M A Rogawski

Publications and source records attributed to M A Rogawski.

At least 73 records · Page 4Linked to original sources
PubMed1993

Anticonvulsant activity of AMPA/kainate antagonists: comparison of GYKI 52466 and NBOX in maximal electroshock and chemoconvulsant seizure models.

The anticonvulsant activities of a noncompetitive (GYKI 52466) and a competitive (NBQX) AMPA/kainate antagonist were compared in the maximal electroshock (MES) seizure test and various chemoconvulsant models. Both antagonists were protective in the MES and pentylenetetrazol tests. GYKI 52466 was also protective against seizures and lethality induced by 4-aminopyridine, kainate and AMPA, but not by NMDA, whereas NBQX was ineffective in these chemoconvulsant tests. Both GYKI 52466 and NBQX produced motor impairment at doses similar to those that were protective in the MES test. Under some circumstances, noncompetitive AMPA/kainate antagonists could offer advantages over competitive antagonists in seizure therapy. However, neurological toxicity is an obstacle to the potential clinical use of both classes of agents.

4-Aminopyridine↗
PubMed1993

Calcium current block by (-)-pentobarbital, phenobarbital, and CHEB but not (+)-pentobarbital in acutely isolated hippocampal CA1 neurons: comparison with effects on GABA-activated Cl- current.

Block of a voltage-activated Ca2+ channel current by phenobarbital (PHB), 5-(2-cyclohexylideneethyl)-5-ethyl barbituric acid (CHEB), and the optical R(-)- and S(+)-enantiomers of pentobarbital (PB) was examined in freshly dissociated adult guinea pig hippocampal CA1 neurons; the effects of the barbiturates on GABA-activated Cl- current were also characterized in the same preparation. (-)-PB, PHB, and CHEB produced a reversible, concentration-dependent block of the peak Ca2+ channel current (3 mM Ba2+ as the charge carrier) evoked by depolarization from -80 to -10 mV (IC50 values, 3.5, 72, and 118 microM, respectively). In contrast, (+)-PB was nearly inactive at concentrations up to 1 mM. The inhibitory action of PHB was decreased at acid pH, indicating that the dissociated (anionic) form of the molecule is the active species. Block by (-)-PB was voltage dependent with the fractional block increasing at positive membrane potentials; calculations according to the method of Woodhull indicated that the (-)-PB blocking site senses approximately 40% of the transmembrane electric field. The time course and voltage dependence of activation of the Ca2+ channel current were unaffected by (-)-PB, PHB, and CHEB. The rate of inactivation was enhanced by (-)-PB and CHEB, with the major effect being acceleration of the slow phase of the biexponential decay of the current. GABA-activated Cl- current was potently enhanced by (-)-PB and PHB (EC50 values, 3.4 and 12 microM), whereas (+)-PB was only weakly active. At concentrations of (-)-PB > 100 microM and PHB > 200-300 microM, Cl- current responses were activated even in the absence of GABA. These results demonstrate that in CA1 hippocampal neurons, PB causes a stereoselective block of a voltage-activated Ca2+ current; PHB is also effective, but at higher concentrations. For (-)-PB, the effect on Ca2+ channel current occurred at similar concentrations as potentiation of GABA responses. In contrast, PHB was more potent as a GABA enhancer than as blocker of Ca2+ current, but the maximal potentiation of GABA responses was 40% of that obtained with (-)-PB. Consequently, the anticonvulsant action of PHB at clinically relevant concentrations may relate to modest enhancement of GABA responses and partial blockade of Ca2+ current, whereas the sedative effects that occur at higher concentrations could reflect stronger Ca2+ current blockade. The powerful sedative-hypnotic action of (-)-PB may reflect greater maximal enhancement of GABA responses in conjunction with strong inhibition of Ca2+ current.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Tityustoxin-K alpha, a structurally novel and highly potent K+ channel peptide toxin, interacts with the alpha-dendrotoxin binding site on the cloned Kv1.2 K+ channel.

The interaction between two nonhomologous K+ channel toxins, Tityus serrulatus (scorpion) toxin tityustoxin-K alpha (TsTX-K alpha) and Dendroaspis angusticeps (snake) toxin dendrotoxin (alpha-DTX), was investigated on K+ currents in B82 fibroblast cells transformed to express the Kv1.2 K+ channel. As demonstrated previously, alpha-DTX was a potent blocker of the K+ current (Kd, 2.8 nM). Recombinant TsTX-K alpha produced a similar block of the current but was 1 order of magnitude more potent (Kd, 0.21 nM). TsTX-K alpha did not affect the kinetic properties of the current or its voltage dependence of activation. Experiments with excised and cell-attached patch recordings demonstrated that TsTX-K alpha blocks the K+ channel by binding to an extracellular site. In the presence of TsTX-K alpha the blocking potency of alpha-DTX was reduced, whereas the potency of 4-aminopyridine, which also blocks the channel, was unaffected. alpha-DTX caused a rightward shift in the scaled concentration-response curve for TsTX-K alpha, the magnitude of which was reasonably well predicted by a model in which there is a competitive interaction between the two peptide toxins. We conclude that TsTX-K alpha and alpha-DTX block the Kv1.2 K+ channel by binding to the same or closely related sites.

Animals↗
PubMed1992

1,10-Diaminodecane and 1,12-diaminododecane block NMDA receptor currents by an open channel mechanism.

In whole-cell recordings from cultured rat hippocampal neurons (VH = -60 mV), 1,10-diaminodecane (DA10) and 1,12-diaminododecane (DA12) produced a concentration-dependent block of NMDA-induced current (IC50 = 30 and 7 microM, resp.). In contrast, the diamines failed to affect AMPA and kainate currents. The inhibition of NMDA currents was highly voltage-dependent and was substantially relieved at positive holding potentials. In outside-out patches, DA10 and DA12 produced a voltage-dependent flickery block of NMDA-activated single-channel currents. These results indicate that DA10 and DA12 antagonize NMDA responses via an open channel mechanism. DA10 and DA12 have been proposed to be inverse agonists at the spermine facilitatory site on the NMDA receptor. However, the channel blocking effects of the diamines complicate the interpretation of their actions at this site.

Animals↗
PubMed1992

Pregnenolone sulfate augments NMDA receptor mediated increases in intracellular Ca2+ in cultured rat hippocampal neurons.

The ability of the neuroactive steroid pregnenolone sulfate to alter N-methyl-D-aspartate (NMDA) receptor-mediated elevations in intracellular Ca2+ ([Ca2+]i) was studied in cultured fetal rat hippocampal neurons using microspectrofluorimetry and the Ca2+ sensitive indicator fura-2. Pregnenolone sulfate (5-250 microM) caused a concentration-dependent and reversible potentiation of the rise (up to approximately 800%) in [Ca2+]i induced by NMDA. In contrast, the steroid failed to alter basal (unstimulated) [Ca2+]i or to modify the rise in [Ca2+]i that occurs when hippocampal neurons are depolarized by high K+ in the presence of the NMDA receptor antagonist CPP. These data suggest that the previously reported excitatory properties of pregnenolone sulfate may be due, in part, to an augmentation of the action of glutamic acid at the NMDA receptor.

Animals↗
PubMed1992

High concentrations of neutral amino acids activate NMDA receptor currents in rat hippocampal neurons.

High concentrations (30 microM-5 mM) of the neutral amino acids L-serine, L-cysteine, L-alanine, L-proline and glycine elicited inward current responses when applied to hippocampal neurons patch clamped at -60 mV in the presence of 1-10 microM glycine and 1 microM strychnine. The amplitude of the response to L-serine increased in a concentration-dependent fashion within the range 0.1-10 mM (EC50, 2.6 mM). L-Serine (1 mM) currents were attenuated by Mg2+ (100 microM) and completely blocked by the competitive N-methyl-D-aspartate (NMDA) antagonist 3-(2-carboxypiperazin-4-yl)-propyl-1- phosphonic acid (CPP) (30 microM). The CPP block could be overcome by raising the concentration of L-serine. We conclude that high concentrations of some neutral amino acids activate NMDA receptor-coupled ion channels by acting as agonists at the NMDA recognition site.

Amino Acids↗
PubMed1992

Protection against dendrotoxin-induced clonic seizures in mice by anticonvulsant drugs.

Various anticonvulsant drugs were evaluated for their ability to protect against clonic seizures induced in mice by intraventricular injection of the K+ channel blocking peptide dendrotoxin (DTX). Phenytoin, the phenytoin-like anticonvulsant carbamazepine and the broad spectrum drug valproate were effective in this model, whereas the GABA-enhancers diazepam and tiagabine, the NMDA antagonists (+/-)-CPP and (+)-MK-801, the AMPA antagonist NBQX, the antiabsence drug ethosuximide and the Ca2+ channel antagonist nimodipine were inactive. In contrast to the lack of activity of other NMDA antagonists, phencyclidine and ADCI [(+/-)-aminocarbonyl-10,11-dihydro-5H-dibenzo [a,d]cyclohepten-5,10-imine] were potent antagonists of DTX-induced seizures.

Animals↗
PubMed1992

Muscarinic antagonists attenuate dizocilpine-induced hypermotility in mice.

Pretreatment of mice with the muscarinic receptor antagonists scopolamine and atropine attenuated the hypermotility (but not the depression of rearing) induced by a low dose of dizocilpine maleate [(+)-MK-801; 0.1 mg/kg, i.p.], a non-competitive NMDA antagonist. In contrast, the muscarinic blockers failed to affect hypermotility induced by equieffective doses of phencyclidine (1 mg/kg, i.p.) or d-amphetamine (2 mg/kg, i.p.). These results suggest differences between the mechanism of behavioral activation produced by dizocilpine and phencyclidine, and demonstrate the potential of muscarinic blockade for diminishing the behavioral toxicity of NMDA antagonists.

Animals↗
PubMed1992

Charybdotoxin, dendrotoxin and mast cell degranulating peptide block the voltage-activated K+ current of fibroblast cells stably transfected with NGK1 (Kv1.2) K+ channel complementary DNA.

The blocking actions of the K+ channel toxins charybdotoxin, dendrotoxin and mast cell degranulating peptide were studied in B82 mouse fibroblast cells transformed to express NGK1 (Kv1.2) K+ channels. All three toxins were potent blockers of the K+ current in these cells, with KD values of 1.7, 2.8 and 185 nM, respectively. The toxin block exhibited a weak voltage-dependence with the degree of inhibition decreasing at positive membrane potentials. For charybdotoxin and dendrotoxin, reducing [K+]i did not increase the fractional block, demonstrating that the relief of block at positive membrane potentials is not due to displacement of the toxin molecules by outward flow of K+ ions. A voltage-jump protocol was used to determine the rates of binding and unbinding of dendrotoxin and mast cell degranulating peptide; binding of charybdotoxin was too rapid to be quantitatively evaluated in this manner. The binding rates (dendrotoxin, approximately 5 x 10(7)/M per s; mast cell degranulating peptide, approximately 0.8 x 10(7)/M per s) were largely voltage-independent, suggesting that association of the toxin molecules with the channel is diffusion limited. The rates of unbinding (dendrotoxin, approximately 0.3/s; mast cell degranulating peptide, approximately 3/s at +60 mV) of both toxins increased e-fold per approximately 40 mV change in membrane potential, thus accounting for the voltage-dependence of the equilibrium block. Internal perfusion with the three toxins failed to affect the K+ current (in contrast to internal tetraethylammonium which strongly blocked the current), indicating that the toxins exert their blocking action by binding to extracellular sites.

Ampicillin Resistance↗
PubMed1992

Effects of anticonvulsant drugs on 4-aminopyridine-induced seizures in mice.

The K+ channel blocker 4-aminopyridine (4-AP) causes epileptiform activity in in vitro preparations and is a potent convulsant in animals and man. In mice, 4-AP produces behavioral activation, clonic limb movements and wild running, followed by tonic hindlimb extension and death (ED97, 13.3 mg/kg, s.c.). We evaluated the ability of a series of anticonvulsant drugs to protect against 4-AP-induced seizures using lethality as the endpoint. Drugs with a phenytoin-like profile of activity were protective with ED50 values (all in mg/kg, i.p.) of 34.4 for phenytoin, 18.6 for carbamazepine, 26.9 for felbamate, and 41.5 for zonisamide. Phenobarbital and valproate also protected against 4-AP-induced seizures and lethality (ED50s, 30.6 and 301, respectively). In contrast the NMDA antagonists (+/-)-CPP and (+)-MK-801 were inactive as were the GABA enhancers diazepam, vigabatrin and tiagabine; the antiabsence drug ethosuximide; and the L-type Ca2+ channel blocker nimodipine. We conclude that drugs like phenytoin which block seizure spread are effective antagonists of seizures induced by K+ channel blockade. Drugs with specific actions on other cellular targets may be weak or inactive, presumably because they are unable to attenuate the spread of intense (non-NMDA receptor mediated) excitation evoked by 4-AP.

4-Aminopyridine↗
PubMed1992

New antiepileptic drugs: from serendipity to rational discovery.

Antiepileptic drug discovery has made enormous progress from the serendipity and screening processes of earlier days to the rational drug development of today. The modern era of research began with the recognition that enhancement of inhibitory processes in the brain might favorably influence the propensity for seizures, gamma-aminobutyric acid (GABA) being the main inhibitory transmitter. Work in this field led to the development of vigabatrin, which inhibits the enzyme responsible for the degradation of GABA. More recently, research has focused on the therapeutic potential of blocking excitatory amino acids--in particular glutamate. Of the three receptors for glutamate, the N-methyl-D-aspartate (NMDA) receptor is considered the one of most interest in epilepsy, and research on a series of competitive NMDA receptor antagonists--especially those that are orally active--is in the forefront of antiepileptic drug development today. A further alternative for diminishing neuronal excitability is to modulate sodium, potassium, or calcium channels. The latter are especially implicated in absence seizures.

Animals↗
PubMed1992

Phencyclidine block of calcium current in isolated guinea-pig hippocampal neurones.

1. Phencyclidine (PCP) block of Ca2+ channel current in enzymatically dissociated neurones from the CA1 region of the adult guinea-pig hippocampus was studied using whole-cell voltage clamp techniques. Ca2+ channel current was recorded with 3 mM-Ba2+ as the charge carrier. Na+ currents were blocked with tetrodotoxin and K+ currents were eliminated by using tetraethylammonium and N-methyl-D-glucamine as the predominant extracellular and intracellular cations, respectively. 2. Peak Ca2+ channel current evoked by depolarization from -80 to -10 mV was reduced in a use-dependent fashion by PCP. The apparent forward and reverse rate constants for block at the depolarized voltage were 10(6) s-1 M-1 and 11-14 s-1, respectively. These values were at least 60 times faster than the corresponding rates at the resting voltage. The steady-state block produced by PCP increased in a concentration-dependent fashion with an IC50 of 7 microM. Other dissociative anaesthetic drugs were substantially weaker inhibitors of the current (tiletamine > dizocilpine (MK-801) > ketamine). 3. The Ca2+ channel current recorded under identical conditions in rat dorsal root ganglion neurones was less sensitive to blockade by PCP (IC50, 90 microM). 4. PCP block of the hippocampal Ca2+ channel current occurred in a voltage-dependent fashion with the fractional block decreasing at positive membrane potentials. Analysis indicated that the PCP blocking site senses 56% of the transmembrane electric field. 5. Analysis of tail currents recorded at -80 mV demonstrated that PCP does not affect the voltage-dependent or time-dependent activation or deactivation of the Ca2+ channel current. 6. The rate and extent of inactivation of the Ca2+ channel current was maximal at -10 mV and diminished at more positive potentials. Experiments with Ba(2+)-free external solution demonstrated that inactivation of the Ca2+ channels is largely voltage-dependent and is not affected by Ba2+ influx. 7. PCP markedly increased the apparent extent of inactivation of the Ca2+ channel current during prolonged voltage steps. This increase in apparent inactivation was more pronounced at depolarized potentials. Inactivation at -10 mV proceeded in two exponential phases; PCP had little effect on the fast decay phase and caused a moderate speeding of the slow decay phase. Although block of the activated state evolved on the same time scale as inactivation, the apparent rate of inactivation was not increased in a concentration-dependent fashion by PCP indicating that the block does not occur by a conventional open channel mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Arcaine blocks N-methyl-D-aspartate receptor responses by an open channel mechanism: whole-cell and single-channel recording studies in cultured hippocampal neurons.

Arcaine, a putative competitive antagonist at the polyamine site on the N-methyl-D-aspartate (NMDA) receptor complex, not only inhibits polyamine enhancement of NMDA-induced [3H]dizocilpine (MK-801) binding but also depresses binding in the absence of polyamines. In the present experiments, we investigated the mechanism of this latter effect in whole-cell and single-channel recordings from cultured rat hippocampal neurons. Arcaine produced a concentration-dependent block of NMDA-evoked inward currents (KD, 61 microM at -60 mV) but not those induced by kainate, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, or gamma-aminobutyric acid. The arcaine block was strongly voltage dependent and was almost completely relieved at positive holding potentials. Analysis of the voltage dependence indicated that the arcaine acceptor site appeared to sense 67% of the transmembrane electric field. In support of an open channel blocking mechanism, arcaine, like Mg2+, prevented dizocilpine from blocking the NMDA receptor channel. Moreover, increasing the dizocilpine concentration partially overcame the arcaine effect, indicating a competitive interaction between arcaine and dizocilpine. Spermine, which in our preparation usually produced only an arcaine-like voltage-dependent block of NMDA currents at high concentrations (greater than 100 microM), had no effect on the block by arcaine at lower concentrations. In single-channel recordings, arcaine caused a concentration- and voltage-dependent decrease in apparent channel amplitude. Assuming a simple model of open channel block, we estimate the arcaine binding and unbinding rates as 4.4 x 10(8) M-1 sec-1 and 1.8 x 10(4) sec-1, respectively, which are comparable to the rates for open channel block by Zn2+ and substantially faster than those of Mg2+. These results indicate that arcaine inhibits NMDA-induced [3H]dizocilpine binding by blocking the open NMDA receptor channel, an action that is independent of the polyamine site.

Animals↗
PubMed1992

Comparison of the effects of the uncompetitive N-methyl-D-aspartate antagonist (+-)-5-aminocarbonyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine (ADCI) with its structural analogs dizocilpine (MK-801) and carbamazepine on ethanol withdrawal seizures.

The ability of [(+-)-5-aminocarbonyl-10,11-dihydro-5H-di-benzo [a,d]cyclohepten-5,10-imine (ADCI) and its structural analogs dizocilipine (MK-801) and carbamazepine to block ethanol withdrawal seizures was tested in mice made physically dependent upon ethanol. Three injections of either ADCI (ranging from 1.0-10.0 mg/kg), dizocilpine (ranging from 0.1-1.0 mg/kg) or carbamazepine (ranging from 17-50 mg/kg) were administered during the first 7 hr of ethanol withdrawal. The severity of ethanol withdrawal seizures was rated during the first 11 hr of withdrawal and again at 24 hr after withdrawal of ethanol. ADCI and dizocilpine suppressed the severity and occurrence of the withdrawal seizures in a dose-dependent fashion, whereas carbamazepine was ineffective in blocking the withdrawal seizures. The relative potencies of dizocilpine, ADCI and carbamazepine in suppressing ethanol withdrawal seizures corresponded with the relative potencies of the compounds in displacing [3H]dizocilpine from mouse cortical membrane preparations. These findings are consistent with the suggestion that blockade of N-methyl-D-aspartate-mediated neurotransmission is an effective treatment for decreasing ethanol withdrawal seizures. ADCI also blocked the occurrence of withdrawal-associated whole body tremors, whereas dizocilpine and carbamazepine were ineffective in blocking the tremors. The doses of ADCI, dizocilpine and carbamazepine that resulted in motor incoordination on an accelerating rotarod task were determined in groups of naive mice. Dizocilpine in doses as low as 0.3 mg/kg produced a decreased ability to remain on the rotarod, whereas ADCI up to 30 mg/kg did not affect rotarod performance.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

A model of the T-type calcium current and the low-threshold spike in thalamic neurons.

1. A model of the transient, low-threshold voltage-dependent (T-type) Ca2+ current is constructed using recent whole-cell voltage-clamp data from enzymatically isolated rat thalamocortical relay neurons. The T-type Ca2+ current is described according to the Hodgkin-Huxley scheme, using the m3h format, with rate constants determined from the experimental data (22-24 degrees C; extracellular Ca2+ concentration [Ca2+]o = 3 mM). 2. The T-type Ca2+ current inactivates rapidly during maintained depolarization (time constant, Tau h approximately 20 ms at -20 mV), yet recovery from inactivation is slow (time constant, Tau r approximately 270 ms at -80 mV). To reconcile these observations, a two-step kinetic scheme is proposed for the inactivation gate. Each of the time constants in this scheme is voltage dependent, with a maximum at about -85 mV (45 ms for one and 275 ms for the other). 3. Numerical simulations of recovery in a two-pulse, voltage-clamp protocol compare favorably with experimental results obtained by Coulter et al. as well as those obtained in an independent series of experiments with guinea pig thalamic neurons ([Ca2+]o = 10 mM). 4. For current-clamp simulations, a leakage current gL (V-VL) is included; with VL = -65 mV, the calculated resting membrane potential is -63 mV. 5. It is shown that the T-type Ca2+ current together with the leakage current suffices to describe the low-threshold spike (LTS), a slow, triangular-shaped depolarizing event that can be evoked only from relatively hyperpolarized membrane potentials and that underlies the burst firing of Na(+)-dependent action potentials in thalamic neurons. Outward currents are not required to reproduce the basic shape of the LTS. 6. The LTS can be activated with either a depolarizing current step from a sufficiently hyperpolarized level or on termination of a hyperpolarizing current step. In either case, the amplitude of the LTS is a monotonically increasing, sigmoid-shape function of the hyperpolarizing current step intensity. 7. Because of the slower kinetic step of the channel's inactivation gate, our model predicts that recovery of the LTS to greater than one-half amplitude would require a prolonged hyperpolarization of greater than 100 ms (at body temperature). This imposes an upper limit (approximately 10 Hz) on the frequency of repetitive hyperpolarization that can elicit a train of LTSs and hence on the frequency of any rhythm that requires LTS-mediated bursting of thalamic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1991

Tetrahydroaminoacridine block of N-methyl-D-aspartate-activated cation channels in cultured hippocampal neurons.

The action of tetrahydroaminoacridine (THA), a centrally active cholinesterase inhibitor that may provide symptomatic benefit in Alzheimer's disease, was studied on responses to the excitatory amino acid N-methyl-D-aspartate (NMDA) in cultured hippocampal neurons, using whole-cell voltage-clamp and single-channel recording techniques. THA produced a concentration-dependent block of NMDA-evoked inward current responses (IC50, 190 microM at -60 mV), without affecting responses to quisqualate or kainate. THA block of NMDA responses was voltage dependent and was nearly completely relieved at positive holding potentials. Analysis of the voltage dependency indicated that the THA binding site senses 56% of the transmembrane electrostatic field. In single-channel recordings from outside-out membrane patches, THA appeared to reduce the frequency and duration of NMDA-evoked single-channel currents, without affecting the single-channel amplitude. The effects of THA on NMDA responses occur at concentrations 1-2 orders of magnitude greater than the therapeutic serum concentrations and, therefore, blockade of NMDA receptor-mediated responses is unlikely to contribute to the putative therapeutic action of THA. However, because NMDA receptors may play a critical role in cognitive and memory function, THA has the potential to produce undesirable central nervous system side effects at high doses.

Animals↗