Effects of ACTH, epinephrine and Met-enkephalin on brain beta-endorphin-like immunoreactivity, and of ACTH, epinephrine, Met-enkephalin and naloxone on retention, in normal and in protein-malnourished rats.
Rats raised and maintained on a normal-protein diet (25% protein) responded to the ip administration of ACTH-(1-24), epinephrine or Met-enkephalin with a decrease in hypothalamic beta-endorphin-like immunoreactivity, which is attributable to a release of this substance. This effect was not seen in rats raised and maintained on a low-protein diet (8% protein). In the normal animals, the pre-test administration of ACTH, epinephrine or Met-enkephalin and the post-training administration of naloxone enhanced retention-test performance of a step-down inhibitory avoidance task. These behavioral effects were absent in the protein-malnourished rats. Previous studies have shown that the behavioral effect of post-training naloxone is secondary to the release of brain beta-endorphin during training, and that the pre-test effect of the hormones is due to a release of brain beta-endorphin induced by the substances themselves. Since it is not likely that the differences were caused by hyperreactivity to the aversive stimuli employed, the suggested interpretation is that protein-malnourished rats present a dysfunction in the brain beta-endorphin system which renders it unresponsive not only to novel training experiences, but also to the pre-test retrieval enhancing effects of ACTH, epinephrine and Met-enkephalin.
Perry
M L
ML
Centro de Memória, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brasil.
Netto
C A
CA
Izquierdo
I
I
D000324:Adrenocorticotropic Hormone / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D001362:Avoidance Learning / Q000187:drug effects*; D001921:Brain / Q000378:metabolism*; D004044:Dietary Proteins / Q000008:administration & dosage / Q000494:pharmacology; D004744:Enkephalin, Methionine / Q000008:administration & dosage / Q000494:pharmacology*; D004837:Epinephrine / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D007274:Injections, Intraperitoneal; D008568:Memory / Q000187:drug effects*; D011247:Pregnancy; D011502:Protein-Energy Malnutrition / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012153:Retention, Psychology / Q000187:drug effects*; D001615:beta-Endorphin / Q000378:metabolism*
D004044:Dietary Proteins; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; D000324:Adrenocorticotropic Hormone; D004837:Epinephrine