Reduction of ECS-induced retrograde amnesia of passive avoidance conditioning after 5,7-dihydroxytryptamine median raphe nucleus lesion in the rat.
5,7-Dihydroxytryptamine (5,7-DHT), median raphe nucleus (MRN)-lesioned and sham-lesioned rats were submitted to one-trial passive avoidance conditioning followed by electroconvulsive shock (ECS) or sham-ECS. On test session (24 h later) MRN-lesioned rats presented a longer conditioned response and, chiefly, a remarkable reduction of ECS-induced retrograde amnesia in comparison to sham-lesioned animals. This effect appeared unrelated to major changes in spontaneous behavior: on training session MRN-lesioned rats exhibited a faster stepping-down from the platform; their exploratory activity into a novel cage was characterized by a slightly higher initial response; moreover MRN lesion did not significantly effect pain threshold. A reduced brain 5-HT functional activity following MRN lesion was suggested by the study of the hyperactivity syndrome induced by tranylcypromine plus L-tryptophan. Lastly, MRN-lesioned rats showed a significantly lower brain 5-HT steady level without differing from the sham-lesioned ones with respect to turnover rate. The reduction of ECS-induced retrograde amnesia observed in 5,7-DHT, MRN-lesioned rats was considered as due to a lower synaptic availability of 5-HT at the time of ECS administration.
D015116:5,7-Dihydroxytryptamine / Q000494:pharmacology*; D006916:5-Hydroxytryptophan / Q000378:metabolism; D000647:Amnesia / Q000188:drug therapy*; D000648:Amnesia, Retrograde / Q000188:drug therapy*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001835:Body Weight; D001933:Brain Stem / Q000502:physiology*; D003213:Conditioning, Psychological / Q000187:drug effects*; D004102:Dihydroxytryptamines / Q000494:pharmacology*; D004597:Electroshock; D006801:Humans; D006948:Hyperkinesis / Q000139:chemically induced; D008297:Male; D009043:Motor Activity / Q000187:drug effects; D010146:Pain; D011903:Raphe Nuclei / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012684:Sensory Thresholds / Q000187:drug effects; D014191:Tranylcypromine / Q000494:pharmacology; D014364:Tryptophan / Q000494:pharmacology
D004102:Dihydroxytryptamines; D015116:5,7-Dihydroxytryptamine; D014191:Tranylcypromine; D014364:Tryptophan; D006916:5-Hydroxytryptophan