Matthew J. Gdovin

Neonatal maturation of the hypercapnic ventilatory response and central neural CO2 chemosensitivity

The ventilatory response to CO2 changes as a function of neonatal development. In rats, a ventilatory response to CO2 is present in the first 5 days of life, but this ventilatory response to CO2 wanes and reaches its lowest point around postnatal day 8. Subsequently, the ventilatory response to CO2 rises towards adult levels. Similar patterns in the ventilatory response to CO2 are seen in some other species, although some animals do not exhibit all of these phases. Different developmental patterns of the ventilatory response to CO2 may be related to the state of development of the animal at birth. The triphasic pattern of responsiveness (early decline, a nadir, and subsequent achievement of adult levels of responsiveness) may arise from the development of several processes, including central neural mechanisms, gas exchange, the neuromuscular junction, respiratory muscles and respiratory mechanics. We only discuss central neural mechanisms here, including altered CO2 sensitivity of neurons among the various sites of central CO2 chemosensitivity, changes in astrocytic function during development, the maturation of electrical and chemical synaptic mechanisms (both inhibitory and excitatory mechanisms) or changes in the integration of chemosensory information originating from peripheral and multiple central CO2 chemosensory sites. Among these central processes, the maturation of synaptic mechanisms seems most important and the relative maturation of synaptic processes may also determine how plastic the response to CO2 is at any particular age.

Focal photodynamic intracellular acidification as a cancer therapeutic

Cancer cells utilize an array of proton transporters to regulate intra- and extracellular pH to thrive in hypoxic conditions, and to increase tumor growth and metastasis. Efforts to target many of the transporters involved in cancer cell pH regulation have yielded promising results, however, many productive attempts to disrupt pH regulation appear to be non-specific to cancer cells, and more effective in some cancer cells than others. Following a review of the status of photodynamic cancer therapy, a novel light-activated process is presented which creates very focal, rapid, and significant decreases in only intracellular pH (pHi), leading to cell death. The light-activation of the H+ carrier, nitrobenzaldehyde, has been effective at initiating pH-induced apoptosis in non-cancerous and numerous cancerous cell lines in vitro, to include breast, prostate, and pancreatic cancers. Also, this intracellular acidification technique caused significant reductions in tumor growth rate and enhanced survival in mice bearing triple negative breast cancer tumors. The efficacy of an NBA-upconverting nanoparticle to kill breast cancer cells in vitro is described, as well as a discussion of the potential intracellular mechanisms underlying the pH-induced apoptosis.

Intracelluar pH (pHi) Measurements in the In Vitro Tadpole Brainstem:Direct Correlations between Changes in pHi and Ventilation

Central respiratory chemoreceptors measure pH in the brain stem and are an integral part of the neural circuitry that modulates respiratory rhythmogenesis, specifically in response to hypercapnic acidosis. Central respiratory chemore- ceptor membrane potential and/or action potential firing rate are altered in response to changes in intracellular pH (pHi), which changes with the hydration of CO2 in both the extracellular and intracellular space, however the role of cellular changes in chemoreceptor properties on respiratory motor output has been difficult to identify. We studied whole nerve respiratory activity while simultaneously visualizing pHi dynamics using the pH-sensitive dye, BCECF, in the spontane- ously active in vitro tadpole brainstem. The isolated, superfused tadpole brainstem is well oxygenated and retains synaptic connectivity among respiratory central pattern generators, central respiratory chemoreceptors, and respiratory motor neu- ronsunder physiological conditions, where mammalian preparations do not. An ammonium prepulse was used to selec- tively induce a decrease in pHi. Our results show intracellular pH is regulated differently in cells located in chemosensi- tive and non-chemosensitive regions of the tadpole brainstem during hypercapnia. We were also able to show an inverse correlation between pHi in cells located in chemosensitive regions of the tadpole brainstem and whole nerve respiratory- related activity. Using this approach, the microenvironment of individual cells may be manipulated while monitoring real time changes in pHi, neuronal activity and ventilatory-related activity to elucidate the role of a variety of signals in elicit- ing changes in ventilation.

Employing a pH Sensitive Fluorophore to Measure Intracellular pH in the In Vitro Brainstem Preparation of Rana catesbeiana~!2009-05-06~!2009-10-29~!2009-12-24~!

We developed an in vitro tadpole brainstem preparation in order to investigate the development of central respiratory chemoreception and rhythmogenesis. pH sensitive fluorescent dyes have been utilized to record intracellular pH (pHi) optically in central respiratory chemoreceptive regions in mammals. Our goal in this study was to develop the ability to record pHi optically while simultaneously recording respiratory motor output in the superfused tadpole brainstem preparation. We developed a dye-loading protocol that demonstrated our ability to adequately load the majority of brainstem neurons. The presence of the dye was not disruptive to ongoing respiratory rhythmogenesis or the respiratory response to central respiratory chemoreceptor stimulation. The tadpole brainstem is an excellent model to study the development of the neural control of respiration, as it is well oxygenated and retains synaptic connectivity among respiratory central pattern generators, central respiratory chemoreceptors, and respiratory motor neurons. Validating of the use of the pH sensitive dyes to record pHi optically in central respiratory chemoreceptors in this preparation will permit further characterization of the pH regulatory responses of central respiratory chemoreceptors.