Effects of neonatal cerebral ventricular injection of ACTH 4-9 and subsequent adult injections on learning in male and female albino rats.

An investigation of permanent developmental effects of a potent, long acting ACTH/MSH 4-10 analogue (Organon 2766) on adult passive avoidance performance and of subsequent peripheral adult injections of the same substance on visual (black and white) discrimination learning and reversal in a Thompson-Bryant box was conducted. A subproblem analysis of visual and position preferences during reversal was performed. No differences in passive avoidance performance or in original discrimination learning were obtained. Both infant and adult treatments enhanced reversal learning and visual orientation (proportion of responese to the previously positive stimulus). Infant treatment suppressed position orientation in males and enhanced position orientation in females. These effects were interpreted as indicating that ACTH-like peptides enhance attention to the relevant stimulus by a direct effect on the brain.