The effect of MSH/ACTH 4-10 on delayed response performance and post-test locomotor activity in rats.
Delayed response performance was measured in male, Long-Evans rats 1 hr after IP administration of various doses of MSH/ACTH 4-10 or control in a Hunter delayed reaction apparatus. Additional treatments consisting of naloxone 500 micrograms/kg (IP) and naloxone 500 micrograms/kg in conjunction with MSH/ACTH 4-10 95 micrograms/kg were also administered. Directly after delayed response performance was assessed, gross locomotor activity was determined. MSH/ACTH 4-10, at a dose of 95 micrograms/kg, significantly enhanced retention of a visual stimulus, while MSH/ACTH 4-10, at doses of 195 and 285 micrograms/kg, significantly impaired delayed response performance. Naloxone treatment resulted in significantly impaired delayed response performance when compared to control. However, naloxone plus MSH/ACTH 4-10 treatment failed to produce a significant difference from control in the delayed response performance paradigm. In post-test locomotor activity determination, an apparent dose-response existed for MSH/ACTH 4-10 with the two highest doses (190 and 285 micrograms/kg) resulting in significantly increased locomotor activity. The observed delayed response performance data support theories implicating MSH/ACTH peptides in attentional processes involving visual stimuli. The fact that large doses of MSH/ACTH 4-10 disrupt delayed response performance while increasing post-test activity suggest that an optimum level of effect caused by the MSH/ACTH peptide exists in this paradigm.
D000324:Adrenocorticotropic Hormone / Q000494:pharmacology*; D000818:Animals; D004305:Dose-Response Relationship, Drug; D008297:Male; D009043:Motor Activity / Q000187:drug effects*; D009270:Naloxone / Q000494:pharmacology; D010446:Peptide Fragments / Q000494:pharmacology*; D011597:Psychomotor Performance / Q000187:drug effects*; D051381:Rats; D013997:Time Factors
D010446:Peptide Fragments; D009270:Naloxone; D000324:Adrenocorticotropic Hormone; C011394:ACTH (4-10)