Rhythmically active networks are typically composed of neurons that can be classified as silent, tonic spiking, or rhythmic bursting based on their intrinsic activity patterns. Within these networks, neurons are thought to discharge in distinct phase relationships with their overall network output, and it has been hypothesized that bursting pacemaker neurons may lead and potentially trigger cycle onsets. We used multielectrode recording from 72 experiments to test these ideas in rhythmically active slices containing the pre-Bötzinger complex, a region critical for breathing. Following synaptic blockade, respiratory neurons exhibited a gradient of intrinsic spiking to rhythmic bursting activities and thus defied an easy classification into bursting pacemaker and nonbursting categories. Features of their firing activity within the functional network were analyzed for correlation with subsequent rhythmic bursting in synaptic isolation. Higher firing rates through all phases of fictive respiration statistically predicted bursting pacemaker behavior. However, a cycle-by-cycle analysis indicated that respiratory neurons were stochastically activated with each burst. Intrinsically bursting pacemakers led some population bursts and followed others. This variability was not reproduced in traditional fully interconnected computational models, while sparsely connected network models reproduced these results both qualitatively and quantitatively. We hypothesize that pacemaker neurons do not act as clock-like drivers of the respiratory rhythm but rather play a flexible and dynamic role in the initiation and stabilization of each burst. Thus, at the behavioral level, each breath can be thought of as de novo assembly of a stochastic collaboration of network topology and intrinsic properties.

A direct-current current-voltage (DCIV) measurement technique of interface and oxide traps on oxidized silicon is demonstrated. It uses the gate-controlled parasitic bipolar junction transistor of a metal-oxide-silicon field-effect transistor in a pln junction isolation well to monitor the change of the oxide and interface trap density. The dc base and collector currents are the monitors, hence, this technique is more sensitive and reliable than the traditional ac methods for determination of fundamental kinetic rates and transistor degradation mechanisms, such as charge pumping.

Carroll MS, Viemari JC, Ramirez JM. Patterns of inspiratory phase-dependent activity in the in vitro respiratory network. J Neurophysiol 109: 285-295, 2013. First published October 17, 2012 doi:10.1152/jn.00619.2012.-Mechanistic descriptions of rhythmogenic neural networks have often relied on ball-and-stick diagrams, which define interactions between functional classes of cells assumed to be reasonably homogenous. Application of this formalism to networks underlying respiratory rhythm generation in mammals has produced increasingly intricate models that have generated significant insight, but the underlying assumption that individual cells within these network fall into distinct functional classes has not been rigorously tested. In the present study we used multiunit extracellular recording in the in vitro pre-Bötzinger complex to identify and characterize the rhythmic activity of 951 cells. Inspiratory phasedependent activity was estimated for all cells, and the data set as a whole was analyzed with principal component analysis, nonlinear dimensionality reduction, and hierarchical clustering techniques. None of these techniques revealed categorically distinct functional cell classes, indicating instead that the behavior of these cells within the network falls along several continua of spiking behavior. neuronal networks; pre-Bötzinger complex; respiration; cell types RHYTHMIC ACTIVITY IS UBIQUITOUS in neural systems, from the slow rhythm generated by the suprachiasmatic nuclei that synchronizes mammalian circadian cycles (Dibner et al. 2010), to the broad frequency spectra covered by various oscillations generated within cortical networks (Buzsaki and Draguhn 2004;Tort et al. 2010;Wang 2010). Many of the underlying rules of rhythm generation have been established in neural circuits that generate rhythmic motor behaviors (Goulding 2009;Grillner 2006;Marder and Calabrese 1996). These motor activities are typically reciprocal in nature (e.g., expiration and inspiration, extension and flexion, protraction and retraction) and are often described by ball-and-stick 1 schematics that assume specific connectivity (sticks) between different types of cells or cell populations (balls). In these models each cell possesses functionally discrete properties firing in distinct phases with respect to a given global activity pattern (Guertin 2009; Selverston 2010). Ball-and-stick representations have been particularly powerful in invertebrate neuronal networks (Antonsen and Edwards 2003), because the firing and connectivity properties of physiologically and anatomically identified individual neurons could be reproducibly characterized across different individuals of the same species (Jing et al. 2010;Katz et al. 2010;Marder and Calabrese 1996;Newcomb et al. 2012; Ramirez, 1998;White and Nusbaum 2011). One of the many important lessons learned from these small invertebrate networks is that even in the case of a truly identified neuron, electrophysiological measures of single-cell properties do not suffice to uniquely specify a ...

Traumatic brain injury (TBI)is a major cause of epilepsy, yet the mechanisms underlying the progression from TBI to epilepsy are unknown. TBI induces the expression of COX-2 (cyclooxygenase-2) and increases levels of prostaglandin E2 (PGE2). Here, we demonstrate that acutely applied PGE2 (2 M) decreases neocortical network activity by postsynaptically reducing excitatory synaptic transmission in acute and organotypic neocortical slices of mice. In contrast, long-term exposure to PGE2 (2 M; 48 h) presynaptically increases excitatory synaptic transmission, leading to a hyperexcitable network state that is characterized by the generation of paroxysmal depolarization shifts (PDSs). PDSs were also evoked as a result of depriving organotypic slices of activity by treating them with tetrodotoxin (TTX, 1 M; 48 h). This treatment predominantly increased postsynaptically excitatory synaptic transmission. The network and cellular effects of PGE2 and TTX treatments reversed within 1 week. Differences in the underlying mechanisms (presynaptic vs postsynaptic) as well as occlusion experiments in which slices were exposed to TTX plus PGE2 suggest that the two substances evoke distinct forms of homeostatic plasticity, both of which result in a hyperexcitable network state.PGE2 and TTX (alone or together with PGE2) also increased levels of apoptotic cell death in organotypic slices. Thus, we hypothesize that the increase in excitability and apoptosis may constitute the first steps in a cascade of events that eventually lead to epileptogenesis triggered by TBI.

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The "bedside-to-bench" Congenital Central Hypoventilation Syndrome (CCHS) research journey has led to increased phenotypic-genotypic knowledge regarding autonomic nervous system (ANS) regulation, and improved clinical outcomes. CCHS is a neurocristopathy characterized by hypoventilation and ANS dysregulation. Initially described in 1970, timely diagnosis and treatment remained problematic until the first large cohort report (1992), delineating clinical presentation and treatment options. A central role of ANS dysregulation (2001) emerged, precipitating evaluation of genes critical to ANS development, and subsequent 2003 identification of Paired-Like Homeobox 2B (PHOX2B) as the disease-defining gene for CCHS. This breakthrough engendered clinical genetic testing, making diagnosis exact and early tracheostomy/artificial ventilation feasible. PHOX2B genotype-CCHS phenotype relationships were elucidated, informing early recognition and timely treatment for phenotypic manifestations including Hirschsprung disease, prolonged sinus pauses, and neural crest tumors. Simultaneously, cellular models of CCHS-causing PHOX2B mutations were developed to delineate molecular mechanisms. In addition to new insights regarding genetics and neurobiology of autonomic control overall, new knowledge gained has enabled physicians to anticipate and delineate the full clinical CCHS phenotype and initiate timely effective management. In summary, from an initial guarantee of early mortality or severe neurologic morbidity in survivors, CCHS children can now be diagnosed early and managed effectively, achieving dramatically improved quality of life as adults.

The paired-like homeobox 2B gene (PHOX2B) is the disease-defining gene for congenital central hypoventilation syndrome (CCHS). Individuals with CCHS typically present in the newborn period with alveolar hypoventilation during sleep and often during wakefulness, altered respiratory control including reduced or absent ventilatory responses to hypercarbia and hypoxemia, and autonomic nervous system (ANS) dysregulation; however, a subset of individuals present well into adulthood. Thermoregulation is altered and perception of shortness of breath is absent, but voluntary breathing is retained. Structural and functional magnetic resonance imaging (MRI) and limited post-mortem studies in subjects with CCHS reveal abnormalities in both forebrain and brainstem. MRI changes appear in the hypothalamus (responsible for thermal drive to breathing), posterior thalamus and midbrain (mediating O 2 and oscillatory motor patterns), caudal raphé and locus coeruleus (regulating serotonergic and noradrenergic systems), the lateral medulla, parabrachial pons, and cerebellum (coordinating chemoreceptor and somatic afferent activity with

Congenital central hypoventilation syndrome (CCHS) is a neurodevelopmental disorder characterized by life-threatening hypoventilation, possibly resulting from disruption of central chemosensory integration. However, animal models suggest the possibility of residual chemosensory function in the human disease. Cardioventilatory function in a large cohort with CCHS and verified paired-like homeobox 2B (PHOX2B) mutations was assessed to determine the extent and genotype dependence of any residual chemosensory function in these patients. As part of inpatient clinical care and evaluation, 64 distinct studies from 32 infants, children, and young adults with the disorder were evaluated for physiological response to three different inspired steady-state gas exposures of 3 min each: hyperoxia [100% oxygen (O2)]; hyperoxic hypercapnia [95% O2 and 5% carbon dioxide (CO2)]; and hypoxic hypercapnia [14% O2 and 7% CO2 balanced with nitrogen (N2)]. These were followed by a hypoxia challenge consisting of five or seven breaths of N2 (100% N2). In addition, a control group of 15 young adults was exposed to all but the hypoxic challenge. Comprehensive monitoring was used to derive breath-to-breath and beat-to-beat measures of ventilatory, cardiovascular, and cerebrovascular function. On average, patients showed a residual awake ventilatory response to chemosensory challenge, independent of the specific patient PHOX2B genotype. Graded dysfunction in cardiovascular regulation was found to associate with genotype, suggesting differential effects on different autonomic subsystems. In addition, differences between cases and controls in the cerebrovascular response to chemosensory challenge may indicate alterations in cerebral autoregulation. Thus residual cardiorespiratory responses suggest partial preservation of central nervous system networks that could provide a fulcrum for potential pharmacological interventions.