Journal of Neuroscience, Vol 11, 96-110, Copyright © 1991 by Society for Neuroscience
Modification of leech behavior patterns by reserpine-induced amine depletion
BA O'Gara, H Chae, LB Latham and WO Friesen
Department of Biology, University of Virginia, Charlottesville 22901.
A single injection of 100 micrograms reserpine into the crop of the
medicinal leech, Hirudo medicinalis, reduced CNS serotonin and dopamine
levels to less than 1% of control values within 3 d. High-pressure liquid
chromotography- (HPLC) determined CNS serotonin and dopamine levels
remained maximally depressed for approximately 1 month following reserpine
injection. Subsequently, amine levels recovered slowly, but remained
depressed 6 months after reserpine injection. Following reserpine
treatment, glyoxylic acid-induced fluorescence or neutral red staining
closely mirrored the HPLC-determined time course of amine depletion and
recovery. Acute exposure of isolated ganglia to 10 microM reserpine for
periods up to 6 hr produced a 20-30% reduction of serotonin and dopamine
content. The threshold concentration of reserpine necessary to produce
amine depletion was approximately 1 microM. We found that reserpine
treatment eliminated biting behavior within 4 d following injection. Biting
behavior remained depressed below control levels for approximately 4
months, but returned to control values while CNS serotonin and dopamine
levels remained significantly depressed at this time. Unexpectedly,
reserpine treatment increased rather than reduced the duration of
stimulus-evoked swimming activity. This behavioral change was evident
within 3 d and persisted for approximately 3.5 months. To rapidly restore
amine levels in reserpine-treated animals, we bathed intact leeches in pond
water containing serotonin, dopamine, or octopamine. We found that biting
behavior was restored following reserpine treatment by bathing intact
leeches in pond water containing serotonin or dopamine, but not octopamine.
Also contrary to expectations, the increase in swim duration was not
reversed by bath exposure to serotonin, dopamine, octopamine, or histamine.
However, all swimming activity in reserpine- treated leeches was eliminated
by the amine antagonist cyproheptadine. We propose that the presence of low
levels of amines is critical for the expression of both biting and swimming
activity in leeches. However, the minimal levels of amines necessary for
the expression of these behaviors are lower for swimming than for biting.
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