Analysis and Modeling of Ensemble Recordings from Respiratory Pre-Motor Neurons Indicate Changes in Functional Network Architecture after Acute Hypoxia

We have combined neurophysiologic recording, statistical analysis, and computational modeling to investigate the dynamics of the respiratory network in the brainstem. Using a multielectrode array, we recorded ensembles of respiratory neurons in perfused in situ rat preparations that produce spontaneous breathing patterns, focusing on inspiratory pre-motor neurons. We compared firing rates and neuronal synchronization among these neurons before and after a brief hypoxic stimulus. We observed a significant decrease in the number of spikes after stimulation, in part due to a transient slowing of the respiratory pattern. However, the median interspike interval did not change, suggesting that the firing threshold of the neurons was not affected but rather the synaptic input was. A bootstrap analysis of synchrony between spike trains revealed that both before and after brief hypoxia, up to 45% (but typically less than 5%) of coincident spikes across neuronal pairs was not explained by chance. Most likely, this synchrony resulted from common synaptic input to the pre-motor population, an example of stochastic synchronization. After brief hypoxia most pairs were less synchronized, although some were more, suggesting that the respiratory network was transiently “rewired” after the stimulus. To investigate this hypothesis, we created a simple computational model with feed-forward divergent connections along the inspiratory pathway. Assuming that (1) the number of divergent projections was not the same for all presynaptic cells, but rather spanned a wide range and (2) that the stimulus increased inhibition at the top of the network; this model reproduced the reduction in firing rate and bootstrap-corrected synchrony subsequent to hypoxic stimulation observed in our experimental data

Statistical Analysis of Multi-Cell Recordings: Linking Population Coding Models to Experimental Data

Modern recording techniques such as multi-electrode arrays and two-photon imaging methods are capable of simultaneously monitoring the activity of large neuronal ensembles at single cell resolution. These methods finally give us the means to address some of the most crucial questions in systems neuroscience: what are the dynamics of neural population activity? How do populations of neurons perform computations? What is the functional organization of neural ensembles? While the wealth of new experimental data generated by these techniques provides exciting opportunities to test ideas about how neural ensembles operate, it also provides major challenges: multi-cell recordings necessarily yield data which is high-dimensional in nature. Understanding this kind of data requires powerful statistical techniques for capturing the structure of the neural population responses, as well as their relationship with external stimuli or behavioral observations. Furthermore, linking recorded neural population activity to the predictions of theoretical models of population coding has turned out not to be straightforward. These challenges motivated us to organize a workshop at the 2009 Computational Neuroscience Meeting in Berlin to discuss these issues. In order to collect some of the recent progress in this field, and to foster discussion on the most important directions and most pressing questions, we issued a call for papers for this Research Topic. We asked authors to address the following four questions: 1. What classes of statistical methods are most useful for modeling population activity? 2. What are the main limitations of current approaches, and what can be done to overcome them? 3. How can statistical methods be used to empirically test existing models of (probabilistic) population coding? 4. What role can statistical methods play in formulating novel hypotheses about the principles of information processing in neural populations? A total of 15 papers addressing questions related to these themes are now collected in this Research Topic. Three of these articles have resulted in “Focused reviews” in Frontiers in Neuroscience (Crumiller et al., 2011; Rosenbaum et al., 2011; Tchumatchenko et al., 2011), illustrating the great interest in the topic. Many of the articles are devoted to a better understanding of how correlations arise in neural circuits, and how they can be detected, modeled, and interpreted. For example, by modeling how pairwise correlations are transformed by spiking non-linearities in simple neural circuits, Tchumatchenko et al. (2010) show that pairwise correlation coefficients have to be interpreted with care, since their magnitude can depend strongly on the temporal statistics of their input-correlations. In a similar spirit, Rosenbaum et al. (2010) study how correlations can arise and accumulate in feed-forward circuits as a result of pooling of correlated inputs. Lyamzin et al. (2010) and Krumin et al. (2010) present methods for simulating correlated population activity and extend previous work to more general settings. The method of Lyamzin et al. (2010) allows one to generate synthetic spike trains which match commonly reported statistical properties, such as time varying firing rates as well signal and noise correlations. The Hawkes framework presented by Krumin et al. (2010) allows one to fit models of recurrent population activity to the correlation-structure of experimental data. Louis et al. (2010) present a novel method for generating surrogate spike trains which can be useful when trying to assess the significance and time-scale of correlations in neural spike trains. Finally, Pipa and Munk (2011) study spike synchronization in prefrontal cortex during working memory. A number of studies are also devoted to advancing our methodological toolkit for analyzing various aspects of population activity (Gerwinn et al., 2010; Machens, 2010; Staude et al., 2010; Yu et al., 2010). For example, Gerwinn et al. (2010) explain how full probabilistic inference can be performed in the popular model class of generalized linear models (GLMs), and study the effect of using prior distributions on the parameters of the stimulus and coupling filters. Staude et al. (2010) extend a method for detecting higher-order correlations between neurons via population spike counts to non-stationary settings. Yu et al. (2010) describe a new technique for estimating the information rate of a population of neurons using frequency-domain methods. Machens (2010) introduces a novel extension of principal component analysis for separating the variability of a neural response into different sources. Focusing less on the spike responses of neural populations but on aggregate signals of population activity, Boatman-Reich et al. (2010) and Hoerzer et al. (2010) describe methods for a quantitative analysis of field potential recordings. While Boatman-Reich et al. (2010) discuss a number of existing techniques in a unified framework and highlight the potential pitfalls associated with such approaches, Hoerzer et al. (2010) demonstrate how multivariate autoregressive models and the concept of Granger causality can be used to infer local functional connectivity in area V4 of behaving macaques. A final group of studies is devoted to understanding experimental data in light of computational models (Galán et al., 2010; Pandarinath et al., 2010; Shteingart et al., 2010). Pandarinath et al. (2010) present a novel mechanism that may explain how neural networks in the retina switch from one state to another by a change in gap junction coupling, and conjecture that this mechanism might also be found in other neural circuits. Galán et al. (2010) present a model of how hypoxia may change the network structure in the respiratory networks in the brainstem, and analyze neural correlations in multi-electrode recordings in light of this model. Finally, Shteingart et al. (2010) show that the spontaneous activation sequences they find in cultured networks cannot be explained by Zipf’s law, but rather require a wrestling model. The papers of this Research Topic thus span a wide range of topics in the statistical modeling of multi-cell recordings. Together with other recent advances, they provide us with a useful toolkit to tackle the challenges presented by the vast amount of data collected with modern recording techniques. The impact of novel statistical methods on the field and their potential to generate scientific progress, however, depends critically on how readily they can be adopted and applied by laboratories and researchers working with experimental data. An important step toward this goal is to also publish computer code along with the articles (Barnes, 2010) as a successful implementation of advanced methods also relies on many details which are hard to communicate in the article itself. In this way it becomes much more likely that other researchers can actually use the methods, and unnecessary re-implementations can be avoided. Some of the papers in this Research Topic already follow this goal (Gerwinn et al., 2010; Louis et al., 2010; Lyamzin et al., 2010). We hope that this practice becomes more and more common in the future and encourage authors and editors of Research Topics to make as much code available as possible, ideally in a format that can be easily integrated with existing software sharing initiatives (Herz et al., 2008; Goldberg et al., 2009)

Leptin counteracts the hypoxia-induced inhibition of spontaneously firing hippocampal neurons: a microelectrode array study.

Besides regulating energy balance and reducing body-weight, the adipokine leptin has been recently shown to be neuroprotective and antiapoptotic by promoting neuronal survival after excitotoxic and oxidative insults. Here, we investigated the firing properties of mouse hippocampal neurons and the effects of leptin pretreatment on hypoxic damage (2 hours, 3% O(2)). Experiments were carried out by means of the microelectrode array (MEA) technology, monitoring hippocampal neurons activity from 11 to 18 days in vitro (DIV). Under normoxic conditions, hippocampal neurons were spontaneously firing, either with prevailing isolated and randomly distributed spikes (11 DIV), or with patterns characterized by synchronized bursts (18 DIV). Exposure to hypoxia severely impaired the spontaneous activity of hippocampal neurons, reducing their firing frequency by 54% and 69%, at 11 and 18 DIV respectively, and synchronized their firing activity. Pretreatment with 50 nM leptin reduced the firing frequency of normoxic neurons and contrasted the hypoxia-induced depressive action, either by limiting the firing frequency reduction (at both ages) or by increasing it to 126% (in younger neurons). In order to find out whether leptin exerts its effect by activating large conductance Ca(2+)-activated K(+) channels (BK), as shown on rat hippocampal neurons, we applied the BK channel blocker paxilline (1 µM). Our data show that paxilline reversed the effects of leptin, both on normoxic and hypoxic neurons, suggesting that the adipokine counteracts hypoxia through BK channels activation in mouse hippocampal neurons

Le stress et les acides gras polyinsaturés oméga-3, deux facteurs environnementaux qui influencent le chémoréflexe laryngé chez le raton

Le chémoréflexe laryngé (CRL), un ensemble de réponses physiologiques servant à protéger les voies respiratoires inférieures, est provoqué par la présence de liquide, consiste en une toux accompagnée de déglutition, de la fermeture du larynx, de l’éveil et de l’augmentation de la pression artérielle systémique. Chez un nouveau-né prématuré ou un raton, le CRL est immature et la stimulation de celui-ci provoque une apnée accompagnée de désaturation en O2, de bradycardie, d’un laryngospasme et d’une redistribution du débit sanguin aux organes vitaux. L’apnée du prématuré, le malaise grave du nourrisson et le syndrome de la mort subite du nourrisson sont des exemples de pathologies qui sont très probablement reliées à des évènements cardiorespiratoires observés chez les nouveau-nés prématurés. Le syndrome de la mort subite du nourrisson atteint principalement les garçons et un CRL immature est fortement soupçonné d’y être impliqué dans certains cas. La séparation maternelle néonatale (SMN) est connue pour provoquer un retard de développement du circuit neuronal contrôlant la respiration, mais quel est son effet sur le développement du CRL? Des études montrent que les n-3 PUFA favoriseraient le développement du poumon et du système nerveux central, mais est-ce que ceux-ci ont un effet au niveau du développement de la respiration au sens plus large? L’hypothèse de cette thèse est que l’environnement est capable d’avoir un impact sur le chémoréflexe laryngé chez le jeune raton. La SMN consiste en la séparation des ratons de leur mère et du reste de la portée dans un incubateur à température (35 °C) et humidité (45 %) contrôlés 3 h par jour du 3e jour de vie au 12e. Les expériences ont eu lieu au 14e et 15e jour. La SMN augmente les effets délétères de la stimulation du CRL, surtout chez les mâles. Nous avons réalisé 3 stimulations du CRL (injections de 10µL d’eau à proximité du larynx) séparées par 5 minutes de récupération. L’inhibition cardio-respiratoire due au CRL augmentait avec le nombre de stimulations. Nous avons étudié les courants des neurones des régions impliquées dans le CRL : le noyau du tractus solitaire (NTS, qui est le centre d’intégration des données provenant entre autres du larynx) et le noyau moteur dorsal du nerf vague (DMNV, impliqué dans la bradycardie). Au niveau du DMNV, nous avons observé une augmentation de la fréquence et de l’amplitude des courants postsynaptiques excitateurs (EPSCs) chez les animaux stressés. La tétrodotoxine (TTX) a un effet plus important chez les animaux stressés vs contrôles. Cela nous permet de déduire qu’au niveau du DMNV les afférences arrivant sur ces neurones sont plus nombreuses chez les animaux stressés vs contrôles. Une explication serait que l’élagage synaptique réalisé par la microglie est perturbé par la SMN. L’analyse de la microglie au niveau du NTS et du DMNV montre que le stress modifie le phénotype de la microglie, ce qui perturberait la fonction d’élagage synaptique. Mais l’étude ne démontre pas d’effet du stress au niveau de la communication neurones-microglie. Le stress provoqué par la SMN a des effets délétères sur le CRL, surtout chez les mâles, en provoquant une augmentation de l’inhibition cardio-respiratoire due au CRL. Cet effet serait dû à un défaut de l’élagage synaptique dans les régions impliquées dans le CRL, notamment au niveau des neurones responsables de la bradycardie. Le système respiratoire étant immature chez le nouveau-né prématuré, nous avons testé l’hypothèse que la supplémentation maternelle en acide gras polyinsaturé n-3 (AGPI n-3) pouvait accélérer la maturation de celui-ci. Les expériences ont eu lieu aux 10e et 11e jours de vie chez les ratons. La supplémentation maternelle en AGPI n-3 réduit l’apnée due au CRL et favorise le développement de la réponse ventilatoire à l’hypoxie et des poumons. Cependant, le traitement augmente le nombre d’instabilités respiratoires et provoque un retard de développement de la microglie dont l’impact est inconnu. Les AGPI n-3 seraient un bon traitement pour favoriser le développement du système nerveux contrôlant la respiration; cependant, il faudrait approfondir l’étude afin de s’assurer que certains effets des AGPI n-3 n’aient pas de conséquences indésirables. Le stress favorise les effets délétères dus à la stimulation du CRL chez le raton en augmentant le signal arrivant sur les neurones impliqués dans la réponse cardio-respiratoire au CRL, ce qui pourrait s’expliquer par un défaut d’élagage synaptique. Si l’on doit favoriser le développement du système respiratoire chez l’animal immature, les AGPI n-3 seraient une bonne option.Laryngeal chemoreflex (LCR) is a set of physiological responses to protect lower airways from liquids and include coughing and swallowing, larynx closure, arousal, and systemic arterial pressure increase. In preterm infants or young rats, LCR is immature and elicits apnea, O2 desaturation, bradycardia, laryngospasm and redistribution of blood flow to vital organs. Apnea of prematurity, apparent life threatening events and sudden infant death syndrome (SIDS) are examples of pathology strongly suspected to be linked to cardiorespiratory events observed in preterm infants. SIDS is more prevalent in males and immature LCR is suspected to be involved in a few SIDS cases. Neonatal maternal separation (NMS) is known to delay development of control of breathing neuronal networks but what is its effect on LCR development? Studies have shown that n-3 PUFA promote lung and central nervous system development but could they have an effect on respiratory development? The thesis hypothesis is that environment could influence LCR in rat pups. NMS consists in the separation of pups from their mother and the rest of the litter in an incubator at a controlled temperature (35°C) and humidity (45%), 3h per day from post-natal day 3 (P3) to P12. Experiments were performed at P14-15. SMN increases deleterious effect of LCR stimulation especially in males. We have performed 3 LCR stimulations (with 10µl of water injected close to the larynx) separated by 5 minutes of recovery for each. We have observed that LCR cardiorespiratory inhibition increased with the number of stimulations. We have studied excitatory currents in neurons in regions involved in LCR: nucleus tractus solitarius (NTS, integration center of information coming from the larynx) and dorsal motor nucleus of the vagus nerve (DMNV, involved in bradycardia). In the DMNV we have seen an increase in excitatory post-synaptic currents (EPSCs) frequency and amplitude in stressed animals. Tetrodotoxin (TTX) has a more important effect on stressed animals vs controls. These findings allow us to hypothesize that afferents arriving on neurons in the DMNV are more numerous in stressed animals than in controls. One explanation of these results could be that synaptic pruning made by microglia is disrupted by NMS. Microglial analysis in the NTS and DMNV shows that NMS changes microglia phenotype which could disrupt synaptic pruning. However, this study did not demonstrate any disturbance from stress in neurons/microglia communication. Stress issuing from NMS delays LCR development, especially in males, by causing an increase in cardio-respiratory inhibition following LCR stimulation. This effect would be due to a synaptic pruning abnormality in neuronal regions involved in LCR, especially those involved in bradycardia. The respiratory system is immature in preterm infants. To accelerate maturation of this system, we have tested the effect of n-3 PUFA maternal supplementation. Experiments were performed in P10-11 rat pups. Maternal supplementation of n-3 PUFA reduced apnea duration caused by LCR stimulation, promoted hypoxic ventilatory response development and lungs development. However, the treatment increases the number of respiratory instabilities and induces a delay of microglial development whose impacts we do not know. N-3 PUFA maternal supplementation could be an interesting treatment to promote control of breathing development. That said, we should further the study to be sure that the unexpected effects of this treatment have no undesirable consequences. Stress increases the deleterious effects of LCR stimulation in rat pups by increasing the signal arriving on neurons involved in LCR cardiorespiratory response. This phenomenon could be explained by a disruption of synaptic pruning. If we look at a treatment to enhance respiratory system development in immature animals, n-3 PUFA is an option which should be considered

Advances in Clinical Neurophysiology

Including some of the newest advances in the field of neurophysiology, this book can be considered as one of the treasures that interested scientists would like to collect. It discusses many disciplines of clinical neurophysiology that are, currently, crucial in the practice as they explain methods and findings of techniques that help to improve diagnosis and to ensure better treatment. While trying to rely on evidence-based facts, this book presents some new ideas to be applied and tested in the clinical practice. Advances in Clinical Neurophysiology is important not only for the neurophysiologists but also for clinicians interested or working in wide range of specialties such as neurology, neurosurgery, intensive care units, pediatrics and so on. Generally, this book is written and designed to all those involved in, interpreting or requesting neurophysiologic tests

Activation of the pro-resolving receptor Fpr2 attenuates inflammatory microglial activation

Poster number: P-T099 Theme: Neurodegenerative disorders & ageing Activation of the pro-resolving receptor Fpr2 reverses inflammatory microglial activation Authors: Edward S Wickstead - Life Science & Technology University of Westminster/Queen Mary University of London Inflammation is a major contributor to many neurodegenerative disease (Heneka et al. 2015). Microglia, as the resident immune cells of the brain and spinal cord, provide the first line of immunological defence, but can become deleterious when chronically activated, triggering extensive neuronal damage (Cunningham, 2013). Dampening or even reversing this activation may provide neuronal protection against chronic inflammatory damage. The aim of this study was to determine whether lipopolysaccharide (LPS)-induced inflammation could be abrogated through activation of the receptor Fpr2, known to play an important role in peripheral inflammatory resolution. Immortalised murine microglia (BV2 cell line) were stimulated with LPS (50ng/ml) for 1 hour prior to the treatment with one of two Fpr2 ligands, either Cpd43 or Quin-C1 (both 100nM), and production of nitric oxide (NO), tumour necrosis factor alpha (TNFα) and interleukin-10 (IL-10) were monitored after 24h and 48h. Treatment with either Fpr2 ligand significantly suppressed LPS-induced production of NO or TNFα after both 24h and 48h exposure, moreover Fpr2 ligand treatment significantly enhanced production of IL-10 48h post-LPS treatment. As we have previously shown Fpr2 to be coupled to a number of intracellular signaling pathways (Cooray et al. 2013), we investigated potential signaling responses. Western blot analysis revealed no activation of ERK1/2, but identified a rapid and potent activation of p38 MAP kinase in BV2 microglia following stimulation with Fpr2 ligands. Together, these data indicate the possibility of exploiting immunomodulatory strategies for the treatment of neurological diseases, and highlight in particular the important potential of resolution mechanisms as novel therapeutic targets in neuroinflammation. References Cooray SN et al. (2013). Proc Natl Acad Sci U S A 110: 18232-7. Cunningham C (2013). Glia 61: 71-90. Heneka MT et al. (2015). Lancet Neurol 14: 388-40

Lycium barbarum (wolfberry) polysaccharide facilitates ejaculatory behaviour in male rats

Poster Session AOBJECTIVE: Lycium barbarum (wolfberry) is a traditional Chinese medicine, which has been considered to have therapeutic effect on male infertility. However, there is a lack of studies support the claims. We thus investigated the effect of Lycium barbarum polysaccharide (LBP), a major component of wolfberry, on male rat copulatory behavior. METHOD: Sprague-Dawley rats were divided into two groups (n=8 for each group). The first group received oral feeding of LBP at dosage of 1mg/kg daily. The control group received vehicle (0.01M phosphate-buffered saline, served as control) feeding daily for 21 days. Copulatory tests were conducted at 7, 14 and 21 days after initiation of treatment. RESULTS: Compared to control animals, animals fed with 1mg/kg LBP showed improved copulatory behavior in terms of: 1. Higher copulatory efficiency (i.e. higher frequency to show intromission rather than mounting during the test), 2. higher ejaculation frequency and 3. Shorter ejaculation latency. The differences were found at all time points (Analyzed with two-tailed student’s t-test, p<0.05). There is no significant difference found between the two groups in terms of mount/intromission latency, which indicates no difference in time required for initiation of sexual activity. Additionally, no difference in mount frequency and intromission frequency was found. CONCLUSION: The present study provides scientific evidence for the traditional use of Lycium barbarum on male sexual behavior. The result provides basis for further study of wolfberry on sexual functioning and its use as an alternative treatment in reproductive medicine.postprintThe 30th Annual Meeting of the Australian Neuroscience Society, in conjunction with the 50th Anniversary Meeting of the Australian Physiological Society (ANS/AuPS 2010), Sydney, Australia, 31 January-3 February 2010. In Abstract Book of ANS/AuPS, 2010, p. 177, abstract no. POS-TUE-19