LACK OF ADAPTIVE-CHANGES IN 5-HT SITES IN PERINATALLY UNDERNOURISHED RATS AFTER CHRONIC STRESS - OPIOID INFLUENCE

The reactivity of 5-HT receptors following repeated immobilization ses sions or after immobilization plus morphine was measured through 5-met hoxy-N,N-dimethyltryptamine (5-MeODMT) or 8-hydroxy-2-(dipropyl-amino) tetralin (8-OH-DPAT)-induced serotonergic syndrome in adult rats under nourished at perinatal age. Repeated stress enhanced the scores of for epaw treading and hindlimb abduction elicited by 5-MeODMT in control a nimals. In a similar way, forepaw treading induced by 8-OH-DPAT was en hanced in chronically stressed control rats. These results indicate th e development of supersensitivity in 5-HT1 receptors. Conversely, this effect was not observed in undernourished animals. Morphine injection s before each stress session instaured the increased reactivity to 5-H T1 sites in malnourished animals. An injection of naloxone prior to mo rphine before each stress session fully antagonized the increased beha vioral reactivity to 5-MeODMT observed in deprived animals. A possible deficiency in the functional role of the opiate system involved in th e process of adaptation to chronic stress in early undernourished rats is suggested.