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Abstract

For electrophysiological studies in the fly's optic lobe, a procedure was required to perfuse the brain at controllable rates with
oxygenated solutions, while recording intracellularly from visual interneurons.
The cornea of the compound eyes has to be left in air, in order not to disturb
their optics, and to allow physiological stimulation. When the head capsule is
opened to get acces to the brain, air sacs and major tracheal trunks tend to
collapse by either of two causes: surface tension may flatten tracheae at too
low fluid levels and hydrostatic pressure may flatten tracheae at too high
levels. Only within a small range of saline levels ( <
± 30µm ) main tracheae and air sacs were found to remain inflated in the
dissected head. Therefore the saline level had to be precisely controlled and
stabilized within a few microns.
With
this procedure, it is possible to maintain the fly's brain (< 5 µl ) alive
for more than 24 hrs in a perfused volume of only 15 µl, and to record
intracellularly from fibres as small as 2 µm. The same procedure should be
applicable wherever small, open volumes have to be precisely perfused, and
mechanical or electrical artifacts cannot be tolerated.