Factors that influence test session performance measured 0, 3, or 6 h after inhibitory avoidance training.
Rats were trained in a step-down inhibitory avoidance task using a 0.3-mA, 60-Hz footshock, and were tested at 0, 3, and 6 h from training. Retrieval scores (test session minus training session step-down latencies) were higher in control groups at 0 than at 3 or 6 h. Test session performance at 0 h was unaffected by the pretraining ip injection of ACTH1-24 (0.2 microgram/kg), epinephrine-HCl (5.0 micrograms/kg), human beta-endorphin (1.0 microgram/kg), or naloxone-HCl (0.4 mg/kg); or by a pretreatment with dexamethasone phosphate (2.0 mg/kg in divided doses 24 and 12 h before training); or by anterior or posterior hypothalamic deafferentation. Test session performance at 0 h was depressed by prior bilateral transection of the fornix, which suggests it depends on hippocampal function. The effect of the fornix lesion on test session performance at 0 h was not counteracted by ACTH, epinephrine, or beta-endorphin administration. When animals were tested 3 h after training, the post-training administration of ACTH and epinephrine caused an enhancement of test session performance; neither post-training beta-endorphin or naloxone, nor pretest ACTH, epinephrine, or beta-endorphin administration, had any effect in these animals. At 6 h from training, the post-training facilitatory action of ACTH and epinephrine was still present and the post-training depressant effect of beta-endorphin and the post-training facilitatory effect of naloxone became manifest, and so did the naloxone-reversible pretest facilitation induced by ACTH, epinephrine, or beta-endorphin. The influence of post-training naloxone or pretest beta-endorphin on retrieval scores at 6 h was not observed in the fornix-lesioned animals.


CONCLUSIONS
Test session performance of this task at 0 h from training is regulated by different mechanisms than those which regulate test session performance at 3 or 6 h; in particular, it is less susceptible to modulation by the drugs used in the present study and it depends on the fornix; At least two major classes of modulatory factors influence retrieval scores at later times: consolidation-enhancing effects of ACTH and epinephrine, which become manifest at 3 h, and mechanisms related to beta-endorphin, which involve a form of state dependency and only become manifest at 6 h from training.
D000324:Adrenocorticotropic Hormone / Q000008:administration & dosage; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001921:Brain / Q000187:drug effects / Q000502:physiology*; D004597:Electroshock; D004723:Endorphins / Q000008:administration & dosage / Q000037:antagonists & inhibitors; D004837:Epinephrine / Q000008:administration & dosage; D005260:Female; D007031:Hypothalamus / Q000187:drug effects / Q000473:pathology; D009270:Naloxone / Q000008:administration & dosage; D009409:Nerve Crush; D051381:Rats; D011919:Rats, Inbred Strains; D011930:Reaction Time / Q000502:physiology; D013997:Time Factors
D004723:Endorphins; D009270:Naloxone; D000324:Adrenocorticotropic Hormone; D004837:Epinephrine