Journal of Neuroscience, Vol 6, 1560-1569, Copyright © 1986 by Society for Neuroscience
5,7-Dihydroxytryptamine lesions of crayfish serotonin-containing neurons: effect on the lateral giant escape reaction
DL Glanzman and FB Krasne
The crayfish's lateral giant escape response, a relatively simple
behavioral reaction, is readily modulated in certain situations. For
example, when a crayfish is restrained, its lateral giant (LG) fibers--
command neurons that mediate the escape response--are strongly inhibited
(Krasne and Wine, 1975). Previous work (Glanzman and Krasne, 1983) had
suggested that serotonin (5-HT) might mediate this restraint- induced
inhibition of the escape response. To test this possibility, we attempted
to lesion serotonergic neurons in crayfish with the 5-HT neurotoxin,
5,7-dihydroxytryptamine (5,7-DHT). We compared the levels of
5-HT-immunoreactive staining in nerve cords from 5,7-DHT-treated and from
normal crayfish to assess 5,7-DHT's effectiveness. Levels of immunoreactive
staining, as judged by ratings of the visibility of immunofluorescence,
were significantly lower in nerve cords from crayfish that had received
injections of 5,7-DHT (1.0-4.0 mg) than in nerve cords from normal
crayfish. In addition, some serotonergic neurons in the neurotoxin-treated
crayfish developed an abnormal brown pigmentation. To assess the behavioral
consequence of central serotonergic lesions, we compared the responsiveness
of escape in crayfish treated with 5,7-DHT (2.0-2.75 mg) and in normal
crayfish. The threshold for firing the LGs was significantly lower in
restrained neurotoxin-treated animals than in restrained normal animals.
Furthermore, the responsiveness of the LGs in neurotoxin-treated crayfish
approximated that in crayfish whose nerve cords had been severed between
the thorax and abdomen, a procedure known to abolish restraint-induced
inhibition (Krasne and Wine, 1975).(ABSTRACT TRUNCATED AT 250 WORDS)