A genotype-dependent hippocampal dynorphinergic mechanism controls mouse exploration.

Following microinjections with two dilutions of anti-dynorphin B antiserum into the hippocampal CA3 region, adult male mice from the inbred strains DBA/2 and C57BL/6 were individually tested for various exploratory behaviors in a novel environment and compared to preimmune serum control animals. Treatment augmented vertically-oriented exploratory acts in strain DBA/2 and reduced the scores in strain C57BL/6 so that strain differences originally present between the controls were reversed or eliminated after antiserum. These opposite effects indicate that a hippocampal dynorphinergic mechanism is involved in the regulation of novelty-induced behavior in mice and that its modulatory function depends on the genotype. It is concluded that DBA/2 animals exposed to novelty, as compared to C57BL/6, are characterized by an over-release of hippocampal dynorphin B which is neutralized in part by small amounts of antibody.