Simultaneous Recording of Chronoamperometric L-Glutamate Current and Field Excitatory Postsynaptic Potentials in Mouse Hippocampal Slice

L-Glutamate is a major excitatory neurotransmitter in the central neuronal systems and plays a vital role in brain development, synaptic plasticity and neuropathology. Simultaneous recording of presynaptically released L-glutamate and postsynaptic events (field excitatory postsynaptic potentials (EPSPs)) is particularly important for investigating the direct relation between presynaptic L-glutamate dynamics and postsynaptic activities. Here we report on combination of field EPSP recordings and time-resolved measurements of stimulus-evoked L-glutamate using the capillary-type enzyme microsensors in mouse hippocampal slices. The capillary-type L-glutamate microsensor was based on glutamate oxidase (GluOx), which was prepared according to ref. (1). It was found that application of electric stimuli to mouse hippocampal slices resulted in generation of a large L-glutamate-insensitive capacitive current both at an L-glutamate microsensor and blank microsensor that lacks GluOx, probably due to an unintentionally formed junction between the circuits of the amperometric and field EPSP measurements. The origin of the capacitive current was investigated using electrical impedance spectroscopy and circuit simulation. Our approach to extract a faradaic signal from the observed current was to sample a current amplitude when the capacitive transient current dropped virtually to zero. After this analysis, a clear response was observed following 2 Hz electric stimulation at the L-glutamate microsensor, while no significant response was observed at the blank microsensor. The reliability of the extracted signal was examined by investigating several treatments that manipulate release probability of L-glutamate.

 

References

(1). S. Hozumi, K. Ikezawa, A. Shoji, A. Hirano-Iwata, T. Bliss and M. Sugawara, Biosens. Bioelectron. 26, 2975–2980 (2011).