Specific [3H]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 predisposed to two basic defense strategies--passive (freezing) or active (aggression) defensive behavior. Specific [3H]8-OH-DPAT binding was assayed in the brain structures of rat strains bred for 40 generations from Wistar stock for predisposition to freezing (catalepsy), and in wild rats bred for low and high aggression to humans. Considerable changes in [3H]8-OH-DPAT binding were found in the brain of rats with hereditary predisposition to catalepsy. A significant decrease in Bmax of specific receptor binding of [3H]8-OH-DPAT in the frontal cortex, and in the striatum as well as an increase in Kd in the hippocampus of cataleptic rats was shown. A clear-cut tendency to decrease of 5-HT1A receptor density was observed in the midbrain and hypothalamus of these rats. A comparison of wild Norway rats bred for aggressiveness against humans with those bred for the absence of affective aggressiveness showed a Bmax decrease without Kd change in the frontal cortex, hypothalamus, 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 the high expression of fear-induced defense is associated with their decrease in the frontal cortex. At the same time, the genetically determined preference for a certain defense behavior strategy depends either on the peculiarities of distribution of these receptor types in the brain regions or on some other types of serotonin receptors.