Steady Potential Level Research Articles

Transducer properties of the rapidly adapting stretch receptor neurone in the crayfish (Pacifastacus leniusculus).

1. The transducer properties of the rapidly adapting stretch receptor neurone of the crayfish (Pacifastacus leniusculus) were studied using a two-microelectrode voltage clamp technique. 2. The impulse response to ramp-and-hold extensions of the receptor muscle typically consisted of a high frequency burst followed by cessation of impulses within a relatively short time depending on the amplitude of extension. The type of adaptation was consistent with earlier studies. The stimulus-response relationship for the impulse frequency was non-linear and had a slope in a log-log plot of 2.9. 3. When impulse generation was blocked by tetrodotoxin (TTX), (block of Na+ channels) the receptor potential was extension dependent and similar to that found in the slowly adapting receptor. For small extensions there was an initial peak followed by a fall to a steady potential level. For large extensions the potential response during the ramp phase consisted of a peak followed by a constant potential level lasting to the end of the ramp. When the extension changed to the hold phase the potential fell towards a steady state. The relation between extension and amplitude of receptor potential was non-linear and saturated at -40 to -30 mV (extensions > 15% of zero length, lo). 4. When potassium channels were blocked by TEA (50 mM) and 4-aminopyridine (4-AP, 5 mM) (and Na+ channels blocked by TTX) the shape of the generator potential become less complex with an increased amplitude for large extensions. 5. When the receptor neurone was voltage clamped at the resting potential, extension of the receptor muscle produced an inwardly directed receptor current, the stretch-induced current (SIC). The response consisted of a fast transient phase which decayed towards a steady state. The SIC peak amplitude was dependent on extension in a sigmoidal fashion and saturated at 190 nA (extensions > 25% of lo). The slope of the steepest part of the stimulus-response relation (between 10 and 20% extension) was 4.7 +/- 0.25 (mean +/- S.E.M.) in a log-log plot. 6. The peak amplitude of the SIC increased with increasing extension speed (ramp steepness), the relation between the slope of the ramp and current amplitude being a first order (hyperbolic) function. The amplitude of the receptor current was voltage dependent and had a reversal potential of +16.2 +/- 1.8 mV (mean +/- S.E.M., 32 cells). From the reversal potential the permeability ratio, PNa/PK, of the transducer permeability system was calculated to be 1.5. The I-V curve of SIC was non-linear.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in steady potential level and in brain bioelectrochemical potential during orienting and conditioned reflexes in rabbits.

1. The orienting reaction in rabbits is accompanied by generalized shifts of SPL in the cortex in the absence of changes in BECP. 2. Changes in BECP appear only during conditioned reflex formation and develop during combination of the conditioned and reinforcing stimuli. During combination shifts of SLP also are observed, and in their configuration and amplitude they differ from those occurring during OR. 3. Simultaneous recording of changes in BECP and shifts of SLP developing during combination of conditioned and reinforcing stimuli shows that the two phenomena are the external manifestation of independent processes. 4. It is postulated that brain activity concerned with the perception and analysis of the informational significance of a stimulus is linked more closely with bioelectrical than with metabolic processes. During a combination of two stimuli in the process of conditioned reflex formation, besides the strengthening of activity linked with bioelectrical processes, a new type of activity accompanied by considerable metabolic shifts appears. 5. Recording changes in the electrochemical potential of an electrode made of inert metal is a highly rewarding method for studying the spatiotemporal organization of metabolic activity of the brain, connected with higher nervous activity.

Correlation between steady potential baseline and event-related slow potential magnitude in the rat.

Event-related slow potential (SP) responses to a warning stimulus were recorded from rat frontal and visual cortex during performance of a reaction-time task. Measurements of steady potential baseline and magnitude of the negative SP response were obtained for individual trials (presented at variable intervals). The correlation between baseline and SP response magnitude was examined utilizing both amplitude and integrated area data. Also, averaged SP responses were obtained by selecting trials for averaging according to baseline potential. Slow potential response magnitude was inversely correlated with baseline negativity. Neither baseline nor SP response amplitude was correlated with trial number of intertrial interval. Averaged SP responses consisting of trials with more positive baselines were larger in magnitude than averaged SP responses consisting of trials with more negative baselines. The steady potential level attained during trials with more positive baselines was not more negative than the level reached during trials with negative baselines. These data are consistent with the concept of "ceiling" effect for event-related slow potentials.

Dynamics of changes in sign of steady potential shifts during conditioning

1. During defensive conditioning of rabbits to photic stimulation, shifts of the steady potential level (SPL) developed in the cortex, exhibiting considerable variability of sign and spatial distribution in recordings from the cortical surface. 2. In the course of conditioning the first SPL shifts in response to photic stimulation appeared in the visual cortex and were negative in direction; electrodermal stimulation produced positive shifts in the sensorimotor cortex. 3. With an increase in the number of combinations, SPL shifts of positive direction developed extensively over the cortex in response to conditional and unconditional stimuli. Subsequently the positive SPL shifts, while remaining generalized, were replaced by negative. 4. During stabilization of the temporary connection, the areas from which negative shifts were recorded were gradually narrowed and the shifts became localized, being recorded only beneath one or two (of the ten) electrodes in the motor and visual cortex. Responses to photic stimulation were characterized by a narrower localization and negative sign, while the zone of recording of responses to electrodermal stimulation remained wide and, whether before or at the beginning of conditioning, shifts of positive sign were predominant. 5. It is postulated that these SPL shifts are basically neuronal in origin, the resultant of vector (algebraic) summation of surface-positive and surface-negative electrical fields from different sources. Consequently, the dynamics of the change in sign of SPL shifts during conditioning must reflect vertical displacement and complex interaction between foci and massive depolarization and hyperpolarization in cortical neurons.

The relationship between neuron activity and cortical steady potentials

Simultaneous recordings of single neuron activity and of the EEG, recorded with nonpolarizable electrodes and a DC amplifier, were obtained from the posterior lateral gyrus in cat encéphale isolé preparations. The cortex was usually negative relative to the reference electrode in one of the frontal sinuses, voltages near −1.2 mV and −3.1 mV being the most frequently encountered values. The neurons observed tended to fire during surface positive waves and to cease firing during surface negative waves, both during evoked potentials produced by light flashes and during spontaneous activity after section of the optic nerves. This correlation was less marked in the cells recorded from when the cortical steady potential level was around −3.1 mV than in those studied when the steady potential was around −1.2 mV. The amplitude of the negative components of the evoked potential was usually smaller when the steady potential was near −3.1 mV. A few neruons studied whent he steady potential level was much more negative showed a reverse relationship, firing mostly during surface negative waves.

Strom-Spannungsbeziehungen von Purkinje-Fasern bei verschiedenen extracellul�ren Calcium-Konzentrationen und unter Adrenalineinwirkung

Voltage-current curves were obtained for short Purkinje fibres of the sheep heart. The bathing solution was completely Na-free and its Ca-concentration was varied (0, 1.8, 7.2 mM). To hold the membrane at a potential difference near 0 mV less current was necessary from an external source if the Ca-concentration was high (Fig. 2). When a square pulse of depolarizing current was applied in Ca-free solution the electrotonic potentials approached their steady-state values with a time-course consistent with capacitative filling. In the presence of Ca-ions the potential-time course showed two steps (Fig. 1). The second step had a “threshold” in the range 30–40 mV (inside negative), with an accelerated rise and an overshoot before reaching a steady potential level. Adrenaline increased the amplitude of the second step if the extracellular Ca-concentration was normal (1.8 mM) or high (7.2 mM), but had no effect on electrotonic potentials if added to a Ca-free solution. A transitory inward Ca current as a consequence of strong depolarizations is thought to provide the most probable explanation for the experimental findings. A decrease of K conductance by Ca ions cannot be excluded, but it seems improbable on the ground of various arguments. Adrenaline is thought to increase Ca influx through a depolarized membrane.

Bioelectrical activity of isolated cortex—II. steady potentials and induced surface-negative cortical responses

Monophasic, surface-negative responses evoked by combined low- and high-frequency shocks to the cerebral cortex of cat were obtained from both intact and isolated cortical tissue. The steady potential level at the cortical recording site was found to be 300–500 μV negative to frontal bone when the responses were evoked. Cortical polarization with currents of 2–10 μA yielded similar steady potential levels, and, when substituted for the original high-frequency shocks, also evoked the responses from both intact and neurally isolated cortex. Many times, when evoked inside isolated slabs, the responses retained their original rate when the frequency of the driving stimulus was lowered. These results suggest that shifts of steady potentials probably served as the agent for ephaptic transmission across the cut.

An analysis of some correlates of steady potentials in mammalian cerebral cortex

An analysis of some aspects of steady potential (SP) phenomena, especially in relation to some earlier experiments on SP correlates of hyperventilation and of epileptiform potentials during spreading depression is presented. The findings by others of SP shift with asphyxia, anoxia, cerebral ischemia and excess CO 2 do not appear to explain the positive cortical SP shift during brief hyperventilation. While the polarity (and amplitude) and the incidence of epileptiform (and other) potentials show some correlations with intrinsic SP level and polarity across cell layers, such as the cerebral cortex, these correlations are far from consistent in degree or direction in all different conditions or neural tissues. On the other hand, the correlations of these functions with changes in SP that are induced by polarizing currents applied across such cell layers are highly consistent. Reasons are offered for considering this latter relationship to be a more significant index of the role of SP in these functions. In discussing the possible mechanisms that may produce the observed synchronization or coupling of epileptiform potentials at different points on the cortex, it is suggested that the local process which permits or facilitates the development of such potentials should be considered as one that is potentially distinct from more purely synchronizing mechanisms.