Dopaminergic modulation of visual responses in toads
I. Apomorphine-induced effects on visually directed appetitive and consummatory prey-catching behavior |
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Authors: | M Glagow J-P Ewert |
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Institution: | Abteilung Neurobiologie, Fachbereich Biologie/Chemie, Universit?t Kassel, D-34132 Kassel, Germany Tel.: +49-561/8044784, Fax: +49-561/8044146, DE
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Abstract: | This study confirms for a phylogenetically basal terrestrial vertebrate that dopaminergic modulations interfere with the
visually directed appetitive and consummatory feeding behaviors orienting and snapping, respectively. (1) In common toads
Bufo bufo, intralymphatic administration of the dopamine D2/D1-receptor agonist apomorphine led to a dose-dependent facilitation of prey-snapping in response to moving objects. The snapping
activity reached a maximum 15–35 min after apomorphine injection. (2) To changes in configurational stimulus features, the
basic pattern of discrimination was maintained; however, the acuity of discrimination was reduced due to the high snapping
response level. (3) The apomorphine-induced facilitation of snapping was accompanied by a suppression of prey-oriented lunging
and turning. Toads snapped only if prey occurred frontally in the visual field at a relatively short distance. The snapping
behavior was fixed in its form and stereotyped regarding its immediate release. (4) About 90 min after apomorphine administration,
prey-oriented turning behavior was restored and displayed a facilitatory rebound. (5) In comparative experiments with the
species B. marinus, both prey-oriented turning and snapping responses were suppressed by apomorphine in a dose-dependent manner. (6) After pre-treatment
with the dopamine antagonist haloperidol, apomorphine showed no measurable effect on the visual release of prey orienting
or snapping. (7) The results contribute to the sensorimotor and the motivation hypothesis of dopamine function proposed for
higher vertebrates and stimulate a comparative discussion of anatomic homologies and functional analogies.
Accepted: 10 July 1996 |
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Keywords: | Prey-orienting Prey-snapping Dopaminergic modulation Apomorphine Toad |
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