RITANSERIN BLOCKS DOI-ALTERED EMBRYONIC MOTILITY AND POSTHATCH LEARNING IN THE DEVELOPING CHICKEN

Developing chicken embryos exposed to cocaine show altered motility, h atchability, and posthatch detour learning. Pretreating such subjects with the serotonin(2) (5-HT2) antagonist ritanserin (RIT) can block th e motility suppression and reduced hatchability, indicating 5-HT2 rece ptor involvement in these cocaine effects. To study behavioral consequ ences of more selective 5-HT2 receptor stimulation and its blockade du ring development and to compare such exposure with that of cocaine, we injected eggs with 15-day-old chicken embryos with the 5-HT2 agonist dimethoxyiodophenylaminopropane (DOI, 1.0 mg/kg egg) and 1 h later, wi th RIT (0.3 and 0.9 mg/kg egg). Motility was recorded 2.5 or 24 h afte r DOI. This DOI dose suppressed motility 2.5 h but not 24 h after admi nistration. Both RIT doses blocked DOI's motility suppression. No trea tment affected hatchability. Subjects were tested on posthatch days 6- 9 for detour learning acquisition. DOI ''enhanced'' learning (i.e., re duced latency), a cocaine-like effect observed in prior work, which wa s also blocked by both RIT doses. Thus, some consequences of DOI expos ure late during embryonic development resemble cocaine's and are block ed by RIT, suggesting a therapeutic role for RIT-like drugs against co caine's potential developmental toxicity. Copyright (C) 1996 Elsevier Science Inc.