Effect of naloxone pretreatment on habituation in the crab Chasmagnathus granulatus.
On sudden presentation of a passing shadow, the crab Chasmagnathus granulatus reacts with an escape response that habituates after repeating the same stimulus. In a first series of experiments, a range of naloxone (NX) doses (0.8, 2.4, 3.2, and 6.2 micrograms/g) was injected into crabs 15 min before one 15-trial habituation session. An enhancing effect of 3.2 micrograms NX/g on responsiveness appeared over trials, that cannot be explained either by a ceiling effect or by a delay in peak drug action. Two doses below 3.2 microgram/g and one dose above had no significant effect. Results from a second series of experiments showed that the 3.2 microgram NX/g effect vanishes after 15 trials (1 h after injection). The hypothesis that crab's habituation involves the action of an endogenous opioid mechanism is put forward to account for the naloxone pretreatment effect.
Romano
A
A
Laboratorio de Fisiologia del Comportamiento Animal, Facultad de Ciencias Exactas y Naturales, UBA, Argentina.
Lozada
M
M
Maldonado
H
H
D000818:Animals; D001143:Arousal / Q000187:drug effects*; D003386:Brachyura / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D005239:Fear / Q000187:drug effects; D006185:Habituation, Psychophysiologic / Q000187:drug effects*; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D011957:Receptors, Opioid / Q000187:drug effects
D011957:Receptors, Opioid; D009270:Naloxone