Transient Signals Trigger Synchronous Bursts in an Identified Population of Neurons

2009 ◽  
Vol 102 (2) ◽  
pp. 714-723 ◽  
Author(s):  
Gary Marsat ◽  
Rémi D. Proville ◽  
Leonard Maler

It is an important task in neuroscience to find general principles that relate neural codes to the structure of the signals they encode. The structure of sensory signals can be described in many ways, but one important categorization distinguishes continuous from transient signals. We used the communication signals of the weakly electric fish to reveal how transient signals (chirps) can be easily distinguished from the continuous signal they disrupt. These communication signals—low-frequency sinusoids interrupted by high-frequency transients—were presented to pyramidal cells of the electrosensory lateral line lobe (ELL) during in vivo recordings. We show that a specific population of electrosensory neurons encodes the occurrence of the transient signal by synchronously producing a burst of spikes, whereas bursting was neither common nor synchronous in response to the continuous signal. We also confirmed that burst can be triggered by low-frequency modulations typical of prey signals. However, these bursts are more common in a different segment of the ELL and during spatially localized stimulation. These localized stimuli will elicit synchronized bursting only in a restricted number of cells the receptive fields of which overlap the spatial extent of the stimulus. Therefore the number of cells simultaneously producing a burst and the ELL segment responding most strongly may carry the information required to disambiguate chirps from prey signals. Finally we show that the burst response to chirps is due to a biophysical mechanism previously characterized by in vitro studies of electrosensory neurons. We conclude that bursting and synchrony across cells are important mechanisms used by sensory neurons to carry the information about behaviorally relevant but transient signals.

1999 ◽  
Vol 202 (10) ◽  
pp. 1255-1265 ◽  
Author(s):  
R.W. Turner ◽  
L. Maler

Oscillatory and burst discharge is recognized as a key element of signal processing from the level of receptor to cortical output cells in most sensory systems. The relevance of this activity for electrosensory processing has become increasingly apparent for cells in the electrosensory lateral line lobe (ELL) of gymnotiform weakly electric fish. Burst discharge by ELL pyramidal cells can be recorded in vivo and has been directly associated with feature extraction of electrosensory input. In vivo recordings have also shown that pyramidal cells are differentially tuned to the frequency of amplitude modulations across three ELL topographic maps of electroreceptor distribution. Pyramidal cell recordings in vitro reveal two forms of oscillatory discharge with properties consistent with pyramidal cell frequency tuning in vivo. One is a slow oscillation of spike discharge arising from local circuit interactions that exhibits marked changes in several properties across the sensory maps. The second is a fast, intrinsic form of burst discharge that incorporates a newly recognized interaction between somatic and dendritic membranes. These findings suggest that a differential regulation of oscillatory discharge properties across sensory maps may underlie frequency tuning in the ELL and influence feature extraction in vivo.


1999 ◽  
Vol 202 (10) ◽  
pp. 1243-1253 ◽  
Author(s):  
N.J. Berman ◽  
L. Maler

The electrosensory lateral line lobe (ELL) of weakly electric fish is the only nucleus that receives direct input from peripheral electroreceptor afferents. This review summarises the neurotransmitters, receptors and second messengers identified in the intrinsic circuitry of the ELL and the extrinsic descending direct and indirect feedback pathways, as revealed by recent in vitro and in vivo studies. Several hypotheses of circuitry function are examined on this basis and on the basis of recent functional evidence: (1) fast primary afferent excitatory postsynaptic potentials (EPSPs) and fast granule cell 2 GABAA inhibitory postsynaptic potentials (IPSPs) suggest the involvement of basilar pyramidal cells in coincidence detection; (2) voltage-dependent EPSPs and IPSPs, dendritic spike bursts and frequency-dependent synaptic facilitation support a sensory searchlight role for the direct feedback pathway; and (3) the contributions of distal and proximal inhibition, anti-Hebbian plasticity and beam versus isolated fiber activity patterns are discussed with reference to an adaptive spatio-temporal filtering role for the indirect descending pathway.


1996 ◽  
Vol 76 (4) ◽  
pp. 2364-2382 ◽  
Author(s):  
R. W. Turner ◽  
J. R. Plant ◽  
L. Maler

1. Three parallel maps of the distribution of tuberous electroreceptor inputs are found in the medullary electrosensory lateral line lobe (ELL) of weakly electric fish. Pyramidal cells in each map are known to respond differentially to the frequency of amplitude modulations (AMs) of external electric fields in vivo. We used an in vitro ELL slice preparation of Apteronotus leptorhynchus to compare the characteristics of spontaneously active single units across the three tuberous maps. It was our objective to determine whether spontaneous bursting activity of pyramidal cells in each map correlates with the known AM frequency selectivities of pyramidal cells in vivo. 2. Single-unit discharges were recorded from the pyramidal cell layer of the centromedial segment (CMS), centrolateral segment (CLS), and lateral segment (LS) of the ELL. Stochastic analysis of interspike intervals (ISIs) was used to identify bursting and nonbursting unit activity, and to separately analyze intra- and interburst ISIs. Four ISI patterns were identified as 1) bursting, 2) regular spiking, 3) irregular spiking, and 4) highly irregular spiking. This work focuses primarily on the characteristics of bursting units across the ELL segments. 3. Spontaneous bursting discharge was identified in all three maps (68 of 97 units), with several characteristics changing in a gradual manner across the maps. The coefficient of variation (CV) of ISIs and intraburst ISIs decreased significantly from the CMS to the LS, whereas the CV of burst periods increased significantly from the CMS to the LS. Autocorrelations and power spectral density analysis identified units discharging in an oscillatory manner with the following ratio: CMS, 75%; CLS, 4%; LS, 8%. 4. The mean period of spike bursts decreased significantly across the segments (CMS, 2.7 s; CLS, 1.2 s; LS, 1.1 s) primarily because of a shortening of mean burst duration (CMS, 1.0 s; CLS, 0.1 s; LS, 0.05 s). The average number of spikes per burst decreased significantly across the maps (CMS, 61; CLS, 8; LS, 8), whereas the average frequency of spikes per burst increased (CMS, 90 Hz; CLS, 130 Hz; LS, 178 Hz), mainly through an increase in the maximal frequencies attained by units within each map. 5. Bursts in the CMS were unstructured in that the intraburst ISIs were serially independent, whereas for many units in the CLS and especially the LS there were serial dependencies of successive spikes, with alternating short and long ISIs during the burst. 6. These data reveal that the characteristics of bursting unit activity differ between the CMS, CLS, and LS maps in vitro, implying a modulation of the factors underlying burst discharge across multiple sensory maps. Because the pattern of change in burst activity between these maps parallels that of pyramidal cell AM frequency selectivity in vivo, oscillatory and burst discharge may represent the cellular mechanism used to tune these cells to specific frequencies of afferent input during electrolocation and electrocommunication.


2009 ◽  
Vol 102 (4) ◽  
pp. 2273-2287 ◽  
Author(s):  
Natalia Toporikova ◽  
Maurice J. Chacron

Understanding the mechanistic substrates of neural computations that lead to behavior remains a fundamental problem in neuroscience. In particular, the contributions of intrinsic neural properties such as burst firing and dendritic morphology to the processing of behaviorally relevant sensory input have received much interest recently. Pyramidal cells within the electrosensory lateral line lobe of weakly electric fish display an intrinsic bursting mechanism that relies on somato-dendritic interactions when recorded in vitro: backpropagating somatic action potentials trigger dendritic action potentials that lead to a depolarizing afterpotential (DAP) at the soma. We recorded intracellularly from these neurons in vivo and found firing patterns that were quite different from those seen in vitro: we found no evidence for DAPs as each somatic action potential was followed by a pronounced afterhyperpolarization (AHP). Calcium chelators injected in vivo reduced the AHP, thereby unmasking the DAP and inducing in vitro-like bursting in pyramidal cells. These bursting dynamics significantly reduced the cell's ability to encode the detailed time course of sensory input. We performed additional in vivo pharmacological manipulations and mathematical modeling to show that calcium influx through N-methyl-d-aspartate (NMDA) receptors activate dendritic small conductance (SK) calcium-activated potassium channels, which causes an AHP that counteracts the DAP and leads to early termination of the burst. Our results show that ion channels located in dendrites can have a profound influence on the processing of sensory input by neurons in vivo through the modulation of an intrinsic bursting mechanism.


Microbiology ◽  
2014 ◽  
Vol 160 (2) ◽  
pp. 330-339 ◽  
Author(s):  
Alimatu Sulemana ◽  
Timothy A. Paget ◽  
Edward L. Jarroll

Giardia trophozoites differentiate into infectious cysts (encystment) in response to physiological stimuli; encystment is crucial for Giardia’s transmission, survival and pathogenesis. In vitro, Giardia encysts when bile sequesters lipids necessary for this lipid auxotroph, and in vivo they encyst to infect new hosts. In this study, we investigated, for the first time, commitment to encystment in Giardia using both molecular and cellular techniques. We show that after 3–6 h in inducing conditions, encysting trophozoites continue to encyst regardless of whether the inducing stimulus remains. We propose that a trophozoite’s inability to revert to a growing or dividing trophozoite represents a commitment to encystment. The onset of commitment correlated with the appearance of encystment specific vesicles (ESVs) and encystment specific protein synthesis. These observations suggest the involvement of regulatory pathways with the ability to ‘remember’ a transient signal long after its removal; a property that enables encysting trophozoites to complete the encystment process should the unfavourable triggering condition(s) change. The ability to form cysts in response to transient signals or, as we have highlighted in this paper, the ability of a small percentage of the population to form cysts without an inducer is vital for the maintenance of infection within populations.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yorick Janssens ◽  
Nathan Debunne ◽  
Anton De Spiegeleer ◽  
Evelien Wynendaele ◽  
Marta Planas ◽  
...  

AbstractQuorum sensing peptides (QSPs) are bacterial peptides produced by Gram-positive bacteria to communicate with their peers in a cell-density dependent manner. These peptides do not only act as interbacterial communication signals, but can also have effects on the host. Compelling evidence demonstrates the presence of a gut-brain axis and more specifically, the role of the gut microbiota in microglial functioning. The aim of this study is to investigate microglial activating properties of a selected QSP (PapRIV) which is produced by Bacillus cereus species. PapRIV showed in vitro activating properties of BV-2 microglia cells and was able to cross the in vitro Caco-2 cell model and reach the brain. In vivo peptide presence was also demonstrated in mouse plasma. The peptide caused induction of IL-6, TNFα and ROS expression and increased the fraction of ameboid BV-2 microglia cells in an NF-κB dependent manner. Different metabolites were identified in serum, of which the main metabolite still remained active. PapRIV is thus able to cross the gastro-intestinal tract and the blood–brain barrier and shows in vitro activating properties in BV-2 microglia cells, hereby indicating a potential role of this quorum sensing peptide in gut-brain interaction.


2012 ◽  
Vol 80 (6) ◽  
pp. 1948-1957 ◽  
Author(s):  
Brooke L. Deatherage ◽  
Brad T. Cookson

ABSTRACTInteraction of microbes with their environment depends on features of the dynamic microbial surface throughout cell growth and division. Surface modifications, whether used to acquire nutrients, defend against other microbes, or resist the pressures of a host immune system, facilitate adaptation to unique surroundings. The release of bioactive membrane vesicles (MVs) from the cell surface is conserved across microbial life, in bacteria, archaea, fungi, and parasites. MV production occurs not onlyin vitrobut alsoin vivoduring infection, underscoring the influence of these surface organelles in microbial physiology and pathogenesis through delivery of enzymes, toxins, communication signals, and antigens recognized by the innate and adaptive immune systems. Derived from a variety of organisms that span kingdoms of life and called by several names (membrane vesicles, outer membrane vesicles [OMVs], exosomes, shedding microvesicles, etc.), the conserved functions and mechanistic strategies of MV release are similar, including the use of ESCRT proteins and ESCRT protein homologues to facilitate these processes in archaea and eukaryotic microbes. Although forms of MV release by different organisms share similar visual, mechanistic, and functional features, there has been little comparison across microbial life. This underappreciated conservation of vesicle release, and the resulting functional impact throughout the tree of life, explored in this review, stresses the importance of vesicle-mediated processes throughout biology.


2007 ◽  
Vol 98 (4) ◽  
pp. 2324-2336 ◽  
Author(s):  
Adriano Augusto Cattani ◽  
Valérie Delphine Bonfardin ◽  
Alfonso Represa ◽  
Yehezkel Ben-Ari ◽  
Laurent Aniksztejn

Cell-surface glutamate transporters are essential for the proper function of early cortical networks because their dysfunction induces seizures in the newborn rat in vivo. We have now analyzed the consequences of their inhibition by dl-TBOA on the activity of the developing CA1 rat hippocampal network in vitro. dl-TBOA generated a pattern of recurrent depolarization with an onset and decay of several seconds' duration in interneurons and pyramidal cells. These slow network oscillations (SNOs) were mostly mediated by γ-aminobutyric acid (GABA) in pyramidal cells and by GABA and N-methyl-d-aspartate (NMDA) receptors in interneurons. However, in both cell types SNOs were blocked by NMDA receptor antagonists, suggesting that their generation requires a glutamatergic drive. Moreover, in interneurons, SNOs were still generated after the blockade of NMDA-mediated synaptic currents with MK-801, suggesting that SNOs are expressed by the activation of extrasynaptic NMDA receptors. Long-lasting bath application of glutamate or NMDA failed to induce SNOs, indicating that they are generated by periodic but not sustained activation of NMDA receptors. In addition, SNOs were observed in interneurons recorded in slices with or without the strata pyramidale and oriens, suggesting that the glutamatergic drive may originate from the radiatum and pyramidale strata. We propose that in the absence of an efficient transport of glutamate, the transmitter diffuses in the extracellular space to activate extrasynaptic NMDA receptors preferentially present on interneurons that in turn activate other interneurons and pyramidal cells. This periodic neuronal coactivation may contribute to the generation of seizures when glutamate transport dysfunction is present.


1997 ◽  
Vol 78 (3) ◽  
pp. 1735-1739 ◽  
Author(s):  
Denis Paré ◽  
Elen Lebel ◽  
Eric J. Lang

Paré, Denis, Elen LeBel, and Eric J. Lang. Differential impact of miniature synaptic potentials on the somata and dendrites of pyramidal neurons in vivo. J. Neurophysiol. 78: 1735–1739, 1997. We studied the impact of transmitter release resistant to tetrodotoxin (TTX) in morphologically identified neocortical pyramidal neurons recorded intracellularly in barbiturate-anesthetized cats. It was observed that TTX-resistant release occurs in pyramidal neurons in vivo and at much higher frequencies than was previously reported in vitro. Further, in agreement with previous findings indicating that GABAergic and glutamatergic synapses are differentially distributed in the somata and dendrites of pyramidal cells, we found that most miniature synaptic potentials were sensitive to γ-aminobutyric acid-A (GABAA) or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonists in presumed somatic and dendritic impalements, respectively. Pharmacological blockage of spontaneous synaptic events produced large increases in input resistance that were more important in dendritic (≈50%) than somatic (≈10%) impalements. These findings imply that in the intact brain, pyramidal neurons are submitted to an intense spike-independent synaptic bombardment that decreases the space constant of the cells. These results should be taken into account when extrapolating in vitro findings to intact brains.


2019 ◽  
Author(s):  
JM García-Lobo ◽  
Y Ortiz ◽  
C González-Riancho ◽  
A Seoane ◽  
B Arellano-Reynoso ◽  
...  

AbstractSome Brucella isolates are known to require an increased concentration of CO2 for growth, especially in the case of primary cultures obtained directly from infected animals. Moreover, the different Brucella species and biovars show a characteristic pattern of CO2 requirement, and this trait has been included among the routine typing tests used for species and biovar differentiation. By comparing the differences in gene content among different CO2-dependent and CO2-independent Brucella strains we have confirmed that carbonic anhydrase II (CA II), is the enzyme responsible for this phenotype in all the Brucella strains tested. Brucella species contain two carbonic anhydrases of the β family, CA I and CA II; genetic polymorphisms exist for both of them in different isolates, but only those putatively affecting the activity of CA II correlate with the CO2 requirement of the corresponding isolate. Analysis of these polymorphisms does not allow the determination of CA I functionality, while the polymorphisms in CA II consist of small deletions that cause a frameshift that changes the C-terminus of the protein, probably affecting its dimerization status, essential for the activity.CO2-independent mutants arise easily in vitro, although with a low frequency ranging from 10−6 to 10−10 depending on the strain. These mutants carry compensatory mutations that produce a full length CA II. At the same time, no change was observed in the sequence coding for CA I. A competitive index assay designed to evaluate the fitness of a CO2-dependent strain compared to its corresponding CO2-independent strain revealed that while there is no significant difference when the bacteria are grown in culture plates, growth in vivo in a mouse model of infection provides a significant advantage to the CO2-dependent strain. This could explain why some Brucella isolates are CO2-dependent in primary isolation. The polymorphism described here also allows the in silico determination of the CO2 requirement status of any Brucella strain.


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