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Biomedical subjects

D Bingmann

Publications and source records attributed to D Bingmann.

At least 55 records · Page 3Linked to original sources
PubMed1991

Rhythm generation in brainstem cultures grown in a serum-free medium.

Electrophysiological studies were carried out on long term cultured brainstem tissue taken from neonatal rats with the object of investigating mechanisms underlying respiratory rhythm generation. The preparations were derived from 360 microns thick horizontal medullary slices which were explanted into a chemically defined nutrient medium and which remained organotypically intact for ca. 1 month. In 44 of the 50 explants examined both periodic and aperiodic bioelectric activity was detected, the cycle length of the former ranging from 0.5 to 10 s (mean, 2.7 s) at a pH of 7.4 and bath temperature of 32 degrees C. Periodic activity could take several forms, but commonly consisted of regularly repeated, 100-300 ms long, depolarizing (D-) waves or sequences of inhibitory and/or excitatory postsynaptic potentials. Lowering the pH of the superfusate by lowering the bicarbonate concentration, increasing the pCO2 or adding H+ shortened the interval between periodic events, and increased both the amplitude and duration of the D-waves. The interval was also shortened when the bath temperature was increased (Q10: ca.2.5). The mean resting membrane potential of neurons exhibiting periodic activity was -49 mV (n = 62) and not significantly different from that of aperiodically discharging neurons either in the same preparations or in cultured explants from the neocortex. These observations suggest that brainstem cultures constitute a useful 'model' system for studying pH-dependent rhythm generation in small neuronal networks of the medulla.

Action Potentials↗
PubMed1991

Reduction in bioelectric GABA and NMDA responses in organotypic neocortical explants by chronic elevation of potassium.

Long-term cultures of organotypic neonatal rat neocortex slices were maintained in a serum-free medium supplemented with 25 mM potassium. Such cultures continue to be bioelectrically silent upon return to a 5 mM potassium medium. The absence of responses to pressure ejected gamma-aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) from neurons in treated explants suggests that one consequence of chronic depolarization is a reduction in the density of postsynaptic transmitter receptors. [3H]Muscimol binding to neocortical membrane preparations shows a large reduction in the binding of this agonist to GABAA receptors. These data show that the quantitative expression of at least one neurotransmitter receptor, the GABAA receptor, relies on voltage-dependent activity in developing neocortical neurons in vitro.

Action Potentials↗
PubMed1991

Caffeine-induced epileptic discharges in CA3 neurons of hippocampal slices of the guinea pig.

In order to analyze the elementary mechanisms underlying caffeine-induced epileptiform discharges, hippocampal slices of guinea pigs were exposed to this drug. When the bath concentration of caffeine exceeded 0.2 mM, periodically occurring paroxysmal depolarizations (PD) in CA3 neurons appeared. They were accompanied by declines of extracellular free calcium concentration and were suppressed by the organic calcium antagonists verapamil and flunarizine. PD-like fluctuations of the membrane potential could be evoked also in CA3 neurons functionally isolated by tetrodotoxin (TTX). The observations indicate that caffeine-induced PD are generated endogenously and that transmembranous calcium currents contribute to these mechanisms.

Animals↗
PubMed1991

Effect of chronic exposure to high magnesium on neuron survival in long-term neocortical explants of neonatal rats in vitro.

In order to assess the effect of elevated magnesium, neuronal morphology and physiology was studied in chronically cultured organotypic neonatal rat occipital neocortex. Explants grown in 10 mM magnesium were found to experience an approximate 30% cell loss (as shown by cell count and DNA-protein analysis), while 12.5 and 15 mM magnesium showed ca. 47 and 60% cell losses, respectively. Intracellular recording from 10 mM magnesium explants revealed that measurable postsynaptic potentials and action potentials could occur, apparently depending on the type of cell examined. All post-synaptic activities ceased in 12.5 mM magnesium cultures, though action potentials could be elicited by current stimulation. The effects of known depolarizing agents, viz. potassium and N-methyl-D-aspartate, on 12.5 mM magnesium-grown explants were also examined. Explants grown in the presence of 12.5 mM magnesium plus 10 mM potassium showed a dramatic increase in the loss of neurons. The simultaneous addition of 6,7-dinitro-quinoxaline-2,3-dione showed this to be due to an increase in non-N-methyl-D-aspartate mediated cell death in response to glutamate release brought about by the depolarizing effects of the potassium. The addition of 10 microM N-methyl-D-aspartate to 12.5 mM magnesium-grown cultures, on the other hand, improved cell survival to control levels. The mechanism of this reciprocal neuroprotective effect of N-methyl-D-aspartate against magnesium has yet to be elucidated. We conclude that these findings are consistent with regard to the opposing actions of N-methyl-D-aspartate and magnesium on calcium influx and various metabolic processes within the explants.

Animals↗
PubMed1991

Elevated potassium prevents neuronal death but inhibits network formation in neocortical cultures.

Chronic depolarization is inimical to neuronal growth and synaptogenesis so that spontaneous action potential generation appears to be required for the normal cytomorphological maturation of neocortical networks. The efficacy of 25 mM K in suppressing spontaneous bioelectric activity was monitored by extra- and intracellular recording from the explants. Intracellular recording from individual neurons showed that membrane potentials were reduced to ca -30 mV in potassium cultures but rapidly repolarized to ca -50 mV when returned to normal growth medium. Though action potentials could be readily evoked from these explants, spontaneous discharges and postsynaptic potentials were absent from potassium-treated cultures. Both spontaneous bioelectric activity and postsynaptic potentials returned to the cultures by 5 days after returning the explants to normal growth medium. Extracellular recordings also showed that the explants were bioelectrically silent in the presence of 25 mM K or 25 mM K plus tetrodotoxin. In contrast to tetrodotoxin alone, bioelectric activity was absent when the cultures (with or without tetrodotoxin) were returned to normal growth medium. The explants gradually began to evince spontaneous bioelectric activity between 3 and 5 days after being returned to normal growth medium. Massive cell death induced by chronic exposure to tetrodotoxin was totally prevented by concomitant addition of 25 mM potassium, though these explants were significantly thinner than controls due to a large decrease in neuropil. We conclude that chronic depolarization of neonatal cortical explants by potassium results in a delayed return of spontaneous bioelectric discharges. Chronic depolarization results in a retardation of network formation in these explants apparently due to a lack of neurite and/or synapse formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Paroxysmal depolarization shifts induced by bicuculline in CA3 neurons of hippocampal slices: suppression by the organic calcium antagonist verapamil.

Organic calcium antagonists have been reported to abolish epileptic neuronal discharges elicited by pentylenetetrazol and penicillin. It was tested whether the organic calcium antagonist verapamil is able to suppress also paroxysmal depolarization shifts (PDS) induced by bicuculline. This is of special interest, since bicuculline is assumed to produce PDS by blocking GABAergic synaptic inhibition. The experiments were performed on CA3 neurons of hippocampal slices (guinea pig). Verapamil (40, 60, and 80 microM) reduced amplitude, duration and frequency of appearance of PDS until the generation of PDS failed. The results indicate that calcium currents are also involved in bicuculline PDS, and that bicuculline exerts its epileptogenic action, at least in part, on extrasynaptic sites.

Animals↗
PubMed1990

Augmentation of N-methyl-D-aspartate induced depolarizations by GABA in neocortical and archicortical neurons.

The influence of the inhibitory transmitter gamma-aminobutyric acid (GABA) on depolarizations elicited by the excitatory amino acid N-methyl-D-aspartate (NMDA) was tested in neurons of organotypic neocortical tissue cultures (newborn rat) and in CA3 neurons of the hippocampal slice (guinea pig). Drugs were applied through a 3-barrelled micropipette by pressure ejection. Applications of GABA before the ejection of NMDA increased the amplitude of the depolarizations induced by the excitatory amino acid. It is suggested that the enhancement of NMDA responses by GABA may be mainly mediated by an intracellular common pathway.

Animals↗
PubMed1990

Membrane potential of rat calvaria bone cells: dependence on temperature.

The membrane potentials of bone cells derived from calvaria of new born rats was shown to be strongly dependent on temperature. When we lowered the temperature from 36 degrees C to 26 degrees C, cells with spontaneous resting membrane potentials (MP) of -80 to -50 mV depolarized (mean amplitude 8 mV; n = 33), and the membrane resistance increased by approximately 80% (n = 20). The temperature response depended on the actual MP, the reversal potential being in the range of -80 to -90 mV. With the application of ouabain (0.1-1 mmol/liter; n = 12), cells depolarized. Simultaneously, the reversal potential of the temperature response was shifted towards more positive values and approached the actual MP level of the cells. Consequently, the depolarization amplitudes induced by lowering temperature were reduced at spontaneous MP levels. The rise of the membrane resistance during cooling was unaffected. When the extracellular chloride concentration was reduced from 133 to 9 mmol/liter, temperature-dependent depolarizations persisted at spontaneous MP values (n = 5). The findings indicate that the marked effects of temperature changes on the MP of bone-derived cells are mainly determined by changes of the potassium conductance.

Alkaline Phosphatase↗
PubMed1990

Time courses of lidocaine effects on sodium membrane currents in small and large neurons.

Time courses of effects of lidocaine on sodium currents and sodium dependent action potentials were studied in somata of small and large neurons. Cultured rat sensory spinal ganglion cells (diameter: 30 microns) and neurons of the buccal ganglion of Helix pomatia (diameter: 150 microns) served as the test cells. The latency of the suppressive action of lidocaine was the longer the larger the of the cells was. Maximal blocking effects occurred within 10 min in sensory spinal ganglion cells and within 40 min in snail neurons. Model calculations based on the assumptions (i) that lidocaine is distributed in the extra- and intracellular space by simple diffusion and (ii) that the drug concentration at the outer surface of the cells is elevated stepwisely, revealed a strong dependency of intracellular concentration changes on the size of the cells. From these findings it is concluded that lidocaine blocks sodium channels primarily from the intracellular side.

Action Potentials↗
PubMed1989

Augmentation of glutamate responses by GABA in the rat's motorcortex in vivo.

The influence of the inhibitory transmitter gamma-aminobutyric acid (GABA) on cortical field potential changes (CFPs) elicited by the excitatory transmitter glutamate and its subreceptor agonists N-methyl-D-aspartate (NMDA) and quisqualate was tested in the motorcortex of anesthetized and artificially ventilated rats. Drugs were applied through a 3-barrelled micropipette by ionophoresis or pressure ejection. Glutamate and its agonists evoked negative and GABA positive CFPs. Applications of GABA before (up to 300 s) the ejection of glutamate, NMDA or quisqualate increased the amplitude of the negative CFP induced by the excitatory transmitters. This augmentation was more pronounced with NMDA and quisqualate than with glutamate. It could be mimicked by the GABAA-agonist muscimol but not by the GABAB-agonist baclofen. It is suggested that the enhancement of glutamate responses by GABA may be mediated by an intracellular common pathway.

Animals↗
PubMed1989

Electrophysiological properties of neurons in neonatal rat occipital cortex slices grown in a serum-free medium.

The electrophysiological properties of individual neurons within organotypic explants of neonatal rat cortex were examined via intracellular recordings. The explants were grown for two weeks in a serum-free medium. The electrophysiological properties of the neurons within these explants were similar to those reported for both adult cortex in vivo and short-term in vitro slice preparations. The results of the present study show that cortical explants grown under serum-free conditions can serve as a useful model for long-term developmental studies associated with the physiological basis of neural network formation.

Action Potentials↗
PubMed1989

Specific suppression of pentylenetetrazol-induced epileptiform discharges in CA3 neurons (hippocampal slice, guinea pig) by the organic calcium antagonists flunarizine and verapamil.

Antiepileptic actions of the organic calcium antagonists flunarizine (cinnarizine derivate) and verapamil (papaverin derivat) on pentylenetetrazol-induced epileptic bioelectric activity were tested in CA3 neurones of hippocampal slices. In all experiments both calcium antagonists reduced the amplitudes and/or durations of paroxysmal depolarizations as well as their rate of occurrence, when the bath concentrations of flunarizine or verapamil exceeded 20 mumol/l. When they were added to the bath solution before pentylenetetrazol application, recordings of the resting membrane potential, of the membrane resistance, of action potentials and of spontaneous as well as of evoked excitatory and inhibitory postsynaptic potentials gave no indication that the antiepileptic effects of these drugs are due to unspecific depressive actions on neuronal excitability or spread of excitation.

Animals↗
PubMed1989

Neuronal and glial responses to hypoxia and hypercapnia.

Changes of membrane properties induced by hypoxia and hypercapnia and/or acidosis were tested on central neurons and glial cells in-vivo and on neurons of hippocampal slices as well as on cultured isolated sensory spinal ganglion (SSG) cells in-vitro. With hypoxia neocortical and spinal neurons as well as glial cells in-vivo depolarized. The same reaction was found in CA3 neurons of hippocampal slices located in layers remote from the bath fluid. The membrane potential of SSG cells were highly insensitive to lowering of bath pO2. The developing response was related to changes of K+ concentration in the extracellular fluid. With hypercapnia the overwhelming majority of neocortical and spinal neurons in-vivo hyperpolarized with the postsynaptic potentials being reduced. In these preparations glial cells depolarized. The extracellular K+ concentration increased which may in part be due to an increase in neuronal K+ conductance. When the extracellular milieu of superficial CA3 neurons in hippocampal slices was predominantly determined by the ionic composition of the bath fluid, hypercapnia depolarized these cells whereas neurons in the innermost layers of the slice hyperpolarized. SSG cells depolarized when pH in the bath was lowered. When pCO2 was elevated at constant bicarbonate concentrations in the bath, SSG cells depolarized as well. In bath fluid, however, containing buffer proteins SSG cells were found to hyperpolarize during hypercapnia. Hyperpolarization occurred also when the bicarbonate concentration in the bath fluid was raised during hypercapnic periods.

Animals↗
PubMed1989

[Functional implication of calcium ions in epileptic seizures. Antiepileptic effects of organic calcium antagonists].

In animal experiments, focal epileptic activity and tonic-clonic seizures were induced by local application of penicillin and repeated intraperitoneal injections of pentetrazol (PTZ), respectively. With epileptic activity neocortical and hippocampal neurons showed typical paroxysmal depolarization shifts. Experimental findings indicate that a calcium inward current and calcium dependent membrane currents participate in the generation of these events. Paroxysmal depolarizations were depressed by intra- and extracellular applications of the organic calcium channel blockers N,N-dimethyl-N-(4-cyan-4-(3,4,5-trimethoxyphenyl)-5-methyl-hexyl)- N-(beta- 3,4-dimethoxyphenylethyl)-ammonium-chloride-monohydrate (D 890) and verapamil. The same depressive effect was exerted by flunarizine in hippocampal but not in neocortical neurons. Paroxysmal depolarizations were enhanced by intracellular injections of the calcium agonist methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5- carboxylate (Bay K 8644) and of the calcium chelator ethyleneglycol-bis(aminoethylether)N,N,N',N'-tetraacetate (EGTA). Focal seizure activity of the neocortex was reduced and often abolished by intracerebroventricular perfusion of verapamil, with the frequency of occurrence of epileptic discharges being decreased. Generalized tonic-clonic seizures were depressed to a great extent and often abolished during an intracerebroventricular verapamil perfusion. Simultaneously, the negative shift of the DC potential evoked by the PTZ injections turned over to a positive displacement. In non-epileptic preparations, organic calcium antagonists had no depressive effects on neuronal bioelectrical activity.

Animals↗
PubMed1988

Differential antiepileptic effects of the organic calcium antagonists verapamil and flunarizine in neurons of organotypic neocortical explants from newborn rats.

Effects of the organic calcium antagonists verapamil and flunarizine on pentylenetetrazol induced paroxysmal depolarizations were tested in organotypic neocortical explants taken from neonatal rats. In these in vitro experiments the papaverin derivative verapamil depressed, and finally abolished, epileptic discharges in all cases. The piperazine derivative flunarizine, however, which is known to suppress epileptic discharges in hippocampal CA3 neurons (Bingmann and Speckmann 1986), showed no significant antiepileptic effects in the explanted neocortical neurons. Thus, the present findings may indicate that the suppressive action of flunarizine on the generation of paroxysmal depolarizations is restricted to distinct populations of neurons.

Animals↗
PubMed1987

Diffusion in slice preparations bathed in unstirred solutions.

A diffusion model is described here, which allows for the estimations of drug concentration changes in porous media, such as in slice tissues of the central nervous system (CNS) bathed in unstirred solutions following abrupt changes of drug concentration. This model may be used for the interpretation of data obtained in neuropharmacological studies if (i) the diffusion coefficient of the molecules under investigation is constant within the excised tissue, (ii) drug molecules are diffusing only in the extracellular space (ECS) and are not bound by the tissue, (iii) drug molecules diffuse mainly within one dimension, (iv) the drug concentration in the bath is changed within 5 s, and (v) the bathing solutions at the surfaces of the slices are stagnant during the period of diffusion. To test this model, estimated tetramethylammonium (TMA) ion concentrations within a tissue slice were compared to actual TMA concentration changes measured at the same depth in the tissue of hippocampal slices by means of TMA-sensitive microelectrodes. A statistically significant correlation (P less than 0.05) was observed between the estimated and measured TMA concentrations which indicates that the model is valid under the defined conditions.

Animals↗