Periodic Spiking Research Articles

Coexistence of two attractors in lasers with delayed incoherent optical feedback

Dynamic phenomena that incoherent optical feedback induces in single-mode class-B lasers are examined. Numerical simulations reveal the coexistence of sustained periodic relaxation oscillations and regenerative periodic spiking oscillations leading to chaotic oscillations.

Ictal spikes: a marker of specific hippocampal cell loss

Spontaneous seizures recorded from mesial temporal depth electrodes in the human are commonly manifested by one of two onset patterns: a high frequency discharge or a periodic spike discharge morphologically similar but clearly distinguished from ongoing interictal activity. We categorized medial temporal lobe seizure onset for the presence of periodic ictal spikes at a frequency of less than 2 Hz lasting for more than 5 sec to investigate the relationship of this ictal pattern to anatomical changes in the resected temporal lobe tissue. Fifty-one patients had hippocampal depth electrode recordings of spontaneous seizures, subsequent hippocampal resection, and quantitative cell counts of hippocampal subfields. Thirty-two of these patients had ictal spikes lasting at least 5 sec in more than 50% of their seizures. The presence of ictal spikes was significantly correlated with decreased cells in CA1 only ( P=0.015). The correlation of a common ictal pattern with focal cell loss in the hippocampus suggests that electrophysiological manifestations of seizures provide a clue to the underlying pathological substrate. Ictal spikes may be a cause or result of the cell loss. These observations should be correlated with independent investigations in humans and animal models that reflect the CA1 cell loss associated with temporal lobe epilepsy.

EEG development in Rett syndrome. A study of 30 cases

EEG development through advancing clinical stages was studied in 30 cases of Rett syndrome, a progressive encephalopathy seen so far only in girls. Besides slowing of background activity and epileptic patterns, which are found in many types of ‘degenerative’ brain diseases, we observed in advanced stages of Rett syndrome unusual EEG patterns resembling those seen in slow virus encephalitis. On the other hand, the EEG was normal in one case of advanced Rett syndrome. The typical steps of EEG development were: initially normal EEG; as the first abnormality rolandic spikes, often followed by other epileptic patterns; and, in more advanced stages, a pseudoperiodic delta pattern and occasionally generalized periodic spike activity. The results motivate a discussion concerning other possible origins of Rett syndrome in addition to the supposed genetic one. The question is raised whether Rett syndrome might be etiologically heterogeneous.

Molecular model for receptor-stimulated calcium spiking.

Many cells exhibit periodic transient increases in cytosolic calcium levels rather than a sustained rise when stimulated by a hormone or growth factor. We propose here a molecular model that accounts for periodic calcium spiking induced by a constant stimulus. Four elements give rise to repetitive calcium transients: cooperativity and positive feedback between a pair of reciprocally coupled (crosscoupled) messengers, followed by deactivation and then by reactivation. The crosscoupled messengers in our model are inositol 1,4,5-trisphosphate (InsP3) and cytosolic calcium ions. The opening of calcium channels in the endoplasmic reticulum by the binding of multiple molecules of InsP3 provides the required cooperativity. The stimulation of receptor-activated phospholipase C by released calcium ions leads to positive feedback. InsP3 is destroyed by a phosphatase, and calcium ion is pumped back into the endoplasmic reticulum. These processes generate bistability: the cytosolic calcium concentration abruptly increases from a basal level to a stimulated level at a threshold degree of activation of phospholipase C. Spiking further requires slow deactivation and subsequent reactivation. In our model, mitochondrial sequestration of calcium ion prevents the cytosolic level from increasing above several micromolar and enables the system to return to the basal state. When the endoplasmic reticulum calcium store is refilled to a critical level by the Ca2+-ATPase pump, cooperative positive feedback between the InsP3-gated channel and phospholipase C begins again to give the next calcium spike. The time required for the calcium level in the endoplasmic reticulum to reach a threshold sets the interval between spikes. The amplitude, shape, and period of calcium spikes calculated for this model are like those observed experimentally.

Variability of Toxic Trace Contaminants in Municipal Sewage Treatment Plants

The variability of toxic trace contaminants in influents and effluents at three full-scale municipal sewage treatment plants was measured by collecting grab samples of degritted raw wastewater and non-chlorinated secondary effluent at two hour intervals over eight consecutive days. The samples were analyzed for metals, conventional contaminants and a range of organic trace contaminants. The metals and volatile organic compounds were the dominant contaminants found in the influents. In the effluents, organic concentrations were close to detectable levels and polyaromatic hydrocarbons were almost never detected. Some influent metal and organic contaminants varied diurnally while others appeared to fluctuate randomly with periodic spike inputs. The variability of most effluent trace contaminant concentrations was considerably attenuated in comparison to influent concentrations.

Intracellular θ-rhythm generation in identified hippocampal pyramids

The hippocampal EEG and the transmembrane potential of CA 1-CA 3 hippocampal pyramids were recorded in curarized and urethanized rats. Pyramids were identified by antidromic driving and intracellular staining with Lucifer yellow. During θ-rhythm most pyramids showed 10–20 mV sustained depolarization and potential oscillations either consisting of 5–10 mV smooth sine-like waves or slow spikes of up to 60 mV. Fast Na + and slow, probably Ca 2+-mediated, spikes were triggered by depolarizing pulses or spontaneously. Depolarizations15mV triggered rhythmic slow spikes at θ-frequency, but if<15 mV, slow spikes were irregular and at lower rates. With depolarizations of <10 mV, no slow spikes were triggered. Sine-like intracellular θ-wave amplitudes increased with hyper-and decreased with depolarizing pulses, showing the behavior of rhythmic EPSPs. Periodic fast spike bursts were θ-correlated. Cells with intracellular θ could either fire periodic fast spike bursts or at random, bu always at a preferred phase of the θ-wave. Slow spikes were generated above a potential threshold by a slow depolarization and driven by periodic EPSPs. Intracellular θ is the reflection of EPSPs and of slow spikes; the oscillatory phenomena are not exclusively generated, as previously hypothesized, by network properties which may, however, contribute as tuning and modulatory elements. The determining events in intracellular θ-generation are the intrinsic biophysical characteristics of the pyramidal neuron membrane.

Features of seizures and behavioral changes induced by intrahippocampal injection of zinc sulfate in the rabbit: a new experimental model of epilepsy.

Seizure produced by intrahippocampal injection of zinc sulfate in rabbits is a new chronic model of experimental epilepsy. In this model, the clinical manifestations are easily observed and are expressed not only as partial clonic seizures, but also by secondary generalized seizures. The electrohippocampalogram (EHG) and electrocorticogram (ECoG) discharges change correspondingly during both types of seizures, and last for weeks. The mechanism for induced seizures may be partly related to the inhibitory effect of zinc sulfate injections on the acetylcholinesterase (AchE) activity in the hippocampus. The commonly used antiepileptic drugs, such as phenobarbital and phenytoin, afforded protection against the zinc-induced secondary generalized clonic seizures and alleviated the partial clonic seizures but had no influence on the EHG- and ECoG-monitored periodic bursts of spike discharges. Nitrazepam was found to antagonize both types of seizures and also transiently restored the EHG and ECoG to normal. D-penicillamine, a metal chelator, may be the most effective agent for the treatment of zinc-induced seizures; the agent, in addition to affording protection against both types of seizures, also caused the periodic burst spike discharges in EHG and ECoG to disappear.

Phase resetting and bifurcation in the ventricular myocardium

With the dynamic differential equations of Beeler, G. W., and H. Reuter (1977, J. Physiol. [Lond.]. 268:177-210), we have studied the oscillatory behavior of the ventricular muscle fiber stimulated by a depolarizing applied current I app. The dynamic solutions of BR equations revealed that as I app increases, a periodic repetitive spiking mode appears above the subthreshold I app, which transforms to a periodic spiking-bursting mode of oscillations, and finally to chaos near the suprathreshold I app (i.e., near the termination of the periodic state). Phase resetting and annihilation of repetitive firing in the ventricular myocardium were demonstrated by a brief current pulse of the proper magnitude applied at the proper phase. These phenomena were further examined by a bifurcation analysis. A bifurcation diagram constructed as a function of I app revealed the existence of a stable periodic solution for a certain range of current values. Two Hopf bifurcation points exist in the solution, one just above the lower periodic limit point and the other substantially below the upper periodic limit point. Between each periodic limit point and the Hopf bifurcation, the cell exhibited the coexistence of two different stable modes of operation; the oscillatory repetitive firing state and the time-independent steady state. As in the Hodgkin-Huxley case, there was a low amplitude unstable periodic state, which separates the domain of the stable periodic state from the stable steady state. Thus, in support of the dynamic perturbation methods, the bifurcation diagram of the BR equation predicts the region where instantaneous perturbations, such as brief current pulses, can send the stable repetitive rhythmic state into the stable steady state.

Evidence for neuronal periodicity detection in the auditory system of the Guinea fowl: implications for pitch analysis in the time domain.

Evidence for periodicity analysis was obtained by recording from 420 single units in the auditory midbrain nucleus (MLD) of awake Guinea fowls (Numida meleagris). The results were compatible with a neuronal correlation model consisting of three main components: an oscillator, an interval multiplier and a coincidence unit. The model makes use of a neuronal time constant in order to measure the periodicities of auditory signals. For 180 units the sequence of spike intervals in response to tone bursts and amplitude modulations (AM) was studied with 10 microseconds resolution. In 69 of these units (38%) amplitude fluctuations like stimulus onset or the modulation cycles produced periodic spike trains resembling damped oscillations. The periods of these oscillations did not correspond to either the best frequency (BF) of these units or the periodicities of the stimuli. They were interpreted as multiples of a neuronal time constant, tau 1 = 0.4 ms, probably a minimal synaptic delay. These units were tuned to AM-signals with particular combinations of the modulation frequency, fm, and the carrier frequency, fc. The corresponding periods tau m and tau c were related to the intrinsic oscillation by a periodicity equation: m X tau m + n X tau c = 1 X tau 1, where a few small integers for m, n and 1 were adequate to describe all observed properties of a unit. Variation of fm or fc shifted the phase delays of the coupled spike activities proportional to m X tau m or n X tau c, respectively. These effects were explained by coincidence of neuronal activity phase coupled to fc, with intrinsic oscillations triggered by the fm-cycles. The coincidence condition at the level of the recorded units was given by the periodicity equation. Psychophysical experiments using AM-signals indicated that the described mechanisms, together with the same neuronal time constant, tau 1, are adequate to explain pitch perception in humans.

Burst discharge in mammalian neuroendocrine cells involves an intrinsic regenerative mechanism.

Intracellular recordings from mammalian neuroendocrine cells showed that steady, injected currents can modify and block periodic spike bursts previously associated with increased neurohormone release. Spike afterpotentials could sum to form plateau potentials, which generated bursts and did not depend on axonal conduction or chemical synapses. Therefore, bursting involves a spike-dependent, positive-feedback mechanism endogenous to single neuroendocrine cells.

The effects of motilin on periodic myoelectric spike activity in intact and transected canine small intestine.

The effects of motilin infusions on periodic myoelectric spike activity were studied in conscious dogs with an intact small intestine and in dogs with established jejunal Thiry-Vella loops (T-V loops). Myoelectric activity was recorded from chronically implanted electrodes on the intact intestine, the anastomosed intestine and on the jejunal T-V loop. During fasting, migrating myoelectric complexes (m.m.c.s) were present in the intact and anastomosed intestine and in the T-V loop; in the latter, intervals between m.m.c.s were significantly shorter (P less than 0.05). Infusion of motilin induced premature m.m.c.s in the intact and anastomosed intestine, reducing the interval between successive m.m.c.s (P less than 0.05). In contrast, in the T-V loop, motilin significantly reduced the number of m.m.c.s (P less than 0.01) and the interval between two m.m.c.s was prolonged. After an infusion of motilin, the number of m.m.c.s in the intact and anastomosed intestine was significantly reduced (P less than 0.01), with a corresponding increase in the intervals between m.m.c.s; no further changes were observed in the T-V loop. These results demonstrate that m.m.c.s are induced by motilin in the proximal gut, suggesting a humoral mechanism for m.m.c. initiation in this region. In contrast, the genesis of m.m.c.s in jejunal T-V loops is delayed by motilin.

Glucose and acetylcholine have different effects on the plateau pacemaker of pancreatic islet cells.

Pancreatic islet cell membrane electrical activity has been studied with intracellular microelectrodes in perifused, isolated mouse islets of Langerhans. The dose-response effects of glucose and of acetylcholine on the pattern of electrical activity are compared and are shown to be qualitatively different. Electrical activity in the presence of glucose consists of periodic alterations between a polarized silent phase potential and depolarized plateau phase with superimposed rapid spiking activity. Increasing glucose concentration prolongs the plateau phase, at the expense of the silent phase, and thus increases the the plateau fraction (the fraction of time in each electrical cycle spent in the plateau phase). By contrast, graded doses of acetylcholine, in the presence of stimulatory levels of glucose, had no effect on plateau fraction. Increasing glucose concentration also slightly reduced the frequency of plateaus, whereas increasing acetylcholine markedly increased plateau frequency. Furthermore, changes of glucose concentration had no effect on the potential levels during the plateau and silent phases, while addition of acetylcholine depolarized the silent phase until, at high concentrations of acetylcholine, the combination of increased plateau frequency and silent phase depolarization produced continuous spiking. Addition of acetylcholine to a slightly substimulatory level of glucose depolarized the membrane without, however, inducing periodic spiking activity. The results suggest aht the effects of acetylcholine and glucose are due to different effects on the plateau pacemaker system involved in the regulation of insulin release.

Early Electrocortical Effects of Unilateral and Bilateral Cranial X-Irradiation in the Albino Rat

The adult nervous system, although sensitive to ionizing radiation during development (1-4), has been regarded as relatively resistant, if histopathological criteria are adopted. However, the intact nervous system can respond physiologically to low doses (5-7), histological effects of which have been reported in the adult (8) after both acute and chronic administration. A variety of central nervous responses have been recently reported to have been affected by radiation, including behavioral arousal (9, 10), the electroconvulsive threshold (11), and motivation (12). Early electrophysiological, both electroencephalographic (E.E.G.) and electrocorticographic (E.Co.G.), effects of irradiation have been studied in monkeys (13) and in rats after whole-body irradiation (14). The cerebellar-evoked response declined (15) and periodic spiking and generalized slowing of E.Co.G. activity occurred after cranial irradiation (16). Lower doses induced spike discharge in the dorsal hippocampus and low-voltage fast activity (17, 18). Spike amplitude and conduction velocity in peripheral nerve diminished (19, 20), and complete electrical blocking of compound action potentials of muscles followed intense irradiation (21). These E.E.G. or E.Co.G. changes caused by ionizing radiation can be explained either by the hypothesis of a nonneuronal general metabolic mechanism of action or by that of a primary and direct neuronal site for the action of radiation-in particular, the volume stimulus concept (10). In an endeavor to decide between these two hypotheses, the effects of bilateral and unilateral irradiation of the head of the rat have been determined on symmetrically derived monopolar E.Co.G.'s from both hemispheres. If E.Co.G. effects were due to nonneuronal metabolic factors, bilateral changes would be predicted after unilateral irradiation, but if these effects were mediated by a direct volume neuronal stimulus, then primarily ipsilateral changes would be expected. A preliminary account (22) of these experiments has been presented.