Pacemaker activity in hydra is modulated by glycine receptor ligands

In the mammalian central nervous system, the neurotransmitter, glycine, acts both on an inhibitory, strychnine-sensitive receptor (GlyR) and an excitatory, strychnine-insensitive site at the NMDA receptor. Here we present electrophysiological evidence that the strychnine-sensitive glycine agonists, glycine and taurine, and the antagonist, strychnine, affect the endodermal rhythmic potential (RP) system and that the ectodermal contraction burst (CB) pacemaker system is modulated by glycine and strychnine in hydra. The RP and CB pacemaker systems are responsible for the respective elongation and contraction of hydra's body column. Activity of the CB system, quantified by the rate of contraction bursts (CBs), the number of pulses per contraction burst (P/CB), and the duration of bursts, was decreased by glycine. Glycine, coadministered with the strychnine-insensitive glycine site blocker, indole-2-carboxylic acid (I2CA), decreased RPs but not CBs or P/CB. The effect was mimicked by taurine. Strychnine increased the duration of RP production, and decreased CB duration. The effect of glycine with I2CA was counteracted by strychnine. The results support the idea that a vertebrate-like GlyR may be involved in modulating activity of the endodermal RP system and suggest that a glycine site on an NMDA receptor may be involved in the CB system.     

GABA and glutamate receptors are involved in modulating pacemaker activity in hydra

The effects of gamma-amino butyric acid (GABA) and glutamate, their ionotropic agonists and antagonists on hydra's ectodermal and endodermal pacemaker systems were studied. GABA decreased ectodermal body contraction bursts (CBs) and the number of pulses in a burst (P/CB) and endodermal rhythmic potentials (RPs); tentacle pulses (TPs) were not affected. The GABA(A) agonist, muscimol, and the benzodiazepine receptor agonist, diazepam, mimicked the effects of GABA on the endodermal system. The GABA(A) antagonist bicuculline counteracted GABA's effects. Low concentrations of glutamate increased CBs and RPs. Higher concentrations required concanavalin A (Con A) to produce the same effect on CBs and P/CB. TPs were increased by high concentrations of glutamate and kainate. The ionotropic glutamate agonist, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) also required Con A to increase CBs and RPs. The effects of AMPA were antagonized by 6-nitro-7-sulfamoylbenzo[f]quinoxaline-2,3-dione (NBQX), which, per se, decreased CBs. The results indicate that GABA and glutamate, acting on their ionotropic receptors, modify the impulses of hydra's pacemaker systems. On the whole GABA decreased the outputs of both ectodermal and endodermal impulse generating systems, while glutamate increased them.     

Neurohormonal alteration of integrative properties of the cardiac ganglion of the lobster Homarus americanus.

The spontaneous burst discharges of isolated lobster (Homarus americanus) cardiac ganglia were recorded with a spaced array of electrodes. Small regions (less than 1 mm) of the ganglion were exposed to the cardioexcitor neurohormone in extracts of pericardial organs (XPO) or to 10(-5) M 5-hydroxytryptamine (5HT). All axons were excited (increased mean firing frequency, f) by both substances, but only by applications in the region between the soma (but excluding it) and proximal site of impulse initiation. Units not so exposed changed their f relatively little despite f increases of as much as threefold in exposed units and changes in burst rate and overall length. Regularity and grouping of all impulse activity into bursts was never disturbed. 5HT increases burst rate at any point of application. The increases are larger if small cells are affected than if only large cells are exposed. Burst length decreases except when the pacemaker is affected. In contrast, XPO affects neither burst rate or length unless small cells are affected. Length is increased if non-pacemaker small cells are affected; both rate and length increase if the pacemaker is affected. The pacemaker usually exhibits an f of intermediate value. Rate changes are not simply related to its f. A small cell can "burst" in the absence of impulses from any other cells. XPO may enhance endogenous "driver potentials," while 5HT may excite by depolarizing at limited sites.     

Spontaneous contractions and nerve net activity in the sea anemone calliactis parasitica

Suction electrodes attached to tentacles of the sea anemone Calliactis parasitica record regular bursts of activity associated with the through‐conducting nerve net. Most bursts consist of 10–15 pulses at a frequency of 1 every 4 sec to 1 every 10 sec. The interval between bursts is usually 10–20 min. Regularity in pulse number and frequency in successive bursts suggests that the activity originates from a pacemaker. Bursts are always followed by slow contraction of endodermal longitudinal (parietal) muscles after a short delay, and endo‐dermal circular muscles after a long delay. A simple model for nervous pacemaker control of rhythmic contractions cannot be proposed as slow contractions can also occur in the absence of recorded nerve net activity.     

Endogenous burst capability in a neuron of the gastric mill pattern generator of the spiny lobster Panulirus interruptus

The gastric system of the lobster stomatogastric ganglion has previously been thought to include no neurons capable of endogenous bursting. We describe conditions under which one of the motorneurons, the CP cell, can burst endogenously in a free-running manner in the absence of other phasic network activity. Isolated preparations of the foregut nervous system were used, and the CP bursting was either spontaneous or was activated by continuous stimulation of an input nerve. Three criteria were applied to establish the endogenous nature of such burst generation in CP: absence of phasic input, reset of the bursting pattern by pulses of current in a characteristic phase-dependent manner, and modulation of burst rate by sustained injected current. (1) The firing of other cells which are known to be related synaptically to CP was monitored in nerve records. These other cells were either silent or fired only tonically. Cross-correlograms showed that CP bursting was not ascribable to phasic activity in these other network cells. (2) A depolarizing current pulse of sufficient strength injected intracellularly between bursts triggered a burst prematurely and reset the subsequent rhythm. A hyperpolarizing pulse during a burst terminated it and reset the subsequent rhythm. Reset behavior was similar to that described for other endogenous bursters. (3) Application of a positive-going ramp current initially caused an increase in burst rate, as described for other endogenous bursters. However, further depolarization caused a slower burst rate due to lengthening of the individual bursts, although mean firing frequency continued to increase throughout the range tested. Such free-running endogenous repetitive bursting appeared to result from the CP's ability to produce slow regenerative depolarizations (“plateau potentials”). When bursting was present, so was the plateau property, as determined by I–V analysis and by the ability of brief current pulses to trigger and terminate bursts. The previous inability to observe endogenous bursting in preparations with central input removed may be due to the usual absence of the plateau property in such preparations.     

Modulation of Activity of One Neuron by Subthreshold Slow Potentials in Another in Lobster Cardiac Ganglion

A direct demonstration is given of interaction between specific neurons without impulses, via graded slow potentials electrotonically spread from one cell to another. Repetitive polarizing or depolarizing current pulses of 50 to 200 msec. and subthreshold intensity were passed through an intracellular electrode in the soma of a follower cell of the isolated ganglion. When the frequency is near the natural rhythm of impulse bursts corresponding to heart beats and arising in a pacemaker cell 5 to 10 mm. posteriorly, the bursts rapidly become synchronized with the pulses. The effect disappears upon withdrawing the intracellular electrode. Brief pulses or full spikes in the follower are not effective. Hyperpolarizing long pulses attract the burst to a fixed period after the end of the pulse, depolarizations after the beginning of the pulse. The natural rhythm promptly reappears when the pulses are stopped and occasionally breaks through during weak repetitive pulses. Current pulses in postsynaptic cells also alter the threshold of a presynaptic neuron to externally applied stimuli. Some kind of direct, low resistance pathway for electrotonic spread, discriminating against spikes because of their brevity, is inferred, providing a basis for subthreshold interaction which is specific and not by way of a field effect. Due to the sensitivity of modulation of ongoing rhythms, electrotonic currents can be effective even after decrementing over several millimeters.     

The Strategies of Behavioral Control in a Coelenterate

Although the cellular substrates of behavioral coordinationare uncertain in the hydroid Tubularia, much is known aboutthe strategies of behavioral control. The picture which emergesis that of an animal with diffusely distributed sites capableof initiating spontaneous activity, regional coordination ofpotential pacemaker loci to form pacemaker systems, and a loosehierarchical organization of pacemaker systems. At least onepacemaker system shows a short term increase in excitabilityand a longer duration depression of excitability following firing.The short-term excitability increase gives a tendency to firein bursts, the long-term depression acts as an intrinsic inhibitoryfeedback to terminate bursts and to control output frequency.All the known interactions between pacemaker systems are excitatory.Exogenous stimuli can excite a conducting system which inhibitsmost of the pacemaker systems, and one pacemaker system specificallyinhibits one set of muscles.     

Effect of the sympathetic nervous system in regulating heart rhythm during burst stimulation of the vagus nerve

In cat experiments, the right inferior cardiac nerve was stimulated at a frequency of 2 and 4 Hz and the right vagus by bursts of 1, 2, 4, 8 and 16 impulses. Stimulation of the inferior cardiac nerve shifted the ranges of the heart rate control up the frequency scale. The shift of the range boundaries was mainly determined by the intensity of sympathetic regulation and by the number of impulses in a burst which stimulates the vagus nerve.     

Self-Organization on Social Media: Endo-Exo Bursts and Baseline Fluctuations

A salient dynamic property of social media is bursting behavior. In this paper, we study bursting behavior in terms of the temporal relation between a preceding baseline fluctuation and the successive burst response using a frequency time series of 3,000 keywords on Twitter. We found that there is a fluctuation threshold up to which the burst size increases as the fluctuation increases and that above the threshold, there appears a variety of burst sizes. We call this threshold the critical threshold. Investigating this threshold in relation to endogenous bursts and exogenous bursts based on peak ratio and burst size reveals that the bursts below this threshold are endogenously caused and above this threshold, exogenous bursts emerge. Analysis of the 3,000 keywords shows that all the nouns have both endogenous and exogenous origins of bursts and that each keyword has a critical threshold in the baseline fluctuation value to distinguish between the two. Having a threshold for an input value for activating the system implies that Twitter is an excitable medium. These findings are useful for characterizing how excitable a keyword is on Twitter and could be used, for example, to predict the response to particular information on social media.     

Electrical potentials from the eye and optic nerve of Strombus: effects of electrical stimulation of the optic nerve.

1. Photic stimulation of the mature eye of Strombus can evoke in the optic nerve 'on' activity in numerous small afferent fibres and repetitive 'off' bursts of afferent impulses in a smaller number of larger fibres. 2. Synchronous invasion of the eye by electrically evoked impulses in small optic nerve fibres (apparently the 'on' afferents, antidromically activated) can evoke a burst of impulses in the larger 'off' fibres which propagate away from the eye. Invasion of the eye via one branch of optic nerve can evoke an answering burst in another branch. 3. Such electrically evoked bursts are similar to light-evoked 'off' bursts with respect to their impulse composition, their ability to be inhibited by illumination of the eye, and their susceptibility to MgCl2 anaesthesia. 4. Invasion of the eye by a train of repetitive electrically evoked impulses in the absence of photic stimulation can give rise to repetitive 'off' bursts as well as concomitant oscillatory potentials in the eye which are similar to those normally evoked by cessation of a photic stimulus. 5. The electrically evoked 'off' bursts appear to be caused by an excitatory rebound following the cessation of inhibitory synaptic input from photoreceptors which can be antidromically activated by electrical stimulation of the optic nerve. 6. The experimental results suggest that the rhythmic discharge of the 'off' fibres evoked by the cessation of a photic stimulus is mediated by the abrupt decrease of inhibitory synaptic input from the receptors.     

Are pacemaker properties required for respiratory rhythm generation in adult turtle brain stems in vitro?

The role of pacemaker properties in vertebrate respiratory rhythm generation is not well understood. To address this question from a comparative perspective, brain stems from adult turtles were isolated in vitro, and respiratory motor bursts were recorded on hypoglossal (XII) nerve rootlets. The goal was to test whether burst frequency could be altered by conditions known to alter respiratory pacemaker neuron activity in mammals (e.g., increased bath KCl or blockade of specific inward currents). While bathed in artificial cerebrospinal fluid (aCSF), respiratory burst frequency was not correlated with changes in bath KCl (0.5-10.0 mM). Riluzole (50 microM; persistent Na(+) channel blocker) increased burst frequency by 31 +/- 5% (P < 0.05) and decreased burst amplitude by 42 +/- 4% (P < 0.05). In contrast, flufenamic acid (FFA, 20-500 microM; Ca(2+)-activated cation channel blocker) reduced and abolished burst frequency in a dose- and time-dependent manner (P < 0.05). During synaptic inhibition blockade with bicuculline (50 microM; GABA(A) channel blocker) and strychnine (50 muM; glycine receptor blocker), rhythmic motor activity persisted, and burst frequency was directly correlated with extracellular KCl (0.5-10.0 mM; P = 0.005). During synaptic inhibition blockade, riluzole (50 microM) did not alter burst frequency, whereas FFA (100 microM) abolished burst frequency (P < 0.05). These data are most consistent with the hypothesis that turtle respiratory rhythm generation requires Ca(2+)-activated cation channels but not pacemaker neurons, which thereby favors the group-pacemaker model. During synaptic inhibition blockade, however, the rhythm generator appears to be transformed into a pacemaker-driven network that requires Ca(2+)-activated cation channels.     

Excessive reflexes in spinal cord injury triggered by electrical stimulation

Interaction of electrocutaneous stimulation with an impaired human motor control system may result in unstable reflex loops causing excessive spastic reactions. These contractions are usually excluded from analysis since the presence of spasm is one of the criteria commonly applied for discarding a contraction. They may, however, provide interesting information on the nature of spasticity. The dorsiflexor muscles of four SCI subjects were activated by means of surface electrical stimulation and the isometric ankle moment was measured. Short bursts of constant stimulation frequency at seven different frequencies (8, 12, 16, 20, 25, 33, 50 Hz) triggered spastic reactions in all subjects. The onset times of spastic activity during an electrically elicited contraction shortened with increased stimulation frequency. A stimulation burst may also have a spasticity reduction effect on a subsequent burst, indicating potential short term therapeutic effects of stimulation on spasticity in isometric conditions.     

Search for species-specific mating signal in courtship songs of sympatric sibling species,Drosophila ananassae and D. pallidosa

Sexual isolation is one of the most important mechanisms that may lead to speciation. Drosophila ananassae and D. pallidosa are useful for the study of sexual isolation, because of their sympatric distribution and no postmating isolation between them. Courtship songs are considered to play a crucial role in sexual isolation between D. ananassae and D. pallidosa. We recorded and analyzed male courtship songs of D. ananassae and D. pallidosa for eight and four geographical strains, respectively. Courtship behaviors of the two species were consistent with those previously described, however, male's middle leg shaking, which had not before been described, was observed in both species. Males sing by wing vibration only during courtship. Their song oscillograms were distinct between species, but those of conspecific strains were very similar, in spite of their different geographical derivation. We found species-specificity in burst length, pulse length, cycle number in a pulse, and frequency spectra of bursts; these results suggest that these song parameters may play a role in mate recognition that enforces their sexual isolation. The specific values of interpulse interval, cycle number in a pulse and intrapulse frequency were involved with the determination of specificity in frequency spectra of bursts. We discussed the possibility that the specific frequency spectra of bursts are recognized by females as the species-specific signal rather than each parameter individually.     

Delayed initiation of SS1 pulses in the sea anemone Calliactis parasitica: evidence for a fourth conducting system.

1. Single electrical shocks to the column sometimes elicit a series of 1-6 pulses in the SS1 (ectodermal slow system) but the first pulse does not appear until 5-28 s after stimulation. These pulses occur in addition to the early SS1 pulse which follows every shock and which has a conduction delay of less than 1 s. 2. The threshold of the delayed SS1 response is different from the thresholds of the three known conducting systems (through-conducting nerve net, SS1, and SS2). 3. In the case of stimulation of the column, the delayed SS1 pulses do not arise at the point of stimulation but probably originate in the tentacles or upper column. The pulse origin can shift during a single burst. 4. The pathway from the point of stimulation to the site of origin of delayed SS1 pulses is endodermal. We propose that this pathway represents a fourth conducting system (Delayed Initiation System--DIS). The DIS must connect, across the mesogloea, with the ectodermal SS1. The long pulse delay and repetitive firing may derive from pacemaker activity in the DIS. The DIS pacemakers closely resemble the pacemakers connected to the through-conducting nerve net. The DIS may be neuronal. 5. Delayed SS1 pulse bursts from unattached anemones showed an earlier onset, and more pulses/burst, than those from attached anemones. 6. Delayed SS1 pulses can also be evoked by electrical, and in some cases mechanical, stimulation of the pedal disc, tentacles, and pharynx, but there are regional differences in the number of pulses evoked, in their delay, and in their site of origin.     

The relationship between the frequency of self-stimulation and parameters of the stimulus]

The dependence of self-stimulation frequency on stimulation parameters (current intensity, stimulation frequency, pulse duration, duration of pulse bursts) was studied in fifteen rats with monopolar electrodes implanted in the lateral hypothalamus, using rectangular current pulses for brain stimulation. All the experiments revealed qualitatively similar response surfaces to the combined change of stimulation frequency and pulse duration Self-stimulation frequency is connected in a non-linear way with the "specific charge" per unit of time, and in an approximately linear way, with the duration of the pulse burst. Regression equations are determined which precisely enough described the kind of response surface (R =0.7 to 0.95).     

Rhythmic swimming activity in neurones of the isolated nerve cord of the leech.

1. Repeating bursts of motor neurone impulses have been recorded from the nerves of completely isolated nerve cords of the medicinal leech. The salient features of this burst rhythm are similar to those obtained in the semi-intact preparation during swimming. Hence the basic swimming rhythm is generated by a central oscillator. 2. Quantitative comparisons between the impulse patterns obtained from the isolated nerve cord and those obtained from a semi-intact preparation show that the variation in both dorsal to ventral motor neurone phasing and burst duration with swim cycle period differ in these two preparations. 3. The increase of intersegmental delay with period, which is a prominent feature of swimming behaviour of the intact animal, is not seen in either the semi-intact or isolated cord preparations. 4. In the semi-intact preparation, stretching the body wall or depolarizing an inhibitory motor neurone changes the burst duration of excitatory motor neurones in the same segment. In the isolated nerve cord, these manipulations also change the period of the swim cycle in the entire cord. 5. These comparisons suggest that sensory input stabilizes the centrally generated swimming rhythm, determines the phasing of the bursts of impulses from dorsal and ventral motor neurones, and matches the intersegmental delay to the cycle period so as to maintain a constant body shape at all rates of swimming.     

Integrative Neurophysiology of the Lobster Cardiac Ganglion

The synchronized bursts of impulses produced by the nine neuronsof the isolated Homarus cardiac ganglion are usually initiatedby Cell 7. Activity in all other cells commences with very shortlatency thereafter. Impulses in most cells originate in triggerzones located 1–2 mm from the cell body, but the firstseveral impulses in Cells 8 and 9 frequently originate in distaltrigger zones some distance from the somata. Large cells fireat a high initial frequency, dropping rapidly to a low frequencyplateau. Small cells exhibit a more tonic behavior and fireat intermediate rates. More anterior small cells tend to firefaster than more posterior ones. The major synaptic interactionsare the impulse-mediated excitatory ones from small cells tolarge cells, and possibly to more anterior small cells. Thereare weak interactions from large cells back onto small cells,and very specific interactions from Cells 1 and 2 onto 3_A, 4_A,5_A, and 3_B 4_B 5_B respectively. The large discrete EPSPs generatedin large cells by small cell impulses appear to be the explanationfor "discrete positioning" in large-cell firing patterns. Inthis situation, large-cell impulses only fire at discrete timesduring the burst, regardless of the actual large-cell pattern. The overall view is of a two-layered neural system in whichthe small cells possess an endogenous oscillatory driver potential,synchronized by synaptic and electrotonic interactions, anddriving a train of impulses in each cell. This activates excitatorysynapses on the large cells, which combined with a triggereddriver potential in each large cell, produces synchronized trainsof motor impulses which activate the heart muscle, causing theheartbeat.     

Temporal interaction between single spikes and complex spike bursts in hippocampal pyramidal cells

Cortical pyramidal cells fire single spikes and complex spike bursts. However, neither the conditions necessary for triggering complex spikes, nor their computational function are well understood. CA1 pyramidal cell burst activity was examined in behaving rats. The fraction of bursts was not reliably higher in place field centers, but rather in places where discharge frequency was 6-7 Hz. Burst probability was lower and bursts were shorter after recent spiking activity than after prolonged periods of silence (100 ms-1 s). Burst initiation probability and burst length were correlated with extracellular spike amplitude and with intracellular action potential rising slope. We suggest that bursts may function as "conditional synchrony detectors," signaling strong afferent synchrony after neuronal silence, and that single spikes triggered by a weak input may suppress bursts evoked by a subsequent strong input.     

基于最大锋电位间隔的爆发检测自适应算法

在各种类型的培养神经元网络、哺乳动物中枢神经系统和切片中,都可以观察到爆发。爆发是空间-时间放电模式的重要特征,它由一系列高频率发放的连续动作电位组成,由于在时间尺度上的复杂性,使其辨识和探测存在许多困难。自适应算法利用爆发外部锋电位间隔超过爆发内部锋电位间隔的累加和识别爆发本身。基于该算法原理,以爆发内部最大锋电位间隔参数作为确定爆发的约束条件,改进爆发检测自适应算法。实验结果表明,改进算法可以有效地避免爆发的漏检和错检,较准确地检测出神经元的爆发活动,确定爆发活动的数目和持续时间等,爆发检测的平均准确率为93.8%,比原自适应算法提高了35.3%。     

Interstitial cell of Cajal-like cells in the upper urinary tract

Autorhythmicity in the upper urinary tract (UUT) has long been considered to arise in specialized atypical smooth muscle cells (SMC) predominately situated in the most proximal regions of the pyeloureteric system. These atypical SMC pacemakers have been thought to trigger adjacent electrically-quiescent typical SMC to fire action potentials which allow an influx of Ca2+ and the generation of muscle contraction. More recently, the presence of cells with many of the morphological, electrical and immunohistochemical characteristics of interstitial cells of Cajal (ICC), the pacemaker cells of the gastrointestinal tract, have been located in many regions of both the upper and lower urinary tract. This article reviews the evidence from the literature and from our laboratory supporting a role of both atypical SMC and ICC-like cells in the initiation and propagation of pyeloureteric peristalsis in the UUT. We propose a new model in which there are 2 populations of pacemaker cells, high frequency atypical SMC and lower frequency ICC-like cells, both of which can drive electrically-quiescent typical SMC. The relative presence of these 2 populations of pacemaker cells and the relatively-long refractoriness of typical SMC determines the decreasing frequency of contraction with distance from the renal fornix. In the absence of the proximal pacemaker drive from atypical SMC after pyeloureteral/ureteral obstruction or surgery, ICC-like cell pacemaking provides a compensatory mechanism allowing the ureter to maintain rudimentary peristaltic waves and movement of urine from the pyelon towards the bladder.