CO2-Induced ATP-Dependent Release of Acetylcholine on the Ventral Surface of the Medulla Oblongata.

Complex mechanisms that detect changes in brainstem parenchymal PCO2/[H+] and trigger adaptive changes in lung ventilation are responsible for central respiratory CO2 chemosensitivity. Previous studies of chemosensory signalling pathways suggest that at the level of the ventral surface of the medulla oblongata (VMS), CO2-induced changes in ventilation are (at least in part) mediated by the release and actions of ATP and/or acetylcholine (ACh). Here we performed simultaneous real-time biosensor recordings of CO2-induced ATP and ACh release from the VMS in vivo and in vitro, to test the hypothesis that central respiratory CO2 chemosensory transduction involves simultaneous recruitment of purinergic and cholinergic signalling pathways.

Interactions between respiratory oscillators in adult rats.

Breathing in mammals is hypothesized to result from the interaction of two distinct oscillators: the preBötzinger Complex (preBötC) driving inspiration and the lateral parafacial region (pFL) driving active expiration. To understand the interactions between these oscillators, we independently altered their excitability in spontaneously breathing vagotomized urethane-anesthetized adult rats. Hyperpolarizing preBötC neurons decreased inspiratory activity and initiated active expiration, ultimately progressing to apnea, i.

A critical role for purinergic signalling in the mechanisms underlying generation of BOLD fMRI responses.

The mechanisms of neurovascular coupling underlying generation of BOLD fMRI signals remain incompletely understood. It has been proposed that release of vasoactive substances by astrocytes couples neuronal activity to changes in cerebrovascular blood flow. However, the role of astrocytes in fMRI responses remains controversial.

Role of parafacial nuclei in control of breathing in adult rats.

Contiguous brain regions associated with a given behavior are increasingly being divided into subregions associated with distinct aspects of that behavior. Using recently developed neuronal hyperpolarizing technologies, we functionally dissect the parafacial region in the medulla, which contains key elements of the central pattern generator for breathing that are important in central CO2-chemoreception and for gating active expiration. By transfecting different populations of neighboring neurons with allatostatin or HM4D Gi/o-coupled receptors, we analyzed the effect of their hyperpolarization on respiration in spontaneously breathing vagotomized urethane-anesthetized rats.

TRPA1 channels are regulators of astrocyte basal calcium levels and long-term potentiation via constitutive D-serine release.

Astrocytes are found throughout the brain where they make extensive contacts with neurons and synapses. Astrocytes are known to display intracellular Ca(2+) signals and release signaling molecules such as D-serine into the extracellular space. However, the role(s) of astrocyte Ca(2+) signals in hippocampal long-term potentiation (LTP), a form of synaptic plasticity involved in learning and memory, remains unclear.

Redefining the components of central CO2 chemosensitivity--towards a better understanding of mechanism.

The field of CO(2) chemosensitivity has developed considerably in recent years. There has been a mounting number of competing nuclei proposed as chemosensitive along with an ever increasing list of potential chemosensory transducing molecules. Is it really possible that all of these areas and candidate molecules are involved in the detection of chemosensory stimuli? How do we discriminate rigorously between molecules that are chemosensory transducers at the head of a physiological reflex versus those that just happen to display sensitivity to a chemosensory stimulus? Equally, how do we differentiate between nuclei that have a primary chemosensory function, versus those that are relays in the pathway? We have approached these questions by proposing rigorous definitions for the different components of the chemosensory reflex, going from the salient molecules and ions, through the components of transduction to the identity of chemosensitive cells and chemosensitive nuclei.

CO2-dependent opening of an inwardly rectifying K+ channel.

CO(2) chemosensing is a vital function for the maintenance of life that helps to control acid-base balance. Most studies have reported that CO(2) is measured via its proxy, pH. Here we report an inwardly rectifying channel, in outside-out excised patches from HeLa cells that was sensitive to modest changes in PCO(2) under conditions of constant extracellular pH.

Connexin hemichannel-mediated CO2-dependent release of ATP in the medulla oblongata contributes to central respiratory chemosensitivity.

Arterial PCO2, a major determinant of breathing, is detected by chemosensors located in the brainstem. These are important for maintaining physiological levels of PCO2 in the blood and brain, yet the mechanisms by which the brain senses CO(2) remain controversial. As ATP release at the ventral surface of the brainstem has been causally linked to the adaptive changes in ventilation in response to hypercapnia, we have studied the mechanisms of CO(2)-dependent ATP release in slices containing the ventral surface of the medulla oblongata.

CO2-dependent opening of connexin 26 and related β connexins.

We have previously shown connexin mediated CO(2)-dependent ATP release from the surface of the medulla oblongata. Given the localization of connexin 26 (Cx26) to the chemosensing areas of the medulla, we have tested in a heterologous expression system (HeLa cells) whether Cx26 may be sensitive to changes in PCO2. Cx26 responded to an increase in PCO2 at constant extracellular pH by opening and to a decrease in PCO2 by closing.

A microelectrode biosensor for real time monitoring of L-glutamate release.

We have developed an amperometric microbiosensor for real time monitoring L-glutamate release in neural tissue, based on enzymatic oxidation catalyzed by the L-glutamate oxidase. By means of a sol-gel coating method, L-glutamate oxidase was entrapped in a biocompatible gel layer that provided a benign environment and retained enzyme activity on the surface of Pt microelectrode. Prior to gel layer formation, a modification on the surface of Pt microelectrode with poly(phenylene diamine) enabled the microbiosensor screen majority of common potential interfering substances existing in physiological samples.