BRAIN CORTICOTROPIN-RELEASING FACTOR IMMUNOREACTIVITY AND RECEPTORS IN 5 INBRED RAT STRAINS - RELATIONSHIP TO FORCED SWIMMING BEHAVIOR

In the present work we studied the relationship between behaviour in t he forced swimming test (FST), a test that presumably measures depress ive-like behaviour in rodents, and central corticotropin-releasing fac tor (CRF) concentration and binding in five strains of rats. The strai ns were: Brown-Norway (BN), Fisher (FIS) 344, Lewis (LEW), spontaneous ly hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). The FST data c orresponding to the pretest showed significant inter-strain difference s in both struggling and immobility: BN and WKY rats displayed lower l evels of struggling and longer periods of immobility, LEW and SHR rats showed intermediate levels, and FIS rats were the most active. The re sults of the pretest were roughly similar to those observed in the tes t, the activity of WKY being extremely low. The CRF binding revealed s ignificant inter-strain differences in prefrontal cortex and hippocamp us, but not in cerebellum, pons-medulla or hypothalamus: in the prefro ntal cortex, BN and FIS rats showed greater CRF binding than LEW, SHR and WKY rats; in the hippocampus BN rats showed higher levels of CRF b inding than the other strains. The study of CRF content in various bra in areas revealed inter-strain differences in prefrontal cortex and po ns-medulla, but not in parietal-temporal cortex or in hypothalamus (CR F concentrations in the hippocampus were not detectable): CRF content in the prefrontal cortex was higher in BN than in the other strains, a lthough the differences with FIS were not statistically significant; i n the pons-medulla, FIS and LEW showed significantly higher CRF conten t than the other strains. From the present results it appears that BN and WKY rats were more prone to adopt passive strategies in the FST, b ut they did not show higher brain CRF immunoreactivity or down-regulat ion of CRF receptors. Hence, although there were inter-strains differe nces in all variables studied, no evidence for a relationship between the FST behaviour and central CRF activity was found.