CHICK IMPRINTING PERFORMANCE AND SUSCEPTIBILITY TO ACUTE STRESS ASSOCIATED TO FLUNITRAZEPAM RECEPTOR INCREASE

One-day-old chicks were selected on their performance in imprinting be haviour and termed high-imprinted (H-I), partially imprinted (P-I) and low-imprinted (L-I) chicks. Then, H-I and L-I chicks were submitted t o acute handling stress and [H-3]flunitrazepam receptor-binding was pe rformed on synaptosomal membranes from forebrain at various times afte r handling. The receptor number significantly increased in L-I but not in H-I chicks at 30 min after handling while the affinity remained un changed at all times. In addition, when the three selected groups were maintained to reach 15 days of age and then they were submitted to ac ute swimming stress, the degree of receptor increase was also inversel y related to the degree of imprinting performance. The receptor increa se associated to swimming stress was higher in the left hemisphere, su ggesting an interhemispheric asymmetry of stress effects. The results suggest that more-imprinted chicks are less susceptible than less-impr inted chicks to acute stress associated to central benzodiazepine rece ptor increase, probably due to differences in the degree of endogenous emotionality.