Magnetic particles control neurons

The
mysteries of the intricate neuronal webs controlling animal behaviour have
recently come under scrutiny by scientists using optical stimulation
techniques. However, there is an
insurmountable problem with this method of investigation: there is a limit to
how far optical light can penetrate into tissues. An ingenious new technique that uses
radio-frequency magnetic fields to heat nanoparticles applied to proteins and
cell membranes takes the exploration much further.

A
team of nanotechnology scientists led by physics professor Arnd Pralle at the
University of Buffalo has recently completed a groundbreaking study on the
application of nanotechnology to animals.
Their research shows that magnetic nanoparticles targeted to cell
membranes can remotely influence neurons, cellular ion channels and even animal
behaviour. The potential medical
applications are exceptionally important, offering the prospect of remote
stimulation of pancreatic cells to release insulin in diabetic patients, or
remote manipulation of targeted proteins or cells in specific tissues to
improve cancer treatments.  It may also
open the door to innovations in the treatment of neurological disorders, which
have been caused by inadequate neuro-stimulation.

The
research, published in the Nature
Nanotechnology Journal in July
2010, unveils a method that allows cells to be stimulated by magnetic fields
both in vitro and in vivo.
It promises to unravel the labyrinthine complexity of the signalling
networks that govern animal behaviour, according to Dr Pralle. As an example of the latter, the team
targeted nanoparticles near the “mouth” of the tiny nematode worms, C. elegans. Before applying a magnetic field, the worms
simply crawled around randomly. However,
once the field was activated, they began to reverse direction.

The
magnetism raises the temperature of the nanoparticles by 34˚ Celsius and the
scientists believe that this is what produced the behavioural change in the
worms. This is the temperature, which,
in nature, provokes an avoidance response in most organisms. The team’s method allows nanoscale
measurements to be made of heat conduction in biological tissues, something
about which very little is known. Dr
Pralle underlines the uniqueness of the approach – it allows heating of tissue
without tissue damage or death. Only the
cell membrane targeted with nanoparticles rises in temperature when a
radiofrequency magnetic field is applied – the intracellular temperature is
unaffected.

The
magnetic field used in the work was similar in strength to that used in
magnetic resonance imaging techniques.
Because it can uniformly activate cells over a large area, the method
can be used in whole body “in vivo” applications, a fact which medics are
likely to capitalise upon. Pralle’s team
developed an ingenious “fluorescent probe” which functioned as a
“nano-thermometer” during the research.
It measured temperature change at the nano-level through alterations in
fluorescence intensity, accurately pinpointing the moment when the all
important 34˚ Celsius level had been reached.