Portal de Periódicos da CAPES

Influence on memory of posttraining or pre-test injections of ACTH, vasopressin, epinephrine, and β-endorphin, and their interaction with naloxone

1985; Elsevier BV; Volume: 10; Issue: 2 Linguagem: Inglês

10.1016/0306-4530(85)90054-x

1873-3360

Iván Izquierdo, Renato Dutra Dias,

Pain Mechanisms and Treatments

The intraperitoneal (i.p.) injection of ACTH1–24 (0.2 μg/kg), lysine — vasopressin (10.0 μg/kg) or epinephrine HCl (5.0 μg/kg) shortly after training or prior to testing caused memory facilitation of a step-down inhibitory avoidance task in rats, acquired with low intensity training footshocks (0.3 mA, 60 Hz). Naloxone HCl (0.4 mg/kg) potentiated their posttraining effect, but antagonized their pre-test effect. Naloxone on its own caused retrograde memory facilitation but had no effect on the test session. Posttraining human β-endorphin (1.0 μg/kg) was amnestic, and its pre-test administration enhanced retention. Both effects were naloxone-reversible. Neither the pre-test facilitation caused by β-endorphin nor those caused by any of the other drugs (which are possible releasers of endogenous β-endorphin) were observed in animals in which the influence of endogenous opioids was prevented at the posttraining period by the administration of naloxone. These results are compatible with, and considerably strengthen, the previously advanced hypothesis that learning of this task, and possibly others, depends on a state induced by β-endorphin after training, and that it would normally be dissociated because this peptide is normally not released during test sessions. In addition, the posttraining facilitation caused by ACTH, vasopressin, and epinephrine stands out as an effect separate from, and in fact normally hindered by, posttraining β-endorphin release.