Manfred R. Klee

Cross-Correlation Analysis of Electroencephalographic Potentials and Slow Membrane Transients

Cross-correlation analysis reveals a close correlation between the waves in an electroencephalogram and slow membrane transients of single neurons of the sensorimotor cortex of cats during spontaneous activity, augmenting and recruiting responses, and after local application of strychnine. Time-series correlation coefficients up to 0.7 have been computed. It is suggested that the waves of the electroencephalogram reflect an integration of the changes of membrane potentials in both the cell bodies and dendrites of cortical neurons.

Different sensitivities to ethanol of three early transient voltage clamp currents of aplysia neurons

SummaryThe effects of ethanol (0.5 to 5 Vol.-%) on identified neurons ofAplysia californica have been studied with the techniques of intracellular voltage recording and voltage and current clamping. In the visceral ganglion ethanol hyperpolarizes one group of identified cells and depolarizes a second group. The depolarizations may be up to the level of complete inactivation and are blocked in sodium-free sea water. While ethanol causes no significant effect on membrane resistance, it reduces spike amplitude, especially the overshoot. This effect on the spike potential correlates in voltage clamp with reductions of both sodium and calcium components of the inward currents by up to 50%, while the delayed potassium outward current is unaffected. In contrast a fast outward potassium-dependent current observable in some cells is slowed and reduced by up to 20%. The relatively smaller reduction of this current in contrast to the strong effect on the inward currents produces shifts in a depolarizing direction of the apparent steady state inactivation curves of the inward current. Ethanol did not alter the rate of the development of inactivation but it doubled the recovery from the inactivation following a conditioning depolarization. All of the ethanol effects are dose-dependent over the concentration range of 0.5 to 5 Vol.-% and are completely reversible.

Intracelluläre Untersuchungen über den Einfluß hemmender Potentiale im motorischen Cortex

Zusammenfassung1.Es werden Befunde bei intracellulären Ableitungen im motorischen Cortex der Katze bei Reizung unspezifischer Thalamuskerne beschrieben.2.Den extracellulär beobachteten Hemmungsphasen während rekrutierender Reizbeantwortungen entsprechen Hyperpolarisationen des Zellmembranpotentials von vergleichbarer Dauer.3.Im Beginn des recruiting treten nach zunehmender Hyperpolarisation verstärkte Depolarisationswellen auf. Sie können sowohl durch Reize ausgelöst werden wie auch im „rebound“ bei starker Hyperpolarisation erscheinen.4.Die Befunde weisen auf eine Abhängigkeit von depolarisatorischen und hyperpolarisatorischen Effekten hin. Bei höherem Zellmembran-potential sind depolarisierende Reizwirkungen verstärkt. Nach spontanen und durch unspezifische Reize ausgelösten Depolarisationswellen überwiegt ein repolarisierender Reizeffekt.5.Der Verlauf der Hyperpolarisation ist dem von spontanen Repolarisationen nach spikes, depolarisierenden Nachpotentialen und Inaktivationsprozessen ähnlich. Er hat bei vergleichbarer Stärke meist nicht den scharf eingrenzbaren Beginn inhibitorischer Potentiale nach Reizen im spezifischen Thalamus. Der excitatorische depolarisierende Effekt ist demgegenüber stärker reizgebunden.

ERG recordings of a primate pure cone retina (Tupaia glis)

The gross configuration of the pure coneTupaia ERG is characterized by well-defineda-,x-,c- andd-waves. The short latency, fast risingx-wave contrasts to the slowerb-wave found in all duplex and rod retinas heretofore tested. Thec-wave, not previously reported for pure cone retinas, can usually be avoked during dark adaptation. The off-effect ord-wave appears predictably when stimulus durations are long enough. Several features are consistent with the exclusive presence of cones and their function, including: (1) high FFF, (2) lack of Purkinje shift, (3) high absolute threshold in the dark and only a small increase in the threshold as a function of light adaptation, (4) restricted range of intensity over which amplitude variations are elicited, (5) peak of spectral sensitivity at 552 nm. The spectral sensitivity curve, in contrast to all the other pure cone mammals, shows congruence with the foveal psychophysical curve of the human and with the absorption curve of iodopsin, with the exception of more marked sensitivity in the blue region.

Differences in baclofen-sensitivity between CA3 neurons and granule cells of the guinea pig hippocampus in vitro

In the slice preparation of the guinea pig hippocampus, the effects of (+/-) baclofen added to the Krebs-Ringer solution on dentate granule cells and CA3 pyramidal cells were investigated by means of intracellular recording techniques. In a 10-25 microM concentration, baclofen reduces the inhibitory postsynaptic potentials of the granule cells evoked by electrical stimulation of the perforant path and hyperpolarizes the granule cell membrane slightly. The reduction of both, the excitatory and inhibitory postsynaptic potentials of CA3 pyramidal cells evoked by mossy fiber stimulation, however, is accompanied by a strong hyperpolarization and conductance increase. Further, repetitive discharges of granule cells elicited in the presence of the convulsant bicuculline (25 microM) are hardly affected by baclofen (50 microM), whereas those of CA3 neurons are blocked.

Valproate enhances inhibitory postsynaptic potentials in hippocampal neurons in vitro

Effects of sodium valproate (0.5-10 mM) on hippocampal cells (CA3 pyramidal cells and granule cells) of the guinea pig in vitro were studied by intra- and extracellular recording. Inhibitory postsynaptic potentials were markedly and reversibly augmented. Their shunting action as well as duration increased by more than 150%. Effects of locally administered gamma-aminobutyric acid (GABA) did not change significantly. Membrane characteristics such as membrane potential, membrane input resistance and action potential did not alter. Valproate suppressed spontaneous spiking and repetitive discharges evoked by GABA antagonists. It is concluded that valproate enhances GABAergic synaptic transmission by a presynaptic mechanism. However, postsynaptic mechanisms might be involved in the limitation of repetitive firing.

Effect of temperature on postsynaptic potentials of cat spinal motoneurones

The effect of spinal cord temperature on excitatory postsynaptic potentials (EPSP) and inhibitory postsynaptic potentials (IPSP) were measured by means of intracellular recordings from lumbar motoneurones of 43 cats. While body temperature and oil bath temperature were maintained between 37 and 38 degrees C, the temperature of the spinal segment under investigation was changed separately in the range between 30 and 42 degrees C. Cooling consistently produced an increase in amplitude and duration of both, mono- and poly-synaptic EPSPs and recurrent and direct IPSPs. Warming caused the opposite effect. The input resistance of the motoneurones was inversely related to the spinal cord temperature, while the latency of action potentials produced by intracellular injection of outward current was directly and exponentially related to spinal temperature. Although the data do not provide a quantitative differentiation of pre- versus postsynaptic temperature effects, they are consistent with the notion that temperature dependent changes on postsynaptic membrane properties contribute to the observed PSP changes. It is further suggested that similar postsynaptic temperature effects may be concerned in temperature sensitivity of proposed specific central neurones.

3. – ACTIONS OF ETHANOL ON NEURONAL MEMBRANE PROPERTIES AND SYNAPTIC TRANSMISSION*

Numerous investigations have revealed effects of ethanol on both neuronal excitability and synaptic transmission (cf., 1 for review). Since these studies have utilized a variety of invertebrate and vertebrate model systems and the concentrations employed have often been beyond those associated with moderate intoxication or ataxia, it is not surprising that a myriad of actions have been described for ethanol and that various mechanisms have been postulated to underlie its effects. Ideally, one would like to correlate actions of ethanol on single neurons and neuronal networks with stereotyped changes in behavior. However, while psychophysical tests,indicate the vertebrate central nervous system is most sensitive to ethanol (1), the majority of the neurophysiological studies have rather utilized peripheral vertebrate or isolated invertebrate preparations. Nevertheless, these investigations have yielded a great deal of neurophysiological information about the cellular mechanisms of action of ethanol. Such mechanisms generally fall in one of the following categories: 1) a specific reduction in neuronal excitability through alterations in the voltage dependent ionic conductances underlying action potential generation (3-6); 2) indirect effects on excitability consequent to changes in passive membrane permeabilities and resting membrane potential (3,4,7,8,9); and 3) preor post-synaptic changes in the efficacy of synaptic transmission, e.g. altered transmitter release or a change in the transmitter sensitivity of the post-synaptic membrane-bound receptors (10-18).

Phorbol diacetate differentially regulates the N-methyl-d-aspartate (NMDA) and non-NMDA receptor-mediated components of the rat hippocampal excitatory postsynaptic currents☆

The effects of phorbol 12,13-diacetate (PDAc) on evoked excitatory transmission were studied in neurons of the CA1 area of hippocampal slices of rats, using whole-cell voltage clamp of pyramidal neurons in situ and stimulation of the Schaffer collaterals. The application of PDAc (10 microM) increased the amplitude of the excitatory postsynaptic current (EPSC) and caused a lengthening of its decay, due to an increase in the contribution of the N-methyl-D-aspartate (NMDA) component to the total EPSC. The latter effect was depend upon the concentration of calcium in the extracellular medium. Experiments in which we separated the two components of the EPSCs by 6-cyano-7-nitroquinoxaline-2,3-dione and by 2-amino-5-phosphonopentanoic acid also demonstrated a more pronounced increase in the NMDA receptor-mediated current under PDAc. The effects of PDAc were markedly attenuated by the extracellular application of the protein kinase C inhibitor H-7 (300 microM), but not by intracellular perfusion with 20 mM of the same drug.

Physiology, pharmacology and development of epileptogenic phenomena

This text aims to throw new light on the fundamental mechanisms of epilepsies and provides a representative cross-section of contributions from experimental groups active in basic research. The factors involved in the generation of epileptic activity are described first, followed by an examination of the developmental aspects of epileptogenesis and the mechanisms of the action of convulsant drugs. This book of proceedings on neurophysiology, electrophysiology, neuropharmacology and neurology is intended for the use of researchers and clinicians.