Discharge properties of neurons in subdivisions of the medial geniculate body of the guinea pig

The activity of 194 neurons was recorded in three subdivisions of the medial geniculate body (74 neurons in the ventral, 62 in the medial and 44 neurons in the dorsal subdivision, i.e. vMGB, mMGB and dMGB) of guinea pigs anesthetized with ketamine-xylazine. The discharge properties of neurons were evaluated by means of peristimulus time histograms (PSTHs), interval histograms (INTHs) and auto-correlograms (ACGs). In the whole MGB, the most frequent PSTH responses to pure tone stimuli were onset (43%) or chopper (32%). The onset responses were mostly present in the vMGB, whereas chopper responses dominated in the dMGB. In the whole MGB Poisson-like and bimodal INTHs were found in 46% and 40% of neurons, respectively. The mMGB revealed fewer bimodal and more symmetrical types of INTH. In the whole MGB, 60% of units were found to have ACGs typical for short bursts (<100 ms), 23% for long bursts (>100 ms) and 15% of units fired without bursts. Neurons in the vMGB were characterized by short bursting, whereas those in the mMGB and dMGB expressed more activity in the long bursts. The results demonstrate that the type of information processing in the vMGB, which belongs to the "primary" auditory system, is different from that in two other subdivisions of the MGB.     

Influence of the pteropod mollusk pedal ganglia locomoter system on anatomically isolated neurons

It was established during experiments on pedal ganglia generating locomotor rhythm isolated fromClione limacina, a pteropod mollusk, that this rhythm was irregular in 30% of preparations; i.e., the locomotor generator worked in bursts which alternated with periods of regular activity. Locomotor bursts were produced by excitation in command neurons located within the pedal ganglia. Single neurons were extracted from the ganglia in these preparations generating locomotor bursts by means of an intracellular microelectrode; their somata were then placed in their original sites amongst the ganglia cells. A total of 35 neurons were isolated showing changed activity during bursts. Nine of these cells renewed their erratic activity (linked to locomotor bursts) following reinsertion into the ganglion. Neurons which had initially shown an excitatory pattern during bursts continued to be excited; the same was true for inhibitory types. These observations indicate that the command neurons governing generator operation can act on target cells when morphological contact with them has been suppressed.Institute for Research into Information Transmission, Academy of Sciences of the USSR, Moscow; M. V. Lomonosov State University. Moscow. Translated from Neirofiziologiya, Vol. 18, No. 6, pp. 756–763, November–December, 1986.     

Non-synaptic interaction between neurons in molluscs

1. Isolated pedal ganglia of the pteropodial mollusc, Clione limacina, generate a locomotory rhythm. In 30% of the pedal ganglia preparations the locomotory rhythm was not regular, i.e. the locomotor generator worked in “bursts” alternating with periods of low activity.2. The “locomotor bursts” were caused by spontaneous activation of command neurons located in the pedal ganglia.3. A single neuron was extracted from burst-generating preparations by means of the intracellular microelectrode and then its soma was put back, into the initial place between the ganglion cells. Twenty-five percent of the isolated neurons renewed the bursts-related changes in their activity after the insertion into the ganglion. The neurons which were originally excited during the “locomotor bursts” continued to be excited after isolation, while those which were inhibited continued to be inhibited during the bursts.4. It is suggested that the command neurons controlling the locomotor generator can exert action on the target cells in the absence of morphological synapses.     

Unit activity of rabbit medial septum in early ontogenesis]

In experiments on 7-20 and 75-day-old rabbits, the activity of units of the septal nuclei, the nucleus of the diagonal band of Broca (NBD), nucleus medialis (NSM) and the EEG of dorsal hippocamp (the CA2-CA3 fields) have been recorded. It was shown that the specific discharge pattern of septal neurons (the bursts) appears on 8-11th days under action of eserine. The distinct bimodal pattern of the interval histograms of the septal units appeared from the 14th day. The burst discharge pattern of NBD and NSM neurones reached a definitive level by the 20th day. The parallel evolution of discharge pattern of the septal units and the EEG of the hippocamp is observed in ontogenesis, the formation of hippocampal theta activity correlating with enhancement of the average frequency of the septal (NBD, NSM) neuronal activity, with shortening to the interval between the discharges within the bursts and with enhancement of the regularity of the bursts.     

Integration and segregation of activity in entorhinal-hippocampal subregions by neocortical slow oscillations

Brain systems communicate by means of neuronal oscillations at multiple temporal and spatial scales. In anesthetized rats, we find that neocortical "slow" oscillation engages neurons in prefrontal, somatosensory, entorhinal, and subicular cortices into synchronous transitions between UP and DOWN states, with a corresponding bimodal distribution of their membrane potential. The membrane potential of hippocampal granule cells and CA3 and CA1 pyramidal cells lacked bimodality, yet it was influenced by the slow oscillation in a region-specific manner. Furthermore, in both anesthetized and naturally sleeping rats, the cortical UP states resulted in increased activity of dentate and most CA1 neurons, as well as the highest probability of ripple events. Yet, the CA3-CA1 network could self-organize into gamma bursts and occasional ripples during the DOWN state. Thus, neo/paleocortical and hippocampal networks periodically reset, self-organize, and temporally coordinate their cell assemblies via the slow oscillation.     

Experimental analysis and computational modeling of interburst intervals in spontaneous activity of cortical neuronal culture

Rhythmic bursting is the most striking behavior of cultured cortical networks and may start in the second week after plating. In this study, we focus on the intervals between spontaneously occurring bursts, and compare experimentally recorded values with model simulations. In the models, we use standard neurons and synapses, with physiologically plausible parameters taken from literature. All networks had a random recurrent architecture with sparsely connected neurons. The number of neurons varied between 500 and 5,000. We find that network models with homogeneous synaptic strengths produce asynchronous spiking or stable regular bursts. The latter, however, are in a range not seen in recordings. By increasing the synaptic strength in a (randomly chosen) subset of neurons, our simulations show interburst intervals (IBIs) that agree better with in vitro experiments. In this regime, called weakly synchronized, the models produce irregular network bursts, which are initiated by neurons with relatively stronger synapses. In some noise-driven networks, a subthreshold, deterministic, input is applied to neurons with strong synapses, to mimic pacemaker network drive. We show that models with such "intrinsically active neurons" (pacemaker-driven models) tend to generate IBIs that are determined by the frequency of the fastest pacemaker and do not resemble experimental data. Alternatively, noise-driven models yield realistic IBIs. Generally, we found that large-scale noise-driven neuronal network models required synaptic strengths with a bimodal distribution to reproduce the experimentally observed IBI range. Our results imply that the results obtained from small network models cannot simply be extrapolated to models of more realistic size. Synaptic strengths in large-scale neuronal network simulations need readjustment to a bimodal distribution, whereas small networks do not require such changes.     

Responses of the antennal bimodal hygroreceptor neurons to innocuous and noxious high temperatures in the carabid beetle,Pterostichus oblongopunctatus

Electrophysiological responses of thermo- and hygroreceptor neurons from antennal dome-shaped sensilla of the carabid beetle Pterostichus oblongopunctatus to different levels of steady temperature ranging from 20 to 35 °C and rapid step-changes in it were measured and analysed at both constant relative and absolute ambient air humidity conditions. It appeared that both hygroreceptor neurons respond to temperature which means that they are bimodal. For the first time in arthropods, the ability of antennal dry and moist neurons to produce high temperature induced spike bursts is documented. Burstiness of the spike trains is temperature dependent and increases with temperature increase. Threshold temperatures at which the two neurons switch from regular spiking to spike bursting are lower compared to that of the cold neuron, differ and approximately coincide with the upper limit of preferred temperatures of the species. We emphasise that, in contrast to various sensory systems studied, the hygroreceptor neurons of P. oblongopunctatus have stable and continuous burst trains, no temporal information is encoded in the timing of the bursts. We hypothesise that temperature dependent spike bursts produced by the antennal thermo- and hygroreceptor neurons may be responsible for detection of noxious high temperatures important in behavioural thermoregulation of carabid beetles.     

Patterns of spontaneous activity in single rat olfactory receptor neurons are different in normally breathing and tracheotomized animals

Spontaneous firing of olfactory receptor neurons (ORNs) was recently shown to be required for the survival of ORNs and the maintenance of their appropriate synaptic connections with mitral cells in the olfactory bulb. ORN spontaneous activity has never been described or characterized quantitatively in mammals. To do so we have made extracellular single unit recordings from ORNs of freely breathing (FB) and tracheotomized (TT) rats. We show that the firing behavior of TT neurons was relatively simple: they tended to fire spikes at the same average frequency according to purely random (Poisson) or simple (Gamma or Weibull) statistical laws. A minority of them were bursting with relatively infrequent and short bursts. The activity of FB neurons was less simple: their firing rates were more diverse, some of them showed trends or were driven by breathing. Although more of them were regular, only a minority could be described by simple laws; the majority displayed random bursts with more spikes than the bursts of TT neurons. In both categories bursts and isolated spikes (outside bursts) occurred completely at random. The spontaneous activity of ORNs in rats resembles that of frogs, but is higher, which may be due to a difference in body temperature. These results suggest that, in addition to the intrinsic thermal noise, spontaneous activity is provoked in part by mechanical, thermal, or chemical (odorant molecules) effects of air movements due to respiration, this extrinsic part being naturally larger in FB neurons. It is suggested that spontaneous activity may be modulated by respiration. Because natural sampling of odors is synchronized with breathing, such modulation may prepare and keep olfactory bulb circuits tuned to process odor stimuli.     

Temporal distribution of rapid eye movements and related monophasic potentials in the brain stem following injection of an anticholinesterase.

The temporal distribution of the horizontal rapid eye movements and the related monophasic potentials recorded from the ascending MLF following intravenous injection of o.i mg/kg of anticholinesterase has been investigated in precollicular decerebrate animals. In particular the intervals between individual MLF potentials occurring during successive REM episodes have been evaluated over a total period of 2000 sec on each experiment. 2. There was a bimodal distribution of intervals due to the fact that all the rapid eye movements and the related MLF potentials were grouped in bursts which occurred at quite regular intervals. 3. During the cholinergically induced episodes of REM, there were usually bursts of REM in one direction followed by bursts of REM in the opposite direction. The mean number of individual eye movements within each burst was 4.67 +/- 0.84, S.D., while the average interval between the individual eye movements corresponded to 167 +/- 36 msec, S.D. 4. There was a great regularity in the periodic occurrence of the bursts of REM. In particular the mean interval between the beginning of a burst of REM in one direction (i.e., towards the left side) and that of the next train oriented in the opposite direction (i.e., towards the right side) was 1.97 +/- 0.47 sec, S.D., while the mean interval between the beginning of this last train and that of the successive train oriented in the former direction corresponded to 2.97 +/- 0.48 sec, S.D. Moreover, the duration of the whole period corresponding to the interval between two successive bursts of REM oriented in the same direction (i.e., towards left or towards right) corresponded on average to 4.94 +/- 0.55 sec S.D. and 4.99 +/- 0.52 sec, S.D. respectively. 5. In addition to these "simple bursts" of rapid eye movements oriented in one direction, there were "complex bursts" in which an alternation of the individual eye movements within each burst was observed. In these instances the mean number of spikes was greater (5.35 +/- 1.20, S.D.) and the mean interval shorter 119 +/- 44 msec, S.D.) than those observed in the "simple bursts", About 10-15% of the bursts occurring during the cholinergically induced REM episodes were of the complex type. 6. These findings obtained from an individual experiment were confirmed in all the decerebrate animals treated with the same dose of anticholinesterase; only slight quantitative differences were detected from case to case. 7. Since the bursts of REM induced by the anticholinesterase depend upon the activity of the vestibular nuclei, it is postulated that cholinergic reticular neurons activate structures which show waxing and waning in their activity before acting on the vestibulo-oculomotor system. This system probably contains the inhibitory interneurons which transform the regularly modulated input into a rhythmic vestibular output...     

幼年大鼠皮层听-视多感觉神经元和听-视信息整合

应用常规电生理学细胞外记录技术,研究了生后3周龄幼年大鼠皮层听-视双模态神经元及听-视信息整合特性,并与成年动物进行对照。在听皮层的背侧,听皮层和视皮层的交界处,即颞-顶-枕联合皮层区,共记录到了324个神经元,其中45个为听-视双模态神经元,占13.9%,远低于成年动物双模态神经元所占比例(42.8%)。这些双模态神经元可分为A-V型,v-A型和a-V型3种类型。根据它们对听-视信息的整合效应,可分为增强型、抑制型和调制型。整合效应与给予的声和光组合刺激的时间间隔有关,以获得整合效应的时间间隔范围为整合时间窗,幼年动物的平均整合时间窗为11.9 ms,远小于成年动物的整合时间窗(平均为23.2 ms)。结果提示,与单模态感觉神经元对模态特异性反应特性一样,皮层听-视双模态神经元生后有一个发育、成熟的过程。研究结果为深入研究中枢神经元多感觉整合机制提供了重要实验资料。     

A self-adapting approach for the detection of bursts and network bursts in neuronal cultures

Dissociated networks of neurons typically exhibit bursting behavior, whose features are strongly influenced by the age of the culture, by chemical/electrical stimulation or by environmental conditions. To help the experimenter in identifying the changes possibly induced by specific protocols, we developed a self-adapting method for detecting both bursts and network bursts from electrophysiological activity recorded by means of micro-electrode arrays. The algorithm is based on the computation of the logarithmic inter-spike interval histogram and automatically detects the best threshold to distinguish between inter- and intra-burst inter-spike intervals for each recording channel of the array. An analogous procedure is followed for the detection of network bursts, looking for sequences of closely spaced single-channel bursts. We tested our algorithm on recordings of spontaneous as well as chemically stimulated activity, comparing its performance to other methods available in the literature.     

帕金森病大鼠中缝背核5-羟色胺能神经元放电频率和放电形式的变化

实验采用玻璃微电极细胞外记录法, 观察了帕金森病(Parkinson’s disease, PD)大鼠中缝背核(dorsal raphe nucleus, DRN)5- 羟色胺(5-hydroxytrypamine, 5-HT)能神经元电活动的变化。结果发现, 对照组和 PD 组大鼠 DRN 中 5-HT 能神经元的放电频率分别为(1.61 ±0.56) Hz 和(2.61 ±1.97) Hz, PD 组大鼠的放电频率显著高于对照组(P<0.05)。在对照组大鼠, 79% 的神经元呈现规则放电, 21% 为爆发式放电;在 PD 组大鼠,具有规则、不规则和爆发式放电的神经元比例分别为 36%、16% 和47%, 爆发式放电的 5-HT 能神经元比例明显高于对照组(P<0.05)。结果表明,帕金森病大鼠 DRN 中 5-HT 能神经元的放电频率增高, 且爆发式放电增多。     

Pattern and correlation of fast and slow spontaneous unit activity in the visual cortex

Spontaneous unit activity in the visual cortex and its changes during stimulation by continuous light or flashes were investigated in waking rabbits. The study of distributions of adjacent intervals showed that the neurons differ in the ratio of burst (fast, with intervals of up to 15–40 msec) and nonburst (slow) activity and in the character of changes from one type of activity to the other. Of the total number of spikes 63% were outside bursts; the ratio of their number to the number of spikes within bursts consisting of two or of three or more spikes was 27:3:1. The relative stability of the burst structure of spontaneous activity and the limited number of spikes in them (on average 2.4) were demonstrated. Bursts of three or more spikes (mean 3.6) were irregular, and in 79% of them a longer interval (18.6±2.4 msec) was observed before the shortest interval (7.9±0.9 msec). Bursts of spikes of most neurons during photic stimulation contain more spikes with shorter intervals; they also began more frequently with the shortest interval, possibly signifying an increase in the steepness and amplitude of the EPSPs lying at their basis. However, in 20% of neurons spontaneous bursts included more spikes and with shorter intervals than bursts evoked by flash stimulation.Research Institute of Psychiatry, Ministry of Health of the RSFSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 4, pp. 311–320, July–August, 1979.     

Ionic mechanisms underlying spontaneous CA1 neuronal firing in Ca2+-free solution

Hippocampal CA1 neurons exposed to zero-[Ca(2+)] solutions can generate periodic spontaneous synchronized activity in the absence of synaptic function. Experiments using hippocampal slices showed that, after exposure to zero-[Ca(2+)](0) solution, CA1 pyramidal cells depolarized 5-10 mV and started firing spontaneous action potentials. Spontaneous single neuron activity appeared in singlets or was grouped into bursts of two or three action potentials. A 16-compartment, 23-variable cable model of a CA1 pyramidal neuron was developed to study mechanisms of spontaneous neuronal bursting in a calcium-free extracellular solution. In the model, five active currents (a fast sodium current, a persistent sodium current, an A-type transient potassium current, a delayed rectifier potassium current, and a muscarinic potassium current) are included in the somatic compartment. The model simulates the spontaneous bursting behavior of neurons in calcium-free solutions. The mechanisms underlying several aspects of bursting are studied, including the generation of triplet bursts, spike duration, burst termination, after-depolarization behavior, and the prolonged inactive period between bursts. We show that the small persistent sodium current can play a key role in spontaneous CA1 activity in zero-calcium solutions. In particular, it is necessary for the generation of an after-depolarizing potential and prolongs both individual bursts and the interburst interval.     

Electrophysiological approach of the antiepileptic effect of dexamethasome on hippocampal slice culture usihg a multirecording system: The physiocard®

The in vitro antiepileptic activity of the synthetic glucocorticoid dexamethasone (DEX) was tested in rat hippocampal organotypic cultures on the field potential epileptiform activity induced by picrotoxin (PTX). Spontaneous as well as evoked electrophysiological activities have been studied through the extracellular multirecording Physiocard® system. PTX typically elicited seizure-like discharges (epileptiform bursts) in the hippocampus neurons. Those epileptiform bursts can be divided in two groups, one rhythmic which lasted 43 ± 24s (mean ± sd) at a frequency of 4.6 ± 1.9Hz and the other arhythmic composed of population spikes, which occurred during 14.3 ± 6.9min. In the presence of DEX at different concentrations, results obtained were: 1) DEX 1μM decreased the occurrence of the two different groups of spontaneous epileptiform bursts, most of the time to zero. 2) DEX 50μM prevented totally the occurrence of epileptiform bursts. 3) DEX 50μM contrarily to DEX 1μM avoided the decrease of evoked field potentials' amplitude induced by PTX 3μM on all simultaneous recorded points. Those results suggest that synthetic glucocorticoid DEX presents an acute antiepileptic effect in a dose dependent manner on the hippocampus tissue.     

Plasticity of recurring spatiotemporal activity patterns in cortical networks

How do neurons encode and store information for long periods of time? Recurring patterns of activity have been reported in various cortical structures and were suggested to play a role in information processing and memory. To study the potential role of bursts of action potentials in memory mechanisms, we investigated patterns of spontaneous multi-single-unit activity in dissociated rat cortical cultures in vitro. Spontaneous spikes were recorded from networks of approximately 50 000 neurons and glia cultured on a grid of 60 extracellular substrate- embedded electrodes (multi-electrode arrays). These networks expressed spontaneous culture- wide bursting from approximately one week in vitro. During bursts, a large portion of the active electrodes showed elevated levels of firing. Spatiotemporal activity patterns within spontaneous bursts were clustered using a correlation-based clustering algorithm, and the occurrences of these burst clusters were tracked over several hours. This analysis revealed spatiotemporally diverse bursts occurring in well-defined patterns, which remained stable for several hours. Activity evoked by strong local tetanic stimulation resulted in significant changes in the occurrences of spontaneous bursts belonging to different clusters, indicating that the dynamical flow of information in the neuronal network had been altered. The diversity of spatiotemporal structure and long-term stability of spontaneous bursts together with their plastic nature strongly suggests that such network patterns could be used as codes for information transfer and the expression of memories stored in cortical networks.     

Multiple neural oscillators and muscle feedback are required for the intestinal fed state motor program

After a meal, the gastrointestinal tract exhibits a set of behaviours known as the fed state. A major feature of the fed state is a little understood motor pattern known as segmentation, which is essential for digestion and nutrient absorption. Segmentation manifests as rhythmic local constrictions that do not propagate along the intestine. In guinea-pig jejunum in vitro segmentation constrictions occur in short bursts together with other motor patterns in episodes of activity lasting 40-60 s and separated by quiescent episodes lasting 40-200 s. This activity is induced by luminal nutrients and abolished by blocking activity in the enteric nervous system (ENS). We investigated the enteric circuits that regulate segmentation focusing on a central feature of the ENS: a recurrent excitatory network of intrinsic sensory neurons (ISNs) which are characterized by prolonged after-hyperpolarizing potentials (AHPs) following their action potentials. We first examined the effects of depressing AHPs with blockers of the underlying channels (TRAM-34 and clotrimazole) on motor patterns induced in guinea-pig jejunum, in vitro, by luminal decanoic acid. Contractile episode durations increased markedly, but the frequency and number of constrictions within segmenting bursts and quiescent period durations were unaffected. We used these observations to develop a computational model of activity in ISNs, excitatory and inhibitory motor neurons and the muscle. The model predicted that: i) feedback to ISNs from contractions in the circular muscle is required to produce alternating activity and quiescence with the right durations; ii) transmission from ISNs to excitatory motor neurons is via fast excitatory synaptic potentials (EPSPs) and to inhibitory motor neurons via slow EPSPs. We conclude that two rhythm generators regulate segmentation: one drives contractions within segmentation bursts, the other the occurrence of bursts. The latter depends on AHPs in ISNs and feedback to these neurons from contraction of the circular muscle.     

帕金森病大鼠中缝背核5-羟色胺能神经元电活动的变化

本实验采用玻璃微电极细胞外记录法,观察了帕金森病(Parkinson’s disease,PD)大鼠中缝背核(dorsal raphe nucleus, DRN)5-羟色胺(5-hydroxytryptamine,5-HT)能神经元电活动的变化。在大鼠右侧中脑黑质致密部内微量注射6-羟多巴胺(6- hydroxydopamine,6-OHDA)制作PD模型。结果显示,对照组和PD组大鼠DRN中5-HT能神经元的放电频率分别是(1．76±0．11)spikes／s(n=24)和(2．43±0．17)spikes／(n=21),PD组大鼠的放电频率显著高于对照组(P<0．001)。在对照组大鼠,92％(22／24)的神经元呈规则放电,8％(2／24)为爆发式放电;在PD组大鼠,具有规则、不规则和爆发式放电的神经元比例分别为9％(2／21)、43％(9／21)和48％(10／21),爆发式放电的5-HT能神经元比例明显高于对照组(P<0．001)。在对照组大鼠,DRN内局部注射5-HT1A拮抗剂WAY-100635(3μg/200nL)显著增加5-HT能神经元的放电频率而不影响其放电形式(n=19,P<0．002);而WAY-100635不改变PD组大鼠5-HT能神经元的放电频率和放电形式(n=17,P>0．05)。结果提示,用6-OHDA损毁黑质致密部造成的PD模型大鼠中神经元5-HT1A受体功能失调,并且DRN参与PD的病理生理学机制。     

Development of patterns of activity in diaphragm of fetal lamb early in gestation

To examine the development of respiratory motor activity early in mammalian development and its relationship to nonrespiratory activity, we recorded spontaneous electromyogram activity from chronically instrumented fetal lambs over the period from 45 to 65 days' gestation (G45 to G65, term = G147). Two distinct forms of motor behavior were observed at G45 in recordings made from the costal diaphragm and longissimus dorsi muscles. The predominant behavior consisted of cycles of sustained, coincident activity in the two muscles alternating with periods of inactivity. The incidence of this type of activity declined between G45 and G65 and the cyclic nature of the discharges disappeared in most animals. The second form of motor behavior at G45 consisted of episodes of repetitive bursting activity lasting up to 20 min that were confined to the diaphragm. These bursts had a duration of 97.5 ± 8.3 ms (mean ± S.E.M.) and frequently occurred as doublets in which two bursts were separated by an intervening period of 100–200 ms. The mean duration of these bursts declined to 69.7 ± 7.7 ms at G65, doublets became rare, and bursts evolved a stereotyped form by G65 that was characterized by an abrupt onset and rapid decline in discharge intensity. Repetitive bursts of this form evolve into the mature respiratory motor pattern over the second half of gestation. At G45, episodes of repetitive bursting were almost always linked with episodes of sustained discharge, while at G65 these two forms of behavior were always segregated. We conclude that the neurons responsible for generating the respiratory rhythm in the lamb are assembled into a functional rhythm generator and make appropriate connections to motor output pathways as early as G45. The generation of the respiratory rhythm at G45 appears to be triggered by episodes of widespread motor activity that occur in both respiratory and nonrespiratory muscles. © 1996 John Wiley & Sons, Inc.