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FIGURE 3
COMPARISONS OF RESPONSES OF
APLYSIA CALIFORNICA NEURONS TO
IONTOPHORETIC AND PRESURE
APPLICATION OF COMPOUNDS
FIGURE 3A:
Superimposed traces of Aplysia buccal neuron
responses to ACh delivered by an iontophoretic
pulse (1µ amp, 80 MSEC) and a pressure pulse (40
PSI, 60 MSEC, 60 µm diameter droplets of 10-3 M
ACh). The amplitude and polarity of the pressure
artifacts (negative square pulse in this case) can be
manipulated.
FIGURE 3B:
Comparisons of responses to pressure ejected
acetylcholine (ACh) in Aplysia neuron in the
absence (control) and presence of an iontophoretic
pipette (70 MEGOHMS) containing 1 M ACh. The
dose-responsive curve is shifted to the right
because of desensitization from ACh leaking out of
iontophoretic pipette. Each point is the mean
re standard error of the mean.
Problems of desensitization can be circumvented
with a pressure pipette since the pipette is usually
filled with agonists in the concentrations of 10-6 to
10-3 M in contrast to iontophoretic pipettes. Braking
current is not necessary for the pressure pipette, thus
avoiding inconsistent ejection of compounds.
FIGURE 3C:
Reproducibility of 12 consecutive responses to
acetylcholine (ACh) delivered by a pressure pulse to
an Aplysia (Sea Hare) neuron. A 10-4M solution of
ACh was ejected by 22 PSI for 5 MSEC to produce a
droplet estimated to be 10 PL (=1 Femtomole of
ACh). Calibration: 2 mV, .02 Sec.
FIGURE 3D:
Comparison of response to iontophoretic (I) and
pressure (P) applied ACh in a drug study. Both
responses are equally antagonized by
hexamenthonium, even though the ACh in the
pressure pipette is ejected in a droplet of normal
artificial seawater. Similar results are obtained during
substitution experiments. The arrows in the figure
point to an input resistance test pulse.
