Microelectrode biosensors for neurochemicals
Chemical signalling underlies every function of the nervous system, from those of which we are unaware e.g. control of the heart, to higher cognitive functions such as emotions, learning and memory. Neurotransmitters and neuromodulators mediate communication between neurons and between neurons and non-neural cells such as glia and muscle. In the past the means for directly studying the production and release of these signalling agents has been rather limited in its temporal and spatial resolution relative to the dynamics of chemical signalling and the structures of interest in the brain. However we (and others) have been devising methods for making microelectrode biosensors. These are much smaller and thus less invasive than methods such as microdialysis. They are sufficiently small to be placed into very specific areas of interest; and their small size means that they are fast responding thus getting closer to the dynamics of physiological signalling.
We have been making biosensors for the purines, ATP and adenosine. These are a particularly interesting class of extracellular signalling agents as they break the conventional paradigms of synaptic transmission in many ways. They can be released by non-exocytotic mechanisms in a diffuse fashion (although ATP is also released by exocytosis). And adenosine can arise in the extracellular space as a breakdown product from previously released ATP. The neurological and physiological functions of purinergic signalling remains a fertile area of investigation, and the ability to measure these agents directly in real time during physiological function is a great advance.
Banner illustration: left, micro electrode biosensors placed in area CA1 of a hippocampal brain slice along with stimulating and recording electrodes to monitor synaptic transmission; right, release of purines measured by the biosensors in response to a period of oxygen-glucose deprivation (black bar).