5,7-Dihydroxytryptamine lesions of crayfish serotonin-containing neurons: effect on the lateral giant escape reaction.
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)
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D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology* / Q000502:physiology; D000818:Animals; D003400:Astacoidea / Q000502:physiology; D001522:Behavior, Animal / Q000187:drug effects* / Q000502:physiology; D004102:Dihydroxytryptamines / Q000494:pharmacology*; D004924:Escape Reaction / Q000187:drug effects* / Q000502:physiology; D009420:Nervous System / Q000187:drug effects; D009424:Nervous System Physiological Phenomena; D009433:Neural Inhibition / Q000187:drug effects*; D012149:Restraint, Physical; D012701:Serotonin / Q000276:immunology / Q000502:physiology
D004102:Dihydroxytryptamines; D015116:5,7-Dihydroxytryptamine; D012701:Serotonin