Behavioral control of the efficiency of pharmacological anesthesia in fish |
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Authors: | L S Chervova D N Lapshin |
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Institution: | 1.Faculty of Biology,Moscow State University,Moscow,Russia;2.Institute for Information Transmission Problems (Kharkevich Institute),Moscow,Russia |
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Abstract: | An original behavioral test was used to study the effect of opioid substances on the thresholds of nociceptive responses to
pain stimuli—a series of electric impulses applied to nerve endings of the caudal fin—in the common carp (Cyprinus carpio). The substances tested included tramadol (μ-agonist of opioid receptors), DADLE (δ-agonist), and U-50488 (κ-agonist) injected
intramuscularly in concentrations 10–100 nmol/g of body weight. Raised thresholds of sensitivity to the pain stimulus were
observed in the studied fish 5 to 15 min after the injection. The degree of analgesia and the rate of its increase varied
depending on the dose. The total duration of analgesia was 40 to 90 min and depended on the concentration of the injected
substance. It was observed in some experiments that the analgesic effect of tramadol (the most efficient of the analgesics
used) could last longer than 4 h. The analgesic effect of opioids was not detected in experiments where they were applied
together with naloxone, an antagonist of opioids. Decreased motor response to pain stimuli after injections of analgesics
was not caused by the immobilization of the animal, because the tested fish individuals released into an aquarium demonstrated
normal swimming and their usual behavior. We concluded that the systems of opioid nociceptive regulation function similarly
in fish and land vertebrates. This regulation can play an important role in defense behavior and in other behaviors in fish. |
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