Adrenocorticotrophic hormone and acquisition of a passive avoidance response: A replication and extension

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Following bar-press training to stable performance, 4 groups of 4 hypophysectomized rats received daily injections of gelatin (placebo control), hydrocortisone, adrenocorticotrophic hormone (ACTH), or ACTH plus hydrocortisone. On Days 5 and 6 of injection, all Ss were administered brief response-contingent shock punishments. 7 days followed in which S had access to the bar and to reinforcement. Both ACTH-injected groups maintained near-complete response suppression over all recovery periods while the other groups evinced gradual return of bar-press rates to prepunishment levels. Basal skin resistance changes paralleled behavioral differences. Mean adrenal weights did not differ between groups. These results strongly support an extraadrenal ACTH-activated mechanism for punishment. (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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