Brain opioid peptides may participate in the reversal of pentylenetetrazol-induced amnesia

Abstract

Post-training administration of pentylenetetrazol (PTZ, 45 mg/kg, i.p.) disrupted 48-h retention, in mice, of an inhibitory avoidance response. The effect was reversed by any of the following treatments given 1 h prior to testing: a) a beta-endorphin injection (0.1 microgram/kg, i.p.), b) PTZ injection, or c) exposure to a novel experience (10 min in a stainless steel box with a wire mesh top). All treatments had a similar time course of effectiveness (up to at least 3 h) and their effects were blocked by naltrexone (0.1 mg/kg, i.p.) but not by naltrexone methyl bromide (10 mg/kg, i.p.). These findings suggest that the recovery of memory is probably due to an activation of central opioid mechanisms and, as a consequence, to the reinstatement of the neurohumoral conditions which were present during the post-training period. These results are consistent with previous evidence indicating that naltrexone given after training prevents the effects of PTZ on memory, and can be interpreted as showing that PTZ did not affect memory storage.