Career Summary

Education

Research Program - Amphibians

Background
The goal of this research program is to capitalize on my extensive training in electrophysiology, optical imaging and computational methods, to bring the amphibian brainstem to the forefront of developmental biology and neuroscience research. Pilot data obtained while I was at Dartmouth College and at Woods Hole will be used to garner grants positioning the amphibian brainstem as preparation to study network development and oscillations. The niche value of some of network model preparations, such as the stomatogastric ganglion of the lobster Homarus americanus (c.f. Marder, E. & Bucher, D. 2007) or the sphinx moth Manduca sexta (c.f. Shields, V.D. & Hildebrand, J.G. 2001) have been invaluable in revealing how ionic channels in neuronal networks develop rhythmic oscillations.

The brain is comprised of neural networks that manifest rhythmic oscillations at one or more preferred frequencies. These synchronous oscillations are tightly linked to physiological outputs (respiration; c.f. Feldman & Del Negro 2006) and / or attentional states (learning and memory; c.f. Buzsáki & Draguhn 2004), result from the entrainment of neuronal discharges within a given network. These network discharges can be generated by intrinsic local mechanisms (i.e. ion channels), extrinsic mechanisms from remote locations (i.e. synaptic neurotransmission), or a combination of the two. When neurons of the network malfunction or die, the oscillations are disrupted and diseases such as Parkinson’s, Alzheimer’s or epilepsy occur. Understanding how the intrinsic and extrinsic mechanisms coordinate rhythms and determining how these mechanisms develop and interact will provide important information on network rhythmicity leading to the development of new medical procedures and protocols to help patients with network and oscillatory pathophysiologies.

In the amphibian tadpole two rhythms transiently co-exist as it metamorphoses from water to an air breathing animal. These two rhythms coordinate respiration through the gills and lung are preserved in the intact isolated tadpole brainstem and can be recorded from cranial (CN: V, VII, IX, X) and spinal nerves (SN: II) (Torgerson et al. 1997). As tadpoles are free living throughout development, and the stage of metamorphosis can be easily ascertained (Taylor and Kollros 1946). Methodologically amphibian tadpoles are a superior model to study networks and oscillatory development because in vitro, both gill and lung rhythms persist for more than twelve hours. Thus a priori the particular metamorphic stages of network development and activity level can be selected. Another benefit to the tadpole brainstem preparation as compared to mammalian, such rat and mouse respiratory preparations (Richter & Spyer 2001) is that the acute brainstem does not become anoxic in vitro, whereas mammalian brainstem slices thicker then 300-500 m usually contain an anoxic core. No previous study has provided any anatomical detail defining the neurons involved in these processes and little is known about the electrophysiological, neurochemical and coordination of these two circuits.

SPECIFIC RESEARCH PROJECTS
1) LOCATING THE RHYTMOGENIC KERNELS IN THE AMPHIBIAN BRAINSTEM
Anatomical and electrophysiological investigation will reveal the locations of the rhythmogenic kernels. I have already discussed a collaborative effort with Dr. Tim Kennedy at McGill University / Montreal Neurological Institute about using retrograde tracing techniques to identify the locations of the rhytmogenic kernels. The value of these anatomical studies will be a comprehensive brainstem atlas of the tadpole respiratory circuitry elements throughout the different developmental stages will be generated. This atlas will serve as a tool for comparison of the amphibian brainstem with mammals, thus providing insight to the evolution of air breathing, identify how networks change throughout metamorphosis, and these types of data will be important when trying to understand how to rebuild networks in patients with network failures, such as Parkinson’s, Alzheimer’s disease.

Concurrently, intracellular recording and staining will complete the neurophysiological characterization of the networks. The benefit of intracellular staining is also important due to the high resolution of morphological detail beyond that of retrograde staining, thus directly correlating function with location. These data will open a number of avenues investigating how single and or small populations of neurons can modulate and entire network(s). Preliminary data for this project has already been completed and published and has previously been awarded a Hitchcock Grant by Dartmouth College.

2) DEVELOP TRANSVERSE SLICE OF THE AMPHIBIAN BRAINSTEM
Another goal is to develop three different type of slice preparations; one that manifests uniquely the gill rhythm, one that manifests uniquely the lung rhythm and one that has both present and persistent. During my Grass Fellowship I have already begun developing a number of the techniques to conduct these experiments (i.e. how to incubate, slice, visualize and record from live neurons in the brainstem). The development of a spontaneously rhythmogenic amphibian brainstem slice preparation would be a huge technological leap forward because slices are stable preparations enabling easier access for focal application of neurotransmitters or stimulating electrodes, a single brainstem would yield a number of different slices, and I could record and stain similar small populations of neurons across different stages.

3) AMPHIBIAN AS BIOSENSOR
Developing the amphibian as a viable biosensor will be as important, if not more so, then the use of canaries in coal mines. Biological systems can be very sensitive to specific toxins, thus determining the specific deleterious effects of pollutants on the known metrics of specific metamorphic stages would be an important step in that direction. I would expect to collaborate with other faculty members of the biology department to investigate meaningful concentrations of pollutants that tadpoles would be expected to encounter in their habitat. As well, comparing the electrophysiological signatures of certain metamorphic populations affected by pollutants will aid in determining the exact effects on the developing amphibian brain. Once developed, the amphibian biosensor model can be used to determine a priori the effects of a single, or combination of pollutants that may be dumped into local waterways.

4) NETWORK MODELING
It is my goal to use all the anatomical and electrophysiological data from the amphibian central nervous system and develop a mathematical model of respiration and network interaction. The model, when developed will have a variety of adjustable parameters to tune the responses for specific stages, neuromodulator or pollutant effects. This would be a profoundly important learning tool not only for investigators, but could be easily be implemented into the classroom.

OTHER RESEARCH PROJECTS
The broad scope of my research is neuronal networks in development, in normally functioning systems and in disease / malfunction. Currently I collaborate with Dr. Laura-Ann Petitto at the University of Toronto investigating neurovascular coupling (specifically the BOLD signal) in bilingual participants. As well, I would anticipate working with Dr. Andrew Chapman from the psychology department, as his work is similar to my PhD work. Finally, I anticipate building and sharing a multimodal optical system similar to the one I use here at Harvard (combined 2-photon, confocal and supercontinuum). The high speed and image resolution of this system would benefit a number of researchers within the Concordia community.

REFERENCES
Buzsáki, G. & Draguhn, A. (2004) Neuronal oscillations in cortical networks. Science. 304(5679):1926-9

Feldman JL, Del Negro CA. (2006) Looking for inspiration: new perspectives on respiratory rhythm. Nat Rev Neurosci. 7(3):232-42.

Shields, V.D. & Hildebrand, J.G. (2001) Recent advances in insect olfaction, specifically regarding the morphology and sensory physiology of antennal sensilla of the female sphinx moth Manduca sexta.. Microsc Res Tech.Dec 1;55(5):307-29

Marder, E & Bucher, D. (2007) Understanding circuit dynamics using the stomatogastric nervous system of lobsters and crabs. Annu Rev Physiol;69:291-316.

Richter D.W. & Spyer K.M. (2001) Studying rhythmogenesis of breathing: comparison of in vivo and in vitro models. Trends Neurosci 24(8):464-72.

Proposed Research Program - Neuronal Networks

Proposed Research Program - Human Imaging

Research Achievements

Teaching Philosophy