The role of the central nervous system functional condition in formation of responses of visual analyser's peripheral and central parts

Nembutal was shown to inhibit formation of early receptor potentials, "a"-wave and oscillatory potential of the retina (ERG), as well as the oscillatory potentials of the superior colliculus and visual cortex. The first oscillatory potential of the retina alone was enhanced. Aminazin exerted rather an opposite effect related, probably, to facilitation of the retina and central structures due to elimination of a constant inhibitory effect of the brain stem RF.     

Synaptic interactions mediating synchrony and oscillations in primate sensorimotor cortex.

The appearance of oscillatory modes of 'gamma' activity in many cortical areas of different species has generated interest in understanding their underlying mechanisms and possible functions. This paper reviews evidence from studies on primate motor cortex showing that oscillatory activity entrains many neurons during periods of exploratory manipulative behavior. These oscillatory episodes synchronize widely spread neurons in sensorimotor cortex bilaterally, including descending corticospinal neurons, as evidenced by correlated modulations in EMG activity. The resulting neural synchronization involves task-related and -unrelated neurons similarly, suggesting that it is more likely to play some global role in attention than mediating any obvious interactions involved in coordinating movements. Intracellular recordings have elucidated the strength and types of synaptic interactions between motor cortical neurons that are involved in both normal and oscillatory activity. Spike-triggered averages (STAs) of intracellular membrane potentials have revealed serial connections in the form of unitary excitatory and inhibitory post-synaptic potentials (EPSPs and IPSPs). More commonly, STAs showed large synchronous excitatory or inhibitory potentials (ASEPs and ASIPs) beginning before the trigger spike and composed of multiple unitary events. ASEPs involved synchronous activity in a larger and more widespread group of presynaptic neurons than ASIPs. During oscillatory episodes synchronized excitatory and inhibitory synaptic potentials occurred in varying proportions. EPSPs evoked by stimulating neighboring cortical sites during the depolarizing phase of spontaneous oscillations showed evidence of transient potentiation. These observations are consistent with several functional hypotheses, but fit best with a possible role in attention or arousal.     

Release of Membrane-Associated L-Dopa Decarboxylase from Human Cells

L-Dopa Decarboxylase is a pyridoxal 5-phosphate (PLP)-dependent enzyme that catalyses the decarboxylation of L-Dopa to dopamine. In this study, we investigated the cellular topology of the active human enzyme. Fractionation of membranes from human cell lines, of neural and non-neural origin, by temperature-induced phase separation in Triton X-114 resulted in the detection of DDC molecules in all separation phases. Solubilization of membrane-associated DDC was observed in a pH and time-dependent manner and was affected by divalent cations and protease inhibitors, suggesting the involvement of a possible release mechanism. The study of the biological properties and function of the solubilization phenomenon described here, as well as, the study of the membrane-associated enzyme could provide us with new information about the participation of the human L-Dopa decarboxylase in physiological and aberrant processes.     

Emergence of oscillations and spatio-temporal coherence states in a continuum-model of excitatory and inhibitory neurons

A neural field model of the reaction-diffusion type for the emergence of oscillatory phenomena in visual cortices is proposed. To investigate the joint spatio-temporal oscillatory dynamics in a continuous distribution of excitatory and inhibitory neurons, the coupling among oscillators is modelled as a diffusion process, combined with non-linear point interactions. The model exhibits cooperative activation properties in both time and space, by reacting to volleys of activations at multiple cortical sites with ordered spatio-temporal oscillatory states, similar to those found in the physiological experiments on slow-wave field potentials. The possible use of the resulting spatial distributions of coherent states, as a flexible medium to establish feature association, is discussed.     

Oscillations of electrical potential along a root of a higher plant

Higher plants exhibit an oscillation of electrical potential near the surface along the root. The oscillation was studied with the aid of both the usual intracellular microelectrode technique and the extracellular multielectrode technique, the latter making it possible to measure simultaneously electrical potentials along the root. It was found that the oscillation of extracellular surface potential showed the largest amplitude in the elongation region, and the phase of the oscillation in this region differed by 180 degrees from that in the mature region, where the oscillation appeared coherent. The measurement of the intracellular electrical potential suggested the existence of oscillatory components localized to the parenchyma/xylem interface in the elongation region. A theoretical analysis based on an electrical circuit network described the above-mentioned behavior. It was shown that the oscillation was propagated along the root over several centimeters without substantial decay in the mature region.     

Coupled oscillators for modeling and analysis of EEG/MEG oscillations.

This study presents three EEG/MEG applications in which the modeling of oscillatory signal components offers complementary analysis and an improved explanation of the underlying generator structures. Coupled oscillator networks were used for modeling. Parameters of the corresponding ordinary coupled differential equation (ODE) system are identified using EEG/MEG data and the resulting solution yields the modeled signals. This model-related analysis strategy provides information about the coupling quantity and quality between signal components (example 1, neonatal EEG during quiet sleep), allows identification of the possible contribution of hidden generator structures (example 2, 600-Hz MEG oscillations in somatosensory evoked magnetic fields), and can explain complex signal characteristics such as amplitude-frequency coupling and frequency entrainment (example 3, EEG burst patterns in sedated patients).     

Microfluorimetric scanning of sympathetic nerve fibers. An improved method to quantitate formaldehyde induced fluorescence of biogenic amines

A two dimensional scanning procedure was developed for studying quantitative aspects of formaldehyde induced fluorescence (FIF) from noradrenaline containing nerve fibers. A computer (PDP 12) controlled scanning device was equipped with a cooled photomultiplier, a 0.5 micron scanning stage and a 0.5 micron measuring spot. Photodecomposition was reduced by a high scanspeed (100/sec) and a small excitation field. Digitized images were obtained with a high resolution. Data (10,000/scan) of large scan areas (2500 micron2) in the iris of the rat were transformed into fluorescence histograms, which allowed statistical evaluation. Visible changes induced in the histochemical preparation by administration of drugs (reserpine, L-Dopa) were reflected in characteristic changes in the histograms. A minor reduction in noradrenaline content, which was too small to be detected by visual observation of the microscopical image and by classical microfluorimetric methods, did evoke a significant change in the histograms. It is concluded that microfluorimetric scanning is a very sensitive technique for detecting changes of formaldehyde induced fluorescence from neuronal networks.     

Neuromodulation of central inhibition on peripheral mechanosensory afferents

100 g reserpine, suspended in sunflower oil, was injected into the crop of six leeches (Hirudo medicinalis). Five leeches were injected with oil alone. The efficacy of delivering reserpine in this manner was assessed by measuring swimming bout duration. Four days after injection, swimming bouts were significantly longer in reserpine-treated leeches than in oil-treated or normal leeches. The amplitude of excitatory potentials elicited in velocity sensitive skin mechanoreceptors (T cells) by action potentials in mechanosensory cells which respond to sustained deformation of the skin (P cells) was no different in reserpine-treated leeches than in untreated leeches. The amplitude of inhibitory potentials in these T cells, produced by interneurons excited by P cells, was significantly larger in reserpine-treated leeches. Depletion of monoamines enhances inhibition in T cells. This is consistent with the established roles played by monoamines in promoting leech swimming and feeding behaviour.     

Learning-induced modulation of oscillatory activities in the mammalian olfactory system: The role of the centrifugal fibres

In the mammalian olfactory system, oscillations related to odour representation have been described in field potential activities. Previous results showed that in olfactory bulb (OB) of awake rats engaged in an olfactory learning, odour presentation produced a decrease of oscillations in gamma frequency range (60-90 Hz) associated with a power increase in beta frequency range (15-40 Hz). This response pattern was strongly amplified in trained animals. The aim of this work was twofold: whether learning also induces similar changes in OB target structures and whether such OB response depends on its centrifugal inputs. Local field potentials (LFPs) were recorded through chronically implanted electrodes in the OB, piriform and enthorhinal cortices of freely moving rats performing an olfactory discrimination. Oscillatory activities characteristics (amplitude, frequency and time-course) were extracted in beta and gamma range by a wavelet analysis. First, we found that odour induced beta oscillatory activity was present not only in the OB, but also in the other olfactory structures. In each recording site, characteristics of the beta oscillatory responses were dependent of odour, structure and learning level. Unilateral section of the olfactory peduncle was made before training, and LFPs were symmetrically recorded in the two bulbs all along the acquisition of the learning task. Data showed that deprivation of centrifugal feedback led to an increase of spontaneous gamma activity. Moreover, under this condition olfactory learning was no longer associated with the typical large beta band. As a whole, learning modulation of the beta oscillatory response in olfactory structures may reflect activity of a distributed functional network involved in odour representation.     

Dopamine D1 Receptors Regulate the Light Dependent Development of Retinal Synaptic Responses

Retinal synaptic connections and function are developmentally regulated. Retinal synaptic activity plays critical roles in the development of retinal synaptic circuitry. Dopamine receptors have been thought to play important roles in the activity-dependent synaptic plasticity in central nervous system. The primary goal of this study is to determine whether dopamine D1 receptor regulates the activity-dependent development of retinal light responsiveness. Accordingly, we recorded electroretinogram from wild type mice and mice with genetic deletion of D1 dopamine receptor (D1−/− mice) raised under cyclic light conditions and constant darkness. Our results demonstrated that D1−/− mice have reduced amplitudes of all three major components of electroretinogram in adulthood. When the relative strength of the responses is considered, the D1−/− mice have selective reduction of the amplitudes of a-wave and oscillatory potentials evoked by low-intermediate intensities of lights. During postnatal development, D1−/− mice have increased amplitude of b-wave at the time of eye-opening but reduced developmental increase of the amplitude of b-wave after eye opening. Light deprivation from birth significantly reduced the amplitudes of b-wave and oscillatory potentials, increased the outer retinal light response gain and altered the light response kinetics of both a- and b-waves of wild type mice. In D1−/− mice, the effect of dark rearing on the amplitude of oscillatory potentials was diminished and dark rearing induced effects on the response gain of outer retina and the kinetics of a-wave were reversed. These results demonstrated roles of dopamine D1 receptor in the activity-dependent functional development of mouse retina.     

In vivo recording of electrical activity of canine tracheal smooth muscle.

Electrical activity of the tracheal smooth muscle was studied using extracellular bipolar electrodes in 37 decerebrate, paralyzed, and mechanically ventilated dogs. A spontaneous oscillatory potential that consisted of a slow sinusoidal wave of 0.57 +/- 0.13 (SD) Hz mean frequency but lacked a fast spike component was recorded from 15 dogs. Lung collapse accomplished by bilateral pneumothoraxes evoked or augmented the slow potentials that were associated with an increase in tracheal muscle contraction in 26 dogs. This suggests that the inputs from the airway mechanoreceptors reflexly activate the tracheal smooth muscle cells. Bilateral vagal transection abolished both the spontaneous and the reflexly evoked slow waves and provided relaxation of the tracheal smooth muscle. Electrical stimulation of the distal nerve with a train pulse (0.5 ms, 1-30 Hz) evoked slow-wave oscillatory potentials accompanied by a contraction of the tracheal smooth muscle in all the experimental animals. Our observations in this in vivo study confirm that the electrical activity of tracheal smooth muscle consists of slow oscillatory potentials and that tracheal contraction is at least partly coupled to the slow-wave activity of the smooth muscle.     

EFFECTS OF L-DOPA ON CIRCADIAN RHYTHMS OF 6-OHDA STRIATAL LESIONED RATS: A RADIOTELEMETRIC STUDY

Temporal variation in the motor function of Parkinson's disease (PD) patients suggests the potential importance of a chronobiological and chronopharmacological approach in its clinical management. We previously documented the effects of striatal injection of 6-OHDA (as an animal model of PD) on the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (A). The present work assessed the possible influence of L-Dopa on these same rhythms in the 6-OHDA animal model of PD. The study began after a four-week recovery period following surgical implantation of telemetric devices to monitor the study variables and/or anaesthesia. The study was divided into an initial one-week control period (W1) for baseline measurement of T, HR, and A rhythms. Thereafter, stereotaxic 6-OHDA lesioning was done. and a second monitoring for two weeks followed (W2, W3). Rats were then randomly divided into two groups: eight control rats received, via a mini-osmotic pump implanted subcutaneously, the excipient saline; the other eight rats received L-Dopa (100?mg/kg SC/day). After a seven-day period (W4), the pumps were removed and the T, HR, and A rhythms were monitored for two weeks (W5 and W6). To control for 6-OHDA striatal dopamine-induced depletion, 12 other rats were injected by identical methods (eight rats with 6-OHDA and four controls with saline) and sacrificed at W1, W3, and W5 for dopamine striatal content determination. To verify the delivery of levodopa from the osmotic pumps, plasma levels of levodopa and its main metabolites 3-OMD, DOPAC, and HVA were determined on separate group of rats receiving the drug under the same experimental conditions (osmotic pumps delivering continuously 10 µl/h for seven days, 100?mg/kg/subcutaneously). Our results agree with previously reported rhythmic changes induced by 6-OHDA—loss of circadian rhythmicity or changes in the main parameters of the registered rhythms. When circadian rhythmicity was abolished, L-Dopa treatment improved or accelerated recovery of the circadian rhythms, the effect being more pronounced for the HR rhythm. When circadian rhythms were not abolished but perturbed, L-Dopa treatment did not improve the 6-OHDA-induced changes in the T and A mesor (24?h mean level), while a significant effect was observed for HR. It appears that constant-rate L-Dopa infusion is unable to totally balance dopamine depletion; taking into account the circadian pattern of many structures implicated in drug effect, a sinusoidal delivery of L-Dopa must be evaluated in future experiments. (Author correspondence: bernard.bruguerolle@univmed.fr)     

Synchronous Ca(2+) oscillation emerges from voltage fluctuations of Ca(2+) stores

Synchronous Ca(2+) oscillation occurs in various cell types to regulate cellular functions. However, the mechanism for synchronization of Ca(2+) increases between cells remains unclear. Recently, synchronous oscillatory changes in the membrane potential of internal Ca(2+) stores were recorded using an organelle-specific voltage-sensitive dye [Yamashita et al. (2006) FEBS J273, 3585-3597], and an electrical coupling model of the synchronization of store potentials and Ca(2+) releases has been proposed [Yamashita (2006) FEBS Lett580, 4979-4983]. This model is based on capacitative coupling, by which transient voltage changes can be synchronized, but oscillatory slow potentials cannot be communicated. Another candidate mechanism is synchronization of action potentials and ensuing Ca(2+) influx through voltage-dependent Ca channels. The present study addresses the question of whether Ca(2+) increases are synchronized by action potentials, and how oscillatory store potentials are synchronized across the cells. Electrophysiological and Ca(2+)-sensitive fluorescence measurements in early embryonic chick retina showed that synchronous Ca(2+) oscillation was caused by releases of Ca(2+) from Ca(2+) stores without any evidence of action potentials in retinal neuroepithelial cells or newborn neurons. High-speed fluorescence measurement of store membrane potential surprisingly revealed that the synchronous oscillatory changes in the store potential were periodic repeats of a burst of high-frequency voltage fluctuations. The burst coincided with a Ca(2+) increase. The present study suggests that synchronization of Ca(2+) release is mediated by the high-frequency fluctuation in the store potential. Close apposition of the store membrane and plasma membrane in an epithelial structure would allow capacitative coupling across the cells.     

视网膜电图振荡电位参数的稳定性

用系列强度１１档刺激闪光记录２０例３０只眼的视网膜电图（ＥＲＧ）振荡电位（ＯＰ）,研究ＯＰ的光强特性和参数稳定性。结果表明,ＯＰ各子波峰时和刺激光强呈指数曲线相关,相关性很高;而振幅和光强的函数关系的变异很大,相关性较低,不同对象间ＯＰ各子波振幅的变异系数较大,而峰时的变异系数较小,ＯＰ的峰时改变比振幅改变更为稳定。     

Electrophysiological and pharmacological analysis of L-dopa-induced dyskinesia and tardive dyskinesia (author's transl)

Electrophysiological and pharmacological analysis of L-Dopa-induced dyskinesia and tardive dyskinesia (L.DD) due to neuroleptics was performed on 12 patients with Parkinson's disease and on 12 others with psychotic diseases. This analysis included the examination of spinal reflexes, monosynaptic H reflex, polysynaptic cutaneous reflex of the lower limb, muscular responses to passive movement [stretch reflex and shortening reaction (SR)] and the study of the motor response to a dopaminergic stimulus (I.V. injection of Piribedil (PBD), a dopamine agonist). There was no difference in EMG activity between L.DD and TD. Three EMG patterns can be distinguished: anarchic discharge pattern (ADA), tonic grouping discharge pattern (AST) and rhythmic burst pattern (ABR). PBD effects indicate a possible relationship between the EMG patterns and the sensitivity level of the motor dopamine receptors. During L-Dopa dyskinesia and tardive dyskinesia, the same changes in spinal reflexes were observed. Muscle tone tested by muscular responses to passive movement (shortening and myotatic reaction) was normal. Monosynaptic excitability explored by H/M ratio was within the normal range. In contrast, the polysynaptic nociceptive reflex was increased in every case. In Parkinsonian patients with L-Dopa dyskinesia, this pattern of the spinal reflexes was significantly different in comparison to the rigid phase. Intravenous infusion of PBD suppressed tremor and provoked the occurrence of dyskinetic activity in Parkinsonian patients with L-Dopa dyskinesia during the rigid phase. During the dyskinetic phase, as in tardive dyskinesia, PBD increases these phenomena and changes EMG activity in rhythmic pattern. It is suggested that L-Dopa dyskinesia and tardive dyskinesia can be determined by testing EMG activity, spinal reflexes and dopaminergic reactivity. There is evidence to suggest that the various types of involuntary abnormal movement represent a single entity, and that dopamine receptor supersensitivity may be involved.     

An electrochemical thin-layer cell for spectroscopic studies of photosynthetic electron-transport components

An electrochemical thin-layer cell, 0.5 ml in volume and 0.25 mm in pathlength, employing an optically transparent gold minigrid electrode has been constructed and used in redox studies of photosynthetic electron-transport components. Light-induced absorption changes accompanying P700 photo-oxidation in photosystem-I subchloroplasts were measured at a series of electrochemically poised potentials at 88°K. The fluorescence-yield changes in photosystem-II subchloroplasts were measured as the poised potential was varied electrochemically. The utility of the cell was further demonstrated by a redox titration of soluble (spinach) ferredoxin using circular dichroism to monitor changes in the redox state. One important advantage of electrochemical vs chemical titration of photosynthetic electron-transport components is that it is possible to attain much more negative potentials than is thermodynamically possible in chemical titrations. This permits the exhaustive titration of certain components at physiologically reasonable pH values not possible chemically.     

Effect of metergoline, a specific serotonin antagonist, on human growth hormone response to arginine and L-dopa.

In seven normal subjects the repeated oral administration of metergoline, a specific antiserotonin agent, has enhanced HGH response to arginine infusion. Following placebo administration, arginine-induced HGH release was slightly but not significantly reduced; similarly, in eight metergoline treated subjects, HGH response to oral L-Dopa was slightly but not significantly reduced. HGH response to i.v. L-Dopa was not modified by the drug. These results suggest that serotonin controls HGH response only in response to arginine, not to L-Dopa.     

Chemical specificity of synapses of frog midbrain tectum

The effects of anticholinesterase preparations and cholinolytics on the potentials of the midbrain tectum evoked by stimulation of the optic tract and the opposite hemisphere were investigated in experiments on the perfused isolatedRana temporaria head. Low concentrations of galanthamine and eserine intensify the first and second postsynaptic components of the evoked potentials connected with the activation of both myelinated and unmyelinated fibers, and in higher concentration, first increase, and then reversibly inhibit them. Amisyl, depending on the concentration, partially or completely blocks both components and these effects are also reversible. Gangleron does not have an effect on the evoked potentials. A clear antagonism was found between anticholinesterase compounds and amisyl. After tetanic stimulation of both optic nerves simultaneously, a substance of acetylcholine nature appears in the perfusate. This makes it possible to assume that the optic terminals in the midbrain tectum form cholinergic synapses and that the corresponding postsynaptic structures contain cholineroreceptors of the muscarine type. Some differences in the dynamics of the changes in the first and second postsynaptic components from the effect of both galanthamine and eserine, as well as amisyl, indicate higher sensitivity of synaptic systems which consist of unmyelinated optic fibers. In contrast to the optic terminals, the transcommissural links do not form cholinergic synapses and anticholinesterase and cholinolytic substances do not have an effect on the transcommissural potentials.A. N. Severtsov Institute of Evolutionary Animal Morphology and Ecology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 386–393, July–August, 1971.     

The evolution of oscillatory behavior in age-structured species

A major challenge in ecology is to explain why so many species show oscillatory population dynamics and why the oscillations commonly occur with particular periods. The background environment, through noise or seasonality, is one possible driver of these oscillations, as are the components of the trophic web with which the species interacts. However, the oscillation may also be intrinsic, generated by density-dependent effects on the life history. Models of structured single-species systems indicate that a much broader range of oscillatory behavior than that seen in nature is theoretically possible. We test the hypothesis that it is selection that acts to constrain the range of periods. We analyze a nonlinear single-species matrix model with density dependence affecting reproduction and with trade-offs between reproduction and survival. We show that the evolutionarily stable state is oscillatory and has a period roughly twice the time to maturation, in line with observed patterns of periodicity. The robustness of this result to variations in trade-off function and density dependence is tested.     

Ion channel density and threshold dynamics of repetitive firing in a cortical neuron model

Modifying the density and distribution of ion channels in a neuron (by natural up- and down-regulation, by pharmacological intervention or by spontaneous mutations) changes its activity pattern. In the present investigation, we analyze how the impulse patterns are regulated by the density of voltage-gated channels in a model neuron, based on voltage clamp measurements of hippocampal interneurons. At least three distinct oscillatory patterns, associated with three distinct regions in the Na-K channel density plane, were found. A stability analysis showed that the different regions are characterized by saddle-node, double-orbit, and Hopf bifurcation threshold dynamics, respectively. Single strongly graded action potentials occur in an area outside the oscillatory regions, but less graded action potentials occur together with repetitive firing over a considerable range of channel densities. The presently found relationship between channel densities and oscillatory behavior may be relevance for understanding principal spiking patterns of cortical neurons (regular firing and fast spiking). It may also be of relevance for understanding the action of pharmacological compounds on brain oscillatory activity.