Application of LIVE Technologies to Neuroscience Discovery Research at Eli Lilly & Co (Science Foundation Ireland, and Eli Lilly & Co.)

 

An electrochemical system for long-term, real-time monitoring of dopamine neurotransmission in discrete brain regions (Science Foundation Ireland)

The proposal describes an approach to exploit the remarkable stability of carbon paste electrodes in order to develop a fast pulsed voltametric technique to detect the dopamine metabolite, homovanillic acid. This novel combination of small stable electrodes (60-micron radius disks) and high time resolution (seconds) will be used to explore real-time acute and chronic effects of repeated administration of dopamine agents over months in the freely moving rat.

 

New Technologies for Monitoring Cell Signalling in the Living Brain: Design, characterisation and in-vivo application to study extracellular glutamate, energy metabolism and their relationship (Science Foundation Ireland)

The development of new technologies for long-term in-vivo electrochemistry (LIVE) in the conscious brain is now possible following major advances in the fabrication of sensing devices using polymer-enzyme composites (PECs) synthesised in situ on the electrode surface. We have already demonstrated the feasibility of using classical microelectrodes to monitor brain ascorbate, oxygen and blood flow, and PEC-based biosensors to monitor brain glucose in vivo. In this Programme we are developing a battery of in-vivo sensors for glutamate, NO and lactate, based on both classical and PEC designs. These will be integrated into our existing LIVE devices to enable unprecedented studies of the interaction of ECF glutamate, energy metabolism and reactive oxygen species in the living brain.

 

Real-time simultaneous monitoring in vivo of glutamate and H₂O₂ in brain tissue, using a novel implantable polymer-enzyme composite device (Health Research Board)

The importance of the neurotransmitter and metabolic pools of glutamate in normal brain function is well recognised, as are its roles in neurodegenerative disorders and the neurotoxic mechanisms associated with severe head trauma. Recent data suggest that H₂O₂ also plays a part in brain function, with neuromodulatory roles, and is involved in oxidative damage to neural tissue. Some have even suggested that glutamate exerts certain of its neurotoxic effects through an H₂O₂-mediated mechanism. This collaboration within the NACL is aimed at the design and application of a state-of-the-art multiple probe microamperometric device for real-time simultaneous monitoring of glutamate and H₂O₂ in brain extracellular fluid in vivo.

This research project involves two distinct, yet complimentary, phases. (1) The use of a range of physicochemical techniques to characterise established electrosynthesised polymers in order to investigate the unique permselectivity of PPD, poly(o-phenylenediamine). These will include electrochemical, EQCM, SEM, AFM and MS studies on three classical polymers: polyphenol, polyaniline and PPD, all fabricated at neutral pH and high anodic applied potentials to generate their respective non-conducting forms. (2) Exploitation of these new insights to synthesise a range of novel polymer composite materials, incorporating proteins, polysaccharides or surfactants, for biosensor designs with enhanced selectivity for their target analyte.

This project is designed to extend the scope of microdialysis to applications involving collection and HPLC analysis of brain dialysate, enabling us to broaden our research strategies in three distinct areas: (a) obtain independent identification of the electrochemical signals generated by these complex sensors fabricated from our novel nanoscale enzyme-polymer composite materials; (b) provide a wider spectrum of neurochemical analytes that have significant interactions with the target systems, e.g., the use of microdialysate dopamine to understand the origin of striatal H₂O₂; and (c) the application of biosensors to clinical monitoring will be accelerated by the availability of the CMA on-line detection system for glutamate, glucose, lactate, etc. The CMA equipment package has two roles in achieving this latter goal. Firstly, biosensors placed directly into the microdialysis probes can, in collaboration with clinicians, be implanted in the human brain as these membranes have been licenced for clinical use. Secondly, the parallel monitoring of specific analytes, such as glutamate and glucose, with the CMA analyser and the newer biosensor technology, will provide corroboration of the latter signal which has superior temporal resolution offering real-time data on the neurochemical status of the patient during brain surgery and post-operative recovery.