Biomedical Engineering Reference
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surfaces. At high magniication, tight interactions between cell membranes
and SWNTs could be visualised. The distributed electrical stimulation of
cultured hippocampal neurons was then investigated. Hippocampal neurons
grown on SWNTs or on control glass substrates exhibited spontaneous
electrical activity. In particular, a signiicant increase in action potentials and
frequency of PSCs was observed for neurons grown on SWNT ilms when
compared with control substrates.
To assess whether SWNTs could perform local network stimulations,
short voltage pulses were delivered to SWNTs to induce the appearance of
Na + fast inward current in the recorded neuron. These stimulations should
also induce action potentials in neighbouring neurons that should generate
monosynaptic responses to the connected neurons. Indeed, brief SWNT
voltage steps effectively delivered PSCs, in 65% of the recorded neurons. To
elucidate the electrical interactions occurring in SWNT-neuron networks,
the modelling of the neuron-SWNT junction was achieved. It was suggested
that the coupling between neurons and SWNTs might be partly resistive.
But the authors led to the conclusion that because of the non-idealities of
the single electrode voltage clamp, eliciting Na + currents through SWNT
stimulation did not conclusively prove a resistive coupling between SWNTs
and neurons. Moreover, the authors pointed out that whole-cell patch-clamp
recordings might yield deceiving results as any resistive coupling between
biomembranes and SWNTs is qualitatively undistinguishable from a coupling
between SWNTs and the patch pipette.
Ballerini and coworkers further investigated the inluence of CNTs on the
electrical properties of isolated neurons. In particular, the presence of after-
depolarisation events in the cell soma was examined. 64 The aim of this study
was to determine if the higher eficiency of the signal transmission of neurons
grown on conductive nanotube substrates was linked to the interactions
between CNTs and neurons at the nanoscale.
Puriied SWNTs were deposited on glass substrates via the
previously described process based on functionalisation and subsequent
defunctionalisation. Rat hippocampal cells were cultured on the thin film
of purified SWNTs. Electrogenesis was studied in single neurons. The
authors injected a brief current pulse into the soma to force the neurons
to ire a regular train of six action potentials and measured the presence of
membrane depolarisation in the soma at the end of the last action potential.
Neurons propagate electrical signals, i.e., action potentials, down an axon.
Backpropagation of the action potentials to dendrites can occur occasionally.
In this case, the propagation of the electrical signals takes place in the
direction opposite to that of the flow. It has been shown that rat hippocampal
neurons grown on SWNT substrates exhibited a signiicantly larger after-
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