SPECIFIC [H-3]8-OH-DPAT BINDING IN BRAIN-REGIONS OF RATS GENETICALLY PREDISPOSED TO VARIOUS DEFENSE BEHAVIOR STRATEGIES

Distribution of 5-HT1A receptors was studied in rats genetically predi sposed to two basic defense strategies-passive (freezing) or active (a ggression) defensive behavior. Specific (H-3]8-OH-DPAT binding was ass ayed in the brain structures of rat strains bred for 40 generations fr om Wistar stock for predisposition to freezing (catalepsy), and in wil d rats bred for low and high aggression to humans. Considerable change s in [H-3]8-OH-DPAT binding were found in the brain of rats with hered itary predisposition to catalepsy. A significant decrease in B-max of specific receptor binding of [H-3]8-OH-DPAT in the frontal cortex, and in the striatum as well as an increase in K-d in the hippocampus of c ataleptic rats was shown. A clear-cut tendency to decrease of 5-HT1A r eceptor density was observed in the midbrain and hypothalamus of these rats. A comparison of wild Norway rats bred for aggressiveness agains t humans with those bred for the absence of affective aggressiveness s howed a B-max decrease without K-d change in the frontal cortex, hypot halamus, and amygdala of aggressive animals. It is hypothesized that 5 -HT1A and probably 5-HT1A-like 5-HT7 serotonin receptors are involved in the mechanisms of both active and passive defense reactions, and th e high expression of fear-induced defense is associated with their dec rease in the frontal cortex. At the same time, the genetically determi ned preference far a certain defense behavior strategy depends either on the peculiarities of distribution of these receptor types in the br ain regions or on some other types of serotonin receptors. (C) 1998 El sevier Science Inc.