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Fig. 1. The in vitro walking leg preparation. (A) The 5th walking leg was
dissected out together with the 3rd to 5th thoracic ganglia (T3–T5) and
the 1st abdominal ganglion (A1) of the ventral nerve cord. In the intact
animal the coxo-basipodite chordotonal organ (CBCO) is attached to dorsal edge
of the coxopodite and an apodeme at the proximal-dorsal edge of the
basipodite. Thus, the tension on the CBCO, which is composed of sensory
neurons embedded in an elastic strand, is released during upward movements of
the leg and is increased during downward movements. The levator (LEV) and
depressor (DEP) muscles are located within the coxopodite. When the depressor
muscle contracts, there is a rotation of the basipodite around a pivot point
causing the downward movement of the leg and deformation of soft cuticle
(dotted line) above and below this point. (B) Extracellular recordings were
made from the various motor nerves as well as the sensory nerve of the CBCO (a
CBCO neuron is represented in red) using en passant electrodes (not
shown, see Materials and methods). Intracellular recordings of the motor
neurons were made from within the neuropil (a Dep MN is represented in blue).
Movements were imposed on the CBCO by a mechanical puller. Stretching the
elastic strand mimicked downward movements of the leg, whereas releasing the
strand mimicked upward movements. The dotted line marks the midline of the
thoracic ganglia.
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