Ceftriaxone preserves glutamate transporters and prevents intermittent hypoxia-induced vulnerability to brain excitotoxic injury.

Hypoxia alters cellular metabolism and although the effects of sustained hypoxia (SH) have been extensively studied, less is known about chronic intermittent hypoxia (IH), commonly associated with cardiovascular morbidity and stroke. We hypothesize that impaired glutamate homeostasis after chronic IH may underlie vulnerability to stroke-induced excitotoxicity. P16 organotypic hippocampal slices, cultured for 7 days were exposed for 7 days to IH (alternating 2 min 5% O2-15 min 21% O2), SH (5% O2) or RA (21% O2), then 3 glutamate challenges.

Respiratory circuits: development, function and models.

Breathing is a rhythmic motor behavior generated and controlled by hindbrain neuronal networks. Respiratory motor output arises from two distinct, but functionally interacting, rhythmogenic networks: the pre-Bötzinger complex (preBötC) and the retrotrapezoïd nucleus/parafacial respiratory group (RTN/pFRG). This review outlines recent advances in delineating the genetic specification of the neuronal constituents of these two rhythmogenic networks, their respective roles in respiratory function and how they interact to constitute a functional respiratory circuit ensemble.

Functional anatomical evidence for respiratory rhythmogenic function of endogenous bursters in rat medulla.

Endogenous burster neurons (EBs) have been found at the level of the facial nucleus (VIIn), and 500 mum caudally, within the pre-Bötzinger complex (preBötC). They have been proposed as either causal to or playing no role in respiratory rhythmogenesis. Little is known about their broader distribution in ventrolateral medulla.

Degeneracy as a substrate for respiratory regulation.

Recent studies in vivo and in vitro suggest that both respiratory rhythmogenesis and its central chemosensory modulation arise from multiple, mechanistically and/or anatomically distinct networks whose outputs are similar. These observations are consistent with degeneracy, defined as the ability of structurally distinct elements to generate similar function. This review argues that degeneracy is an essential feature of respiratory networks, ensuring the survival of the individual organism over the course of development, and accounting for the transformation of respiratory biomechanics over evolutionary time.

Semi-automated region of interest generation for the analysis of optically recorded neuronal activity.

Bath-applied membrane-permeant Ca(2+) indicators offer access to network function with single-cell resolution. A barrier to wider and more efficient use of this technique is the difficulty of extracting fluorescence signals from the active constituents of the network under study. Here we present a method for semi-automatic region of interest (ROI) detection that exploits the spatially compact, slowly time-varying character of the somatic signals that these indicators typically produce.

Belt-and-suspenders as a biological design principle.

Recent studies have shown both the pFRG and the preBötC are sufficient to generate respiratory rhythm, and are hypothesized to do so via distinct mechanisms (Onimaru and Homma 2003; Mellen, Janczewski, Bocchiaro and Feldman 2003). The coexistence of mechanistically distinct, functionally matching networks (defined as degeneracy, Edelman and Gally 2001) is a ubiquitous feature of motor networks in both invertebrates (Selverston and Miller 1980) and vertebrates (DiDomenico, Nissanov and Eaton 1988). In almost all cases, a consensus exists about which subsystem is the "primary" rhythm generator, yet consistently, the effect of modulators on the isolated primary rhythm generator is qualitatively different than their effect on the more intact network (Ayali and Harris-Warrick 1999) and, in the intact animal, all rhythmogenic networks are active during motor pattern generation.

A vibrating microtome attachment for cutting brain slice preparations at reproducible compound angles relative to the midline.

Slice preparations isolate functional networks, permitting single unit recording under visual control, and the use of fluorescent indicators. Circuits of interest often lie at a tilt in both the rostrocaudal and ventrodorsal axis, thus exposing circuits of interest at the cut surface of a slice would require a device for tilting a preparation along two orthogonal axes relative to the blade. Such a device, designed to be used in conjunction with a vibrating microtome, permitting the isolation of slice preparations at reproducible angles, is described here.

Functional imaging reveals respiratory network activity during hypoxic and opioid challenge in the neonate rat tilted sagittal slab preparation.

In mammals, respiration-modulated networks are distributed rostrocaudally in the ventrolateral quadrant of the medulla. Recent studies have established that in neonate rodents, two spatially separate networks along this column-the parafacial respiratory group (pFRG) and the pre-Bötzinger complex (preBötC)-are hypothesized to be sufficient for respiratory rhythm generation, but little is known about the connectivity within or between these networks. To be able to observe how these networks interact, we have developed a neonate rat medullary tilted sagittal slab, which exposes one column of respiration-modulated neurons on its surface, permitting functional imaging with cellular resolution.

Afferent modulation of neonatal rat respiratory rhythm in vitro: cellular and synaptic mechanisms.

In mammals, expiration is lengthened by mid-expiratory lung inflation (Breuer-Hering Expiratory reflex; BHE). The central pathway mediating the BHE is paucisynaptic, converging on neurones in the rostral ventrolateral medulla. An in vitro neonatal rat brainstem-lung preparation in which mid-expiratory inflation lengthens expiration was used to study afferent modulation of respiratory neurone activity.

Opioid-induced quantal slowing reveals dual networks for respiratory rhythm generation.

Current consensus holds that a single medullary network generates respiratory rhythm in mammals. Pre-Bötzinger Complex inspiratory (I) neurons, isolated in transverse slices, and preinspiratory (pre-I) neurons, found only in more intact en bloc preparations and in vivo, are each proposed as necessary for rhythm generation. Opioids slow I, but not pre-I, neuronal burst periods.

Hypothermia and recovery from respiratory arrest in a neonatal rat in vitro brain stem preparation.

This study was designed to examine the possibility that respiratory arrest during hypothermia occurs at the level of premotor or motor neurons rather than at the level of the central rhythm generator itself. Specifically, we sought to determine the consequences of hypothermic cooling until respiratory arrest, and subsequent rewarming, on neurons in the pre-Bötzinger Complex, as an indication of the output of the entire rhythmogenic network; and from cervical spinal (phrenic) ventral roots, as an indication of motor neuron output, in an in vitro neonatal rat brain stem-spinal cord preparation. We found that hypothermia led to a slowing of the respiratory rhythm with little or no decrease in the magnitude of phrenic motor output or the field potential of pre-Bötzinger Complex neurons.